FATIGUE BEHAVIOR OF ARAMID NONWOVEN FABRICS UNDER HOT-PRESS CONDITIONS - PART V - EFFECT OF PUNCHING DENSITY ON MECHANICAL-PROPERTIES

Changes in the mechanical properties and durability of a nonwoven fabr ic with repeated hot-press fatiguing treatment depend on the propertie s of the fiber material and the structure of the nonwoven. Following P art IV, which deals with fiber fineness, in this paper we focus on pun ching density, which greatly affects the nonwoven structure, and we di scuss the influence of punching density on the mechanical properties o f nonwoven fabrics after hot-press fatiguing cycles. We hypothesize th at a nonwoven with greater punching density will have a larger number of fibers reaching perpendicularly across its width. This will increas e fiber entanglement because more fibers will be caught by the needle. In Part IV, we found that a nonwoven fabric with more entangled fiber s has a higher tensile breaking strength, so it is natural to believe that a nonwoven with a higher punching density has a higher tensile st rength than one with a low punching density. The experimental results show, however, that a nonwoven with too much punching density has a lo wer tensile strength due to fiber breakage by too much needle punching . Thus, there is an optimum punching density that gives the highest te nsile strength. Regarding compressive behavior, a nonwoven fabric with higher punching density has a small compressive strain and high compr essive modulus, meaning it is stiffer. We have found that changes in t ensile and compressive behaviors with hot-press fatiguing closely rela te to nonwoven fiber packing factors.