Superhydrophobic Biopolymer-Coated Controlled-Release Fertilizer:Fabrication And Nutrient Release Mechanism

Over the last decades,with the development of modern agriculture,polymer-coated controlled-release fertilizers have obtained increasing attention due to a variety of advantages,such as the high nutrient utilization efficiency,one-time fertilization mode,time saving.Nowadays,the coating materials of commercial controlled-release fertilizer are mainly derived form the petrochemical-based polymers,such as polyethylene,polyurethane etc.However,the high prices,non-renewable resources,non-biodegradable characteristic and other shortcomings,limit the large-scale promotion and application of controlled release fertilizers in agriculture.Therefore,the applications of natural bio-based coating materials to substitute petroleum-based coating materials have obtained increasing interests.Although commercialized slow-release fertilizers coated with petrochemical polymers have revolutionarily promoted agricultural production,the super hydrophilicity of biopolymer coating materials caused the short nutrient controlled-release longevity of biopolymer-coated contrllled-release fertilizer(often less than 2 months).Therefore,relevant technology should be developed to enhance the hydrophobic properties of biopolymer coating materials and improve nutrient controlled-release performance.Inspired by the natural creatures with superhydrophobic surfaces,researchers have developed biomimicry technologies to fabricate biomimetic superhydrophobic materials with superhydrophobic characteristics.The biomimetic superhydrophobic materials have been designed for various applications including antifouling,anticorrosion,antisnow,antifreezing,antimicrobial,and self-cleaning.Despite the biomimicry technologies have not been employed in the filed of controlled-release fertilizer,the relevant technologies and theories can be employed to fabricate superhydrophobic biopolymer-coated controlled-release fertilizer(SBCF).The overarching objectives of this paper are:The optimum fabrication condition of organosilane-modified SBCF and the mechanism of superhydrophobic surface to regulate the access of water into coating materials and dissolution of nutrient out of coating materials;The optimum fabrication condition of magnetic-sensitive nanoparticle self-assembled superhydrophobic biopolymer-coated controlled-release fertilizer;The direct observation of the air membrane on the interfaces between water and SBCF using synchrotron radiation-based X-ray phase-contrast imaging technology and the mechanism of superhydrophobic surface to regulate the access of water into coating materials and dissolution of nutrient out of coating materials;The two consecutive application of SBCF in field using rice as test crops.The main results were listed below:(1)Organosilane-modified superhydrophobic biopolymer-coated controlled-release fertilizer:Fabracation and mechanismThe biopolymer-coated controlled-release fertilizer was prepared by uniformly spraying the mixture of coating materials(cottonseed oil polyol and isocyanate)to the constantly rolling urea prills,which was preheated at(60±2)°C for 10 min in a rotating coating machine;The SBCF was fabricated by uniformly spraying the Si O₂ and diatomite hydrosols onto the constantly rolling biopolymer-coated controlled-release fertilizer to construct micronanoscale structure,and subsequent silanization process by grafting perfluorinated silane to reduce surface energy.SEM,SEM-EDX and XPS results revealed the successful fabrication of superhydrophobic biopolymer-coated controlled-release fertilizer.The water contact angle was 155.8°.Furthermore,the nutrient release longevity of SBCF revealed2-fold enhancement compared with the unmodified biopolymer-coated controlled-release fertilizer.The mechanism of superhydrophobic surface to regulate the access of water into coating materials and dissolution of nutrient out of biopolymer coating has also been clarified.(2)Magnetic-sensitive nanoparticle self-assembled superhydrophobic biopolymer-coated controlled-release fertilizer:Fabracation and mechanismThe SBCF with superior slow-release performance,water tolerance,and good feasibility for large-scale production was self-assembly fabricated using a simple,solvent-free process.The superhydrophobic surfaces of SBCF with uniformly dispersed Fe₃O₄ superhydrophobic magnetic-sensitive nanoparticles(SMNs)were self-assembly constructed with the spontaneous migration of Fe₃O₄ SMNs toward the outermost surface of the liquid coating materials(i.e.,pig fat based polyol and polymethylene polyphenylene isocyanate in a mass ratio 1.2:1)in a magnetic field during the reaction-curing process.SEM,AFM and XPS results revealed the successful fabrication of superhydrophobic biopolymer-coated controlled-release fertilizer.The water contact angle was 154.6°,water contact angle hysteresis was 1.5°.SBCF showed longer controlled-release longevity(more than 100 days)than those of unmodified biopolymer-coated controlled-release fertilizers.The governing slow-release mechanism of SBCF was clarified by directly observing the atmosphere cushion on the superhydrophobic biopolymer coating using the synchrotron radiation-based X-ray phase-contrast imaging technique.Liquid water only contacts the top of the bulges of the solid surface(10.9%),and air pockets are trapped underneath the liquid(89.1%).(3)Application of superhydrophobic biopolymer-coated controlled-release fertilizer in fieldThe SBCF was tested with two consecutive applications in field using rice as test crops on Dongying.The experiment has twelve treatment with two urea(biopolymer-coated controlled-release urea and uncoated urea),two nitrogen application amount(100%and 80%)and three potassium humate application amount(50,100 kg/ha and 150 kg/ha).Result revealed the treatment(SBCF,300 kg N/kg)can significantly enhance rice yields(9.35%),N utilization rate(17.72%);the treatment(SBCF,240 kg N/ha;potassium humate,150 kg/ha)can significantly enhance rice yields(14.48%),N utilization rate(59.16%)compared with traditional nitrogen application amount(300 kg N/ha)on experiment site.These showed SBCF has the potential to increase rice production.