LEE- Tekstil Mühendisliği-Doktora
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ÖgeEv tipi yıkamalarda suyun tekrar kullanımı için yıkama atık suyundan renk giderme sisteminin geliştirilmesi(Lisansüstü Eğitim Enstitüsü, 2021-11-23)Son yıllarda temiz su kaynaklarının hızla kirlenmesi nedeniyle su geri kazanımının önemi günden güne daha da artmaktadır. Bu tez çalışması öncelikle su kaynaklarının sürdürülebilir olmasını desteklemek ve kullanılan atık suyu tekrar kullanabilmek amacıyla tetiklenmiştir. Pazarda yaygın bulunan yüksek kapasiteli ve önden yüklemeli ev tipi çamaşır makinelerinde her çevrimde yıkama ve durulama adımlarının tamamında minimum 50 L ve üzerinde su tüketimi gerçekleşmektedir. Sunulan tez çalışmasında, ozonlama yöntemi kullanılarak renkli çamaşırların yıkanmasıyla ortaya çıkan çamaşır makinesi atık sularındaki rengin giderilmesi ve rengi giderilen suyun bir sonraki yıkamada tekrar kullanılması hedeflenmiştir. Bu hedef doğrultusunda, çamaşır makinesi atık suyundaki boyarmadde konsantrasyonunu tahminleme, ozon ile renk giderme sistemine sahip makine prototipinin hazırlanması çalışmaları ve bu makinede renk giderme testleri yürütülmüştür. Çamaşır yıkama sonucunda oluşan atık su, gri su kategorisindedir, hanelerde evsel aktiviteler için kullanılan toplam su içerisinde yüksek bir paya sahip olup (%27) geri kazanım ve tekrar kullanım için potansiyel oluşturmaktadır. Günümüzde yaygın olarak tercih edilen pamuk içerikli tekstil ürünleri çamaşır makinelerinde sıklıkla yıkanmakta olup, bu ürünlerin renklendirilmesinde çoğunlukla reaktif boyarmaddeler kullanılmaktadır. Bu reaktif boyarmaddeler içerisinden azo ve antrakinon boyarmaddeler yaygınlık, suda yüksek çözünürlük göstermeleri, life fikse oranlarının düşük olması ve atık suda risk oluşturmaları nedeniyle tercih edilmiştir. Yıkamaya karşı renk haslığı düşük ve lekeleme konusunda problemli olarak bilinen kırmızı ve mavi renkler belirlenerek, bu renklerin elde edilmesi için azo boyarmadde sınıfından reaktif kırmızı 195 ve antrakinon boyarmadde sınıfından reaktif mavi 19 boyarmaddeleri seçilmiştir. Çalışmada yaygın kullanılan ve sık yıkama ihtiyacı bulunan örme kumaşlar tercih edilmiş ve ticari koşullarda üretilip boyanmıştır. Tekstil atık sularında organik kirleticilerin fazla bulunmasından dolayı, bu sulardan reaktif boyarmaddelerin giderilmesinde oksidasyon yöntemlerinden ozonlamanın ve ozon ile diğer yöntemlerin kombinasyonlarının sıklıkla tercih edildiği belirlenmiştir. Teknolojisinin olgunlaşmış olması, yan ürün açığa çıkarmaması, yerinde renk giderimini hızlı şekilde gerçekleştirebilmesinden dolayı çamaşır makinesi için ozonlama yöntemi tercih edilmiştir. Çamaşır makinesinde renk giderimi için yıkama çevrimindeki uygun yıkama adımının -hedef atık su çözeltisinin- belirlenmesi için yapılan deneysel çalışmada, yapılan ölçümlerde deterjan konsantrasyonu düşük olan ve yumuşatıcı içermeyen birinci durulama adımının renk giderim için daha uygun olduğuna karar verilmiştir. Literatür araştırması sırasında renk giderimi çalışmalarında çoğunlukla konsantrasyonu bilinen yapay çözeltiler ile çalışıldığı saptanmıştır. Oysa, çamaşır makinesinde yapılan yıkamalar sonunda ortaya çıkan atık suların içeriği farklı (lif, hav, deterjan vb.) ve oldukça kaotiktir. Literatürde rastlanmaması nedeniyle tezin yenilikçi yönü olarak yapay çözeltiler yerine "evsel çamaşır makinesi atık suları" ile çalışılmıştır. Ev tipi çamaşır makinesinden kaynaklı boyarmadde içeren atık suyun renginin giderilmesi için ozonlama ile renk giderme sistemi önerisi yapılmıştır. Yaşanan en büyük zorluk, yıkama sırasında boyalı kumaşlardan elde edilen atık suların boyarmadde konsantrasyonunun bilinememesidir. Bu atık suların boyarmadde konsantrasyonunun tahmin edilmesi için iteratif bir yaklaşım geliştirilmiştir. Boyarmadde konsantrasyonunun belirlenebilmesi için VIS spektrofotometre cihazı ile renkli atık su çözeltilerinin absorbans taraması yapılmış ve spektrumda maksimum absorbans değerini veren dalgaboyu tespit edilmiştir. Ancak, çamaşır makinesi atık suyunda yapılan ölçümlerde maksimum absorbans değeri elde edilememiştir. Boyarmadde konsantrasyonunun tahmin edilebilmesi için geliştirilen yaklaşımda, birinci adımda, saf su ile yapay olarak hazırlanan kontrol boya çözeltilerinin spektrum taramalarından maksimum absorbans değerlerinin elde edildiği dalgaboyları Reaktoset Red RFT (C.I. RR 195) için 540 nm, Reaktoset BRL Blue R Spec (C.I. RB 19) için 592 nm olarak belirlenmiştir. İkinci adımda, boya konsantrasyonları ve deterjan konsantrasyonları, sırasıyla, ana yıkama adımı için 10 –– 100 mg/L aralığında ve 4,6 g/L olarak; durulama adımı için 1 – 40 mg/L aralığında ve 0,5 g/L olarak hazırlanmış ve çözeltilerin absorbans ölçümlerinden kırmızı (RR 195) ve mavi (RB 19) boyalar için ana yıkama ve durulama kalibrasyon eğrisi denklemleri elde edilmiştir. Üçüncü adımda, renkli atık su çözeltileri tergotometer cihazında boyalı kumaşların yıkanması sonucunda elde edilmiştir. Bu çözeltiler ilgili dalgaboyunda net bir absorbans değeri vermediğinden, boyarmadde konsantrasyonunun hesaplanması için adım 2'de elde edilen kalibrasyon eğrilerine ait denklemlerin (kırmızı atık su için: A=0,0186C+0,0427, R² = 0,9997; mavi atık su için: A=0,0115C+0,0540, R² = 0,9966) kullanılmasına karar verilmiştir. Doğrulama testlerinde, denklemlerden hesaplanan boya konsantrasyonuna en yakın konsantrasyondaki deterjanlı yapay boya çözeltilerinin spektrumları ile renkli kumaşlardan elde edilen spektrumların karakteri farklı olmasına rağmen belirlenen dalgaboyunda üst üste çakıştığı saptanmıştır. Çamaşır makinesi ve tergotometer cihazından elde edilen atık su çözeltilerinin absorbans ve konsantrasyon değerleri arasında güçlü bir ilişki olduğu belirlenmiş ve tergotometer cihazının su ve kumaş sarfiyatını azaltmak amacıyla çamaşır makinesi yerine kullanılabileceği kanaatine varılmıştır. Renk giderme sistemine sahip makine prototipi için, bir ozon düzeneği kurularak çalışmalara başlanmıştır. Kurulan düzenekte hava kompresörü, hava kurutucu, akış ölçer, ozon jeneratörü, ventüri, su haznesi, iki adet su pompası ve debimetre yer almaktadır. Ozon düzeneğinde yapılan deney tasarımı sonucunda renk giderme etkinliği üzerinde en etkili faktörlerin sırasıyla %22,0 ile boyarmadde*ozon jeneratörü ikili etkileşimi, %15,4 ile ozon jeneratörü*ozonlama süresi ikili etkileşimi ve %14,8 ile tek başına ozon jeneratörü olduğu saptanmıştır. 