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Plastics glazing materials have properties which allow their widespread use in construction, for example as rootlights. However, they are more susceptible than is glass to degradation by weathering, notably the combined effects of ultraviolet light, heat and moisture. Examples of unacceptable durability have been seen in practice, particularly when high operating temperatures occur in sunlight. Artificial weathering tests are used to assess plastics glazing materials in a reasonably short time, two main types being utilised in this study. The applicability of ultra-fast methods of accelerated degradation has been shown to depend on the extent to which the mechanisms of degradation simulate practical weathering, since different procedures were found to promote different mechanisms in the materials tested. Misleading information was obtained when the full spectrum of solar UV and much of the visible was not adequately reproduced in the accelerated tests. In particular an established grade of PVC-U performed unexpectedly poorly under fluorescent lamps. Procedures based on xenon arc sources were found to be the most generally applicable because they better reproduce the full solar spectrum range and, hence, the typical effects observed in plastics materials in practice. Several analytical techniques were used to characterise the virgin polymers and to assess the weathered materials. Two commercial grades of each polymer type (poly[vinylchloride], polycarbonate and poly[methylmethacrylate]) were studied, and measured changes explained in terms of initial polymer properties. Profiling of chemical (e.g. carbonyl index measured by photo-acoustic fourier transform infrared), physical (e.g. molecular weight, surface gloss/roughness), optical (e.g. colour, light transmission) and mechanical properties (e.g. impact resistance) as a function of exposure period and environmental conditions enabled degradation rates and mechanisms to be established for each material. In conducting these tests particular attention was given to the control and effects of sample temperature during weathering, and to the wavelength range of the light source used. Poly(vinylchloride) was affected much more by weathering at higher temperatures, and by exposure to short wavelength radiation, than was polycarbonate, with acrylic being the most durable overall. Practical applications of this work are through Standards committees primarily. in particular with plastics rootlights (B/542/8 and CEN/TCI28/SC9).

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The degradation of amorphous and orientated PET is investigated by several analytical methods. In this study, samples of both amorphous and orientated PET material were exposed to wet and dry soil, various humidities and temperature as well as UV irradiation. Results of accelerated ageing studies indicate that the amorphous sheet and biaxially orientated bottles degrade mainly due to de-esterification and oxidative chain scission due to their low crystallinity. At high temperatures (70-90) breakdown, as characterisedb y viscosity and chain scission measurements,is indicative of significant polymer deterioration. Breakdown is enhanced by increasing temperature, increasing relative humidity and UV irradiation. In this regard the polyester bottles are more stable than sheet due to a greater degree of orientation and hence higher degree of crystallinity. However, the rate of degradation is also a function of the surrounding environment. During the course of degradation, an increase in crystallinity was observed for both sheet and bottles. The rate of increase in crystallinity is initially rapid and is associated with plasticization by moisture and subsequent annealing. The dry conditions and UV irradiation cause negligible increase in crystallinity . An increase in the number of end groups was observed which is due to chain scission. Whilst the carboxyl and hydroxyl end groups were increased at the same rate asthermally degraded samples, the increase of carboxyl end groups for UV degraded samples was significantly higher than hydroxyl end groups. This increase is initially sharp and then more gradual with almost the same rate as hydroxyl end groups. A higher level of carboxyl end groups is due to the release of carbon dioxide and carbon monoxide mainly on the surface of the polymer. In this work two methods were used to introduce stability to the polymer. The first was preconditioning the polymer in an inert atmosphere for 48 hours at 600C which had a better effect for bottles This stabilizing effect was observed for both thermal degradation and UV irradiation of polyester materials. The second method was stabilizing polyester against UV irradiation by the incorporation of naphthalenea nd benzophenoned erivatives to the structure of the polyester. In this case the dihydroxybenzophenone showed the greatest stabilizing effect. Hydroperoxide formation during hydrolytic degradation is found to be both temperature and humidity dependent and appears to play a secondary role in thermal oxidation.

The need to tailor release-rate profiles from polymeric microspheres remains one of the leading challenges in controlled drug delivery. Microsphere size, which has a significant effect on drug release rate, can potentially be varied to design a controlled drug delivery system with desired release profile. In addition, drug release rate from polymeric microspheres is dependent on material properties such as polymer molecular weight. Mathematical modeling provides insight into the fundamental processes that govern the release, and once validated with experimental results, it can be used to tailor a desired controlled drug delivery system. To these ends, PLG microspheres were fabricated using the oil-in-water emulsion technique. A quantitative study that describes the size distribution of poly(lactide-coglycolide) (PLG) microspheres is presented. A fluid mechanics-based correlation that predicts the mean microsphere diameter is formulated based on the theory of emulsification in turbulent flow. The effects of microspheres’ mean diameter, polydispersity, and polymer molecular weight on therapeutic drug release rate from poly(lactide-co-glycolide) (PLG) microspheres were investigated experimentally. Based on the experimental results, a suitable mathematical theory has been developed that incorporates the effect of microsphere size distribution and polymer degradation on drug release. In addition, a numerical optimization technique, based on the least squares method, was developed to achieve desired therapeutic drug release profiles by combining individual microsphere populations. The fluid mechanics-based mathematical correlation that predicts microsphere mean diameter provided a close fit to the experimental results. We show from in vitro release experiments that microsphere size has a significant effect on drug release rate. The initial release rate decreased with an increase in microsphere size. In addition, the release profile changed from first order to concave-upward (sigmoidal) as the microsphere size was increased. The mathematical model gave a good fit to the experimental release data. Using the numerical optimization technique, it was possible to achieve desired release profiles, in particular zero-order and pulsatile release, by combining individual microsphere populations at the appropriate proportions. Overall, this work shows that engineering polymeric microsphere populations having predetermined characteristics is an effective means to obtain desired therapeutic drug release patterns, relevant for controlled drug delivery.