Synthesis And Properties Of Phosphorite Powder/Poly Superabsorbent Composite

Integrating of the function of fertilizer-supplying and water-retention, one of research and development in supperabsorbent plymer materials ,has been the hot spot in home and abroad now.In this paper, the composite prepared by modified phosphate powder and water supperabsorbent polymer is based on this point, having the phosphorus-supplying and water-retention functions with a view to gain a broader application in agriculture and forestry and drive the development and use of middle and low-grade phosphate rock at the same time.In this paper, the main research work are as follows:1. We have a research on modifying phosphate rock with the method of combinating partly acidification and inorganic mineral activation, and use XRD to characterize the crystal structure of minerals and compare the changes before and after modification to expatiate why the modified Phosphate powder can release phosphorus.2.We use the modified phosphate powder as a main added raw materials to supper absorbent polymer to prepare the modified phosphate powder/suppeabsorbent polymer composite. Through a series of five factors and four-level orthogonal experiment,We Study the influence of the addition of modified phosphate powder, neutralization degree of crylic acid and the amount of acrylamide, crosslinker, initiator on absorption properties of the composites, then we get the best experimental conditions after a range analysis analysis.we also set a series of single factor experiment on basis of the optimal conditions of the orthogonal to find the best condition for preparation.3. We have a research on the water retention and water absorbent speed of the composite sapmle added 10% modified phosphate powder with pure sample as a contrast.We also have a stuy on the influence of the amount of acrylamide,modified phosphate powder on swelling performance of the composites.4. We focus our research on phosphorus-release performance of the composite.at first, we find out the difference of phosphorus-release performance between modified phosphate powder and copmsite sample in the same immersion method,then we get the phosphorus-release performance of the same sample in different immersion method.we also stuy the phosphorus-release performance in shower method and the influence of samples with different amount of crossing linker and modified phosphate powder on phosphorus-release performance. 5. Finally, we have a deeply research on the absorbency capacity of the composite from the perspective of water potential. we based on the contrast of mechanism of plant cell and superabsorbent, and research the water potential of the composite which compound with modified and polysodium acrylate and acrylamide. We use hydrogel- liquid- exchange method to test water potential of a series of samples with different amount of modified phosphate powder and use different methods to fitg curve fitting on the water potential of composite materials to get empirical formula.then weahve a comparison to the result of water potential got from different methods of fitting. Through the water potential extrapolation formula, we get the limit of water potential value. at last, we have a discuss on the relation of water potential of composite, fluid absorbency rate and the amount of modified phosphate powder.Study findings were as follows:1 .The char of modified phophate powder still remain the characteristics diffraction peak of apatite and quartz, but the main characteristics of phosphate rock shaped passivation. While the the proportion of crystalline phase reduces, amorphous increases. Crystal size of the sample become smaller.It apears a series of new characteristic diffraction peaks at the same time,such as the characteristic diffraction peak of CaHPO₄.2H₂O(20=11.696, 20.786, 29.161, 33.408) and Ca(H₂PO₄)₂.2H₂O(2θ=7.595,14.790, 22.944, 24.165, 26.701, 29.777 ). It to say that the role of phosphorus in the modification change to the effective state.2. A modified phosphate powder/superabsorbent polymer composite was synthesized with acrylic and acrylamide as monomer, modified phosphate powder as main added raw materials, K₂S₂O₈ as initiator, and N,N-methylene-bis-acrylamide as crosslinking agent by means of water solution polymerization. The orthogonal experiment results show that the influence of the factors to composite sample on distilled water absorbency as follows: content of modified phosphate powder> neutralization degree of crylic acid >content of acrylamide>content of crosslinker > content of initiator. We choose the optimum conditions under two conditions which meet the absorbency of distilled water, normal saline ratio is greater than 150g/g, 30g/g respectively and the amount of modified phosphate powder added is largest.The optimum conditions are: 25% monomer concentration, reaction temperature is 75℃, content of modified phosphate powder is 40%, neutralization degree of acry acid is 70 percent, 20% acrylamide, content of crosslinker is 0.04%, initiator content is 0.3%.The results of the single factor experiment based on orthogonal experiment show that the best conditions for synthesis is 25% monomer concentration, polymerization temperature at 75℃, 0.04% cross-linker, 0.50% initiator, neutralization degree of crylic acid by 65%, 20% acrylamide, 40% modified phosphatepowder. Composite materials maximum absorption capacity of distilled water and 0.9% NaCl solution are 335g/g and 32g/g respectly.3. The water retention property of the composite can be improved by adding a certain amount of modified phosphate powder. The hydrogel loss about 50% water at the first 3 hours in the blast drying at 60℃,but the water content of hydrogels also around the 20-30% at 6 hours.When put at room temperature, the hydrogel can retain 50% water at 7 days. The swelling characteristics index values of samples are greater than 1,which is to say that relaxation of macromolecular chains is the main factors controlling the swelling ratio. Addiing modified phosphate powder to composite can increase the swelling speed, as well as reduce the contribution macromolecular chain relaxation to swelling ratio, and the influence can be amplifed by addition more modified phosphate powder to composites.4. Modified phosphate powder can release phosphorus as much as 36% in one day and there is still a certain amount of phosphorus released but very slow while the composite phosphorus-release is about 29% after soaking in a day in the same immersion method,and it remains the performance of phosphorus-release well.The amount of phosphorus released by the same ocmposite sample is about the same in two different immersion method. The amount of phosphorus remain the same in later in the liquid unchanged immersion method while it keep increasing in the liquid changed immersion method. With the amount of cross-linking agent changes, the amount of phosphorus released begin to reduce at first and become bigger later, but there is no big blank in the amount of phosphorus of the different samples.5.The modified phosphate powder can leacha large part of phosphorus under the shower method, the amount of phosphorus reach about 43% at the two days and there is still a certain amount of phosphorus released but very little. The phosphorus release speed of composite materials is slower than modified phosphate powder at the first days, then become faster than the modified phosphate powder, Which is different to the result got from the immersion method mainly due to different testing methods.The phosphorus-release rate of the samples which content less modified phosphate powder is bigger than the sample s content more at first while it become inverse in later. We received the total of phosphorus-release rate is smaller with the addition of modified phosphate powder increasing in the test of time, while combinatiing to the development trend of the two curves of the map can see that the total of phosphorus-release rates will tends to close the gap with the time extented.6.We use hydrogel- liquid- exchange method to test the value of equilibrium concentration of the samples soaked for different time, and converted the value into the corresponding water potential value.We use two different fitting method to the values of the samples which content different amount of modified phosphate powder to get the empirical formula.The two empirical formulas areψ=-e^a+bt andψ=a-bc'.By comparing the correlation coefficient R of the two fitting curves,we find that the second fitting method is accurater than the first one. The limit water potential value of the six samples content different amount of modified phosphate powder calculated by extrapolation with the second empirical formulas are as follows:That is to say adding a small amount (5%) of modified phosphate powder to composite materials can reduce the water potential (59%),and increase the water absorbency capacity. However, the water potential of composite materials increase and water absorption capacity began to reduce with the addition of modified phosphate powder continued to increase. We also find that the absorbent time have the similar inluency on water potential and water absorbency of the composites at the same time. with the suction time goes, water potential of the composites become bigger and water absorption capacity becomme weaker while water absorbency ratio become bigger. there must be relevant relationship between the water potential and water abosrbency ratio. Composites which have the least water potential can absorbentnthe largest amount of water.