500 mg/sa kapasiteli (500-B kodlu) ozon jeneratörü ile en yüksek renk giderme oranlarına ulaşıldığından bu ozon jeneratörünün kullanılmasına karar verilmiştir. Ventüri sistemi ve geri kazanılan suyun bulunacağı depoya sahip 9 kg kapasiteli çamaşır makinesi prototipi hazırlanmıştır. Sistemin çalışma prensibi şu şekildedir: Dışarıdan hava kompresörü yardımıyla çekilen ortam havası ozon jeneratöründen geçirilerek ozon üretilmekte ve ventüri elemanına taşınmaktadır. Pompalar yardımıyla ventüri elemanında renkli su ve ozon buluşmakta, belirli süre yapılan sirkülasyon sonrasında ozonlama yoluyla renksiz su elde edilmektedir. Önerilen denklemler kullanılarak boya konsantrasyonları hesaplandığında, renkli kumaşların farklı tüketici koşullarında yıkanması sonucu atık su boya konsantrasyonunun 15 mg/L ile 90 mg/L arasında değişkenlik gösterdiği saptanmıştır. Çamaşır makinesinde ozonlama testleri iki aşamada yürütülmüştür. Birinci aşamada, çamaşır makinesinde 14 L olarak deterjanlı, 20 – 40 – 60 – 80 mg/L boya konsantrasyonuna sahip yapay çözeltiler hazırlanmış ve ozonlanmıştır. İkinci aşamada, gerçek yıkama koşulunu temsilen ticari koşullarda üretilen kumaşların (1 kg) Beko 9 kg çamaşır makinesinde pamuklu 40 programında 52 g standart deterjan ile yıkanmasından elde edilen birinci durulama suları toplanarak ozonlanmıştır. Kırmızı ve mavi yapay boya çözeltilerinde renk giderme oranı %95 ve üzerinde gerçekleşmiştir, görsel olarak rengin tamamen giderildiği tespit edilmiştir. Renk giderimi etkinliğinin başlangıç boya konsantrasyonuna ve boyarmadde tipine bağlı olduğu belirlenmiştir. Boya konsantrasyonu arttıkça renk giderimi daha uzun sürede gerçekleşmiştir. Reaktif kırmızı 195 boyarmaddesi ile hazırlanan çözeltilerde renk gideriminin reaktif mavi boyarmadde ile hazırlanan çözeltilere göre daha uzun sürdüğü belirlenmiştir. Kırmızı ve mavi kumaşlardan elde edilen birinci durulamaya ait atık suların boya konsantrasyonu sırasıyla 35,1 mg/L ve 42,3 mg/L olarak belirlenmiştir ve kırmızı ve mavi renkli atık su çözeltilerinde %80 civarında renk giderimi sağlanmıştır. Renk giderimi mavi atık su çözeltisi için yaklaşık üç kat daha hızlıdır. Kırmızı renkli atık sularda 240 dakikada %76 oranında renk giderimi; mavi renkli atık sularda ise 70 dakikada %82 oranında renk giderimi gerçekleşmektedir. Ozonlama ile boyarmaddenin kromofor grubunun parçalanıp parçalanmadığının analizi için, 100 mg/L boya konsantrasyonuna sahip deterjansız çözeltiler ozonlanmış ve dondurularak kurutulmuştur. FTIR cihazı analizleri sonucunda, kırmızı çözeltilerde ozonlama etkisiyle 1540 cm-1 civarında görülen N = N bağının kırıldığı, dolayısıyla azo kromofor grubunun parçalandığı; mavi çözeltilerde ozonlama etkisiyle 1575 cm-1 civarında görülen kromofor grubu temsil eden antrakinon halkasına ait bağların kaybolduğu belirlenmiştir. Ozon ile rengi giderilen suyun kalitesi incelendiğinde, çıkış suyu parametrelerinin giriş suyu parametrelerine göre daha iyi seviyede olduğu saptanmıştır. AKM, bulanıklık, KOİ (%54 düşüş) ve TOK (%35 düşüş) parametrelerinde ozonlama işlemi etkisiyle belirgin düşüş sağlanmıştır. Hazırlanan prototip makinede geri dönüştürülen su bir sonraki çevrimin ana yıkama adımında kullanılmıştır. 10 çevrim süresince ozonlanmış su ile yıkanan çeşitli tekstil numunelerinde herhangi bir tekstil hasarlanma etkisi görülmemiştir. Geri kazanılmış su ve şebeke suyu ile yapılan yıkamaların yıkama performansı değerleri arasında belirgin bir fark tespit edilememiştir. Çamaşır makinesi ozon ile renk giderme sisteminin enerji tüketimi, mavi kumaştan elde edilen suyu ozonlamak için pamuklu 40 programının enerji tüketiminin yaklaşık beşte biri, kırmızı kumaştan elde edilen suyu ozonlamak için pamuklu 40 programının yaklaşık üçte ikisidir. Ozon ile renk giderme sistemine sahip çamaşır makinelerinin yaklaşık dörtte bir oranında su tasarrufu sağlayacağı tahmin edilmektedir. 8-9-10 kg kapasiteli çamaşır makinelerinde çevrim başı yaklaşık 14 L'lik su tasarrufunun bir yılda yaklaşık 1,24 hm3'lük su tasarrufu sağlaması beklenmektedir. Çamaşır makinesi ortamında atık suyun kendi kaynağında renginin giderilmesi, geri kazanımı ve tekrar kullanımı ile sürdürülebilir yaşam desteklenebilecektir. Geliştirilen ürünün hem ticari açıdan hem çevresel açıdan başarı potansiyeli bulunmakta hem de sürdürülebilir ürün gamında kalıcı bir yer edinmesi beklenmektedir.
