مقاله انگلیسی رایگان در مورد مدل تخریب UV برای پلیمرها و کامپوزیت های ماتریکس پلیمری – الزویر 2018

Severe exposure to UV radiation can rapidly accelerate degradation processes in polymeric materials [1e20]. UV radiation causes photooxidative aging, which results in the breakage of polymer chains, produces free radicals and reduces the molecular weight of polymers, resulting in a loss of surface gloss and the significant deterioration of many material properties with time. Extensive research has been performed on systematic experimental evaluations of degradations mechanisms in polymer coatings, polymer resins and Polymer Matrix Composites (PMCs) after long-term artificial UV exposures [1e20]. However, few studies have concentrated specifically on the development of analytical models of UV aging of polymeric materials [7e12]. For a polymer subjected to UV radiation, photodegradation is the main damage mechanism. Photodegradation initiates with the absorption of UV photons by chromophores i.e. hydroperoxides, catalyst residues, carbonyls, and unsaturated molecules containing double and triple bonds, and/or rings [13]. The activation processes initiated by UV photons excite states in macromolecules which leads to surface discoloration, yellowing and a loss of surface gloss [14,15]. Further exposure to UV light results in the formation of a thin layer consisting of loosely adherent particles called chalking [1,16e18]. Depending on the type of a polymer, flaking of surface resin, pitting and microcracking may also occur [6,19]. In addition, chemical aging such as chain scission by UV will result in a loss of low molecular weight or highly volatile products, which can vaporize very quickly at elevated temperature [13,20]. Most current environmental aging models for polymers and PMCs are limited to one individual degradation factor such as UV light, elevated temperature, water diffusion and others [21e26]. Few studies have concentrated on synergistic aging under multiple aging conditions involving UV [1,2,27e31]. It was shown, for example in Refs. [1,2], that the combined cyclic UV-temperaturemoisture conditions resulted in severe damage to the polymer matrices of several different PMCs, and that the damage under the cyclic conditions was more severe than under consecutive but noncyclic UV and water conditions. It has also been concluded in Ref. 1 that UV alone can damage PMC surfaces by a formation of microparticles, as shown in Fig. 1a, and that the process rapidly accelerates if slow moving water is present on the surface of the composites for debris removal purposes (Fig. 1b). Without the involvement of water, however, the particles formed by UV tend to stay on the surfaces and prevent further development and progression of UV degradation of the undelaying virgin material [1,2]. At the same time water alone does not cause much degradation in comparison with UV [1,28]. The strong UV/water condensation aging of the composites observed in Ref.