ISTANBUL TECHNICAL UNIVERSITY  GRADUATE SCHOOL 

M.Sc. THESIS 

DESIGN AND DEVELOPMENT OF A CUSTOM BATCH FOAMING 

REACTOR AND ITS VALIDATION THROUGH BEAD FOAMING OF 

BIOPLASTICS 

Arda KESLER 

 

Department of Material Science and Engineering 

 

Material Science and Engineering Programme 

JUNE 2025 



 

  



 

   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ISTANBUL TECHNICAL UNIVERSITY  GRADUATE SCHOOL 

DESIGN AND DEVELOPMENT OF A CUSTOM BATCH FOAMING 

REACTOR AND ITS VALIDATION THROUGH BEAD FOAMING OF 

BIOPLASTICS 

 

M.Sc. THESIS 

Arda KESLER 

 (521201001) 

Thesis Advisor: Assoc. Prof. Dr. M. Reza NOFAR 

Department of Material Science and Engineering 

 

Material Science and Engineering Programme 

JUNE 2025 



 

 

  



 

 

   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
HAZİRAN 2025 

İSTANBUL TEKNİK ÜNİVERSİTESİ  LİSANSÜSTÜ EĞİTİM ENSTİTÜSÜ 

ÖZGÜN BİR OTOKLAV KÖPÜRTME REAKTÖRÜNÜN TASARLANMASI, 

GELİŞTİRİLMESİ VE BİYOPLASTİKLERİN BONCUK 

KÖPÜKLENDİRİLMESİ DENEYLERİ İLE DOĞRULANMASI 

 

YÜKSEK LİSANS TEZİ 

Arda KESLER 

(521201001) 

Tez Danışmanı: Doç. Dr. M. Reza NOFAR 

 

Malzeme Bilimi ve Mühendisliği Anabilim Dalı 

 

Malzeme Bilimi ve Mühendisliği Programı 



 

 

  



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Thesis Advisor :  Assoc. Prof. Dr. Mohammadreza NOFAR ............................ 

                                Istanbul Technical University  

Jury Members :  Assoc. Prof. Dr. Yonca ALKAN GÖKSU  .............................. 

Istanbul Technical University                 

                                Prof. Dr. Nadir AYRILMIŞ   ............................. 

                                Istanbul University - Cerrahpaşa                

 

                                 

Arda KESLER, a M.Sc. student of İTU Graduate School student ID 521201001, 

successfully defended the thesis/dissertation entitled “DESIGN AND 

DEVELOPMENT OF A CUSTOM BATCH FOAMING REACTOR AND ITS 

VALIDATION THROUGH BEAD FOAMING OF BIOPLASTICS”, which he 

prepared after fulfilling the requirements specified in the associated legislations, 

before the jury whose signatures are below. 

 

 

 

Date of Submission :  30 May 2025 

Date of Defense :  24 June 2025 
 



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To my family, 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  

  



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ix 

FOREWORD 

This M.Sc.Thesis is aimed at developing a laboratory-scale batch foaming reactor to 

be used for bioplastic foaming research at İTÜ. The project required a 

multidisciplinary work, including research, academic support and collaboration from 

the Materials Science and Mechanical Engineering disciplines, procurement of various 

specialty tools, materials and the use of welding and CNC workshop facilities. 

I would first like to thank my supervisor Assoc. Prof. Dr. M. Reza NOFAR for his 

invaluable guidance and academic mentoring which was essential for successful 

completion of this project. Prof. NOFAR was always willing and ready to help when 

I had questions or when I encountered bottlenecks in my project. He steered me in the 

right direction whenever he thought I needed it, but he also gave me freedom and 

flexibility to make my own research and choices in the mechanical engineering design 

and implementation stages of my project. 

I would also like to thank Mr. Yavuz AKDEVELİOĞLU and Ms. Simay YANIK for 

their support during the research and testing stages and for patiently answering my 

questions. 

Finally, the development of the foaming reactor would not have been possible without 

the aid of Mr. Özden ÖLMEZ and Üçaslar Company, who manufactured major parts 

of our reactor chamber design in their facilities free of charge, and ETA Company, 

who helped with the assembly of the system. 

I would like to acknowledge the financial supports from Istanbul Technical University 

Scientific Research Project (ITU-BAP) – Master Thesis Project (BAP YL 45134). 

 

 

 

May 2025              Arda KESLER 

        (Makine Mühendisi) 

 

 

 

 

 

  



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xi 

TABLE OF CONTENTS 

Page 

FOREWORD ............................................................................................................. ix 
TABLE OF CONTENTS .......................................................................................... xi 
ABBREVIATIONS ................................................................................................. xiii 

LIST OF TABLES ................................................................................................... xv 

LIST OF FIGURES ............................................................................................... xvii 

SUMMARY ............................................................................................................. xix 
ÖZET ........................................................................................................................ xxi 
1. INTRODUCTION .................................................................................................. 1 

1.1 Background ........................................................................................................ 1 
1.2 Aims and Objectives .......................................................................................... 2 

1.3 Thesis Structure .................................................................................................. 3 

2. LITERATURE REVIEW ...................................................................................... 5 
2.1 Introduction to Sustainable Polymers ................................................................ 5 
2.2 PLA .................................................................................................................... 5 
2.3 Foaming Processes and PLA as a Foaming Material ......................................... 6 

2.3.1 Foaming processes ...................................................................................... 6 
2.3.1.1 Injection................................................................................................ 6 

2.3.1.2 Extrusion .............................................................................................. 6 
2.3.1.3 Batch foaming ...................................................................................... 6 

2.3.2 PLA as a foaming material .......................................................................... 7 
2.4 Blowing Agents and Supercritical CO2 as a Blowing Agent ............................. 7 
2.5 Batch Foaming Systems ..................................................................................... 8 

2.5.1 Introduction to batch foaming ..................................................................... 8 

2.5.2 Applications and advantages of batch foaming .......................................... 8 
2.5.3 Pressure-induced batch foaming ................................................................. 9 
2.5.4 Design of batch foaming devices .............................................................. 10 
2.5.5 Variations and innovations in device design ............................................. 11 

3. DESIGN AND DEVELOPMENT OF THE REACTOR ................................. 13 
3.1 Introduction ...................................................................................................... 13 
3.2 Design Requirements and Specifications ......................................................... 14 

3.2.1 Performance goals ..................................................................................... 14 
3.2.2 Material selection requirements ................................................................ 15 
3.2.3 Compatibility ............................................................................................ 16 
3.2.4 Safety and ease of use ............................................................................... 16 

3.3 Conceptual Design ........................................................................................... 16 

3.3.1 Selection of reactor type ........................................................................... 16 
3.3.2 Reactor geometry and physical layout ...................................................... 17 
3.3.3 Integration with pre-existing equipment ................................................... 18 
3.3.4 Process flow and operation concept .......................................................... 18 
3.3.5 Design flexibility ....................................................................................... 19 

3.4 Detailed Design Process ................................................................................... 20 



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3.4.1 Foaming chamber design .......................................................................... 20 

3.4.1.1 Geometric design ................................................................................ 22 
3.4.1.2 Closure mechanism ............................................................................ 28 
3.4.1.3 Ports and fittings ................................................................................. 34 

3.4.1.4 Mounting and support ........................................................................ 37 
3.4.2 Heating and insulation system design ....................................................... 39 

3.4.2.1 Heating method .................................................................................. 39 
3.4.2.2 Temperature monitoring and control .................................................. 40 
3.4.2.3 Insulation ............................................................................................ 40 

3.4.3 Gas delivery system .................................................................................. 41 
3.4.3.1 Pressurisation device .......................................................................... 41 
3.4.3.2 Depressurisation device ...................................................................... 41 

3.5 Manufacturing and Integration Process ............................................................ 41 
3.5.1 Manufacturing of the foaming chamber .................................................... 41 

3.5.2 Manufacturing of the workbench .............................................................. 43 
3.5.3 Procurement of the heaters ........................................................................ 44 

3.5.4 Manufacturing of the insulation ................................................................ 45 
3.5.5 Assembly ................................................................................................... 46 

4. EXPERIMENTAL SETUP AND METHODOLOGY ...................................... 49 
4.1 Overview .......................................................................................................... 49 

4.2 Materials and Equipment Used ........................................................................ 49 
4.2.1 Material list ............................................................................................... 49 

4.2.2 Equipment list ........................................................................................... 50 
4.3 Experimental Setup .......................................................................................... 50 

4.3.1 Physical setup ............................................................................................ 50 

4.3.2 Flow of operation ...................................................................................... 51 

4.4 Methodology..................................................................................................... 52 
4.4.1 Sample preparation .................................................................................... 52 
4.4.2 Parameters ................................................................................................. 52 

4.4.3 Process ....................................................................................................... 54 
4.4.4 Analysis ..................................................................................................... 54 

5. RESULTS AND DISCUSSION........................................................................... 55 
5.1 Overview of Experimental Findings ................................................................ 55 
5.2 SEM Analysis of PLA samples ........................................................................ 55 

5.3 Additional Observations ................................................................................... 58 

6. CONCLUSION ..................................................................................................... 61 
6.1 Key Findings .................................................................................................... 61 

REFERENCES ......................................................................................................... 63 
CURRICULUM VITAE .......................................................................................... 67 
 

 

 



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ABBREVIATIONS 

ASME : American Society of Mechanical Engineers 

CAD : Computer Asisted Design 

CNC : Computer Numerical Control 

İTÜ : İstanbul Technical University 

PLA    : Polylactic Acid (Polylactide) 

SEM : Scanning Electron Microscope 

SGPL : Sustainable Green Plastics Laboratory 

 

 

 

  



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xv 

LIST OF TABLES 

Page 

Table 3.1 : Chemical composition of S355J2 steel . ................................................. 21 
Table 3.2 : Mechanical properties of S355J2 steel ................................................... 21 
Table 3.3 : Transformation temperatures of S355J2 steel . ....................................... 21 
Table 3.4 : Table comparing the proof loads of 8.8 metric bolts at normal conditions 

and 300°C. The data is computed from empirical values. . .................... 32 
Table 4.1 : Table showing the parameters used for the experiments on the neat PLA 

samples. ................................................................................................... 53 
Table 4.2 : Table showing the parameters used for the experiments on the 

PLA+0.5wt% Joncryl samples. ............................................................... 53 
Table 4.3 : Table showing the parameters used for the experiments on the 

PLA+1wt% Joncryl samples. .................................................................. 53 

 

 

 

  



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xvii 

LIST OF FIGURES 

Page 

Figure 3.1 : Variations of mechanical properties of St52 with temperature . ........... 22 
Figure 3.2 : Simple cross sectional drawing showing the interior dimensions of the 

foaming chamber (original). ................................................................. 22 
Figure 3.3 : Cross sectional view of the foaming chamber with at least 50mm wall 

thickness. The design is fitted inside a cylindrical outer geometry of 

168mm diameter and 85mm height for the feasibility of manufacture. 

Exported from SolidWorks (Original). ................................................. 26 
Figure 3.4 : Image of the foaming chamber body. Exported from SolidWorks. 

