Type: M.sC/ Textile Engineering
Thesis advisor: Prof. Dr. Hale KARAKAŞ
Co-Advisor: Prof. Dr.Steven De MEESTER
Student's name/surname: Esen ÇAKIR

Summary
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 (PES). 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.

Type: M.sC/ Textile Engineering
Thesis advisor: Prof. Dr. Hale KARAKAŞ
Student's name/surname: Büşra Nur ÖZTÜRK

Summary
Enterprise resource planning (ERP) is a system designed to enable the business to use all its resources efficiently and effectively. ERP systems combine the basic processes and functions that enable companies to achieve their goals and enable most business applications to be carried out in an integrated manner. Thanks to these systems, information flows and communication is provided between departments in the business. However, the textile industry has a different product structure than many other sectors. For example, in garment companies, production is carried out according to the orders received. In this process, there are non-standardizable features such as variants, seasons, accessories and processes. For this reason, when choosing an ERP system, a company in the sector must choose software that suits its features.

In this thesis study, it is aimed to contribute to the improvement of deficiencies in ERP modules in order for an ERP system used in denim production to meet the requirements of the sector. In this context, studies were carried out in a leading joint-stock company of the sector, based in Istanbul, which produces denim and non-denim ready-made clothing. Microsoft SQL database was used, and Delphi language and C# language were used in the interface design developer. The problems identified are, respectively, the inability to physically track the samples, the delivery of fabric rolls to production in different lots and specifications, the inability to maintain stock tracking and warehouse order, and the lack of a systematic record of the tests in the physical/chemical test laboratory. In order to ensure sample tracking, a production movement was defined for each stage in the process and these movements were scanned and kept in the system at each stage. In order to prevent the wrong fabric roll from being issued, the roll reservation interface has been defined and the roll is prevented from being released without making a reservation for the order.

The handheld terminal device is connected to the database to ensure physical order and stock tracking in the warehouses. Two interfaces were created to record test data, test selection was made according to customers' requests, and an improvement was made where the results were entered and automatic pass-fail results were displayed. As a result of this study, benefits such as reducing fabric waste, saving labor and time in warehouse counting, measuring production performance and storing data in a healthy way have been achieved.

Type: PhD/ Textile Engineering
Thesis advisor:  Assoc. Prof. Dr. Senem KURŞUN
Co-Advisor: Prof. Dr. Selçuk PAKER
Student's name/surname: Meltem TEKÇİN
Supporting organization / Project information: TÜBİTAK, Proje ID: 119M976

Summary
This thesis aims to develop a textile-based, wearable, flexible, lightweight and comfortable RFID enabled moisture sensor structures that detects moisture and wetness while transmitting RF signals. Furthermore, the objective lies on printing techniques and ink formulations for crafting these sensors. This thesis consists of three articles, arranged by paying attention to the integrity of the scope. All of the articles given within the scope of the thesis are original and add innovation to the literature. In the articles, important and unique results of the thesis topic are discussed.

Type: Master / Innovative Technical Textiles 
Thesis advisor: Prof. Dr. Hale KARAKAŞ
Student's name/ surname: Hazal YILMAZ

Summary

Denim fabrics, which have a great importance in the textile industry, are always developing from past to present. Denim fabrics, which have been used for a long time and have not lost their popularity, have a very wide usage area today. Even if the perception of fashion changes, denim products have always maintained their place in the industry. Although denim fabrics are most frequently used as trousers in the textile industry, they are also widely used in products such as dresses, skirts, bags, home accessories and shoes. In addition to its product diversity, it is highly preferred in the textile industry due to its durability. The most important stage that makes denim fabrics visually appealing to the fashion industry is the washing process. The final appearance of the denim is achieved by giving the desired effects to the product with the washing processes carried out at the final stage. With different washing methods, denim is given many visual effects such as worn, vintage, faded, shiny etc.

A lot of water and chemicals are being used during denim washing processes, and this problem has been a subject of many researches for a long time. Re-using the waste obtained from denim washing causes another energy loss. This problem exists not only in denim manufacturing but also in many areas of the textile industry. When the damage caused to the environment by the textile and apparel clothing industry is examined, many concepts such as sustainability, ecological production and waste-free production have come to the fore. For this reason, many companies, factories and organizations are looking for new researches and initiatives to do their production using less water, chemicals and energy. Denim production is one of the process that consume much water and chemicals in the textile industry. Many denim manufacturers and brands are still looking for new solutions to reduce this damage. Today, alternative and sustainable searches still continue.

Stone washing is one of the most common washing methods used in the denim industry for many years. Stone washing is being processed in industrial washing machines by using pumice stones. Washing times vary depending on the effect desired to be achieved. With the rotation inside the industrial washing machines,  dyestuff on the garment wears off due to the friction between garment and stones and the desired effect is achieved. During this process, a lot of water is being consumed and the pumice stone damages the garment when friction is high. Therefore, after the washing process is completed, pumice stones must be carefully removed from the garment and should be cleaned. The process of removing pumice stone requires another rinsing process, and pumice stone that is not completely cleaned from the garment can be harmful for human health and the product. In addition, pumice stone becomes unusable by shrinking or decomposing after a few washing processes. Unusable stones causes waste problem, and also recycling or stock processes of these left stones causes another workload and energy loss.

For this reason, washing processes that can be an alternative to stone washing have been the subject of many searches since the past. There are methods that have been developed and are still being developed by many researchers to reduce the use of water and chemicals or to prevent the use of pumice stones.

The aim of this thesis, in cooperation with Ereks Blue Matters Factory, is to offer a new sustainable method in which less water and chemicals are being used and the use of pumice stones is eliminated, as an alternative to stone washing. For this purpose, a new technology, the foam washing method, was investigated and washing experiments were carried out. Washing trials were carried out to obtain the effects given by friction of the pumice stone on the fabric in industrial washing machines, by spraying foam on the same washing machines.

In the study, firstly stone washing and foam washing recipes and washing process stages were compared. Secondly, the physical properties of the fabrics obtained from stone washing and foam washing were analyzed and compared with each other.

For this study, 7 different denim fabrics with different compositions and weights, which are most commonly used in production at the Ereks Blue Matters factory, were selected. Two of the same fabrics were produced, processed as same until washing stage. For the washing process, one fabric was washed with stone while the other fabric was washed with foam. Washing trials were carried out separately for 30, 60 and 90 minutes for each fabric type. As a result of the washing trials, a total of 42 washed denim fabric samples were obtained, 21 stone washed and 21 foam washed.

