Improvement in physico-mechanical and structural properties of rigid polyurethane foam composites by the addition of sugar beet pulp as a reactive filler

Abstract

Green polymeric composites, which are obtained from cheap, renewable, and environmentally friendly natural resources that can replace petrochemicals, have gained great attention from the researchers in recent years. To that end, we aimed at preparing a type of bio-based rigid polyurethane foam (RPUF) composites which incorporated sugar beet pulp (SBP) particles as a reactive filler. The obtained composite foams were evaluated through the effect of the increasing amount of SBP particles on the microstructure, thermal and mechanical properties. To eliminate the density effect of foams on the physico-mechanical properties, the foams were obtained such that their densities were kept at 37 $$\pm$$ 0.5 kg.m−3. Besides, the heat transfer mechanism of foams in terms of radiative transfer, conduction through polymer matrix and gas phase were analyzed by using a predictive model for the efficient thermal conductivity. Based on FTIR results, the functional groups on SBP have a tremendous tendency to react with isocyanates in the presence of a catalyst. The introduction of 3 wt% SBP according to the total mass provided high compressive strength (166 kPa), low thermal conductivity value (20.46 mW/m.K) and excellent dimensional stability in harsh conditions. SEM images show that the distribution of cells was uniform and any broken cells were not detected in all composite foams. The addition of SBP particles generally decreases the radiative contributions and enhances the contribution of conduction through the polymer matrix. It is clear that for all foams, the conduction through gas-phase gave the biggest contribution to the total thermal conductivity. Thermogravimetric analysis data displayed that the inclusion of SBP in RPUF slightly improved the thermal stability of RPUF composites. All results indicate that SBP waste, which is the most produced by-agriproduct in sugar refining industry, is an advantageous natural filler in many aspects for preparing RPUF. The obtained environmentally friendly RPUF composites have all of the properties needed to meet the demand for thermal insulation engineering materials.