Effect of Hyperbranched Vegetable Oil Polyols on Properties of Flexible Polyurethane Foams

Molded polyurethane foams for car seats are based on petrochemical polyols of molecular weight 4000-6000 and copolymer polyols containing micron size polymeric particles. Copolymer polyols (CPP) typically constitute 30% of the mixture with the base polyol. They help cell opening, increase load bearing and tear strength of the foams, but they are relatively expensive. Hyperbranched polyols of petrochemical origin were used in molded foams.[1] They are solid in the pure form and due to high crosslinking density could be incorporated at low concentration in conjunction with copolymer polyols. Instead, we have made hyperbranched polyols which could be a total replacement for CPP in molded foams. Six hyperbranched polyols with primary and secondary hydroxyl groups and different hydroxyl numbers were prepared from soybean oil and tested in flexible foams. Novel polyols were liquid even at very high molecular weights and could completely replace copolymer polyols. Functionality of these polyols increased linearly with molecular weight to very high values, resulting eventually in their high crosslinking power. The effects of the type of hydroxyl groups (primary vs. secondary), hydroxyl number (from 85 to 135 mg KOH/g), and concentration (7.5-30%) in the mixture with the base polyol on foam properties were analyzed. It was found that hyperbranched polyols could replace copolymer polyols completely but their effect on cell morphology and mechanical properties varied with the type of polyol and concentration.