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ÖgeEnvironmental impact and sustainability of recycling tufted carpets through selective dissolution process(Graduate School, 2024-06-28)According to the European Union Community Research and Development Information Service (CORDIS) report, the European Union's carpet consumption reaches nearly 1,8 million tonnes (Mt) annually, with approximately 1,6 Mt generated as waste each year. Post-consumer carpet waste occupies a significant space in landfills by volume and poses serious environmental threats due to the chemicals they contain. The collection process for carpet recycling has a different dynamic from other textile materials. This process usually occurs when a new carpet is installed or collected from a designated location by a specific recycler. Globally, in major carpet import centers such as America, Europe, and the United Kingdom, waste carpet collection organizations have been established through government-supported initiatives. However, in the US in 2019, only 8% of carpet waste could be collected, and only 5% of this could be recycled. In the EU, only about 3% of carpets are recycled, while 60% end up in landfills and 37-40% are incinerated. One of the reasons causing these low recycling rates is the heterogeneity of carpets containing various types of polymers, additives, adhesives, fillers, and dyes. For example, tufted carpets consisting of 42% of the world carpet trade share, are produced from different types of polymers such as synthetic fibers, especially polyamide (PA), polypropylene (PP), and polyester (PET). Polystyrene butadiene rubber (SBR) latex and Poly(vinyl acetate:ethylene) (EVA) latex are the mostly used adhesives, usually together with calcium carbonate (CaCO₃) as a filler material. Considering this broad variety in carpet composition, a tailored recycling route needs to be followed for each specific carpet sample. At the outset of this research, a detailed examination of 12 different carpet samples with the front faces made of wool, viscose, polyamide, and polypropylene, and backings composed of polypropylene and polyester was conducted to understand their composition and features. These carpet samples have action, felt, and fusion types of backings, and they are bonded with Carboxylated styrene butadiene rubber (XSBR), Polyvinyl butyral (PVB), SBR, EVA adhesive materials and contain calcium carbonate filler material. According to international trade statistics, carpets with PA6 face yarn are the most traded. Therefore, among the samples examined, experimental studies focused on recycling Sample PAPP_SBR which consists of 40% PA6 face yarn, 14% PP backings, 42% CaCO₃ filling, and 4%SBR adhesive. There are several studies about the chemical recycling of PA6 in the literature, and depolymerization is generally accepted by the industry. However, depolymerization processes and following monomer purification and repolymerization steps are complex and energy consuming. In this study, solvent-based selective dissolution techniques were utilized to separate polymers of a tufted carpet. Life Cycle Assessment (LCA) was made to check the environmental feasibility of the selective dissolution process. Mechanical separation methods were examined in the first place to determine the most effective and environmentally friendly approach. This involved shredding and pulverizing carpet samples to minimize filler content without chemical involvement, followed by their introduction into a flotation unit. Utilizing this process, polypropylene (PP) with a lower density of 0,93 g/cm³ was initially separated, followed by polyamide6 (PA6) with a density of 1,13 g/cm³, using water-based bubbles, achieving significant separation from filling material without chemicals. However, due to their fibrous structures, PA6 and PP became entangled, requiring a subsequent chemical process for complete separation. Before conducting the selective dissolution method, the maximum solubility limits of the polymers in suitable solvents were first studied. Calcium carbonate (CaCO₃) which is a common filler material in most tufted carpets, dissolves yielding calcium acetate, along with the release of carbon dioxide when it undergoes a reaction with acetic acid. Experimental studies conducted with pure acetic acid and acetic acid/water mixture revealed that water presence is needed to dissolve calcium carbonate. PA6 can dissolve in both pure acid and acetic acid/water mixture, while polypropylene can be dissolved in xylene. Experimental studies were evaluated by using solid/liquid (S/L) ratios of 0,02, 0,04, and 0,10 kg/L. On a laboratory scale, maximum solubility limits were identified for PA6 with 0,10 kg/L in acetic acid at 80 °C, for PP with 0,10 kg/L in Xylene at 130 °C and CaCO₃ with 0,04 kg/L in 75% acetic acid at 80 °C. In this study, the selective dissolution method by using acetic acid, which is a milder acid, at a reduced temperature of 80°C employed to dissolve PA6. This approach effectively enabled the dissolution and isolation of PA6 from other polymers such as polypropylene and SBR in the carpet through a subsequent hot filtration process which helps maintain the solvent's temperature during filtration to avoid any precipitation. In the dissolution of PA6, two distinct processes