FTIR研究聚氨酯包膜尿素的溶胀度与控释机理

FTIR Spectra Study on the Swellbility and Controlled-Release Mechanism of Polyurethane Coated Urea

采用傅里叶变换红外光谱(FTIR)分析了聚氨酯包膜控释尿素(PCU)养分溶出过程膜层的结构变化。对比发现,随着溶出时间的延长,膜层的结构产生明显的改变,当养分累积释放量达到50%,膜层的红外谱图在3 435,3 342,1 671,1 621,1 448,1 159cm-1出现了新的吸收峰,与尿素的特征吸收峰3 440,3 347,1 667,1 624,1 460,1 154cm-1吻合,当养分累积释放量达到70%,新出现吸收峰的强度继续增加,此时膜层的红外谱图新增的吸收峰与尿素的红外谱图有较高的相似度。结果表明,新吸收峰的出现及增强是由于尿素在膜层连续相中含量增加引起的,含量越高表明膜层溶胀度越大,此时膜层微孔尺寸发生变化,导致养分释放速率的改变,养分释放曲线呈"S"形状。

The nutrient release experiment of polyurethane coated urea （PCU） was carried out in pure water at 25 ℃. With the release of urea, the structural variation of polyurethane coating was investigated by Fourier transform infrared spectroscopy （FTIR）, then a series of curves were collated and compared so as to better reflect the relation between diffusion rate of urea and coating structure. It was found that when the nutrient was released by 50% wt, new absorption peaks at 3 435, 3 342, 1 671, 1 621, 1 448 and 1 159 cm-1 appear in the FTIR spectra of polyurethane coating, moreover, the height of these absorption peaks was increased gradually when the nutrient was released by 70% wt, more importantly, these new absorption peaks are consistent with the characteristic absorption peaks of urea fertilizer, the spectra of urea were mainly characterized by bands at 3 440, 3 346, 1 672, 1 621 and 1 461 cm-1. The results show that the IR spectra variation was caused by the content of urea, existing in the polyurethane coating, and was increased gradually, The more the urea content, the greater the swelling degree of the polyure- thane coating. The swelling of polyurethane coating leads to the pores size change, and release rate is increased, so the ＂S＂ pat- tern curve of the nitrogen accumulative release is formed.