Abstract:

Objective Polylactic acid (PLA) is an environmentally friendly polymer material, but it has problems such as high brittleness and poor toughness, which to some extent limit its application. Therefore, toughening modification of PLA is of great significance for improving its mechanical properties and expanding its applications in fields such as packaging and biomedicine.

Method PLA/PCL and PLA/PCL/ADR composite fibers were prepared via melt spinning and hot drawing processes, using poly(lactic acid) (PLA) as the matrix, poly(ε-caprolactone) (PCL) as the toughening agent, and a multifunctional epoxy oligomer (ADR) as the compatibilizer. The cross-sectional morphology, crystallization behavior, and thermal properties of the blends were characterized. The study focused on the influence of adding PCL at mass concentrations of 10%, 15%, 20%, 25%, and 30% on the toughening of PLA; and on adding ADR at mass concentrations of 0.25%, 0.5%, 0.75%, 1%, 2%, and 5% on the compatibilization between PLA and PCL and its influence on the mechanical properties of the fibers.

Results As the PCL content increases, the PLA/PCL system gradually shows obvious phase separation. Since the decomposition temperature at the maximam mass loss rate (T_max) of PCL (401.02 ℃) is higher than that of PLA (363.79 ℃), the addition of low content PCL to some extent worked to improve the thermal stability of the blend, but when the PCL content exceeded 20%, the decomposition temperature began to decrease. when the PCL content was 30%, T_maxdropped to 357.57 ℃, which is related to the intensification of phase separation and the increase of interface defects. A small amount of PCL would cause a heterogeneous nucleation effect. When the PCL content was 10%, the crystallinity of PLA increased from 30.39% to 31.72%, but as the PCL content further increased, the crystallinity of PLA decreased due to poor compatibility and the interference of flexible chain segments. When the PCL content was 20% and the draw ratio was 3, the elongation at break of the blended fibers was increased by 36.73% compared to the pure PLA, but the break strength decreased by 24.46%. After introducing ADR to 0.75% for reactive reinforcement, the compatibility of the system was significantly improved, T_max increases to 367. 83 ℃, and the break strength and elongation at break of the blended fibers were increased by 5.98% and 72.92%, respectively, compared to pure PLA.

Conclusion Introducing PCL into the PLA system can effectively improve the toughness of the fibers. When the PCL content is 20% and the draw ratio is 3, the elongation at break of the blended fibers is approximately 36.73% higher than that of pure PLA, but the breaking strength decreases by about 24.46%. This indicates that there are still certain compatibility issues between PLA and PCL. After introducing ADR as a reactive compatibilizer, the interfacial compatibility of the system is significantly improved. When the ADR content is 0.75%, the PLA/PCL20/ADR0.75 blended fibers exhibit superior comprehensive performance, with their breaking strength and elongation at break increasing by 5.98% and 72.92%, respectively, compared to pure PLA. At the same time, the thermal stability of the blended system is enhanced, with the T_max reaching 367. 83 ℃, which is approximately 4 ℃ higher than that of pure PLA. The results indicate that by reasonably regulating the PCL content and introducing an appropriate amount of ADR for reactive reinforcement, the toughness of PLA can be improved while maintaining its degradability.

Key words: polylactic acid fiber, polycaprolactone, multifunctional epoxy chain extender, melt spinning, toughening modification, interfacial compatibility, mechanical property