were employed. In Process-1, a 75% acetic acid solution was used, which enabled the dissolution of both PA6 and the residual CaCO₃ in the sample. After the selective dissolution of PA6 in acetic acid through hot filtration, PP and SBR remained on the filter paper. Subsequently, a suitable ethanol/water mixture was prepared to separate PP and SBR from each other based on their density differences. However, the dissolution of CaCO₃ necessitates the use of virgin raw material as a replacement. In Process-2, 100% acetic acid was utilized to prevent the dissolution of CaCO₃, leaving it in the residue. The experimental studies have demonstrated that pure CaCO₃ does not dissolve in pure acetic acid; rather, water needs to be present in the solvent for dissolution to occur. PA6, which dissolved in the acid, was isolated through hot filtration. The remaining CaCO₃, SBR, and PP on the filter paper were separated from each other based on their density differences using an appropriate ethanol/water mixture. It was visually observed that the presence of CaCO₃ in the solution resulted in more CaCO₃ residual material on PP. Process-3 was developed to address the CaCO₃ residue issue observed on PP in Process-2. Similar to Process-2, only PA6 was dissolved by using 100% acetic acid, while the remaining PP was selectively dissolved using 130°C Xylene. As a result, only CaCO₃ and SBR remained as residues. However, this approach necessitated a second dissolution process, leading to additional energy consumption. The recovered components from these three processes were analyzed using Fourier Transform Infrared Spectroscopy (FTIR) to ensure they retained their desired properties and composition. The results showed that the spectra of recovered PA6 and PP polymers matched those in library databases and the original carpet yarns. Additionally, 5 g of recovered PA6 powder and PP samples obtained from Process-1 were sent to Centexbel (Belgium) for thermal stability analysis. According to Differential Scanning Calorimetry (DSC), the melting temperature (Tm) of PA6 was observed at 216-220°C, with no peaks at lower temperatures, indicating an effective dissolution process with no residue of other carpet components such as PP, SBR, CaCO₃. The crystallization temperature (Tc) of the recovered PA6 at 189°C remained within the average range, suggesting the preservation of the material's thermal properties. Thermogravimetric Analysis (TGA) results demonstrate compatibility with reference values, and no thermal degradation has been observed in the recovered PA6 and PP. These results demonstrate the successful maintenance of essential thermal characteristics during the recycling process. This thesis aims to determine the most effective and environmentally friendly approach for the recycling of tufted carpets. For this purpose, a Life Cycle Assessment (LCA) analysis was conducted using open source openLCA software for each applied process. This analysis calculated and evaluated the environmental impacts of all possible recycling methods. Considering the developments in industrial applications, LCA calculations were performed for 3 possible S/L ratios 0,02, 0,04, and 0,10 kg/L. In the reference scenario of the PAPP_SBR carpet sample, the carbon footprint for 1 kg of this carpet sample was calculated to be 5,40 kg CO₂-equivalent. Of this emission, 85% is attributed to the virgin production and incineration of PA6, with 93% of this portion directly resulting from the virgin production of PA6. In Process 1, a 30% reduction in global warming potential was observed at an S/L ratio of 0,02 kg/L. This reduction increased to 67% at an S/L ratio of 0,10 kg/L when compared to the reference scenario. Similarly, in Process 2, a 42% reduction in global warming potential was noted at an S/L ratio of 0,02 kg/L, which escalated to 74% at an S/L ratio of 0,10 kg/L compared to the reference scenario. For Process 3, the reduction in global warming potential was 38% at an S/L ratio of 0,02 kg/L, reaching up to 73% at an S/L ratio of 0,10 kg/L relative to the reference scenario. These results underscore a significant decrease in carbon footprint correlating with higher S/L ratios. Particularly, the shift from an S/L ratio of 0,02 to 0,10 kg/L leads to a maximum reduction of 55% in the carbon footprint across the processes. This finding emphasizes the critical influence of the S/L ratio over the type of process, highlighting its importance in evaluating and optimizing recycling strategies for more effective environmental impact mitigation. In conclusion, at the end-of-life scenario of Sample PAPP_SBR, by recycling it through selective dissolution method at a 0,10 kg/L S/L ratio, we can achieve a 74% reduction in global warming potential without any degradation of thermal characteristics compared to production with virgin raw materials and subsequent incineration. These results underscore the significant potential of the selective dissolution process in facilitating the efficient recycling of tufted carpet components.
