Devulcanization of nitrile butadiene rubber in nitrobenzene

Abstract

Sulfur-crosslinked nitrile butadiene rubber (s-NBR) was found to be devulcanized when it was heated with nitrobenzene at 200°C for 3 h. The tetrahydrofuran (THF)-soluble fraction from s-NBR heated with nitrobenzene was purified by reprecipitation with THF/n-hexane, chloroform/ n-hexane, and THF/n-hexane systems and was then characterized by means of Fourier transform infrared (FTIR) spectroscopy, 1 H-NMR, gel permeation chromatography, dynamic thermogravimetry/differential thermal analysis (DTA), and differential scanning calorimetry (DSC). FTIR and 1 H-NMR results revealed that the THF-soluble fraction contained aromatic rings derived from nitrobenzene. Furthermore, the molecular weight of the THF-soluble fraction was much lower than that of the parent noncrosslinked poly(acrylonitrile-cobutadiene). Although the weight loss of THF-soluble fraction began at a lower temperature than that of the nonheated original nitrile butadiene rubber, the residual weight at 700°C tended to be higher for the former. This tendency became more marked with increasing time of heat treatment with nitrobenzene. The DSC-determined glass-transition temperature of the THF-soluble fraction was higher than that of the original s-NBR. To elucidate the devulcanization mechanism, we investigated two types of model reactions; one was the reaction of diphenyl disulfide with nitrobenzene, and the other was the reaction of polybutadiene with nitrobenzene. The former reaction, carried out at 250°C in diphenyl ether, yielded diphenyl sulfide with a loss of diphenyl disulfide and nitrobenzene. The use of a higher molar ratio of nitrobenzene to diphenyl disulfide resulted in a depression of diphenyl sulfide formation. The reaction of p-chloronitrobenzene with diphenyl disulfide also gave diphenyl sulfide. The reaction of polybutadiene with nitrobenzene at 200°C resulted in the backbone scission of the polymer. The THF-soluble solid product of the latter model reaction was found by FTIR and 1 H-NMR to contain aromatic rings derived from nitrobenzene. The devulcanization mechanism is discussed on the basis of a comparison of the results of the model reactions with those of the s-NBR devulcanization.

Caracterização térmica e reológica de borracha de pneu desvulcanizada por microondas

“…Dentre estas modificações pode-se citar: a quebra das ligações cruzadas, normalmente formadas por átomos de enxofre; a quebra de ligações C-C e C=C da cadeia principal do polímero; a formação de estruturas secundárias na cadeia do polímero, devido à quebra das ligações químicas e o conseqüente aparecimento de radicais livres; a formação de ramificações; e a diminuição da massa molar do polímero. As modificações na estrutura polimérica dos elastômeros têm um reflexo direto nas propriedades mecânicas e reológicas do material reciclado e ocorrem em maior ou menor grau dependendo do processo de desvulcanização utilizado [11][12][13] . Devido ao surgimento de novas propriedades no material desvulcanizado torna-se necessário realizar uma caracterização completa destes materiais.…”

Soluble hyperbranched copolymer via initiator-fragment incorporation radical copolymerization using a trivinyl monomer

“…l0 3 ) and the molecular weight distribution (M w /M n Z1. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] were also enlarged with increasing TMPTM concentration.…”

“…The resulting copolymer was isolated by pouring the polymerization mixture into a large excess of n-hexane. The conversions of the vinyl groups of TMPTM and MSt were followed in situ as a function of time by Fourier-transform near-infrared (FT-NIR) spectroscopy, where the copolymerization was conducted in a degassed and sealed Pyrex glass tube (5 mm diameter) in a custom-made aluminum furnace with an FT-NIR measurement system [11].…”

Radical polymerization behavior of dimethyl vinylphosphonate: Homopolymerization and copolymerization with trimethoxyvinylsilane

“…Homo‐ and copolymerizations of dialkyl vinylphosphonates were carried out in a degassed sealed Pyrex tube (5 mm in diameter) in the custom‐made aluminum furnace in which Fourier transform near‐infrared (FTNIR) spectroscopic measurements were performed 16. The polymerization mixtures were degassed by the freezing and thawing method before sealing in a vacuum.…”