(Original). ............................................................................................. 27 
Figure 3.5 : Top down view of the Foaming chamber body. Exported from 

SolidWorks. (Original) 1: Foaming chamber interior, 2: 6 radially 

symmetric 60mm deep M20 threaded axial bolt holes, 3: 3 radially 

symmetric 10.5mm axial through-holes. .............................................. 27 
Figure 3.6 : Exploded view of the foaming chamber and the closure excluding the 

nuts and bolts. From top to bottom: Main(upper) lid, Inner(pressure 

plate) lid, Soft metallic(copper or aluminium) gasket. Exported from 

SolidWorks (Original). ......................................................................... 28 

Figure 3.7 : Top and side view of the Inner(pressure plate) lid. Exported from 

SolidWorks (Original). ......................................................................... 30 

Figure 3.8 : Cross section view showing the contact zones between the 30° chamfer 

on the foaming chamber inner rim and the hyperbolloidal fillets on the 

inner lid. Exported from SolidWorks (Original). ................................. 30 
Figure 3.9 : Cross section view showing the contact zones between the inner lid and 

the main lid. Exported from SolidWorks (Original). ............................ 31 
Figure 3.10 : Cross section view of the foaming chamber assembly showing the 

placement of one stud bolt. The hole has a diameter of 20mm which is 

the thread diameter of the M20 bolt making the hole appear larger in 

diameter than the actual end product. The CAD model will be re-

iterated in the manufacturing stage where a 16mm would need to be 

drilled before adding the threading. Exported from Solidworks 

(Original). ............................................................................................. 33 
Figure 3.11 : Isometric view of the foaming chamber assembly showing the 

placement of one bolt with a washer and a heavy duty nut. Exported 

from SolidWorks (Original). ................................................................. 33 
Figure 3.12 : Cross section view of the foaming chamber from the top plane 

showing the radial placement of the three 5mm ports. Exported from 

SolidWorks (Original). ......................................................................... 34 
Figure 3.13 : Cross section view of the foaming chamber from the side showing the 

vertical placement of one of the three 5mm ports on the right side. 

Exported from SolidWorks (Original). ................................................. 35 



xviii 

Figure 3.14 : Top view of the foaming chamber showing the placement of the 3 

radially symmetric 10.5mm axial through-holes created for the heating 

carthridge numbered 1 to 3. Exported from SolidWorks (Original). .... 37 
Figure 3.15 : Image demonstrating the correct height of the workbench.      

(Original) ............................................................................................... 38 
Figure 3.16 : Drawing showing the general shape of the foaming chamber 

workbench (Original). ........................................................................... 38 
Figure 3.17 : Photographs showing the parts of the foaming chamber after they were 

machined by lathe and before the holes were made by the CNC. The 

parts are placed on their corresponding engineering drawing    

(Original). .............................................................................................. 42 
Figure 3.18 : Photograph of the foaming chamber after the machining was comleted 

with all 6 of the stud bolts attached (Original). .................................... 43 
Figure 3.19 : Photograph showing the foaming chamber with both the inner lid and 

the main lid assembled and clamped (Original). .................................. 43 
Figure 3.20 : Photograph showing the mounting of the foaming chamber on the 

workbench before the white paint was applied (Original). ................... 44 
Figure 3.21 : Photograph showing the heaters after their procurement (Original). .. 45 
Figure 3.22 : Three photographs showcasing the insulation jacket. Top: The 

insulation jacket in its loose form. Bottom left: Insulation jacket 

partially covering the foaming chamber. Bottom right: Insulation jacket 

in its taut form, completely covering the foaming chamber (Original). 46 

Figure 3.23 : Photograph of the finished setup. Showing all the members of the 

batch foaming system (Original)........................................................... 47 
Figure 4.1 : Photograph showing the batch foaming reactor setup with each 

equipment marked by the number in read. 1: Batch foaming reactor, 

2:Emko ESM-3720 temperature controller and the custom integrated 

relay switch, 3: TELEDYNE ISCO 260HP syringe pump and its 

integrated digital controller, 4: CO2 cylinders that feed the syringe 

pump. .................................................................................................... 51 
Figure 5.1 : SEM images of the cross sections of thre PLA foaming samples. Top to 

bottom: Neat PLA at 160°C, PLA+1% wt. Joncryl at 160°C, 

PLA+0.5% wt. Joncryl at 157°C........................................................... 56 
Figure 5.2 : SEM image of the foam structure of neat PLA at 157°C (left) and neat 

PLA at 160°C (rigth). ............................................................................ 56 
Figure 5.3 : SEM image of the foam structure of PLA+0.5% wt. Joncryl at 157°C 

(left) and PLA+0.5% wt. Joncryl at 160°C (rigth)................................ 57 

Figure 5.4 : SEM image of the foam structure of PLA+1% wt. Joncryl at 155°C. .. 57 
Figure 5.5 : SEM image of the foam structure of PLA+1% wt. Joncryl at 157°C. .. 58 

Figure 5.6 : Two SEM images taken from different areas on the cross-section of the 

same sample (PLA+1% wt. Joncryl at 160°C). .................................... 58 

Figure 5.7 : SEM images  different foaming samples showing the different degrees 

of delamination occurred during the foaming process. ......................... 59 
Figure 5.8 : SEM  image of a foamed PLA sample, showing the strained cross –

section, completely preventing the foam structure to be observed. ...... 59 
  



xix 

DESIGN AND DEVELOPMENT OF A CUSTOM BATCH FOAMING 

REACTOR AND ITS VALIDATION THROUGH BEAD FOAMING OF 

BIOPLASTICS 

SUMMARY 

Sustainable polymers have gained worldwide importance as they have started to 

become viable alternatives for petroleum-based plastics. This is mainly due to their 

potential to overcome environmental detriments such as plastic pollution, carbon 

emissions, and the possible depletion of natural resources. 

Türkiye, having very limited fossil fuel resources, and increasing use of plastics, is 

even more exposed to negative economic and environmental consequences of using 

plastics. As an agriculture country, Türkiye will benefit much more from any progress 

in the bioplastics field, and possible gradual replacement of petroleum-based plastics 

with bioplastics. 

Polylactic acid (PLA) is a sustainable plastic because it can be produced efficiently 

from various agricultural products, and has rapid biodegradation properties. PLA has 

suitable mechanical properties for foam production and has long attracted the attention 

of both academics and industry. On the other hand, bioplastic foams that can compete 

economically and technically with petroleum-based foams on an industrial scale have 

not yet been produced. Research on this subject is being conducted at our university, 

as well as in many major universities around the world. Extensive testing of bioplastic 

samples under controlled laboratory environments and with varying production 

methods is needed before industrial processes that enable large-scale foam production 

from bioplastics can be designed. 

İTÜ, as one of the leading universities in academic research on the subject of 

sustainable polymers, has been planning to equip its Sustainable Green Plastics 

Laboratory (SGPL) with a laboratory-scale batch foaming reactor. The main aim of 

this project is to develop an autoclave batch foaming reactor to be used for bioplastic 

foaming research at İTÜ. 

The project started with a general literature survey on the subject, and continued with 

the design of the autoclave body using CAD software, design of a special workbench 

dedicated to the autoclave, materials selection and procurement, production of 

individual parts, assembly of the autoclave foam production device and the 

workbench. Design and procurement of an autoclave insulation sleeve, arrangement 

of the reactor setup to work with existing temperature control device, syringe pump 

etc., optimizing the reactor setup for ergonomics and preparation of health and safety 

documentation were also within the scope of this project. Finally, operational testing 

of the device in SGPL with PLA samples and supercritical carbon dioxide as blowing 

agent was carried out using different temperatures, pressures and foaming times. 

After successfull operational tests, the autoclave foaming device which is unique in 

Türkiye, has been added to ITU infrastructure facilities to be used in different research 



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projects after this thesis project, and is expected to benefit researchers significantly by 

facilitating their testing work. 

 

 



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ÖZGÜN BİR OTOKLAV KÖPÜRTME REAKTÖRÜNÜN TASARLANMASI, 

GELİŞTİRİLMESİ VE BİYOPLASTİKLERİN BONCUK 

KÖPÜKLENDİRİLMESİ DENEYLERİ İLE DOĞRULANMASI 

ÖZET             

Sürdürülebilir polimerler, petrol bazlı plastikler için bir alternatif haline gelmeye 

başlamalarıyla birlikte dünya genelinde büyük önem kazanmışlardır. Bu ilgi özellikle 

plastik kirliliği, karbon salınımları ve doğal kaynakların tükenme riski gibi çevresel 

sorunlara potansiyel çözüm arayışlarından kaynaklanmaktadır. Fosil yakıt kaynakları 

son derece sınırlı olan Türkiye, plastik kullanımının da giderek artmasıyla birlikte 

plastik tüketiminin ekonomik ve çevresel olumsuz etkilerine daha fazla maruz 

kalmaktadır. Bir tarım ülkesi olan Türkiye, biyoplastikler alanındaki gelişmelerden ve 

petrol bazlı plastiklerin biyoplastiklerle kademeli olarak değiştirilmesinden önemli 

ölçüde fayda sağlayacaktır. 

Polilaktik asit (PLA), çeşitli tarım ürünlerinden verimli bir şekilde üretilebilmesi ve 

hızlı biyobozunma özelliği sayesinde sürdürülebilir bir plastik türü olarak öne 

çıkmaktadır. PLA’in, köpük üretimi için uygun mekanik özelliklere sahip olması uzun 

süredir hem akademi hem de sanayi çevrelerinin dikkatini çekmektedir. Diğer yandan, 

endüstriyel ölçekte petrol bazlı köpüklerle ekonomik ve teknik açıdan rekabet 

edebilecek biyoplastik köpükler henüz üretilememiştir. PLA düşük erime 

mukavemeti, köpürme için dar sıcaklık aralığı ve yavaş kristalizasyon kinetikleri 

sebebiyle henüz petrol bazlı plastik köpüklerin üretim kolaylığına ve mekanik 

performansına ulaşamamıştır. Bu konuda üniversitemizde olduğu gibi dünyanın önde 

gelen birçok üniversitesinde de araştırmalar sürdürülmektedir. Biyoplastiklerin 

köpüklerin endüstriyel ölçekte üretimine olanak sağlayacak proseslerin 

geliştirilebilmesi için, bu malzemelerin kontrollü laboratuvar koşullarında ve farklı 

üretim yöntemleriyle kapsamlı şekilde test edilmesi gerekmektedir. 

İstanbul Teknik Üniversitesi (İTÜ), sürdürülebilir polimerler konusundaki akademik 

araştırmalar açısından öncü üniversitelerden biri olarak, Sürdürülebilir Yeşil Plastik 

Laboratuvarını (SGPL) laboratuvar ölçekli bir parti tipi köpük üretme reaktörü (batch 

foaming reactor) ile donatmayı planlamaktadır. Bu projenin temel amacı, biyoplastik 

köpürtme araştırmalarında kullanılmak üzere bir otoklav tipi parti köpük üretme 

reaktörü geliştirmek ve test etmektir. 