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ÖgeInvestigation of laser fading and effect of preparation processes on laser faded fabric quality(Graduate School, 2022)In the textile industry, laser technology is used to achieve effects on textiles in both micro and macro levels by changing the structure of fibers, since the 19th century. Laser fading is one of the main process of laser technology and is commonly used in denim. Fabric surface from 0.1mm to 0.5mm is processed and faded with this method. Resolution and pixel time are crucial parameters of laser source influencing the result of laser treatment. Resolution controls the density of laser dots per unit area, which is expressed in dpi (dots per inch). Pixel time, expressed in µs, controls the required time to place the laser beam at each point. Longer pixel time means more energy and so higher degree of fading effect. With the increase of pixel time and resolution, laser power density increases. Laser fading is a dry and computer-controlled process. Less manpower is required in this method. No or fewer consumables are used and there is no toxics caused by the disposal of products as on conventional wet finishing methods. With the arrangement of laser processing parameters at the desired level, it provides fast, precise and accurate production with sufficient reproducibility and repeatability, without environmental and health problems. Despite these advantages, laser fading may cause decrease in mechanical properties and higher yellowness on the color of the fabric. In this thesis, firstly, it was aimed to identify the most effective conditions of denim fading by laser treatment with different laser parameters followed by enzyme washing. Secondly, it was intended to observe the effects of chemical pre-treatment applications before laser fading at the optimum laser parameters reported, following by simple rinsing instead of enzyme washing, thereby minimizing the disadvantages of conventional laser fading (laser fading followed by enzyme washing). For this purpose, two different type of commercially used 100% organic cotton denim fabrics with 3/1 twill construction were selected for experimental study. The first fabric sample denoted as G was 435 gr/mt² and dyed with sulfur bottom and indigo. The second fabric F was 480 gr/mt² and only indigo dyed. CO2 laser machinery with a wavelength of 10.6µm and a power of 60% was used for laser treatment. Resolution and pixel time were set into three different levels; 32, 40, 48 dpi, and 300, 500, 700 µs. Subsequently, all laser-treated fabric samples were exposed to enzyme washing at a liquir ratio of 1:10 at 40°C for 10 min. Rucolase STG New enzyme was used for enzyme washing. Change in fabric unit weight, tensile strength (TS EN ISO 13934-1), abrasion resistance (TS EN ISO 12947-2) were evaluated for all fabrics. Color values (CIE L*a*b*, DE*, h*, C*, and K/S), yellowness and whiteness indexes were measured by Datacolor spectrophotometer. Colorfastness against washing (TS EN ISO 105-C06), rubbing (TS EN ISO 105-X12), artificial light (TS EN ISO 105-B02), water (TS EN ISO 105 E01) and perspiration (TS EN ISO 105 E04) were tested and evaluated under D65 artificial day light using the lightbox. From the first part of the experimental work, optimum laser parameters were reported as 40 dpi resolution and 300 µs pixel time. It was observed that, required fading effect with sufficient mechanical properties and good color values can be obtained with lower tensile strength loss and minimum yellowness with the application of enzyme washing under these determined process conditions. In the second part of experimental work, conditioned G fabric samples were washed with nonionic (0.5 g/L) surfactant at 40 °C for 60 min to remove the impurities and sizing agent and then pre-treated with polysilicic asid (PA), bicarbonate (BC), boric acid (BA), borax (BX) and mixture of boric acid/borax (BA/BX), separately. Chemicals were applied on fabrics with impregnation method at a liquir ratio of 1:10. PH was adjusted to 5-6 with acetic acid. Dried test specimens were exposed to laser fading at determined laser parameters, 40 dpi resolution and 300 μs pixel time. After laser fading, test specimens were rinsed at 40 °C for 40 min. With the pretreatment of polysilicic acid and mixture of boric acid/borax, comperable results to enzyme washing were achived in terms of yellowness and whiteness values. 16% decrease in yelowness was obtained and closest whiteness value to enzyme washing was obtained by 12% decrease in whiteness.Preliminary experiments on chemical pretreatment applications were carried out by using G fabric. Based on the results, the sample pretreated with 40 g/L PA has a comparable whiteness index (80.7) with the lowest ΔE value (0.8) compared to laser-treated and subsequently enzyme-washed G4 sample which the whitness index is 91.9. It was followed by BA/BX application with a WI of 80.2 and DE value of 2.2. Lightness values (L*) of polysilicic acid and bicarbonate applications were the closest ones to enzyme washing with the ratio of 2.5%. Considering the results of preliminary experiments, color values and mechanical properties of PA application in different concentrations; 20 g/L, 30 g/L and 40 g/L and BA/BX application were evaluated for both two fabric types; sulphure/indigo dyed (G) and indigo dyed (F). Chemical pre-treatments were applied in same prosedure. It was reported that, pre-treatment applications on G fabric decreased the yellowness and whiteness values of the fabric caused by laser treatment. Maximum decrease on yellowness was observed with the application of boric acid/borax (BA/BX) pre-treatment by 25%. Minimum decrease in the whiteness index of G fabric was observed with the pre-treatment of 30 g/L Polysilicic Acid by 2.5%. Maximum lightness was performed with 20 g/L polysilicic acid pre-treatment. 