The role of capillary force promoters in dry coating procedures--evaluation of acetylated monoglyceride, isopropyl myristate and palmitate.

Previous studies described several dry powder coating procedures. Most of these techniques used polymer powders and plasticizers for attaining film formation. Thermo analytical methods showed that some of the used plasticizers did not reduce the glass transition temperature of the polymer markedly and consequently did not act as a plasticizer in a typical way. Further studies suggested that these substances were promoting capillary forces between the polymer particles thereby promoting the adhesion of the polymer on the cores and enhancing the coating efficiency. In this study these substances will be called capillary force promoters (CFP). The aims of this study are to evaluate the effectiveness of acetylated monoglyceride, isopropyl myristate and palmitate in terms of coating efficiency enhancement and to shape the idea about the way of action of CFPs in dry coating procedures. One of the main features of a good CFP represents its ability not to be taken up by the polymer but to remain on the polymer's surface being able to build up interparticle capillary forces. A CFP is further characterised by a good spreadability on the polymer. In this context, the lowering of the glass transition temperature has been found to be a good indicator for the affinity of the CFP to the polymer and its uptake by the polymer, whereas the contact angle between the polymer and the CFP represents a measure of its spreadability.