The degradation of guayule rubber and the effect of resin components on degradation at high temperature

Abstract

SynopsisDegradation of pure guayule rubber and rubber in the presence of stearic, oleic, linoleic, and linolenic acid, has been studied at high temperatures (from 150 O C to 600 O C) using thermogravimetric analysis (TGA). On-line mass spectrometric analysis of the products of decomposition has also been done to understand the mechanisn of degradation.Degradation of rubber starta around 230° C in air and 330° C in nitrogen. Presence of acids changes the onset of degradation, because of low decomposition temperature of the acids. In the derivative curve, there is one T , , for degradation in nitrogen; two for rubber; and three for rubber containing acids are observed for degradation in air. The activation energy of degradation, as observed by isothermal kinetics, in the 1-10% weight lass region, is 225 kJ/mol in nitrogen and 167 kJ/mol in air. In the 10-100% region, however, the activation energy of degradation measured by the Freeman and Carroll method using dynamic thermogravimetry, is 239 kJ/mol in both nitrogen and air atmosphere. The main products of pyrolysis in inert atmosphere are propylene, propane, isobutylene, methyl butene, isoprene, 2,3-dimethyl cyclopentene, octene, 2,4-dimethylcyclohexene, dipentene, etc. Isoprene is found to be the most abundant. Fragments having m/e values of 136,121,107,93,79, and 53 are also produced in large quantities. The ratio of concentration of dipentene to isoprene increases marginally with temperature. The concentration of other fragments however increases drastically with temperature. The additives have no effect on the nature of products obtained. The conversion to different fragments depends upon the temperature of degradation and the stability of intermediate products. All smaller molecules are obtained from either dipentene or isoprene. A mechanism of formation of these products has been suggested.

Pyrolysis of latex gloves in the presence of Y-zeolite

“…The peak decomposition temperature for both samples was 376°C and the pyrolysis was completed at 472 o C and 450 o C for Y and W gloves respectively. Previous authors have investigated the thermal decomposition of natural rubber (Bhowmick et al, 1987;Williams and Besler, 1995) and have reported similar decomposition temperatures to those reported here.…”

A review of dipentene (dl-limonene) production from waste tire pyrolysis

“…Cataldo shows that these allylic radicals can be terminated by adventitious agents (such as oxygen) under milder conditions than pyrolytic conditions (temperatures not exceeding 380 • C), resulting in a liquid polyisoprene with a lower average molecular weight [24]. However, under pyrolytic conditions, both radicals can depropagate or unzip towards the monomer isoprene [18,19,22]. In Fig.…”

“…Whereas Bhowmick et al also considered radical formation by scission of the ˛ bond and methyl scission, Chien argues, due to differences in bond strengths, that scission of the ˇ bond is energetically the most favorable among these [18,19]. Fig.…”

“…The degradation or depolymerization of natural rubber (NR) or (synthetic) cis-1,4-polyisoprene is a radical reaction, initiated by scission of the ˇ bond with respect to the double bonds of the main polymer chain [18][19][20][21][22][23]. Whereas Bhowmick et al also considered radical formation by scission of the ˛ bond and methyl scission, Chien argues, due to differences in bond strengths, that scission of the ˇ bond is energetically the most favorable among these [18,19].…”

Kinetics of scrap tyre pyrolysis under fast heating conditions

“…Studies on the kinetics of scrap tyre pyrolysis have been carried out in the literature by means of techniques based on thermal analysis, such as thermogravimetry (TG), differential thermogravimetry (DTG) or differential scanning calorimetry (DSC) [24][25][26][27][28][29][30][31][32][33][34][35]. It must be pointed out that there are notable differences between the results obtained.…”