Sofie Gårdebjer

Permeability of water and oleic acid in composite films of phase separated polypropylene and cellulose stearate blends.

Cellulose esters with long carbon side chains (e.g. stearate) were produced via a homogenous reaction in ionic liquids. The degree of substitution was calculated to approximately 2. The melt rheology was studied for the pure cellulose esters but also combinations of the esters and polypropylene to study the processability of a blended composite material. It was shown that the compatibility between the two components was weak, which resulted in a phase-separated composite material. The morphology and permeability of water and oleic acid of the composite films were studied and it was shown that the water permeability decreased upon addition of the cellulose ester to the polymer. The permeability of oleic acid was however unchanged, which is most probable a result of high solubility in the cellulose ester rich domains of the composites. Also, the following hypothesis is stated: cellulose stearate influence the polypropylene crystallization process by decreasing the size of spherulites.

The importance of the molecular weight of ethyl cellulose on the properties of aqueous-based controlled release coatings

Previous investigations of aqueous based ethyl cellulose (EC) latex dispersions have mainly focused on the commercially available viscosity grade 20cps. In this study, dispersions of EC with varying viscosity grades (which correspond to molecular weights), ranging from 4 to 100 cps, were produced and characterised. The dispersions showed particle sizes around 200nm and highly negative ζ-potentials (approx. -100mV), which indicated stable dispersions as confirmed by sedimentation studies. The different latexes were used to produce free-standing film coatings. We hypothesised that the different viscosity grades of EC would result in different properties of the films. We found that an increase in viscosity grade (and higher molecular weight) resulted in lower coalescence between the particles during film formation and thus to higher water permeability than in film coatings of lower molecular weight. After exposure to water the EC 4cps and 20cps film coatings had a more porous structure in the side facing the air during production and drying after immersion in water. Molecular weight is therefore a factor that should be considered when producing pharmaceutical coatings for controlled release.