Enhanced characterization of wheat straw-PLA composites with silane coupling agent and alkali pretreatment

Polylactic acid (PLA) composites with high straw content face several challenges, primarily due to the inherent brittleness of straw and its poor compatibility with the polymer matrix. In this study, scanning electron microscopy (SEM) was used to analyze the microscopic structure of wheat straw chemically modified by NaOH and the silane coupling agent, and it was concluded that both treatments effectively removed waxes and silica from the surface of the straw, enhanced fiber roughness, and improved interfacial adhesion. Notably, the silane coupling agent treatment not only facilitated the formation of chemical bonds between the straw fibers and the PLA matrix but also filled the interfiber pores, significantly increasing the structural density. Furthermore, the mechanical properties of composites synthesized by hot pressing 60 % pretreated straw, 33 % PLA and 7 % compatibilizer were evaluated, and the results demonstrated that the silane coupling agent-modified composites exhibited superior mechanical properties, with tensile, flexural and impact strengths of 15.07 MPa, 30.83 MPa and 9.95 kJ/m², respectively-approximately 1.2 times higher than those of the NaOH-treated composites. These findings highlight the significant improvement in the mechanical performance of PLA composites through the use of silane coupling agents.