Electron radiation of aqueous methyl cellulose solutions

Abstract

AbstractSolutions (4%) of commercial methyl cellulose (85,000 weight‐average moleculas weight) were radiated with electrons under varied atmospheres of oxygen at dose rates of 0.15, 0.45, and 4.5 Mrad/min. to total doses of 0.45, 4.5 and 10.0 Mrad. Sampler irradiated at the highest dose rates formed gels whose strength was estimated in a Brook‐field viscometer. After dispersing by stirring, the gels were clarified by centrifugation before viscosity, light‐scattering, and sedimentation measurements were made. Molecular weight increases to as high as 270,000 were found, and the sedimentation coefficients increased correspondingly. The intrinsic viscosity of the irradiated polymer solutions, on the other hand, did not increase as the molecular weight doubled or tripled. This is interpreted to be the result of recoupling of hydrolyzed fragments to produce branched molecules of smaller volume and greater weight. High dose rates promoted molecular weight increases while the presence of oxygen, low dose rates, and low polymer concentration favored degradation. The carboxyls evidently produced in the oxidative degradation resulted in a lowered pH of the irradiated solution and in polyelectrolyte viscosity behavior. Boiling an irradiated polymer solution at pH 10.5 reduced molecular weight from 270,000 to 165,000, showing the presence of alkali‐labile as well as alkali‐stable bonds. The gels on the other hand could be dispersed by stirring or heat as well as by alkali. Although branching may affect gelation to some extent, the molecular weight and sedimentation of the samples in solution appear to be approaching a maximum at the dosage level where the more labile bonding of the gelation phenomenon sets in.