In order to compare the physical performances of obtained samples, color fastness to domestic and commercial washing, color fastness to rubbing, abrasion resistance according to the Martindale method, color analysis with spectrophotometer, stiffness of fabric by the circular bend procedure, tear and tensile strength tests were carried out in Istanbul Technical University Textile and Apparel Quality Control Laboratory. With James H. Heal Titan machine, tear strenght test according to TS EN ISO 13937-2 and tensile strenght test according to TS EN ISO 13934-2 were evaluated. Abrasion test according to Martindale method was evaluated in James Heal Martindale & Pilling Tester according to TS EN ISO 12947-2. Color fastness to rubbing test was evaluated in SDL Atlas Crockmeter according to TS EN ISO 105-X12. Color fastness to washing test was evaluated in Linitest machine according to TS EN ISO 105-C06, stiffness of fabric by the circular bend procedure was evaluated in A&T Machine according to ASTM D4032 and color analysis was evaluated with Datacolor 650ᵀᴹ spectrophotometer. Test results were compared according to washing durations 30, 60 and 90 minutes for foam and stone washed fabrics.

When the test results were evaluated, it was seen that less water was used during the foam washing process compared to stone washing. When the test results were compared, the tear strength test results were higher in all fabrics washed with foam for both weft and warp yarns. Tensile strenght test results varied and no generalizable result could be determined for foam or stone washed fabrics. When the wet/dry rubbing fastness and washing fastness test results were evaluated, it was observed that the rubbing and washing fastness values of foam washed fabrics were generally better than stone washed fabrics. As a result of the evaluation, it was determined that the rubbing and washing fastness values of foam washed fabrics were better or the same as stone washed fabrics. After abrasion resistance test according to the Martindale method, no yarn breakage was observed for foam 40,000 cycles. For all fabrics, weight loss was observed as the rpm increased, but a regular rate was not detected in decreasing weights. In most of the tested fabrics, it was seen that the weight loss after 15,000 rpm was less for foam washed fabrics than for stone washed. It was determined that only for 4 types of foam washed fabrics, the weight loss was higher than stone washed, but this difference was less than 3%.

When all test results were evaluated, it was determined that the physical properties of denim fabrics washed with the foam washing method were preserved or better. Therefore, it has been proven that the new method can be used in the industry. Although the test results of foam washed fabrics are not significantly superior to stone washed ones, the difference in the ratio of water and chemicals used is quite high. Also, the use of pumice stones is eliminated with the foam washing process, and energy consumption in the process of removing pumice stones or stock waste will be prevented. When these results were evaluated, it was determined that the foam washing method can be used as a sustainable alternative to the stone washing method. Thus, an environmentally friendly method has been developed which can be accepted in the textile industry.

Type: Master / Innovative Technical Textiles
Thesis advisor: Prof. Dr. Selin Hanife ERYÜRÜK
Student's name/ surname: Ari HAKGÖR

Summary

Type: Master/ Textile Engineering
Thesis advisor:  Prof. Dr. Selin Hanife ERYÜRÜK
Student's name/surname: Sümeyye GÖRKEM
Supporting organization / Project information: İTÜBAP, Project ID: 42891

Summary
The textile sector has the second highest share in the Turkish economy and is a strategically important sector for Turkey. In global markets where the level of competition is very high, companies need to be successful and maintain their market shares. For this purpose, they should increase their production efficiency and capacity and try to maintain their position in the sector by developing new strategies. Having an effective strategy in this regard is seen as an important factor for all firms to achieve success.This study focuses on the factors that are effective in increasing the capacity of firms and making strategic decisions. Their importance is also mentioned. Capacity, importance and types of capacity, capacity planning, capacity utilization rates, capacity calculation methods, capacity measurement criteria and capacity increase in the textile and apparel industry are explained in detail. In addition, information on strategy, strategic management and types of strategy is also given. Accordingly, the current situation analysis of the apparel sector was made in the first stage. Then, strategy determination and evaluation criteria were investigated. The survey method, which is one of the data collection tools, was used. This method is followed by the stages of collecting data and evaluating the criteria. Finally, the study is completed with conclusions and recommendations.

Type: Master/ Innovative Technical Textiles
Thesis advisor:  Assoc. Prof. Dr. İkilem GÖCEK
Student's name/surname: Gözdenur ULU
 
Summary
Nonwoven textiles have found numerous applications in various fields today. They have the potential for use in automotive industry as upholstery materials, in the healthcare sector for surgical masks and sterile garments, and in the packaging industry for packaging materials, among many other areas. Nonwoven textiles are textile materials produced without the need for weaving or knitting, using different bonding or entangling methods. They are typically obtained by combining fibers through thermal, mechanical, or chemical processes. Nonwoven textiles offer a faster production process compared to traditional textile manufacturing methods such as weaving or knitting. This provides a significant advantage in mass production and meeting urgent demands. Additionally, the production of nonwoven textiles generally requires less labor and energy, reducing costs and offering a more economical option.

The automotive sector constitutes a significant area where nonwoven surfaces are utilized. One of the key requirements expected from textiles used in the automotive industry is acoustic performance. Various sources such as the engine, powertrain, suspension system, tire and road noise, aerodynamic sources, and other noise-vibration sources are known as acoustic sources that affect passengers and drivers in a vehicle during driving. Materials developed for the automotive sector are expected to deliver acoustic performance. Acoustic performance encompasses sound absorption and sound insulation. Acoustics is the branch of science that studies sound. Accordingly, sound is a form of energy that generates sound waves through vibrations. When sound waves emitted from a sound source encounter a surface, they can interact in different ways. One of these interactions is sound absorption by the surface. Sound absorption refers to the partial loss of sound energy within the surface, in contrast to sound reflection. On the other hand, sound insulation is related to sound transmission loss, indicating how much energy of a sound wave passing through a surface is transferred to the second medium. Sound insulation aims to minimize the transmission of sound from one environment to another, while sound absorption aims to maximize the absorption of sound energy by the material within the environment.

The experimental study focuses on improving the acoustic performance of polymer-coated nonwoven textiles that can be specifically used as floor mats or trunk mats in the automotive sector. In line with this purpose, the study has been completed by following the roadmap outlined below:

Firstly, nonwoven textiles with different weights were tested to determine the optimum weight. The term "weight" refers to the mass per unit area and is related to the thickness of the nonwoven textile.

In the next step, two different types of polymer coatings with two different weights were applied to the selected weight (thickness) of the nonwoven textile, and the acoustic performance behavior depending on the type and thickness of the polymer coating was observed.

In the polymer-coated samples, in order to observe which side of the sample was efficient to employ for acoustic performance, the samples were tested twice by flipping the front and back sides.