ÖgeDevelopment of textile based temperature sensor for wearable electronics(Graduate School, 2021-09-30)Due to their compressibility, bendability, and compatibility with irregular and curvilinear surfaces, flexible and stretchable devices are attracting attention and have a wide range of applications. The increasing number of publications in this field demonstrates the growing popularity of flexible sensors. Flexible sensors provide mechanical robustness, biocompatibility, multifunctionality, and comfort when compared to conventional rigid sensors. For this reason, next-generation wearable technologies are expected to be driven by interest in flexible, stretchable, and soft devices. Textiles, in addition to their protective and aesthetic functions, provide an exceptional flexible platform for providing sensing functions and comfort to the wearer with diverse range of fibers, yarns, and fabric structures. New developments in printed electronics enable mass production of sensors using efficient printing processes by considerably minimizing costs and enhancing the potential of large-scale production. In this thesis, at first, the capabilities of temperature sensors, their sensing method, and previous research that has been conducted on them are presented. Additionally, the techniques and uses of inkjet printing are examined in detail. A comprehensive explanation of inkjet printing technology and printing challenges are issued. Dispersion is required for the development of inks that include carbon nanotubes. Due to the hydrophobic nature of carbon nanotubes, they must be distributed using a combination of mechanical and chemical methods. Numerous methods, including ultrasonication, non-covalent and covalent alterations, were used to disperse nanotubes. The use of various types of carbon nanotubes in CNT ink formulations is also studied. The development of conductive inks formulations containing CNT, PEDOT:PSS and CNT/PEDOT:PSS with a proper evaluation guideline is studied. Moreover, the concepts and properties of functional materials, as well as the critical additives used during the printing process that can have a significant influence on the printing process of conductive inks are discussed. The physical, structural, morphological, and electrical properties of the materials are investigated using various techniques (UV-Vis, FTIR, optical profilometer, SEM, AFM, optic microscope, multimeter, etc.). With relevant to print quality, the textile basis material should be dependable, maintaining a level surface and good uniformity during the printing process. In order to create conductive material sensors for temperature measurement, the inkjet printing process was used, which has the advantage of reducing ink waste while also being a low-cost and simple method. Following the procurement of CNT-based inkjet suitable dispersion, a PEDOT:PSS/CNT composite ink and a PEDOT:PSS inkjet appropriate dispersion are manufactured for temperature sensing. Appropriate ink formulations have been developed to produce high-quality inkjet-printed sensors, which are typically characterized by low imperfection points throughout the surface of the printing material. The sensor manufacturing process is then completed by including silver yarn, followed by the application of silver based conductive glue and an encapsulating operation. Spectrophotometer studies were conducted to determine the qualities of carbon nanotube printing when many print passes are used, as well as the color characteristics of the produced specimens. The properties of CNT based, PEDOT:PSS based and CNT/PEDOT:PSS composite based sensors are compared to investigate their temperature sensing performance. Hence, proper ink formulations with appropriate physical and chemical properties that typically affects homogeneous printing surface characteristics and sensing properties, were successfully developed by analysing their morphologies and printing parameters. It was determined whether the printed temperature sensors performed properly by subjecting them to a temperature range ranging from 25 to 50 degrees Celsius. Furthermore, wear and performance tests, such as durability against bending, folding, humidity, rubbing, washing, light, and human sweat, were carried out with the help of some characterization methodologies in order to investigate the sensor's reliability and durability under unfavorable situations. The sensor real time measurement using of a mannequin and human gloved hand are reported with discussions. As a result, during our proof-of-concept inquiry, our newly designed temperature sensor was placed to a mannequin's skin and human body on a gloved hand for temperature monitoring. Our developed wearable sensor provides highly accurate temperature monitoring. Lastly, the application based on artificial intelligence for the modeling of wearable sensors in various temperature and humidity conditions is described. Artificial neural networks (ANN) are used to model wearable sensors in various temperature and humidity conditions. The relationship between temperature, humidity, and electrical resistance is presented with the use of ANN. This innovative wearable temperature sensor development process is expected to aid development of smart wearable technologies. The developed sensor with its good mechanical properties and excellent sensing performance is believed to be useful for use in the textile products. Moreover, this developed sensor also offers the opportunity to be directly included in wearable smart systems in industrial production. In addition to the lack of standardized and consistent manufacturing techniques, there are unfortunately not yet any regular and comparable tests that can be used for the development and implementation of wearable e-textile sensors. Hence, this study will pave a way for development phases and implemenation of wearable e-textile sensors, in particular, contribute to industrialization in this area. To conclude, the developed textile-based sensor might be a solution instead of rigid device components for human body temperature monitoring and it can be directly utilized by sticking the sensor on various garment types while maintaining the user's comfort. Hence, it reveals a strong potential for use in wearable healthcare and biomedical applications.
