Renewable resource-based green composites of surface-treated spent coffee grounds and polylactide: Characterisation and biodegradability

The morphology, mechanical properties, and biodegradability of composite materials containing polylactide (PLA) and spent coffee grounds (SCG) were evaluated. Maleic-anhydride-grafted polylactide (PLA-g-MA) and treated, i.e. cross-linked, spent coffee grounds (TSCG) were used to enhance the desired characteristics of these composites. PLA-g-MA/TSCG materials exhibited desirable mechanical properties relative to those of PLA/SCG. This effect was attributed to greater compatibility between the grafted polymer and TSCG. The dispersion of TSCG in the PLA-g-MA matrix was highly homogeneous due to ester formation and resulted in branched and cross-linked macromolecules. Additionally, the PLA-g-MA/TSCG composites exhibited lower melt viscosities and were therefore more easily processed. The water resistance of the PLA-g-MA/TSCG composite was greater than that of PLA/SCG and the mass losses following burial in soil compost indicated that both materials were biodegradable, especially at high levels of SCG substitution. The PLA/SCG and PLA-g-MA/TSCG composites were more biodegradable than neat PLA.