Based on the selected polymer coating and weight (thickness), different types of fillers were used in the coating to achieve superior acoustic performance. Finally, the selected types of fillers were added to the coating in different proportions to evaluate the effect of filler dosage on acoustic performance.

In the first step, the tested samples for determining the optimum weight of the nonwoven textile were made of PET (polyethylene terephthalate) fibers and had weights of 120, 220, 300, and 400 gsm. These surfaces were produced in the facilities of Hassan Tekstil Sanayi ve Ticaret A.Ş. using the needle-punching method. PET fibers were chosen because they are commonly used fibers in automotive textiles.

In the second step, experiments were conducted with different types of polymer coatings, and the preferred polymers were polypropylene and polyethylene. Both polymers were tested at weights of 400 and 800 gsm. The application of the polymers onto the nonwoven textiles was done using the extrusion coating technique. Only one side of the samples was coated with the polymer using the extrusion technique. The production of the polymer-coated samples was done in the facilities of Hassan Tekstil Sanayi ve Ticaret A.Ş.

In the third step, samples were prepared using different types of fillers in the polymer coating. The fillers used were pumice, barite, dolomite, calcite, and talc minerals. In this step, these fillers were added to the polymer coating at a constant ratio of 30%.

In the final stage, selected types of fillers were added at ratios of 25.5% and 18%, and they were also tested separately to examine the effect of filler amount and determine the optimum quantity.

The acoustic performance analysis was conducted through the tests on sound absorption coefficient and sound transmission loss. The impedance tube method was used as the measurement technique. The sound absorption coefficient test was performed using a two-microphone setup. Samples were prepared and tested separately for the large tube and small tube configurations. The measurements from the large tube and small tube were combined using software to obtain a general distribution. For the sound absorption coefficient measurement, the sample was placed in the apparatus in contact with a rigid support, ensuring there are no gaps. The sound transmission loss test was conducted using a four-microphone setup. The test was performed for two conditions: with and without sound reflection. The samples used for the sound absorption coefficient test were also used for the sound transmission loss test since both of the tests are non-destructive tests, and no additional samples were prepared.

At the end of the thesis study, it was observed that increasing the weight or thickness of nonwoven textiles without coating improved both the sound absorption coefficient and sound transmission loss. As expected, the frequency-dependent variation of the sound absorption coefficient in nonwoven textiles increased. It was observed that the sound absorption coefficient values of nonwoven textiles increased as the frequency increased, indicating better sound absorption performance at higher frequencies. In terms of sound transmission loss, there was no significant frequency-dependent variation. However, in general, the sound transmission loss values of nonwoven textiles were quite low. In determining the appropriate weight, not only achieving high results was considered but also taking the production process and costs into account. As a result, the 220 gsm sample was considered optimal.

When deciding on the type and weight of the polymer coating, both the sound absorption and sound transmission loss properties were evaluated together. The 800 gsm polypropylene-coated nonwoven textile was selected as the optimal choice.

When the samples were tested on both sides, it was observed that the sound transmission loss results remained almost the same, but there were changes in the sound absorption coefficient. This is due to the fact that in the measurement of sound transmission loss, the sound wave passes through the entire material. In other words, the order of the layers does not significantly affect the sound transmission loss. What matters is the type of layers. However, in terms of sound absorption performance, the surface characteristics with which the sound wave interacts are important. Therefore, the absorbed energy will not be the same when the sound wave hits the polymer coating or the nonwoven surface.

In order to differentiate the effect of filler type on the acoustic performance of the samples coated with a polymer containing 30% pumice, dolomite, barite, calcite, and talc fillers, behaviors obtained at low frequencies were specifically examined. Therefore, experiments were conducted using pumice, calcite, and talc in the final stage.

In addition to the experiment conducted with a 30% ratio of talc, another experiment was conducted with an 18% ratio, considering the negative effects caused by talc on the mechanical properties of the final composite nonwoven structure. It was decided that despite meeting the acoustic expectations, talc was not a suitable option due to the undesirable mechanical effects.

Increasing the filler amount had different effects on the samples with pumice and calcite fillers. While increasing the filler amount improved sound transmission loss in pumice-filled samples, it had a negative effect on sound absorption performance. In calcite-filled samples, on the other hand, increasing the filler percentage had a negative effect on sound transmission loss but provided good results in terms of sound absorption. When looking at the overall distribution, fluctuations were observed, especially in the sound absorption graphs, indicating frequency-dependent variations for both fillers. The sound transmission loss results were more stable in this regard.

Type: Master/ Textile Engineering
Thesis advisor:  Assoc. Prof. Dr. İpek YALÇIN ENİŞ
Student's name/surname: Suzan Özdemir
Supporting organization / Project information: TÜBİTAK, Proje ID: 121M309; BAP, Proje ID: 43368
Summary
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 PCL,PLA, PLCL, and PLGA and also their combinations with different fiber orientations and constructions and assess their physical, morphological, and mechanical properties.

  

Type: Master/ Textile Engineering
Thesis advisor:  Prof. Dr. Burçak KARAGÜZEL KAYAOĞLU
Student's name/surname: Hisham Ali Muhammad Ali MOUSSA

Summary

Textile materials have always been utilized in the medical field. The unique properties they offer, biocompatibility and versatility are the major reasons behind that. They can be found in applications ranging from a simple bandage to full on blood vessels. Nanofiber-based textile materials are textile materials known for their high surface area and interconnected porosity. Nanofiber- based textile materials can be fabricated with a variety of methods yet; the most dominant method is electrospinning. Furthermore, in the recent years there has been a rise of interest in different materials as well such as; aerogels.

Aerogels are porous materials that have unique properties that make them good candidates for drug careering and releasing. Aerogels can be made of different materials   such as polymers, biopolymers and metal oxides but the most common types of aerogels are silica, carbon and metal oxide aerogels. The process of synthesizing aerogel consists mainly of three stages; gelation, aging and drying. The process of drying aerogels affects the synthesized aerogel greatly as you can have three different types of aerogels by just using a different drying technique. Xerogel is one of the types of aerogels and it is achieved by drying aerogels at ambient pressure.

This study aimed to design and develop a PVA/hydrocortisone loaded xerogel electrospun mat for topical drug delivery. The silica xerogel was synthesized using TMOS as a silica precursor, Ammonium hydroxide as a catalyst and Methanol as a co-solvent. The xerogel was ball-milled into fine powder and had its surface area, pore size and volume analyzed. In addition to that, hydrocortisone was loaded into three different samples; one consisting of only xerogel, the second of only PVA nanofibrous mat and the third consisting of both xerogel and PVA nanofibrous mat. In vitro drug release analysis was carried out for all of these samples. PVA was chosen for its biocompatible properties and stability. SEM and EDAX analyses were carried out to investigate the surface of the fibers and elements existing in the samples respectively. In addition to that, FTIR analysis was performed to identify the different materials making up the nanofibrous mats.

The synthesized silica xerogel had a surface area of around 505 m²/g, pore size of around 3.8 nm and a pore volume of 0.48 cm³/g. SEM images showed the hydrocortisone loaded xerogel inside the PVA nanofibrous mat and the EDAX analysis confirmed the existence of silicone in the samples due to the existence of silica xerogel as well as a high concentration of Carbon due to hydrocortisone. The hydrocortisone loaded xerogel showed a slow sustained drug delivery release behavior and around 69.3% of the loaded hydrocortisone was released in 25 days. The PVA/xerogel/hydrocortisone nanofibrous mat showed a similar drug release behavior with a release of around 79.2% of the hydrocortisone initially loaded with PVA was released in just 30 minutes. Demonstrating a conventional or retarded drug release behavior. Meanwhile, the PVA/hydrocortisone electrospun mat showed a completely different drug release behavior. Around 98.55% of the hydrocortisone initially loaded into the PVA.

In conclusion, Silica xerogel as a drug carrier was successfully synthesized. It was loaded with hydrocortisone. Hydrocortisone loaded silica xerogel drug release was investigated as well as PVA/xerogel/hydrocortisone and PVA/hydrocortisone. The result of these three different sample types were collected and compared. Both hydrocortisones loaded xerogel and PVA/xerogel/hydrocortisone showed a slow sustained drug release behavior. Meanwhile PVA/hydrocortisone showed a retarded drug release behavior. These results suggest the capability of PVA/hydrocortisone load xerogel mat to work as a sustained/controlled topical drug delivery carrier.

Type: Master/ Innovative Technical Textiles
Thesis advisor:  Assoc. Prof. Dr. İpek YALÇIN ENİŞ
Student's name/surname: Sinem Hazal AKYILDIZ
Supporting organization / Project information: BAP, Proje ID: 43387
Summary
Microplastic pollution emerges as a critical environmental problem resulting from the decomposition of macro-sized plastics into micro- or nano-sized plastics in nature. There are many sectors that cause the formation of microplastics. At the beginning of these, the textile sector took its place. Petroleum-derived textiles are generally produced from various raw materials such as polyester, polyamide and acrylic, and synthetic fabrics produced from these fibers generate a large amount of microfiber wastes from their production to consumption and even disposal processes. This thesis focuses on the necessary steps for the most effective detection, separation and analysis of microplastics originating from the textile industry.  Experimental studies carried out within the scope of the thesis are examined in three separate sections.  The process of removing organic substances by treating artificially obtained textile wastewater with various chemicals constitutes the first experimental stage of the thesis. Then, the processes of removal and analysis of microfibers in industrial textile wastewater were realized. While the first two parts of the study focus on the production phase, the third part focuses on the user phase. In this context, the structural properties of the fabrics were taken into account, and it was examined how the properties such as the fabric type, thickness, basis weight and raw material type of the fabrics could be effective for microfiber release. When the outcomes of the experimental processes are evaluated, it can be said that important steps have been taken in terms of the determination, separation and analysis of microfibers in textile wastewater.

  

Student: Ayşe Berna Karabulut
Thesis Advisor: Prof. Dr. Banu NERGİS

Summary
Sportswear, the clothing including footwear, worn during sports or physical exercise, has an increasing demand and the sports apparel with improved comfort properties have become more popular than ever. Enhancing the wearer’s comfort is possible by engineering fabric structures by incorporating suitable fibers. For doing so, in this study, bilayered spacer fabric samples were produced from sustainable fibers namely, recycled PA66 and PA6-Umorfil yarns, together with 44 dtex elastane. A PA6 FDY monofilament yarn was employed as the spacer yarn. The results showed that comfort properties of sports apparel can be improved by using recycled and Umorfil poliamide fibers in different parts of the garments depending on the intended use and purposes. Use of such sustainable fibers in the fabric structure is not only suitable for achieving active sportswear comfort but also is respectful to the environment.

 

Type: Master
Thesis advisor:  Assoc. Prof. Dr.Umut Kıvanç Şahin
Student's name/surname: Ayşin Acır Sükuti

Summary

With the development of technology, the need for drying machines, which entered our lives, is increasing day by day as people are more involved in working life. People who want to save time and space and want to spend less effort for washing-drying processes are more attracted to this machine. Although the dryer appears to be a useful product in theory, it is a product that people use hesitantly. The main reason for this feeling is that drying machines shrink certain types of textiles, especially cotton-containing textiles. Within the scope of this study, a survey was conducted in order to determine the main source of the problem and to get to know the laundry habits of the users in daily life. According to the results of the survey, the shrinkage problem was determined and a phased experiment plan was designed by procuring fabric samples to simulate the textile products that the users most frequently observed shrinkage in daily life. Drying machines of different brands and models specified in the questionnaire were purchased and detailed algorithm analysis and shrinkage tests were applied. This study was carried out as a preliminary study and as a result, it was seen that there was no obvious difference between the shrinkage rates of the dryers available in the market, and all of them caused shrinkage at similar rates. It has been determined that slow drum rotation and high drum inlet temperature are the parameters that partially affect the shrinkage positively.

Then, the test plan was designed considering the user conditions and the ½ Fractional Factorial  Design of Experiment (DOE)  study was planned. All data obtained as a result of experimental design tests and preliminary study were collected to form a mathematical model. The mathematical model was developed using the R program. By feeding 111 test data directly to the model, it is aimed to predict the shrinkage regardless of the dryer brand and model. The created model can make predictions with an accuracy rate of 97.5%.

