Abstract
The mechanical properties of films prepared from a series of fractions of cellulose acetate, varying widely in molecular chain length (DP)2 were determined. A frac tion of DP 30 would not form a coherent film; fractions of higher DP showed a rapid improvement of mechanical properties with increase in DP, but above 150, further improvement was slight. A close correlation was found between the results of folding endurance and ultimate elongation measurements. These properties are more sensitive than tensile strength to changes in DP and to heterogeneity with respect to DP. Investigation of the properties as a function of both weight-average and number-average DP indicated that at any given weight- average DP, the fractions are superior to the blends and furthermore, those blends which contain fractions of low DP are inferior to those which do not. In contrast, at any given number-average DP within the range studied, the properties of the fractions and all of the blends are approximately equal.
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