## 3 Results
### Thermal Performance of the Green Composite Pieces  
Figure 5 shows the DSC thermograms of PLA and its green composites with CHF and TCHF. Table 3 gathers the main thermal properties obtained from the cooling and the second heating scans, once the thermal history was removed from the samples. The neat PLA sample showed a glass transition temperature (\(T_{g}\)) of 62.3 \({}^{\circ}\)C and the incorporation of TCHF led to a slight decrease in the values up to 60.7 \({}^{\circ}\)C for the green composite filled at 50 wt%. In all curves, a low-intense endothermic peak was observed, which can be ascribed to the aging process of the biopolymer [42]. It can also be observed in Figure 5a that, during cooling, the PLA samples did not crystallize from the melt  
Figure 4: Field emission scanning electron microscopy (FESEM) images of the fracture surfaces of the injection-molded pieces of polylactide (PLA) with coffee husk flour (CHF) and torrefied coffee husk flour (TCHF): (**a**) Neat PLA; (**b**) PLA/20 CHF; (**c**) PLA/20 TCHF; (**d**) PLA/30 TCH; (**e**) PLA/40 TCH; (**f**) PLA/50 TCH. Images were taken at 500\(\times\) with scale markers of 10 \(\mu\)m.  
In contrast, in Figure 5b, one can see that the neat PLA samples showed an exothermic peak centered at 122.7 \({}^{\circ}\)C for neat PLA, which is ascribed to the biopolymer chain rearrangement during cold crystallization. The green composites showed slightly higher values of both cold crystallization temperature (\(T_{cc}\)) and cold crystallization enthalpy (\(\Delta H_{cc}\)), showing the highest values for TCHF contents of 20 wt% and 30 wt%, respectively. The cold crystallization process is an exothermic process that takes place when the biopolymer chains become flexible, above PLA's \(T_{g}\), which is caused by a primary nucleation, by which an ordered state is achieved. Since more PLA mass could cold crystallize, one can consider that intermediate filler amounts favored crystallization of PLA. A second endothermic peak, corresponding to the melting temperature (\(T_{m}\)), was observed at 151.3 \({}^{\circ}\)C for neat PLA, which slightly increased for filler contents of 20 wt% and then decreased for higher contents. An anticipation of the melting phenomena was also observed in HDPE by [PERSON] et al. [65] after the addition of biochar particles derived from waste coffee grounds. This behavior was explained by the presence of specific interactions occurring between the biopolymer chains and the particle interfaces. In fact, the lower \(T_{m}\) values attained at the highest contents, that is, 40 wt% and 50 wt% of TCHF, in combination with the higher \(\Delta H_{cc}\) values, suggest that the biopolymer chains were immobilized onto the surface of the lignocellulosic fillers. The maximum degree of crystallinity, that is, \(X_{C\_max}\), which does not consider the crystals that are formed during cold crystallization [50], increased progressively up to a TCHF content of 30 wt% and then slightly lower values were observed. This result indicates that the lignocellulosic fillers induced a nucleating effect that favored the formation of crystals in the green composites. In the case of the lower \(X_{C\_max}\) values for the green composites containing 40 wt% and 50 wt% of TCHF, one can consider that the fillers presence at these contents also supposed an obstacle for the biopolymer chains to form stable crystals, generating a negative effect on crystallinity and leading to the formation of a more amorphous structure [66; 67; 68]. Furthermore, one can also observe that the torrefaction process did not yield any significant effect on the thermal properties of PLA at the studied filler loading, suggesting that nucleation was based on a physical phenomenon. Figure 5: Differential scanning calorimetry (DSC) thermograms taken during (**a**) cooling and (**b**) second heating of the injection-molded pieces of polylactide (PLA) with coffee husk flour (CHF) and torrefied coffee husk flour (TCHF).