ÖgeSynthesis of bleach activators for textile industry(Graduate School, 2021-06-29)Cotton fiber, is the most widely used natural fiber worldwide, contains undesired natural yellowish-brown coloring matters that hinder absorbency (wetting), reduce the natural whiteness of the fibers. These coloring impurities, which may cause poor dyeing quality, poor finishing performance and end product defects, must be removed by bleaching process to prepare the textile materials for dyeing and finishing. Hydrogen peroxide (H2O2), a universal and environment-friendly bleaching agent, is widely used for cotton and cotton blends. Conventional hot hydrogen peroxide bleaching is conducted under alkaline medium (pH 10.5–12) at high temperatures near boiling (at around 98 °C), leading extensive use of energy and severe chemical damage to textiles. Increasing demands for textile bleaching include reduction in processing costs (energy and water consumption), reduction in environmental impact and improvement in quality. Since energy is one of the main cost factors in textile industry, there has been considerable interest in recent years in ''low temperature'' bleaching. Activated peroxide systems have been investigated as an alternative approach to cotton bleaching at lower temperatures. Although there have been many reports on the use of cationic bleach activators for cotton bleaching, yet it has never reached the commercial success due to either production cost on a large scale, environmental concerns and/ or activity. This study focuses on the development and synthesis of novel, sustainable based on aliphatic acid chloride and more cost-effective cationic bleach activators, with the aim of reduced production cost, improved affinity and bleaching performance, reduced fiber damage for low temperature cotton bleaching to overcome the drawbacks of conventional hot hydrogen peroxide bleaching and other cationic bleach activators based on aromatic acid chloride. Compared to conventional peroxide bleaching, using a bleach activator in a peroxide bleaching bath is an effective and kinetically more potent oxidation generating highly reactive peracid in situ, providing low-temperature bleaching. Activated bleach systems have the potential to produce more efficient kinetically potent bleaching systems through increased oxidation rates with reducing energy cost, saving time and, hence, causing less cellulose polymer chains damage or degradation than conventional hot peroxide bleaching. Cationic bleach activators have been investigated as the next generation bleach activators with inherent substantivity towards cellulosic fibers. In this study, facile synthesis of more sustainable and cost-effective bleach activators (N-[4-(N,N,N)-triethylammoniumchloride- butyryl] caprolactam, TBUCC, and N-[4- (N,N,N)-triethylammoniumchloride- butanoyl] butyrolactam, TBUCB, based on an aliphatic acyl chloride (4- chlorobutyryl chloride), was reported. Fourier transform infrared and high resolution mass spectrometry and 1HNMR confirmed the molecular structure of the synthesized bleach activator. Bleaching performance of newly- synthesized bleached activators was evaluated in terms of whiteness index, water absorbency and fiber damage (degree of polymerization) and compared with conventional peroxide system. Central composite design (CCD) (orthogonal blocks) was used to establish an optimized TBUCB-activated hot peroxide-cotton bleaching system at lower temperature for providing reduced energy cost and maintaining the integrity of cellulose polymer chains. The significance of the process parameters (independent variables) and their interactions were statistically evaluated using Minitab. First principles density functional theory (DFT) calculations were performed to elucidate the reaction mechanism via identifying plausible transition state(s) of the nucleophilic attack of perhydroxyl anion (HOO-) with different carbonyl carbons and identifying the advantages and limitations of TBUCB activator for hydrogen peroxide bleaching for cotton. The synthesis of bleach activators was conducted using a two-step reaction procedure. In the first step, intermediate product was synthesized by condensation reaction of 4- chlorobutyryl chloride with lactam leaving groups (caprolactam and butyrolactam). In the second step, quaternization step was performed to obtain the cationic bleach activators. Experimental results show that, in TBUCC-H2O2 system, the whiteness index (WI) of bleached samples improved when 1:8 and 1:10 molar ratio of TBUCC: H2O2 was used at 60 °C for 30 min. Using 1:8 molar ratio of TBUCC: H2O2 at 36.7 mmol/L activator provided a WI of 70. As the temperature increased from 60 to 70 °C, WI increased to 75.72 and 78.97 at 1:10 and 1:12 molar ratio of TBUCC to H2O2, respectively. The optimum pH was found to be 11.5 for effective bleaching performance. It was concluded that the effective concentration of generated PAA depends on the concentration of H2O2 up to a certain level. Based on the results of the experimental design and statistical analysis, a WI higher than 70 was achieved for TBUCB-activated bleach system at 9.47 g /L (29.7 mmol/L) and higher activator concentrations and at a molar ratio of 1:6-1:10 activator: H2O2. WI higher than 80 can be achieved between 11.7 g/L (36.7 