| Nowadays, recycled paper is broadly used due to the low cost and environmental impact. Furthermore, the addition of starch as a dry strength additive improves the properties of recycled paper. However, the use of starch leads to microbiological growth and doesn't improve wet strength and water resistance of paper. Poly-lactic Acid (PLA), a product from biorefinery process, has recently been shown to act as a promising strength additive that could be used in combination with starch to further improve the strength of paper.;In this study, the use of PLA of three molecular weights (MW) in combination with four different starches was investigated. Three recycled pulps from different origins, with the kappa number of 27.9 to 66 were used. Paper handsheets were made, and selected paper properties were tested in accordance with TAPPI standards. The results indicate that handsheet properties were influenced by the MW of PLAs, the type of starch used, and the lignin content of the pulp.;The paper handsheets made from lignin-rich pulp (pulp A, kappa number 66), combined with 0.1% medium MW PLA (PLA_1) and 0.9 % cationic starch containing 0.43 % N gave the highest improvement for tensile strength, wet tensile strength, air and water resistance. This result verifies that a higher kappa number pulp has better attraction to the hydrophobic PLA. Moreover, the higher charge cationic starch led to higher tensile strength due to the increase of affinity to the anionic fiber surface.;Interestingly, results show that amphoteric starch is a promising substitute for high cationic charge starch when combined with the medium MW PLA to improve tensile strength of paper.;This study demonstrated that a starch-PLA blend represents a promising approach in improving properties of recycled paper. Future studies should be performed to adjust the ratio of starch-PLA in accordance with the lignin content of recycled pulp to produce the most beneficial effect. |
