Oxidation/oxidative induction time

As appHed to hydrocarbon resins, dsc is mainly used for the determination of glass-transition temperatures (7p. Information can also be gained as to the physical state of a material, ie, amorphous vs crystalline. As a general rule of thumb, the T of a hydrocarbon resin is approximately 50°C below the softening point. Oxidative induction times, which are also deterrnined by dsc, are used to predict the relative oxidative stabiHty of a hydrocarbon resin. 

DSC can yield both qualitative and quantitative information, and is a relatively fast technique, with typical heating rates being about 10°Cmin 1. It is routinely used to determine oxidation-induction time, see Section 2.1, which can be a useful parameter in assessing the thermal stability of a series of materials [103]. 

ISO 11357-6 Plastics - Differential scanning calorimetry (DSC)- Part 6 Determination of oxidation induction time, International Organization for Standardization, Geneva, Switzerland. 

ASTM D3895-07 Standard Test Method for Oxidative-Induction Time of Polyolefins by Differential Scanning Calorimetry, Book of Standards Vol. 08.02, ASTM International (formerly known as American Society for Testing and Materials), West Conshohocken, PA, USA. 

S.M. Marcus and R.L. Baine, Estimation of bias in the oxidative induction time measurement by pressure DSC, Application note TA-228, TA Instruments, Inc., New Castle, DE, USA. 

Chemiluminescence is the emission of light in the 300-500 nm region due to exothermic chemical reactions. With a suitable detection system this can be used to monitor the chemical reactions that occur when materials age. This technique is sensitive enough to produce results more rapidly and at lower temperatures. Chemiluminescence has been used to investigate the effect of different additives on the oxidation of polymers as well as to determine oxidation induction times which are more meaningful than those obtained from the DSC method. 

Municipal solid waste Near infrared Oxidation induction time Partial least square Post-consumer recyclate Post-consumer waste Principal component analysis Principal component regression Root-mean-square error of prediction... 

Oxidation Induction time by differential scannig calorimetry ... 

Stavinoha and Kline (2001) adapted ASTM method D 6186 (Oxidation Induction Time of Lubricating Oils by Pressure Differential Scanning Calorimetry [P-DSC]) for analyzing the oxidative stability of SME treated with antioxidants. This report concluded that isothermal P-DSC analysis is suitable for screening the effectiveness of antioxidants for treating biodiesel. 

Figure 1. Typical shape of kinetic curves of O2 absorption. Determination of oxidation induction time (tj and maximum oxidation rate (r. ...

The changes (against time) of Q02 have been calculated for PE at different temperatures, with the parameter values reported in Table I, and compared to literature data (13). At temperatures higher than 100°C, good agreement has been obtained between theory and experiment (Figure 2). However, at temperatures lower than 100°C, deviations have been observed the core of the model overestimates the oxidation induction time tj and underestimates the maximum oxidation rate rs, both deviations increasing when the temperature decreases. 

Figure 3. Arrhenius plot of the oxidation induction time for PE in oxygen excess (Po2 2 10 Pa). Points Experimental data. Continuous line kinetic model based on equations 5—9.

Figure 1. Schematic representation of the method to predict lifetime ofpipes from oxidation induction time (OIT) data. Drawn after a chart presented in Viebke and Gedde, (10).

Figure 2. Oxidation induction time (OIT not the log-scale) for samples taken at a certain depth (0.9-1.0 mm from the inner wall from PB pipes pressure-tested at 90 C with internal chlorinated water (0.5, 1.0 and 1.5 ppm Cl) as a function of the exposure time. The line is a linear fit of the data. The insert figure shows the results of extrapolation to 01T= 1 min based on OIT data from exposures shorter than tfnax- From Lundback et al.(12) and with permission from Elsevier, UK.

Thermal analysis measurements were made using a duFont 990 Thermal Analyzer using aluminum pans and a heating rate of 10 C/ min. Melting endotherms were determined In the presence of helium. Oxidative Induction times were measured Isothermally at 200 C In the presence of oxygen. A detailed description of this technique Is given in reference 4. 

The oxidation induction time can also be used as an indication of oxidation stability. No correlation has been determined between the results of this test and service performance. In the test (ASTM D-5483), a small quantity of grease in a sample pan is placed in a test cell. The cell is heated to a specified temperature and then pressurized with oxygen and is held at a regulated temperature and pressure until an exothermic reaction occurs. The extrapolated onset time is measured and reported as the oxidation... 

Figure 1.41. (a) Oxidation induction time, t, for various concentrations of oxidation inhibitor (antioxidant) as determined from oxygen uptake (or carbonyl index) plots, (b) Estimation of intrinsic inhibitor concentration, Cg, from a plot of t versus [Inhibitor]. The inverse of the slope of the plot reflects the rate of initiation. 

In reactive processing, such as reactive extrusion of thermoplastics, the use of DSC may be seen in determining the stability of the polymer formulation by measuring the oxidation induction time (OIT) (Bair, 1997). This is an isothermal experiment in the presence of air... 

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