While creating the mathematical model, the importance and degree of influence of the parameters added to the model were determined and it was determined that the most important parameter affecting the shrinkage was the drum speed and drying time. Before the algorithm was designed, the shrinkage rates of the test samples were measured at different capacities periodically every 20 minutes in order to understand the development of shrinkage in the dryer and its relationship with humidity. By graphing the obtained data, it has been determined that there is a point where shrinkage gives the best results from the beginning of drying. This point is called the “Critical Moisture Point”. In the periodic follow-up tests, it was determined that cotton textiles were not affected by any mechanical action and did not show shrinkage until the critical moisture point. On the contrary, it has been determined that when the textile, which comes from the washing machine with a certain amount of shrinkage, is put into the dryer, it releases itself and expands in size until it reaches the critical moisture point. It has been observed that when drying is continued after the critical moisture point, the textile starts to shrink and shrinks until the drying is complete. By combining the findings obtained as a result of all the experiments, an algorithm was designed to reduce the shrinkage rate during tumble drying of cotton textiles. Since the most important criterion in the algorithm design is the drum rotation, various iterations have been made by constructing drum stop and rotation durations at low speed and high speed. The purpose of the design is providing minimum mechanical drum movement. After drying in the 2800 RPM configuration until the critical humidity level, the configuration where the drum is slowed down to 1800 RPM and rotated for 2,5 minutes, then stopped for 7,5 minutes gives the lowest shrinkage rate among all trials. In order to ensure homogeneity and faster drying in the determined algorithm design, the system was supported with an additional heater. In the preliminary studies and as a result of the DOE tests, since the drying time directly affects the shrinkage, the shrinkage rate is further improved with the addition of an additional heater. While the lengthwise shrinkage rate of the reference Cotton Economic program was 9,2% in the knitted test sample and 2,1% in the woven test sample, the lengthwise shrinkage rate was measured as 6,6% in the knitted test sample and 1.6% in the woven test sample after the innovative algorithm design was developed. As a result of the new algorithm design, the lengthwise shrinkage rate has been improved by 28% in knitted textiles and 24% in woven textiles.

Type: Master/ Textile Engineering
Thesis advisor:  Prof.Dr.Gülay Özcan
Student's name/surname: Muhammed Emin Çoban
Supporting organization / Project information: Arçelik

Student: Nursema Pala Avcı
Thesis Advisor: Prof. Dr. Banu NERGİS- Dr. Nebahat Aral YILMAZ

Summary

Atopic dermatitis (AD) is a chronic, itchy, and inflammatory skin disease that causes dry skin, rashes, and inflammation. Various complementary treatments such as hydrogels, wet dressings or natural oil-added wound dressings have been developed as an alternative to drug therapy for AD. Natural oils have been widely used in recent studies as an alternative to synthetic drugs. The antibacterial properties of thyme oil (TEO), the contribution of St. John's wort oil (HPO) to wound healing, and the essential fatty acids of borage oil (HO) that cannot be synthesized by the body in AD patients and must be taken externally, were preferred as additives to nanofiber surfaces to fabricate wound dressings in this thesis. Biocompatible polyvinylalcohol (PVA), polycaprolactone (PCL), polyvinylprolidone (PVP) were used as the polymers for the production of the dressings using emulsion and co-axial electro spinning processes. The nanofiber structures were characterized and tested in terms of fiber properties, nanofiber surface properties, antibacterial activity and release behavior.

Type: Master/ Textile Engineering
Thesis advisor:  Prof.Dr.Fatma Kalaoğlu
Student's name/surname: Özlem Yüksel
Supporting organization / Project information: 

Summary

The aim of study is to make an experimental investigation of how fiber crosssectional shape and filament numbers of yarn affect the fabric's ability to transmit moisture. Yarns was produced from the nylon6 70/17 round,70/24 round,70/34 round,70/48 round,70/68 round, 70/40 dog bone, 70/48 trilobal, 70/36 hollow crossec-section yarns. These yarns were knitted in the same settings as single jersey in seamless knitting. Then, yarn and fabric wicking, air permeability, water vapor permeability, thermal conductivity, thermal resistance and thermal absorvity, transfer wetting, water evaporation rate and drying rates of knitted fabrics were measured. Data collected through the experimental studies were evaluated statistically using IBM SPSS Statistics v26 software. One way or two-way analaysis of variance, one way/two way-ANOVA, has been used in order to understand whether there is any interaction between the independant variables on dependant variable. Some curve function estimations were made using the regression analysis.

It was concluded that the fiber cross-section and filament numbers of the yarn have a direct effect on the comfort properties of the garment. Firstly, it has been determined that the differences in the wicking behavior of knitted fabrics are directly caused by the fiber cross-section and the differences in the number of filaments in the yarn. With the change in shape factor and filament numbers of yarn, the wicking rate through a fabric is observed to rise with an increase in fiber specific surface area, although the fabric's permeability to air and water vapour decreases. It has been seen that hollow fiber, dog bond fiber cross-section yarns give good results in terms of comfort properties. Secondly, the thermal conductivity of fabric is significantly impacted by the trapped air in the porous areas of the fabric structure. Hollow fiber and dog bone fiber cross-section fabrics show higher thermal resistance, lower thermal conductivity between different crossection fabrics. The knitted fabrics made with hollow and doge bone cross-section yarns display the highest values of thermal resistance and diffusivity and the lowest thermal absorptivity and heat flow because of the higher amount of air in the fabric structure, which slows the heat transfer process. Lastly, the fiber's macromolecular structure also affects the fiber's capacity to dry. 70/36-HLW and 70/40-DB have the highest drying speeds, which is concluded to be due to having highest capillary suction. Moreover, the small filament number is quite effective on drying speed. According to results, hollow fiber, dog bone fiber shows better performance wicking ability and drying capability compared to other cross-section fibers in the first 5 minutes of the tests. To sum up, when the test results were evaluated, suggestions were made for different usage purposes related to the end-use area. Due to insufficient scientific studies, it is recommended to conduct experimental studies on dog bone fiber in different cross-sections for underwear and sportswear in the future.

Type: Master/ Innovative Technical Textiles
Thesis advisor:  Prof. Dr. Ali DEMİR
Student's name/surname: Mohammad Shohag ALAM
Supporting organization / Project information: İTÜBAP, Project ID: 42891

Summary

The global automotive industry is highly focused on application natural fibers with thermoplastic polymers due to its commercial applicability. Due to being environmentally friendly and having better advantages such as lightweight behavior, good strength to weight ratio and weather resistance, jute fiber has become a very suitable option to make composite material with thermoplastic materials such as polypropylene (PP). Application of jute fiber with PP matrix is growing day by day. In addition to that, flame retardant jute/PP composites have become a new set of trends of reliability. However, to achieve flame retardancy without compromising mechanical properties is a key concern to be noticed. 

