**4. Results and discussion**

#### **4.1 Morphological and thermal characterization**

**Figure 2** shows the cryogenic fractured specimen for comparison between PP, PPr1/GP, and PPr3/GP. Poor interaction can be observed between the polymer matrix and glass particles due to the presence of small voids, gaps, and unattached particles.

The addition of PPMA in GP/PPr composites resulted in the smoothing of fractured surfaces (**Figure 3**). Furthermore, unattached particles, micro-voids and the gap between the matrix and the filler were slightly reduced. As such, filler-matrix interaction improved due to the addition of the coupling agent. **Table 3** shows the thermal properties of composites containing GP.

The melting temperatures (Tm) of all samples were similar to those of neat PP, except for the presence of a small endothermic peak in some composites at 127°C. Based on literature data [57], the small peak at 127°C can be attributed to the polyethylene and contamination in PPr, which is very common due to the difficulty in separating PP from PE during the recycling process.

In general, the composites showed similar crystallinity degrees (χc) to those of neat PP (**Table 3**). The results are noteworthy because they suggest that the presence of post-consumer materials (PPr and GP) did not disturb the crystal formation of the final composite, which leads to the assumption that the final properties of the composite are maintained, even with the addition of postconsumer materials.

#### **Figure 3.**

*SEM micrographs in two sizes (100 and 50 μm) of PP/PPr1/GP/PPMA (75/10/5/10%w/w/w/w) and PPr3/GP (55/30/5/10%w/w/w/w) composites.* 


#### **Table 3.**

*Thermal properties of PP and PP/PPr/GP-base composites.* 
