Fabrication and characterization of new eco-friendly composites obtained by the complete recycling of exhausted coffee capsules

Spent coffee grounds (SGC) have been separated from exhausted coffee capsules, mainly made in polypropylene (PP), and subsequently melt mixed in different percentages (10 and 20%wt.) with the same empty grinded capsules to obtain new composites formed by different parts of the same waste. The obtained composites have been compared with pristine neat PP and recycled neat PP in terms of thermal, rheological and thermomechanical properties to evaluate the effect of the SGC filler and to determine the degradative contributes. 3-aminopropyltriethoxy-silane (SIL) and maleic anhydride grafted PP (PPgMA), have been also tested at 2%wt. as coupling agents and experimental data have been fitted with micromechanical models to better understand the behaviour of these new composites. Results have shown the SGC ability to improve the thermo-mechanical properties such as tensile (from +4% to +24%) and storage moduli (from +20% to +50%) and creep resistance (from +3% to +14%) and recovery (from +4% to +7%) of the recycled capsules in a way almost proportional to the SGC loading. In parallel, the use of 20%wt. of SGC particles has counterbalanced and restored the loss of processability due to the degradation of the recycled capsules as testified by the MFR values (around 11 g/10'), which have been similar to those of pristine neat PP (9 g/10'). The proposed method offers a cost-advantage route of recycling able to fabricate new eco-friendly particle-filled polymers completely formed by exhausted coffee capsules.