蓖麻油基聚氨酯-丙烯酸酯复合乳胶膜的水白化研究

Study on Water Whitening of Castor Oil-Based Polyurethane-Acrylate Composite Film

采用蓖麻油基聚氨酯作为大分子乳化剂制备聚氨酯-丙烯酸酯(PUA)复合乳液。采用红外光谱表征了PUA乳胶膜的结构;用紫外分光光度计、动态热机械分析仪和差示扫描量热仪对PUA乳胶膜的水白化进行了表征。结果表明:在实验的时间范围内,乳胶膜的水白化程度随其浸水时间和浸水温度的增加而增加;当浸水温度(4℃)远低于干膜的玻璃化转变温度(Tg=57.8℃)时,乳胶膜浸水24 h不会水白化,湿膜的Tg及其储能模量与干膜相比几乎没有变化;在28℃的水中浸泡24 h时,湿膜的Tg小于干膜的Tg,其储能模量也降低,乳胶膜出现轻微水白化,将乳胶膜再次烘干后,胶膜可恢复原有清晰度。当乳胶膜在高于干膜Tg的水中(70℃)浸泡24 h时,其储能模量下降,湿膜的Tg大于干膜的Tg,再次烘干乳胶膜不会恢复原有的清晰度,其原因是膜内出现了与PUA分子依靠氢键紧密相连的冻结键合水。

Polyurethane - acrylate （ PUA ） castor oil-based polyurethane as macromolecule composite emulsions were prepared by using emulsifier. The structure of the PUA film was characterized by infrared spectroscopy. The water whitening of PUA latex film was characterized by UV spectrophotometer, dynamic thermomechanical analyzer and differential scanning calorimeter. The results showed that with the time of experiment, the degree of water whitening of the latex film increased with the increase of the immersion time and temperature. When the immersion temperature （4℃ ） was much lower than the glass transition temperature （ 57.8 ℃） of the dry film, the coating film did not occur water whitening after immersed in water for 24 h, the Tg and storage modulus of the wet film almost unchanged. When the film was immersed in the water of 28 ℃ for 24 h, the Tg of the wet film is lower than the glass transition temperature of the dry film, the storage modulus was also reduced, and the coating was slightly whitened. When the coating was dried again, the film can regain the original clarity. When the coating film was immersed in water at 70 ℃ which was higher than the Tg of the dry film, the storage modulus of the wet film decreased, but the Tg of the wet film was higher than that of the dry film, and the dried film could not recover the original clarity, because the freeze-bonded water in the film was closely connected to the PUA molecule by hydrogen bonds.