Bello Kabirat O, Yan Ning
Graduate Department of Forestry, University of Toronto, 33 Willcocks Street, Toronto, ON M5S 3B3, Canada.
Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200 College Street, Toronto, ON M5S 3E5, Canada.
Polymers (Basel). 2024 Jul 25;16(15):2119. doi: 10.3390/polym16152119.
Isocyanates are critical components that affect the crosslinking density and structure of polyurethane (PU) foams. However, due to the cost and hazardous nature of the precursor for isocyanate synthesis, there is growing interest in reducing their usage in polyurethane foam production-especially in rigid PU foams (RPUF) where isocyanate is used in excess of the stoichiometric ratio. In this study, lignin-containing nanocellulose fibrils (LCNF) were explored as mechanical reinforcements for RPUF with the goal of maintaining the mechanical performance of the foam while using less isocyanate. Different amounts of LCNF (0-0.2 wt.%) were added to the RPUF made using isocyanate indices of 1.1, 1.05, 1.0, and 0.95. Results showed that LCNF served as a nucleating agent, significantly reducing cell size and thermal conductivity. LCNF addition increased the crosslinking density of RPUF, leading to enhanced compressive properties at an optimal loading of 0.1 wt.% compared to unreinforced foams at the same isocyanate index. Furthermore, at the optimal loading, LCNF-reinforced foams made at lower isocyanate indices showed comparable stiffness and strength to unreinforced foams made at higher isocyanate indices. These results highlight the reinforcing potential of LCNF in rigid polyurethane foams to improve insulation and mechanical performance with lower isocyanate usage.
异氰酸酯是影响聚氨酯（PU）泡沫交联密度和结构的关键成分。然而，由于异氰酸酯合成前体的成本和危险性，人们越来越关注在聚氨酯泡沫生产中减少其用量，尤其是在异氰酸酯用量超过化学计量比的硬质PU泡沫（RPUF）中。在本研究中，探索了含木质素的纳米纤维素原纤维（LCNF）作为RPUF的机械增强剂，目的是在使用较少异氰酸酯的情况下保持泡沫的机械性能。将不同量的LCNF（0 - 0.2 wt.%）添加到异氰酸酯指数为1.1、1.05、1.0和0.95的RPUF中。结果表明，LCNF作为成核剂，显著减小了泡孔尺寸并降低了热导率。添加LCNF提高了RPUF的交联密度，与相同异氰酸酯指数下的未增强泡沫相比，在0.1 wt.%的最佳添加量下，压缩性能得到增强。此外，在最佳添加量下，较低异氰酸酯指数下制备的LCNF增强泡沫表现出与较高异氰酸酯指数下制备的未增强泡沫相当的刚度和强度。这些结果突出了LCNF在硬质聚氨酯泡沫中具有增强潜力，可在降低异氰酸酯用量的情况下提高保温性能和机械性能。
