Isothermal degradation of cis‐1,4‐polyisoprene vulcanizates

Abstract

SynopsisThe isothermal degradation of high cis-l,4-polyisoprene Vulcanizates having different crosslinking structures was investigated by a measurement of weight loss of sample, I R and NMR, gel permeation chromatography (GPC), and gas chromatography (GC). The degradation behavior of dicumy peroxide-cured sample is similar to that of the uncrosslinked one. On the other hand, a sulfur-cured sample is very different from the other samples. At the initial stage of the degradation, weight loss in this sample is faster than that in an uncrosslinked one. Furthermore, a microstructural change in this polymer occurring by thermal degradation is also very much larger than microstructural changes in the others. This will be attributed to polythiyl radicals produced by the scission of polysulfide crosslinkages. Although the polyisoprene chain undergoes random scission along the main chain above 473 K under inert gas or in uacuo, a molecular weight distribution of the residue after thermal degradation was broadened as the degradation proceeded. That is to say, the fragments having enormous molecular weight increase together with the production of lower molecular weight compounds. This indicates the occurrence of crosslinking reaction and the addition of polymer radicals to carbon-carbon double bonds in another polymer molecule in the thermal degradation process. Such reactions are thought to take place in the crosslinked polymers, in particular the sulfur-cured polymer, in larger quantities. Thermal degradation mechanisms were discussed in some detail.

Characterization of the liquid products obtained in tyre pyrolysis

“…Limonene (t R = 22.71 min) is the one present in the highest concentration. Several researchers have reported that limonene decreases as the pyrolysis temperature is increased [8,[34][35][36]. Table 5 also shows a very important decrease of limonene concentration with temperature (from ≈21 to 3%).…”

Limonene-Rich Liquids from Pyrolysis of Heavy Automotive Tire Wastes

“…Then the reactor was purged before experiments by the flow of N 2 gas of 4 L/min for 5 min to remove air inside. The reactor heater (power system) and LPG burner were switched on, and the sample was heated at heating rates of [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] o C/min to a desired value of temperature of either 375, 425, 475, 525 or 575 o C and hold at that temperature for 50 min, or no further visible vapor product coming out. Nitrogen gas was supplied in order to maintain the inert atmosphere in the reactor and also to sweep away the pyrolyzed vapor product to the condensers.…”

“…Tamura et al (19) have also shown that isoprene and D,L-limonene are formed in high concentration in natural rubber pyrolysis and they suggest that they are produced by depolymerisation from polymer radicals, by β-scission of the double bond. The polymer radicals are liable to form six-membered rings, especially under mild pyrolysis Heat conditions and therefore the D,L-limonene is formed predominantly at lower temperature.…”

“…One is the composition of raw material; formation of aromatic rings from alkenes via the Diels-Alder reactions dominantly occurred during pyrolysis of BR part in the tire wastes (3) . Another one is that limonene and/or limonene precursors might have thermally degraded into aromatic compounds at high temperature (4,19) . Therefore it is the opinion of the authors that as the pyrolysis temperature is raised, more non-aromatic compounds link to aromatic structures yielding as a result a greater proportion of aromatic compounds.…”

Limonene ethers from tire pyrolysis oil

“…It has been known that tire pyrolysis oil contains DLlimonene produced by depolymerization of natural rubber occurring by b-scission at double bonds [1] or by monomer recombination via a Diesel-Alder reaction [2]. The major products of the isoprene dimer species are DL-limonene [1-methyl-4-(1-methylethenyl)-cyclohexene] and 1,4-dimethyl-4-vinylcyclohexene.…”