## 3 Results
### Results of DMA Characterization  
DMA is a powerful tool for evaluating the properties of composites. It consists of applying an oscillating force to a sample and evaluating the material's response. The capacity to absorb or dissipate energy is reported. Furthermore, the damping factor or Tan \(\delta\) that is obtained from the loss ratio and the storage modulus can help in the evaluation of the dispersion level when a filler or reinforcer is added to a polymer matrix. Figure 5 depicts the storage modulus versus temperature for the 3D-printed PP and PP-GHP composites, and it can be clearly observed that the 3D-printed PP-1 GHP composite showed a similar behavior to that of the 3D-printed pristine PP, but when the GHP content was increased, there was a significant decrease in the modulus, indicating that there is a loss of capacity to support stress. It is possible that there was an increase in the sliding or flow to the polymer chains and particles, which was reflected in the decrease in the storage modulus. A diminishing storage modulus in polymer composite materials was previously reported, and it was found that, with an increase in temperature, the composites exhibited more ductility and became softer than the bulk matrix, reflecting lower storage modulus values [39]. Another observation is that the storage modulus was higher when the temperature was increased for all 3D-printed composites compared with the pristine PP; this could be attributed to the motions of the polymer matrix being restricted due to the presence of GHPs with the increase in temperature.  
In composites, there is a damping factor due to the nature of the matrix and filler materials, the friction generated due to slipping in the resin/fiber interface, energy dissipation at cracks, and delaminations produced at damaged locations, in addition to viscoplastic and thermoelastic damping. Figure 6 depicts the Tan \(\delta\) curves for the 3D-printed PP and PP-GHP composites, and it is possible to observe two transitions. The first transition occurred around 10 \({}^{\circ}\)C and was associated with the glass transition of the polymer matrix; this did not show a significant change when GHPs were added, but the peak height was lower for the 3D-printed pristine PP compared with that of the 3D-printed composites. This was because the presence of GHPs restricted the mobility of segments of the amorphous phase of PP. The height of the Tan \(\delta\) peak also varied when GHPs were added. The higher value of the 3D-printed PP-3 GHP composite indicated that the particles  
Figure 5: DMA thermogram of storage modulus versus temperature for 3D-printed PP and PP-GHP composites.  
the chain segments in the amorphous phase, and the composites had a nonelastic strain component. It has been reported that a higher Tan \(\delta\) peak value is associated with a less elastic than viscous nature compared with that of pristine PP [40]. Another interesting observation was that the width of the Tan \(\delta\) peak increased for the 3D-printed PP-GHP composites, which was indicative of a more complex structure and suggested that there were molecular relaxations in the 3D-printed composites that were not present in pristine PP because the peak became broader with the increase in GHPs. The second transition was observed around 80 \({}^{\circ}\)C; this was associated with the crystalline structure of PP and was related to the laminar and rotational sliding of ordered crystalline structures. The Tan \(\delta\) value increased for the 3D-printed composites, indicating that there was a more ordered structure in the filaments. This was in accordance with the DSC results, indicated that the crystallinity of the 3D-printed PP-GHP composites had a high percentage in comparison with that of the 3D-printed pristine PP. Similar results were reported before, attributing this to the relaxation of restricted amorphous PP macromolecules in the crystalline phase and to mechanisms of lamellar slip and rotation in the crystalline phase [41].