Kappa-carrageenan–polyethylene oxide hydrogel blends prepared by gamma irradiation

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Abstract

A composite hydrogel system from kappa-carrageenan (KC) and polyethylene oxide was prepared by γ irradiation. KC was blended with low (LPEO) and medium (MPEO) molecular weight PEO having a concentration of 5% (w/w) at a ratio of 1:1. The properties of the blended hydrogels were evaluated in terms of gel fraction, swelling behavior and gel strength. KC/MPEO hydrogel system has a gel content of 75% at a dose of 10 kGy while 60% gel content was noted for KC/LPEO at the same dose. Water gain of more 10,000% was exhibited by both systems investigated. Gel strength of KC/MPEO was higher compared to KC/LPEO hydrogel. KC/MPEO hydrogel retained 88% (364 N) of its gel strength even after autoclave sterilization.

Introduction

Development of hydrogels is a dynamic field of study wherein there is a continuous search for materials that have the potential for biomedical, biotechnological or agricultural utilization. Polymers are the largest group of materials being exploited for developing hydrogels. They are used separately and/or as composites of natural and synthetic materials (Rosiak et al., 1995). Natural-derived polymers, such as polysaccharides, represent an interesting class of materials that can be explored in combination with synthetic polymers for developing hydrogel systems.

Carrageenans are commercially important hydrophilic polymers which occur as matrix materials in numerous species of seaweeds (e.g. Chondrus, Gigartina, Eucheuma, Fucellaria). Chemically, they are linear sulfated-polysaccharides composed of d-galactose and 3,6-anhydrogalactose units. Due to their half-ester sulfate moieties, they are strongly anionic polymers. Different types of carrageenans exist but only kappa and iota types are capable of forming thermo-reversible gels. At present, some 70% of all carrageenan products are utilized by the food industry. Of the remaining commercially used products, the major applications are in the cosmetics and personal care industries (Tye, 1989).

Considerable interest has been shown in polyethylene oxide (PEO) for diverse applications in food, drug and cosmetic products and commercialization of PEO hydrogels has been realized in recent years (Anon., 1982). This paper presents the preliminary results on the properties of kappa-carrageenan (KC)/PEO hydrogel blends prepared by gamma irradiation.

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Materials

KC samples with a molecular weight of around 3.0×105 were obtained from Shemberg Corp., Philippines and were used as-received. Low and medium molecular weight PEO (LPEO=1–1.17×105 and MPEO=3–5×105) were supplied by Ichimaru Pharcos Co. Ltd, Japan. Distilled water was used for the preparation of the hydrogel blends.

Response of KC gels to radiation

The idealized structure of KC is shown in Fig. 1. The AB repeat unit consists of 1,3-linked β-d-galactose residue (A) and 1,4-linked 3,6-anhydro-α-d-galactose residue (B). Hot solutions of KC, often containing quite low concentrations of polymer (∼1% w/w), tend to form rigid gels upon cooling. The gelation process of carrageenan solutions has been described by two mechanisms. In the first mechanism, crosslinks are formed by segments of a double helix. These segments are then aggregated by ions (

Conclusion

Blending of KC with low molecular weight and medium molecular weight PEO was undertaken in this study. KC blended with MPEO showed better properties in terms of gel content, swelling behavior and gel strength. Variation of MPEO ratio with respect to KC revealed that synergism exists between KC and PEO at a 50/50 ratio. Above and below this ratio, gel content, swelling and gel strengths are lower. Heat sterilization can be used for KC/MPEO hydrogel with a corresponding 88% retention in gel

Acknowledgements

Ms C. T. Aranilla wishes to thank the International Atomic Energy Agency (IAEA) for the fellowship.

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