Volatile substances such as perfumes, insect pheromones and volatile corrosion inhibitors can be released into the atmosphere from polymer matrices. The release characteristics of the volatile substances depend on the original concentration of the substances, and also on the type and geometry of the matrix. The design of the matrix can be done with a trial and error process involving several iterations of tool making followed by testing of the release characteristics. However, this is a costly and time-consuming method. The objective of this study is to propose and evaluate a mathematical model based on Fick's second law of diffusion. The model can be used to predict the release profiles of volatile substances from polymer matrices based on the initial volatile concentration, matrix geometry and the coefficient of diffusion of the volatile through the polymer. The alcohols I-propanol, I-butanol, I-hexanol and I-octanol and the polymer ethylene-eo-vinyl acetate (EVA) were chosen as a model system for this study. The coefficients of diffusion of all the alcohols through the EVA were determined with the time lag test using a diffusion cell and polymer sheets. Several methods of making polymer sheets were evaluated. Injection moulded disks was the most suitable method for the system under consideration. Based on the results of the time lag tests, the proposed model was used to predict the release characteristics of the different alcohols from two EVA matrix designs. Injection moulded test pieces of both designs were prepared. All the test pieces contained ca. 10% of one of the alcohols. The test pieces were aged at ambient conditions and the release of the alcohols was monitored. It was found that the proposed model gave a good prediction of the residual mass of the dispensers, never diverging more than 10% from the experimental result. The experimental results tended to show faster release than predicted. This was expected since the model does not consider the effect of concentration on the coefficient of diffusion. It was concluded that the model gave accurate predictions of the release characteristics of the system investigated. It would be a useful tool in the design and development of polymer dispensers for volatile substances. The smaller number of tool modifications and release tests required will lead to cost and time savings in the development process. / Dissertation (M Eng (Chemical Engineering))--University of Pretoria, 2006. / Chemical Engineering / unrestricted

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The relationship between polymer chain architecture, crystallization behavior, and morphology formation was investigated. The structures formed are highly dependent on chain configuration and crystallization kinetics. Poly(lactic acid) (PLA) and Poly(ethylene-co-vinyl acetate) (EVA) random copolymers were studied. Sample characterization was performed using a variety of techniques, including spectroscopy, scattering, and calorimetry. In PLA, structural differences between α’ and α crystalline phases were analyzed using cryogenic infrared and Raman spectroscopy. Compared to the  crystal, the ’ crystal has slightly looser packing and weaker intermolecular interactions involving carbonyl and methyl functional groups. Simulations in conjunction with Raman scattering analyzed the conformational distortion of the α’ phase. The conformation of an α’ chain was determined to have tg’t-103 conformation with tg’t-31 units randomly distributed along the chain. Departure of the O-C α dihedral angle was also confirmed. The structural disorder leads to different thermal properties for α’ and α crystalline forms, which was quantified by measuring the enthalpic change at melting for both crystals ( = 57 ± 3 J/g and =9 6 ± 3 J/g). The transformation from α’ to α and the mechanism of order formation in PLA were also elucidated. The relationship between chain configuration of EVA random copolymers and crystallization behavior was established. For three different EVA samples, the distribution of methylene sequences was calculated and compared to a distribution of crystallite sizes formed. This comparison revealed that only a small fraction of the total methylene segments present actually crystallized. Cocrystallization with highly mobile oligomers was explored to enhance the crystallization of EVA copolymers. When blended, EVA28 (28 weight percentage) cocrystallizes with C36H74 n-alkane resulting in faster crystallization kinetics and a higher degree of crystallinity. The observed increase in degree of crystallinity was directly related to the chain configuration. Compositional mapping using Raman spectroscopy provided evidence for oligomer nucleation. The cocrystallization kinetics and morphology of EVA and n-alkane blends was found to depend on the chain length of oligomer. In both systems studied, crystallization kinetics determines the morphologies formed, which are undoubtedly related to the details of molecular architecture.