The present work puts the Circular Bioeconomy’s concept into action, originally valorizing residues of spent coffee grains from the beverage liquor coffee industry to develop green composite pieces of polylactide (PLA). The as-received spent coffee grains were first milled to obtain the so-called spent coffee grounds (SCGs) that were, thereafter, incorporated at 20 wt.% into PLA by extrusion. Finally, the resultant green composite pellets were shaped into pieces by injection molding. Moreover, two oligomers of lactic acid (OLAs), namely OLA2 and OLA2mal, the latter being functionalized with maleic anhydride (MAH), were added with SCGs during the extrusion process at 10 wt.%. The results show that, opposite to most claims published in the literature of green composites of PLA, the incorporation of the liquor waste derived SCGs increased the ductility of the pieces by approximately 280% mainly due to their high lipid content. Moreover, the simultaneous addition of OLA2 and OLA2mal further contributed to improve the tensile strength of the green composite pieces by nearly 36% and 60%, respectively. The higher performance of OLA2mal was ascribed to the chemical interaction achieved between the biopolyester and the lignocellulosic fillers by the MAH groups. The resultant green composite pieces are very promising as disposable food-serving utensils and tableware.

This work puts the Circular Bioeconomy’s concept into action, originally valorizing residues from the beverage liquor coffee industry into reinforcing fillers for green composites of polylactide (PLA). The as-received spent coffee grains derived from liquor waste were first milled to obtain the so-called spent coffee grounds (SCGs), which were then incorporated at 20 wt.% into PLA by extrusion. With the aim of improving the compatibility between the biopolyester and the lignocellulosic particles, two oligomers of lactic acid (OLAs), namely OLA2 and OLA2mal, being the latter functionalized with maleic anhydride (MAH), were both added during the extrusion process at 10 wt.%. The resultant compounded pellets were finally shaped into pieces by injection molding for characterization. Results showed that, as opposite to most claims published in the literature of PLA composites based on lignocellulosic fillers derived from soluble coffee wastes, the incorporation of liquor waste derived SCGs increased the ductility of the pieces by nearly 280% due to their high coffee oil content. The incorporation of OLA2 and OLA2mal contributed to improve the impact strength of the pieces by approximately 6% and 12.6%, respectively. The higher performance of OLA2mal was ascribed to a reduction of crystallinity in the green composite due to the chemical interaction by the MAH groups. However, the incorporation of SCGs into PLA slighlty reduced the thermal stability and yielded a dark-to-brown color, whereas it also delayed the disintegration rate of the pieces in controlled compost soil. Therefore, the results attained herein open up novel opportunities for the development of green composites of PLA with higher ductility and toughness through the valorization of liquor coffee wastes.

BioHDPE loaded composites with different amounts of spent coffee powder (up to 30 wt.%), were succesfully produced. The use of coffee residues coming from the alcoholic beverage industry into a bioHDPE matrix resulted in a remarkable improvement on the antioxidant properties of composites. Waste spent coffee powder gave reduced the elastic modulus, hardness and storage modulus, which was proportional to the amount of by-product considered. To improve the interaction between the highly hydrophobic BioHDPE matrix and the highy hydrophilic spent coffee powder, a copolymer, namely poly(ethylene-grafted-maleic anhydride) (PE-g-MA) was used. PE-g-MA addition resulted in an improved interaction between the particles and PLA as confirmed by field emission scanning electron microscopy (FESEM). On the other hand, the presence of the lignocellulosic filler resulted in a low load transfer between the two components, which led to a decrease in tensile strength. The introduction of coffee powder provided an improvement in the thermal stability as confirmed by thermogravimetry (TGA) and differential scanning calorimetry (DSC). Finally, antioxidant activity was also observed in the composites, reporting a 27% of DPPH reduction for the highest coffee content composite. The presence of antioxidant substances (coffee oil) was confirmed by Fourier transformed infrared spectroscopy (FTIR).