Synergistic Effects of Surface-Modified Glass Fiber on Polylactic Acid Matrix Composites Reinforcement and Toughening

To address the challenges of high brittleness and poor crystallization capability in polylactic acid (PLA), glass fiber (GF), and polycaprolactone (PCL) were selected as reinforcing and toughening agents, respectively, for property modification. In the resulting composites, an interfacial layer forms between the polymer matrix and GF, significantly influencing the interfacial adhesion quality and the overall mechanical properties of the material. To enhance interfacial compatibility, oleic acid (OA) was introduced as a coating via the hydrophilic  Si  O  Si  bonds on the GF surface. Combined with treatment using a silane coupling agent (KH550), this process resulted in dual-surface modification of glass fiber (OKGF). PLA/PCL/GF (or OKGF) composites with mass fractions of 5%, 10%, 15%, and 20% OKGF were fabricated using solution dissolution and melt blending techniques. Scanning electron microscopy analysis revealed excellent interfacial adhesion between OKGF and the polymer matrix. The composite with 15% OKGF content exhibited optimal mechanical properties, achieving maximum tensile strength (65.5 MPa) and modulus (1113.0 MPa), representing a significant enhancement. Moreover, OKGF served as an effective heterogeneous nucleating agent, resulting in a crystallinity of 19.1% at 15% OKGF content—an 88% increase compared with the PLA/PCL blend (10.2%).