[FTIR spectra study on the swellbility and controlled-release mechanism of polyurethane coated urea].

The nutrient release experiment of polyurethane coated urea (PCU) was carried out in pure water at 25 degrees C. 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 polyurethane coating. The swelling of polyurethane coating leads to the pores size change, and release rate is increased, so the "S" pattern curve of the nitrogen accumulative release is formed.

[FTIR spectra study on the film of polyurethane coated urea controlled-release fertilizer].

The polyurethane films were prepared to wrap the urea in order to achieve a desirable release rate by mixing isocyanate, polyols and wax. The effect of wax, urea and isocyanate on the structure and properties of the films was investigated by FTIR. The structural changes were monitored as the polyurethane films together with the wrapped urea were immersed into ammonia water for 28 days, which is used to model soil conditions. The FTIR results showed that the width and intensity of the NH-free band increased remarkably with time, and all kinds of carbonly bands shifted to high wavenumber and their intensity increased obviously. The results suggest that the structure of the polyurethane films was destroyed more heavily in soil than in water, and this explains the relatively fast release rate of urea in soil. It was observed that the increase in the chemical crosslinking density in the polyurethane films can effectively decrease the release rate of the urea nitrogen in soil.