Influence of thermal ageing on surface degradation of ethylene‐propylene‐diene elastomer (original) (raw)
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Influence of ethylene–propylene ratio on the thermal degradation behaviour of EPDM elastomers
Thermochimica Acta, 2001
The effect of ethylene/propylene content on the thermal degradation behaviour of ethylene±propylene-diene (EPDM) elastomers was investigated using conventional non-isothermal and isothermal thermogravimetric analysis (TGA) as well as modulated thermogravimetric analysis (MTGA 1 ). Kinetic parameters of degradation were evaluated using single heating rate data under a pseudo-®rst order assumption; the Flynn±Wall±Ozawa isoconversional method; isothermal methods; and MTGA 1 . Although the ethylene/propylene ratio in¯uences the onset and peak temperatures of degradation, it appears that not only the ethylene content but microstructure is also a controlling factor in determining the activation energy of degradation. Pseudo-®rst order analyses show that at least two different ®rst-order degradation reaction mechanisms dominate the degradation process. MTGA 1 analyses show that the activation energy of degradation increases throughout the reaction. Isothermal TGA con®rms that the degradation processes for PE, PP and EPDM are complicated and do not follow an nth order reaction path, rather they follow a random degradation process. #
Polymer Degradation and Stability, 2003
The thermal degradation behavior of a range of ethylene-propylene-diene (EPDM) elastomers, covering the whole range of composition, has been examined under isothermal conditions between 410 and 440 C using thermogravimetric analysis. The kinetic parameters of degradation for the polymers have been evaluated using different mathematical models based on different proposed mechanisms of degradation. The experimental data were fitted to the models using non-linear regression analysis technique based on Marquardt-Levenberg algorithm. It appears that the degradation of EPDMs follows the Avrami-Erofeev twodimensional nucleation model or a random chain-scission mechanism. No observable trend was found between the ethylene content of EPDM and the activation energy of degradation. #
Some kinetic and thermodynamic aspects of thermal degradation of lightly stabilised elastomers
Polymer Testing, 1998
The thermal stability of ethylene-propylene elastomers in the presence of light stabilizing antioxidant (Topanol OC) is studied. The oxygen uptake method was performed for determination of thermal oxidation in air atmosphere at constant temperatures (165°C, 175°C and 185°C). The experimental unit used for oxygen uptake measurements is described. The dependence of absorbed oxygen on various oxidation times reveals marked dissimilarity between the two ethylene-propylene elastomers, because the terpolymer contains 3.5% ethylidene-norbornene. Changes in the activation energy of oxidation are evaluated over the whole process time. Free energy vs reaction time curves for all degradation experiments are presented and some remarks on entropy change for the overall process are made in order to explain oxygencontaining product accumulation. Using Arrhenius plots the durability of EPDM/Topanol OC system was calculated.
Thermal behaviour of ethylene–propylene elastomer
Polymer Testing, 1998
Thermal behaviour of ethylene-proplyene rubber (EPR) during oxidation is evaluated. Rubber samples were thermally aged at 100°C for 250, 400 and 700 h in air. Thermal stability of EPR was tested by the oxygen uptake method. Measurements were performed in air at normal pressure over the temperature range from 180°C up to 200°C. Oxidation rates of thermally exposed films pointed out competition between scission, crosslinking and oxidation. Change in the free energy of degraded elastomer illustrates the manner in which the oxidation process takes place, namely peroxyl radicals previously produced in aged polymers are involved in the propagation step of oxidation.
Cross-linking assessment after accelerated ageing of ethylene propylene diene monomer rubber
Polymer Degradation and Stability, 2007
The ageing of filled and cross-linked ethylene propylene diene elastomer (EPDM) has been studied under accelerated UV irradiation (l ! 290 nm) at 60 C, thermal ageing at 100 C and in nitric acid vapours for different time intervals. Hardness measurements were performed. DSC-thermoporosimetry was used to estimate the mesh size distribution and cross-linking densities for each ageing. The development of functional groups was monitored by ATR spectroscopy. An increase in oxidation with exposure time after the different types of ageing was observed. The thermal stability of EPDM was assessed by TGA and evolved volatile gases were identified using FTIR spectroscopy.
