Photo-oxidation of polymers—2. Photo-chain reaction of peroxide radicals in polystyrene

Kuzina, S. I.; Михайлов, А. И.

doi:10.1016/s0014-3057(97)00169-9

Cited by 32 publications

(19 citation statements)

References 9 publications

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“…To date, a rather large amount of data has been accumulated on the photochemistry and radiation chemistry of polystyrene [11][12][13][14].…”

Section: Introductionmentioning

confidence: 99%

“…However, obviously the initial step of such mechanisms is formation of radicals on exposure to radiation. This process has been quite well studied for polystyrene [9,13,14].…”

mentioning

confidence: 99%

“…On exposure to gamma radiation or UV light under vacuum or in an inert medium, initially an active radical (R alk ) and then an allyl radical (R all ) is formed in polystyrene [14]:…”

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confidence: 99%

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Fluorescence and absorption of a polystyrene-based scintillator exposed to UV laser radiation

et al. 2007

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We have established that exposure of polystyrene-based scintillator samples to UV laser radiation (248 nm) leads to a significant decrease in the fluorescence intensity. We have carried out a spectral analysis of the luminescent and absorption properties of the scintillator, which allowed us to determine the major factor in the decrease in luminescence intensity of the samples exposed to UV radiation. We propose a new hypothesis for the mechanism of the processes leading to the decrease in light output of the scintillator during operation. Introduction.A plastic scintillator is a composite consisting of an optically transparent plastic and added luminophores. A plastic scintillator displays bright luminescence when exposed to ionizing radiation and is rather stable relative to such exposure. Scintillators are made from such composites in the form of optical fibers, films, and plates with large surface area, and also bulk blocks of any size or shape, which significantly expands the possibilities for their application. The advantage of plastic scintillators is their fast response (the radioluminescence lifetime ranges from fractions of a nanosecond to several nanoseconds). They are used for radiation detection and dosimetry.The most widely used plastic scintillators are based on polystyrene with added luminophores: p-terphenyl (p-TP) and 1,4-bis(2-(5-phenyloxazolyl))benzene (POPOP). Polystyrene plastic is the most radiation resistant among the known synthetic polymers [1]; it has high transparency over a broad spectral range (λ > 290 nm). However, we should point out that the indicated characteristic is seen only in the very pure polymer. Commercial polystyrene contains impurities and structural defects absorbing in the 290-400 nm region [2][3][4].A general disadvantage of plastic scintillators is gradual loss of scintillation efficiency during operation. As the absorbed dose of ionizing radiation increases, the light output of the scintillator decreases. As the characteristic for radiation resistance, we take the value of the absorbed dose D 1/2 at which the light output is half of the initial value. For polystyrene scintillators, D 1/2 ≈ 600 kGy [3].The radiation-induced physicochemical changes leading to a decrease in the light output of a plastic scintillator have been the subject of many studies [3,[5][6][7][8][9][10]. Special attention has been focused on the loss of transparency in the plastic. It has been established that this is due to the appearance of "induced" absorption bands that are relatively intense in the 300-400 nm region and low-intensity in the visible region. The bands that appeared were assigned to macroradicals formed on exposure to radiation, some of which proved to be short-lived while others were rather stable. These data provided the basis for established ideas about the reasons for radiation-induced wear in plastic scintillators. We should point out that in some papers (see, for example, [9]), bands were seen which could not be attributed to radicals, and they were assigned to unident...

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“…To date, a rather large amount of data has been accumulated on the photochemistry and radiation chemistry of polystyrene [11][12][13][14].…”

Section: Introductionmentioning

confidence: 99%

“…However, obviously the initial step of such mechanisms is formation of radicals on exposure to radiation. This process has been quite well studied for polystyrene [9,13,14].…”

mentioning

confidence: 99%

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Fluorescence and absorption of a polystyrene-based scintillator exposed to UV laser radiation

et al. 2007

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“…Therefore, the polymer is sensitive to UV degradation, which, according to the literature, begins with the formation of alkyl and alkyl radicals. Under oxygen-containing atmosphere these are transformed into peroxide radicals with photochemical activity, which shift the absorption edge to the long-wavelength range, leading to the so-called photochain dissociation (Kuzina and Mikhailov, 1998). Only 10% of the radicals are converted by the ordinary hydroperoxide mechanism (Kuzina and Mikhailov, 2001).…”

Section: Polymer Weatheringmentioning

confidence: 99%

Evaluation of several commercial polymers as support for TiO2 in photocatalytic applications

2014

Global NEST Journal

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This work is aimed to select the best synthetic polymers available in the market with high transmittance in the TiO2 activation range that can be coated with the semiconductor and withstand the photocatalytic oxidation conditions. Among eleven commercial organic polymers with different additives and processing techniques, only polypropylene, polystyrene, sheet moulding processed poly (methyl methacrylate) and rigid polyvinyl chloride presented transmittances higher than 80% at 360 nm , which allows irradiation there through. The selected polymers were coated without a calcination step with anatase-TiO2 obtained by sol-gel. Their weathering was studied during 150 days of exposure to solar radiation, with and without the TiO2 layer. It was observed that only poly (methyl methacrylate) retains the titania and the good optical and mechanical properties after the natural weathering, and thus is the best candidate for immobilization of TiO2 for air photocatalytic treatment applications.