Proje, konuya yönelik genel bir literatür taramasıyla başlamış ve ardından otoklav 

gövdesinin CAD yazılımı kullanılarak tasarımı, otoklava özel bir çalışma tezgâhının 

tasarımı, malzeme seçimi ve tedariki, parçaların üretimi ve köpükleme cihazı ile 

çalışma tezgâhının montajı gibi adımlarla devam etmiştir. Ayrıca, otoklav yalıtım 

kılıfının tasarımı ve tedariki, mevcut sıcaklık kontrol cihazı ve şırınga pompası ile 

birlikte sistemin çalışabilirliğinin sağlanması, reaktör kurulumunun ergonomi 

açısından optimize edilmesi ve iş sağlığı-güvenliği belgelerinin hazırlanması da 

projenin kapsamına dâhildir.  



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Projede kullanılan köpürtme yöntemi, parti tipi köpük üretme yöntemi olup, bu 

yöntemde polimer numuneleri belirli bir sıcaklık ve basınç altında köpürtücü gazla 

doyurulmakta ve hızlı dekompresyonla köpürme sağlanmaktadır.  

Projede tasarlanan reaktör, 300°C sıcaklığa ve 30 MPa basınca dayanabilecek şekilde 

S355J2 çeliğinden imal edilmiştir. Ayrıca, otoklav gövdesinin duvar kalınlığı, hem 

basınç dayanımı hem de ısıl kararlılık için optimize edilmiştir. Reaktör tasarım 

sürecinde, ASME Boiler and Pressure Vessel Code (BPVC) Section VIII standartları 

referans alınmış ve özellikle güvenlik katsayıları detaylı şekilde hesaplanmıştır. 

Tasarımda kullanılan SolidWorks çizimleri, üretim aşamasında tolerans kontrolleri ve 

delik yerleşimleri için referans oluşturmuştur. Otoklav kapatma sistemi, iki parçalı 

(ana kapak ve basınç plakası) olup, haznedeki kuvvetin eşit dağılımını sağlayacak 

şekilde 6 adet M20 cıvata ile sabitlenmiştir.  

Isıtma sistemi, eşit ısı dağılımı için radyal simetride yerleştirilmiş üç adet kartuş 

rezistans ve PID sıcaklık kontrol cihazı ile oluşturulmuştur.  

Gaz sistemi, sisteme entegre edilen şırınga pompası ile yüksek basınçlı CO₂ uygulama 

kapasitesine sahiptir. Ayrıca, köpürtme haznesinin tasarımında basınç, sıcaklık, 

satürasyon süresi gibi parametrelerin hassas kontrolü sağlanmıştır. Projede, şırınga 

pompasının basınç stabilizasyon özelliği sayesinde, satürasyon fazı boyunca basınç 

dalgalanmaları kontrol edilmiştir.  

Son olarak, PLA numuneleri ve şişirici gaz olarak süperkritik karbondioksit 

kullanılarak, farklı sıcaklık, basınç ve satürasyon süresi parametreleri altında cihazın 

laboratuvar ortamında operasyonel testleri gerçekleştirilmiştir. Testlerde, 

NatureWorks PLA Ingeo Biopolymer 2500HP kullanılmış ve bu numunelere %0.5 ve 

%1 oranlarında Joncryl ADR 4468 zincir uzatıcı eklenmiştir. Deneyler sırasında 

reaktör, 12Mpa basınca ayarlanmış ve her deneyde 30 dakikalık sabit satürasyon süresi 

uygulanmıştır. Deney sıcaklıkları ise 90°C ile 170°C arasında, 10°C’lik artışlarla 

seçilmiştir. 120°C altında herhangi bir köpürme veya morfolojik değişim 

gözlenmezken, 150-160°C aralığında numunelerde genişleme ve köpük yapıları 

oluşumu gözlemlenmiştir. 170°C’de ise numuneler erimiş ve köpük oluşumu 

gerçekleşmemiştir.  Numunelerin görsel muayenesinin ardından optimal köpük üretme 

sıcaklığı aralığı belirlenerek daha dar sıcaklık aralıklarıyla deneylere devam edilmiştir. 

155°C, 157°C ve 160°C’de başarılı köpürme sonuçları gözlenmiştir. 

Numunelerin köpük morfolojisi, SEM görüntülemesi ile incelenmiş; ortalama hücre 

boyutu, hücre yoğunluğu ve genişleme oranı analiz edilmiştir. Özellikle %1 Joncryl 

katkılı PLA numunelerinde kapalı hücreli köpük yapısının elde edilmesi, reaktörün 

sıcaklık ve basınç kontrol hassasiyetini kanıtlamıştır. 

Ayrıca, gerçekleştirilen SEM analizleri sonucunda köpürtme işlemi sırasında 

numunelerde katman ayrılmaları (delaminasyon) gözlemlenmiştir. Bu ayrılmaların her 

zaman numunenin kesit düzlemine dik yönde gerçekleştiği belirlenmiştir. Bu 

durumun, köpürtme öncesinde sıcak pres ile şekillendirilen PLA pullarının tam olarak 

eriyip kaynaşmamasından kaynaklandığı düşünülmektedir. Bu sonuçlar, presleme 

sıcaklığının polimerin tam birleşmesini sağlayamayacak kadar düşük olduğu veya 

presleme sürecinin çok hızlı gerçekleşerek malzemenin tamamen erimesine fırsat 

vermediğini düşümülmektedir. Ayrıca, SEM görüntülemesinde numunelerin kesilmesi 

sırasında oluşan yüzey bozulmaları nedeniyle kesitlerin çoğunun köpük yapısını 

detaylı göstermediği, yalnızca sınırlı bölgelerin güvenilir analiz edilebildiği tespit 

edilmiştir. Bu gözlemler gelecekteki test numunelerinin hazırlama yöntemlerinin 

geliştirilmesinde önemli katkı sağlayacağı düşünülmektedir. 



xxiii 

Başarılı operasyonel testlerin ardından, Türkiye’de benzeri bulunmayan bu otoklav 

köpükleme cihazı İTÜ altyapısına kazandırılmış ve bu tez çalışmasının ardından farklı 

araştırma projelerinde kullanılmak üzere araştırmacıların test süreçlerine önemli katkı 

sağlayacak şekilde üniversite envanterine eklenmiştir. Bu cihazın İTÜ araştırmacıları 

tarafından farklı termoplastik türleri ile de kullanılabilmesi, gelecekte farklı 

modifikasyonlarla sürdürülebilir polimerler gibi diğer yeni nesil polimer köpükleme 

araştırmalarına da altyapı sağlayacaktır. Bu proje, İstanbul Teknik Üniversitesi’nin 

sürdürülebilir malzeme teknolojileri alanındaki lider konumunu güçlendirmiş ve 

Türkiye’de biyoplastik köpükleme araştırmalarına yönelik önemli bir boşluğu 

doldurmuştur. 

  



xxiv 

 



1 

 

1.  INTRODUCTION  

1.1 Background 

The vast majority of plastics in widespread use today are produced from petroleum 

and petroleum-based sources. The limited oil reserves in the world, and the fact that 

the waste of these materials do not decompose in nature and cause significant 

ecological damage, have paved the way for many studies to be conducted to replace 

petroleum-based plastics with bioplastics as a sustainable alternative [1]. 

Türkiye, having very limited fossil fuel resources and increasing use of plastics, is 

even more exposed to the negative economic and environmental consequences of 

using plastics. As an agricultural country, Türkiye will benefit much more from any 

progress in the bioplastics field, and the possible gradual replacement of petroleum-

based plastics with bioplastics [2]. 

Polylactic acid (PLA) is a sustainable plastic because it can be produced efficiently 

from various agricultural products. There is a potential for the use of agricultural 

products such as corn, sugar beets, etc, which are widely produced in Turkey, in the 

production of bioplastics. The savings that can be achieved from monetary resources 

spent on importing plastic raw materials and on domestic production using imported 

fossil fuels, and also the growth and value added that will be provided in the 

agricultural economy, highlight the potential of bioplastic use for Türkiye [3]. 

With respect to environmental protection, considering their rapid biodegradation 

properties, new generation bioplastics are ideal candidates for replacing petroleum-

based plastics, which cannot be effectively recycled and have a high waste volume [4]. 

Polymer foams, which are widely used in many areas, especially in the packaging 

industry, are produced from petroleum-based plastics and cannot be recycled due to 

the transportation costs of the high volume/mass ratios of the material [5-6]. 

PLA has suitable mechanical properties for foam production, however it is a material 

open to development due to its narrow temperature range for foaming, slow 



2 

 

crystallization kinetics, and brittle structure. The use of PLA and other bioplastics for 

foam production has long attracted the attention of both academics and industry. 

Bioplastic foams that can compete economically and technically with petroleum-based 

foams on an industrial scale have not yet been produced. Research on this subject is 

being conducted at our university, as well as in many major universities around the 

world, and significant academic progress has been made. However, there are still many 

obstacles to overcome before industrial infrastructure investments become feasible and 

widespread industrial production is possible. Extensive testing of bioplastic samples 

under controlled laboratory environments and varying production methods is needed 

before industrial processes that enable large-scale foam production from bioplastics 

can be designed [7]. 

İTÜ, as one of the leading universities in academic research on this subject, has been 

planning to equip its Sustainable Green Plastics Laboratory (SGPL) with a laboratory 

scale batch foaming reactor, which is expected to benefit researchers significantly by 

facilitating their testing work. 

1.2 Aims and Objectives 

The aim of this project is to develop a laboratory-scale batch foaming reactor to be 

used for bioplastic foaming research at İTÜ. 

The project starts with a general literature survey on the subject, and continues with 

the design of the autoclave body and workbench using CAD software, materials 

selection and procurement, production of individual parts, assembly of the autoclave 

foam production device, and the workbench. Finally, operational testing of the device 

in SGPL with PLA samples and under various experimental parameters was planned. 

Specific objectives of this project are: 

 Design and production of an autoclave foaming device 

 Design and production of a workbench 

 Design and procurement of the autoclave insulation sleeve 

 Procurement of cartridge type heaters and thermocouples 

 Arrangement of the reactor setup to work with existing temperature control 

device, syringe pump etc. in SGPL 



3 

 

 Optimizing the reactor setup for ergonomics 

 Preparation of health and safety documentation 

 Functional testing of the complete reactor setup by foaming different PLA 

samples with supercritical carbon dioxide under various operational 

parameters  

1.3 Thesis Structure 

The thesis starts with a literature survey in the second chapter.  Since the study largely 

consists of design work and machine manufacturing, the literature review focused on 

the planned area of use of the device, foaming of bioplastics with supercritical CO2,  

and also on research on the design of similar reactors. 

The third chapter, as the main body of the thesis, documents the design, manufacturing 

and assembly of the foaming reactor. This section includes project specific design 

considerations, related calculations, technical drawings of individual 

parts/components of the setup, as well as reasoning for main design parameters and 

practical choices made during the manufacturing and assembly. 

