Hydrogen bond forming polymers such as aliphatic polyamides and polyvinyl alcohol are important engineering plastics with good mechanical properties, high melting point and good chemical resistance. However, any further attempt at improving their mechanical properties gets thwarted due to the presence of intermolecular hydrogen bonding. Many approaches have been attempted in the past to suppress hydrogen bonding in aliphatic polyamides and have met with little or no success. These include, plasticizing the structure, dry spinning, wet spinning, gel spinning, and zone drawing/annealing. We have employed a new technique that involves the dry-jet wet spinning and drawing of GaCl3/nylon 66 complex. This new method allows traditional low draw ratios for nylon 66 to be increased by disrupting the interchain hydrogen bonded network. Fibers with a high modulus were obtained when high molecular weight nylon 66 was used. Further, we have also reviewed the concept of thermoreversible gelation and its application for gel spinning of ultra high molecular weight polyethylene fibers. We developed high strength and modulus nylon 6 and PVA fibers from the gels of these polymers in N-methyl pyrrolidinone. High molecular weight is essential for achieving more drawing of polymer chains which leads to high molecular orientation. Electrostatic spinning or electrospinning has received considerable research attention in recent years. It involves the application of an electric filed to a polymer solution or melt to facilitate production of fibers in the sub-micron down to nanometer range. We have investigated the complexation of GaCl3 with nylon 6 and developed porous nanofibers via the technique of electrospinning. Pores are generated by removal of salt from the as spun nanofibers via dipping in water. Researchers have tried in the past using a highly volatile solvent, or selective removal of one polymer from a bicomponent nanofiber for developing pores in nanofibers. However, using a metal salt proved to be a simple and fast approach for generating pores in electrospun nanofibers.

A numerical model has been developed that successfully predicts heat transfer through thermally protective clothing materials and garments exposed to intense heat. The model considers the effect of fire exposure to the thermophysical properties of materials as well as the air layers between the clothing material and skin surface. These experiments involved characterizing the flash fire surrounding the manikin by measuring the temperature of the flame above each thermal sensor in the manikin surface. An estimation method is used to calculate the heat transfer coefficient for each thermal sensor in a 4 second exposure to an average heat flux of 2.00cal/cm2sec. A parameter estimation method was used to estimate fabrics dynamic thermophysical properties. The skin-clothe air gap distribution of different garments was determined using three-dimensional body scanning technology. Multi-layer skin heat transfer and a burn prediction models are used to predict second and third degree burns. The integrated generalized model developed will validated using the "Pyroman" Thermal Protective Clothing Analysis System with Kevlar/PBI® and Nomex®?A coverall garments. A parametric study conducted using this numerical model indicated the influencing parameters on garment thermal protective performance in terms of burn damage subjected to 4 second flash fire exposure. The importance of these parameters is analyzed and distinguished. These parameters includes fabric thermophysical properties, Pyroman® chamber generated flash fire characterizes, garment shrinkage and fit factors, as well as garment initial and test ambient temperature. Different skin models are also investigated using this model.

Functional bone tissue engineering has been necessitated by the need to treat critical size defects in bones due to birth abnormalities, trauma, and pathological conditions. Appropriate conditions for in vitro osteogenesis need to be identified to establish protocols for engineering bone tissues. The success of in vitro osteogenesis lies on the type of cell source, stimuli, and scaffold material used for engineering bone constructs. Recent investigations have established the pluripotency of mesenchymal stem cells (MSCs) and their ability to differentiate down a multitude of pathways including osteogenenic. In vivo studies have shown that MSCs are primarily responsible for bone growth and regeneration and therefore have become a major candidate for bone tissue engineering. Osteogenic differentiation of MSCs via chemical stimuli has been extensively investigated using both monolayer and three-dimensional (3D) culture conditions. These investigations provided useful information on media conditions, cell seeding densities, and differentiation capabilities of MSCs. However, chemical stimulation alone might not be sufficient to accelerate osteogenesis and impart necessary mechanical strength to the final tissue construct. Mechanical strength of the final tissue construct is vital to maintain its structural integrity when exposed to physiological stresses in vivo. Stimulation of MSCs using mechanical strain might provide another method to induce MSC osteogenesis while also obtaining desired mechanical strength of the final tissue constructs. Although in vivo studies and experimental models have indicated that cyclic tensile strain could induce MSC osteogenesis, its effect on MSC osteogenesis in 3D cultures in vitro has not been investigated. The need to maintain cell viability and be able to provide chemical or mechanical cues to cells in 3D cultures requires improvements in scaffold architecture and design. While collagen provides a natural matrix for cell adhesion and growth, its contraction during culture can greatly limit culture duration and mechanical stability of the matrix. Although fibrous scaffolds can be used as an alternative to collagen scaffolds, insufficient media diffusion to the center of these 3D scaffolds could detrimentally affect uniform cell growth throughout the scaffold; hence, scaffolds with better diffusional properties need to be developed. This study investigated the use of 3D collagen matrices as a scaffold material to determine the effects of strain and chemical stimuli on osteogenic differentiation of human MSCs (hMSCs). Major attention was given to the analyses of: cell viability, matrix contraction, nuclei morphology, expression of osteogenic markers and proinflammatory cytokines, as well as changes in mechanical properties of the final tissue construct. As an approach to develop 3D fibrous scaffolds with enhanced diffusional properties, fabrication of melt spun microporous fibers using a blend of poly (lactic acid) (PLA) and sulfopolyester that could be used in 3D nonwoven scaffolds was also investigated. The findings of this study clearly illustrated the ability of cyclic tensile strain to induce osteogenic differentiation of hMSCs when cultured in a 3D environment. Expression of proinflammatory cytokines by strained hMSCs suggested that cyclic strain might have induced modulation of bone resorption in hMSCs. The results also illustrated the effects of strain on the mechanical properties of the final tissue construct. Microporous fibers created from melt spun composite fibers using binary blends of poly (lactic acid) and sulfopolyester could enhance diffusional properties of 3D nonwoven scaffolds fabricated using these fibers. As this body of work demonstrates, use of cyclic tensile strain combined with chemical stimulation to induce osteogenic differentiation of hMSCs could greatly assist the engineering of functional bone tissues in vitro. Microporous fibers created using polymer blends could provide an effective method to improve diffusional properties of 3D polymeric scaffolds.

Yarn tension control is an important parameter for quality and efficiency in textile processes. It has a significant influence on productivity in various processes such as winding, twisting and cabling. There have been several articles based on theoretical models, which discuss the effect of various factors on yarn tension variation in direct cabling, but very few have addressed the possibility of measuring and controlling it practically while the yarn is being twisted. Quality control system manufacturers like TEMCO (Textile Machinery Components) and BTSR (Best Technologies Studies and Research) have come up with smart tension scanning systems that perform online tension monitoring in various textile machines. However, these systems cannot be installed on the direct cabling machine due to their size and cost. The fact that the supply yarn package is housed inside the rotating yarn balloon restrains any wired tension sensor from performing online measurement. As such, there is an immediate need for using a wireless sensing device to perform online yarn tension measurement and execute a control mechanism that will control yarn tension adaptively. The objective of this research is to demonstrate the possibility of applying MEMS (MicroElectroMechanical Systems) technology with radio frequency (RF) transmission to effectively carry out dynamic online measurement for the control of yarn tension. A novel technique to achieve online control using the measured real-time data has been implemented. A device that ensures uniform tension in the yarn has been designed and developed. Ways of measuring twist in the cabled yarn using optical micrometers and digital imaging systems have also been explored, because variation in tension manifests variation in twist. Using the twist values obtained from these sensors, the individual tensions in the component yarns can be adjusted, resulting in the formation of a uniform cabled yarn with equal lengths of both component yarns.

The purpose of this research has been to develop a textile finish based on chitosan that is a biopolymer. A fiber-reactive chitosan derivative was synthesized from chitosan with a low molecular weight and a high degree of deacetylation. The synthesis was composed of two steps. As a first step, a water-soluble chitosan derivative was prepared by introducing quaternary ammonium salt groups on the amino groups of chitosan. The derivative was further modified by introducing functional groups (acrylamidomethyl) on the primary alcohol groups of the chitosan backbone, which can form covalent bonds with cotton. The fiber-reactive chitosan derivative (NMA-HTCC) itself showed complete bacterial reduction against Staphylococcus aureus and Escherichia coli at the concentration of 10 ppm. The NMA-HTCC was applied to cotton fabrics by a pad-batch method in the presence of an alkaline catalyst. The 1% NMA-HTCC treated cotton showed 100% bacterial reduction against S. aureus. The fabric maintained over 99% of bacterial reduction even after 50 home launderings. The NMA-HTCC cotton was dyed with direct and reactive dyes without addition of salt. The color yield was higher than that of untreated cotton, which required a large amount salt for dyeing. The NMA-HTCC cotton showed better washfastness than untreated cotton, but the lightfastness was inferior to that of untreated cotton. The antimicrobial activity of the NMA-HTCC cotton was considerablely decreased after dyeing due to the blocking of the cationic groups of the NMA-HTCC by dye molecules.

Poly(ethylene terephthalate) (PET), poly(trimethylene terephthalate) (PTT), poly(ethylene isophthalate) (PEI), and poly(trimethylene isophthalate) (PTI) were synthesized in a Parr reactor and melt-spun. Thermal and physical properties of the as-synthesized polymers and melt-spun fibers were determined. As-synthesized PEI and PTI were amorphous polymers and did not show any melting peaks by DSC analysis. All the polymers were thermally stable (TGA analysis). Amorphous films were made by a melt-press method with PET and PEI for determination of CO2 gas barrier properties. PEI, which has the meta-linkage of ester groups on the phenyl ring, had much lower CO2 gas permeability around one tenth that of PET, which has the para-linkage of ester groups on the phenyl ring. This is because in PET the phenyl rings are substituted in the para (1,4) positions, which allows for their facile flipping, effectively permitting gases to pass through. However, the meta-substituted phenyl rings in PEI do not permit such ring flipping, and thus PEI may be more suitable for barrier applications. The coalesced PEI was prepared from the inclusion compound of PEI with ?×-cyclodextrin. The coalesced PEI may have retained partially highly extended and parallel chains from the narrow channels of the inclusion compound, resulting in better/tighter packing among the PEI chains and exhibited a higher glass-transition temperature. Cyclic oligoesters of PET, PTT, PEI, and PTI were prepared by cyclo-depolymerization of these polyesters. The cyclic oligoesters were mixtures of different sized cyclic oligomers. PET cyclic oligomers showed four melting peaks at 59, 122, 194, and 276 o C. The cyclic oligomers of PTT, PEI, and PTI showed single melting peaks at 241, 335o C and 147o C, respectively. The cyclic oligoesters could be converted to linear polyesters by ring-opening polymerization. PTT was also prepared by ring-opening polymerization of its cyclic dimer obtained as a by-product in the conventional manufacturing plant. Antimony, tin, and titanium catalysts were used with various concentrations. The highest molecular weight, 40,000 g/mol was obtained when 0.25 mol% of titanium(IV) butoxide was used.

