Studies on the Mechanical Properties of the Fiber Oriented Sheet

Abstract

A special handsheet-making apparatus, in which the velocity component of the pulp suspension is parallel to the forming wire, was constructed. The tensile properties of the fiber oriented handsheets were compared with those of the TAPPI standard handsheets. Holocellulose and sulfate pulp of softwood were also used for making handsheets. The fiber angle distribution φ (θ) was expressed in Fourier series : φ (θ) =1+α1cos 2θ+α2 cos 4θ+α3 cos 6θ+…The coefficientsα1 andα2 were used for the characteristic values of the fiber orientation. It was found that the fiber orientation of the sheet prepared from holocellulose was higher than that of sulfate pulp.Astress-strain curve at a constant rate of elongation was normalized in such a way that the stress at 1mm elongation (2% strain) was one unit. Such a normalized curve was called a master curve. The master curves of the sheets prepared from the same pulp are almost the same irrespective of the degree of fiber orientation. The master curves in the machine and cross directions are also the same one.Namely, it may be possible to express the stress-strain curve by the shape of master curve, the stress at the constant strain and the ultimate strain. The value of f/w is the stress (at 2% strain) divided by the weight of test strip. The value of (f/w) r is the ratio of f/w of machine direction to that of cross direction, and it represents the degree of anisotropy of the sheet. The (f/w) r of the sheet treated with resins (melamine resine and polyvinyl acetate resin) is lower than that of the untreated sheet. The ultimate strain has no relation to the fiber orientation.