30 g/L polysilicic acid application caused highest increase in tensile strength in warp direction by 4% and 40 g/L polysilicic acid application in weft direction by 27.5% compared to enzyme washed, laser faded reference fabric. On the other hand, 40 g/L polysilicic acid pre-treatment decreased the tensile strength by 3.5% in warp direction and the mixture of boric acid/borax caused minimum increment in weft direction by 14.5%. According to Levi's Denim standard, tensile strength values obtained with pretreatment applications were acceptable. It was observed that, yellowness and whitness indexes increased with the pre-treatment applications on the fabric indigo dyed (F) as compared to reference F4 fabric. BA/BX application caused minimum increase by 11% in yellowness with a WI value of 110.0. With the application of 40 g/L polysilicic acid pre-treatment, a WI value of 129.3 was obtained, resulting in an increase of 27% compared to reference fabric. Maximum lightness (L*=26.4) was obtained with 20 g/L polysilicic acid pre-treatment. The highest increase in tensile strength in warp direction of indigo dyed fabric (F) was observed with the pre-treatment of 30 g/L polysilicic acid. Highest increase in tensile strength in weft direction by 36.4% was obtained with 20 g/L polysilicic acid application. 40 g/L polysilicic acid pre-treatment has the lowest increase in tensile strength for warp direction as 1.5% and caused a decrease in weft direction by 2.5% which is also in the range of tensile strength values specified in Levi's Denim standard. As can be seen from findings obtained in this study, lower yellowness and higher whitness values were obtained on laser faded sulphure and indigo dyed G fabric with pre-treatment applications. However, for indigo dyed F fabric, whiteness index increased but there was also a slight increase in yellowness with pre-treatments. Pre-treatment of polysilicic acid and mixture of boric acid/borax provided suitable fading effects compared to laser faded and subsequently enzyme washed reference samples while maintaining the mechanical properties. Considering higher or comparable whiteness index, lightness and tensile strength values both in warp and weft directions and minimum yellowness, it can be suggested that for sulphure/indigo dyed 100% organic cotton denim fabric, 30 g/L and 40 g/L polysilicic acid pre-treatments before laser fading can be done followed by simple rinsing, instead of enzyme washing. With the application of 30 g/L and 40 g/L polysilicic acid pre-treatment, whiteness value remains almost the same with enzyme washing and yellowness values decreases by 32% and 35% respectively. The pre-treatment of the mixture of 10 g/L boric acid and borax can be recommended for the indigo dyed 100% organic cotton denim fabric. By this pre-treatment, yellowness and whiteness of the fabric remain the same as laser faded and enzyme washed reference fabric with 35% increased tensile strength in weft direction. It is concluded that, by chemical pre-treatment applications before the laser process, the mechanical properties of laser-faded denim fabric can be preserved by eliminating the enzyme washing, which reduces the tensile strength up to 25%. Besides, all after-treatments were performed with the usage of water, no additional chemicals were used. Thus, environmentally friendly, ecological processes with sufficient denim fading effect, recommended in the market, can be obtained without any enzyme washing.
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ÖgeDeveloping filters for laundry machines to prevent microfiber release(Graduate School, 2025-01-27)Microplastics (MPs) represent one of the most pervasive environmental pollutants in the modern era, with profound implications for ecosystems and human health. Among these, microplastic fibers originating from synthetic textiles during laundering are a particularly significant source of pollution. These fibers are released during washing cycles, bypass standard wastewater treatment processes due to their small size, and accumulate in aquatic, terrestrial, and even atmospheric environments. The resulting contamination poses risks not only to marine life but also to human health, as these fibers enter food chains, water supplies, and the air creatures breathe. If current trends persist, it is projected that over 22 million tons of synthetic fibers will be discharged into the environment by 2050, making this a critical environmental and public health issue. This thesis tackles the urgent problem of microplastic fiber pollution by focusing on the design, development, and optimization of textile-based filtration systems for household washing machines. The primary objective is to prevent the release of microplastic fibers into wastewater at their source. Unlike broad strategies that target post-discharge remediation or changes in textile production, this study emphasizes source reduction through effective filtration mechanisms integrated into washing