EFFECT OF IONIZING RADIATION ON THE PROPERTIES

In developing or improving methods for modifying various polymcrs, interest in ionizing radiation is steadily rising. Increasing the reactivity of celluloses, grafting synthetic materials and dyes to it, the manufacture of microcrystalline cellulose, and stcrilization of celluiosic materials -this is only a partial list of the possibilities of the radiochemical method in cellulose chcmistry [1-5]. However, individual questions in this region have remained unclarified and require refining and additional studics. Thus, no uniform opinion has been developed about the effect of ionizing radiation on the crystallinity and d'egree of polymerization of celluloses of various morphoiogies at comparativelylow absorbed doses [6, 7]. A study of the sorption of watet vapor by irradiated and unirradiated ceiluiosic materials and the changc in thcir physico-mechanical properties also presents practical interest. These questions are examined in the present article. The objects of study were cotton, wood suifite and sulfate celluloscs, and also unplasticized cellulose film. Irradiation of the indicated specimens was carried out in a cobalt UK-250000 unit at room temperature in the range of absorbed doses from 5-200 kGy (dose rate, 0.3 kGy/scc). Sorption of water vapor was measured in a vacuum sorption unit at 25°C. In the specimens studied from x-ray diffraction mcasurements, we calculated the crystallinity index X c and determined the mean viscosity degree of polymerization ~ ~ , In Table 1, we give data on the change in '13"15v and in X c at various absorbed doses. From the data presentcd, it is evident that at an identical absorbed dose the values of ~ v for the celluloses are not identical and the intensity of their change upon irradiation depends on the initial DP values in the original unirradiated cellulose. In Fig. 1, wc give data on the change in 13"~ v as a function of the absorption dose D presented in coordinates of log(l / l~v. -1/13"Pro ) -logD, where D'~v. and '13"~v0 are the mean viscosity degrees of polymerization of the radiated and original celluloses, ~ respectively. Here, we also giv~e data which were presented in 16, 8]. A linear dependence is observed between the indicatcd quantitics, which may be written as foilows: