Properties and Potential Applications of Carboxymethyl-kappa-carrageenan Hydrogels Crosslinked by Gamma Radiation

Carboxymethyl derivatives of k-carrageenan(CMkC), with different degrees of substitution, were gamma-irradiated in viscous or paste solutions. Successfully obtained chemically crosslinked hydrogels showed dependence on the degree of substitution(DS), concentration, and radiation dose. The highest gel fraction was 76% exhibited by CMkC-3s hydrogel with a DS of 1.58. The hydrogels showed different swelling degrees in water and saline. Swelling behavior versus time, in both solvents, corresponded to 2nd order kinetics. The CMkC-3s at 20% concentration irradiated at 15 kGy had the highest water absorption of 324 g water/g dry gel. Selected hydrogels were evaluated for applications as wound dressing, as water retainer in sandy soil, and as metal adsorbent. As a wound dressing, CMkC-2s and CMkC-3s hydrogels exhibited considerable tensile strengths, abilities to absorb pseudo extracellular fluid and extractables with pH/conductivity conducive for healing promotion. In addition, the CMkC-3s hydrogel had no cytotoxic potential based on the MTT test. As water retainer in sandy soil, test samples with 0.1, 0.3 and 0.5% CMkC-3s granules retained 25.1%, 32.2%, and 42.6% water, respectively, at day 0 compared to 19.2% of the sandy soil alone. On day 7, the three sandy soil-CMkC groups still had 13.7%, 19.4%, and 29.3% water while the control had only 3.85%. In the batch adsorption studies, the hydrogels adsorbed heavy metals (Cu2+, Zn2+, Cd2+ and Pb2+) in the solution at different capacities, with Cd2+ as the highly adsorbed and Pb2+ as the least. The CMkC-3s hydrogel showed the highest metal uptake and adsorption efficiency, followed by CMkC-2s, then CMkC-1s. The CMkC-3s hydrogel, further tested on pH effect, had optimum metal uptake at neutral pH

Radiation-synthesized polysaccharides/polyacrylate super water absorbents and their biodegradabilities

Different super water absorbents (SWA) based on polysaccharides/poly(acrylic acid) (PAAc) were prepared by gamma irradiation to be used as soil water retainers. Polysaccharides, kappa-carrageenan (seaweed and semi-refined forms) and cassava starch were used in the preparation of SWA to improve biodegradability. Gel fraction of the different SWAs ranged from 31% to 97% and degree of swelling reached up to about 5890 g H2O/g dry gel. The physico-chemical and mechanical properties of the SWA were influenced by the degree of neutralization, macromolecular properties of the polysaccharide and irradiation dose. FTIR and TGA analyses showed successful incorporation of polysaccharides in the network structure through formation of covalent bond. Biodegradability test by microbial oxidative degradation analyzer (MODA) showed that cassava starch/PAAc SWA biodegraded at a rate of 42% in 85 days compared to 11% of pure PAAc. The cassava starch/PAAc SWAs retained water up to more than 20 days in sandy soil and still absorbed water after 62 days with wet/dry cycles in pot experiment