The experimental setup for testing the completed foaming reactor and operational 

testing methodology is explained in the fourth chapter. 

Finally, project results and deliverables are presented together with suggestions for 

potential improvements and discussion for further work on the subject in the last 

section. 

 

  



4 

 



5 

 

2.  LITERATURE REVIEW  

2.1 Introduction to Sustainable Polymers 

Sustainable polymers have gained great importance as they have started to become 

viable alternatives for petroleum-based plastics.  This is mainly due to their potential 

to overcome or at least reduce environmental detriments such as plastic pollution, 

carbon emissions, and the possible depletion of natural resources. One of the foremost 

advantages of sustainable polymers is their biodegradability, as most traditional 

plastics do not biodegrade, making them persist in the environment for centuries. Some 

biodegradable polymers, such as polylactic acid (PLA) and polyhydroxyalkanoates 

(PHAs), emit harmless byproducts such as carbon dioxide and water when they 

eventually decompose. This biodegrading property significantly reduces plastic waste 

accumulation, especially in landfills and natural habitats. This also profits the 

overburdened waste management systems and inefficient recycling processes, 

reducing the environmental harm. 

2.2 PLA 

Polylactic acid (PLA) is a biodegradable and bio-based thermoplastic polyester, 

derived primarily from renewable resources such as cornstarch, sugarcane and 

sugarbeets. Due to its sustainability, biodegradability, and mechanical properties it can 

be compared to conventional plastics like polystyrene (PS) and polyethylene 

terephthalate (PET). PLA has gained considerable attention as a candidate for foam 

production in both general use applications and biomedical applications [7]. 

 

 

 



6 

 

2.3 Foaming Processes and PLA as a Foaming Material 

2.3.1  Foaming processes 

2.3.1.1 Injection 

Injection foaming is a method which can produce complex three-dimensional 

geometries and structurally demanding components. During the process, physical or 

chemical blowing agents are injected into molten polymer within the injection molding 

apparatus. The brittleness and low melt elasticity of neat PLA often result in limited 

foam expansion unless modified with additives such as talc or nanoclays. Experimental 

results demonstrate that injection foaming yields improved mechanical performance 

compared to unfoamed PLA [7]. The value of injection foaming is well established in 

packaging and structural applications where dimensional accuracy and impact 

resistance are critical. Process optimization and formulation tuning remain central to 

achieving consistent foam morphologies when using PLA as a foaming material [8]. 

2.3.1.2 Extrusion 

Extrusion foaming is one of the most established methods for producing thermoplastic 

foams, especially at industrial scales. It is a method that operates and uses a rapid 

pressure drop to achieve the cell nucleation and growth required for foaming. For the 

foaming of PLA, the process is generally hindered due to the material’s low melt 

strength and slow crystallization rate. Foamability improvements can be made via the 

addition of chain extenders or nucleation enhancers. These additives improve the 

strain-hardening behavior of PLA, allowing for greater cell expansion and improved 

structural stability. Supercritical CO₂ and chemical blowing agents are both commonly 

used in this process, but for PLA, the high solubility and non-toxic nature of 

Supercritical CO₂, which facilitates fine and uniform cell structures, is highly favored 

[7,9]. 

2.3.1.3 Batch foaming 

Batch foaming involves saturating a polymer sample with gas under controlled 

temperature and pressure conditions, followed by rapid depressurization and/or 

heating to induce foaming. This method is crucial in understanding the effects of 

variables such as temperature, pressure and saturation time on gas solubility, diffusion, 



7 

 

and crystallization. This process is the main focus of this thesis and will be detailed 

thoroughly in the proceeding sections [7]. 

2.3.2  PLA as a foaming material 

Despite the mechanical advantages of the material, the foaming of PLA presents 

significant technical challenges. The mains limitations that prevent PLA from 

becoming a replacement for petroleum-based polymers is its inherently low melt 

strength, slow crystallization kinetics, and brittle nature, which collectively hinder the 

production of low-density foams with fine, closed-cell morphologies [7]. 

To improve the foamability of the material, many strategies have been attempted by 

the researchers. Incorporating chain extenders were used to achieved a branched chain 

PLA and nucleating agents such as talc were added to improve the matierials melt 

strength, crystallization and cell nucleation. Although, many of these methods showed 

varying degrees of success, problems like high open-cell content still presists [7]. 

2.4 Blowing Agents and Supercritical CO2 as a Blowing Agent 

In a polymer foaming process, blowing agents are used to create desired cellular 

structures and end product properties. Physical or chemical blowing agents are used, 

depending on the manufacturing process, performance objectives of the foam, and 

expected physical properties like density. Physical blowing agents can be in a gas, 

supercritical, or liquid phase. In gas and supercritical phases, expansion is achieved by 

depressurizing, while physical blowing agents in the liquid phase create foaming by 

changing to the gas phase during the process. Chemical blowing agents form a gas by 

decomposing or through a chemical reaction [9]. 

Environment and safety are also critical concerns when choosing a blowing agent. 

Many conventional physical and chemical agents are known to have serious risks. N2 

or CO2 are blowing agents that can dissolve in gas or supercritical phases in a polymer 

melt under pressure and diffuse out as gas to expand the polymer during 

depressurizing. Being chemically inert gases, N2 and CO2 are less corrosive to their 

surroundings, and also do not pose environmental and safety risks compared to many 

other blowing agents. For low density foams where larger expansions are required, 

CO2 is a preferred blowing agent because of its higher solubility in polymers [10-11]. 



8 

 

Supercritical CO2, with its gas-like viscosity and liquid-like density is a preferred agent 

in various applications including polymer foaming. Density can be tuned easily by 

small changes in pressure within the critical region, its supercritical phase is easily 

reached and it can easily be removed by depressurization [12-13]. 

2.5 Batch Foaming Systems 

2.5.1  Introduction to batch foaming 

Batch foaming is a widely used mostly laboratory-scale foaming process used for 

studying the foaming behaviour of polymers. Unlike continuous processes such as 

extrusion foaming, batch foaming allows more precise control over individual 

parameters like temperature, pressure and saturation time, making the process highly 

favourable in research applications. In the batch foaming method, the polymer samples 

are placed inside a pressure chamber and saturated with a physical blowing agent (e.g., 

carbon dioxide or nitrogen) for a set amount of time allowing the gas to 

dissolve/diffuse into the polymer matrix. The foaming is achieved by creating 

thermodynamic instability, either via rapid depressurization or a rapid increase in 

temperature. The process is essential for understanding the mechanism of gas 

dissolution and diffusion as well as cell nucleation and cell growth [14]. 

2.5.2  Applications and advantages of batch foaming 

Batch foaming systems hold great valuable in understanding the foaming behaviours 

of various polymers as they serve as a controlled environment where the operator can 

precisely control and monitor the major parameters. These properties aid researchers 

in optimizing foaming conditions and studying new formulations. Flexibility and high 

precision make batch foaming systems ideal for studying various material specific 

phenomena such as crystallization, polymer-gas interactions, or the effects of 

additives. These systems also allow the reliable generation of microcellular and 

nanocellular foams as controlling the foaming uniformity is simple and reproducible. 

The static nature of the process enables the researchers to use smaller quantities of 

material, which is an advantage when working with expensive polymers or small scale 

novel materials. Many continuous foaming process are effected by inconsistencies 

which can be eliminated or minimized by the use of a well designed bacth foaming 

system [15]. 



9 

 

Corre et al. (2011) investigated the batch foaming behavior of chain-extended 

polylactic acid (PLA) using supercritical carbon dioxide(CO₂), focusing mainly on the 

effects of rheological properties and processing parameters on cell morphology. In the 

study, PLA modified with chain-extender was used due its enhanced melt strength and 

elasticity. The batch foaming process saturation parameters were 165 °C for 2 hours 

under pressures ranging from 9.6 to 14.2 Mpa. The foaming was induced by rapid 

depressurization (~20 bar/s). It was found that chain extension enabled higher cell 

nucleation and finer foam structures. The enhanced viscoelasticity and increased 

crystallinity of the modified PLA contributed to the formation of stable microcellular 

foams but excessive crystallitiny caused the inhibition of cell growth. It was concluded 

that optimal foam quality in batch foaming processes is achieved by balancing melt 

elasticity, crystallization kinetics, and gas absorption behavior [16]. 

2.5.3  Pressure-induced batch foaming 

Pressure induced batch foaming is batch foaming variant where the foaming is initiated 

by a rapid decrease in pressure. In this method, the sample is saturated with the 

physical blowing agent at high temperatures (usually above the glass transition 

temperature of the material) and pressures for a desired duration. When the 

predetermined saturation phase is over, a discharge valve is opened releasing the gas 

and rapidly depressurizing the system, causing the spontaneous nucleation of gas 

bubbles inside the supersaturated polymer. This method is often preferred due to 

several advantage over the temperature induced method. The simplicity of achieving 

the saturation and foaming in a single chamber makes the setup easier to manufacture 

and operate. The method poses minimal thermal degradation risk if percise 

temperature control is achieved, which is essential when working with polymers that 

are sensitive to high temperatures. Another key benefit is the ability to achieve very 

high rates of depressurization, promoting higher nucleation rates. This results in finer 

and more uniform cell structures, often desired in many researches and applications. 

Formation of nanocellular structures are reported at pressure drop rates exceeding 

1000 Mpa/s, which can be critical in advanced insulation and biomedical applications 

[17]. 

 

 



10 

 

2.5.4  Design of batch foaming devices 

Designing a batch foaming device, especially one suitable for pressure-induced 

foaming, requires attention to several engineering and scientific criteria. The main 

components of the system include a pressure vessel (autoclave), gas delivery system, 

temperature controller and various sensors for the monitoring of the parameters. To 

achieve high depressurization rates, electronically contolled solenoid valves are 

incorporated which can open instantly [14]. 

The most critical component in batch foaming system designs are the pressure vessels. 

This is especially true for pressure-induced batch foaming where the vessel contains 

gasses under very high pressures while staying at elevated temperatures throughout 

the operation. Like any other pressure vessel, the design of the batch foaming 

autoclave must adhere to internationally accepted standards to ensure the safety of 

operation. The designs should be carried out with structural integrity and durability in 

mind. The most widely recognized and applied standard for this purpose is the ASME 

Boiler and Pressure Vessel Code (BPVC), Section VIII, which governs the 

construction of pressure vessels. It is a very comprehensive guide that is internationally 

accepted and implemented [18]. 

The ASME BPVC outlines fundamental design rules, material requirements, 

fabrication processes, testing procedures, and inspection criteria for pressure vessels 

operating at pressures above 1 bar. ASME divides the code into three divisons: 

Division 1 includes lower pressure vessel with simple designs; Divison 2 cover 

moderate-to-high pressure vessels, providing more detailed analysis and stricter safety 

standards; Division 3 is used for the highest pressure vessels. For laboratory scale 

batch foaming systems, using Division 2 standards is the most suitable option as the 

foaming devices constantly experience cyclic loading at high pressures. 

