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Effects of the hydroxyl value of polyol in rigid polyurethane foams

机译：硬质聚氨酯泡沫中多元醇的羟值的影响

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摘要

Rigid polyurethane foams (RPUFs) have been fabricated from crude MDI(CMDI) and polypropylene glycols (PPGs) of various hydroxyl values (OHVs) of 300-600 with an environmentally friendly blowing agent (HFC 365 mfc). The closed cell content, compression strength, and dimensional stability of the foam increased with increase in the OHV due to the increased crosslink density, which was evidenced from the increased glass transition temperature (T{sub}g). The cream time, gel time, tack-free time, and density of the foam showed a minimum at 500 OHV. The decrease and increase around the minimum were, respectively, interpreted in terms of increased mixture mobility and extensive allophanate crosslinks, which retard gelling as well as foaming reactions. The thermal conductivity also showed a small minimum at 500 OHV.
机译：硬质聚氨酯泡沫（RPUF）是由300-600的各种羟值（OHV）的粗MDI（CMDI）和聚丙二醇（PPG）与环保的发泡剂（HFC 365 mfc）制成的。由于交联密度的增加，泡沫的闭孔含量，压缩强度和尺寸稳定性随着OHV的增加而增加，这可以通过增加的玻璃化转变温度（T {g}）来证明。乳化时间，胶凝时间，不粘手时间和泡沫密度在500 OHV下显示为最小值。分别以增加的混合物流动性和广泛的脲基甲酸酯交联来解释大约在最小值附近的减少和增加，这延迟了胶凝和发泡反应。热导率在500 OHV时也显示出很小的最小值。

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