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Nowadays, recycled paper is broadly used due to environmental reasons. Furthermore, the addition of starch as a dry strength additive improves the properties of recycled paper. Poly-Lactic Acid (PLA), a product from bio-refinery 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. The results indicate that handsheets 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.

Increasing the filler content in paper to reduce the cost of materials is an ongoing effort among papermakers. Selecting the proper calcium carbonate additive for each type of paper is the key to achieving this goal. Calcium carbonate is the most widely used filler material in the paper industry. On average, it is applied at levels of 18% to 30%. Quality requirements of each type of paper vary widely, according to use; understanding the effect that different types of calcium carbonate have on paper properties allows producers to choose the best filler for each use. Given that the market for uncoated digital printing paper is expected to grow, this study focused on selecting the optimal calcium carbonate for the production of uncoated digital printing paper made from 100% eucalyptus pulp. In this study, 13 varieties of calcium carbonates were used to prepare handsheets for the detailed analyses of structural, optical, and strength properties. The samples included nine varieties of precipitated calcium carbonate (PCC) (two rhombic and seven scalenohedral, covering a particle size range from 1.2 μm to 2.9 μm) and four varieties of ground calcium carbonate (GCC) (three anionic and one cationic, with a particle size range of 0.7 μm to 1.5 μm). From the results of this study, we determined that the optimal calcium carbonate for uncoated digital printing paper made from eucalyptus pulp is scalenohedral PCC with a particle size of 1.9 μm, because of its positive effects on caliper, stiffness, brightness, and opacity.

Anaerobic digestion can be used to degrade food waste and recover energy. Methane is a biogas that can be efficiently converted in electricity. Organic loading rate, temperature, time, pH, carbon to nitrogen ratio are important factors to be operated in the bioreactors and still are challenges in this process to increase biogas production. It has been reviewed the single phase and two-stage bioreactors in the anaerobic digestion of food waste as well organic loading rates and the rate of methane produced.