Study On Synthesis And Properties Of Modified Bentonite/Polyurethane Composites For Slow Release Fertilizer

The nutrients utilization rate of the coated fertilizer could be significantly improved,which could reduce the farming cost and environmental pollution.It has become the focus and hotspot in the research of the fe rtilizer.The key to controlthe nutrient release rate of coated fertilizerwas the choice of coating materials.The renewable soybean oil and bentonite as raw material of this study,a series of modified bentonite/polyure thane composites were made from soybean oil-based polyols,modified bentonite and polyisocyanate by means of solution blending.The soybean oil-based polyols were prepared through transesterification.Coated urea was prepared by drum method.In this paper,we study the main influencing factors of the modified performance of modified bentonite/polyurethane composites and the nitrogen slow release curve of coated urea.The results of the study were as follows:(1)The modified bentonite were prepared using Ca-bentonite as raw material,polyethylene glycol(PEG)or cetyl trimethyl ammonium bromide(C TAB)as modifying agent through solution intercalation way under the condition of ultrasonic dispersion.The structure and thermostability were characterized by XRD,FT-IR and TG.Results indicate that the interlayer spacing of modified be ntonite increasing which declare the modifier successfully intercalated into the layers of bentonite and the dispersion properties of modified bentonite in the organic phase was improved.The layer spacing of 10% PEG-bent and 30% C TAB-bent were 1.48 nm and 1.52 nm,respectively,which were selected with polyurethane composite.(2)The modified bentonite/polyurethane composites were obtained via solution blended process.Exploring the influence factors of composites such as the additive amount of modified bentonite,OH/NCO and temperature.At the same time,the mechanical properties and surface wettability of composites were studied.The best preparation conditions for composite materials were as follows: modified bentonite addition amount was 5 wt%,OH/NCO mole ratio was 1:1,curing film forming temperature was 65?.The tensile strength of the MBT/PU and OBT/PU composites were 13.53 MPa and 11.33 MPa,respectively,under the optimum preparation conditions.Meanwhile,the MBT/PU composite has certain hydrophobic and OBT/PU has certain hydrophilicity.(3)The structure and property of modified bentonite/polyurethane composites were characterized by FT-IR,TG,SEM,etc.Results showed that when the modified bentonite addition amount of 5 wt%,the clay could be spread evenly in the polyurethane matrix and composited with polyurethane effectively;and the composites had good thermal stability.The MBT/PU,OBT/PU and soybean oil-based polyurethane were buried in soil three months.The results show that the mass loss of the soybean oil-based polyurethane,MBT/PU,OBT/PU and illegal cooking oil-based polyurethane was 2.74%,3.23%,3.86%,respectively.The morphology of the three films was observed by optical microscope,and the structure of the films was found to be destroyed.(4)Under the same coating process conditions,coated urea was prepared by drum method.The initial release rate of the three layers of pure polyurethane coated urea was 9.21%,and the cumulative release rate of 28 days was 82.17%.taking into account the costs and nutrient release rate,the coated urea was prepared using the composite material as the coating material and the number of layers of the three layers.(5)The initial release rates of MBT/PU composite coated urea and OBT/PU composite coated urea were 5.01% and 5.32%,respectively.The 28 days cumulative release rate of MBT/PU composite coated urea and O BT/PU composite coated urea was 48.42 % and 50.36 %,respectively.And those in line with sustained standard GB/T 23348-2009.Through the testing of wear resistance of coated urea,the nitrogen initial release rate of coated urea prepared by composite material was less than 15% after three hours of wear by ball mill.However,the nitrogen initial release rate of pure PU coated urea was more than 15% after three hours of wear by ball mill,which does not meet the standard.The wear resistance of composite coated urea is better than that of pure PU coated urea,which is convenient for storage and transportation.