Influence of Hygrothermal Aging on Mechanical Properties of Short Flax/Basalt Fiber Hybrid Composites

ABSTRACT With the advantages of excellent lightweight effect, environment‐friendliness, and heat insulation properties, plant fiber‐reinforced polylactic acid composites show promising application in automotive and other industrial applications. However, severe performance degradation under hygrothermal conditions is the main limitation of plant fiber‐reinforced green composites. Hybrid high‐performance synthetic fibers provide a promising approach to this problem. This study assesses the durability of injection‐molded short flax/basalt fiber hybrid composites with varying fiber contents under hygrothermal aging. The hygroscopic behavior of the composites was investigated by soaking specimens in distilled water at 25°C and 40°C, and the wettability of the fiber and composites to water was analyzed through the contact angle test. Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) were used to examine the influence of hybrid basalt fiber on the aging properties of the composites. Mechanical properties were measured by quasi‐static tensile and three‐point bending tests, and failure mechanisms were revealed by scanning electron microscopy (SEM). Long‐term mechanical performance was predicted with machine learning. Results showed that the moisture absorption rate increased as the temperature increased, and the increment followed Fickian and Dual–Fickian laws at 25°C and 40°C, respectively. The moisture absorption rate was reduced, and the mechanical properties were enhanced by basalt fiber incorporation. Optimal performance was achieved at 30% flax and 7% basalt fiber contents. Excessive basalt fiber caused agglomeration and property deterioration. The support vector regression (SVR) model demonstrated good correlation and accuracy in this experiment.