Nazire Deniz Yilmaz

Multi-fiber needle-punched nonwoven composites: Effects of heat treatment on sound absorption performance

Nonwovens have been increasingly used in car interiors for noise reduction. Most of these nonwovens are subjected to thermal treatments to give the nonwovens their final three-dimensional forms. Therefore, it became crucial to investigate the effects of thermal treatment on sound absorption characteristics of nonwovens. In this study, the effects of the material and treatment parameters on airflow resistivity and normal-incidence sound absorption coefficient of thermally treated three-layered nonwoven composites have been studied. The material parameters included fiber size and porosity. The treatment factors included the temperature and duration. The thermally treated three-layered nonwoven composites are classified into three types based on the material content and fiber blend. Sandwich structures consisting of polylactide/hemp/polylactide and polypropylene/glassfiber/polypropylene layers were called LHL and PGP, respectively. The sample which consisted of three layers of an intimate blend of polypropylene-glassfiber was named as PGI. Both temperature and duration of thermal treatment have been found to affect air flow resistivity and sound absorption. An increase in air flow resistivity and a decrease in sound absorption have been detected with heat treatment. A similarity has been observed between the thermal behaviors of PGP and PGI, which included the same thermoplastic polymer fiber. Variation in air flow resistivity of sandwich structure nonwoven composites increased with the increase in temperature, which was not observed in the intimate blend ones. The air flow resistivity of heat-treated nonwovens followed a steeper trend compared to unheated nonwovens per change in material parameters. In terms of treatment parameters, the difference between the thermal treatment and the melting point of the thermoplastics constituent of the nonwoven composite was found to be a significant factor on sound absorption. This effect of treatment temperature on sound absorption changed with treatment duration. The sound absorptive characteristic of the nonwoven composites in terms of sound frequency underwent a change with thermal treatment due to the structural changes with exposure to high temperature.

Hemp-fiber based nonwoven composites: Effects of alkalization on sound absorption performance

The effects of the material and treatment parameters on airflow resistivity and normal-incidence sound absorption coefficient of alkalized three layered nonwoven composites have been studied. The material parameters included fiber size and porosity. The treatment factors included the temperature, duration and concentration. The alkalized composite was a three-layered nonwoven sandwich structure consisting layers of Polypropylene/Hemp/Polypropylene. Alkalization treatment has been found to result in a loss of basis weight and a decrease in air flow resistivity. Among treatment factors, only temperature was found to be a statistically-significant factor on air flow resistivity. Higher-temperature alkalization leads to higher air flow resistivity compared to the lower-temperature treatment. Alkalization at higher temperature and higher concentrations gives better results in normalized sound absorption performance compared to lower-temperature and lower-concentration treatments, respectively.

Effects of enzymatic treatments on the mechanical properties of corn husk fibers

Corn husk fibers were extracted by water retting, alkalization, and enzymatic processes at different concentration and duration levels. The effects of extraction process parameters on the mechanical and thermal properties and chemical characteristics of corn husk fibers were investigated. Chemical structures of the fibers were studied by IR measurements. The finest and the stiffest fibers were produced by water retting followed by an enzymatic treatment. The highest breaking strength and breaking tenacity were obtained by water-retted fibers. While resulting in loss of breaking tenacity and elongation in water-retted fibers, enzymatic treatment resulted in increase in initial moduli and breaking tenacity of alkalized fibers. No significant effect of enzymatic treatment duration was obtained on the mechanical properties of corn husk fibers. Alkalized fibers gave higher elongation and lower stiffness compared to water-retted ones. The IR spectra showed higher amount of lignin and hemicellulose in water-retted fibers compared to alkalized and enzyme-treated ones. Enzymatic treatment and alkalization enhanced the thermal durability of the fibers. The ranges for properties of the produced corn husk fibers can be summarized as a linear density 17.0–25.6 tex, initial modulus 150.9–401.8 cN/tex, breaking tenacity 6.8–21.7 cN/tex, and elongation 9.6–18.2%.

Design of Acoustic Textiles: Environmental Challenges and Opportunities for Future Direction

Textiles have begun to find use in acoustical applications for the past few decades. In order to consolidate the position of textiles as noise control materials, their performance characteristics should be further enhanced to a level comparable to conventional acoustic materials, the most common ones of which are glass fibre mats and polyurethane foams. The same recent history has also witnessed substantial growth in public concern related to environmental effects of industrial progress. As much as this situation imposes a burden on textile producers, it also opens a new battlefield against acoustic materials, where textiles can prevail. Conventional acoustic materials, mineral wool or polyurethane foam among others are under line of fire due to their adverse effects on the ecosystem as well as on human health. This situation can offer business advantage to textile producers, provided that the damage inflicted on the environment throughout the whole life cycle of the textile product is minimized and the functional properties are improved. This can be realized by implementing a sound design stage based on functional and environmental requirements related to acoustic textiles.

