Research On Starch-Based Biodegradable Coated Material For Granuled Slow-Release Fertilizer

The low fertilizer use efficiency is one of the main restriction factors in agricultural production and environmental protection, the common slow release fertilizers is difficult to be used widely for its slow release materials and complicated process. So the study of coating fertilizer was focus on reducing the production cost to expand the application, this research put forward a new method to prepare coating material from corn starch, and the starch based biodegradable films were prepared by a solution casting method. The permeation performances of starch based biodegradable films were tested by water and soil column leaching experiment, The main conclusions were as follows: 1. The process optimization for the preparation of starch based biodegradable films.(1) The optimal process condition of starch based biodegradable film was determined by orthogonal experiments. The results indicated that there was a significant effect of PCA and GPA on the tensile strength of starch film, and WPA, PCA and GPA had affected extremely significantly on the water absorption ratio of starch films. By orthogonal test, the optimum formula was: based on content of starch, WPA 20%, PCA 80, GPA 9 and glutaraldehyde 6. in this proportion, the tensile strength and water absorption ratio of starch film were 21.16MPa and 12.18% respectively.(2) The response surface analysis is used to confirm the optimal operating conditions of starch based biodegradable film, The results indicated that Crosslinking temperature had the most influential to tensile strength of starch film, then the stirring speed, the stirring time had little influence on tensile strength. By the response surface analysis, the optimal process conditions were: the crosslinking temperature was 90℃, the stirring time was 1.9h and the stirring speed was 611r/min. under this condition, the tensile strength of starch film reached to 21.35MPa.(3) The structures of the films were characterized by Fourier transform infrared spectrometry (FTIR) and scanning electron microscopy (SEM). The results indicated that the gel network was formed with glutaraldehyde in the films, there was not obviously phase separation in components. The microscope photos showed that the starch film had good biodegradability. 2. The permeation performances of starch based biodegradable films.(1) The weight loss rate experiment of starch based biodegradable film coated fertilizers showed that the slow release fertilizers had bad solution and slowly degrades (60%) in de-ionized water in 35 days. The dissolution rate of SPNPK was faster in first week, and the weight loss rate reached above 40% at the 7th day, then the nutrient release rate increased slowly, which was shown the good slow-release characteristics of starch based biodegradable film.(2) The water and soil column leaching experiment indicated that the release of N, P, K was slow at first, and then the release is quick, the nutrient released curve of slow release fertilizers showed "S" shape. The N, P, K dissolving percentage of SPNPK was less than 15% in 24h, and the total nutrient release of fertilizers is less than 75% in 28 days. The dissolving percentage of SPNPK decreased with capsular thickness increased and temperature decreased. The release mechanism is fit for the requirements of crops growth and is helpful to improve the utilization ratio of fertilizer.