Optimization of response surface methodology and performance of oxidized wheat straw/polylactic acid composites

To solve the problem of poor interfacial compatibility of wheat straw fiber/poly(lactic acid) (WF/PLA) composites, WF was treated with H₂O₂ as oxidant, and the effects of pH, treatment temperature, and mass ratio of H₂O₂ on the mechanical properties of oxidized wheat straw fiber (OWF)/PLA composites were investigated by response surface method. The results show that there is a significant interaction between pH and treatment temperature, pH and mass ratio, and treatment temperature and mass ratio. The optimal process parameters predicted by the regression equation are as follows: The pH of H₂O₂ is 8.9, the treatment temperature of H₂O₂ is 52.3℃, and the mass ratio of H₂O₂ is 2%. Under these conditions, the tensile strength and elongation at break of the composite material are 38.89 MPa and 7.85% respectively, which are 15.64% and 15.20% higher than before modification. FTIR results indicate that some hydroxyl groups in OWF are oxidized to carboxyl groups by H₂O₂. SEM results indicate that OWF can better bind with PLA, and the composite materials prepared after melt blending have better interfacial compatibility. In addition, XRD and DSC results indicate that the addition of H₂O₂ promotes the heterogeneous nucleation process of the polymer, resulting in an increase in its crystallinity.