machines. By leveraging advancements in textile engineering, the research identifies optimal materials, structural configurations, and designs that maximize microplastic fiber capture without compromising the functionality of washing machines. The thesis commences with a comprehensive review of the literature, which underscores the environmental significance of microplastics, particularly those derived from textiles. Microplastic fibers, which account for 34.8% of global microplastic pollution, are released during the washing of synthetic garments, such as polyester and polyamide, which constitute a significant portion of global textile production. A single wash cycle can shed hundreds of thousands to millions of fibers, which subsequently evade conventional wastewater treatment and infiltrate natural environments. These fibers are not only ingested by marine and terrestrial organisms but have also been detected in human food sources, drinking water, and the air, posing significant health risks such as oxidative stress, hormonal disruption, and even cancer. The environmental review also highlights the limitations of existing filtration systems. While some commercially available products, such as Guppyfriend bags and Cora Balls, capture a fraction of the fibers during laundering, they are insufficient to address the magnitude of the problem. Similarly, current wastewater treatment plants are only partially effective in removing microplastic fibers, especially the smallest particles. Consequently, integrating filtration systems directly into washing machines emerges as a practical and impactful solution. The experimental section of this thesis focuses on developing and testing woven textile-based filters designed specifically for household washing machines. Key variables examined include yarn structure, number of filaments, weave pattern, and weft density. These parameters were selected for their significant impact on filtration efficiency, durability, and compatibility with washing machine operations. Twelve fabric samples were produced using three different types of polyester yarns (monofilament, 36-filament multifilament, and 96-filament multifilament) and assessed for physical and functional properties, including basis weight, thickness, tensile strength, tear strength, stiffness, air permeability, and vacuum filtration efficiency. The samples were manufactured with plain and 2/2 twill weaves at two different weft densities (33 and 17 picks/cm). Additionally, surface morphologies were examined using scanning electron microscope (SEM). The results showed that increasing weft density led to higher basis weight and thickness across all samples. While twill weave fabrics generally exhibited slightly higher basis weight than plain weaves, the differences were not statistically significant. Twill weave fabrics consistently demonstrated greater thickness than plain weaves, attributed to the float structure in twill weaves that creates a looser and bulkier fabric. For tensile strength, plain weaves outperformed twill weaves due to their higher interlacing points, and an increase in yarn count further enhanced tensile strength. Regarding tear strength, loosely constructed fabrics with fewer interlacing points exhibited higher resistance in twill weaves as yarns moved and bunched together under force. Twill weave structures also had higher air permeability due to their more open structure. This research also explored broader considerations in filter design, including the influence of yarn type (monofilament vs. multifilament). Monofilament yarns, characterized by their smooth surfaces, exhibited advantages in terms of durability but were less effective at capturing smaller particles. In contrast, multifilament yarns, with their higher surface areas, demonstrated greater filtration efficiency but were prone to clogging and reduced throughput. The study concluded that an optimal filter design would likely involve a hybrid approach that combines the strengths of both yarn types. Stiffness tests confirmed that monofilament yarns exhibited greater rigidity than multifilament yarns, while air permeability tests showed higher values for twill weave and monofilament fabrics. These findings underscore the critical influence of fabric structure, yarn type, and weft density on both filtration efficiency and physical durability. Vacuum filtration tests revealed that plain weave fabrics had superior microplastic retention compared to twill weaves, owing to their compact structure and smaller pore sizes. The highest filtration efficiency, 96.60%, was achieved by the plain weave sample P36T-33-P, made with 36-filament yarns at a weft density of 33 picks/cm. This was followed by its twill counterpart P36T-33-T (92.87%) and the plain weave sample P36T-17-P (92.30%). Monofilament fabrics generally demonstrated filtration efficiencies below 90%. Results of the experiments revealed that woven filters with tighter structures and higher densities demonstrated superior microfiber retention capabilities. However, these configurations also may pose challenges such as increased pressure drop and reduced mechanical durability, necessitating a careful balance between filtration efficiency and operational practicality. The thesis further contextualizes its findings within