Abstract
Cellulose tripropionate (CTP) was prepared from cotton cellulose employing a heterogeneous method for propionylation and using zinc chloride as a catalyst, Viscosity-concentration studies for solutions of cellulose tripropionate in the mixed solvents, chloroform-propionic anhydride, tetrachloro-ethane-propionic anhydride and dichloromethane-propionic anhydride were carried out. Molecular weights of the samples used throughout this work were determined using a high-speed membrane osmometer (Hewlett Packard Model 502). The Mark-Houwink viscosity-molecular weight relationship was studied for the above systems and the respective k and a values were evaluated. The degradation of cellulose tripropionate in the solvents mentioned above was investigated and the separate effects of nature of catalyst, catalyst concentration, solvent, and temperature effect on the rate of degradation were studied. The extent of degradation was followed by the decrease in viscosity with time and molecular weights were evaluated using a single-point viscosity relationship to determine limiting viscosity numbers. The catalysts investigated were HC1O4, H2S04, FeCl3, SbCl5, SnCl4, SbC13, AlCl3, HgC12, PBr3, ZnCl2. The degradation reaction was found to be a first order random process which was explained by a mechanism based on the hydrogen and propionylium ions as catalytic species. In many cases the kinetics plots were found to be non linear as a result of a side-reaction between catalyst and the propionic anhydride whose kinetics were also investigated. For the degradation reaction, rate constants at zero-time and activation energies were evaluated and compared for the various catalysts. Side-reaction rate constants were determined by direct titration and use of degradation data in the case of the acid catalysts.