Quantitative model for the time development of diffusion-limited oxidation profiles

is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. Thermal oxidation in air at atmospheric pressure, in the 80e140 C temperature range and in oxygen at 100 C in the 0.02e3 MPa pressure range, of unvulcanized, unstabilized, unfilled polychloroprene (CR) has been characterized using FTIR and chlorine concentration measurement. The kinetic analysis was focused on double bond consumption. A mechanistic scheme involving unimolecular and bimolecular hydroperoxide decomposition, oxygen addition to alkyl radicals, hydrogen abstraction on allylic methylenes, alkyl and peroxyl additions to double bonds and terminations involving alkyl and peroxy radicals was elaborated. The corresponding rate constants were partly extracted from the literature and partly determined from experimental data using the kinetic model derived from the mechanistic scheme in an inverse approach. Among the specificities of polychloroprene, the following were revealed: The rate of double bond consumption is a hyperbolic function of oxygen pressure that allows a law previously established for the oxidation of saturated substrates to be generalized. CR oxidation is characterized by the absence of an induction period that reveals the instability of hydroperoxides. The kinetic analysis also reveals that peroxyl addition is faster than hydrogen abstraction but slower in CR than in common hydrocarbon polydienes.

Section: Physical Meaning Of Rate Constant Values and Their Hierarchysupporting

confidence: 79%

Oxidation of unvulcanized, unstabilized polychloroprene: A kinetic study

Gac

Roux

Verdú

et al. 2014

“…This hypothesis allows using certain laws established for oxygen absorption, where the oxygen pressure dependence is taken into account. For instance, it was established that in certain conditions, especially stationary state and long kinetic chains, the oxidation rate can be described as an hyperbolic function of oxygen pressure [22]. To put in evidence the oxygen pressure dependence in our case, the initial carbonyl growth rate is plotted against oxygen pressure in Fig.…”

Section: Infrared Spectramentioning

confidence: 85%

Molecular and macromolecular structure changes in polyamide 11 during thermal oxidation

Okamba-Diogo

Richaud

Verdú

et al. 2014

“…It turns out that such DLO effects are quite often observed for polymers under typical accelerated aging conditions [4, 11,16]. There are many experimental methods that can be used to screen for such effects [17].…”

Section: Wear-out Example When Superposition Appears To Be Valid-nitrmentioning

confidence: 99%

“…There are many experimental methods that can be used to screen for such effects [17]. One of the most useful for elastomers is modulus profiling [7], which involves an instrument that allows the modulus to be quantitatively mapped (typical experimental scatter of 35°/0) across the cross-section of a material with a resolution of approximately 50 p.m. Figure 11 shows modulus profiles across the 2-mm thick nitrile rubber material after aging for various times at the four highest accelerated aging temperatures [11 ]. The x-axis variable, P, gives the percentage of the distance from one air-exposed surface to the opposite air-exposed surface.…”

Section: Wear-out Example When Superposition Appears To Be Valid-nitrmentioning

confidence: 99%

“…As the temperature is lowered, the rate of oxygen consumption goes down faster than the oxygen permeation rate, leading to reductions in the importance of DLO. At the lowest temperature of 64.5°C, where DLO effects are no longer important, the degradation gives steady homogeneous increases in modulus [11]. Besides various experimental methods capable of monitoring DLO effects, it is now possible to theoretically model DLO and therefore estimate its importance before any accelerated aging experiments are initiated [11, 14,1 5].…”

Section: Wear-out Example When Superposition Appears To Be Valid-nitrmentioning

confidence: 99%

See 1 more Smart Citation

The wear-out approach for predicting the remaining lifetime of materials

Gillen

Celina

2000

Failure models based on the Palmgren-Miner concept that material darnage is cumulative have been derived and used mainly for fatigue life predictions for metals and composite materials. Wexeview the principles underlying such models and suggest ways in which they may be best applied to polymeric materials in temperature environments. We first outline expectations when polymer degradation data can be rigorously time-temperature superposed over a given temperature range. For a step change in temperature after darnage has occurred at an initial temperature in this range, we show that the remaining lifetime at the second temperature should be linearly related to the aging time prior to the step. This predicted linearity implies that it should be possible to estimate the remaining and therefore the service lifetime of polymers by completing the aging at an accelerated temperature. We refer to this generic temperature-step method as the "Wear-out" approach. We next outline the expectations for Wear-out experiments when timetemperature superposition is invalid. Experimental Wear-out results are then analyzed for one material where time-temperature superposition is valid and for another where evidence suggests it is invalid. In analyzing the data, we introduce a procedure that we refer to as time-degradation superposition. This procedure not only utilizes all of the experimental data instead of a single point from each data set, but also allows us to determine the importance of any "interaction effects".