Synergistic effect of chemically modified CNC nanofiller concentration on the mechanical and thermal properties of additively manufactured PLA-TPU-CNC composites

The continual application of renewable cellulose nanoparticles has led to several advancements in their performance as a reinforcing component for the fabrication of high-performance additively manufactured nanocomposite products. Nonetheless, incorporating hydrophilic cellulose nanocrystals into hydrophobic thermoplastics, such as polylactic acid and thermoplastic urethane, remains a substantial challenge for achieving successful and smooth compatibility as an additional component in 3D-printed composites. This study has successfully investigated the effects of chemically modified cellulose nanocrystals at concentrations of 0.05%, 1%, and 3% when blended with hexadecyltrimethylammonium bromide and polylactic acid-thermoplastic urethane (PLA-TPU) at an 80:20 ratio. This study demonstrates the use of a fused deposition modeling (FDM) printer to manufacture 3D-printed PLA-TPU-CNC (cellulose nanocrystal) composites through additive manufacturing. The composite with 0.05% modified CNC exhibits 19.12 MPa higher tensile strength and 58.3% higher flexural strength than the unmodified one. Furthermore, the PLA-TPU blend with 1% modified CNC obtained the highest Izod impact strength, 63.43 MPa. The 3D-printed composite with 1% modified CNC displayed significantly better compressive strength than other modified variations and concentrations in the unmodified group. Composites with 1% unmodified CNC exhibited 2.33% higher heat deflection than blended PLA-TPU. The composites with 0.05% modified CNC showed an increase of 1.12% compared to the PLA-TPU blend and a modest increase of up to 2.71% compared to the other modified CNC concentrations. The composite with 1% modified CNC was superior to all the variations in terms of hardness, with a 29.6% increase above the 1% unmodified composite. The utilization of cationic surfactants, such as hexadecyltrimethylammonium bromide (HDTMA-Br), enhances CNC infiltration, interfacial adhesion, and hydrophobicity control, thereby improving the mechanical performance of the composites and making them suitable for specific medical and engineering material designs and applications. The F-statistics for all concentration levels yielded a ratio substantially greater than the F-critical value, and the p-value was considerably less than 0.05, indicating a significant and favorable design criterion.