Enhancing thermal and mechanical properties of rigid polyurethane foam with eco-friendly silane-modified cellulose nanocrystals

Cellulose nanocrystals (CNC) are promising candidates for strengthening polymeric matrices, offering unique features like biodegradability, renewability, and exceptional mechanical properties. However, efficiently dispersing CNC in these matrices and finely adjusting their interfacial characteristics are critical for harnessing their full potential in novel nanomaterial development. Herein, we developed novel eco-friendly and effective method to modify the surface of the CNC with three types of silane coupling agents – (3-Aminopropyl trimethoxysilane (APTMS), N-ethyl-2,2-dimethoxy-4-methyl-1-aza-2-silacyclopentane (ASCP1), and N-(2-aminoethyl)-2,2,4-trimethyl-1-aza-2-silacyclopentane (ASCP2) by using chemical vapor deposition (CVD). The sustainable rigid polyurethane foams (RPUFs) were then prepared by incorporating three modified CNCs (CNC-APTMS, CNC-ASCP1, and CNC-ASCP2) from 0.5 to 5 wt%. Afterward, the influence of these three modified CNCs with increasing content on the morphology, thermal, and compressive properties of RPUFs was examined. It was observed that the RPUFs containing 0.5 wt% and 1 wt% of CNC-ASCP2 exhibited a lower thermal conductivity (0.043 ± 0.002 and 0.045 ± 0.001 W/m·K, respectively) compared to standard RPUF sample (0.049 ± 0.005 W/m·K). Furthermore, these foams also showed enhanced compressive strength (1.96 ± 0.08 and 2.03 ± 0.5 MPa) in comparison to the standard RPUF sample (1.25 ± 0.09 MPa). This improvement in thermal and compressive properties is attributed to the better compatibility of CNC-ASCP2 with polyol and foam components, promoting efficient nucleation of cells and uniform dispersion within the foam.