Bazafkan, S 1996, Radiation protection on polysaccharide solutions and gels , PhD thesis, University of Salford.
The effects of ionizing radiation on solutions of (1) sodium alginate, (2) alginate gels (wet and dry), (3) xanthan gum, (4), locust bean gum (LBG) and (5) carboxymethyl cellulose (CMC), have been investigated. Problems arise in the radiation sterilization of these gums (either as a solution or gel) due to reduction in their viscosity and the gel strength, caused by the high doses (25kGy) commonly used for the purpose of sterilization. The alginates used here were manugel DMB, manugel DPB and manucol DMF. The irradiations were carried out using 'Co-ry-source and the gels and solutions were analysed by measurement of their apparent viscosities using a Brookfield viscometer L.V.T. The data shows that 2% solutions of the sodium salt of the three alginates used here are all pseudoplastic. There is a rapid decrease in viscosity of solutions irradiated up to a dose of 0.5kGy, and the initial rate of viscosity decrease is unaffected by the presence or absence of air. Inclusion of mannitol at high concentration (15%) could, at least partially, protect the alginate solutions degradation by scavenging -OH radicals. The possibility of using 60Co-7-radiation to sterilize alginate gels (wet gels) was also studied. Gels of this type have potential use of wound care. Those prepared here could bend easily. Irradiated to 25 kGy, the gels readily crack by becoming more brittle, are easily squashed and lose water. Inclusion of mannitol improved the quality of the gels and again indicates its protective role in these systems. When alginate solutions containing mannitol and the gelling agents 5-gluconolactone and calcium orthophosphate were irradiated separately and then mixed, gels were formed, indicating that pre-sterilization of the components by irradiation is a feasible method of preparation of sterile gels. Gels that were concentrated (dry) by water evaporation were more stable to radiation (25 kGy). The gels that had the greatest capability to take up saline and to be manipulated most easily (both before and after irradiation) were those that contained initially 2% alginate and 5% mannitol, and dried to a quarter of the original weight (ie. the gel now contained 8% alginate and 20% mannitol). These gels were clear and pliable and after irradiation to 30 kGy remain stable in saline for up to 24 hours. The effect of ionizing radiation on xanthan and LBG solutions are also studied. The initial studies indicated that these solutions were also pseudoplastic. Irradiation of xanthan gum solutions caused a rapid initial decrease in apparent viscosity. t-Butanol had some protective effect on xanthan-LBG and xanthan-NaC1 solutions. Addition of mannitol (20%) to xanthan gum solutions again only partially protects the solutions. The solutions with highest apparent viscosity were those prepared by mixing equal volumes of solutions of LBG 1%, mannitol (20%) and ascorbic acid (10" mol dm') and solutions of xanthan gum (1%), mannitol (20%) and ascorbic acid (10' mol dm'). The viscosity of this solution falls from 300,000 cps to 250,000 (shear rate 0.07s4), after irradiation to 25 kGy. Therefore, whereas xanthan gum solutions containing readily depolymerized by irradiation, very high viscosity irradiated xanthan solutions containing thickening agents (LBG) and radiation protectors (mannitol - ascorbic acid) can be prepared. Solutions of CMC are also pseudoplastic. Irradiation to 25 kGy resulted in a decrease in the apparent viscosity of solutions of CMC/mannitol/ascorbic acid from — 180,000cps to 8,000cps, whereas for solutions of CMC alone and for CMC/mannitol solutions the viscosity was less than 500cps. This further illustrates the protective effect of ascorbic acid as was observed for xanthan solutions and also suggests that mannitol radicals cause depolymerization of CMC.
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