Polymeric interactions in tablet coating films.
The objective of this work was the investigation of the polymeric
interactions in tablet coating films in relation with effective film
The polymeric interactions were studied by means of torsional braid
analysis. For this purpose an existing torsional braid analyser was
improved and successfully interfaced to a microprocessor for data
acquisition and reduction. Discussion on the contribution of the substrate
to the thermomechanical spectra of the TBA as well as factors associated
with the optimisation of the technique are presented.
The dynamic mechanical behaviour of EC, HPMC, HPMCP-HP50, HPMCP-HP55,
HPC and CAP film formers was studied with particular attention to structure-
Tg relationship. The plasticisation of two of the most common film formers,
namely EC and HPMC, with a series of polyethylene glycols was investigated.
It was shown that PEGs efficiently plasticise HPMC, whereas they exhibited
limited interactions with EC. The relation of the plasticising efficiency
to the size and concentration of the PEGs with respect to the optimisation
of the tablet coating formulation is also discussed.
The thermomechanical behaviour of blends of EC with water-/pH-dependent
film formers was also studied with TBA, in conjunction with the requirements
for controlled release coatings. All polyblends exhibited phase separation
and the required domain morphology, which was shown capable of retaining
small amounts of water-/pH-dependent components even after prolonged
Moreover, the modification of the thermomechanical performance of
80/20 w/w EC/HPMC blends plasticised with PEG200 and PEG400 was investigated.
These studies indicated diffusion of the plasticisers into both phases.
Finally, the effects of blend composition and interactions in terms of
efficient sustained release coatings are identified and discussed.