## 3 Results  
### Results of the DSC Characterization  
The crystallization and melting behaviors of the PP and PP-GHP composites during 3D printing were studied using DSC. Figure 2 shows that the typical DSC thermograms for the 3D-printed PP and PP-GHP composites presented a similar path; the quenching cycle and second heating cycle were used to calculate \(T_{c}\), \(\Delta H_{c}\), and \(T_{m}\), and those data are reported in Table 2. It was possible to observe that the \(T_{c}\) value of the 3D-printed PP-GHP composites was not affected by the presence of GHPs, suggesting that the crystallization rate was not affected. However, \(\Delta H_{c}\) showed an increase for the 3D-printed PP-GHP composite compared with that of the 3D-printed PP, but with a higher content, and the enthalpy decreased to a value similar to that of pristine PP. This behavior can be associated with the threshold percolation involved in the generation of a modification of this property. Regarding the melting process, the presence of GHPs caused a decrease in \(T_{m}\) compared with the value in pristine PP; a lower GHP content resulted in a greater effect (8 \({}^{\circ}\)C), which was associated with the fact that the presence of particles advanced the fusion process, and the crystallinity content increased when using a content of 3 phr. \(\Delta H_{m}\) increased with the presence of GHPs when the content was 1 or 3 phr, and with 5 phr, it decreased to a value similar to that of pristine PP.  
Figure 2: DSC thermogram for 3D-printed PP, 1 st heating step (red), cooling step (green), and 2 nd heating step (blue).  
On the other hand, the percentage crystallinity increased compared with that of pristine PP for the 3D-printed PP-1 GHP and PP-3 GHP composites, showing an increase of up to 15% for the PP-3 GHP composite, but it decreased for the 3D-printed PP-5 GHP composite, to a values similar to that of pristine PP, meaning that GHPs generated a nucleating effect in the PP matrix. This was associated with an improvement in the interfacial interaction between the PP matrix and GHPs. The later increase in the GHP content and decrease in crystallinity could have been due to a threshold percolation limit, meaning that after a certain particle content, the matrix was not positively affected. One of the main reasons to provide a matrix modifi-cation it the adhesion between particles and matrix, when this adhesion is low, void formation increases, and the presence of crack nucleation leads to smaller property modifications [15]. A similar behavior was already reported by our group in a previous work in compounds prepared from PP and GHPs through compression molding. However, the highest values reported were with a higher GHP content (8 phr) [32]. This difference could be associated with the processing conditions used to obtain the filaments; when they flowed through the printer nozzle, a higher shear rate was generated, meaning that the particles could be better oriented in the PP matrix to favor the generation of a greater number of crystalline zones. However, this behavior has not been reported in works that obtained PP composite filaments reinforced with waste lignocellulosic particles. Previous work reported that the addition of untreated and chemically treated bamboo fibers to PP and PLA had a nucleating effect, accelerating the crystallization speed and increasing the crystallinity of the PP/PLA bamboo fiber filaments for 3D printing.  
The crystallinity of 3D-printed composites is an important property, since it can be associated with the shrinkage capacity of a material when deposited on a printing bed. [PERSON] et al. (2021) [19] reported that a decrease in the crystallization temperature of composite PP-rice husk filaments reduced the presence of shrinkage during the printing process in comparison with that of r-PP. Other reports indicated that the presence of amorphous compounds, such as hemicellulose and lignin, produced a decrease in the content of crystalline zones in PP-cocoa shell filaments for 3D printing [20].