Use of Dynamic Differential Scanning Calorimetry in Identifying Glass Transition Temperatures of Ethylcellulose and Surelease Films

Abstract

The thermal properties of ethylcellulose and Surelease films were evaluated by differential scanning calorimetry (DSC) and dynamic differential scanning calorimetry (DDSC). DDSC is a novel thermoanalytical technique that allows the identification of glass transitions when they are overlapped by other phenomena such as decomposition or dehydration. Films containing different amounts of plasticizer (triethyl citrate) were prepared from solutions of ethylcellulose in acetone. Additionally, films were prepared from Surelease dispersions at different coalescent temperatures. DSC was sensitive enough to identify the glass transitions in ethylcellulose films but not in Surelease films. DDSC, because it separates the heat flow into two components—loss and storage curves—allowed the identification of the glass transitions in the storage curve. The addition of different amounts of triethyl citrate to ethylcellulose films led to a reduction in the glass transition temperature (Tg). The Tg temperature in Surelease films decreased with an increase in the temperature of coalescence, probably because at higher temperatures the movement of the polymer strands was higher and enhanced the action of the plasticizers included in the Surelease film. For simple polymeric films containing ethylcellulose, Tg values were identified by DSC and DDSC was not required. However, for Surelease films, containing materials of different molecular weight, plasticizers and variable moisture content, DDSC was required.