Mechanical and Biodegradable Properties of Flax/ PLA Core‐Sheath Composite Yarns Manufactured by Braiding and Post‐Thermal Processing

ABSTRACT

During the manufacturing of thermoplastic composites, the thermoplastic resin is difficult to penetrate into the reinforcement structure due to its high viscosity, leading to complexity and inefficiency in the process. To address this issue, polylactic acid (PLA) filaments (300D) were braided onto flax yarn (200 tex) using a braiding machine, and flax/PLA core‐sheath composite yarns were obtained after post‐thermal processing. To investigate the effect of the PLA sheath layer, three spindle counts (4, 8, and 12) were adopted. The results show that, among all the braided yarns, the tensile strength of the 8‐spindle specimen (BY 8) was the lowest (88.49 MPa). However, after thermal curing, the 8‐spindle composite specimen (CY 8) exhibited the highest tensile strength (131.02 MPa) among all specimens, representing the greatest enhancement (48.06%) compared with BY 8. SEM analysis confirmed that thermal consolidation effectively eliminated voids in the flax yarn, forming a compact flax/resin structure. Furthermore, the 45‐day soil composting test demonstrated the material's excellent environmental adaptability; the composite yarns exhibited a cumulative weight loss of 33.3%, with the degradation mechanism transitioning from surface erosion to deep matrix fragmentation and fiber splintering. This work provides a controllable fabrication strategy for green composites, balancing structural integrity with predictable biodegradability for advanced textile applications.