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AAPS PharmSciTech. 2003 December; 4(4): 469–479.
Published online 2003 September 18. doi:  10.1208/pt040460
PMCID: PMC2750653

Studies on the interaction of water with ethylcellulose: Effect of polymer particle size

Abstract

The purpose of this research was to investigate the interaction of water with ethylcellulose samples and assess the effect of particle size on the interaction. The distribution of water within coarse particle ethylcellulose (CPEC; average particle size 310 μm) and fine particle ethylcellulose (FPEC; average particle size 9.7 μm) of 7 cps viscosity grade was assessed by differential scanning calorimetry (DSC) and dynamic vapor sorption analysis. The amounts of nonfreezing and freezing water in hydrated samples were determined from melting endotherms obtained by DSC. An increase in water content resulted in an increase in the enthalpy of fusion of water for the two particle size fractions of EC. The amount of nonfreezable water was not affected by the change in particle size at low water contents. Exposure of ethylcellulose to water for 30 minutes is sufficient to achieve equilibration within the hydrated polymer at 47% wt/wt water content. The moisture sorption profiles were analyzed according to the Guggenheim-Anderson-de Boer (GAB) and Young and Nelson equations, which can help to distinguish moisture distribution in different physical forms. The amount of externally adsorbed moisture was greater in the case of FPEC. Internally absorbed moisture was evident only with the CPEC. In light of these results, and explanation is offered for the success of FPEC in wet-granulation methods where CPEC was not successful.

Keywords: ethylcellulose, fine particle ethylcellulose, differential scanning calorimetry, dynamic vapor sorption, GAB equations, Young and Nelson equations

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.
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