Gajanan S. Bhat

Meltblown nanofiber media for enhanced quality factor

Nanofibers definitely hold great advantage and promise in filtration as they have very high specific surface area, which ensures greater probability of capturing the particles and hence, the filtration efficiency of the nanofiber filter media is high. Electrospun nanofibers are prohibitively expensive due to extremely low production rate. With recent advances in melt blowing technology, nanofibers could be produced at production rate few orders of magnitude higher than that of conventional single syringe electrospinning and hence, quite cost effective. Influence of air pressure and die to collector distance (DCD) were studied on the number average fiber diameter for the nanofibers as well as the performance properties of the nonwoven webs, each factor at three discrete levels. The nanofibers were as fine as 260 nm. A very encouraging observation of the study is very high values of quality factor observed for nanofiber nonwoven filter media. In order to compare the filtration efficiency of different nanofiber nonwoven media samples with different basis weight, a novel term of specific filtration efficiency is proposed and was found that the specific filtration efficiency with the increase in DCD or air pressure.

New aspects in the stabilization of acrylic fibers for carbon fibers

Abstract The kinetic and morphological influences of nitrogen, air and ammonia in the environment for stabilization of PAN-based precursors for carbon fibers have been investigated. A careful thermal analysis conducted earlier by Peebles et al., had identified ammonia to be a possible accelerator of the concerned reactions. The present study shows clearly that ammonia does increase the rate of stabilization, but the presence of oxygen with ammonia is essential to reach rapidly the “stabilized state,” suitable for carbonization. The preliminary results from X-ray scattering and elemental analyses also suggest that the influence of ammonia is not just to accelerate the stabilization reactions, but also to cause the reaction paths to be different.

Nonwovens as Three-Dimensional Textiles for Composites

Abstract Three-dimensional textiles are those materials which have a system or systems in all the three axes of plane. These offer particular properties, such as interlaminar shearing force, and mechanical and thermal stability along all three axes of space, which are not achievable with other reinforcements. The demand for these types of fabrics is expected to increase, especially in the areas of high performance composites in automobile industry, housing, construction and reinforcement materials. Reduction in manufacturing and raw materials costs has to be brought about in order to make the advanced composites competitive in the current market and acceptable in the future new markets. Nonwovens, which are a major constituent of this class of textiles are becoming important because of their ease of manufacture and low production cost. This is a comprehensive review of different methods of manufacturing 3-D textiles with an emphasis on nonwovens.

Thermal properties of elastic fibers

Abstract Spandex has now become a standard fiber in lingerie, hosiery, leisurewear, and sportswear. New applications, from men’s suits to children’s wear, diapers to footwear, continue to be developed. Manufacturers have refined their technology, making possible the explosion of new applications. In this study, some commercially available spandex filaments were evaluated for their mechanical and thermal properties. The differences in performance of soft, medium and high modulus spandex fibers are elaborated.

Biodegradable and Tensile Properties of Cotton/Cellulose Acetate Nonwovens

A possible candidate as an environmentally friendly nonwoven fabric is one that can be formed from the thermal calendering of a cotton/cellulose acetate blend. Our results focus on biodegradable properties of the fibers as well as tensile properties of the fabric. Cotton, which is a comfortable, absorbent, biodegradable fiber, is the base fiber in the nonwovens. Cellulose acetate, which is a thermoplastic, hydrophilic, mod ified cellulosic fiber, is used for the binder fiber. We examine the biodegradability of cellulose acetate, cotton, and these fibers in the blend using an ASTM standard pro cedure in which the amount of CO 2 evolved from the decomposition of cellulose acetate and cotton fibers due to microbial activity is monitored. Increased biodegra dation rates in fiber blends are attributed to the synergistic effects of multi-enzyme systems. Opening, blending, carding, and thermal calendering processes are used to fabricate the nonwovens. Pretreatment with solvent vapors is introduced to modify the softening temperatures of the cellulose acetate and to lower the calendering tem peratures. The success of this procedure is demonstrated in enhanced tensile strength of the nonwoven. In addition, modifying tensile properties with solvent vapor pre treatment shows how enhanced strength can be obtained with lower calendering tem peratures.

