Influence of humidity cycling parameters on the moisture-accelerated creep of polymeric fibers

Accelerated creep is a curious and poorly understood transient moisture effect. The creep rates of most hydrophilic materials increase greatly with moisture content. However, when these same materials are subjected to creep loads in cyclic humidity environments, they often exhibit much higher creep rates than in a constantly humid state. This is called accelerated creep. Previous experimenters reported that accelerated creep was less likely to occur in polymeric fibers. We demonstrate experimentally that this happened only because of their choice of humidity cycling parameters. New results are given for Kevlar, lyocell, nylon-6,6, and ramie fibers. Other paper scientists have argued that the absence of accelerated creep in single fibers supports a explanation based on fiber network effects for accelerated creep in paper. We argue here that accelerated creep is a more general phenomenon consistent with sorption-induced stress-gradient explanations. (C) 2001 John Wiley & Sons, Inc.