A comprehensive research of low-density bio-based rigid polyurethane foams from sugar beet pulp-based biopolyol: From closed-cell towards open-cell structure

Abstract

The effective using of industrial agricultural crop residues in the polymer industry is still challenging. Herein, sugar beet pulp-based polyol (SBpol) was synthesized using an acid-catalyzed solvothermal liquefaction method, and then a series of bio-based rigid polyurethane foams (sPUFs) was produced using one-shot and free-rising technique by replacing up to 100 php of the petroleum-based polyol with biopolyol. The effects of an increasing amount of SBpol on the morphological, physico-mechanical, thermal, and flame retardant properties of sPUFs were evaluated. SEM pictures revealed that the cell windows of sPUFs opened as the amount of biopolyol increased, and in parallel with these results, the decreases in the closed-cell contents were determined. While the insulation properties of sPUFs containing up to 40 php biopolyol are superior, the mechanical properties of sPUFs containing 20 php biopolyol are higher than that of reference petroleum-based foam. The water absorption ratio of sPUF100 was almost 5 times higher than that of the reference foam at the end of 76 h due to the high porosity. A 6-week abiotic hydrolysis test showed that the sPUF100 sample started a partial degradation. Thermogravimetric analysis indicated that all the sPUFs were thermally stable at temperatures up to 247 °C. The flame retardant properties of sPUFs were not satisfactory because the addition of biopolyol increased both heat release rate and total smoke production; therefore, the flame resistance of sPUFs has to be increased by the incorporation of flame retardant chemicals. This study proves a useful, promising, and sustainable strategy for the development of sugar beet pulp-based polyurethane foams in the polyurethane industry.