Degradation of polyurethane coating materials from liquefied wheat straw for controlled release fertilizers

ABSTRACT Polyurethane (PU) was synthesized by liquefied wheat straw and isocyanates for controlled release fertilizers (CRFs). CRFs coated by PU were buried in soil for 12 months. The degradation degree and mechanism of PU coating materials were observed by thermogravimetric analysis (TGA), Atomic Force Microscope (AFM), differential scanning calorimetry (DSC), X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Fourier transform infra‐red spectroscopy (FTIR). Significant microscopic morphology of PU exhibited many small chips or stereovision holes caused by biodegradation or hydrolytic degradation due to the presence of natural polymer wheat straw. AFM results depicted the plane and height topography changes of PU before and after 12 months burial time, showing the swelling morphology of buried PU. TGA and FTIR results confirmed the disintegration of PU polymer due to the presence of isocyanates monomers in the PU12. XPS revealed an accumulation of biofilm on the surface of buried PU, providing the evidence of biodegradation mechanism. Pot experiment indicated the resin residual coating has a positive effect on soil quality. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44021.