Influence of residual lignin content on physical and mechanical properties of kraft pulp/pp composites

The effect of residual lignin content on the mechanical strength and water absorption of kraft pulp/polypropylene composites was studied. To meet this objective, hornbeam wood chips were converted to kraft pulp at three different alkalinities (15, 20, and 25%) and three different cooking times (60, 90, and 120 min). The residual lignin contents of these pulps were determined according to the TAPPI standard. Kraft pulp was mixed with polypropylene (PP) at 50% weight ratios. The amount of maleic anhydride (MAPP) coupling agent was fixed at 4 per hundred compounds (phc) for all formulations. The results indicated that the lignin residual content decreased with increasing cooking time and alkalinity in kraft pulp. Also, it was found that tensile strength, tensile modulus, flexural strength, and flexural modulus were increased by increasing the alkalinity and cooking time; however, the notched impact strength and water absorption decreased. Overall, decreasing the lignin content had a positive impact on the flexural and tensile properties and had a negative effect on the notched impact strengt