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About Differential Scanning Calorimeter(DSC) measuring oxidation induction time(part 2)

Nov 23, 2018

OIT(oxidation induction time) application:

Although the oxidation induction period is a test method for the plastics industry, it can be used in the CCL industry for rapid testing of the heat-resistant oxygen aging properties of CCL, providing a strong basis for formula screening and guiding research and development.

2 Polyolefin materials are commonly used for the protection and insulation of optical cables and cables, and the thermal oxidative stability of polyolefins used on optical cables and cables can be used to judge their lifetime, and the level of material stabilization can be evaluated by the oxidation induction period.

The test is described in the following aspects:


1 test instrument:

DSC-500  Differential Scanning Calorimeter 


2 According to the standard:

ISO 11357-6:2008

Plastics -- Differential scanning calorimetry (DSC) -- Part 6: Determination of oxidation induction time (isothermal OIT) and oxidation induction temperature (dynamic OIT)

 

3 principle overview:

Oxidation induction time (isothermal OIT):

The sample and reference were warmed at a constant rate in an inert atmosphere. When the specified temperature is reached, switch to the same flow rate of oxygen or air. The sample was then held at this constant temperature until an oxidation reaction was shown on the thermal analysis curve. Isothermal OIT is the time interval between the start of oxygen or air to oxidation. The starting point of oxidation is indicated by the sudden exotherm of the sample. It is embodied in the DSC curve.

Oxidation induced temperature (dynamic OIT):

The sample and reference were warmed at a constant rate in an oxygen or air atmosphere until an oxidation reaction was shown on the thermal analysis curve. Dynamic OIT is the temperature at which the oxidation reaction begins. The starting point of oxidation is indicated by the sudden increase in exotherm of the sample, which can be observed by the DSC curve.

 

4 crucibles:

Place the sample in the opening or in a sealed, but ventilated bowl. It is best to use aluminum crucibles.

5 gas flow rate:

The gas flow rate is usually 50 ± 5 ml / min. The following is an example of isothermal OIT:

 

6 Take the isothermal OIT as an example to measure the main steps:

1 .Nitrogen gas for 5 minutes before starting to heat up

2 .20 ° C / min heating rate, the temperature is selected as much as 10 times the integral temperature

3 .When the OIT is less than 10min and greater than 60min, it should be retested at lower and higher temperatures respectively.

4 .Constant temperature 3min when the set temperature is reached

5 .After the end of the constant temperature, switch the oxygen at the same flow rate, and continue to constant temperature until at least 2 minutes after the significant change point of the exotherm occurs.

6 .test completed

7 . Example curve:


image

Note: 1 The calibration of the isothermal OIT point is the intersection of a smooth curve before oxygenation and a smooth curve after oxidation of the sample (tangential analysis)

2 The higher the temperature of the sample, the shorter the oxidation induction time; the faster the heating rate, the higher the temperature during the oxidation induction period. The oxidation induction time and the oxidation induction temperature are also related to the surface area of the sample subjected to oxidation.

It is known from the above curve that the DSC curve extends downward at 11.6 min after oxygenation, which is an exothermic phenomenon, that is, the oxidation reaction of the sample occurs, that is, the oxidation induction period of the sample is 11.6 min.


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