In this thesis, flame-retardant jute/PP composites based on ATH/ZB and APP/ZB at a ratio of 80:20 were produced via combination of extrusion process and hot press method. Zinc borate (ZB) was used for creating a synergetic effect with aluminium tryhydride (ATH) and ammonium polyphosphate (APP). Before infusing flame retardant fillers to jute/PP composites, fiber loading levels were optimized with PP matrix at 20 wt.% of loading level based on long jute fiber (LJF) and short jute fiber (SJF) by the presence of 5 wt.% of maleic anhydrate-grafted polypropylene (MA-g-PP). The results indicated that length of short jute fiber was having a positive impact over mechanical properties (tensile strength and flexural strength). A maximum tensile strength value of 37.32±0.75 MPa and flexural strength value of 34.68±1.70 MPa have been achieved. Tensile modulus was reached to 1811±81 MPa and flexural modulus was reached to 1181±95 MPa. Further investigations were carried out with 20 wt.% SJF by increasing fiber loading up to 60 wt.% since the 20 wt.% SJF had been found to performed better than the 20 wt.% of LJF one in the initial mechanical property experiments. It was evident that increasing jute fiber content decreases tensile strength as well as strain (%) value. A clear noticeable decrease of tensile strength value (19.50±2.04 MPa) was found when 60 wt.% of SJF was infused within PP matrix. Until 40 wt.% of loading of short jute fiber flexural strength remains high (38.98±3.45 MPa) and consistent compared to others. But, when 60 wt.% loading of SJF was infused flexural strength value was decreased to minimum of 37.77±1.25 MPa was reached a tensile strength value of 19.50±2.04 MPa. Morphological analysis was carried out via scanning electronic microscope (SEM). Better adhesion was noticed for 30 wt.% loading of SJF which ensured optimum mechanical properties (tensile properties: strength-29.5±2.74 MPa, strain- 4.97±0.84 % and young modulus-1517±198 MPa; flexural properties: strength: 38.17±1.9 MPa, strain-7.18±1.17 % and flexural modulus- 1488±88 MPa) that was achieved. By keeping SJF loading level constant at 30 wt.%, as flame-retardant additives ATH/ZB and APP/ZB were incorporated at a loading level of 30 wt.% and 40 wt.% to achieve better flame-retardant properties without compromising mechanical properties.

Char formation were greatly influenced via APP/ZB on jute/PP composites. To analyze flame-retardant behavior and thermal properties, UL-94 (Vertical burning and Horizontal burning), LOI, Cone calorimetry and TGA were carried out to investigate. An excellent flame retardancy was achieved at 40 wt.% loading of APP/ZB into jute/PP composites. V-0 classification level was achieved and ‘no burning effect’ was found which ensured self-extinguished (LOI- 28.8%) manner of flame-retardant jute/PP composite. A clear increment of LOI value was achieved up to 76.61% compared to unmodified jute/PP composite at a loading level of 30 wt.% of short jute fiber. Peak heat release rate (pHRR) was reached to 197.5 kW/m² with total smoke production (TSP) value of 10.5 m². Total heat release (THR) was 86.42 kW/m². Effective hear of combustion value was 23.47 MJ/kg. Tensile strength and flexural strength increased by 15.86% and 81.21%, respectively. However, impact properties were negatively affected due to the high loading of APP/ZB. 35.68% decrease was noticed. Density was increased 18.75% compared to unmodified short jute fiber at a constant loading level of 30 wt.%. Inclusion of flame-retardant additives increased wear rate as well as value of co-efficient of friction (COF) significantly. A maximum increase of 195.75% was observed due to high pin temperature with self-extinguished APP/ZB based jute/PP composites. COF value was moderate compared to ATH/ZB at a loading level of 40 wt.%. Thermogravimetric analysis (TGA) results showed the maximum degradation rate temperature of the composite structures containing 40 wt.% of APP/ZB to be 481.62 ^oC, which was approximately 16 °C higher than that of the unmodified jute/PP composite at a short jute fiber loading of 30 wt.%. Fourier-transform infrared (FTIR) spectroscopy results was showed no significant differences within chemical structures of APP/ZB or ATH/ZB compared to unmodified jute/PP composites which signifies flame retardants were acted just as a filler to improve flame retardancy without any sorts of drastic changes into produced composites.

Type: PhD / Textile Engineering
Thesis advisor:  Assoc. Prof. Dr. Ali KILIÇ
Student's name/surname: Ali TOPTAŞ

Summary

Airborne particulate matter (PM), particles in the air with a size of 10 microns and smaller, poses serious health problems due to its density and dimensions, leading to various respiratory and cardiovascular diseases. The escalating industrial activities driven by increasing population worldwide have exacerbated air pollution, making PM a subject of extensive research from scientific, economic, ecological, and health perspectives. According to the World Health Organization (WHO), over 4 million people die annually due to prolonged exposure to polluted air containing particles smaller than 10 microns. Particles in the air are classified based on their size as PM₁₀, PM_2.5, and PM_0.3. Among them, PM_0.3 particles with a size of 300 nm pose the greatest danger as they are challenging to capture, remain suspended in the air for extended periods, and carry toxic properties.

To address this issue, air filters, especially High-Efficiency Particulate Air (HEPA) or Ultra-Low Particulate Air (ULPA) filters, are crucial, especially in environments like intensive care units, operating rooms, and places with individuals with health issues. These filters use micro and/or nano-porous nonwoven fabrics that are produced via spunbonding or melt-blowing processses.

Polyester (PET), polypropylene (PP), aramid, cellulose, and glass wool are among the materials used to create these fabrics. They are primarily utilized in deep filtration processes. Achieving high filtration performance in these microfiber fabrics often involves electrically charging the fabric. However, the filtration efficiency significantly diminishes when the fabric loses its electrical charge.

Nanofiber fabrics, with pore sizes in the nano range, can capture nano-sized particles without the need for electrical charging. Yet, the small size of the fibers can result in a tightly woven structure, increasing pressure drop in the filter material. Bimodal filter fabric structures, incorporating both nano- and microfibers, aim to filter nano-sized particles through nanofibers while allowing air passing through the fabric via the voids created by microfibers. Nanofibers generally have low mechanical resistance, and the presence of microfibers enhances the fabric's mechanical strength. Therefore, producing bimodal fabrics can yield durable filter elements with high filtration efficiency and low pressure drop.

An ideal air filter should provide high filtration efficiency and low pressure drop (ΔP) simultaneously. Traditional fibrous filter media, composed of micrometer-sized fibers, offer low ΔP but exhibit limited submicron particle capture efficiency due to their large pores. On the other hand, filters composed of nanofibers, with smaller pore sizes, offer high filtration efficiency but impede air flow, causing a high ΔP. Additionally, faster pore clogging during filtration leads to quicker cake formation and reduced filter lifespan. Researchers are exploring new approaches, such as bimodal fibrous filters  and electrostatic modifications  to enhance filtration performance and address varying particle sizes.

