Effect of spent coffee grounds modified with cellulose nanofiber on polylactic acid matrix bio-composites for sustainable SM.E.X.MEX producing

Abstract

Purpose – The purpose of this study is to develop spent coffee grounds (SCG)-enhanced poly(lactic acid) (PLA) matrix biocomposites for improving the interfacial bonding between the enhancement and the matrix to increase their mechanical properties. The aim is to develop a sustainable material composition that can be used in the material extrusion-based additive manufacturing (MEX) method and has higher mechanical properties than neatPLA. Design/methodology/approach – Surface modification of SCG with cellulose nanofiber (CNF) was applied to improve the interface between the matrix and enhancement and to increase the mechanical properties. CNF-modified SCG (mSCG) and SCG enhancement PLA biocomposites were compounded in a twin-screw extruder. SCG (PLASCG5) and mSCG (PLAmSCG5) were added into the PLA matrix at 5 wt% to be produced in the MEX method. Mechanical test specimens were produced using the MEX method with biocomposites. Tensile, charpy and impact tests were performed to determine and compare the mechanical properties; thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis were performed for thermal properties and SEM images were examined. Findings – The elongation at break (%) value of PLASCG5 and PLAmSCG5 specimens increased an average of sixfold compared to neatPLA. In Impact strength values, a 5% increase was observed in PLASCG5 specimens and a 19% increase in PLAmSCG5 specimens compared to neatPLA. SCG and mSCG reinforcements did not affect the thermal stability of PLA matrix biocomposites. Originality/value – The findings obtained in this study show that the surface modification of SCGs with CNF positively contributes to their mechanical properties and that waste SCF can be used as an upcycle. The SCG enhancements and CNF interfacial modification are the unique aspects of the research.