Formation And Control Of Porous Structure Of Acrylate Super-absorbent Resin Micro-spheres And Mechanism Research Of Pore-forming

Super-absorbent resin (SAR) which can absorb and retain a lot of aqueous liquid has been playing an more important role in many fields, such as medicinal products, hygienic products, agriculture, and forestry horticulture, etc.. Desiring features of SAR should have the capacity of super-absorbent, super-absorbent rate and good strength of the swollen gel. Porous SAR has been considered as an important process in increasing absorbent capacity and absorbent rate. At present, the most study of porous SAR are on synthetical methods, especially on aqueous solution polymerization., but without the study of mechanism and control of pore-forming in domestic research. Therefore, porous SAR micro-spheres were synthesized by inverse suspension polymerization (ISP) in this work and the relationship between porous structure and performance, the formation and control of the pore, the mechanism of pore-forming have already been explored in this work.(1) Ammonium persulfate as an initiator and N,N'-methylene-bis-acrylamide (NMBA) as a crosslinking agent, the porous micro-spheres of AA-AANa-AM copolymer were synthesized by ISP. Then the product was filtered and washed by methanol. The morphology, constitution and micro-spherical structure of the copolymer are characterized with FT-IR, SEM and EDS. It is indicated that the porous SAR micro-sphere has been successfully synthesized. When the mass ratio of AM/AA was 1/2 and the mass ratio of (APS+NMBA)/(AA+AM) was up to 0.46wt%, the porous structure is optimal with connecting and open pore. Exploring the mechanism of the pore-forming, it is indicated that the differences in the mass ratio of AA/AM during the polymerization of copolymer, the outside induction and the rigidity of network are the main factors for formation of the porous structure. The more bigger difference of the copolymer's structure, the stronger outside induction and the stronger the rigidity of the network, the more number of the pore can be found in the micro-spheres.(2) Acrylate porous SAR micro-spheres were synthesized with PEG as a pore-forming agent. The promotion of pore-forming can be promoted by PEG assisting. When the content is up to 13.33% PEG600 (calculated by the amount of AA+AM), the alveolate porous morphology appeared and as a pore-forming agent, the PEG6000 has a negative effect on pore-forming. It is shown that some obligations of porosigen technique are inevitable which are facile and removable pore-forming agent, eluate by which pore-forming agent can be washed completely and appropriate network stabilizer which assists porous stabilization. Methanol plays a role as network stabilizer and eluate which fulfills the pore-forming and stabilization. Increasing crosslinking and rigidity of network can improve porous stabilization.The porous SAR micro-spheres which were synthesized in this work have remarkable capillary effect and high soaking rate. The water absorbtion rate is 9s/(100g·g^-1), one order of magnitude faster than that of non-porous SAR micro-sphere. Because of more loosen structure which is easer to be expanded, the porous SAR micro-spheres have higher absorbent capacity. The more number of the pore is, the better absorbent performance the porous SAR micro-spheres have.The structure of SAR micro-spheres which were cross-linked with Al³⁺, Ba²⁺ or Ca²⁺, is still porous, which possessed many disperse small pores on the surface and many dense big pores inside. However, the thermal properties of SAR micro-spheres are highly improved, especially thermal decomposition temperature up to above 100℃.