ABSTRACT
VIII. Preliminary Constitutive Models 219
IX. Methods to Inhibit Moisture-Accelerated Creep 222
X. Conclusion
References
I. INTRODUCTION
The mechanical response of paper in a variable relative humidity climate is quite different from that in constant relative humidity. Because water facilitates the bond ing of the hydrophilic pulp fibers to form paper, moisture has a strong influence on the mechanical properties of paper. The mechanical response of paper is determined by the interaction of the external forces on the paper structure with the ambient relative humidity as well as temperature. A mechanosorptive effect is one arising from the interaction of loads with moisture sorption mechanisms. Moisture-acceler ated creep occurs in the special case in which the load on the specimen is held constant while the ambient relative humidity is varied. Variations in the ambient conditions, such as relative humidity and temperature, magnify the mechanical creep strain response in paper compared to that measured at any constant ambient con dition and can cause earlier failure. This behavior is observed under both tensile and compressive loads. Therefore, worst-case testing of paper products at high constant relative humidity is not a sufficient design strategy. This mechanosorptive problem has been studied by experimentalists, but there is as yet no universally accepted explanation of the physical mechanisms underlying such behavior.
