Synthesis Of Mechanical Activated Starch Graft Acrylic Acid Superabsorbent In Inverse Emulsion

Superabsorbent (SAP) is a special functional polymer material with three-dimensional structure, and widely used in health care, food packaging, construction engineering, agriculture landscape, oil drilling, and storage. Inverse emulsion polymerization method has fast polymerization rate, high solid content and mild reaction conditions, overcoming the cooling difficult and gel formation of solution polymerization method. The article synthesized the resin by inverse emulsion polymerization, and then modified it by surface crosslinking. The details were as follows:(1) The stability of inverse emulsion with mechanical activated starch and acrylic had been researched. Factors including HLB value and the amount of emulsifier, stirring rate, monomer-starch quality ratio, and oil-water volume ratio, which had effects on the emulsion stability, were considered. The results showed that when the amount of emulsifier was5%-6%, HLB value was6.5-7.8, oil-water volume ratio was1.0-1.4, monomer-starch quality ratio was1.0-5.0, and stirring rate was400-600rmin-1, the inverse emulsion had well stability.(2) Superabsorbent was prepared by inverse emulsion polymerization of acrylic onto mechanical activated starch, with N, N’-methylene-bisacrylamide as crosslinker. The monomer-to-starch quality ratio, neutralization degree, and concentrations of the cross-linker and initiator, on the water absorption of the SAP were considered. The optimum conditions were obtained by orthogonal experiment:initiator content was0.6%, cross-linker content was0.12%, neutralization degree was80%, and monomer-starch quality ratio was10:1, under which conditions, the distilled water absorbency was931g-g’1, and the saline absorbency was91g-g-1. Compared with cassava starch grafted acrylic superabsorbent (prepared by Chen Zhanyun, distilled water absorbency was835g-g-1), the distilled water absorbency was greatly improved.(3) Surface crosslinking was carried out to improve the properties of the SAP, using CaCl2、AlCl3and ECH as surface crosslinker, and factors as surface crosslinking time, concentration and type of surface crosslinker, et al were investigated. It was suggested that surface crosslinking could significantly increase the absorption properties. Under the experimental investigated conditions, the suitable surface crosslinking time was1.5h, and0.3g-L-1AlCl3-ethanol solution had the best modification performance, in which case, the absorbent capacity of the resin achieved maximum, respectively, distilled water absorbency was972g-g-1, and saline absorbency was119g-g-1. Compared with uncross-linked superabsorbent that described as (2), the saline absorbency increased by about31%, indicated that the surface crosslinking can improve the salt-resistant performance of the resin.(4) The repeated water absorption, water retention, and water absorption rate of superabsorbents were tested. The resins had good repeated absorbent capacity to keep a long service life, and water retention capacity and water absorption rate were significantly increased by surface crosslinking.(5) FTIR, DSC, SEM and XRD were used to characterize the structure of starch and resin products. FTIR and DSC had inferred that the polymerization of mechanical activated starch graft acrylic had successful occurred. It could be seen from the SEM photo that, surface crosslinking reaction on the surface of the superabsorbent had happened. And the XRD pattern had proved that superabsorbent had amorphous structure.