## 3 Results  
### Mechanical Performance of the Green Composite Pieces  
Table 2 includes the mechanical properties of PLA and its green composite pieces to ascertain the effect of the TCHF content on PLA. One can notice that neat PLA resulted in a brittle piece with an elongation at break (\(\varepsilon_{b}\)) of nearly 9%. The tensile strength at yield (\(\sigma_{y}\)) was approximately 50 MPa and  
the tensile modulus (\(E_{t}\)) was 3.58 GPa. One can observe that the incorporation of both CHF and TCHF induced a progressive reduction in all the \(\sigma_{y}\) and \(\varepsilon_{b}\) values and an increase in \(E_{t}\). For instance, with the addition of 20 wt% of CHF, the \(\sigma_{y}\) values diminished to 39.16 MPa and with the addition of 20 wt% of TCHF, the \(\sigma_{y}\) values diminished to 43.29 MPa, which represent a percentage decrease of 21% and 13%, respectively. Further reductions in the mechanical strength were observed at higher TCHF contents. For instance, the addition of 50 wt% of TCHF induced a percentage decrease of \(-\)44%. Alternatively, the incorporation of CHF and TCHF improved the mechanical elasticity of the pieces. Thus, \(E_{t}\) increased to 3.48 GPa for the PLA/CHF composite and it was in the 3.59-4.45 GPa range for the PLA/TCHF composite pieces. This result suggests than an efficient dispersion and wettability of the torrefied filler in the biopolymer matrix was achieved. With regard to ductility, the addition of the lignocellulosic fillers led to a percentage decrease from 8.91%, for the neat PLA piece, to 6.98% for the PLA/20 CH piece, 7.10% for the PLA/20 TCH piece, and finally to the lowest value of 5.18% for the PLA/50 TCH piece. It can be thus considered that the coffee waste derived fillers acted as a stress concentrator rather than a reinforcing element in the biopolymer matrix. Furthermore, this result highlights the lack of miscibility between both composite components and also the low particle-polymer interfacial interactions. This effect was, however, more noticeable in the piece containing the untreated CHF and, most notably, for the pieces filled with the highest TCHF contents. The latter observation may suggest that TCHF poorly disperses in the PLA matrix at high content [52; 53]. Therefore, as also demonstrated by [PERSON] et al. [54] for chitosan films containing waste coffee grounds (WCG), high amounts of TCHF cannot be efficiently distributed in the biopolymer matrix. Nevertheless, one should also consider that this mechanical reduction was relatively low in terms of the high amount of lignocellulosic filler when compared with those attained in previously prepared green composites of PLA and coffee waste derived fillers. For instance, in the work reported by [PERSON] et al. [55], the tensile strength at break (\(\sigma_{b}\)) of PLA films decreased from 79.20 MPa (transverse direction, TD) and 72.79 MPa (machine direction, MD) to 20.77 MPa (TD) and 18.31 MPa (MD) after the incorporation of 10 wt% of SCG. In another study, the \(\sigma_{b}\) value of PLA films decreased from 44.3 MPa to approximately 20 MPa after the incorporation of 40 wt% of SCG, which was attributed to the poor filler dispersion in the biopolymer matrix due to its low compatibility [56]. The improvement attained here may be attributed to the removal of impurities and other volatile TCHF components during torrefaction that would otherwise decrease the strength of interfacial interactions and adhesion between the filler and PLA matrix. Furthermore, the resultant increase in hydrophobicity of the lignocellulosic filler after torrefaction can also be a meaningful explanation for the improved mechanical properties attained in the green composite pieces with TCHF in comparison with the pieces based on untreated CHF. In this regard, one can expect that the higher presence of moisture in CHF can promote a larger decrease in the PLA's \(M_{W}\) during processing at high temperature due to hydrolysis of the ester groups, which can result in impairment of the final mechanical properties [57].