Synthesis And Properties Of Polyaspartic Acid And Its Hydrogel Materials

Polyaspartic acid(PASP)is a green and biodegradable polymer material that has attracted much attention.It has been widely used in various fields such as agriculture,medicine,and water treatment.In this paper,maleic anhydride and ammonia water were used as raw materials to synthesize PASP in three steps.The processes of solid phase polymerization and liquid phase polymerization were compared and the process conditions were systematically discussed.A series of intermediate polysuccinimide(PSI)and final product PASP were prepared and characterized.The results of infrared characterization analysis confirmed the successful synthesis of PASP.We tested its relative molecular weight by gel chromatography and ubbelohde viscosity and investigated the yield of the product.In order to obtain the best process conditions,a series of single factor research experiments were carried out,such as temperature,time,catalyst and solvent.The results show that the catalyst has a great effect on the molecular weight.For the characteristics of liquid phase polymerization,a solid acid catalyst is used.Under the optimal conditions,the molecular weight of PASP synthesized exceeds 10,000,and the molecular weight distribution is concentrated.Solid phase polymerization uses a multiple polymerization method instead of the use of a phosphoric acid catalyst,which increases the molecular weight of PASP to a certain extent,but the molecular weight distribution is relatively dispersed.The PASP yields obtained by the two polymerization methods are all higher,and can reach more than 95%.Synthetic dyes have great harm,so the research on the purification technology of dye wastewater is of great significance.Among them,the adsorption method has become an important means of dye wastewater treatment with its unique advantages.Polyaspartic acid molecules contain carboxyl,amide bond and other active groups,so it has good hydrophilicity and high chemical activity.As a result,PASP has a good decolorizing effect on the dye,and it can be used as a material for treating dye wastewater.However,good water solubility makes it difficult to separate and recover,it is difficult to be widely used in water treatment.Therefore,it is necessary to develop new composite materials and expand the application of PASP in this respect.In this paper,PASP was used as the skeleton to prepare PASP/MMT composite hydrogel with acrylamide and montmorillonite(MMT)under the action of initiator ammonium persulfate and crosslinker N,N methylene bis acrylamide.We successfully proved the PASP/MMT composite hydrogel by FTIR and XRD characterization techniques,and systematically discussed its swelling and adsorption properties.And the adsorption conditions and adsorption process of methylene blue dyes by composite hydrogels were studied.In order to obtain the best adsorption conditions,we conducted a single factor variable study on a series of conditions such as pH,temperature,initial concentration and MMT dosage.At the same time,we discussed the adsorption isotherms,adsorption kinetics and adsorption thermodynamics of the adsorption process.The results show that the composite has good adsorption effect on methylene blue,and the removal rate can reach more than 99%.The adsorption behavior of the hydrogel belongs to the Langmuir type monolayer adsorption,and the kinetic behavior accords with the second-order kinetic model.The adsorption process is an endothermic reaction,so the elevated temperature is favorable for the adsorption.