Application case of differential scanning calorimeter for testing PE plastic pipeline oxidation induction

Polyethylene (PE) pipes have excellent chemical stability, are non-toxic, and are resistant to various chemicals such as hydrochloric acid, fluoric acid, phosphoric acid, formic acid, amines, potassium hydroxide, sodium hydroxide, etc. at room temperature. Polyethylene pipes are flexible, tough, lightweight, and have strong wear resistance. They are widely used in various fields of life, such as petroleum, chemical, water supply, drainage, natural gas, etc.

　　Application of DSC in measuring the oxidation induction period of PE pipes

The thermal oxidative stability of polyethylene pipes is one of the main reasons for their qualitative change and brittle failure. It directly affects the shelf life and service life of the pipe. The service life of polyethylene materials is usually determined by measuring their oxidation induction period time (OIT). Oxidation induction time is the time at which a sample begins to undergo an automatic catalytic oxidation reaction under high temperature (200 ℃) oxygen conditions. It is an indicator for evaluating the material's ability to resist thermal degradation during molding, storage, welding, and use. The longer the oxidation induction period, the longer the service life of the pipeline; The shorter the oxidation induction period, the shorter the service life of the pipeline. The oxidation induction period method is a simple and feasible test method for accelerating aging. Although it cannot represent the actual results of materials in complex usage environments, it can predict the thermal oxidative stability of materials to a certain extent, which can be used to guide production material selection and optimize products.

Measurement standards

Part 6 of GB/T19466 "Plastic Differential Scanning Calorimetry (DSC)": Determination of Oxidation Induction Time (Isothermal OIT) and Oxidation Induction Temperature (Dynamic OIT).

measuring instrument　

1. Instrument: DZ-DSC100A Differential Scanning Calorimeter

2. Gas: Nitrogen, Oxygen

3. Test sample: PE pipeline material

　　experimental parameters　　

1. Sample weight: 10 ± 3mg

2. Gas flow rate: 50 ± 10ml

3. Heating rate: 20 ℃/min

4. Cut off temperature: 200 ℃

　　Experimental operation　

Trim and weigh the sample to about 10mg, then place it inside an aluminum crucible, and take another aluminum crucible for comparative experiments. Then place the two crucibles separately inside the furnace body of the instrument. Cover the lid one by one. Raise the temperature to 200 ° C under the protection of a nitrogen atmosphere and maintain a constant temperature for 5 minutes. After 5 minutes of constant temperature, immediately switch to oxygen and measure the time required for the sample to reach the oxidation induction temperature point and decompose under oxygen gas conditions. This time is the oxidation induction time of PE plastic, also known as OIT. The following figure shows the software settings and OIT results:

　　graph analysis

From the above curve, it can be seen that the PE material's curve extends upwards at around 44 minutes, and an exothermic reaction occurs, that is, an oxidation reaction occurs on the surface of the sample. Therefore, the oxidation induction time of the sample is 44.3 minutes.

Attention: The higher the cut-off temperature of the experiment, the shorter the OIT time; The faster the temperature rises, the higher the oxidation induction temperature.

　　Experimental precautions

1. Different surface area to volume ratios of samples, poor uniformity of samples, residual stress, and poor contact between samples and sample dishes can all have adverse effects on the accuracy of test results.

Accurate temperature control and pure gas atmosphere are essential for eliminating the influence of non material factors on the results, which is crucial for measuring the oxidation induction period.

3. It is necessary to compare the OIT time according to a unified standard, as different standards have no comparable properties.

　　Instrument advantages

1. The new furnace structure ensures better baseline stability of the instrument during operation, thereby guaranteeing the accuracy and reliability of the test results.

2. Bidirectional control interface: DZ-DSC100A supports bidirectional control (host control and software control), making operation more convenient.

3. Alloy sensor: DZ-DSC100A uses professional alloy sensors, which have strong corrosion and oxidation resistance. Even in harsh experimental environments, they can maintain high performance and long-term stability, ensuring the accuracy and reliability of experimental data.

4. Software analysis. The supporting analysis software can collect measurement spectra in real time, perform online data analysis, and has the function of saving data

5. One click calibration function. Equipped with a one click calibration function for standard substances, users can calibrate temperature and enthalpy by themselves. This flexibility greatly facilitates user use and maintenance, while also ensuring the accuracy and consistency of test results.