mmol/L) and 13.93 g/L (43.7 mmol/L) of activator concentrations at a temperature of 80 0C. Considering the significance of the process parameters (independent variables) and their interactions, temperature (D) followed by molar ratio of activator: H2O2 (B) and concentration of activator (A), respectively, have the highest statistical relevance on whiteness index. On the other hand, it was revealed that the two-way interaction between the concentration of activator (A) and the molar ratio of activator: H2O2 (B) is greater than the other two-way interactions. When the bleached samples with similar whiteness values were compared (WI= ~ 75) in terms of fiber damage for conventional and activated peroxide bleaching systems, a 19.5% decrease in the average degree of polymerization (DP) was observed in conventional peroxide bleaching, while a decrease of 11.4% and 9.8% was observed in the TBUCC and TBUCB activated peroxide bleach systems, respectively. All these results show that whiteness index greater than 80 for cotton can be achieved by using TBUCC and TBUCB activated peroxide bleaching systems at lower temperature, providing reduced energy cost while maintaining the integrity of cellulose polymer chains. Density functional theory calculations were performed to elucidate the reaction mechanism of the bleach activator with cellulose and rationalize the superior efficiency of the bleach activator while maintaining the integrity of cellulose polymer chains compared to conventional hydrogen peroxide bleaching. DFT calculations elucidated the reaction mechanism, reactivity and peroxide bleaching reaction pathway of the perhydroxyl anion attack at carbonyl group of the butanoyl segment not at the carbonyl carbon of the butyrolactam, which is consistent with the experimental results. Reactions were found to follow two step mechanisms, which are perhydroxyl anion attack at the carbonyl carbon and the peracid formation. Reaction barrier for the perhydroxyl anion attack at the carbonyl carbon was calculated by using sum of electronic and thermal free energies at 70 ̊C under water solvation effect and determined as 12.55 kcal/mol. For perhydroxyl anion attack, TBUCB was found to have a lower reaction barrier and higher solubility than TAED, which was determined as 13.72 kcal/mol. These newly developed and synthesized aliphatic acid chloride-based cationic bleach activators, which are more cost-effective, sustainable and highly reactive compared to other aromatic based cationic bleach activators, enable peroxide bleaching possible at lower temperature (70 0C) compared to conventional hot peroxide bleaching (98 0C). With a sustainable production approach, using these novel cationic bleach activators in hot peroxide bleaching bath provides many advantages such as energy savings, reduced production cost, improved affinity and bleaching efficiency (whiteness index), and less fiber damage. This study provides key fundamental science principles and suggestions at the molecular level of novel and sustainable bleach activators for cotton using a combined experimental and first principles DFT calculations. This study is expected to provide a great contribution to the commercialization of these novel, more sustainable and effective cationic bleach activators for cellulose and cellulosic materials and to the future development of cost-effective industrial bleach activators and sustainable bleaching systems.
ÖgeDevelopment of ensete fiber based composites and their characterization(Graduate School, 2021-09-07)Composite materials are developed from two or more components having dissimilar properties to create the desired materials' physical, chemical, and mechanical properties. The main constituents of composite materials formulations include matrices, fibers, and additives or fillers. When composite matrices are from polymers, it is considered polymer composite. Fibrous materials from different sources classified as synthetic and natural fibers are used to reinforce the polymeric matrices. The composites from renewable raw material sources either bio-based polymers or natural fibers have been given attention by recent research works. Due to increasing environmental awareness and concern about sustainability, the academic and industrial sectors have started to focus on greener technologies, a major part of which is played by material development. This thesis aims to develop ensete fiber-based composite materials by characterizing their properties. Ensete fiber is extracted by decortication of pseudostem and leaf parts of the Ensete plant as a by-product. Ensete plant known as ensete ventricosum (scientific name) is a perennial plant that has leaves, a large underground corm, pseudostem, and one of the main food plants grown for traditional diet in East Africa especially in Ethiopia. Besides its abundance, Ensete fiber has a tensile strength of 513 MPa, fracture strain of 3.2%, fineness of 8-16tex, crystallinity index of 64.9%, and moisture content of 12.2%. Ensete fiber chemical composition is from 56% of cellulose, 24% of hemicellulose, 2.2% of lignin, and 17.8 % of other extractives, wax, and ashes. These properties of ensete fiber indicate its competitive candidate to make natural fiber-based biocomposites. The novelty of this research contributed to academic literature through its first extensive work on the effects of ensete fiber surface modification and grafting of compatibilizers to polymers on developed composites properties. Additionally, the effects of hybridization and stacking sequences on composite structures and properties; the