The first design principle for any pressure vessel is to calculate the internal pressure 

loading. ASME BPVC stress analysis allows the designers to calculate the minimum 

wall thickness of cylindrical vessels which is the shape of most batch foaming 

autoclaves. A sufficient wall thickness is defined as the thickness that can withstand 

the internal pressure without yielding. The calculations of this section always include 

safety factors that are integrated into the formulas provided by ASME. The vessels are 



11 

 

also evaluated for external loads, thermal stresses, corrosion allowances and repeated 

pressure cycles [18]. 

The rest of the equipment used in the batch foaming system must be evaluated by the 

designer. The electrical connection must abide by IEC 60364 – Low-voltage electrical 

installations standard as safety should always be the highest priority. The control 

systems should be acquired or designed according to the users/researchers needs as 

there are no standards for precision required for the experiments [19]. 

Tammaro et al. (2016) introduced a compact, low-cost pressure-induced batch 

foaming apparatus known as the "mini-batch." The device was constructed using 1/2" 

NPT fittings for gas inlet, gas outlet, thermocouple insertion and pressure. The design 

allowed researchers to achieve pressure drop rates as high as 1800 MPa/s, mainly made 

possible by the quick release valve and the small internal volume compared to its outlet 

diameter. The small internal volume also provides uniform gas diffusion and heating, 

which are very important parameters for reliable and uniform foam production. The 

main dowside of the design is that the small internal volume only allows several pellets 

of polymer to be placed inside at one time. The use of standard parts and fittings make 

this setup highly affordable and practical for research purposes [14]. 

2.5.5  Variations and innovations in device design 

Various labs around the world have develpoed custom batch foaming system designs 

tailored for specific reasearch purposes just like the “mini-batch. The have been some 

designs where the systems are equiped with taransparent high strength glass or 

polycarbonate pressure chambers allowing the optical imaging of the foaming process. 

Also, there have been designs with real-time data collection systems, monitoring 

pressure, temperature and expansion rates synchronously. There have been proposals 

o modular systems to enable quick changing of experimental conditions. Azimi et al., 

(2022) designed a lab-scale device with interchangeable reaction chambers, allowing 

the operator to test different test samples under the same foaming conditions [20]. 

Another innovation in the field was the custom-made ‘matricial foaming’ apparatus 

developed by Tammaro et al. (2022), which enabled high-yielding experimentation 

within a single batch foaming operation. This autoclave is constructed from three 

stainless steel pieces allowing simultaneous foaming of sixteen polymer samples. The 

device can be set to create four distinct temperature settings and four different 



12 

 

depresurization rates in a single cycle. The different pressure drop rates are achieved 

by discharge holes of varying diameters placed on the central component, creating 

different flow routes. Four different temperature setting are achieved by by heating 

cartridges on either side of the foaming chamber assembly creating a linear 

temperature gradient between them. Theadvantage of this design is to map the 

processing conditions of foaming temperature and depressurization rate in a single 

expreiment. This device was validated by tests preformed with poly(ε-caprolactone) 

and CO2. The results showed significant variations of foam density and crystalinity 

with the variation of both processing parameters. This system and many more custom 

batch foaming setups are crucial for researches focusing on developing new polymers 

for foaming [21]. 

 

 



13 

 

3.  DESIGN AND DEVELOPMENT OF THE REACTOR 

3.1 Introduction 

The batch foaming is a critical method for producing thermoplastic foams with 

uniform foam quality. Batch foaming processes have the ability to control temperature, 

pressure and saturation time more precisely than other methods. These parameters are 

key aspects of creating foams with the desired uniformity, cell size and density. 

This section focuses on the design and development of a batch foaming reactor 

intended for conducting thermoplastic foaming experiments in İTÜ SGPL. The reactor 

serves as a controlled environment where thermoplastic materials are exposed to gas, 

typically CO2 or N2, under specific pressure and temperature conditions and saturated 

for set durations to induce foaming by decompression. This process requires an 

intricate balance of temperature stabilization, pressure regulation, and efficient gas 

dissolution to saturate the material with the foaming agent. The reactor produces foam 

by rapidly and safely decompressing the chamber creating stable foam structures 

within the polymer matrix. 

The aim of this chapter is to describe the design and development of the foaming 

reactor by explaining the design choices, various pre-existing or custom components 

which had to be integrated to the system and the methodologies employed to achieve 

the desired effectiveness as well as to ensure safety and ease of use. This includes an 

overview of the conceptual design, the selection of suitable materials and 

manufacturing methods, the integration of essential control systems and 

supplementary devices, the challenges encountered during the development and 

testing of the reactor. By understanding the principles and considerations involved in 

the reactor's design, this section aims to provide a clear understanding of how the 

reactor functions in producing thermoplastic foams with precise and reproducible 

characteristics. 



14 

 

3.2 Design Requirements and Specifications 

The design of the batch foaming reactor is driven by several critical factors related to 

the nature of thermoplastic foaming and the specific requirements of the experiments 

to be conducted. The primary objective is to create a controlled environment where 

thermoplastic materials can be uniformly foamed using a specific foaming agent under 

varying temperature and pressure conditions. The reactor must provide the necessary 

conditions to achieve repeatable, reproducible results while also ensuring ease of 

operation and safety. The reactor should be able to accommodate any thermoplastic 

material and should be able reach temperatures and pressures sufficient for the 

saturation of the foaming agents. 

3.2.1  Performance goals 

The most important goals of the reactor design are precise temperature and pressure 

control during the saturation phase of the process and the ability to rapidly decompress 

the chamber to initiate foaming. Consistency of the foaming results are highly 

dependent on the simultaneous control of these factors. 

Temperature uniformity and precision 

The foaming reactor should be able to heat the samples to the desired temperature in a 

uniform fashion. The working range should be between room temperature and 300°C. 

The reactor should be able to keep the samples at the demanded temperature for the 

duration of the saturation phase. The acceptable temperature fluctuations should be 

less than +/- 1 °C to ensure the reliability of the experimental results. 

The reactor should be able to stabilize its temperature quickly during the pressurization 

phase to prevent the overheating of the samples. (The desired effect can also be 

achieved by controlling the pressurization rate) 

Precise pressure control 

The foaming reactor should be pressurized with the desired foaming agent to the 

desired pressure. 

The pressure of the foaming chamber should be kept at the desired pressure for the 

duration of the saturation phase. The acceptable pressure fluctuations should be less 

than +/- 1kPa and pressure should be accurate to +/- 0.2%. 



15 

 

The foaming reactor system should be able to control the pressurization rate to prevent 

non-uniform forces to be exerted on the sample and to ensure the stability of 

temperature. 

Uniform gas dissolution and expansion 

The foaming reactor’s chamber should be large enough to allow uniform gas 

dissolution through the surfaces of the sample. 

The Foaming reactor should be able to decompress the chamber down to atmospheric 

pressure in less than 1 second without damaging the sample. 

Processing flexibility 

The reactor design must accommodate a wide range of thermoplastic materials. It has 

to be equally effective in experimenting with many common polymers and 

experimental thermoplastics. 

The reactor should be able to make use of any inert gas as a foaming agent (Main 

planned for CO2 and N2). 

3.2.2  Material selection requirements 

The choice of materials for the reactor vessel and components had to take into account 

their thermal conductivity, resistance to pressure, and compatibility with the 

thermoplastic materials being used. The main body of the reactor have to withstand 

internal pressures up to 30 MPa and should not experience marginal fatigue for at least 

10,000 cycles (20-40 experiments per week for 5-10 years). The Materials to have 

withstand up to 300°C. 

When using bolts or other fastening methods the fasteners should be made out of a 

material that has lower strength and toughness compared to the main reactor body. 

Allowing easier parts replacements and improving the longevity of the main reactor 

components. All fasteners should be made out of ductile materials to prevent sudden 

failures when the parts are accidentally overloaded, instead they should deform to 

allow the operators to comfortably analyse faults via visual inspection. 

No material should cause or accelerate corrosion on the coupled material and should 

be non-toxic at the all operating conditions. 

 



16 

 

3.2.3  Compatibility 

The foaming reactor should be compatible with the laboratory environment and should 

use the pre-existing pumps and control devices if possible. Gas connection and valves 

should be of standardized sizes. 

When finished, the whole foaming reactor assembly, including the pumps, heaters and 

control devices should cover a footprint not greater than 1m2. The design should 

include a specialized workbench where all the equipment can be mounted if need be. 

Said workbench should be stable enough to not require external fixation and should be 

capable of being moved or relocated with relative ease without the need of specialized 

equipment. 

3.2.4  Safety and ease of use 

Safety is a top priority in the design of the batch foaming reactor. The reactor must be 

equipped with several safety features to protect operators from potential hazards, such 

as high temperatures and pressures. 

3.3 Conceptual Design 

The design of the batch foaming reactor began with the development of a robust 

conceptual framework that would accommodate the specific operational and research 

needs of thermoplastic foaming experiments. The reactor needed to offer precise 

control over process variables such as pressure, temperature, and saturation time, while 

also being safe, easy to operate, and adaptable to future experimental modifications. 

This section details the foundational decisions made during the conceptual design 

stage, including the selection of reactor type, geometry, process configuration, and the 

rationale behind key design features. 

3.3.1  Selection of reactor type 

A batch foaming reactor configuration was selected based on its suitability for 

controlled laboratory-scale experiments where precision and repeatability are 

paramount. Unlike continuous or semi-continuous systems, batch reactors are 

inherently flexible, allowing for the isolation of variables and close monitoring of each 

experimental run. This is especially advantageous in thermoplastic foaming studies, 



17 

 

where process sensitivity to factors like gas diffusion, pressure release rate, and heating 

profile demands fine control over each stage of the experiment. 

In a batch foaming system, the sample is statically exposed to a pressurized gas 

environment at a controlled temperature for a defined duration, followed by a rapid 

but controlled depressurization to initiate foaming. This setup allows researchers to 

systematically vary conditions such as saturation time, pressure level, and processing 

temperature to evaluate their influence on cell morphology, foam density, and 

mechanical properties. 

3.3.2  Reactor geometry and physical layout 

The reactor vessel was conceptually designed as a vertically oriented cylindrical 

pressure chamber, which offers several key advantages from a mechanical and thermal 

standpoint as well as improving the ease of use. Cylindrical geometries in pressure 

vessel designs are well-known for their ability to evenly distribute stress under internal 

pressure, thus reducing the likelihood of failure or deformation. The geometry also 

allows for better heat distribution by the use of equidistant radially mounted heaters. 

The heat loss is also reduced due to the lower surface area and can be improved by 

uniform insulation.  The vertical orientation allows for a hatch to be situated at the top 

of the chamber to facilitate the insertion and removal of samples with greater ease. 

The internal dimensions of the vessel were determined based on several 

considerations: 

 The size and shape of the desired thermoplastic specimens. The typical 

specimens are small discs, sheets, or pellets (beads) smaller than 10mm in 

diameter. The chamber should be able to accomodate multiples of the refered 

samples or tensile test samples with lengths up to 60mm.  

 The need for sufficient clearance around the samples to ensure uniform gas 

exposure. 

