Mechano-Sorptive Creep : Structural Originon the Single Fiber Level

Abstract: The consuming of paper and fibrous products is nowadays tremendous in our dailylife. The raw material used in the paper industry is mainly wood fibers. A betterunderstanding of properties of these fibers will help to improve the performance ofthe paper industry. Fiber deforms with time when subjected to a load, which has to be compensated for in packaging materials by the use of thicker papers thus morematerial. This deformation increases in the variable climate. This well-known complex phenomenon is called mechano-sorptive creep and leads to large losses in the paper industry every year. In order to understand the influence on the creep phenomenon of different fibermorphology, and how and to what extent the fibril angle affects the mechano-sorptive creep, the creep behavior of four series of fibers from spruce were measured by DMA(Dynamic Mechanical Analyzer) at a constant humidity climate followed by animmediately cyclic humidity. The fibers used were mature latewood fibers, matureearlywood fibers, juvenile latewood fibers and juvenile earlywood fibers. The CLSM(Confocal Laser Scanning Microscopy) was used to determine the microfibril angle ofthe fibers. The results of the tests show a higher creep rate at cyclic humidity than thatat constant humidity. The comparisons among fibers show that latewood fibers havehigher mechano-sorptive creep ratio (creep rate at cyclic humidity/ creep rate atconstant humidity) than earlywood fibers and that juvenile wood fibers have highercreep ratio than mature wood fibers. One of the main conclusions drawn in this study was that the higher the fibril angle, the lower was the mechano-sorptive creep ratio.