Effect of the combination of a benzophenone‐type ultraviolet absorber with thermal stabilizers on the photodegradation of poly(vinyl chloride)

Abstract

The effect of the combination of a UV absorber (Chimassorb 81) with different types of thermal stabilizers, including an organic calcium complex and an organotin mercaptide, on the photodegradation of poly(vinyl chloride) (PVC) was investigated by color difference measurements, UV-Vis spectroscopy, Fourier-transform infrared spectroscopy, thermogravimetric (TG) analysis, and viscosity-average molecular weight determination. Films of PVC containing 0.5 phr of Chimassorb 81, with and without 2 phr of a thermal stabilizer, were prepared by solution casting. Then the accelerated UV weathering of the films was carried out under xenon light with an irradiance of 0.51 W/(m 2 Á nm) at 658C. The results showed that both Chimassorb 81 and the mixture of Chimassorb 81 with the organic calcium complex showed good behavior in inhibiting the photodehydrochlorination and photooxidation of PVC. In contrast, the combination of Chimassorb 81 and methyltin mercaptide significantly accelerated initial color development during the final 200 h of exposure because of the UV sensitivity of the organotin. Moreover, when Chimassorb 81 and the methyltin mercaptide were used together to stabilize PVC films, the expected antioxidant effect of the mixture was not observed, in contrast to the behavior found with other stabilized systems, perhaps because the Chimassorb 81 had been depleted by the methyltin mercaptide during the UV irradiation. The TG analysis revealed that ultraviolet irradiation had caused severe destruction of the PVC chains. However, addition of Chimassorb 81 or the combination of Chimassorb 81 with the organic calcium complex effectively prevented the destruction, as was demonstrated by changes in the activation energies for thermal degradation.

Photodegradation profiles of PVC compound and wood/PVC composites under UV weathering

“…L* represents the lightness, whereas a* and b* are the chromaticity coordinates. The total color changes or discolorations of the weathered specimens were calculated from differences of lightness and chromatic coordinates (#E) of unweathered and weathered PVC and WPVC specimens [25].…”

Nanocompósitos PVC/Nanotubos de Carbono: Avaliação da Resistividade Elétrica e Efeito do Solvente Utilizado na Obtenção dos Nanocompósitos nas Propriedades Térmicas

“…A primeira etapa da degradação inicia a 250 °C e é atribuída a reação de desidrocloração do PVC e formação de estrutura linear poliênica. A segunda etapa ocorre acima de 450 °C sendo atribuída à ruptura das duplas ligações da estrutura poliênica, formando hidrocarbonetos voláteis além de resíduo sólido de carvão [20,21] . Na Figura 3 estão mostrados os espectros na região do infravermelho para filmes de PVC após desmoldagem e após tratamento por 48 h a 90 °C.…”

Principles of Stabilizer Selection

“…15 In the case of PVC (true for other polymers as well), a six-membered quasi-ring formed by intramolecular hydrogen bonding constitutes the key to the stabilizing mechanism of tautomerism between the phenolic and quinoid forms. 16 But this has been found to be affected by the methyltin mercaptide thermal stabilizer which is UV-sensitive, and the SCH 2 COOC 8 H 17 radical generated by decomposition of tin stabilizer is reactive enough to abstract an H atom from the ortho-OH group of Chimassorb 81, according to the following equation: 16 This reaction causes the UV absorber to no longer have its protective effect. 16 It is also proposed that HAS attraction to polar hydroperoxide groups is a consequence of hydrogen bonding to the lone pair of electrons on the nitrogen atom of the HAS piperidine group.…”

“…16 But this has been found to be affected by the methyltin mercaptide thermal stabilizer which is UV-sensitive, and the SCH 2 COOC 8 H 17 radical generated by decomposition of tin stabilizer is reactive enough to abstract an H atom from the ortho-OH group of Chimassorb 81, according to the following equation: 16 This reaction causes the UV absorber to no longer have its protective effect. 16 It is also proposed that HAS attraction to polar hydroperoxide groups is a consequence of hydrogen bonding to the lone pair of electrons on the nitrogen atom of the HAS piperidine group. 17 This strong affinity concentrated on the deleterious oxidized areas of a polymer accounts for why HAS are such efficient photostabilizers.…”