Application of Fracture Toughness Understanding to Improve Papermaking Runnability

Abstract

Runnability of paper is important for increasing the productivity of papermaking, converting, and printing processes. Fracture mechanics theories have been applied to paper for reducing paper breaks and improving their runnability. Fracture toughness has a stronger effect on the paper break phenomenon than tensile strength. Paper breaks when a higher force is applied to paper during the papermaking process than the paper can hold. Efficient methods to improve the toughness of paper will be beneficial to reduce paper breaks. In this study, various factors such as fiber length, intrinsic fiber strength, coarseness, refining, addition ratio of Kraft pulp (KP) related to the fracture toughness of paper were reviewed. Further, the effects of the fiber properties, extent of refining, mixing ratio of KP, recycled fibers and fillers, and moisture content were analyzed. The following were beneficial for increasing the fracture toughness of paper: long fiber length, high intrinsic fiber strength, low fiber coarseness, high refining, high addition ratio of KP for the strengthening effect, low recycling pulp and filler addition ratio, and high moisture content of paper. The mixing ratio of KP had strong effects on improving the fracture toughness whereas the refining effects had weak effects on that. Regarding fiber shapes, straight fibers had a high critical fracture load, whereas curly fibers resulted in a high critical fracture elongation. In the future, detailed research on the fracture toughness of paper is needed, including the dynamic factors, for better understanding of paper breaks during papermaking processes.