Surface sizing of testliner paper with aminated soda lignin and evaluation of the surface, barrier and mechanical properties of produced papers

The use of starch in the future will face limitations due to food competition in the paper industry. Therefore, in this research, soda lignin was chemically modified using the amination method to extend its reactivity and improve water solubility. Sizing solutions were prepared using both unmodified and aminated lignin, as well as a combination of starch and lignin in a 25:75 ratio. The surface, barrier, and mechanical properties of the sized testliner papers were measured using the aforementioned sizing solutions. SEM images show that both unmodified and aminated lignin almost completely fill the voids and spaces between the fibers, creating a relatively uniform and homogenous sizing layer on the paper surface. The roughness values increased for the sized papers using both unmodified and aminated lignin. Applying a sizing layer with unmodified lignin reduced the air resistance of the paper, while papers treated with aminated lignin showed a slight increase in air resistance, though not as high as those sized with pure starch. Contact angle evaluation confirmed the positive effect of chemical modification through amination on the hydrophobicity rate of the paper. Surface sizing with aminated soda lignin, even without starch combination, resulted in increased stiffness, burst index, and Ring Crush Test (RCT) compared to the control papers.