Effect of different chemical surface treatments on interfacial compatibility and properties of polyhydroxyalkanoates/coffee grounds composites

The aim of this study was to improve the interfacial compatibility of polyhydroxyalkanoates (PHA) with coffee grounds (CGs) in order to enhance the properties of the composites. Three different methods including alkali, silane, and alkali/silane treatments were used for the surface modification of CGs to construct compatible interfaces and were compared to obtain the most effective modification method. The results showed that the alkali treatment increased the tensile strength, flexural strength, and elongation at break of the composites by 12.61%, 9.81%, and 3.81%, respectively. The silane coupling agent treatment increased the tensile strength, flexural strength, and elongation at break of the composites by 15.51%, 17.78%, and 14.00%, respectively. The mechanical properties of the composites were further improved by the alkali/silane treatment. The three surface treatments improved the compatibility of CGs with the PHA matrix to different degrees, with the alkali/silane treatment being more effective than treatment with alkali or silane coupling agent alone. In addition, the different surface treatments also improved the thermal properties and water resistance of the composites to different degrees. Mechanisms have been proposed to interpret the observed changes in mechanical and thermal properties as a result of fiber treatments by performing SEM, XRD, and FTIR tests on CGs. It is expected that alkali/silane treatment surface modification methods have broad application prospects in the preparation of modified CGs reinforced polymer composites.