Instant catapult steam explosion pretreatment of wheat straw liquefied polyols to prolong the slow-release longevity of bio-based polyurethane-coated fertilizers

Abstract

The direct liquefaction product of crop straws for bio-based polyurethane-coated fertilizers (BPCFs) has low hydroxyl values and complicated composition types, resulting in poor crosslinking degree, high hydrophilicity, and short release longevity. This study created an efficient physicochemical instant catapult steam explosion pretreatment wheat straw (SEWS) technology to remove small molecular hemicellulose and difficult-to-film-forming ions, improve straw liquefied polyol quality, and extend the release longevity of BPCFs. The results revealed that the steam explosion process (2.0 MPa for 5 min) broken the straw cell wall, hydrolyzed hemicellulose, and significantly decreased the difficult-to-film-forming ions (K+, Ca2+, and Mg2+). The SEWS liquefied residue rate dropped 38.1% to 5.5%, while the hydroxyl value increased 36.51% to 125.32 mg KOH g−1. The liquid polyol of SEWS and diphenyl-methane-diisocyanate formed a tightly cross-linked, homogenous bio-based membrane with no visible holes. Under the condition of 3% weight of the core fertilizer, the release longevity of SEWS increased from 14 to 32 days. The use of instant catapult steam explosion technology for high-efficiency pretreatment of biomass materials is conducive to improving the quality of bio-based polyols and the industrial production of bio-based controlled-release fertilizers. Furthermore, the pretreatment technology promotes the use of biomass for sustainable agriculture.