 Clearance requirements for the gas inlet and outlet holes as well as the 

thermocouple.  

In addition to functional performance, practical factors like benchtop footprint, 

accessibility for maintenance, and compatibility with existing laboratory infrastructure 

were taken into account. 



18 

 

3.3.3  Integration with pre-existing equipment 

The reactor design was planned to be compatible with the pre-existing lab equipment 

for the purpose of reducing the requirements of cost, space and production time; 

allowing the commisioning date of the machine to be brought forward. 

The pre-existing equipments planned to be integrated into the design are as follows: 

 Teledyne Syringe pump: A syringe pump capable of compressing gas and 

holding it at a precise pressure. The required gas cylinder was planned to be 

connected to the syringe pump via a stainless steel pipe allowing the machine 

to be fed with the required gas. The machine would allow the gas to be 

compressed to the desired pressure and once the foaming reactor is ready to be 

pressurized, it would release the gas into the chamber. It would stabilize the 

pressure at the desired level for the duration of the experiment allowing the 

saturation of the sample. All the gas connections of the foaming reactor sould 

be compatible with the pipes of the syringe pump. 

 EMKO temperature controller: A PID temperature controller with a digital 

display which can power the heater and control the temperature by the help of 

a thermocouple. The heaters and the thermocouple of the foaimg chamber 

should be compatible with the temperature controller. If the required power 

would risk the overheating of the internal relays, an external relay of the 

appropriate capacity should be integrated to the device. 

All of the components of the batch foaming reactor system were planned to be situated 

at close proximity to each other for the efficiency of operation which required a 

specialized workbench to be designed and manufactured.  The workbench was 

designed to allow stable mounting of the foaming reactor for safety. 

3.3.4  Process flow and operation concept 

The operation of the batch foaming reactor was divided into four primary stages, each 

requiring specific environmental conditions and control systems. These stages were 

defined as follows: 

 Heating phase 

In this initial phase, the reactor is heated to the desired temperature by the radially 

mounted heaters. The temperature is controlled by the EMKO temperature controller. 



19 

 

The temperature measurement is done by a thermocouple with its tip positioned on the 

inner wall of the chamber. After the desired temperature is reached, the temperature is 

allowed the stabilize. Once the temperature reading is completely stabilized the hatch 

of the reactor can be opened and the sample can be placed inside. 

 Pressurization phase 

The hatch of the reactor is sealed after the placement of the sample and the discharge 

valve is closed. The syringe pump is used to pressurize the chamber with the desired 

blowing gas. At this phase the pressurization speed and the final pressure is controlled 

by the syringe pump. 

 Gas saturation phase 

In the gas saturation phase, the sample is allowed to saturate with the blowing gas for 

the desired amount of time. During the saturation, temperature and pressure is kept 

stable. 

 Foaming phase 

The final stage involves inducing thermoplastic foaming by triggering cell nucleation 

and expansion. This is achieved via rapid depressurization. When the desired 

saturation time is reached, the operator opens the release valve, rapidly depressurizing 

the chamber. This induces foaming and also cools the sample rapidly. At this point, 

the chamber is opened and the sample is removed as fast as possible to prevent 

reheating possible reheating. 

3.3.5  Design flexibility 

Ensuring the modularity and future-proofing of the reactor system was a vital part of 

the conceptual design process. Given the evolving nature of research, it was important 

to allow for the easy reconfiguration of components and the ability to expand the 

reactor's functionality over time. To this end, several design strategies were integrated 

from the outset: 

 Modular sample holders for accommodating various shapes and sizes of 

polymer specimens. Making it easier to remove or change the type of specimen 

and to eliminate the need of cleaning the foaming chamber. 



20 

 

 Minimum use of welding to make assembly and disassembly of the parts easier 

and faster when maintenance or part changes are required. 

3.4 Detailed Design Process 

3.4.1  Foaming chamber design 

The foaming chamber forms the core of the batch foaming reactor. The chamber 

provides a secure, high-pressure and high temperature environment necessary for the 

saturation and foaming of thermoplastic samples. The design was carried out with 

great emphasis on safety, structural integrity and thermal efficiency. Compatibility 

with the instrumentation equipment was taken into account when designing the 

necessary connection points.   

Design objectives 

The vessel was designed to meet the following operational goals: 

 Sustain an internal pressure of at least 300 bars safely and without significant 

gas loss. 

 Operate at an elevated temperature of up to 300°C. 

 Provide acceptable chemical compatibility with the blowing agents (CO2 and 

N2) at working pressure and temperature 

 Allow the integration of thermocouples and heaters without compromising the 

mechanical and thermal integrity 

 Allow for easy and quick loading and unloading as well as easy cleaning. 

 Allow multiple pellets or longer (60mm) tensile test samples to be loaded 

inside the chamber. 

 Ensure safety when operator errors occur when sealing the closure, valve or 

fittings. 

 Material selection 

The foaming Chamber was constructed using S355J2 steel which is a type of ST52 

structural steel with low alloy content. The main alloying content of the steel is shown 

on Table 3.1. 



21 

 

The selection was made considering several key factors: 

 High toughness, tensile strength and surface hardness as well as adequate yield 

strength even at the elevated temperatures of the working conditions. These 

values and relations are detailed further in Table 3.2 and 3.3 as well as Figure 

3.1. 

 Good weldability and machinabilty for fittings and connections 

 Adequate resistance to air corrosion and chemical compatibility with both CO2 

and N2 at dry conditions. 

 High thermal conductivity and low specific heat capacity for faster heating and 

better heat transfer to the foaming sample. 

 Easy to acquire in Türkiye. Produced in large solid billets, suitable for the size 

of the foaming chamber allowing machining from a single piece of material.   

Table 3.1 : Chemical composition of S355J2 steel [22]. 

Variant Cast Weldability  C % Si % Mn % P % S % Cr % Ni % Mo % V % Cu % 

S355J2 (M) CC 

CEV 0.5max Min - - - - 0.020 - - - - - 

Pcm 0.3max Max 0.20 0.55 1.60 0.035 0.040 - - - 0.150 - 

Table 3.2 : Mechanical properties of S355J2 steel [22]. 

Variant Condition Format 
Yield strength 

min [MPa] 

Tensile 

strength [MPa] 

Elongation 

A5 [%] 
Hardness 

Impact (ISO-V) 

strengthmin 

S355J2(M) +AR 
All 

formats 
355 490-630 22 150-190 HB 

-20 °C 27 J 
(long) 

Table 3.3 : Transformation temperatures of S355J2 steel [22]. 

 Temperature °C 

MS 400 

AC1 720 

AC3 815 



22 

 

 

Figure 3.1 : Variations of mechanical properties of St52 with temperature [23]. 

3.4.1.1 Geometric design 

The vessel was designed as a vertical cylindrical chamber with a flat end on one side 

and an open end on the other, where the chamber hatch is positioned. The inner 

chamber corners were rounded to minimize stress concentrations under pressure 

loading. 

First, the inner dimensions of the foaming chamber were decided, which are illustrated 

in Figure 3.2: 

 Inner diameter: 68mm 

 Inner height:35mm 

 Inner corner fillet radius: 5mm 

 

Figure 3.2 : Simple cross sectional drawing showing the interior dimensions of the 

foaming chamber (original). 

To calculate the minimum wall thickness of a cylindrical pressure vessel with flat ends, 

ASME Boiler and Pressure Vessel Code (BPVC)—specifically Section VIII, Division 

1 for thin walled vessels—was used. 



23 

 

 Type: Cylindrical pressure vessel with flat ends 

 Internal diameter: 68 mm 

 Internal pressure: 300 bar = 30 MPa 

 Temperature: 300°C 

 Material: S355J2 steel 

 Fillet radius: 5 mm at junctions 

 Construction: Monolithic (no welds or seams) 

Per EN standards (similar to ASME assumptions for allowable stress), S355J2 has the 

following properties: 

Yield Strength at room temperature: 355 Mpa 

Yield strength at 300°C: ~250Mpa (Conservative estimate) 

Ultimate tensile strength at room temperature: ~500Mpa 

Ultimate tensile strength at 300°C: ~440Mpa (Conservative estimate) 

ASME Code incorporates safety factors through the allowable stress S, which is: 

𝑆 = min⁡(
𝑌𝑖𝑒𝑙𝑑⁡𝑆𝑡𝑟𝑒𝑛𝑔𝑡ℎ

1.5
,
𝑈𝑙𝑡𝑖𝑚𝑎𝑡𝑒⁡𝑇𝑒𝑛𝑠𝑖𝑙𝑒⁡𝑆𝑡𝑟𝑒𝑛𝑔𝑡ℎ

3.5
)                      (3.1) 

So the allowable stress is: 

𝑆 = 𝑚𝑖𝑛(166.7, 125.7) = 125.7⁡𝑀𝑃𝑎                              (3.2) 

For calculating the cylinder shell thickness, theformula for thin-walled cylinders under 

ASME VIII-1 was used: 

𝑡 =
𝑃.𝑟

𝑆𝐸−0.6𝑃
                                                     (3.3) 

Where: 

 t = minimum required wall thickness (mm) 

 P = internal pressure (MPa) = 30 MPa 

 r = inner radius = 34 mm 

 S = allowable stress = 200 MPa 

 E = weld efficiency = 1 (monolithic, no welds) 



24 

 

    𝑡 ≈ 9.47𝑚𝑚                                                  (3.4) 

For calculating the flat end thickness the formula for flat heads with fillet and stay or 

integral construction was used: 

𝑡 = 𝐾.√
𝑃.𝐷2

𝑆
                               (3.5) 

Where: 

 K = coefficient depending on support and edge geometry 

 D = diameter = 68 mm 

 P = 30 MPa 

 S = 200 MPa 

To determine the K value, Figure UG-34 from the ASME code can be used. For a 

monolithic flat head with a 5 mm fillet, per ASME Figure UG-34, Sketch (b-2), the 

applicable coefficient is: 0.2. But for this calculation an overly conservative value of 

0.5 was chosen to further increase the safety factor 

When calculated: 

𝑡 ≈ 16.61𝑚𝑚                  (3.6) 

The previous calculation showed that the foaming chamber is in fact a thick walled 

cylinder as the resulting wall thicknesses were larger than the assumed wall thickness 

of the formula: 

𝑡

𝑟
< 0.1                       (3.7) 

We can recalculate the results using the formula for thick-walled cylinders (Lame’s 

Formula) 

𝜎𝜃 =
𝑃𝑖𝑟𝑖

2(𝑟0
2 + 𝑟2)

𝑟2(𝑟0
2 − 𝑟𝑖

2)
 

𝜎𝜃 =
𝑃𝑖𝑟𝑖

2(𝑟0
2 + 𝑟2)

𝑟2(𝑟0
2 − 𝑟𝑖

2)
 

(3.8) 

Where: 

 𝜎𝜃: hoop stress 



25 

 

 𝜎𝑟: radial stress 

 𝑟𝑖 = internal radius 

 𝑟𝑖 = external radius = 𝑟𝑖+t 

 𝑃𝑖 = internal pressure 

For the purpose of this design, we want to solve the Lame’s Formula for the minimum 

wall thickness (𝑡 = 𝑟0 − 𝑟𝑖). 