Polymer Degradation and Stability, 1999
The crosslinking of ethylene propylene diene monomer (EPDM) resulting from photooxidation was followed by DSC. The thermograms of solvent con®ned in the gel at equilibrium were recorded. A decrease of the freezing point of the solvent with the irradiation time was observed, together with a decrease of the heat of solidi®cation of the solvent and a widening of the crystallization peak involving a modi®cation of the size distribution of the mesh within the polymeric network. A correlation was established between the energy of solidi®cation and the volume fraction of polymer in the gel. # 1999 Elsevier Science Ltd. All rights reserved. 0141-3910/99/$ -see front matter # 1999 Elsevier Science Ltd. All rights reserved. P I I : S 0 1 4 1 -3 9 1 0 ( 9 9 ) 0 0 0 3 0 -0 Polymer Degradation and Stability 65 (1999) 415±420
Mechanism and kinetics of the non-isothermal degradation of ethylenepropylene diene monomer (EPDM)
Journal of Thermal Analysis and Calorimetry, 2009
The thermal degradation behaviour of ethylenepropylene-diene (EPDM) elastomer, was examined under non-isothermal conditions at different heating rates (5, 7, 10 and 12°C/min) using thermogravimetric analysis. Kinetic parameters of degradation were evaluated using the Flynn-Wall-Ozawa isoconversional method, as well as the integral method of Coats and Redfern. A comparison between the two methods showed that the degradation of EPDM follows the Avrami-Erofeev two-dimensional nucleation model. The thermodynamic parameters were also calculated and the effect of the heating rate on each was deduced.
Journal of Non-Crystalline Solids, 2003
Photo-aging of elastomers results in two competitive processes: chain-scissions and crosslinking. The solid-to-solid cyclohexane phase transition was used to investigate the crosslinking extent in photo-oxidised ethylene propylene diene monomer (EPDM) samples by thermoporosimetry technique. Before apply this technique to EPDM, texturally wellknown silica gel samples were used to calibrate the method. By contrast to the case of liquid-to-solid heptane transition, no linear relationship was obtained between the solid-to-solid point depression (DT ) and the pore radius (R p ). The following correlation was obtained: R p ð A AÞ ¼ 16:93 þ 125:43 exp À 1=DT þ 0:0756 0:0205 with 0 > DT > À55°C:
Polymer Degradation and Stability, 2007
The thermal oxidation of an unvulcanized, unstabilized polyisoprene rubber (IR) has been studied in the 40e140 C temperature range. Ageing was monitored by FTIR determination of double bonds and carbonyl groups, mass uptake measurement, and weight average molar mass determination. A mechanistic scheme based on the standard scheme for radical chain oxidation, but taking into account the diversity of initiation processes and the existence of inter-and intramolecular radical additions to double bonds, was built. The kinetic model derived from this scheme is composed of seven differential equations to be solved in discrete thickness layers to take into account the kinetic control by oxygen diffusion. This system was numerically solved using a Matlab program dedicated to stiff systems of differential equations. The elementary rate constants and other kinetic parameters were then determined from experimental data, using an inverse approach. A set of physically reasonable parameter values was obtained, thus allowing us to envisage lifetime predictions at low temperature (long term). The results led to observations difficult to make from classical analytical studies, for instance the predominance of bimolecular hydroperoxide decomposition among other initiation modes or the competition between intermolecular hydrogen abstraction and intramolecular addition of peroxy radicals to double bonds.
The effect of accelerated aging on the surface mechanical properties of polyethylene
2003
The surface mechanical properties of polyethylene subjected to accelerated aging in Weathering Tester (QUV) and weatherometer (WOM) chambers were determined by a nanoindentation technique. It was observed that the apparent surface hardness was three times greater than that of the bulk after 1600 h of exposure in the WOM chamber, and a similar increase was also observed after 800 h of exposure in the QUV chamber. The elastic modulus at tip penetration depths of 500 nm also shows a significant increase from 400 to 2000 MPa for samples aged in the QUV chamber during 800 h. For aging times of 200 h and lower the variations in surface mechanical properties are small and restricted to a thin layer, with thickness lower than 1 mm for samples aged in both WOM or QUV chambers. The modifications in nanomechanical properties were correlated with the corresponding chemical processes due to aging, measured through the carbonyl index profile obtained from ATR-FTIR. An interpretation for the surface cracking of aged LDPE based on differential increases in elastic modulus at different depths is presented.