Refining pulp for tensile strength

Abstract

Abstract Increased tensile strength of paper is a primary objective of low consistency refining. Although refining is typically controlled by Specific Refining Energy and Specific Edge Load, these parameters are not independent because both depend directly on power. To overcome this shortcoming, we derived simplified expressions for the number and intensity of impacts on pulp. The number of impacts reflects the capacity of the refiner to impose loading cycles on pulp. The intensity, combined with a response parameter, reflects the probability of a successful refining event at each impact. Based on these parameters, we employed an equation based on cumulative probability to predict tensile strength of pulp after refining. Non-linear fits of this equation to data from the literature for a wide range of pulps refined by various refiners gave response parameters that were remarkably similar ranging from 1.6 – 3.3 × 10 − 6 1.6\text{--}3.3\times {10^{-6}}  kg/J. The resulting probability of successful refining events at each impact was found to be quite small, about 1–3 %. We postulated that this is likely due to most force being imposed at fibre crossings in the pulp network. Consequently, multiple cycles are required to expose other parts of fibres and new fibres to loadings. In summary, this new approach to characterizing refining reflects the stochastic nature of the process and enables a direct quantitative link between refiner operation and fibre development.