Preparation Of Wheat Straw/Attapulgite Composite Super Absorbent Polymer And Its Application In Cucumber Substrate Cultivation

In this study,wheat straw and attapulgite clay were used as raw materials to prepare wheat straw/attapulgite composite super absorbent polymer.The effects of monomer mass ratio,neutralization degree of acrylic acid,initiator dosage,crosslinking agent dosage,wheat straw and attapulgite dosage on the absorbency of super absorbent polymer were studied,and the optimal synthesis process conditions of wheat straw/attapulgite composite super absorbent polymer were determined.On this basis,the structure and morphology of the super absorbent polymer were characterized by FTIR and SEM,and the characteristics of water and fertilizer absorbency,absorption rate and reusability of the super absorbent polymer were studied,which provided a theoretical basis for the application of the super absorbent polymer in substrate cultivation.Then,the effects of different amount of super absorbent polymer and nutrient solution concentration on physicochemical properties of substrate,growth and development of the cucumber,and the fruit yield and quality were studied by using the fruit-type cucumber‘Deltasta’as the material,in order to screen out the amount of super absorbent polymer suitable for cucumber substrate cultivation,provide theoretical basis and practical guidance for the effective utilization of agricultural waste straw and inorganic clay mineral resources,and the application of super absorbent polymer in substrate cultivation.The main results are as follows:1.Using wheat straw and attapulgite as raw materials,acrylamide（AM）and partially neutralized acrylic acid（AA）as composite monomers,N,N’-methylenebisacrylamide（MBA）as crosslinking agent,potassium persulfate and sodium thiosulfate pentahydrate redox initiator system as initiator,the wheat straw/attapulgite composite super absorbent polymer was successfully prepared by microwave assisted polymerization.The optimum synthesis conditions of SAP were obtained by single factor and orthogonal experiments as follows:the mass ratio of AA to AM was 2:1,the neutralization degree of acrylic acid was 60%,the mass ratio of initiator to monomer was 1.0%,the mass ratio of crosslinking agent to monomer was 0.15%,the mass ratio of wheat straw powder to monomer was15.0%,and the mass ratio of attapulgite powder to monomer was 5%.Under these conditions,the average water absorbency of the synthesized super absorbent polymer in deionized water was 929.64 g/g,and in 0.9%NaCl solution was 42.97 g/g.Moreover,the raw material cost calculation shows that the addition of wheat straw and attapulgite reduces the raw material cost of SAP by about 15%.2.FTIR analysis showed that the wheat straw/attapulgite composite super absorbent polymer was successfully prepared.SEM photos showed that the microporous and wrinkle structure on the surface of the SAP was beneficial to improve the water absorption capacity.The performance test results of wheat straw/attapulgite composite super absorbent polymer showed that the absorbency of SAP in NaCl,CaCl₂ and FeCl₃ solutions was NaCl>CaCl₂>FeCl₃,and the water absorbency decreased with the increase of salt concentration and metal cation valence in solution.The absorbency of super absorbent polymer in KCl and Yamazaki nutrient solution decreased with the increase of solution concentration,but the water absorbency of SAP in urea solution was almost unaffected.The optimum pH range of SAP is 5～11.In the range of 10～90°C,the absorption rate of SAP increases slowly with the increase of temperature,and the temperature adaptability is good.At high temperature,the water retention rate of the SAP can still reach more than50%,which has excellent water retention performance.At room temperature,it takes 5h for the SAP to reach water saturation,and the absorbency decreases with the water absorption process,showing a three-stage change.After repeated water absorption and water release for five times,the SAP still had a water absorption ratio of 223.17 g/g in deionized water,with good reusability.3、The wheat straw/attapulgite composite super absorbent polymer was added to the substrate for soilless cultivation of cucumber.The results showed that the use of SAP could improve the physicochemical properties of the cultivation substrate.When the dosage of water retaining agent was 0.4%（C）,the saturated bulk density,total porosity and water holding porosity of the substrate were significantly increased,and the effect on aeration porosity was small.Meanwhile,the SAP significantly increased the EC value of the substrate at each growth stage under the management of 1.0 and 0.8 times of nutrient solution concentration,and increased the contents of available N,P and K in the substrate at the fruit stage under C1.0 and C0.8 treatments.Among all treatments,C1.0（SAP dosage0.4%×1.0 times nutrient solution）had the most significant effect on cucumber plant growth promotion and photosynthesis at all stages.Furthermore,at flowering stage,the fresh weight and dry weight of aboveground and underground parts of C1.0 were significantly increased,the root activity was significantly enhanced,and the relative water content of leaves was significantly increased.The results of fruit yield and quality data analysis showed that the single fruit weight,fruit number per plant and yield per plant of C1.0 treatment was significantly increased.Moreover,the contents of soluble protein,soluble sugar and Vc in cucumber fruit were also significantly increased,while the content of titratable acid was significantly decreased.Treatment C1.0 also significantly improved the water use efficiency and fertilizer partial productivity of cucumber.The comprehensive analysis of the results showed that when the SAP was mixed with the cultivation substrate at the mass ratio of 0.4%and the nutrient solution dosage was 1.0 times the standard,the physicochemical properties of the cultivation substrate and the growth and quality of cucumber were the best.