Hidrogéis e copolímeros de goma do cajueiro e poliacrilamida

Abstract

Semi IPN hydrogels and graft copolymers based on acrylamide and cashew gum were prepared and characterized. The polymerization reaction was done in solution, using redox initiation. A series of graft copolymer varying in acrylamide concentration and keeping the concentration of the initiator and polysaccharide constant was prepared. These grafts copolymers were characterised by elemental analysis, infrared and 13C NMR spectroscopy, rheological studies, differential scanning calorimetry and theriuogravimetric analyses. Comparisons amongst grafting parameters of various natural polysaccharides reaction with polyacrylamide (PAM) were done. High percentage of acrylamide conversion and grafting efficiency were obtained for cashew gum (CG), even with low acrylamide/gum ratio. All copolymers presented intrinsic viscosity and so the hydrodynamic volume much higher than CG value and closer to the PAM. Grafting of PAM chains onto the polysaccharide enhances its thermal stability. A series of hydrogels with different amount of gum and cross-linking agent was obtained. Theimogravimetric analysis, dynamic rheology, scanning electron microscopy and elemental analysis were the techniques used for hydrogels characterization. Swelling capacity of IPNs in presence of water and in salt were evaluated. The equilibrium swelling (Weq) of gels was very low ( 22 - 80 g H20/g gel). However, Weq value could be increased by decreasing cross-linker concentration and adding sodium bicarbonate. Superabsorbent materials were obtained by hydrogels hydrolysis with NaOH. Fickian mechanism of water diffusion was observed for non hydrolyzed gels, different of hydrolyzed material, that presented non Fickian mechanism. Maximum Weq was registered as 986 g H20/g gel. Swelling capacity depends on pH and salt concentration. Rheological study led to characterize the materials as strong gels. Cycles of swelling and dryness decrease the Weq, but not substantially. The hydrogel was loaded with KNO3, used as agrochemical model, and the delivery studied. The results indicate that IPN hydrogels of polyacrylamide and cashew gum could be applied as soil conditioner, as water superabsorbent.