Exploring macro- and microlevel connectivity of the urea phase in slabstock flexible polyurethane foam formulations using lithium chloride as a probe

Urea phase connectivity has been probed by systematically varying the hard segment content, and lithium chloride content, in a series of plaques based on slabstock flexible polyurethane foams. The plaque formulations are identical to those of slabstock polyurethane foams with the exception that a surfactant is not utilized. Small angle X-ray scattering (SAXS) is used to demonstrate that all materials investigated are microphase separated with similar interdomain spacings, irrespective of hard segment content (21-37 wt%) or LiCl content. Several complimentary characterization techniques are employed to reveal that urea phase connectivity is present at different length scales. Macrolevel connectivity, or connectivity of the large-scale urea rich aggregates typically observed in flexible slabstock polyurethane foams, is probed using SAXS, TEM, and atomic force microscopy. These techniques collectively show that the urea aggregation increases as the hard segment content is increased. Incorporation of LiCl is shown to systematically reduce the urea aggregation behavior, thus leading to a loss in the macroconnectivity of the urea phase. Wide angle X-ray scattering is used to probe the regularity in segmental packing, or the microlevel connectivity between the hard segments, which is observed to decrease systematically on addition of LiCl. The loss in microlevel connectivity is suggested to increase chain slippage, and leads to increased rates of stress-relaxation for the samples containing LiCl. Materials containing LiCl also display relatively short rubbery plateaus as compared to their counterparts which do not contain the additive. Modulus values, as obtained at ambient conditions by stress-strain analyses, are found to be a stronger function of LiCl content when the hard segment content is higher. (C) 2002 Elsevier Science Ltd. All rights reserved.