A novel approach for dry powder coating of pellets with Ethylcellulose. Part I: Evaluation of film formulation and process set up

An innovative dry powder coating technology was developed in a high-shear granulator using ethylcellulose (E10) as polymer. Several solid plasticizers were investigated with the aim of decreasing the polymer Tg at least to the highest possible working temperature (80 °C). DSC analysis of physical mixtures of E10 and plasticizers evidenced that lauric acid (LA) was the most effective plasticizer. In order to reach the target temperature a liquid plasticizer, oleic acid (OA), was introduced in the coating formulation. Free films were then prepared and the target minimum film forming temperature (MFFT) was established in the range 70-80 °C. Depending on the LA:OA weight ratio, Kollidon VA64 was included to decrease the LA recrystallization, while talc served as anti-sticking agent. Curing at the MFFT ensured the formation of homogeneous and stable films with good stability on storage. The dry powder coating process of placebo pellets was then developed, consisting of a combination of liquid assisted and thermal adhesion methods. The best coating formulations in terms of yields, coating efficiency (expressed as Relative Standard Deviation of the weight applied) and low pellets aggregation were based on E10:LA:OA in a weight ratio of 65:20:15 and 60:20:20. Moreover pellets remained stable after 1 year of storage (25 °C/60% R.H.).

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