Improvement in the Performance of the Polylactic Acid Composites by Using Deep Eutectic Solvent Treated Pulp Fiber

As the most favorable alternative to petroleum-based polymers, polylactic acid (PLA) which is the most promising degradable polymer has attracted increasing attention. However, the addition of cellulose to improve its strength often results in a reduction in its toughness. In this work, microscale cellulose is first prepared from pulp fibers by using a deep eutectic solvent, and then is used as the reinforcement of PLA. A microcrystalline cellulose (MCC)/PLA sheet with uniform texture is obtained by the solution mixing, melt blending, hot-pressing and cold-pressing process. The effects of MCC on the crystallization, thermal stability and mechanical properties of the PLA matrix were studied. Upon the addition of 1% cellulose fiber, the tensile strength of MCC/PLA composite sheet increased by 27%, and the elongation at break did not shown an evident decrease. The strength enhancement mechanism was elucidated using scanning electron microscopy, differential scanning calorimetry, and dynamic thermomechanical analysis. The energy dissipation during the deformation process and the compatibility of AMCC and rougher surface of MCC play important role in the strength enhancement. Additionally, UV spectroscopy showed that the composite material absorbed some ultraviolet light. Our results show that the combined use of a deep eutectic solvent and solution mixing is an effective approach for improving the strength of PLA while maintaining its toughness.