| summary(En) : | A heterogeneous hydrolysis of cotton cellulose was investigated at 60, 70, 80°C in 1, 2.5, 4N HCl solutions. The observed rate based on weight loss of the residue was expressed as the following equation, adopted from Philipp, Nelson and Ziffle: y = At = 0e-k't + Ct = 0e-kt, where, y is the fraction of the residue, At = 0 and Ct = 0 are the apparent amount of the amorphous and crystalline region respectively, and k and k ' are the corresponding rate constants of hydrolysis. These constants were statistically estimated. The values obtained are comparable to those of Daruwalla and Shet. The so-called "recrystallization" was assumed to take place during hydrolysis; i. e. while a rapid hydrolysis in the amorphous region and a slow hydrolysis in the crystalline region proceed and the cellulose chains in the amorphous region cleave randomly, a portion of cleaved chains rearranges itself to form crystalline region. On the basis of this assumption, the following relationship between At = 0 and k ' can be deduced, 1/At = 0 = (1/a0)(1 + γ/k '), where, k ' refers to the probability of cleavage of the chain in the amorphous region. The constant α0 means an intrinsic value of amorphous region in the sample, and γ is a fraction of the rate constant for rearrangement of the mobile segment produced by the chain cleavage. This equation is in keeping with the results within the range of experimental error. The estimated values for α0 was 0.1 and γ was 10-4 - 10-5sec-1. Another set of estimation for γ calculated from Daruwalla and Shet's data tends to give a somewhat lower value, resulting an activation energy 5 - 25kcal/mole. |
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