Polyvinylchloride absorptive

Modification of polymers with supercritical carbon dioxide (scCO ) Absorption of scCO into polyvinylchloride (PVC) sheets at elevated temperatures. 

The kinetics of combination of radical pairs formed by quenching of the triplet excited state of B by 2,4,6-trimethylphenol (HR) in films of rigid and plasticized polyvinylchloride (PVC) were studied by the method of laser flash photolysis by Levin et al. At high concentrations of the phenol quencher ( 15 wt%), most of the triplet excited state of the ketone is quenched and the formation and disappearance of the ketyl and phenoxyl radicals can be followed from changes in their characteristic transient absorptions at 540 and 390 nm, respectively. 

Fig. 3.20 UV absorption spectra of (a) paraffin, (b) atactic polystyrene and (c) polyvinylchloride. Reproduced with permission of the Japanese Physical Society from Onari (1969).

Fig. 47. Absorption spectrum of thermally degraded polyvinylchloride (Vestolit SK 55), polyvinylbromide and a copolymer vinyl chloride—isobutene in tetrahydrofuran. The absorption maxima correspond to polyene sequences with n = 4, 5, 6, etc. [ 184 ].

Fig. 40. Absorption spectra of polyvinylchloride at 25°C irradiated at —196°C and stored at 25°C in vacuum [356].

The structure —CHC1—CH2—CO—CH2 — was found by Kwei [99] in polyvinylchloride after photo-oxidation. Such j3 chloroketones decompose by the Norrish type I mechanism without loss of chlorine atoms. Hydrogen chloride is obtained only when polyvinylchloride is photo-oxidized above 30°C [98]. It seems that zipper dehydrochlorination plays little role in the reaction occurring on exposure to ultraviolet light at temperatures below 150°C in the presence of air [97], and that hydrogen chloride is mainly a product of thermal decomposition rather than photolysis [98], The following mechanism can be proposed which takes into account the experimental results namely, that chain scission and crosslinking occur simultaneously on irradiation at 253.7 nm [100] and that carbon dioxide is evolved, while an absorption band at 1775 cm-1 (ascribed to peracids) is detected in the infrared spectrum [98]. 

Figure 28 shows that substituted cinnamic acid derivatives have a relatively low absorption in the 310—320 nm region, so that they are relatively ineffective ultraviolet absorbers. Their main advantage is that they have no phenolic hydroxyl group which could be sensitive to alkali or heavy metal ions. The alkali sensitivity is a severe shortcoming for textile applications. On the other hand, with polyoxymethylene for instance, the thermal degradation can be catalysed by phenols, and with polyvinylchloride, side reactions can occur with metal stabilizers. 

Most composite decking manufacturers utilize high-density polyethylene, (HDPE), polypropylene, or polyvinylchloride (PVC) as polymer matrix, and wood flour or rice hulls as the principal filler for their products. Some manufacturers also add mineral fillers, such as talc. These and other changes in compositions make composite materials to vary in their appearance, shape, strength, deflection, moisture absorption, fade resistance, microbial resistance, slip resistance, flammability, and other properties, which will be discussed later in this book. 

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