Improvement of Physical and Mechanical Properties of Testliner Coated by Unmodified and Modified Lignins

The production of a coating agent based on the extracted lignin from black liquor of bagasse soda pulping was investigated. The crude lignin was modified via sulfomethylation method to increase its solubility. Both unmodified and sulfomethylated lignins were applied on the testliner papers with and without starch and physical, surface and mechanical properties of the coated testliners were evaluated. The viscosity of coated solution containing 100 percent of crude lignin was very low and similar as that of water. Addition of starch to coating solution resulted in increasing of the viscosity of formulation. Evaluation of hydrophobicity of coated testliners showed that compared to papers treated with unmodified lignin and starch, the papers treated with sulfomethylated lignin had significantly lower water absorption, wetting rate, absorption rate of water droplet, which resulted in hydrophobicity of papers. Colorimetric analyses showed a decrease in lightness (L*) of the coated testliners with only unmodified lignin compared with untreated control ones. In contrast, the lightness of testliners coated with sulfomethylated lignin was significantly improved and was almost as high as control samples and samples, which coated by the starch solution without lignins. Air permeability of the coated testliners with only lignin was significantly lower than that of lignin-starch coated samples. The results also showed that the tensile indices of samples coated with unmodified and modified lignins were significantly higher than that of control ones. The tensile index of testliners coated with starch-lignins solutions was almost near to that of samples treated with only starch solution.