Mechanical properties of cellulose acetate as related to molecular chain length

Abstract

The mechanical properties of films prepared from a series of fraction s of cellulose acetate, varying widely in molecular chain length (DP), were determined. A fraction 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 tha.n tensile strength to changes in DP and hetero-geneity 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 eto not. In contrast , at any given number-average DP within the range studied, t he properties of the fractions and all of the blends are approximately equal. CONTENTS Pose I. IntroducUon __ ___ __ _______ _____ __ __ ______________________ __ __ 1 II. Experimental procedure____ ___ __ ____ __ __ _ _ _ __ _ __ _ _ __ _ _ _ _ _ _ _ _ ___ _ 3 1. Materials_____ __ __ __ __ __ _ _ _ _ _____ _ _ __ ___ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ 3 2. Methods___ _________ ___ ____ __ ______ ______ ______ ___ ____ _ 3 (a) Preparation of films-_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 3 (b) Estimation of relative weight-average chain length_ _ _ _ _ 3 (c) Measurement of mechanical properties of films_ _ _ _ _ _ _ _ _ 3 III. Results __________ ___ ____ _____ ___ ____ ______ ____________ ____ ___ 4 1. Mechanical properties of the fractions___ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 4 IV.. 2. ,IVIechanical properties of blends of the fractions_ _ _ _ _ _ _ _ _ _ _ _ _ 6 DlscllsslOn _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 13 V. References. _ _ __ _ _ ___ ____ __ __ __ _____ ____ __ _ _ ____ _ __ __ ______ _ ___ 14