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出典(authority):フリー百科事典『ウィキペディア(Wikipedia)』「2015/03/23 15:28:40」(JST)
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Photo-oxidation is the degradation of a polymer surface in the presence of oxygen or ozone. The effect is facilitated by radiant energy such as UV or artificial light. This process is the most significant factor in weathering of polymers. Photo-oxidation is a chemical change that reduces the polymer's molecular weight. As a consequence of this change the material becomes more brittle, with a reduction in its tensile, impact and elongation strength. Discoloration and loss of surface smoothness accompany photo-oxidation. High temperature and localized stress concentrations are factors that significantly increase the effect of photo-oxidation.
Effect of UV exposure on polypropylene rope
Contents
- 1 Photo-oxidation protection
- 1.1 Effects of dyes/pigments
- 1.2 Chemical mechanism
- 2 References
- 3 Further reading
- 4 See also
- 5 External links
Photo-oxidation protection
Poly(ethylene-naphthalate) (PEN) can be protected by applying a zinc oxide coating, which acts as protective film reducing the diffusion of oxygen.[1] Zinc oxide can also be used on polycarbonate (PC) to decrease the oxidation and photo-yellowing rate caused by solar radiation.[2]
Effects of dyes/pigments
Adding pigment light absorbers and photostabilizers (UV absorbers) is one way to minimise photo-oxidation in polymers. Antioxidants are used to inhibit the formation of hydroperoxides in the photo-oxidation process.[3]
Dyes and pigments are used in polymer materials to provide color changing properties. These additives can reduce the rate of polymer degradation. Cu-phthalocyanine dye can help stabilize against degradation, but in other situations such as photochemical aging can actually accelerate degradation. The excited Cu-phthalocyanine may abstract hydrogen atoms from methyl groups in the PC, which increase the formation of free radicals. This acts as the starting points for the sequential photo-oxidation reactions leading to the degradation of the PC.[4]
Electron transfer sensitization is a mechanism where the excited Cu-phthalocyanine abstracts electrons from PC to form Cu-Ph radical anion and PC radical cations. These species in the presence of oxygen can cause oxidation of the aromatic ring.[5]
Chemical mechanism
Aldehydes, ketones and carboxylic acids along or at the end of polymer chains are generated by oxygenated species in photolysis of photo-oxidation. The initiation of photo-oxidation reactions is due to the existence of chromophoric groups in the macromolecules. Photo-oxidation can occur simultaneously with thermal degradation and each of these effects can accelerate the other.
The photo-oxidation reactions include chain scission, cross linking and secondary oxidative reactions. The following process steps can be considered:[6]
- Initial step: Free radicals are formed by photon absorption.
- Chain Propagation step: A free radical reacts with oxygen to produce a polymer peroxy radical (POO•). This reacts with a polymer molecule to generate polymer hydroperoxide (POOH) and a new polymer alkyl radical (P•).
- Chain Branching: Polymer oxy radicals (PO•) and hydroxy radicals (HO•) are formed by photolysis.
- Termination step: Cross linking is a result of the reaction of different free radicals with each other.
where[6] PH = Polymer
P• = Polymer alkyl radical
PO• = Polymer oxy radical (Polymer alkoxy radical)
POO• = Polymer peroxy radical (Polymer alkylperoxy radical)
POOH = Polymer hydroperoxide
HO• = hydroxy radical
References
- ^ L. Guedri-Knani, J. L. Gardette, M. Jacquet, A. Rivaton, Photoprotection of poly(ethylene-naphthalate) by zinc oxide coating, Surface and Coatings Technology, Volumes 180-181, 1 March 2004, Pages 71-75
- ^ A. Moustaghfir, E. Tomasella, A. Rivaton, B. Mailhot, M. Jacquet, J. L. Gardette, J. Cellier, Sputtered zinc oxide coatings: structural study and application to the photoprotection of the polycarbonate, Surface and Coatings Technology, Volumes 180-181, 1 March 2004, Pages 642-645.
- ^ "Photo-oxidisation of electroluminescent polymers studied by core level photoabsorption specttroscopy". American institute of physics 1996. Retrieved 9 February 2011.
- ^ "THE PHOTO-OXIDATION OF POLYMERS - A comparison with low molecular weight compounds". Pergamon Press Ltd. 1979 - Pure & Appi. Chem., Vol. 51, pp.233—240. Retrieved 9 February 2011.
- ^ Clodoaldo Saron, Fabio Zulli, Marco Giordano, Maria Isabel Felisberti, Influence of copper-phthalocyanine on the photodegradation of polycarbonate, Polymer Degradation and Stability, Volume 91, Issue 12, December 2006, Pages 3301-3311
- ^ a b Rabek, JF 1990, Photostabilization of Polymers:Principles and Application, ELSEVIER SCIENCE PUBLISHER LTD, England
Further reading
- Grassie, N & Scott, G 1985, Polymer Degradation Stabilisation, Press Syndicate of University of Cambridge, England
- Schnabel, W 1981, Polymer Degradation: Principles and Practical Applications, Macmillan Publishing Co., Inc, New York
See also
- forensic polymer engineering
- Polymer degradation
- Factors of polymer weathering
External links
- , Photo-Oxidation accessed 9 February 2011
UpToDate Contents
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English Journal
- A high-precision sampling scheme to assess persistence and transport characteristics of micropollutants in rivers.
- Schwientek M1, Guillet G2, Rügner H3, Kuch B4, Grathwohl P2.
- The Science of the total environment.Sci Total Environ.2016 Jan 1;540:444-54. doi: 10.1016/j.scitotenv.2015.07.135. Epub 2015 Aug 15.
- Increasing numbers of organic micropollutants are emitted into rivers via municipal wastewaters. Due to their persistence many pollutants pass wastewater treatment plants without substantial removal. Transport and fate of pollutants in receiving waters and export to downstream ecosystems is not well
- PMID 26283620
- Solar oxidation and removal of arsenic - Key parameters for continuous flow applications.
- Gill LW1, O'Farrell C2.
- Water research.Water Res.2015 Dec 1;86:46-57. doi: 10.1016/j.watres.2015.06.010. Epub 2015 Jun 11.
- Solar oxidation to remove arsenic from water has previously been investigated as a batch process. This research has investigated the kinetic parameters for the design of a continuous flow solar reactor to remove arsenic from contaminated groundwater supplies. Continuous flow recirculated batch exper
- PMID 26093797
- Interfacial band alignment for photocatalytic charge separation in TiO2 nanotube arrays coated with CuPt nanoparticles.
- Farsinezhad S1, Sharma H, Shankar K.
- Physical chemistry chemical physics : PCCP.Phys Chem Chem Phys.2015 Nov 28;17(44):29723-33. doi: 10.1039/c5cp05679a. Epub 2015 Oct 19.
- n-Type anatase-phase one-dimensional TiO2 nanostructure arrays coated with nanoparticles of Cu or CuPt have emerged as high performance photocatalysts for both photooxidation and photoreduction. The properties of the catalyst-promoter interface are recognized to be critical to this high performance
- PMID 26478516
Japanese Journal
- Long-term (2001-2013) observations of water-soluble dicarboxylic acids and related compounds over the western North Pacific: trends, seasonality and source apportionment
- ニワトリとウズラ卵殻のプロトポルフィリンとビリベルジン分布
- 生物試料分析 = Journal of analytical bio-science 40(3), 168-175, 2017
- NAID 40021259120
- 二次有機エアロゾル(SOA)低濃度条件のモノテルペンのO<sub>3</sub>分解反応における2生成物モデルのSOA生成パラメータ
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