Physical and Chemical Properties of Water-Retted Fibers Extracted from Different Locations in Corn Husks

ABSTRACT Corn is the most commonly produced crop in the world producing immense agricultural residues, including corn husks. In search for handling corn husks as a fiber source, the quality of fibers extracted from different parts of corn husks by water retting is investigated. The effects of the location of the leaves in the husks and the part of the leaves where the fibers were extracted from on the mechanical, physical, and chemical characteristics of the fibers have been investigated. The coarseness of extracted fibers decreases from outer to the inner leaves in the husk and from the lower to the upper parts of the leaves. Breaking tenacity, breaking force, and elongation at break values of the fibers increase from the upper to the lower parts of the husk leaves. The fibers from the lower parts of the leaves showed greater hemicellulose, pectin, moisture content, and water absorption capacity compared to fibers obtained from the upper part of the corn husk leaves. With superior mechanical properties and lower moisture content and water absorption fibers from the lower parts of corn husk leaves may be considered advantageous for technical use such as in fiberboards. The fibers from the upper portion that are finer and can hold more moisture are more advantageous in terms of comfort aspects. The mechanical properties of the obtained water-retted fibers have been found to be superior to the corn husk fibers of prior studies produced by alkalization.

Comparative Advantage of Textiles and Clothing: Evidence for Top Exporters in Eastern Europe

The comparative advantage and intra-industry trade of five countries: Czech Republic, Hungary, Poland, Romania and Turkey, are analyzed in the global textile and clothing markets by employing Balassa’s revealed comparative advantage (RCA) index and intraindustry trade (IIT) index for the period 2002-2013. The results have revealed that while Turkey is the only one among the countries selected to have comparative advantage in the global textile market, Romania joins Turkey in this in the world’s clothing market. The comparative advantage of these two countries in the global clothing market presents a stronger declining trend compared to that in textiles, which is probably due to the entrance of cheap-labour eastern Asian countries into the global clothing market, as this market is more labor-intensive compared to textiles. Moreover, while a high intra-industry trade index is found in Czech Republic, Hungary and Poland, an inter-industry trade structure is observed in Romania for textiles and clothing. Turkey presents intra-industry specialisation in textiles, while possessing inter-industry trade structure in terms of clothing.

Multicomponent, Semi-interpenetrating-Polymer-Network and Interpenetrating-Polymer-Network Hydrogels: Smart Materials for Biomedical Applications

Multicomponent, semi-IPN, or IPN hydrogels are interesting materials which are composed of at least two different components and are able to respond to various stimuli, that is the change in certain properties of the medium such as temperature, pH, ion concentration, and so on. Based on this unique feature, these environmentally responsive materials may find use in biomedical applications in terms of changes in the properties of the medium in the human organism which occur naturally or induced by an outside source. Environmentally responsive hydrogels respond to changes in the physical, chemical, or biological properties of the medium by exhibiting a change in their size, shape, color, solubility, and so on. They can be fabricated from natural or synthetic components by a number of production methods including physical cross-linking and chemical cross-linking techniques as well as other novel fabrication methods such as cross-linking with genetically engineered protein domains. Environmentally responsive hydrogels have found in various subfields of the biomedical research area including drug delivery, biosensors, tissue engineering, actuators, and so on. Whereas hydrogels are promising materials, there are some drawbacks which should be overcome before these materials can be used clinically. To address the major concerns, the response rates should be increased while maintaining the necessary mechanical performance. Biodegradability and biocompatibility are other development fields. Environmentally responsive hydrogels with the desired properties can be prepared by use of the right components, production methods and forming the right polymer architecture.

Okra Fibers: Potential Material for Green Biocomposites

Okra bahmia (Abelmoschus esculentus) plant is considered as one of the abundant sources of natural fibers. Huge amount of okra plant stem is discarded on the field annually after collecting vegetable, without proper utilization. However, this biomass from the okra plant is a renewable, biodegradable, cost efficient and low-density source for production of bast fibers, and other industrial cost-efficient eco-friendly materials. The research on okra bast fiber has started in 2007. After that, the fiber extraction process, composition of fiber, morphology and performance properties of fiber, fiber modification techniques, and some important applications of the fiber etc. have been established. It was found that the okra bast fiber contains high cellulose content, excellent mechanical strength and stiffness, and good thermal resistance which are comparable to some traditional bast fibers like jute, hemp and ramie. Some okra bast fiber reinforced biocomposites were successfully fabricated with different matrices including biodegradable corn starch, Poly(lactic acid), P(vinyl alcohol), urea formaldehyde resin etc. via application of various processing methods. These studies revealed that the okra bast fiber biocomposites exhibited better mechanical properties, water resistance and thermal properties at optimized processing conditions. Therefore, by suitably optimizing the fiber, matrix, processing conditions, the future expectations of the okra bast fibers can be dramatically enhanced and its usage in composite field can be widened.