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

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