Development of biobased poly(ethylene) composites with improved antioxidant properties with coffee by-products coming from the alcoholic beverages industry

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).