Performance of chitosan and polyamide epichlorohydrin (PAE) on wet strength and water absorption of deinked pulp

Increasing the application of tissue papers and its competitive market, particularly in respect to the water absorbency and wet strength, is important and utilization of necessary chemicals especially bio-based ones, for required specification is extensive. Therefore, the aim of this is to focuses on the bio-based chemical and its efficiency. Effects of the chitosan biopolymer compared to the common synthetic polyamide epichlorohydrin (PAE)on the wet and dry strengths, whiteness, brightness and water absorbency of handsheets prepared from deinked pulp of mixed office waste paper were carried out at 0.5, 0.75 and 1% addition levels of the wet strengths agents. SEM images proved the sedimentation of additives and higher advent of chitosan fibers than PAE. Higher dry tensile, burst and wet tensile strengths, lower rate and content of water absorption of treatment with chitosan were determined mainly caused due to creation of cross links among the paper ingredients during the drying. Due to the high similarity between the cellulose and chitosan and also plenty of amine and hydroxyl functional groups of the chitosan, the bonding increased while water uptake sites decreased. Extensive bonding resulted in lower flexibility and higher bending stiffness, which was higher in PAE than chitosan treatments at 0.5%. In spite of declining trend, variations in whiteness (111%) and brightness (86%) of chitosan reinforced handsheets were insignificant. Generally, 0.5% of the chitosan compared to 1% of PAE, provided higher strengths values and minimum reduction in water absorption (~10%) and optical properties while higher flexibility donated to the paper. Also an improvement in the wet strengths of the fibrous network could be resulted in better machine runnability.