extraction of micro cellulose crystals from ensete fibers were investigated. The nanocomposite developed from nano cellulose fibrils filled thermoset resin was also characterized for its thermal stability improvements and dynamic mechanical properties. The outcomes of this study have been given in the form of research articles published in high-impact factor journals such as Composite Structures and Composite Science and Technology. The methodology used to develop ensete fiber-based composites includes manufacturing techniques such as vacuum-assisted resin transfer moulding (VARTM), carding of fiber webs, twin-screw melt compounding and granulating, hot press moulding, and liquid cast moulding of composites. The design of experiments was prepared for each research article to address specific objectives and to contribute to the purpose of the thesis in general. Surface modification of ensete fiber by varying alkali concentration was investigated for its effects on the fiber properties and ensete fiber-based unsaturated polyester (UP) composite physical, mechanical, dynamic mechanical, and morphological properties. Mechanical test results revealed that 5.0 wt% alkali treated Ensete fibers and unsaturated polyester composites showed 14.5% and 43.5% increase in flexural strength and Young's modulus respectively when compared with untreated fiber composite. A positive shift in glass transition temperature (Tg) of composites after alkali treatment and tensile fracture surface morphology and roughness of ensete fiber SEM images indicates better interfacial interaction in treated ensete fibers and UP composites. The hybrid composites developed from carded ensete fiber webs and woven glass fiber fabrics reinforcing unsaturated polyester were characterized for the effects of stacking sequences. A hybrid composite GGEE and GEEG showed improvement in tensile properties when compared to polyester composites from pure ensete fiber in its carded web form. The composites stacked as glass-ensete-glass (GEEG) showed higher storage modulus as compared to glass-ensete (GGEE) composites whereas the loss modulus of the composites reinforced with glass fiber exhibited the maximum value of 407 MPa and the height of the damping curve decreased in the GEEG composite. As observed from fracture surfaces, a more extensive fiber pullout was observed for the GEEG sample compared to the only ensete fiber composite sample. Tg of composites was increased for ensete-glass hybrid composites which might be related to more restrictions and a higher degree of reinforcements in hybrid composites. The ensete/glass fiber hybrid polyester composites can be used as load-bearing structures and components where high resistance to deformations and thermal stability is necessary. Ensete fiber and high-density polyethylene (HDPE) composites were developed in the presence of maleic anhydride grafted polyethylene (Ma-g-PE) as a compatibilizer. The grafting process was done by optimized maleic anhydride concentration of 1.5% by weight fraction and 0.5% of reaction initiator called dicumyl peroxide (DCP) and the rest 98% of HDPE polymer. The formulated and premixed composite constituents (chopped ensete fiber, MA-g-PE, and HDPE) were melt compounded by twin-screw extrusion, granulated, and then composite plates were molded using a hot press machine. Increasing the ensete fiber loading from 15 wt.% to 30 wt.% has resulted in the composites being stiffer and harder leading to a decrease in elongation at the break of the composites. The physical properties such as density and water absorption % increased with fiber loading increments while melt flow index reduced. The addition of 5wt% compatibilizer into 25wt% ensete fiber-filled HDPE improved the fiber-matrix adhesion. Its tensile strength, flexural strength, and impact absorption energy increased by nearly 43%, 46%, and 56% respectively when compared to composites with the same fiber loading and without compatibilizer. Morphological analysis on micrograph images taken by SEM confirmed the failure mechanism of the composites. The results of the study show that ensete fiber-HDPE composite could be commercialized in the industry for construction and building, low-density furniture, and moldable structures in need of design flexibility. The micro or nanometer cellulose fillers extracted from green material sources such as ensete fiber are needed to be utilized to develop biocomposites. The study focused on the extraction of micro cellulose crystals from lignocellulosic ensete fiber and additions of nano cellulose fibrils to epoxy resin were investigated. The process of isolating micro cellulose includes chemical and mechanical methods. Lignin and hemicellulose of ensete fibers were removed by soaking chopped short fibers in an alkali solution (17.5 wt% NaOH concentration) for 4 hr. at room temperature. The alkali treated fibers were washed with deionized water several times to keep PH value at 7; filtered to remove lignin and hemicellulose, and dried at 80 ℃ for 24 hr. Acid hydrolysis by 1M hydrochloric acid was done at 80 ± 5 ℃ for 2 hr. to remove hemicelluloses, pectin, and some of the suspended cellulose amorphous, and then fibrils of cellulose were mechanically ball milled to micro cellulose crystals. The analysis from FTIR measurements, x-ray diffraction, optic microscope, and SEM images revealed the removal of lignin, hemicelluloses, pectin, wax, and also hydrolysis of amorphous cellulose parts during the chemical process. The diameters of extracted MCC were ranging from 1-10µm. The epoxy resin filled with varying