the broader landscape of microplastic pollution mitigation. The research also emphasizes the need for regulatory action to mandate the inclusion of effective filtration systems in new washing machines, as proposed by the European Union's recent initiatives on plastic pollution. In addition to its scientific contributions, this thesis underscores the potential for academia-industry partnerships in addressing global environmental challenges. The research was conducted in collaboration with industry stakeholders, leveraging their resources and expertise to develop practical, scalable solutions. The findings are not only relevant to the academic community but also offer actionable insights for manufacturers, policymakers, and environmental organizations working to mitigate the impacts of microplastic pollution. In conclusion, this thesis marks an important progress in addressing microplastic pollution by presenting a scientifically supported and practical approach to a critical environmental challenge. By integrating textile engineering principles with real-world applications, the research offers a pathway for reducing microfiber emissions at their source, thereby contributing to the broader goal of preserving environmental and public health. The innovative filtration systems proposed in this study have the potential to transform household laundry practices and set a new standard for sustainable textile management.
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ÖgeDetection and classification of fabric defects with an innovative model and perspective(Graduate School, 2025-01-24)The global textile and ready-wear industries represent a substantial and highly competitive sector of the global market, regulated by both quality and price. Fabric defects significantly impact the quality of ready-wear items. Likewise, undetected defects during traditional quality control processes can lower the value of fabrics. Consequently, detecting and classifying fabric defects becomes crucial for companies aiming to remain competitive in the market, whether through quality leadership or price rivalry. While the literature includes various studies on fabric defect detection and classification, these often rely on open-source or custom datasets and employ well-known deep learning architectures or propose novel architectures. However, no study to date has specifically accounted for the structural differences between woven and knitted fabrics when designing models for fabric defect detection and classification. To address this gap, the present study developed two new datasets – the Woven Fabric dataset and the Knitted Fabric dataset – and designed a novel deep learning architecture using Convolutional Neural Networks (CNNs). As the study method, an open-source dataset (TILDA) was first utilized to evaluate well-known architectures (VGG19, ResNet50, InceptionV3) and inspire the design of a custom CNN model. This custom architecture was then optimized using 3-factor, 2-level factorial design experiments to refine structural parameters. The model's performance was validated on three custom datasets (Woven, Knitted, and Woven-Knitted Fabric datasets). Subsequently, the hyperparameters affecting model performance were optimized using a 4-factor, 2-level factorial design, and the model was revalidated on both open-source and custom datasets. The model was evaluated using additional metrics, including recall, precision, specificity, and F1-score, demonstrating superior performance. Training performance was analyzed using Accuracy/Loss curves, confirming no signs of overfitting. Furthermore, confusion matrixes indicated the model's effectiveness and robustness in classifying different defect classes. The final model achieved 97.37% accuracy on the TILDA dataset, 97.73% accuracy on the Woven Fabric dataset, 96.92% accuracy on the Knitted Fabric dataset, and 98.36% accuracy on the Woven-Knitted Fabric dataset. The results including recall, precision, specificity, and F1-score all suppressed the expected criteria. These results demonstrate the model's capability to detect and classify fabric defects effectively, accounting for the structural differences between fabric types. Future studies will focus on expanding the datasets to include more fabric types and design samples, aiming to enhance the model's generalization ability and performance across different fabric domains. In conclusion, this study successfully identified a custom CNN model suitable for both woven and knitted fabric types, considering their structural differences. It lays the foundation for future research and industrial implementation in automated fabric quality control.
