Transitions in plasticized and unplasticized cellulose acetates

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AbstractThe temperature‐dependence of specific volume, rigidity modulus, and mechanical losses of plasticized and unplasticized cellulose acetates in the temperature range −100 to +200°C. has been studied. Two cellulose acetates, a triacetate and a cellulose (2.2) acetate were used, these being plasticized with varying amounts of either benzyl acetate, m‐cresol, o‐ethylphenol, γ‐butyrolactone, monomethylaniline, benzylphenol, or Santophen 7 (a phthallyl glycolate). The specific volume measurements, made using an extremely sensitive dilatometer, indicated three apparent second‐order transitions and one first‐order (melting) transition in cellulose triacetate and three or possibly four apparent second‐order transitions but no first‐order transition in the cellulose (2.2) acetate. Both the first‐order and second‐order transitions were depressed by the addition of plasticizer, the depression being most marked with the phenolic‐type plasticizers. Because of polymer decomposition at temperatures above 200°C., it was not possible to study the melting of mixtures containing less than 30% plasticizer and subsequently no reliable values for the melting temperature, the entropy, and the heat of crystallization could be determined. Rigidity modulus measurements, obtained using a torsional pendulum technique and the mechanical loss (damping) measurements, confirmed the existences of these second‐order transitions in both acetates and indicated that only the highest temperature transition, 175°C. in the triacetate and 195°C. in the secondary acetate, had the characteristics of a normal glass to rubber transition.