The Study On Starch Coating Material Of Slow Release Fertilizer

The study of coating fertilizer was focus on reducing the production cost to expand the application. This study put forward a new method to prepare coating material from corn starch. The corn starch acetate was prepared to improve the processability, mechanical property and the compatibility of native starch with polymer. The compound coating materials were prepared by starch acetate blended with PVA or EVAMA. The permeability of the coating material was tested by determine the releasing rate of urea. The slow-release effect of the coating fertilizer was proved by determine the nutrient releasing rate in water.Main conclusion of this paper:1. The property of low degree of substitution starch acetate (LSA) was studied. The results indicated that with the increase of DS, the transparent ratio rose, the anti-shear force enhanced and the freeze-thaw stability improved. DSC curves showed that the thermal stability was improved.2. The transparence ratio of LSA/PVA film rose with the increase ofDS (DS≤0.13), which indicated that the compatibility of LSA with PVA was very good.3. The optimal process condition of LSA/PVA film was determined by orthogonal experiments. The optimal reaction condition was as follows: PVA 85%, nano-SiO₂ 5%, hexamethylene tetramine 14% and glycerol 12%. The FTIR spectrum, DSC and SEM results showed that n-SiO₂ combined with PVA and LSA to a new three -dimensional network configuration and the compatibility and thermostability of the film modified by n-SiO₂. The microscope photos showed that the LSA/PVA film had good biodegradability.4. The microwave catalytic technology was used in the procedure of high degree of substitution starch acetate (HSA). The results showed that the microwave could accelerate the reaction rate. The parameters of starch acetate such as solubility and thermostability were evaluated. The results showed that thermostahility and liposolubility of HSA was improved compared with native starch. X-ray diffraction pattern demonstrated that crystal structure of HSA was destroyed evidently.5. Molau experiment results showed that the compatibility of HSA with EVAMA was good and EVAMA acted d as emulsification in the solution. The transparence ratio of LSA/PVA film rose with the increase of DS (DS≤0.13), which indicated that the compatibility of LSA with PVA was very good. The tensil strengh of HSA/EVAMA film rose with the increase of DS (DS≤2.2). 6. The reaction of malefic anhydride melt-grafted ethylene vinyl acetate copolymer was studied. It was confirmed by FTIR that the graft reaction did take place.7. The response surface analysis is used to confirm the optimal operating conditions of HSA blends with EVAMA. The results were: EVAMA180%, plasticizer110%, the mould temperature 190℃. X-ray diffraction pattern demonstrated that crystal structure of blends was destroyed through the plasticization and its crystallinity drops evidently. In comparation with unmodified EVA, compatibility between HSA and modified EVA is enhanced according to the results of SEM. The microscope photos showed that the HSA/EVAMA film had poor biodegradability.8. The para-dimethylamine benzaldehyde colorimetry was used as a rapid assessment of the film property of controlled release. The results of the permeability of urea indicated that starch acetate compound film can be applied as material for controlled release. The results indicated that the release rate of urea of LSA/PVA film decrease when the film thickness beyond 0.193mm, and the release rate declined with the prolong of time. In the case of same thickness, the accumulation release rate of HSA/EVAMA film was lower than LSA/PVA film, which indicated that the permeability property of HSA/EVAMA film was poorer.9. The release rate of coated fertilizer in water was studied by conductivity method. The results indicated that temperature had significant effect on the release rate in water. The release rate rose by increases in temperature. The accumulation release rate of LSA/PVA coated fertilizer in water for a month had reached to about 93% and that of HSA/EVAMA coated fertilizer was about 80%, which meant that HSA/EVAMA coated fertilizer could control the release rate of nutrient longer comparatively.