When we rearrange the equation to solve the maximum hoop stress at the inner wall, 

where it is the greatest, we get: 

𝑡 = 𝑟𝑖 (√
𝜎𝑎𝑙𝑙𝑜𝑤+𝑃

𝜎𝑎𝑙𝑙𝑜𝑤−𝑃
− 1)            (3.9) 

Where: 

 𝜎𝑎𝑙𝑙𝑜𝑤= allowable stress=125.7 Mpa (as shown in the previous calculation) 

So, 

𝑡 = 9.39𝑚𝑚               (3.10) 

This closely matches the thin-wall result (9.47 mm), so in this specific case, both 

approaches agree. 

For the flat ends, same formula used in the previous thin-walled calculation applies: 

𝑡 = 𝐾.√
𝑃. 𝐷2

𝑆
 

𝑡 ≈ 16.61𝑚𝑚 

(3.11) 

After the minimum wall thickness was decided, which are 10mm for the cylinder walls 

and 17mm for the flat end (rounded up from the calculations above). The real wall 

thickness was decided based on couple factor. Such as the desired heat capacity and 

the placements of the inserts of the heaters, thermocouples and the closure bolts. 

The main body of the foaming chamber works both as a pressure chamber and a heat 

sink. For this reason, keeping the temperature fluctuations to a minimum when then 

chamber is being pressurized and depressurized requires the foaming chambers heat 

capacity to be as great as possible. To achieve this, the walls of the foaming chamber 

was designed to be 50mm thick in both the side walls and the flat end. The cross 



26 

 

sectional view of the foaming chamber at this design step can be seen in Figure 3.3. 

This thickness also allowed the heaters, thermocouples and the closure bolts to be fitted 

onto the body of the foaming chamber without compromising its structural integrity. 

 

Figure 3.3 : Cross sectional view of the foaming chamber with at least 50mm wall 

thickness. The design is fitted inside a cylindrical outer geometry of 168mm diameter 

and 85mm height for the feasibility of manufacture. Exported from SolidWorks 

(Original).  

Rest of the design was carried out on 3D CAD using SolidWorks 2017. The use of 3D 

CAD allowed for better visualisation of the design elements as well as the precise 

placements needed for the manufacturing and fitting of the foaming chamber. 

 For the fitting of the closure, 6 radially symmetric 60mm deep M20 threaded 

axial bolt holes were created on the foaming chamber body 

 For the fitting of the carthridge heaters 3 radially symmetric 10.5mm axial 

through-holes for the heating cartridges were created.  

 For the fitting of the gas inlet, outlet and the thermocouple, 3 radially 

symmetric 5mm radial through-holes were created, connecting the exterior of 

the chamber to the interior. 

All of these fittings and the reasoning behind their design choices are further explained 

in their corresponding chapters in greater detail below. The placements of the fitting 

can be seen on Figures 3.4 and 3.5. 



27 

 

 

Figure 3.4 : Image of the foaming chamber body. Exported from SolidWorks. 

(Original).  

 

Figure 3.5 : Top down view of the Foaming chamber body. Exported from 

SolidWorks. (Original) 1: Foaming chamber interior, 2: 6 radially symmetric 60mm 

deep M20 threaded axial bolt holes, 3: 3 radially symmetric 10.5mm axial through-

holes. 



28 

 

3.4.1.2 Closure mechanism 

The foaming chamber is sealed using a two piece bolted lid: 

 The main (upper) lid made from the same steel alloy as the body of the foaming 

chamber. 

 The inner (pressure plate) lid made from the same steel alloy as the body of the 

foaming chamber. 

 6 radially symmetric 60mm deep M20 threaded axial bolts are used to secured 

the lid 

 Soft metallic (copper or aluminium) gaskets are used to create a complete seal 

All the listed components can be seen in an exploded view in Figure 3.6. 

 

Figure 3.6 : Exploded view of the foaming chamber and the closure excluding the 

nuts and bolts. From top to bottom: Main(upper) lid, Inner(pressure plate) lid, Soft 

metallic(copper or aluminium) gasket. Exported from SolidWorks (Original). 



29 

 

The main lid was designed to have the same diameter as the foaming chamber and to 

have 25mm of thickness. Making it easier to manufacture from the same billet of steel. 

An inner lid with at diameter of 90mm and a thickness of 15mm is placed between the 

main lid and the foaming chamber. This inner lid is designed to be centered on the rim 

of the foaming chamber opening, creating greater pressure than a wider lid would. 

Additional copper or aluminium gaskets were also proposed to be located between the 

inner seal and the foaming chamber rim enhancing the seal. 

It was decided that 6 bolts were going to be used to secure the lid to the foaming 

chamber body. The main reason behind using 6 bolts was to achieve a better seal than 

3 or 4 bolts designs while having less stress on each bolt. 8 or 10 bolt designs were 

also considered but the time it would take to tighten, loosen and remove higher number 

of bolts would make the design impractical in a laboratory environment.  

Before the clamping force is calculated and the required bolt sizes are chosen, the 

geometry of the inner lid and its contact surface is designed. A 30° chamfer is placed 

on the inner rim of the foaming chamber. Both rims of the disc shaped inner lid is 

designed to have an hyperboloidal external fillet. When the inner lid is placed on the 

foaming chamber rim, the chamfered surface and the hyperboloidal fillet coincide on 

a circular contact line. This decreased contact area creates allows a higher stress to be 

exerted on any soft metallic gasket to be placed between the part during normal 

operation enhancing the seal performance. The CAD images of the part can be seen in 

Figure 3.7. The same hyperboloidal fillets were used both on the bottom and the top 

side of the inner lid creating a symmetric design, allowing the inner lid to be flipped 

onto its opposite side in case of an abrasion or any other kind of surface defect. The 

contact points of the components are demonstrated in Figure 3.8. 



30 

 

 

Figure 3.7 : Top and side view of the Inner(pressure plate) lid. Exported from 

SolidWorks (Original). 

 

Figure 3.8 : Cross section view showing the contact zones between the 30° chamfer 

on the foaming chamber inner rim and the hyperbolloidal fillets on the inner lid. 

Exported from SolidWorks (Original). 

The stability of the inner lids top surface and the main lids lower surface is achieved 

by an indent on the lower surface of the main lid that is 1mm deep that is made to fit 

the geometry of the inner lid with minimal movement. The contact points of the 

components are demonstrated in Figure 3.9. 



31 

 

 

Figure 3.9 : Cross section view showing the contact zones between the inner lid and 

the main lid. Exported from SolidWorks (Original). 

To choose the appropriate bolt size and material for securing the lid, the tension load 

on each bolt is calculated. First the pressure load on the gasket is calculated at the 

maximum operating pressure of the foaming chamber: 

𝐹𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 = 𝑃. 𝐴 = 𝑃. 𝜋. 𝑟2             (3.12) 

Where: 

 P: Maximum operating pressure (30Mpa) 

 A: Area of the inner lid 

𝐹𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 = 108,900𝑁          (3.13) 

To calculate the gasket seating force, first the gasket contact area has to be calculated. 

For the next calculation the gasket diameter(D) is taken as 70mm and the gasket 

seating width(ω) as 3mm: 

𝐴𝑔𝑎𝑠𝑘𝑒𝑡 = 𝜋.𝐷.𝜔 = 6.60 × 10−4𝑚2         (3.14) 

Yield strength of annealed copper gaskets are 69 MPa. To achieve optimal sealing, the 

aimed compression stress should be above this value. For the sake of this calculation, 

𝝈𝒈𝒂𝒔𝒌𝒆𝒕 is chosen to be 80 MPa [24]. 

𝐹𝑔𝑎𝑠𝑘𝑒𝑡 = 𝜎𝑔𝑎𝑠𝑘𝑒𝑡. 𝐴𝑔𝑎𝑠𝑘𝑒𝑡 = 52,800𝑁          (3.15) 

So, 

𝐹𝑡𝑜𝑡𝑎𝑙 = 𝐹𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 + 𝐹𝑔𝑎𝑠𝑘𝑒𝑡 = 161,700𝑁    (3.16) 



32 

 

When we calculate the preload for each of the 6 bolts: 

𝐹𝑏𝑜𝑙𝑡 =
𝐹𝑡𝑜𝑡𝑎𝑙

6
= 26,950𝑁⁡𝑝𝑒𝑟⁡𝑏𝑜𝑙𝑡        (3.17) 

The bolt material is chosen to be grade 8.8 for its high tensile strength and ductile 

characteristics. 9.8 or higher grade were not preferable due to their increased hardness 

which can wear the threads on the foaming chamber after repeated tightening and 

untightening. When we refer to the table of coarse threaded metric bolts. The proof 

loads of 8.8 metric bolts can be seen in Table 3.4. 

Table 3.4 : Table comparing the proof loads of 8.8 metric bolts at normal conditions 

and 300°C. The data is computed from empirical values [25-27]. 

Thread (mm) Grade 8.8 Proof Load – Fp (N) Grade 8.8 Proof Load at 300°C 

M10 33700 25275 

M12 48900 36675 

M14 66700 50025 

M16 91000 68250 

M18 115000 86250 

M20 147000 110250 

It can be seen that the M12 bolt is the minimum allowable bolt for the application. In 

this case a safety factor of 4 is chosen due to the frequent tigthening and unthightening 

the bolts which will be inevitable during the operation of the foaming chamber: 

𝐹𝑝 = 𝐹𝑏𝑜𝑙𝑡 × 𝑆𝐹 = 107,800𝑁      (3.18) 

In this case the suitable bolt for the application becomes the M20 bolt. Larger bolts are 

more resilient to accidental misthreading as well as being more suitable for visual 

inspection in case of a possible thread wear. A very large safety factor could also 

prevent damage due to overtightening as the required preload for the bolts are the 

quarter of its proof load. For the ease of operation, the bolts are chosen to be stud bolts 

that penetrate 60mm into the foaming chamber body. This design allowed for the 

tightening of the bolt by the use of only one nut making single operator operation 

feasible. The foaming chamber body will need to have 6 M20 threaded blind holes 

bored into it to keep the stud bolts in place. While the main lid will have 6 unthreaded 

20mm through holes that will allow the bolts to pass through, protrudeding 25mm 

above the whole assembly. This would allow the placement of a 2mm washer and an 



33 

 

heavy duty M30 nut as the fasteners. The cross sectional view of the assembly can be 

seen in Figures 3.10 and 3.11. 

 

Figure 3.10 : Cross section view of the foaming chamber assembly showing the 

placement of one stud bolt. The hole has a diameter of 20mm which is the thread 

diameter of the M20 bolt making the hole appear larger in diameter than the actual 

end product. The CAD model will be re-iterated in the manufacturing stage where a 

16mm would need to be drilled before adding the threading. Exported from 

Solidworks (Original). 

 

Figure 3.11 : Isometric view of the foaming chamber assembly showing the 

placement of one bolt with a washer and a heavy duty nut. Exported from 

SolidWorks (Original). 



