Viscoelastic recovery behavior and imperfection in reactive polymer network of viscoelastic polyurethane memory foams

摘要

The relationship between polymer network parameters and speed of viscoelastic (VE) recovery was studied for viscoelastic polyurethane foams. Reactive network simulation method was developed which use relative reactivity parameters derived from literature and from experiment. Relative reactivity of butylene oxide (BO) based secondary hydroxyl groups were estimated by comparing simulation results with experimentally derived sol fraction. From the analysis, it is found that BO and propylene oxide (PO) hydroxyl end groups have relative reactivity to isocyanates that are not very different. We also find that the isocyanate conversion is lower only about 91-96%, even though the isocyanates are the limiting factor (i.e. molar ratio NCO:OH = 0.9). It is also found that a foam with faster VE recovery is predicted to have smaller elastically effective chain (EEC) mass fraction (i.e. more imperfect polymer network) and higher sol fraction. Surprisingly, the same foam after solvent extraction was found to have slower VE recovery. It is concluded for foam systems with T-g near ambient temperature, that while lower EEC fraction can lead to slower VE recovery, a large amount of sol fraction in the foam system can cause faster VE recovery via plasticization of the polyurethane matrix. (C) 2017 Elsevier Ltd. All rights reserved.