## 3 Results
### Thermal Performance of the Green Composite Pieces
The TGA and first derivate thermogravimetric (DTG) curves of the injection-molded pieces of PLA and its green composite pieces with CHF and TCHF are shown in Figure 6, whereas Table 4 shows the relevant values extracted from the curves. In relation to the thermal degradation profiles of CHF and TCHF, in both cases they presented three stages; however, the torrefied fillers showed significantly higher stability. The first mass loss, which occurred below 100 \({}^{\circ}\)C, being in both cases less than 5% but slightly higher for CHF, is associated with the evaporation of moisture and volatiles present in the lignocellulosic fillers. The second one occurred between approximately 240 and 380 \({}^{\circ}\)C, was the most intense, and was associated with a mass loss of over 60% and 35% for CHF and TCHF, respectively. This degradation stage, which was also more intense for CHF, is mainly caused by the thermal decomposition of the molecular bonds of hemicellulose, cellulose, and small amounts of lignin, which overlapped with the thermal degradation of PLA. The third stage started at 385 \({}^{\circ}\)C and continued for the whole thermal range tested. This last mass loss is due to the degradation of the lignin fraction present in CHF and TCHF [11; 69]. In this regard, [PERSON] et al. [70] showed that green coffee cake (GCC), a solid by-product of the coffee processing industry, resulting from the extraction of oil by the cold pressing technique, also presented three regions of mass loss, similar to other lignocellulosic biomasses. The first one was observed between 50 and 100 \({}^{\circ}\)C, the second one between 200 and 300 \({}^{\circ}\)C, and the last one between 275 and 400 \({}^{\circ}\)C. The authors ascribed the second and third mass losses to hemicellulose depolymerization in combination with temperature-induced glycosidic cleavage and to lignin components and cellulose degradation, respectively. Finally, after the degradation steps, a significant residue of approximately 25% and 40% was found for CHF and TCHF, respectively, remarking the higher stability of the carbon formed during the torrefaction step. The TGA results also indicated that TCHF was thermally stable up to more than 250 \({}^{\circ}\)C, which makes it useful as a reinforcing agent in most WPCs. In the case of PLA, it can be observed that the biopolymer degraded in a quick step process at approximately 350 \({}^{\circ}\)C. The main products generated during the thermal degradation of PLA have been ascribed to lactic acid, oligomers of lactic acid (OLAs), acetaldehydes, carbon dioxide, carbon monoxide, and ketones [60]. The TGA curves of the PLA/TCHF pieces showed a slight increase in the thermal stability for the lowest filler content. In particular, the DTG curves showed an increase in the pyrolysis peak related to the degradation temperature (\(T_{dg}\)) from 347.4 \({}^{\circ}\)C, for neat PLA, up to 354.7 \({}^{\circ}\)C, for the PLA/20 TCHF composite. The increase in the thermal stability of the green composite pieces can be related to the \"barrier\" effect of the decomposition of the biopolymer material by the lignocellulosic fillers, which promoted an increase of the degradation temperature [70]. However, a decrease in the temperature at the mass loss of 5% (T\({}_{5\%}\)), which corresponds to the onset degradation temperature, was observed for TCHF contents above 30 wt%. The lower T\({}_{5}\)% values attained at higher filler contents can be related to the \"chimney\" effect of the coffee waste lignocellulosic fillers, which prevails their \"barrier\" effect, and favored the movement of heat in the PLA matrix [57]. In particular, T\({}_{5\%}\) was reduced from 320.4 \({}^{\circ}\)C, for the unfilled PLA piece, down to approximately 300 \({}^{\circ}\)C for TCHF contents of 40 wt% and 50 wt%. Therefore, a slight improvement in the PLA's thermal stability was attained