Influence of cellulose nanocrystal incorporation on the properties of polypropylene filaments for 3D printing

Polypropylene (PP) is among the most widely produced polymers worldwide. However, its application in fused filament fabrication is limited by excessive crystallization during solidification, which induces internal stresses and warpage. This study investigates the incorporation of cellulose nanocrystals (CNCs) as a nanoreinforcement for PP filaments intended for additive manufacturing. PP/CNC filaments containing 0, 1, 2, and 3 wt% CNCs were produced by extrusion and characterized. Differential scanning calorimetry revealed an increase in crystallinity from 22% for neat PP (PP0) to 26% for PP1, indicating a nucleating effect. Thermogravimetric analysis confirmed thermal stability compatible with 3D printing (around 260 °C), while FTIR analysis showed no chemical interactions between matrix and reinforcement. Mechanical testing showed a progressive reduction in ductility with increasing CNC content, with elongation at break decreasing from 132% (PP0) to 86%, 49%, and 17% for PP1, PP2, and PP3, respectively. Despite this reduction, tensile strength increased from 27.75 MPa (PP0) to 29.05 MPa for PP1, while PP2 and PP3 exhibited values statistically equivalent to neat PP. All CNC-reinforced composites showed higher tensile elastic modulus than PP0 (561 MPa), reaching 687.7 MPa for PP1, with no statistically significant differences among PP1, PP2, and PP3. SEM analysis revealed uniform CNC dispersion at 1 wt% and agglomeration at higher contents. Overall, the incorporation of 1 wt% CNC provided the best balance between mechanical performance and ductility, highlighting a strategy for enhancing the performance of PP-based materials in additive manufacturing.