Influence of Strain Rate and Temperature on the Radial Compression Behavior of Wet Spruce

Abstract

In the mechanical pulping process, wood is treated in compression and in shear at high temperatures in the wet state, to separate the fibers and also to increase the bonding ability and flexibility of the fibers in order to obtain strong paper sheets. This is probably enhanced by permanent deformation and collapse of the fibers. In this study, the influences of moisture content, density, strain rate and temperature on the mechanical response of spruce compressed radially to 50 percent strain were investigated. Regression models were obtained for the plateau stress (≈collapse stress), energy absorption, plastic strain and reduction of plateau stress after the first compression. Temperature and strain rate had a great influence on the mechanical behavior of spruce. It was found that lumen (= cell void) water had a significant effect on the deformation process at high strain rates. The reduction in plateau stress after one compression was about 30–55 percent, which might increase the collapsibility of the wood fibers.