Structure–properties relations in flexible polyurethane foams containing a novel bio-based crosslinker

The structure, morphology and properties of PU foams containing the novel bio-based crosslinker 3-hydroxy-N,N-bis(2-hydroxyethyl)butanamide (HBHBA) were investigated in comparison with PU foams containing the conventional crosslinker diethanolamine (DEOA). FTIR results indicate that HBHBA increases the degree of microphase separation in the foam and hydrogen bond concentration in the hard domains, suggesting that the incorporation of HBHBA produces better ordering of hard domains as compared with DEOA-crosslinked foam. Uniquely, the tri-functional crosslinker, HBHBA, can act as a chain extender due to the presence of a low reactivity secondary hydroxyl, reducing the crosslink density of the HBHBA foam vs. that of DEOA foam. Concerning foam morphology, the lower reactivity of HBHBA tends to favor larger cell sizes and more complete cell opening as compared to the more reactive DEOA. This behavior may in turn be related to the onset of phase separation and the rate of viscosity build-up. Mechanical properties measurements indicate that the elongation at break and the tensile strength of the HBHBA foam are ∼33% and 41% higher than the DEOA foam, respectively. The HBHBA foam also exhibits 40% greater tear strength and 10% greater compression strength without any loss in resilience. These results indicate that this bio-based crosslinker enhances properties and has clear potential in molded foam applications.