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ÖgeInvestigation of mechanical properties of small caliber fibrous vascular grafts(Graduate School, 2023)Cardiovascular diseases remain the most common cause of mortality worldwide, resulting in the deaths of 17.9 million people in 2019. Furthermore, previous cardiovascular diseases are a significant risk factor for COVID-19-related complications and deaths. According to the World Health Organization, the number of deaths would increase by 24.5% by 2030. The most frequent type of cardiovascular disease is coronary artery disease, which necessitates a surgical procedure called bypass grafting that involves arterial replacement. In bypass surgery, an autologous vein or synthetic graft is used to restore a diseased blood vessel that has become damaged or clogged. However, autologous grafts pose significant challenges due to scarcity and difficulties in graft harvesting operations. On the other hand, commercial synthetic ones are also problematic to be used as smaller diameter vascular grafts (< 6 mm) due to poor patency rates, thrombogenicity, and compliance mismatches, as well as neointimal hyperplasia in the peri-anastomotic regions. The compliance mismatch between the native vessel and the rigid synthetic graft at the anastomosis sites results in low blood flow rates and turbulent blood flow in small-diameter grafts. These mechanical issues lead to thrombosis and luminal narrowing due to intimal hyperplasia, which results in poor long-term patency, together with the thrombogenicity of the scaffold material and a lack of endothelialization. In order to address the demand for suitable scaffolds that can be utilized in bypass procedures by using new materials and production processes, researchers have concentrated on building an alternative tissue-engineered small-caliber vascular graft that can imitate the native artery in all ways. There is currently no small-caliber biodegradable vascular graft that has reached commercial success, despite the fact that significant breakthroughs have been made in the research that has intensified in recent years. The vascular graft is supposed to give structural support and promote cellular activity for the body to generate its vessels. The fundamental difficulty with vascular tissue engineering is still creating a perfect vascular graft that can replicate the structural, biological, and mechanical characteristics of the native blood vessels and be used in place of the disabled blood vessel. In this context, morphology and cellular analysis are typically given top priority, whereas mechanical aspects are only briefly discussed. To improve the clinical performance of vascular grafts, expose physiological stresses, and prevent graft failure brought on by intimal hyperplasia, thrombosis, aneurysm, blood leakage, and occlusion, it is essential to create grafts with good mechanical qualities comparable to native vessels. The mechanical characteristics of scaffolds, such as compliance, burst pressure, nonlinear elasticity, modulus, and suture retention strength, must match those of the native tissues because even a slight mechanical mismatch between the graft and the native vessel can cause graft failure. The mechanical properties of the vascular grafts are significantly influenced by the material and design. In this thesis, a detailed literature review was carried out to understand the native blood vessel structure and to provide a broad and comparative overview of recent studies on the mechanical properties of fibrous vascular grafts, with an emphasis on the effect of structural parameters on mechanical behavior in the experimental part. The purpose is to shed light on the design parameters needed to maintain the mechanical stability of vascular grafts that can be used as a temporary and biodegradable backbone, allowing an autologous vessel to take its place. An experimental study is carried out to produce fibrous vascular scaffolds made out of various biopolymers and their combinations with different fiber orientations and constructions and assess their physical, morphological, and mechanical properties. The first experimental part of the thesis is a preliminary study that includes the production of planar and tubular scaffolds made of neat PCL and PLA and their blends with the PCL/PLA blending ratios of 90/10, 80/20, 70/30, 60/40, and 50/50 by using an open system electrospinning unit. PCL is a flexible biopolymer with a long biodegradation time, whereas PLA is a strong polymer with high brittleness, higher biocompatibility, and a faster biodegradation time than PCL. The reason for utilizing these polymers together is to combine their mechanical and biological advantages and eliminate their inadequacies. The effect of the polymers and collector type on the fiber morphologies, diameters, and orientations, sample thickness, as well as the mechanical properties was assessed. It was observed from the results that all the samples were successfully produced, and they all have distinctive morphologies with smooth and continuous fibers. The tensile stress and elongation results revealed that polymer composition is highly effective on the tensile properties. Neat PCL samples had considerable elongation value with 390% whereas PLA showed good tensile strength with 2.73 MPa. When the blended samples were observed, it was seen that the blending affected the mechanical properties negatively based on the blending ratio that was used because of the immiscible characteristics of the polymers. The addition of PLA gradually improved the tensile properties, while using PCL in higher amounts caused better elongation values in blended samples, which shows the importance of the selection of a suitable blending ratio. According to the results of the planar samples, the PCLPLA90 and PCLPLA80 samples can be selected as they have moderate stress and strain values among the blended samples. Also, the