Compressive viscoelastic properties of softwood kraft lignin-based flexible polyurethane foams
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Softwood kraft lignin (SKL)-based water-blown flexible polyurethane foams were prepared using SKL as a crosslinking agent and a hard segment polyol. Polyethylene glycol (PEG) as a soft segment diol and 2,4-toluene diisocyanate (TDI) were used. While increasing hard segment content caused the increase in crosslink density in foams, the foams became more and more viscous with increasing hard segment content due to the distinctive phase heterogeneity in foams. In this case, the contributiveness of the filler-like behaviors of separated hard segments always overtook the crosslinking effects derived from SKL in terms of overall viscoelasticity, thus the resultant viscometric properties such as tanδmax and hysteresis loss increased as hard segment content increased. Furthermore, increasing Mn,PEG caused the severer microphase separation and intensified the filler effects in foams, thus the foams became more viscous with increasing Mn,PEG. The 25 % and 65 % CFD values and Young’s moduli of foams increased with increasing hard segment content due to the increase in crosslink density for foams, and the properties also increased with increasing foam density. Most of foams showed the support factors in the range of 2–3, which are suitable values for cushioning use. Even though the microscopic deformation behaviors in foams are irrelevant to foam density, the cyclic compressive tests showed that the higher foam density possess the better shape recovery performances.
KeywordsLignin Polyurethane foam Viscoelasticity
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