Preparation And Property Research Of Degradable Polymer Coating For Controlled Release Fertilizers

The slow/controlled release fertilizer can effectively solve the problems such as the low utilization rate and environmental pollution caused by using chemical fertilizer.Polymer-coated urea(PCU)has good controlled release property and can be divided into polyolefin and polyurethane(PU)and other types.However,these polymers are high-cost but non-biodegradable,which can be potentially harmful to the soil environment.Corn starch is low-cost,renewable,and rich in hydroxyl groups.Thus,starch is a potential raw material for coatings.In this study,the effects of liquefaction parameters including solvent dosage,time,temperature,catalyst dosage,and ratio of corn starch and solvent on physical property of liquefied products were studied by means of single factor experiment.The effects of the percentage of liquefied starch and liquefaction parameters on coated fertilizers’ properties were studied by means of single factor experiment.Furthermore,the structure of coatings prepared under the different liquefaction time was explored.Finally,the effects of molecular sieve on structure and property of coating were studied after adding different amounts of homemade molecular sieve into coating.Results were as follows:1.It was deduced that liquefied products’ residue rate and viscosity decreased with the increase of catalyst and ratio of solid to liquid,but change of hydroxyl value was different.Liquefied products’ residue rate increased with the increase of glycerol in liquefacient,and the viscosity firstly increased and then decreased,hydroxyl value firstly increased and then decreased.Liquefied products’ residue rate firstly decreased and then increased with the increase of liquefaction time and liquefaction temperature,but change of viscosity and hydroxyl value were different.FTIR spectra of liquefied products showed that they were polyether polyols.2.It was shown from single factor experiment that the ratio of 1:1 was appropriate to replace polyol by starch liquefaction product.And coated fertilizer with good controlled release performance was synthesized under the following factor:5%of catalyst,1:6 of mass ratio of solid to liquid,7:3 of mass ratio of PEG 400 to GL,120 min of liquefaction time,and 170 ℃ of liquefaction temperature.3.The coating layers prepared using liquid products with different liquefaction time were characterized by SEM,TG,FTIR and water absorption.It was indicated that the surface of coating was smooth,dense and no significant defect existed,and the thickness was about 42 μm.The interface of coating and urea closely combined.TG and DTG measurements showed that coating prepared under the liquefaction time of 60 min film displayed best thermal stability.SEM images showed that a large number of micro cracks and residue appeared on the surface of coatings after buried in soil for ten months,which implyed that the coatings were biodegradable.Carbamate,methyl and methylene groups became weak based on FTIR analysis.With the increasing of liquefaction time the water absorption of coating reduced at first and then increased.4.Homemade SBA-15 molecular sieve was added into the coating liquid for the purpose of modifying the liquefaction product based coating.At the amount of 1%the N release duration was 140 d,which had doubled over the blank.