Bimodal (This term, in the thesis title, is a term that will be used widely throughout the entire study. It indicates that there are fibers with two different average thicknesses (diameters) on the filter surface.) fibers represent a novel approach achieved by using micro and nanofibers either in a single layer or in multilayer configurations. The integration of at least two different fiber size ranges allows the filter to efficiently capture a wide range of particles. While microfibers provide mechanical strength and stability to the filter, nanofibers offer a complex network with a high surface-to-volume ratio for effective particle capture. By optimizing the arrangement of the filter layers and distribution of fiber diameters, increased ղ, low ΔP, and enhanced dust-holding capacity can be achieved

In the study where PVDF-based electret (In the scope of this study, the term 'electret' is commonly used. This term refers to the charging of polymer surfaces with negative or positive charges, which occurs as a result of the orientation of free ends of polymer chains towards the polymer surface due to external factors applied to the polymer.) nanofiber mats were optimized with the electro-blowing technique, where the experimental parameters were systematically designed using the Taguchi three-level L9 orthogonal design and the results were then analyzed using ANOVA. In this context, it was determined that the most important factors affecting fiber diameters among the parameters examined (concentration, air pressure and electric field) were concentration and electric field strength. It was observed that the increase in air pressure had a negligible effect on fiber diameters but reduced the defects like droplet density. The optimal parameters yielding the thinnest fiber (124±71 nm) were determined as 9 wt.% concentration, 2 bar air pressure and 30 kV electrical voltage. Additionally, applying corona discharge treatment to the samples resulted in a remarkable increase in quality factors of over 70%. Additionally, the corona discharge process provided 78,7% improvement in QF, increasing the filtration performance to 98,97% in the best sample. This work highlights the potential of the electroblowing method in processing highly efficient PVDF nanofibers for air filtration.

In the second chapter where PVDF (polyvinylidene fluoride) based nanofiber nanogenerators were produced by the electroblowing method, the effects of the applied electric field and the air pressure used on the fiber morphology and piezoelectric properties were examined. was investigated. As expected, the resulting mats contained entangled fibers due to turbulent measurements of air, but the number of entangled fibers was minimized by applying voltage. Samples produced at 2 bar air pressure had lower avarage fiber diameters than samples produced at 3 bar pressure. In addition, 2 bar air pressure is more beneficial in terms of β phase formation than 3 bar air pressure. Additionally, it was observed that the β-phase content increased with the increase in the treatments applied. Among the samples produced with 2 bar air pressure, the S2 sample with 30 kV voltage showed the highest β-phase percentage. The maximum piezoelectric output was obtained from sample S2, where AFD was 224±60 nm, β phase was 88%, and Vmax was 1,92 V. Polarization effect at the strongest power to maximize the β phase and piezoelectric output of the produced PVDF fibers by electro-blowing method.

In the third chapter nanostructured filters were produced using the electroblowing method from solutions containing polyvinylidene fluoride (PVDF) and polyethylene glycol (PEG) polymers at different rates. By increasing the water-soluble, low molecular weight PEG content and applying water bath treatment to the produced mat, fiber diameters were reduced and a more porous structure was obtained. In particular, the PVDF:PEG (3:7) sample with the highest PEG content exhibited clustered nanofiber/nanonet-like structures with average diameters of 170 nm and 50 nm. Removal of PEG after the water bath process enabled the formation of a nanonet structure, especially at the intersections of the fibers. Although this process resulted in a more porous structure and a slight decrease in filtration efficiency (-1,3%), the observed significant reduction in pressure drop led to a significant improvement in quality factors. Additionally, by exploiting the polarizability of PVDF under an electric field, the filtration efficiency of nanostructured PVDF filters was increased by 3,6% after corona discharge treatment, resulting in a 60% improvement in quality factor. As a result, the PVDF:PEG (3:7) sample offered an impressive filtration efficiency of 99,57%, a pressure drop (∆P) of 158 Pa, and a quality factor of 0,0345. This study has shown that nanostructured high performance filters can be obtained from PVDF-PEG mixtures by electro-blowing method.

In the fourth chapter, the filtration performances of nanofibrous mats obtained by combining layered and bimodal approaches were evaluated. Fibrous layers produced by melt-blowinng (MB) method were obtained with similar fiber diameters and different thicknesses with different feeding speeds. Bimodal structures obtained by fibers with an average diameter of 225 nanometers produced by the solution blowing (SB) method to fibers with an average diameter of around 800 nm obtained at 1, 5 and 10 rpm screw rotation/feed speeds had higher filtering performance than the samples without SB nanofibers. Then, among the 3 samples with an average basis weight of 15 gsm, only the MB sample (electro-blown nanofiber); The sample (L) containing 4 gsm EB nanofiber and the 4-layer sample (4L) containing 4 gsm EB nanofiber (138 nm) were compared. The 4L sample had the highest quality factor (0,0353) with a filtration efficiency of 96,01% and a pressure drop of 135 Pa. Although the filtration efficiency increased in all samples with the subsequent corona discharge, the highest value (99,34%) was obtained from the 4L sample.

In the fifth chapter the impact of the “bimodal” structural design was explored using fibrous mats composed of fibers with different diameters produced through MB, SB, and methods in various layer configurations and electrostatic charging While maintaining the basis weight of the filter samples as 30 gsm, using 4-layered filter (4L) resulted in structures in improved air permeability compared to single-layer samples. The 4L sample exhibited the highest performance at an airflow rate of 95 L/min, achieving 99,52% filtration efficiency at 148 Pa. Moreover, replacing MB layer in the 4L structure with bimodal mats (BM) obtained by homogeneously incorporating SB nanofibers into the MB layer increased the filtration efficiency 99,61%, keeping the ΔP nearly the same. The corona discharge treatment yielded the highest efficiency (99,99%) in the 4BML sample, produced by using PVDF:PP masterbatch and a bimodal approach. Even after one month the filtration efficiency was maintained at 99,90% which shows clear advantage of bimodal fiber distribution in electret electret filters.

In the sixth chapter, the changes in fiber morphology and filtration performance of PVDF nanofibers, which show high filter performance with their electret property, were examined with the additives added to the structure. In the study, where it was aimed for droplet-free, smooth and thin nanofibers to show an electrostatic effect for a long time, the thinnest fiber diameter and the smoothest nanofiber networks were obtained from solutions in which Al(NO₃)₃.9H₂O, NaCl, LiCl, KCl additives were added to the structure at an amount of 1% of the PVDF solution weight. fiber morphology was obtained from the sample with Al(NO₃)₃.9H₂O additive material. In addition, 99,95% filtration efficiency and 195 Pa pressure drop values were obtained after corona discharge. The highest values in the measured solution conductivity result belonged to this sample. As a result of all these measurements, the Al(NO₃)₃.9H₂O sample, became the best sample with 99,95% filtration efficiency.

