Synthesis and Swelling Behavior of Carrageenans-Graft-Poly(Sodium Acrylate)/Kaolin Superabsorbent Hydrogel Composites
In the present paper, a novel superabsorbent hydrogel composite based on carrageenan have been prepared via graft copolymerization of acrylic acid (AA) in the presence of kaolin powder using methylenebisacrylamide (MBA) as a crosslinking agent and ammonium persulfate (APS) as an initiator. The certain variables of the graft copolymerization (i.e. the monomer, the initiator and the crosslinker concentration as well as kaolin/carrageenan weight ratio) affected on the ultimate water-swelling capacity were optimized. The composite structure was confirmed using FTIR spectroscopy. A new absorption band at 1707 cm in the 1 composite spectrum confirmed kaolin-organic polymer linkage. The effect of kaolin amount and MBA concentration showed that with increasing of these parameters, the water absorbency of the superabsorbent composite was decreased. Because of their exceptional properties, i.e. anhydrogalactose units (13). The types of carrageenans biocompatibility, biodegradability, renewability and differ only in the position and number of ester sulfate non-toxicity, polysaccharides and proteins are the groups. Following a continuous research on modification main part of the natural-based superabsorbent of carrageenans (14), in this work, we attempt to hydrogels. The higher production cost and low gel synthesize and characterize new superabsorbent strength of these superabsorbents, however, restrict composites based on carrageenan in the presence of their application widely. To improve these limitations, kaolin particles. The preparation of the biopolymer-based inorganic compounds with low cost can be used. The superabsorbent composites can also improve the introduction of inorganic fillers to a polymer matrix mechanical properties of materials and can lower the cost increases its strength and stiffness properties. of the finished product compared with the synthetic Among inorganic compounds, special attention has counterparts as well as providing biodegradable been paid to clay minerals in the field of nanocomposites characteristics.
Applications of nanocomposite hydrogels for biomedical engineering and environmental protection
Nanocomposite hydrogels are polymeric networks that possess a unique property of hydration. The presence of alcohols, carboxylic acids and amides as hydrophilic moieties in structure of nanocomposite hydrogels enhances their stiffness and water-absorbing capacity. Addition of cross-linker in the synthesis of hydrogels increases their stability under extreme conditions of temperature, pH and pressure. Natural polymer-based nanocomposite hydrogels are biodegradable, highly hydrophilic and possess good mechanical strength. Gelatin, chitin, cellulose, pectin, carrageenan, starch and alginate are natural polymers commonly used to fabricate nanocomposite hydrogels. Nanocomposite hydrogels have special characteristics such as high swelling rate, selectivity and stimuli-sensitive nature. Here we review nanocomposite hydrogels for environmental protection and biomedical engineering. Applications in biomedical engineering include drug delivery agents, wound dressing, tissue engineering and antibacterials. Applications in environmental protection include ion exchangers, adsorption, photocatalysis and soil conditioning. Many nanocomposite hydrogels show excellent adsorption selectivity for heavy metal ions: Cu2+ up to 30.35 mg/g, Pb2+ up to 35.94 mg/g, and Zn2+ and Fe3+ up to 94.34 mg/g. Xanthan gum-based nanocomposite hydrogel has removed 96% dye from industrial effluent as reported. In addition, most of the nanocomposite hydrogels showed better adsorption capacity for pollutants in the pH range from 5 to 7. The nanocomposite hydrogels could also be regenerated and successfully utilized for several times. Nanocomposite hydrogels are therefore good bio-absorbent materials for environmental detoxification.
Magnetic properties of Lu2Fe17 crystals
Abstract We present the results of crystal structure and magnetization studies of three single crystals grown from melts of different nominal compositions in the vicinity of the Lu2Fe17 stoichiometry. The ferromagnetic state of the crystals is strongly dependent on the real sample composition and the local atomic ordering. A drastic difference is observed in the behaviour of the ferro–antiferromagnetic transition, even in crystals for which almost identical composition and crystal parameters were determined by microprobe and X-ray analysis.