Affecting the bonding between PLA fibrils and kraft pulp for improving paper dry-strength

Polylactic acid fibrils (PLAf) were employed as a fiber component in papermaking. The addition of 5 wt % of PLAf to bleached kraft birch pulp increased the tensile index of the resulting 100 g/m(2) paper sheets by 20 % in comparison to sheets produced without PLAf. By heat-treating the paper sheets containing 5 wt % PLAf, a 35 % higher tensile index in comparison to sheets produced without PLAf was achieved. SEM imaging showed that the heat-treatment caused the PLAf to melt, which formed a film on the fiber web. The PLAf was ultrasonicated in an attempt to make its surface more hydrophilic and anionic and thus more compatible with cellulose. Chemical additives (cationic polyacrylamide, polyethylene imine and polyethylene glycol) were added to the PLAf/cellulose pulp mixture in order to increase the binding between the ultrasonicated PLAf and cellulose. Ultrasonication caused the PLAf length to decrease and the PLAf surface charge changed by 36 %, indicating that the PLAf became significantly more anionic. Neither ultrasonication of PLAf nor the chemical additives improved the paper sheets' stretchability. Polyethyleneimine as an additive in an amount of 1 % increased the tensile index of heat-treated sheets made with 5 wt % of PLAf by 19 %.