use of tubular collectors enables the production of scaffolds with desired construction. On the second part, the monolayer tubular vascular prostheses were produced in a closed electrospinning system by using two rotational speeds to achieve scaffolds with randomly distributed or radially oriented fibers. In addition to the neat and blended samples made of PCL and PLA, two more polymers were added to the production stage, which are PLCL and PLGA. As PLCL is the copolymer of PCL and PLA and thought of as a better candidate to be used instead of physically blended scaffolds to eliminate the mechanical failure caused by blending, it was also used in the vascular graft fabrication process. On the other hand, PLGA has good biocompatibility and faster biocompatibility with good mechanical properties, which make it a good option to be used in vascular applications. When the physical and morphological results were investigated, it was seen that in a closed system, it is possible to produce vascular grafts with the desired thickness levels. Fiber orientation was also observed from SEM images in the radial direction within the tubular samples produced by using a high collector speed. The tensile test was performed on all the tubular samples in longitudinal and radial directions to see the effect of polymer composition, fiber orientation, and test direction on the tensile properties of the specimens. Results revealed that the neat PCL scaffolds showed more flexibility than the neat PLA samples, and the neat PLA samples show higher tensile strength than the neat PCL samples in general. Also in blended samples, tensile stress and elongation values were improved in some cases depending on the blending ratio, such as in PCLPLA90 and PCLPLA80 specimens. Also, neat PLCL samples had both higher elongation and strength values than all neat and blended scaffolds, with some exceptions. Generally, when the PLA ratio is increased, the tensile strength improves gradually, whereas the elongation values decrease. The maximum tensile strength belonged to PLCL100_O in the radial direction with 12.12 MPa, whereas it showed its highest elongation in the longitudinal test direction with 832%. In addition, PLGA100_R showed higher strength than the samples made of PCL and PLA, with very limited elongation. The strength values of PLGA samples were really promising, as it is a rigid polymer. On the other hand, radial fiber orientation greatly contributed to the tensile stress values in the radial direction and the elongation values in all directions compared to the samples with randomly oriented fibers. Higher stress values were obtained in the direction of the orientation whereas higher elongation values were achieved in the direction without fiber alignment. On the other hand, a custom-designed test device was specifically designed for vascular graft specimens to measure their burst strength and compliance. When the burst pressure values were assessed, the best results were obtained from the vascular grafts made of PLGA and then PCL/PLA blends with radial fiber orientations. The addition of PLA results in an increment in burst pressures up to a certain limit of PLA ratio. PLGA100_O showed the highest burst pressure at 2889 mmHg. According to the compliance measurements made using three different physiological blood pressure ranges, the scaffolds with higher flexibility possessed better compliance values. Thus, the samples with randomly distributed fibers had the highest compliance results when compared with the samples consisting of radially oriented fibers. PLCL100_R demonstrated the highest compliance with 4.924 mmHg %/100 mmHg at a 50–90 mmHg pressure range as the most flexible biopolymer among the others. Finally, considering the previously obtained biological analysis results, bilayer vascular grafts were fabricated by combining monolayer scaffolds with the best mechanical properties to obtain a prosthesis that could mimic the topography of the natural artery. The inner layer was constructed from randomly distributed fibers, whereas the radially oriented fibers were included in the outer layer. PCL100_R and PCLPLA80_R monolayers were selected as the inner layers while PLCL_O was used in the outer layers of the bilayered grafts due to their appropriate mechanical advantages. Results indicated that although the samples had a delamination problem in some cases, they had improved mechanical advantages in the tensile and bursting testing processes. On the other hand, the compliance results were still sufficient and comparable with the native blood vessels. All the results that have been achieved in this thesis shed light on the examination of the mechanical properties of vascular grafts and contain significant information for vascular prostheses to be produced in further research. The bilayered grafts that will be constructed in the future studies will be designed by considering the results of the mechanical assessments of the samples that have been optimized by using PCL, PLA, PLCL, and PLGA within the scope of this thesis and the biological examinations. In the following process, it is aimed to switch to in-vivo studies with the most appropriate bilayer scaffold designs to be obtained and to study the biological process in an interdisciplinary manner.