Effect of Polylactic Acid Fiber on the Properties of Thermoplastic Starch Plastics

Considering the environmental pollution and the lack of oil resources, degradable polymers have been widely concerned by researchers in recent years. As one of the research focuses, the strengthening of mechanical properties and water resistance of thermoplastic starch (TPS) have been studied. In order to enhance the mechanical and water resistance properties of TPS, the polylactic acid fiber (PLAF) reinforced TPS plastics (PLAF/TPS) were prepared by extrusion and injection molding. The effects of mass fraction of PLAF (0.5%~2.5%) on mechanical, section morphology, water resistance, thermal stability and torque rheological properties of PLAF/TPS were studied in detail. Results show that PLAF with the appropriate mass fraction can be dispersed uniformly in the TPS matrix and form hydrogen bonds with starch molecules, which can significantly enhance the mechanical and water resistance properties of TPS. Compared with 1.98 MPa and 33.45 kJ/m² of the unreinforced TPS, the maximum values of tensile strength and impact strength of 1.0% PLAF/TPs can reach 6.79 MPa and 43.71 kJ/m² respectively, which due to the uniformly dispersed PLA fibers in the TPS matrix and the interaction between PLA fibers and starch macromolecules. In the meantime, the elongation at break decreases due to the increasing brittleness of the PLAF/TPS, and the surface contact angle is enhanced from 46.3° to 88.5°, proving that the water resistance is improved effectively because the hydrophobic PLA fibers disperse uniformly in TPS matrix. The thermal stability of PLAF/TPS is also improved slightly due to small amount of the PLA fibers dispersing in TPS. The processing performance of PLAF/TPS composite is poor with the increasing PLAFs, which is due to the entanglement of PLA fibers and the interaction between PLA fibers and starch macromolecules. The 1.0%PLAF/TPS is easier to be processed compared with other PLAF/TPS composites with higher PLAF content.