Radiation crosslinking of biodegradable hydroxypropylmethylcellulose

In general, cellulose and its derivatives irradiated with ionizing radiation in solid state or in dilute aqueous solution undergo mainly degradation by the cleavage of glycoside bonds in its main chain. Hydroxypropylmethylcellulose (HPMC) with different degree of substitution (1.9 and 1.4) was irradiated with electron beam (EB) radiation at ambient temperature and different doses (0–100 kGy) and concentrations (0.5–60 wt%). Irradiation of HPMC in aqueous solutions at reasonable concentrations (paste-like condition) resulted in the formation of gels. Gel content was found to increase with increase of radiation dose and decrease of HPMC concentration within the range studied. Ten and 30 wt% concentrations of HPMC irradiated at 30 Gy dose were chosen as the working systems for further experiments. HPMC with higher degree of substitution gave higher gel contents at every concentration and irradiation doses. HPMC gels (1.9) swelled by absorbing more than 2500 g of water per gram of dry gel at a low applied dose. Swelling experiments of HPMC gels were carried out in different solvents, at different pHs and temperatures. Experimental results showed that HPMC has both hydrogel and organogel characters showing pH dependence only at pH values greater than 8.0. HPMC gels are also highly swollen at low temperatures, gradually deswelling as temperature rises, usually sharply over a limited temperature range similar to temperature-sensitive hydrogels. To investigate the radiation induced degradation of HPMC at low concentrations, viscosity of degraded samples was measured using rotational viscometer. Viscosity of HPMC samples after irradiation became smaller with increasing dose because of the cleavage of glycoside bonds. Biodegradation study of crosslinked HPMC gels was carried out with cellulase enzyme in buffer solutions. The enzymatic degradation tests showed within 24 h, the weight loss of HPMC gel obtained at 30 kGy irradiation was 95%. It has also been observed that biodegradation of HPMC with high degree of substitution was relatively slow than that of HPMC with low degree of substitution due to its structural properties.