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Title: Swelling properties of polymers with or without surfactants
Authors: Shtaya, Hani Naseef
Keywords: Polymers - Properties;Polymers and polymerization;Surface active agents;Polymers - chemistry
Issue Date: 1998
Abstract: The scope of the first part of the present study was to study and evaluate the effect of powder packing and porosity of specimens on the swelling properties of polymeric materials, in various swelling liquids, such as distilled water phosphate buffer pH 5,8 and 0.1 N hydrochloric acid solution. Capsules, tablets and films of hydroxypropyl methylcellulose, poly(ethylene oxide) and sodium alginate were prepared, and their weight uptake after immersion into the above solutions was recorded as a function of time, in order to assess the swelling process. Measurements of some characteristics of the as-received powders were also performed in an attempt to classify the specimens prepared according to their porosity. Within the experimental conditions of this work, it was shown that the porosity of polymeric specimens is a dominant factor that controls their swelling behaviour. Increased porosity leads to fast initial rates of weight uptake and high extent of equilibrium swelling. On the other hand, dissolution and possible degradation of polymers susceptible to acid hydrolysis results in some variations from the above mentioned behaviour. With respect to the application in controlled release systems, theoverall delivery rate from a polymeric specimen is expected to be a function of both swelling and disintegration characteristics of a specimen, and therefore, the weight uptake can be considered a measure of the release only in the case of polymers with low water solubility and increased stability to hydrolysis The scope of the second part of the present study was to study the effect of an ampholytic surfactant on the swelling properties of polymeric materials was studied, using various swelling liquids. Tablets were prepared consisting of hydroxypropyl methylcellulose, poly(oxyethylene) and sodium alginate. Tego betain was the non-ionic surfactant used as an additive in a series of samples made of the above polymers. Those tablets were immersed in distilled water, phosphate buffer and 0.1 N HCl, and their weight uptake was recorded as a function of time, in order to assess the swelling process. Measurements of the contact angle of the above systems were also carried out for estimating their wetting properties. The results of this study showed a selectivity among polymers, surfactant and surrounding liquid. Clearly, an enhancement of the swelling capacity of hydroxypropyl methylcellulose tablets due to the surfactant was recorded. An unclear effect was observed in the case of poly(oxyethylene), whereas for sodium alginate, the dominant factor is its water solubility that controls swelling behaviour.
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