Preparation of High Bio-Content Polyurethane Coatings from Co-Liquefaction of Cellulosic Biomass and Starch for Controlled Release Fertilizers

Abstract

To manufacture high bio-content degradable polyurethane-coated fertilizer, the co-liquefaction of corn straw and starch was carried out to convert more biomass into bio-polyol so as to substitute petroleum-based polyol. The effect of the corn straw to starch ratio on liquefaction behavior was mainly investigated by monitoring acid value, hydroxyl value, and liquefaction rate. Both chemical structures and properties of bio-polyols and their coatings were characterized by Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), etc. The results indicated that adding a certain amount of starch to corn straw for co-liquefaction could contribute to a higher hydroxyl content of bio-polyol than that from sole biomass. Compared to molecular weight, the hydroxyl value was a more significant index to ensure coating quality. The incorporation of starch segments to bio-polyol led to good thermal stability, limited residual small molecules, and high crosslinking density of the coating. The controlled-release ability of coated urea prepared by co-liquefied bio-polyol was better than that of corn-straw-based bio-polyol, and the optimal ratio of corn straw to starch was 3:1. Overall, this study provides a new route to fabricate corn straw as a cost-effective and degradable coating with good controlled-release properties, which benefits solid biomass recycling.