Preparation And Properties Of Clay/Polyacrylic Acid (Potassium Polyacrylate) Used For Controlled Or Slow-Release Fertilizer

In this paper, the composites of clay/polycyclic acid (potassium polyacrylate)were prepared through the method of solution polymerization by meerschaum,attapulgite, montmorillonite and partly neutralized acrylic acid, and the structure ofthe samples were characterized by FTIR and SEM. The effects of reaction conditionon the water absorbency, water retention and NH4+permeability of the compositeswere investigated and optimized. The clay/polyccrylate coated compound fertilizerswere prepared by drum coating machine, and their water absorbencies,biodegradable performance and the nutrients release behaviors were studiedsystematically. The variation of nitrogen, phosphorus and potassium in coatedfertilizer with time was investigated by infusion and intermittent leaching method.And the release rule of nutrient was also explored with math equation. The mainresults were as follows:(1) The slow-release, hydroscopic property and water-retention properties ofthe composites were remarkably improved as a certain amount of meerschaum,attapulgite, montmorillonite were added into the polymerization system separately.This reflects that the water absorbency of the composite is affected by the varietiesof clay and the content of clay, crosslinker, as well as initiator. The optimumcondition, which has been obtained in this experiment is as as follows: initiatorcontent was1.2%, crosslinker content was0.1%. In addition, When the attapulgitecontent was2%, the water absorbency of the composite reached a maximum. When5%of meerschaum was added to the reaction system, the product also had anexcellent water absorbency, while the reaction system contained10%ofmontmorillonite, that the composite had the largest water-holding ratio. Moreover,the transmission of ammonium could be reduced by the membrane of the compositefilm.(2) The compound fertilizer were successfully coated by the composites ofclay/polyacrylic acid (potassium polyacrylate) prepared in this paper. They areenvironmentally-friendly and have the function of biodegradability. The water absorbency of the coated fertilizer is affected bythat of the coating material. Therelease rate of nutrient reduces when the encapsulation increases. With the sameencapsulation, the slow-release property of potassium polyacrylate coated fertilizeris most inferior. While, that of meerschaum/polycyclic acid (potassiumpolyacrylate) coated was strongest. When the encapsulation was5%, the releaserate of nutrient of potassium polyacrylate coated fertilize reached34.5%which wasthe maximum value. The value of meerschaum/polyacrylic acid (potassiumpolyacrylate) coated fertilizer was only14.1%. Moreover, the release rate isdifferent among nitrogen, phosphorus and potassium in the coated fertilize with thesame coating material.(3)The relationship between the release ratio of nutrient and time can bedescribed as y=a·x~bwhere a and b are the functions of nutrient release andcharacteristic of coating material. The diffusion behavior of nutrient can be alsoexpressed as D=A·x~Bwhere D is diffusion coefficient, as well as A and b arefunctions of diffusive temperature and time. The diffusion coefficient decreasesover time and increases with the rise of temperature. The diffusion coefficient ofnitrogen, phosphorus and potassium are lowered accordingly under the same testingcondition. Furthermore, in the initial stage of release, the diffusion coefficientreaches a maximum value.