| Polyaspartate(PAsp)superabsorbent resin,as a novel biodegradable polymeric material,has been widely used in many fields.However,its application is limited due to the poor performance of salt tolerance and low gel strength resulted from the simplex functional group.In this paper,polysuccinimide(PSI)was prepared by the thermal polycondensation method using L-aspartic acid as the raw material.Kaolin was modified and introduced into the inverse-phase suspension system to prepare the composite of PAsp/organo-kaolin.PAsp superabsorbent resin was prepared from PSI using hexamethylendiamine as the crosslinking agent,liquid paraffin as the dispersing medium,and DMF as the polar solvent.When the content of dispersant and crosslinking agent,the stirring rate,the volume ratio of two solutions,the concentration of PSI in DMF solution was 0.6 and 4.5 wt%,200 rpm,3:1,20%,respectively,the average diameter of particles was about 400?m.Moreover,the average diameter of particles got bigger as the amount of crosslinking agent increased and that of dispersant decreased.In order to improve the properties of PAsp resin and cut production cost,kaolin was modified and introduced into the resin.First,organo-kaolin was prepared through the reaction between kaolin and the hydrolyzate of 3-Triethoxysilylpropylamine(KH550)in order to introduce the amino groups on the surface of particle.Then organo-kaolin was introduced into PAsp resin to synthesize PAsp/organo-kaolin composite.The effects of the reaction paramenters on the contents of amino groups on the surface of kaolin were studied through orthogonal experiments:the content of KH-550>the content of kaolin>temperature>reaction time.The equilibrium swelling ratio of the composite was investigated as a function of the organo-kaolin content.When the content of organo-kaolin was 3%and the content of amino groups on the surface of kaolin was 0.051 mmol/g,the swelling ratio of PAsp/organo-kaolin could reach 753 and 125 g/g in distilled water and 0.9%NaCl solution,respectively,which was improved by 29.6%and 28.9%compared with PAsp.The SEM characterization of PAsp/organo-kaolin revealed an structure with uniform surface,compact pores,which supported the good swelling behaviors of the superabsorbent resin.The XRD analysis revealed that the thermal stability temperature of PAsp/organo-kaolin was 275.6?,which was improved by 4.8?compared with PAsp.The salt resistance,pH sensibility and temperature response of the composites were also intensively studied.The results indicated that he water absorbencies of PAsp/organo-kaolin as a function of pH,temperature and concentration of inorganic salt were all superior to that of PAsp.Moreover,the water absorbency decreased as the concentration of inorganic salts increased.During the experiments of the temperature response,the water absorbency increased until the critical point was reached,and then decreased as the temperature increased.In addition,the polymeric networks sharply swelled as the external pH value increased until a plateau was reached for both PAsp/organo-kaolin and PAsp.The water retention capacity and multiplied water absorption were also tested.The results showed that the water retention ratio of PAsp/orgao-kaolin was 92.3%and 81.5%after 7h at 40°Cand 60°C,respectively,which was improved by 3.6%and 4.2%compared with PAsp.After four times of water absorption,the ratio of PAsp/organo-kaolin was kept at 81.1%,which was improved by 3.7%compared with PAsp.Moreover,the swelling kinetics were also discussed and it's believed that the introduction of organo-kaolin could change the Fick diffusion in PAsp to non-Fick diffusion in PAsp/organo-kaolin composite resin. |
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