ABSTRACT:The release process of three osmotically active solutes with various solubilities in water (NaCl, CsNO 3 , and CsCl) from silicone rubber matrices is presented. The kinetics of release for different initial loads of the salts were supplemented by measurements of the kinetics of concurrent water uptake. To gain insight on the relevant non-Fickian transport mechanisms, the morphology, the diffusion and sorption properties and the physicochemical state of water in the salt-depleted matrices were studied. In addition, both salt-loaded and saltdepleted matrices were characterized with respect to their mechanical properties. The combined information, derived from these techniques, supported the operation of a release mechanism carried out through the formation of microscopic cracks, interconnecting the permanently formed cavities inside the matrices. The results indicate that these microscopic cracks may have healed upon drying.

ABSTRACT:The release process of a water soluble, model drug (proxyphylline) with small, yet not negligible osmotic action, from silicone rubber (SR) matrices is presented. The kinetics of release for different initial loads of the drug is supplemented by measurements of the kinetics of the concurrent water uptake. To gain insight on the relevant non-Fickian transport mechanisms, the morphology, the diffusion, and sorption properties of the drug-depleted matrices are studied. In addition, both drug-loaded and drug-depleted matrices are characterized with respect to their mechanical properties. The combined information derived from these techniques support-at least below the percolation threshold-the operation of a release mechanism occurring through a uniformly swollen polymer matrix without formation of cracks, in contrast to the release observed in the case of water soluble, inorganic salts where release takes place through a network of microscopic cracks.

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We present a comparative study between two different types of modification applied on a highly hydrophobic, yet biocompatible polymer, aiming to increase its hydrophilicity. More specifically, silicone rubber (SR) was modified by the introduction of low‐molecular weight poly(ethylene glycol), through either (a) blending or (b) addition‐grafting reaction. The modifications were first evaluated in neat films with respect to their water sorption capacity, stability of ethylenoxy groups' embedment, mechanical and thermal properties. The results from this series of tests showed that blending offered better results in terms of hydrophilicity, both surficial and in the bulk, while the films maintained better mechanical properties. Subsequently, the release kinetics of a relatively hydrophilic drug (theophylline) along with the concurrent water uptake was examined in drug‐loaded, pure and modified SR films. As in the case of the drug‐free films, blending appeared to offer better possibilities in controlling the drug's release rate through increased water sorption. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Nanocomposites of poly(vinyl alcohol) (PVA) and single-walled carbon nanotubes (SWNTs) in pristine form, or modified with poly (sodium 4-styrene sulfonate), were prepared in the form of films. The effect of SWNTs modification on their dispersion in the polymer matrix and on certain properties of the resulting composites, including tensile mechanical and thermal properties and swelling ability upon exposure to various moisture levels was studied. The composite films based on the modified SWNTs: (i) were characterized by a much higher degree of transparency up to 10%w/w loads, due to better dispersion, (ii) presented a higher hydrophilicity, and (iii) tended to promote thermal degradation of PVA to a lesser extent, as compared with the composites based on pristine SWNTs. A reinforcing effect was observed for the dry, 1% and 2.5% w/w modified-SWNTs-PVA nanocomposites, without serious detrimental effects on the elongation at break. The effect of moisture on the mechanical properties was more intense in the case of composites based on modified SWNTs, as compared with those based on pristine SWNTs, in line with the observed higher hydrophilicity in the former case.