Hybrid polyether-palm oil polyester polyol based rigid polyurethane foam reinforced with cellulose nanocrystal

Abstract

The development of sustainable rigid polyurethane foam (RPUF) using biologically renewable materials remains a challenge in both academia and industry. This study focuses on the cellulose nanocrystal (CNC) reinforcement of a model RPUF based on a hybrid polyol system of 80:20 ‘polyether’ and palm-kernel oil based ‘polyester’ polyols (PKObP), in order to simultaneously enhance thermal insulation and/or mechanical properties. The addition of 0.4 wt.% CNC in the RPUF afforded a 2.4% improvement (i.e. reduction) in the thermal conductivity (from 24.1 ± 0.4 mW/mK to 23.5 ± 0.3 mW/mK). This is statistically insignificant improvement and the same order of magnitude reported by other studies investigating the effect of micro and nanofiller in RPUF. It was unexpected, as we have previously observed a 5% reduction in thermal conductivity with the same loading (0.4 wt.%) of acid-hydrolysed CNC in the RPUF formulation using the same polyether polyol alone due to improved nucleation. Microscopic and cell content measurements indicated that the presence of the PKObP, which has the basic structure of a non-ionic surfactant, prevented the CNC from acting as a nucleation agent. The nature of interaction between the CNC and PKObP has decreased the specific compressive strength both parallel (−12.0%) and perpendicular (−1.8%) to foam rise. However, the specific Young’s modulus perpendicular to foam rise was significantly improved (8.5%), and this was attributed to the alignment of the CNC in the direction of foam rise.