Drainability, permeability and formation of RCF pulps blended with sugar beet pulps

摘要

Influence of retention systems and shear forces on drainage time and air permeability of handsheets prepared from a furnish of recovered fibres containing 10% enzymatically modified sugar beet pulp has been investigated. Addition of cationic coagulant neutralised the anionic soluble and colloidal particles present in suspensions and increased the effect of retention aids. Aluminium sulphate was more effective in the elimination of the negative effect of enzymatically modified sugar beet pulp and shortened the drainage time more then PDADMAC. The cationic coagulant aluminium sulphate, in a retention system with a cationic and anionic poly-acrylamide flocculant, shortened drainage time of recovered fibres and enzymatically modified sugar beet pulp mixture by a factor of 3.3, increased air permeability by 88% and, in comparison with PDADMAC, improved the formation of handsheets. The retention system containing aluminium sulphate, cationic and anionic poly-acrylamide flocculant was most effective with regard to drainage time and air permeability if shear forces were acting. The retention system containing an inorganic anionic flocculant based on modified ben-tonite or colloidal silica was equally effective, but the effect was reduced by shear forces. Best formation of handsheets was achieved by the application of a retention system consisting of aluminium sulphate, cationic polyacrylamide and anionic colloidal silica. These results should provide good initial guidance whenever the addition of a pulp with high anionic charge and high level of fines is being considered.