Effects of softwood kraft pulp refining on fracture behaviour of TMP-based paper

摘要

The objective of the study was to optimise the refining of softwood reinforcement pulp in TMP-based paper. One of the problems was to select the critical runnability-related strength properties of wood-containing printing paper. The study was concentrated on analysing in-plane fracture energy and fracture toughness. Microscopic fracture behaviour was also analysed in order to determine the effect of kraft pulp refining on sheet structure. Kraft pulp proportions of 30-50%, corresponding to the typical range of LWC base paper, were used. The results indicate that the fracture toughness of TMP-kraft pulp mixtures is not linearly dependent on component toughness values. The fracture toughness and fracture energy of paper containing TMP and kraft pulp can be even higher than that of either of the components. The fracture toughness of TMP-based paper initially increases with kraft pulp refining, but levels of rather quickly. The fracture energy of a TMP-kraft mix did not increase as a result of kraft pulp refining. Refining could not fully compensate for the loss of bonding caused by filler addition or TMP fines removal. Kraft pulp refining appearently cannot increase the energy consumption related to interfibre bond openings in mixture sheets to any major extent.