weight fractions of cellulose nanofibrils was moulded and cured by liquid cast moulding techniques. The effects of incorporating nano cellulose fibrils filler into epoxy at different loading (1wt%, 3wt%, and 5wt%) were investigated. The results of thermal properties from DSC, TGA, and DMA discussed thermal stability and stiffness of epoxy nanocomposites. From DMA test results, the reduction in tan delta peak height of nanocomposites with the increase in NCF loading shows increments of stiffness imparted by fillers. The glass transition temperature of nanocomposites shifted to a higher temperature as the filler loading and uniform dispersion were attained. The thermal stability of CNF filled nanocomposites can be compared from TGA results. The temperature where maximum weight loss happened is shifted to a higher temperature when compared with pure epoxy polymer. CNF fillers acted as a thermal insulating barrier to the epoxy polymer and resulted in less thermal degradation of nanocomposites relatively. From overall test results, 3wt% CNF is the optimized cellulose nanofibrils filler loading for better thermal properties and modulus of the epoxy-based nanocomposites. In conclusion, based on currently available technologies the utilization of an ensete fiber which is from renewable sources to be used as reinforcements of polymeric matrices and alternative new green composite products were able to be developed for desired engineering applications as recommended in each specific study done.
ÖgeComposite nanofiber patches for topical drug delivery systems(Graduate School, 2021-04-19)Nanofibers are ultrafine, continuous, solid state textile fibers that have diameters less than 1 micrometre. Nanofibers possess remarkable properties such as high interconnected porosity, specific surface area, ability to imitate the Extra Cellular Matrix (ECM) and potential carrier for drug delivery. Due to these fascinating properties, nanofibers are attractive candidates for medical applications for instance wound dressings, tissue scaffolds and artificial blood vessels. Electrospinning is the simplest and most practical among all methods to produce fine fibers with diameters ranging from micrometres to nanometres. Basic electrospinning equipment includes a high voltage source, a solution feeding unit, a syringe with a tip and a collector. At first, high voltage is applied to the polymer solution to produce an electrical field between the tip and the collector to shape the droplet on the tip as Taylor Cone. When the electrostatic force is higher than the surface tension of the polymer solution, polymer jet is ejected from the tip to the collector. Then, polymer jet reaches to collector following a spiral way by getting longer and thinner. Finally, nanoscale fibers are obtained on the collector. Topical drug delivery systems are composed of a formulation that applied to the skin directly to heal disorders or disease of the skin which guide/target pharmacological effect of the drug to the skin surface. Different pharmaceutical dosage forms can be used in topical drug delivery such as gels, creams, ointment, liquid preparation, sprays and solid powders. Electrospun nanofibers are excellent materials for drug delivery systems due to high interconnected porosity, high surface area, ability to imitate the Extra Cellular Matrix (ECM), potential carrier for drug delivery. Utilization of nanofibers in drug delivery systems is based on the principle that the high surface area of the nanofibrous formulation increases the dissolution rate of the drug. Compared with other dosage forms such as; liposomes, micelles and hydrogels, major advantages of nanofibers are increment in drug loading efficiency and loading capacity, low systemic toxicity and excellent stability. Furthermore, several drugs can be carried within nanofibers with high local drug concentration due to their excellent targeting and drug transportation ability in a safe way. Electrospinning offers the opportunity for direct loading of drugs or biological agents for instance antibacterial molecules, antibiotics, enzymes, growth factors, proteins, peptides, vitamins, DNA into the electrospun nanofibers. Poly (ε-caprolactone) (PCL), Poly Lactic Acid (PLA) and Poly (ethylene oxide) (PEO) were used as carrier polymers for drug delivery. PEO is a highly aqueous soluble polymer, that interacts with the body fluid quickly due to its hydrophilicity resulting in dissolution. PEO is widely used in the polymer matrix to enhance bioavailability and solubility of drugs because of its high aqueous solubility and unique properties in drug delivery applications. The compatibility of PCL and PLA with different types of drugs enables uniform drug distribution in the polymer matrix and the slow degradation rate makes them favourable for prolonged drug delivery systems. In recent years, various studies were reported on the fabrication of drug delivery systems, generated by electrospinning of PCL, PEO, PLA and their blends. PCL, PEO, PLA nanofibers or their blends were loaded with different drugs and biological agents such as; Niclosamide, Silver nanoparticles, Vitamin B12, Curcumin, Lysozyme, AgNO3, Metronidazole (MNA). Polymer blending is an effective approach to prepare functional nanofibers by incorporating the favourable properties of the component polymers. Furthermore, polymer blending facilitates the manipulation of physical, mechanical or biochemical properties of nanofibers. Hydrophilic/hydrophobic polymer blends have been electrospun into nanofibers to fabricate controlled DDS. The hydrophobic