Purpose -A series of all-atom molecular-level computational analyses is carried out in order to investigate mechanical transverse (and longitudinal) elastic stiffness and strength of p-phenylene terephthalamide (PPTA) fibrils/fibers and the effect various microstructural/topological defects have on this behavior. The paper aims to discuss these issues. Design/methodology/approach -To construct various defects within the molecular-level model, the relevant open-literature experimental and computational results were utilized, while the concentration of defects was set to the values generally encountered under "prototypical" polymer synthesis and fiber fabrication conditions. Findings -The results obtained revealed: a stochastic character of the PPTA fibril/fiber strength properties; a high level of sensitivity of the PPTA fibril/fiber mechanical properties to the presence, number density, clustering and potency of defects; and a reasonably good agreement between the predicted and the measured mechanical properties. Originality/value -When quantifying the effect of crystallographic/morphological defects on the mechanical transverse behavior of PPTA fibrils, the stochastic nature of the size/potency of these defects was taken into account.
Severe tensile strength loss is the major disadvantage of durable press finished cotton fabrics. Such strength losses have been attributed to two main factors: acid-catalyzed depolymerization and crosslinking of cellulose molecules. In this research, we inves tigate the effects of acid degradation and cellulose crosslinking on the tensile strength of cotton fabric crosslinked by polycarboxylic acids. Multifunctional carboxylic acids such as butanetetracarboxylic acid (BTCA) are used as nonformaldehyde crosslinking agents for cotton fabrics. The strength loss caused by acid degradation is an irreversible process, and the magnitude of the loss is determined by the curing temperature and time, the dissociation constants of the acid, and the concentration and pH of the acid solution applied to the fabric. Crosslinking of cellulose molecules by a polycarboxylic acid causes a reversible fabric strength loss, which increases as the degree of crosslink ing increases. The magnitude of tensile strength loss caused by acid degradation and that by crosslinking for cotton fabrics treated with BTCA is measured. Losses caused by crosslinking can be restored after the ester crosslinking is hydrolyzed under alkaline conditions.
Durable press finishing processes are commonly used in the textile industry to produce wrinkle-free cotton fabrics by crosslinking cotton cellulose. The most common crosslink ing agents are formaldehyde-based N-methylol reagents, such as dimethyloldihydroxyl ethyleneurea (DMDHEU). In recent years, multifunctional carboxylic acids have been employed as nonformaldehyde durable press finishing agents. In this research, we use a multiple angle laser light scattering photometer to measure the change in cellulose molecular weight as a result of cotton cellulose depolymerization caused by a polycar boxylic acid, a Lewis acid used as a catalyst for DMDHEU, or their combination. Cellulose depolymerization takes place on the fabric treated with a polycarboxylic acid or a Lewis acid. The combination of Lewis and polycarboxylic acids as an "activated" catalyst for DMDHEU causes more severe cellulose depolymerization. Our results indicate a direct correlation between tensile strength loss of the treated cotton and the molecular weight of cellulose.
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