The aims of this series of studies were to improve the characteristics of polylactic acid (PLA) composites, including toughness modification and photo-degradability suppression. For toughness modification, polybutylene succinate (PBS) was used to modify the toughness of PLA material, and for photo-degradability suppression, ultraviolet (UV) absorbers and hindered amine light stabilizers (HALS) were used to restrain the photo-degradability of PLA material. The composite granules were produced by twin-screw extrusion followed by film extrusion, and the Taguchi method and principal component analysis are used to optimize processing parameters for toughening modification analysis. Through differential scanning calorimetry testing and melt flow index analysis it was determined that this combination of PLA-based composite material had good compatibility, processing flowability and weather resistance. Compared with pure PLA, it was found that the bending strength was decreased by 27.49%, the tensile strength was increased by 13.47% and impact strength was increased by 22.95%, when the processing parameter of the PBS blending ratio was 10 wt% and the mixing of UV absorbers and HALS blending ratio was 0.5 wt%. The screw speed of the twin-screw mixer extruder was 200 rpm, and the die head temperature was 220℃. After 480 hours of UV accelerated aging testing, the retention rate of tensile strength was 94.86%, which is higher than that of pure PLA by 44%. The retention rate of breaking elongation was 85.17%, which was higher than that of pure PLA by 35.17%.

Two biodegradable polymers (polylactic acid (PLA) and polybutylene succinate (PBS)) were mixed with ultraviolet absorbers and hindered amine light stabilizers to improve the durability of this composite fiber outdoors. Filament was obtained from this composite material under the optimum conditions by using melt spinning to investigate the effects of spinning temperature, spinneret rotation speed and take-up roller speed in the fiber spinning process on the quality characteristics of newly spun threads. The response surface method was used to build a regression model for different quality characteristics. Moreover, multi-objective particle swarm optimization was applied to optimize the model of these quality characteristics and parameter limits. According to experimental validation, the composite material of PLA/PBS was better than the composite material of PLA/polycaprolactone. The denier of the composite fiber obtained under the optimized conditions was 40.07 d, with an increase of 5.3% compared to the denier before optimization. The fiber strength after optimization was 1.69 (g/d), with an increase of 42%. The breaking elongation was 176.04% and increased 27% after optimization. The prediction error rate of an optimum regression model showed that the model has good reproducibility.