New insights on the influence of manufacturing conditions and molecular weight on phase-separated films intended for controlled release

Abstract

The aim of this work was to investigate how manufacturing conditions influence phase-separated films of ethyl cellulose (EC) and hydroxypropyl cellulose (HPC) with different molecular weights of HPC. Two HPC grades, SSL and M, with weight average molecular weights (Mw) of 30×103g/mol and 365×103g/mol, respectively, were combined with EC 10 cps (70:30w/w EC/HPC) and spray-coated from ethanol solutions onto a rotating drum under well-controlled process conditions. Generally, a low spray rate resulted in a more rapid film drying process and, consequently, in smaller HPC-rich domains in the phase-separated film structure. For EC/HPC films with the low Mw HPC (SSL) the most rapid drying process resulted in a shift from a HPC-discontinuous to a partly bicontinuous structure and an increase in the permeability for water. In contrast, films containing the high Mw HPC (M) all showed bicontinuous structures, which resulted in overall higher water permeabilities and polymer release compared to the low Mw films. Interestingly, a maximum in permeability was observed for the high Mw films at intermediate spray rates. Below this spray rate the permeability decreased due to a lower amount of polymer released and at higher spray rates, the permeability decreased due to a loss of pore connectivity (or increased tortuosity). To conclude, this study shows that different Mw systems of EC/HPC can respond differently to variations in manufacturing conditions.