| Popis: |
IT IS known [1-3] that cyanoethylated cellulose in the glass-like state has good dielectric permit t ivi ty owing to relaxation of the cyanoethyl groups. However, there are contradictory data on the dielectric permit t ivi ty (e') and the dielectric losses (tan J) of cellulose with varying degrees of cyanoethylation. Thus for tr icyanoethyl cellulose (degree of substitution 7c~--~300, i.e. the hydrogen of all three hydroxyls in the ring is replaced by --CI-I2CH2CN groups) authors give values of d (at room temperature, 1000 e/s) varying from 13 [1] to 15-17 [2, 3]. Data on the values of tan j of these materials also vary widely. This could be the result of disregarding a number of factors which may have a considerable influence on d and tan J, chiefly the residual moisture content of the sample and the method of film preparation. With films produced by casting from solution values of e' and tan J are generally much lower than for samples obtained by moulding from a melt [3]. The present paper deals with the effect of sample preparation and the amount of moisture sorbed by the samples on the dielectric properties of several mixed cyanoethylated esters of cellulose. Compared with cyanoethylated cellulose, its mixed esters, and in particular those indicated above, have the advantage that in case of incomplete substi tution by cyanoethyl groups (~c~ |