Processing and Characterization of Flame Retardant Cotton Blend Nonwovens for Soft Furnishings to Meet Federal Flammability Standards

Effective from July 1, 2007 it is mandatory that all mattress sets meet the federal flammability standard CFR 1633. It is necessary to impart flame resistance that would provide at least 30 min for occupants to escape fire. Changes in the flammability laws are expected on other soft furnishings of sleep products like comforters and pillows. Generally these products are often the first to be engulfed by the fire. Currently many inherently flame retardant (FR) fibers and chemicals are available in the market. We have developed barrier fabrics with FR properties by incorporating these fibers in blends with cotton that either meet or exceed the standard. Results from this ongoing research are discussed in this article.

Structure and properties of polypropylene fibers during thermal bonding

The role of fiber morphology in a thermal point-bonding operation was investigated. Polypropylene fibers were spun to produce fibers with a wide range of structure, keeping the diameter same. The fibers were characterized for their structure and properties before and after bonding by differential scanning calorimeter (DSC), thermo-mechanical analysis (TMA), birefringence measurement and tensile testing. The results show that the fiber samples with different morphology vary in their bonding behavior, which in turn determine the fabric properties. Significant changes were observed in fiber structure during thermal bonding. The extent of change taking place during the process was dependent on the initial morphology of the fibers.

Evolution of Structure and Properties in a Spunbonding Process

The inherent properties of filaments are of utmost importance in spunbonded webs. A good understanding of structure and property development in individual filaments is helpful in better comprehending the whole process. A polypropylene homopolymer and a copolymer (PP/PE) are processed on the Reicofil® spunbonding line at the Textiles and Nonwovens Development Center of the University of Tennessee. The properties of the filament samples taken before thermal bonding are determined through a variety of experimental techniques, such as differential scanning calorimetry. thermomechan ical analysis, scanning electron microscopy, density, x-ray diffraction, and mechanical properties. The performance properties of the bonded nonwoven fabrics from the same set of filaments are evaluated and the structure and properties of the fibers are compared with those of the bonded fabrics. Primary air temperature and throughput have a strong influence on the structure and properties of both filaments (before bonding) and non wovens (after bonding). As primary air temperature and throughput decrease, filament diameter tends to decrease, accompanied by a simultaneous increase in crystallinity. birefringence, tensile strength, initial modulus, thermal stability. and density.

Thermal properties of a polyimide fiber

A commercially available polyimide fiber was investigated as a possible precursor for the formation of carbon fibers. The thermal response of the fiber was thoroughly investigated using DSC, TMA and TG. These responses were dependent on the atmosphere and tension during scanning. The fiber was stabilized at high temperatures both in inert and oxidative environments and the effect of these stabilization treatments on the structure and properties of the fiber was carefully followed. During heating, the fiber showed shrinkage tendency at small tensions, but at higher tensions the fibers could be stretched. Among the two environments investigated, air was more effective than nitrogen in getting a more stable fiber.

Structure and properties of polypropylene filaments in a spunbonding process

Polypropylene homopolymer (PP) and a copolymer (P/E) were processed using the Reicofil® spunbonding line at the Textiles and Nonwovens Development Center of the University of Tennessee, Knoxville. The properties of the filament samples taken before thermal-bonding were determined through a variety of techniques such as differential scanning calorimetry, thermomechanical analysis, thermal deformation analysis and mechanical properties. The two process variables investigated, primary air temperature and throughput had a strong influence on the structure and properties of both the filaments and the bonded nonwovens. As the primary air temperature and throughput decreased, there was a tendency for decrease in filament diameter with a simultaneous increase in their crystallinity, birefringence and thermal stability. The copolymer filaments showed lower crystallinity and orientation for all the corresponding processing conditions.