Fotodegradação de polímeros solúveis em água e moléculas modelo via processos oxidativos avançados / Photodegradation of water soluble polymers and model molecules via advanced oxidative processes

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

The aim of this work was to investigate polymer photodegradation mechanisms and stabilizing agents. The course of photooxidative degradation of some water soluble polymers (poly(vinylpyrrolidone), PVP; poly(acrylamide), PAM and poly(ethylene glycol), PEG) in the presence of hydrogen peroxide, Fenton reagent and iron salt has been investigated. PVP showed the lowest photostability while PAM had the greatest photostability. Iron salt was not efficient promoting degradation. PEG has been photooxidized in Fenton, photo-Fenton and UV/H2O2 systems. Samples were analysed using GPC and HPLC. GPC analysis of PEG solutions showed that in all oxidizing conditions used, the photooxidation of PEG aqueous solutions leads to an abrupt decrease of Mw, which means that the degradation of PEG implies a random chain scission mechanism. Polydispersity increases after degradation in all the systems used, confirming a random chain scission mechanism. GPC analysis also showed that the rate of degradation is much higher for the photo-Fenton system (kd = 1,010-4 mol.g-1.min-1), followed by UV/H2O2 system (kd = 3,610-5 mol.g-1.min-1 ). Fenton reagent has the lowest degradation rate (kd = 1,110-6 mol.g-1.min-1). The degradation products of PEG in all oxidizing systems, were analyzed by HPLC and lower molecular weight products were detected, i.e., EG, 2EG, 3EG, 4EG, glycolic and formic acids. The mechanism involved a consecutive process, were the larger ethyleneglycols gave rise, successively, to smaller ones. This suggested that the mechanism involved successive scissions of the polymer chain. Ethyleneglycols were successfully used as model molecules to predict PEGs photodegradation mechanism. Primary hindered phenols in combination with phosphorous-based secondary antioxidants are one of the most effective stabilizing systems, widely used in the processing stabilization and long-term application of polyolefins. The hydrolysis reaction mechanism of phosphite antioxidants, chosen to differ in chemical structure and phosphorus content, is investigated by mass spectrometric means. The analytes under investigation are exposed to accelerated humid ageing conditions and their hydrolytic pathway and stability is investigated. Different substituents around the phosphorus atom are shown to have a significant effect on the stability of the phosphites with phenol substituent producing very hydrolytically stable structures.

ASSUNTO(S)

polímeros fenton reaction photodegradation fotodegradação hydrogen peroxide reação de fenton polymers peróxido de hidrogênio

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