Optimization of flax–SAN composite manufacturing for enhanced mechanical and thermal performance

The processing–structure–property relationships of flax fiber (FF) and hybrid flax/glass fiber cut-off (FF/GF) composites based on a styrene–acrylonitrile (SAN) matrix were systematically investigated. A Taguchi experimental design combined with signal-to-noise ratio and ANOVA analyses was employed to optimize the compression molding parameters. Processing temperature was identified as the dominant factor governing the mechanical performance of the composites. The optimum processing condition (200 °C, 10 min, and 7 MPa) produced the best overall performance, achieving a flexural modulus of 10.7 GPa, a flexural strength of 139.8 MPa, and the highest interlaminar shear strength. X-ray microtomography and microscopy revealed that insufficient processing temperatures resulted in incomplete polymer impregnation, whereas excessive temperatures led to deterioration of the composite mechanical properties. The hybrid FF/GF laminate exhibited substantially higher Charpy impact resistance but lower stiffness than the all-flax composites. Dynamic mechanical analysis showed similar glass transition temperatures (≈128 °C) for all composites. These findings demonstrate that optimizing compression molding parameters significantly improves the performance of FF/SAN composites, highlighting their potential as sustainable materials for semi-structural applications.