Study On Preparation Of Bio-based Polyurethane And Its Sustained Release Properties Of Coated Fertilizer

Bio-based polyurethanes are widely used in agricultural coatings,cling film and fertilizer coatings due to its sustainable recycling,degradability and low cost,etc.As a by-product of the production process of hogwash oil,the recovered oil had often been casually treated and ignored for it is used less frequently,not only it maintains the original oil molecular structure,but also innocuous and harmless,resulting in waste of some resources and pollutes the environment.Fertilizer,as a key factor in sustainable agriculture and crop production,has been concerned about its utilization efficiency and increase crop yield.The coated fertilizer with controlled-release behaviors is a research hot-spot in the fertilizer industry,and its coating materials is the key to the coated fertilizer.However,most of coating materials are high cost and environmentally harmful,which limits the application of coated fertilizers.Therefore,we hope that the recovered oil can be used as the raw material of the synthetic polyurethane to realize the combination of recycled oil’s reuse and fertilizer coating materials.We expect to provide a new field for the application of the recovered oil,which can not only save resources,but also reduce the cost of coated fertilizers.In this article,we developed the organic silicone-modified recycled-oil-based polyurethane as a coating material to prepare degradable polymer coating urea for constant fertilizer release.The moisture,heat resistance,and sustained release properties of polyurethane coating materials were investigated by modification with hydroxyl-terminated polydimethyl silicone(HTPMS)andγ-Aminopropyl triethoxy silane(KH550).In order to improve the brittleness of the modified polyurethane,the modified polyurethane was toughened by polycaprolactone(PCL),and the moisture,heat resistance,and flexibility of the modified polyurethane were investigated.The main results are as following:(1)The recycled oil was achieved by purification of the recovered oil,and it has maintained the molecular structure of carbon-carbon double bonds groups.After pre-modification of recycled oil,the content of hydroxyl groups was increased and novel bio-based polyurethanes were synthesized.Compared with the unmodified PUs,the hydrophobicity of modified PUs was increased by 48%to 74%;the coating water permeability of modified PUs was reduced by 31%to 54%;the thermal stability of modified PUs was increased;the N cumulative release of modified PCUs was less than 70%on the 30th days,which were considerably lower than that of unmodified PCUs(over 90%on the 30th day).When the content of KH550 was 20%,the water contact angle of modified PUs was the biggest(113.31 ~o),and the water permeability of modified PUs was the lowest(10.91%).(2)The hydrophobicity of modified PUs was increased:compared to the unmodified shells,which the value was 65.1°for contact angle,the water contact angles of H-PUs-1,H-PUs-2 and H-PUs-3 were 94.6°,108.9°and 123.3°,respectively.The thermal stability of modified PUs was increased:the decomposition temperature of PCUs-1#,PCUs-2#and PCUs-3#were increased,and the glass transition temperature(T_g)of PCUs-1#,PCUs-2#and PCUs-3#were increased to 88.8℃,94.9℃and 98.1℃,respectively(PCUs-0 was 87.5℃).The coating water permeability of modified PUs was reduced:the water permeability of K-PUs and H-PUs were 11.0%and 10.0%(the unmodified shells was 23.6%).The release percent of nitrogen from the modified polyurethane was significantly reduced:the release percent of unmodified PCUs reached 30percent after 5 days and the release percent reached 90 percent after 25 days;however,the release percent of modified PCUs reached 18 percent after 5 days,the release percent reached 50 percent after 15 days and the release percent reached 70 percent after 30 days.(3)Compared to the unmodified shells,which the value was 65.1°for contact angle,the hydrophobicity of modified PUs was greatly increased(the value of contact angle was about 100°).The water permeability of modified polyurethanes was greatly decreased,which the value was7.8%for water permeability(the water permeability of PUs,K-PUs and H-PUs were 23.6%,11.0%and 10.0%,respectively).The thermal stability of modified PUs was increased and the release percent of nitrogen from the modified polyurethane is greatly reduced:the release percent of unmodified PCUs reached 90 percent after 30 days,however,the release percent of modified PCUs by KH550/HTPMS reached 15 percent after 5 days(except for the ratio of KH550/HTPMS was 0.5:0.5,which the release percent reached 18 percent),the release percent reached 30 percent after 15 days(except for the ratio of KH550/HTPMS was 0.5:0.5,which the release percent reached 40 percent)and the release percent reached 60 percent after 30 days.(4)Toughening of KH550/HTPMS modified polyurethanes with PCL was achieved by miscibility between two phases.When the content of PCL was 30%,the best miscibility and elemental distribution between K-H-PU and PCL,and the high crystallinity of PCL does not affect the amorphous structure of modified polyurethanes.After the modified of organic silicon and the toughened of PCL,the temperature of polyurethane’s decomposition in the first stage was raised about 100℃and in the second stage was almost unchanged.Therefore,toughened of modified polyurethanes with PCL does not have a negative effect on its thermal stability.The bonding degree of modified polyurethane after toughened was significantly improved,when the content of PCL was 30%,the bonding degree reaches the maximum(80.8%),the water permeability reaches the minimum(1.6%)and the water contact angle reaches the maximum(120.9°).According to the cross-sectional microscopic morphology of P/K-H-PU before and after acetone treatment,it can be seen that the miscibility between K-H-PU and PCL were increased with the content of PCL increases.When the content of PCL was 30%,the bonding degree of P/K-H-PU was greatly increased,due to the formation of a mosaic network structure and a wrap structure of imitating"pomegranate"between K-H-PU and PCL.The bending test results show that toughened of modified polyurethanes with PCL,P/K-H-PU gradually changes from brittleness to toughness,and the toughness of P/K-H-PU were increased with the content of PCL increases.It has good sustained release properties.