Preparation And Properties Of Biodegradable Coating Materials For Slow Release Fertilizers

A series of slow-release fertilizer coating materials were prepared with widely distributed, cheap and biodegradable polylactic acid (PLA) and starch as raw materials,by the method of physical blending of PLA and chemical modification of starch,respectively. The as-prepared coating materials were characterized by infrared spectroscopy (FTIR), X- ray diffraction (XRD), scanning electron microscopy (SEM),thermogravimetric analysis (TG) and contact angle analysis method, At the same time,the water absorption rate, urea permeability of and biodegradability under national conditions of coating material were studied. The main research contents and results are as follows:(1) A series of PLA/PVA blend membrane were prepared with two dimethyl sulfoxide(DMSO) as solvent and polyvinyl alcohol (PVA) was used to modify high molecular weight PLA by the method of casting. The SEM photos indicate poor compatibility between PLA and PVA and there is a certain phase separation. The urea permeability test showed that when m (PLA): m (PVA) equal to 19:1, the blend membrane had certain permeability, but with the increase of PVA content, the penetration efficiency becomes worse gradually.(2) A series of PLA/PEG blend membrane were prepared with Chloroform (CHCl3)as solvent and polyethylene glycol (PEG) was used to modify high molecular weight PLA by the method of casting. SEM photos and contact angle test indicated the blend membrane has good compatibility, and because of the introduction of PEG into PLA,the hydrophilicity increased. The urea permeability of urea solution and biodegradability test showed that the accumulated permeability of urea of 7 days increased form almost no release of unmodified PLA to the highest degradation of 31.7% of blend membrane. The biodegradation rate of 60 days increased from 8.2% to the highest degradation of 47.5%.(3) A series of crosslinked modified membrane were prepared with crosslinking modification of starch by PVA and formaldehyde used as crosslinking agent by the method of casting, The experimental results showed that the contact angle of the modified membrane increased, the water absorption rate decreased, the hydrophobicity increased and the accumulated permeability of urea of 7 days decreased with the increasing amount of cross-linking agent or increasing ratio of PVA to starch. Compared with the pure starch film, the urea permeability of the modified membrane was decreased, and the slow-release ability of nitrogen fertilizer was increased.(4) A series of graft modified membrane were prepared with pyridine as solvent, graft modification of Starch with Stearyl chloride by the method of casting. The experimental results showed that the hydrophobicity increased and the water absorption rate of 24 h is decreased from 272% of pure starch film to less than 12% with the increase of grafting degree. And the accumulated permeability of urea of 7 days decreased, with a minimum of up to 23.6%. After the modification, the biodegradation rate of the membrane decreased, and the degradation rate of 60 days decreased from 86% of pure starch to the highest was only 29.3%.