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“…• OH) que tem alto poder oxidante e pode promover a degradação de vários compostos poluentes em pouco tempo [27][28][29][30][31][32][33][34] . Dentre os vários processos para a obtenção destes radicais livres, destacam-se a utilização de ozônio, peróxido de hidrogê-nio, mistura destes (O 3 /H 2 O 2 ou O 3 /H 2 O 2 /UV), fotocatálise e o reagente de Fenton (mistura de peróxido de hidrogênio e sais ferrosos) 16,25 .…”

Section: Introductionunclassified

Peróxido de hidrogênio: importância e determinação

Mattos¹,

Shiraishi²,

Braz³

et al. 2003

Quím. Nova

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Recebido em 28/6/02; aceito em 9/10/02 HYDROGEN PEROXIDE: IMPORTANCE AND DETERMINATION. A brief discussion about the hydrogen peroxide importance and its determination is presented. It was emphasized some consideration of the H 2 O 2 as reagent (separated or combined), uses and methods of analysis (techniques, detection limits, linear response intervals, sensor specifications). Moreover, it was presented several applications, such as in environmental, pharmaceutical, medicine and food samples. 1,2 . Apesar do poder de reação, peróxido de hidrogênio é um metabólito natural em muitos organismos o qual, quando decomposto, resulta em oxigênio molecular e água. É formado pela ação da luz solar na água (foto-reação) em presença de substâncias húmicas (material orgânico dissolvido) [3][4][5] . É reconhecidamente citado como o oxidante mais eficiente na conversão de SO 2 em SO 4 2-, um dos maiores responsáveis pela acidez das águas de chuva [6][7][8] . Estudos têm demonstrado que a formação de peróxido de hidrogênio pode estar relacionada com a presença de espécies químicas, tais como SO 4 2-, NO 3 -e H + , nível de precipitação das chuvas, temperatura, direção do vento, intensidade da radiação solar etc. Acredita-se também que as descargas elétricas (raios) contribuem para incrementar a sua concentração 7,8 . De fato, amostras de águas de chuva coletadas antes e após temporal com raios e trovões apresentaram dados de H 2 O 2 iguais a 3 e 15 µmol L -1 respectivamente 7-9 . A primeira comercialização de H 2 O 2 data de 1800, e sua produção mundial aumenta a cada ano. Acredita-se que o peróxido de hidrogênio, na forma isolada ou combinada (principalmente) seja um dos reagentes mais empregados nas mais diversas aplicações [10][11][12] . Certamente a sua utilização deve ser conduzida com segurança e responsabilidade, para se evitar riscos de queimas e explosões 13 . Em adição ao controle da poluição, muitas vezes com ênfase ao monitoramento ambiental 6-13 , o peróxido de hidrogênio é empregado nos processos de branqueamento nas indústrias têxtil, de papel e celulose [13][14][15][16] . Também a determinação de peróxido de hidrogênio tem grande importância na área médica, pois sua presença deve ser monitorada para se evitar que as células sofram estresse [17][18][19][20][21][22][23][24] . , "estes radicais livres podem combinar-se para formar algumas moléculas ativas, as quais são de grande utilidade para o tratamento de água, tais como peróxido de hidrogê-nio e de ozônio, produtos importantes também do ponto de vista de desinfecção".O peróxido de hidrogênio é também importante nas áreas envolvidas com alimentos [36][37][38][39] , medicamentos [40][41][42] , monitoramento de processos [43][44][45] , dentre outras. Está presente em inúmeras reações bioló-gicas como principal produto de várias oxidases 2,46 , e é um parâmetro importante na quantificação destes bio-processos 46,47 . O H 2 O 2 pode ser determinado por volumetria 48,49 , espectrofotometria [50][51][52] , fluorimetria 53,54 , quimiluminescência 55,56 , algumas...

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Photo-oxidation of polymers—2. Photo-chain reaction of peroxide radicals in polystyrene

Cited by 32 publications

References 9 publications

Fluorescence and absorption of a polystyrene-based scintillator exposed to UV laser radiation

Fluorescence and absorption of a polystyrene-based scintillator exposed to UV laser radiation

Evaluation of several commercial polymers as support for TiO2 in photocatalytic applications

Peróxido de hidrogênio: importância e determinação

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