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      Plasticizing effect of water on poly(lactide-co-glycolide).

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          Abstract

          The purpose of this research was to evaluate the effect and nature of hydration on the glass transition temperature (Tg) of poly(D,L-lactide-co-glycolide) and investigate the physical state of water within the polymer during hygrothermal aging. The polymer was incubated in water at 23, 30, 37 and 55 degrees C, while the vapor sorption studies were carried out at 37 degrees C using saturated salt solutions. The water content and the thermal behavior of PLGA-water system were assessed by Karl Fischer titration and modulated differential scanning calorimetry, respectively, the hygrothermal aging was monitored by gel permeation chromatography. Water depressed reversibly the Tg by about 15 degrees C regardless of the incubation conditions. The Tg then remained constant at approximately 30 degrees C for five days, except when degradation occurred. A broad ice melting peak was detected around 0 degrees C. In the sorption studies, a linear correlation (r2 0.9837) between the Tg and the moisture content was observed in the range of 0.3-2.6% w/w, but there was no discernible endothermic event associated with the melting of ice. Data were found to fit reasonably well to the Gordon-Taylor/Kelley-Bueche equation. There were no differences between bulk and vapor water aging. It is proposed that the water responsible for plasticizing the polymer was non-freezable (bound) water and the small fraction of such water which was absorbed at high relative humidity caused polymer degradation in the same manner as bulk water.

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          Author and article information

          Journal
          J Control Release
          Journal of controlled release : official journal of the Controlled Release Society
          Elsevier BV
          0168-3659
          0168-3659
          Nov 02 2005
          : 108
          : 1
          Affiliations
          [1 ] Dipartimento di Chimica e Tecnologia del Farmaco, Università degli Studi di Perugia, Via del Liceo, 1-06123 Perugia, Italy.
          Article
          S0168-3659(05)00313-5
          10.1016/j.jconrel.2005.07.009
          16098624
          31f0cbb9-0b31-4c0f-af94-ade6c8c9f0a3
          History

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