<p>HUANG, WENSHENG. Online Characterization of Fabric Compressional Behavior. (Under the direction of Tushar K. Ghosh and Winser E. Alexander)Response of a fabric to applied forces normal to its plane is known as fabric compressional behavior. It is one of the important properties that determine fabric performance in many applications. The principle of a system used to measure fabric compressional characteristics, online, is proposed in this paper. A controllable nip formed by a pair of rollers is employed to apply compressional deformation to a moving fabric while the compression force and displacement are continuously recorded. The influence of various system parameters on the sensitivity of the system has been analyzed. By assuming a stepwise anisotropic behavior in the thickness direction, Incremental Differential Algorithm (IDA) is developed to calculate the pressure-displacement relationship from the measured force-displacement data obtained from the online system. A prototype online measurement system has been developed based on this principle. A number of woven and nonwoven fabrics have been evaluated using the online system as well as a number of other commercially available fabric compression testers. The compressional characteristics obtained from the online measurement system compare well with the same parameters measured using the other commercially available compressional testers.<P>

<p>IKIZ, YUKSEL. Fiber Length Measurement by Image Processing. (Under the direction of Dr. Jon P. Rust.) This research studied the accuracy and feasibility of cotton fiber length measurement by image processing as an alternative to existing systems. Current systems have some weaknesses especially in Short Fiber Content (SFC) determination, which is becoming an important length parameter in industry. Seventy-two treatments of five factors were analyzed for length and time measurements by our own computer program. The factors are: Sample preparation (without fiber crossover and with fiber crossover), lighting (backlighting and frontlighting), resolution (37-micron, 57-micron, 106-micron, and 185-micron), preprocessing (4-neighborhood and 8-neighborhood), and processing (outlining, thinning, and adding broken skeletons). The best results in terms of accuracy, precision and analysis time for images without fiber crossovers were: 106-micron resolution with frontlighting using an 8-neighborhood thresholding algorithm and using an outline algorithm for length determination. With fiber crossovers, 57-micron resolution with backlighting using an 8-neighborhood thresholding algorithm and using a thinning algorithm combined with an adding algorithm for combining broken skeletons. Using the above conditions, 1775 area can be analyzed using our current equipment in 15 seconds. In the case of images with crossovers, only 117 can be analyzed in 15 seconds. This research demonstrates that successful sample preparation without fiber crossovers would create the best fiber length measurement technique, however with fiber crossovers the system efficiency has been proven as well.<P>

<p>Bauer-Kurz, Ina. Fiber Crimp and Crimp Stability in Nonwoven Fabric Processes. (Under the direction of Dr. William Oxenham and Dr. Donald A. Shiffler.)In nonwovens, crimp characteristics of synthetic fibers are, along with finish, major contributors to processing efficiency, web cohesion, fabric bulk and bulk stability. However, the meaning of measurable crimp parameters and their influence on processing and fabric characteristics has not been quantified. The purpose of this study is to quantify the mechanical fiber behavior during crimp removal, and relate it to fundamental fiber properties, nonwoven fabric properties, and processibility in nonwoven equipment.Single fiber tensile tests in the crimp removal region have been performed on various fibers with the Textechno FAVIMAT and have also been monitored optically. Based on empirical evidence, a basic understanding of the physical crimp removal mechanism is obtained. A methodology is developed, to identify the true crimp removal region of the whole single fiber load-extension curve during a tensile test. A mechanical model accounting for the nonlinear load-deflection behavior during crimp removal is developed. According to this model, a logarithmic function can be used to describe the material behavior in the crimp node during crimp removal. This function is fit to experimental data and delivers two fitting parameters that characterize the shape of the experimental load-extension curve in the crimp region.The extracted characteristic crimp parameters are being evaluated in terms of fiber material characteristics, such as fiber type, crimp processing settings and carding performance during nonwoven production. A dependence of the shape of the crimp removal curve on crimping settings during crimp production is established. The characteristic crimp parameters are also correlated to the sequence of processing stages during nonwoven production and cylinder speed during carding.<P>

Thesis (M. Phil.)--University of Hong Kong, 2005. / Title proper from title frame. Also available in printed format.