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The sorption and permeation of moisture in moisture barrier polymer film coatings

Mwesigwa, Enosh; (2006) The sorption and permeation of moisture in moisture barrier polymer film coatings. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Several moisture barrier coatings for use as barriers to moisture uptake into solid dosage forms of moisture-sensitive drug substances are commercially available. The aim of this study was to investigate the moisture sorption and permeation characteristics of four moisture barrier coatings, formulated from the following polymers, i.e., ethyl methacrylate copolymer (Eudragit L30 D-55®), aminobutyl methacrylate copolymer (Eudragit EPO®), poly(vinyl alcohol) (Opadry AMB ®) and hypromellose system (Sepifilm LP 10®). The gravimetric vapour sorption technique, utilising a dynamic vapour sorption apparatus (Surface Measurement Systems, UK), was the main method used to determine the extent of moisture sorption and desorption. Cast free films of the moisture barrier coatings, and uncoated and coated model tablet cores were investigated. The model tablet cores were designed to exhibit hygroscopic, non- hygroscopic or waxy characteristics. Additional tests with near-infrared spectroscopy, thermogravimetric analysis and dissolution testing were done to ascertain the hydration characteristics and/or the water- coating interactions. Sepifilm LP and Opadry AMB films sorbed comparatively more moisture than the Eudragit L30 D-55 and Eudragit EPO films. Differences in hygroscopicity of the films were attributed to differences in the hydrophilicity of the constitutive polymers. Analysis of sorption-desorption kinetics showed that all the film samples exhibited non-Fickian kinetics. The calculated permeability coefficients for moisture in the films were of the order of 10-6 to 10-7 cm3 [(STP) cm/cm2 s cmHg)]. Thus, the moisture barrier coatings were comparatively inferior to conventional barriers like high density polyethylene or polyvinylidene (cling film), with reported permeabilitities of the order of 10-10 to 10-11 [(STP) cm/cm2 s cmHg)]. Application of the moisture barrier coatings onto the model tablet cores resulted in a net reduction in the extent of sorption over the uncoated cores only for the hygroscopic cores. Thus, there was no benefit of applying a moisture barrier coating to the waxy or non-hygroscopic tablet formulations. Results obtained from the stability profile of aspirin used as a model moisture-sensitive compound in the tablet cores confirmed this outcome. However, when the barrier coatings were applied onto the aspirin model cores, the coated samples exhibited higher degradation than the uncoated samples. No correlation between the degradation of aspirin in the cores and the permeability of the films was established. As the moisture barrier coatings were not able to completely seal the tablet cores from moisture uptake, it was speculated the sorbed moisture decreased the adhesion of the coatings to the underlying cores. This facilitated the collection of water at the coating- core boundary, from where aspirin hydrolysis could have taken place. Therefore, if moisture barrier coatings are to protect moisture sensitive compounds in tablet cores, the ability to prevent hydrolysis at the coating-core boundary is deemed essential.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: The sorption and permeation of moisture in moisture barrier polymer film coatings
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: Health and environmental sciences; Barrier; Coatings; Film; Moisture; Permeation; Polymer; Sorption
URI: https://discovery.ucl.ac.uk/id/eprint/10119468
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