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Exposure to UV radiation is known to result in the development of skin cancer and the use of protectants m the form of topically applied sunscreens is becoming widespread. The compounds used within sunscreen formulations are subject to stringent tests and must be approved for use by such bodies as COLIPA (EC), or the FDA (U.S.). Despite these testing procedures the photochemical and photophysical properties of many of the active ingredients are poorly understood and not well documented. This study presents the results of detailed photophysical investigations of two sunscreen agents. Menthyl anthranilate is currently approved for use m commercially available formulations by the FDA, and N-acetyl-menthyl anthranilate has been synthesised as an analogue of N-acetyl-homomenthyl anthranilate, a compound approved for use by COLIPA until 1989. This work has highlighted some disturbing properties of these compounds. Following absorption of light both compounds fluoresce m UV-A region. Population of the triplet state also occurs to a significant extent, producing long lived species which are readily quenched by oxygen generating singlet oxygen, a potentially damaging species that has been linked to DNA damage. Furthermore, the triplet state energy of N-acetyl-menthyl anthranilate has been shown to be -315 kJmol(^-1)"', high enough to sensitise the formation of thymine dimers m the skin, another potential source of DNA damage. A thorough understanding of the behaviour of sunscreen formulations m contact with skin is vital. In vivo studies are made difficult due to restrictions in the sampling methods for currently used spectroscopic techniques such as UV and fluorescence. This work demonstrates the use of infixed spectroscopy, utilising an ATR probe and a flat ATR crystal, to analyse sunscreen formulations present on skin at normal usage levels. The technique has been used successfully to identify the individual active components within the formulations, probe the water-resistance properties and monitor changes that occur within the formulations following irradiation. A relationship between the IR absorbance values and Sun Protection Factor (SPF) values of any given formulation has been demonstrated and this has been used to test the water resistance claims of the manufacturers.

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No description available.

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The extinction of solar radiation by atmospheric aerosols influences the Ultraviolet (UV) flux at the surface, which in turn has implications on both human and environmental health. In this study we present measurements of aerosol optical depth ( and #964;a) in the UV at Boulder, Colorado and Atlanta, Georgia using direct measurements of solar UV radiation. The wavelength dependence of and #964;a and the single scattering albedo ( and #969;o) are determined from the measured values of and #964;a. Daily averages of and #964;a range between 0.09 and 0.52 at Boulder and between 0.23 and 2.09 for Atlanta between the wavelengths of 332 and 340 nm. The average ngstrm exponent ( and #945;) is 0.83 at Boulder and 1.43 in Atlanta. Results clearly show that aerosols have a significant effect on the UV Index. Day-to-day changes in the UV index during the one month measurement period in Atlanta range between 2-3 UV Index units at solar noon. It is estimated that when changes in and #964;a and and #969;o occur simultaneously, the UV Index can change up to 6 units from one day to the next at solar noon in the Atlanta area. The single scattering albedo ( and #969;o) was estimated to range between 0.8 and 0.99 for Atlanta. The results suggest an increasing trend in and #969;o with increases in and #964;a. In addition, a new synthetic current UV Index is developed which expands to nearly 10,000 cities the number of current UV Index reports that can be distributed to the public in the United States. Right now, current UV Index values are limited to specific UV measuring sites, constrained by the difficulties of maintaining accurate calibration within the network of UV instruments. The distribution of UV Index values to more cities will increase the publics awareness of the harmful effects of the sun. This new UV Index can be accessed through The Weather Channel website.

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 present study employs a range of soft-ionisation mass spectrometry techniques to study the degradation of model compounds of poly(methyl methacrylate), poly(n-butyl acrylate) and poly(2-hydroxyethyl methacrylate) under conditions designed to simulate the worst-case scenario that would be experienced by a polymer used in a surface coating on a steel roof. Vinyl-terminated and saturated polymers were degraded for periods of up to 2 years under simulated solar radiation at a temperature of 95??C, temperature of 95 ??C in the dark, and simulated solar radiation at 35??C. Similar degradation mechanisms were observed under heat and UV radiation. The presence of UV radiation accelerated the degradation occurring at high temperature, and vice versa. The combination of heat and UV radiation is far more detrimental to the polymers than either of these conditions alone. Both vinyl-terminated and saturated pMMA degraded under UV radiation at 95??C, whereas under conditions of UV radiation alone or high temperature alone, the saturated polymer was found to be stable. The vinyl-terminated pMMA degrades in all cases via the formation of ethylene oXide-type end groups, which subsequently rearrange under the expulsion of formaldehyde and 2-oxo-propionic acid methyl ester. This is in contrast to all previous literature, in which pMMA degrades via depolymerisation and is stable at 95??C. Degradation of pBA included a degradation mechanism similar to that of pMMA in addition to other polymer fragments, some of which cannot be assigned. pBA (both saturated and vinyl-terminated) showed a tendency to crosslink under all degradation conditions in this study. Only saturated pHEMA was stable under thermal degradation. In all other cases, pHEMA showed some degradation, but displayed a much greater tendency to crosslink rapidly. Terminal vinyl bonds were shown in all cases to be a weak point in the polymer with respect to degradation. pMMA was found to be the least reactive of these polymers. pHEMA showed some small degradation but had a greater tendency to crosslink via the hydroxyethyl side groups. pBA does not have any such reactive groups, and its crosslinking reaction may be explained via the acrylate backbone, or the longer alkyl ester group.