Utilisation of spent coffee grounds in biocomposite cup production: Influence of filler source and biopolymer type
Abstract
In this study, two types of spent coffee grounds (SCG, Machine and Turkish) were tested in the production of SCG-biopolymer composite cups. The objective was to develop a simple and sustainable preparation approach for SCG-based biocomposites, ensuring sufficient mechanical and thermal stability for practical applications. Biocomposite cups, containing 55 to 72% of SCG were produced using sodium alginate as the primary polymer binder. To enhance mechanical performance, a secondary binder (additional polymer), either cellulose ether (carboxymethyl cellulose (CMC) or hydroxypropyl cellulose (HPC)) or natural polysaccharides (dextran or pectin), was incorporated. Comprehensive characterisation was performed using fluorescence and FTIR spectroscopy, tensile testing, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Fluorescence spectroscopy/microscopy revealed a higher content of naturally fluorescent organic compounds in Machine SCG compared to Turkish SCG. FTIR spectroscopy confirmed the successful SCG incorporation into the biopolymer matrix. Tensile testing showed that Machine SCG-based biocomposites were slightly more flexible than those prepared with Turkish SCG. Glass transition temperature (Tg) of SCG biocomposites depends on their composition and varied from around 75 to 100°C. The TGA results demonstrated that SCG exhibit a greater thermal stability than both SCG–alginate biocomposites and SCG biocomposites containing additional polymers.