34 

 

3.4.1.3 Ports and fittings  

The foaming chamber includes several integrated ports for the gas delivery system and 

the thermocuple. As well as inserts for the heating elements: 

 Gas inlet port of 5mm diameter. 

 Gas outlet port of 5mm diameter. 

 Thermocouple insert of 5mm diameter 

 3 radially symmetric 10.5mm axial through-holes for the heating cartridges 

The ports of the gas inlet, gas outlet and the thermocouple are the only through holes 

on the foaming chamber that connects the outer environment to the interior of the 

chamber except the lid. For this reason these 3 ports have to have fittings that are 

perfectly sealed, preventing gas loss. For these ports, 3 radially symmetric 5mm radial 

through-holes were created. The holes were centered 10mm below the opening of the 

foaming chamber. The high placement of the ports were designed to provide less 

aerodynamic disturbance and heat transfer when the chamber is pressurized and 

depressurized. The placement of these ports can be seen from different angles in 

Figures 3.12 and 3.13. 

 

Figure 3.12 : Cross section view of the foaming chamber from the top plane 

showing the radial placement of the three 5mm ports. Exported from SolidWorks 

(Original). 



35 

 

 

Figure 3.13 : Cross section view of the foaming chamber from the side showing the 

vertical placement of one of the three 5mm ports on the right side. Exported from 

SolidWorks (Original). 

The inlet port was designed to connect inlet pipes with variable diameters. To achieve 

this a directly welded pipe idea was abandoned. A 6mm double-sided pipe fitting 

would be placed inside the inlet hole by creating the appropriate threading inside. 

Then, it would be fillet welded around its central hex frame to strengthen the joint and 

create a gas-tight fitting. The welded joint would not cause a problem as the fitting will 

never need to be removed when changing the pipes. 

The outlet hole was not designed to connect variably size pipes. So, it was designed to 

be a solely fillet welded joint with a short length of 5mm high pressure pipe protruding 

outwards, where it will be connected to a release valve via a ferrule. 

The thermocouple insert was also prepared to fit a threaded thermocouple similar to 

the threaded connection of the inlet pipe ftting mentioned earlier. The central hex 

frame of the thermocouple would also be fillet welded to ensure optimal sealing. 

When we calculate the pressure load on one of the portsat the maximum operating 

pressure of 300MPa. 

𝐹𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 = 𝑃. 𝐴 = 𝑃. 𝜋. 𝑟2 

𝐹𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 = 589𝑁 

(3.19) 

So, this minimum tensile load should be tolerated by the weld if we assume there is no 

threading on the inserts. To calculate the expected strength of the welding points, the 

effective throat size must be calculated.   



36 

 

𝑡𝑒𝑓𝑓 = 𝑎. sin(45°)                  (3.20) 

Where, 

a=leg size of the weld. For this case the leg size assumed to be 3mm. 

𝑡𝑒𝑓𝑓 = 2.12𝑚𝑚                 (3.21) 

Next the effective area of the weld is calculated: 

𝐴 = 𝑡𝑒𝑓𝑓 . 𝐿             (3.22) 

Where, 

L=length of the weld. For this case 12mm hexagonal centers of the fitting will be 

assumed as perfectly circular. Making their circumference the weld length. 

𝐴 ≈ 79.92𝑚𝑚2                (3.23) 

Then we can calculate the weld strength with: 

𝐹𝑤𝑒𝑙𝑑 = 𝐴. 𝜏𝑎𝑙𝑙𝑜𝑤                 (3.24) 

Where,  

𝜏𝑎𝑙𝑙𝑜𝑤 = 0.3 × 𝜎𝑢𝑡𝑠        (3.25) 

For the tensile strength of the weld, 250MPa is chosen as a conservative estimate at 

300°C. 

𝜏𝑎𝑙𝑙𝑜𝑤 = 75𝑀𝑃𝑎      (3.26) 

So, 

𝐹𝑤𝑒𝑙𝑑 = 5,994𝑁      (3.27) 

As it could be seen from the above calculations, the welding strength of the 

connections are sufficient on their own when bearing the pressure load. There is a 

safety factor of 10. 

For the heater carthridges 3 radially symmetric 10.5mm axial through-holes were 

created. 3 symmetric heater cartridges allow better temperature uniformity throughout 

the foaming chamber, especially for the central area where the foaming samples will 

be placed. The placement of the heater cartridges can be seen in Figure 3.14. 



37 

 

 

Figure 3.14 : Top view of the foaming chamber showing the placement of the 3 

radially symmetric 10.5mm axial through-holes created for the heating carthridge 

numbered 1 to 3. Exported from SolidWorks (Original). 

3.4.1.4 Mounting and support 

The foaming chamber was designed to be mounted on a workbench. The first goal was 

to fix the foaming chamber on a workbench so it can be operated including tightening 

of the nuts with minimal movement. The body of the foaming chamber was also 

required to be around 60-100mm above the table surface so the cables of the heaters 

that protrude beneath can bend without compromising their integrity. This high 

mounted position would also allow the maintenance crew to reach below to check the 

cables or visually inspect for any defects. The height of the foaming chamber would 

also effect the ease of operations as the bolts on the lid are tightened and untightened 

between each experiment. 

Ergonomics 

The ergonomics of operating was also taken into consideration when designing the 

table and the mounting. The standing operator would use a torque wrench while 

tightening and untightening the lid. Using a wrench or any other hand tool is the most 

comfortable when the object that is operated on is around elbow level. For this reason, 

the level of the clamping nuts on the lid should be between 95-110cm above the ground 



38 

 

for the average Turkish operator. This position is demonstared in Figure 3.15. The 

foaming chamber together with the proposed mount mentioned above has a height of 

23±2cm. In this case it was decided that the workbench should be 76cm in height with 

extendable feet in case of need for increasing the height. 

 

Figure 3.15 : Image demonstrating the correct height of the workbench (Original). 

Space requirements 

The laboratory workbenchs in SGPL are stationary tables fixed both on the ground and 

the back wall. They are measured to be around 90cm deep. The aim for the foaming 

chamber workbench was for it to be mobile enough to go through doors and be 

repositioned without any damage if needed. With these constraints in mind the 

workbench was design to have a square tabletop with each side being 67cm. The 

drawings of the workbench can be seen in Figure 3.16. 

 

Figure 3.16 : Drawing showing the general shape of the foaming chamber 

workbench (Original). 



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Material choice 

The material chosen for the workbench structure was carbon steel profiles. The 

workbench top was chosen to be manufactured from carbon steel sheet with sufficient 

thickness to hold the foaming chamber and the mounts. The table was planned to be 

coated with white paint to make it suitable for the laboratory environment. Steel was 

chosen over a ceramic benchtop due to the brittle characteristic of ceramic benchtops. 

Continuously exerting force on the foaming chamber and the mounts might cause the 

bolted connection between the benchtop and to mounts to degrade making the whole 

assembly loosen. The problem is completely negated when a sufficiently thick steel 

table is used.  

The dimensions of the steel profiles were not determined and detailed engineering 

drawings were not created during this stage. This was to enable the manufacturer of 

the workbench to choose these parameters according to their expertise, building the 

products using the main constraints discussed above. Detailed design of the 

workbench, outside the main parameters, were not in the scope of this project. 

Mounts: The mounts that stabilize the foaming chamber were designed to be L-

brackets that are connected to the side surface of the foaming chamber via M10 bolts 

while the other side is bolted to the table via same sized bolts. The rest of the ports, 

fittings and holes on the foaming body have either a 3-fold or a 6-fold radial symmetry, 

making the choice of placing 3 radially symmetric bracket the most feasible and 

convenient.  

3.4.2  Heating and insulation system design 

Uniform and controlled heating is essential to reach the polymer's foaming temperature 

without thermal gradients. The heating and insulation system should achieve uniform 

heating of the foaming chamber with precise temperature control. The maximum 

operating temperature was chosen as 300°C allowing foaming experiments to be done 

on most industrial polymers.  

3.4.2.1 Heating method 

The heating is achieved via three cartridge heaters inserted into the foaming chamber 

via 3 radially symmetric 10.5mm axial through-holes mention in the previous sections. 

The cables of the heater were made to protrude from the bottom of the foaming 



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chamber curving out through the gap created by the 3 mounting brackets. The heaters 

were planned to be at least 300 watts each to achieve heating to the desired temperature 

as quickly as possible. 

3.4.2.2 Temperature monitoring and control 

For temperature monitoring and control the pre-existing EMKO ESM-3720 

temperature control device was planned to be used for controlling the heating.  

 One thermocouple of 5mm diameter and 50mm length was devised for fitting 

into the insert created on the foming chamber. The length of the thermocouple 

would allow the tip be level with the inner surface of the foaming chamber 

allowing for more precise reading. The type of the thermocouple was chosen 

to be Fe-Const due to the lack of PT-100 connection on the control device. 

 3 Carthridges menntioned above have to be fitted onto the controller for them 

to be PID controlled to achieve the desired temperature with precision. This 

posed a challenge as the ESM-3720 control devices relay switch was only rated 

for a maximum current of 2 Ampers. A modification of the device with an 

individually powered external relay and switch was devised to overcome this 

issue. Where, the heaters would be directly connected to the external relay and 

the switch would be controlled by the internal relay of the control device. 

3.4.2.3 Insulation 

To achieve the desired temperatures an insulation jacket was needed to be place on the 

foaming chamber. The jacket would prevent heat loss from the side and top surfaces 

of the fomanig chamber assembly. To keep the lid and the nuts holding the lid 

accessible to the operator, the insulation jacket was designed to be a two piece 

construction. One piece was to cover the side surfaces of the foaming chamber while 

allowing the inlet pipe, outlet pipe and the thermocouple cable to protrude through 

dedicated holes on the jacket. The second piece was to cover the top of the foaming 

reactor, which can be removed to access the lid betweeen experiments. The general 

construction of the insulation jackets was planned to be an high temperature insulating 

fiber encased in an fire proof casing to ensure the jacket is compliant when it is needed 

to be removed. 

 



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3.4.3  Gas delivery system 

3.4.3.1 Pressurisation device 

A critical aspect of the process is to pressurize the foaming chamber with the blowing 

gas which is achieved by the pre-existing Teledyne Syringe Pump. In the process of 

operation, the syringe pump’s column will be filled by the compressed gas cannisters 

until the pressure is equalized. Then the inlet valve on the device would be closed and 

the machine would compress the gas to the desired pressure which can be monitored 

on the display. To pressurize the foaming chamber the outlet valve of the machine 

which is connected via a steel pipe to the inlet fitting of the foaming chamber would 

be opened. During the saturation phase of the experiment, the outlet valve of the 

syringe pump is kept open to allow the machine to compansate for any pressure 

fluctuations in real-time. After the saturation phase is completed, the outlet valve of 

the syringe pump is closed. 

3.4.3.2 Depressurisation device 

The depressurization of the foaming chamber was achieved by a high pressure 

spherical release valve attached to the outlet pipe of