Polyurethane molded foams with high content of hyperbranched polyols from soybean oil

This paper examines the feasibility of using polyols from vegetable oils as base polyols (i.e. with 50% or more in a blend with petrochemical polyols) for flexible molded polyurethane foams. A series of hyperbranched (HB) polyols were synthesized by transesterification of hydroxy fatty acid methyl esters and different modifiers to control viscosity, hydrophilicity, molecular weight, and functionality. All HB polyols had hydroxyl numbers around 85 mg KOH/g, with the exception of one which was 105 mg KOH/g. When mixed with petrochemical polyols with OH numbers 35 and 28 mg KOH/g, the HB polyols acted primarily as high molecular weight crosslinkers that increased the stiffness of the polymeric network and the load-bearing properties but decreased the tensile strength, elongation, and tear strength. However, most of the foams met the targeted tensile and tear strength values while some of the foam formulations provided satisfactory elongation. The best mechanical properties were obtained from foams with phthalic anhydride-modified HB polyols. It was demonstrated that flexible molded foams with satisfactory properties can be obtained with 50% and 65% of HB soy polyols in a blend with PPO polyols.