Effects of molecular weight on permeability and microstructure of mixed ethyl-hydroxypropyl-cellulose films
Journal article, 2013

Films of ethyl cellulose (EC) and water-soluble hydroxypropyl cellulose (HPC) can be used for extended release coatings in oral formulations. The permeability and microstructure of free EC/HPC films with 30% w/w HPC were studied to investigate effects of EC molecular weight. Phase separation during film spraying and subsequent HPC leaching after immersion in aqueous media cause pore formation in such films. It was found that sprayed films were porous throughout the bulk of the films after water immersion. The molecular weight affected HPC leaching, pore morphology and film permeability; increasing the molecular weight resulted in decreasing permeability. A model to distinguish the major factors contributing to diffusion retardation in porous films showed that the trend in permeability was determined predominantly by factors associated with the geometry and arrangement of pores, independent of the diffusing species. The film with the highest molecular weight did, however, show an additional contribution from pore wall/permeant interactions. In addition, rapid drying and increasing molecular weight resulted in smaller pores, which suggest that phase separation kinetics affects the final microstructure of EC/HPC films. Thus, the molecular weight influences the microstructural features of pores, which are crucial for mass transport in EC/HPC films.

ethyl cellulose


pore geometry

hydroxypropyl cellulose

molecular weight


Helene Andersson

SuMo Biomaterials

Chalmers, Materials and Manufacturing Technology, Polymeric Materials and Composites

Johan Hjärtstam

AstraZeneca AB

Mats Stading

Chalmers, Materials and Manufacturing Technology, Polymeric Materials and Composites

Christian von Corswant

AstraZeneca AB

Anette Larsson

SuMo Biomaterials

Chalmers, Chemical and Biological Engineering, Pharmaceutical Technology

European Journal of Pharmaceutical Sciences

0928-0987 (ISSN)

Vol. 48 1-2 240-248

Subject Categories

Pharmaceutical Sciences

Medical Engineering

Bio Materials

Chemical Engineering

Polymer Technologies

Other Materials Engineering

Medical Materials

Areas of Advance

Materials Science



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