Value-added use of spent coffee ground for low-cost poly(3-hydroxybutyrate-co-3-hydroxyvalerate) biocomposite development

Manufacturing PHBV biocomposites with spent coffee ground (SCG) is an eco-friendly approach of repurposing waste materials to improve sustainability. Although, as shown previously, pretreatments of SCG can improve its interaction with PHBV to obtain enhanced properties, the chemical or biological treatment could be time-consuming, costly, and environmentally harmful. Therefore, this study developed a method of manufacturing PHBV/SCG biocomposites via a simple and industrially viable reactive extrusion method requiring no SCG pretreatment. The present work aims at investigating the impact of untreated SCG combined with different processing additives (peroxide, coagent, and chain extender) on the morphological, thermal, mechanical, and water absorption properties of PHBV-based biocomposites. Overall, the introduction of the untreated SCG (10–30 wt.%, without processing additives) decreased the crystallinity (by 3.8%–6.8%), degradation temperature (T_peak, by 6.2%–8.2%) and tensile strain (by 33%–43%) of PHBV. SCG addition had no significant effect on PHBV tensile strength or Young's modulus. However, the presence of processing additives decreased the melting temperature (by up to 4.5°C), crystallinity (by up to 8.4%) and Young's modulus (by up to 17%) and increased the degradation temperature (T_peak, by up to 12.5°C) of the PHBV/SCG biocomposites (10% wt.% SCG). Lastly, SCG addition improved water absorption ability of PHBV by up to 250%, while the addition of peroxide further improved the water absorption ability by approximate 320%. The PHBV/SCG developed in this study have good renewability and biodegradability, improved water absorption property, reduced cost and acceptable mechanical properties. They are promising in applications where biodegradability is favorable and high mechanical performance is not required such as plant pots and containers.