In the seventh chapter, layered studies were obtained from PVDF and PA-6 nanofibers in different triboelectric series. To examine the bimodal effect as well as the triboelectret effect, bimodal filter structures obtained from PA-6 nanofibers with an average diameter of 60 nm and PVDF nanofibers with a diameter of 176 nm reached a filtration efficiency of 99,997% and a pressure drop of 193 Pa after corona discharge. After 4 weeks of discharge with the IPA method, the samples subjected to filtration testing proved their triboelectric properties with both 0,26 kV surface potential and 99,829% filtration performance.

Type: Master/ Textile Engineering
Thesis advisor:  Assist. Prof. Dr. İpek YALÇIN ENİŞ
Student's name/surname: Janset Öztemur
Supporting organization / Project information: TÜBİTAK,  Proje ID: 121M309
Summary
Within the scope of the thesis, PLA, PLLA, and PCL polymers with excellent biocompatibility and an ambitioned biodegradation time are chosen to match the needs of vascular graft surfaces. These biopolymers and their blends at different polmer ratios are electropun into fibrous web structures using solvent systems that have low toxicity and less influential on human health. The solution and production parameters are optimized during the surface fabrication phase to meet the standards for cell activity on the graft surface. The usability of surfaces that perform morphological, thermal, chemical and biological analyzes as small-caliber vascular graft material will be tested. It is thought that the findings of the thesis will offer an innovative material alternative for small-caliber vascular grafts, which is a very current and commercially unsuccessful study subject, and will shed light on the studies conducted in this direction.

 

Type: Master/ Textile Engineering
Thesis advisor:  Assoc. Prof. Ali Kılıç
Student's name/surname: Merve Nur Sağırlı

Summary

In this thesis, electrostatically charged during and after production of the filter media and performance was investigated. Polyvinylidene fluoride (PVDF) was used as raw material due to its superior chemical and physical properties. The production method was determined as solution blowing and electroblowing. Nanofiber production was carried out by solution blowing method and then the produced nanofibrous structure was electrically charged by corona discharge method. Using the same solution, nanofiber production was also carried out by electroblowing method and the filter performance of these two structures was compared. The filtration efficiency of the fibers obtained by solution blowing was only 55% and the pressure drop was 43 Pa. With the corona application, while the pressure drop remains constant, the filter efficiency increased by about 10% and reached 68%. In the nanofiber webs obtained by electroblowing, 97% efficiency was achieved. However, in this method, the pressure drop also increased and it was obtained as 175 Pa.
In order to evaluate whether the filter performance comes from electrostatic or mechanical filtration mechanisms, neutralization using isopropyl alcohol (IPA) was applied. Additionally, to observe stability of efficiency, stocking conditions measurements (day 1, day 3, day 7, day 17) were carried out. After the IPA treatment, the efficiency and pressure drop of the fibers without any loading process were recorded as 41% and 43 Pa, for the corona applied fibers as 45% and 45 Pa, and for the fibers obtained by electroblowing 85% and 160 Pa. In this case, it is observed that the solution blown mats have approximately 10% efficiency coming from electrostatic capture mechanism. Electro blown mats also showed 10% efficiency from electrostatic capture. On the other hand, the electrostatic capture mechanism in the corona charged mats had 20% efficiency. In periodic measurements, at the end of 17 days, the efficiency of nanofiber webs produced by solution blowing decreased by 2%, the efficiency of corona treated fibers by 8%, and the efficiency of nanofiber webs obtained by electroblowing decreased by 15%. The decreasing rate of filter efficiency in the electro blown mats is seen as higher compared to other samples.

Type: Master/ Innovative Technical Textiles
Thesis advisor:  Prof. Dr.Cevza Candan
Thesis co-supervisor: Dr. Öğ. Üyesi Nebahat ARAL YILMAZ (Yeditepe University)
Student's name/surname: Bilge Koyuncu
Supporting organization / Project information: İTÜ BAP,  Proje ID: 42927 

Summary

In many fields of work, including medical diagnosis and therapy, nuclear power plants and space exploration, ionizing radiation (e.g X-ray) is found. These radiation source create serious risks to human health, including mutagenic and carcinogenetic effects on bodily-organs. Therefore, it is important to limit the amount of radiation that proffesionals who operate in the radiation areas are exposed to.

Beer-Lambert equation states that the atomic number, density and thickness of X-ray absorbing materials strongly impact X-ray attenuation performance. Lead (Pb), bismuth (Bi), tungsten (W) and barium (Ba) are common examples of the types of high- atomic number metal compounds utilized to provide efficient shielding fillers in composites with types of polymers. But lead’s (Pb) toxicity and density means that it can not be used withouth precautions as a shielding material. High atomic number, lightweight and non-Pb radiation shielding apparel has become the focus on recent research.

Accordingly, this study was conducted in order to develop lightweight, environmentally friendly, textile-based materials which has effective radiation protection using conventional textile coating technology. For this purpose, in preliminary work a coating mixture was prepared utilizing micro copper particles and water-based polymers. In addition to these, micro and nano bismuth oxide powders were employed in preparation of a coating mixture with the help of water-based polymers for this purpose. For advanced characterizing of the coated textile surfaces developed, Fourier Transform Infrared-Attenuated Total Reflectance (FTIR) and Scanning Electron Microscopy (SEM), and Energy Dispersive Spectroscopy (EDS) techniques were used. The radiation attenuation performance of the samples was, on the other hand, measured in accordance to Narrow Beam geometry described in the standard TS EN 61331-1:2014 at Nuclear Energy Research Institute, Turkish Energy, Nuclear and Mineral Research Agency (TENMAK- NÜKEN).

The findings of the study have shown that it is possible to produce textile based shielding materials offering lead-equivalent protection without using any lead. Furthermore, it has been shown that the samples with nano powder doping had a greater radiation attenuation rate than those with the micro powder doping, while having almost identical volumetric ratios of powder and coating thicknesses. When comparing the samples with a volumetric ratio of 60%, the 3 plied composite textile based materials containing nano bismuth oxide powder with a thickness of 0.9225 mm provide 83% attenuation at 40 kV whereas the same material present 71.3 % protection at 60 kV. When it comes to the measurement results of the micro bismuth oxide powder with the same values however show 60.2% attenuation at 60 kV. In the study, it was demonstrated that nano-sized powders had a more uniform dispersion in the materials developed than the micro-sized powder particles. The results have also suggested that the layered textile based composite material may attain a sufficient level of lead equivalent. Also, it was found that the attenuation ratio of such materials decreases as the X-ray energy increases. Moreover, by increasing the thickness of the materials the X-ray shieldings levels can be increased by 95% and over.

In conclusion, it has been shown that lead-free, nature-friendly textile based materials which contain nano and micro powder for use in the field of medical industry can have sufficient lead equivalent protection against X-rays by using traditional textile production methods.