| Coated slow/controlled release fertilizers can improve the efficiency of fertilizer use by regulating the release of nutrients to maintain a balance between the amount of nutrients released in the soil and the amount of nutrients absorbed by crops.At present,the coating materials of coated slow/controlled release fertilizers in research and application generally use a large number of difficult-to-degrade high-molecular polymers,which increases production costs and pollutes the environment.Aiming at the above two important issues,this paper first uses castor oil widely existing in nature as a natural vegetable oil-based polyol to prepare biodegradable polyurethane coating materials,and then uses a drum coating technology to obtain a polyurethane coated controlled release fertilizer.In addition,by adding nano-carbon black（CB）and nano magnesium hydroxide@stearic acid（Mg（OH）2@STA）as modifiers,the castor oil-based polyurethane film was hydrophobized to improve Controlled release properties of coated fertilizers.Through scanning electron microscopy,hydrostatic release,and pot experiment,the membrane shell structure and its nutrient controlled release properties were characterized and evaluated.The main results are as follows:（1）The effects of the types and proportions of castor oil-based polyurethane coating materials on the controlled release of coated fertilizers were investigated.Compared with isophorone diisocyanate and 2,6-toluene diisocyanate,the coating material synthesized with polymethylene polyphenyl polyisocyanate as the hard segment showed the best controlled release effect.In addition,as the amount of isocyanate added as the hard segment increases or the hydroxyl value of the castor oil polyol increases,the nutrient release period of the coated fertilizer becomes longer.When the coating fertilizer coating ratio is 5%,the castor oil polyol has a hydroxyl value of 208 mg KOH/g and an OH/NCO molar ratio of 1.0:1.2.The coated fertilizer obtained by the preparation has a nutrient release period of 140 days,and the coating can be easily adjusted by Material to material ratio,to achieve a nutrient release period of 20 days to140 days.（2）The effects of the amount of nano-carbon black on the surface hydrophobicity,thermal stability,morphology of coated fertilizers,and the controlled-release effect of coated fertilizers were investigated through nano-carbon black modified polyurethane coating materials.At the same time,the effect of coating material thickness on the controlled release effect of coated fertilizer was also explored.After the addition of nano-carbon black,the contact angle of the film surface can reach 152.6°.In addition,when the nano-carbon black modified polyurethane is used as the coating material,the nutrient release period of the coated controlled release fertilizer with coating rates of 2%and 3%is 21 days and 30 days,respectively.Compared with unmodified coating materials,the nutrient release period is extended by 10-12 days.（3）Corn pot experiments showed that compared with ordinary urea fertilizer treatment,the addition of nano-carbon black modified polyurethane-coated fertilizer can significantly promote the growth of corn.Under the same conditions,the plant height,weight and root length of corn pots with modified polyurethane-coated fertilizers increased by 26.8%,37.5%,39.76%,and 42.4%,respectively.（4）The effects of the addition amount on the surface hydrophobicity of the coating material,the morphology of the coating fertilizer,and the controlled release effect of the coating were explored through nano-Mg（OH）2@STA and paraffin modified polyurethane coating materials.At the same time,the effect of coating material thickness on the controlled release effect of coated fertilizers.Adding nano-magnesium hydroxide@stearic acid and paraffin-modified polyurethane changed the surface wettability of the film,significantly improved the hydrophobicity,and its surface contact angle reached 153.1°.In addition,the coating fertilizer coating rate is only1.5%,and the cumulative release period of unmodified polyurethane nutrients is less than 1 day.When the modified amount of nano-Mg（OH）2@STA and paraffin is 0.2g and 0.4g/200g urea,the cumulative release period of coated fertilizer nutrients can reach 33 days.It can be used to prepare low-coverage controlled-release fertilizer and reduce production costs. |
