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Abstract
This article experimentally investigates various physical properties of Kevlar and Nomex plied yarns. The tensile properties of a yarn decide the performance of post spinning operations - warping, weaving and knitting - hence its accurate technical evaluation carries much importance in industrial applications. For this purpose, Nm 50 Kevlar and Nomex yarns were twisted in various combinations with a DirecTwist machine. Multi-yarn twisting and cross-yarn covering methods were used to produce plied yarns. Surface roughness (both pin friction coefficient and yarn-to-yarn friction coefficient), lint generation, hairiness, breaking force and breaking elongation properties of the yarns were tested. Furthermore, the effect of twisting technique, twist amount and yarn type on these physical properties of yarns were statistically investigated.
Keywords
Kevlar, Nomex, plied yarns, surface roughness, breaking force, lint generation
Many flame-resistant clothing systems and ballistic protection clothes need to be made from Nomex and/or Kevlar fabrics to meet the protection requirements.1 Kevlar and Nomex are registered trademarks of DuPont for a group of synthetic organic fibers in the aromatic polyamide family.2,3 Kevlar fibers have many desired engineering properties, such as high modulus, high strength, light weight, good chemical resistance and thermal stability. Thus, Kevlar fibers are widely used as the functional material in flexible body armors.3 Nomex brand fiber, a member of the aramid family of fibers, offers excellent flame resistance, good textile properties, dimensional stability and resistance to degradation by a wide range of chemicals and industrial solvents. Nomex has a flexible polymer chain that gives it more textile-like qualities, while retaining hightemperature properties similar to Kevlar.4
Depending on the application, the choice between Kevlar and Nomex is one of comfort and protection requirements. Kevlar is much more abrasive resistant then Nomex and is therefore used in a higher concentration percentage in professional fire-fighters' turnout gear. Nomex is a softer feeling fiber and is used to a higher degree in daily use garments because of its greater comfort provided to the wearer. Kevlar is, however, added to Nomex to provide a higher degree of strength to the apparel.5 Kevlar is also added to the Nomex to help establish a stronger break open point for the garments.
Aramid and other high-strength fibers and fabrics have been studied extensively due to their application in a...