Cross-linking of Poly(sodium acrylate)-Based Hydrogels by a Non-vinyl Cross-linker

Polyvinyl-based cross-linkers are most frequently used for internal cross-linking of hydrogels, while non-vinyl cross-linkers are used for surface cross-linking of hydrogels by reactions between the pendant groups of hydrogel and functional groups of cross-linkers. The type of internal or external cross-linking of hydrogels strongly affects their final properties. The type of internal or external cross-linking of hydrogels strongly affects the final properties of the products. In this research, the superabsorbent polymers (SAPs) based on partially neutralized acrylic acid (AA-NaAA) were synthesized by solution polymerization, using a series of new multifunctional cross-linkers such as polyethylene glycol diglycidyl ether (PEGDGE-300), ethylene glycol diglycidyl ether (EGDGE), 1,4-butane diol (BDO) and [3-(2,3-epoxypropoxy)-propyl]-trimethoxysilane (GPS) in the presence of ammonium persulfate-tetramethyl ethylene diamine (APS/TMEDA) as initiator. The molecular structures of PEGDGE and GPS hydrogels were detected by FTIR and EDX analyses. The type and concentration of cross-linkers were studied in relation to hydrogels’ free swelling capacity in distilled water and 0.9 wt% NaCl solution and their absorbency under load (AUL) and resulting rheological behavior. The result showed that the order of free swelling capacity in the hydrogels synthesized by these four cross-linkers was GPS PEGDGE EGDGE BDO. In a constant free absorbency capacity (about 200 g/g), the cross-linked PEGDGE showed the highest amount of AUL. Furthermore, the rheological results showed the higher swollen gel strength in this hydrogel and confirmed the AUL result. The swelling properties of non-vinyl cross-linkers strongly depended on drying temperature, and hydrogels cured at different temperatures exhibited different rheological properties achieved by a constant amount of cross-linker. The use of non-vinyl cross-linker is a new approach to synthesize hydrogels without any polyvinyl-based cross-linkers.