polymer forms the backbone structure and it degrades slowly, creating a long term but steady-state drug release. On the other hand, the hydrophilic polymer degrades with a more rapid process, faster than hydrophobic, which accelerates the drug release. In this study, hydrophilic water-soluble PEO was selected for the polymer matrix to enhance the solubility and bioavailability of insoluble SSD. The hydrophobic character of PCL and PLA offers a long period SSD release therefore hydrophilic PEO was blended with hydrophobic PCL and PLA. Thus, PCL/ PEO and PLA/PEO composite polymer matrix was used to provide both increased solubility and controlled release of SSD. Silver sulfadiazine (SSD) is a non-ionized, water-insoluble, topical agent with a wide range of antimicrobial activity that is affected both on bacteria and fungi. SSD is a sulfonamide based drug that is formed by the reaction of sulfadiazine with silver nitrate to form complex silver salt. SSD is used extensively in the topical treatment of infected burns. Silver sulfadiazine provides a long-term release of silver ions, whereas in the case of other silver salts, such as silver nitrate, large amounts of silver ions are released all at once. Thus, the use of SSD decreases the need for frequent application. This makes SSD a desirable and favourable agent since the frequent application is not always practical or possible for patients. However, the low aqueous solubility (3.4 mg/l at pH = 6.8) restricts the drug efficiency, bioavailability and potential antimicrobial activity of SSD thus its applications are limited. Drug solubility is an important issue since efficient drug release and antimicrobial efficiency is contributed just by decomposition of SSD to sulfadiazine and silver ions. Also, the solubility problem of SSD makes it difficult to be stabilized and incorporated into the polymer matrix. The aim of the thesis is to produce a novel SSD loaded topical drug delivery system by using advantages of electrospun nanofibers. Also, a new buffer, Water/Propylene Glycol/ Phosphoric Acid (82:16:2) was utilized to investigate the dissolution and release behaviour of SSD. Thereby SSD containing PCL/PEO and PLA/PEO composite nanofiber carriers were electrospun to achieve the enhancement in solubility, effective drug release and efficient drug loading of SSD. For this purpose, initially, the water-insoluble SSD was incorporated into highly aqueous soluble PEO to increase the solubility. Afterwards, the PEO+SSD solution was blended with PCL and PLA solution to produce composite PCL/(PEO+SSD) and PLA/(PEO+SSD) nanofibers and PCL/(PEO+SSD) casting films for topical drug delivery. SEM method was used to enable the observations of fiber defects and irregularities in the nanofibers structures and to measure the average fiber diameters of the nanofibers. The morphological characterization of the casting films was carried out by SEM and Optical Profilometer. Energy dispersive spectra (EDS) analysis was performed to confirm that the composite nanofibers and casting film which contain SSD, by detecting the Silver (Ag), Nitrogen (N), Sulphur (S) content of the nanofibers. Moreover, EDS-Mapping was carried out to show the distributions of these elements in the composite nanofibers and casting films. The stability of SSD in the fiber structure and the molecular interactions in the drug-free and drug loaded nanofibers were examined by Attenuated Total Reflectance Infrared (FTIR-ATR) Spectroscopy. The crystalline structure of the SSD loaded composite electrospun nanofibers were investigated with X-ray diffraction (XRD) analysis. Atomic Force Microscopy (AFM) was used to determine the surface roughness of the composite nanofibers. 3D AFM Images show the roughness structure of nanofibers. Water contact angle measurements were performed to evaluate the wettability properties of the fabricated nanofibers and casting films surfaces. In vitro drug release media and release conditions were optimized and the controlled drug release profile was obtained for 24 hours. Drug loading efficiency of the nanofiber formulations and casting film were calculated. To understand the SSD drug release mechanisms from SSD loaded formulations; Zero Order, First Order, Higuchi, Hixon Crowell and Korsmeyer-Peppas kinetics models were applied in the drug release profiles of the formulations. Drug release studies were also verified with conductivity measurement due to the conductive nature of SSD. Antibacterial activities of the composite nanofibers against gram-positive Staphylococcus aureus (S. aureus) and gram negative Pseudomonas Aeruginosa (P. aeruginosa) Escherichia coli (E. Coli) bacteria were performed for the period of 24, 48 and 72 hours according to disc diffusion test method. Also, the antibacterial activity of commercial SSD cream was tested for comparison with nanofiber formulations. Furthermore, antibacterial activity of the SSD loaded PCL/PEO and PLA/PEO nanofibers were examined with determining MIC and MBC values. Stability studies of the composite nanofibers were done for 3 and 6 months periods. Nanofiber samples were kept both at refrigerator conditions (+4ºC) and room conditions (25ºC ±2 and 65 % ±2ºC relative humidity) to evaluate stability of nanofiber patches. Stability tests were performed with calculating drug loading amount, cumulative drug release by UV absorption measurements and analysing surface morphology by SEM analysis. Finally, the cytotoxicity studies of the drug loaded and drug-free PCL/PEO and PLA/PEO nanofiber patches were done with using the cell viability assay (MTT assay).