Introduction
High-DensityThe mass density is defined as the ratio between mass and volume. density polyethylene (HDPE) pipes are widely used in various industries, including water distribution, gas transportation, and industrial applications, due to their excellent mechanical properties, chemical resistance, and long-term durability. However, their service life is highly dependent on their resistance to oxidative degradation, which can lead to embrittlement, loss of mechanical strength, and ultimately, failure of the material.
The evaluation of oxidative stability is crucial for predicting the long-term performance of HDPE pipes, particularly those exposed to challenging environmental conditions, such as temperatures. One of the most effective methods for assessing the OxidationOxidation can describe different processes in the context of thermal analysis.oxidation resistance of polymers is the OxidationOxidation can describe different processes in the context of thermal analysis.Oxidation Induction Time (Oxidative-Induction Time (OIT) and Oxidative-Onset Temperature (OOT)Oxidative Induction Time (isothermal OIT) is a relative measure of the resistance of a (stabilized) material to oxidative decomposition. Oxidative-Induction Temperature (dynamic OIT) or Oxidative-Onset Temperature (OOT) is a relative measure of the resistance of a (stabilized) material to oxidative decomposition.OIT) test, which is performed using a differential scanning calorimeter (DSC). This method is standardized by international protocols, including ASTM D3895-19 and ASTM D6186- 19 [1,2].
This study aims to determine the activation energy of HDPE black pipes through kinetic analysis derived from Oxidative-Induction Time (OIT) and Oxidative-Onset Temperature (OOT)Oxidative Induction Time (isothermal OIT) is a relative measure of the resistance of a (stabilized) material to oxidative decomposition. Oxidative-Induction Temperature (dynamic OIT) or Oxidative-Onset Temperature (OOT) is a relative measure of the resistance of a (stabilized) material to oxidative decomposition.OIT tests.
Measurement Conditions
To ensure the reproducibility of the Oxidative-Induction Time (OIT) and Oxidative-Onset Temperature (OOT)Oxidative Induction Time (isothermal OIT) is a relative measure of the resistance of a (stabilized) material to oxidative decomposition. Oxidative-Induction Temperature (dynamic OIT) or Oxidative-Onset Temperature (OOT) is a relative measure of the resistance of a (stabilized) material to oxidative decomposition.OIT tests, the HDPE samples were prepared in the same manner, and three measurements were obtained [3]. The test involves several stages:
- The sample is heated to a temperature above its Melting Temperatures and EnthalpiesThe enthalpy of fusion of a substance, also known as latent heat, is a measure of the energy input, typically heat, which is necessary to convert a substance from solid to liquid state. The melting point of a substance is the temperature at which it changes state from solid (crystalline) to liquid (isotropic melt).melting point under a dynamic nitrogen flow;
- An IsothermalTests at controlled and constant temperature are called isothermal.isothermal segment is held for 3 minutes under a nitrogen atmosphere;
- The atmosphere gas is changed from nitrogen to oxygen.
The termination of the test is marked by the onset of degradation. This is automatically identified through utilization of the Proteus® measurement software. The measurement conditions are summarized in table 1.
| Instrument | NETZSCH DSC, low-temperature version |
|---|---|
| Crucible | Concavus® Al, open |
| Sample Mass | 9.90 to 10.10 mg |
| IsothermalTests at controlled and constant temperature are called isothermal.Isothermal temperature | 200, 205, 210, 215, 220 and 225°C |
| Purge gas rate (N2) | 50 ml/min |
| Atmosphere | O2/N2 |
Measurement Results
Figure 1 depicts the test results. The endothermal peak detected during heating is due to melting of the high-DensityThe mass density is defined as the ratio between mass and volume. density polyethylene black pipe. The OxidationOxidation can describe different processes in the context of thermal analysis.oxidation induction time (Oxidative-Induction Time (OIT) and Oxidative-Onset Temperature (OOT)Oxidative Induction Time (isothermal OIT) is a relative measure of the resistance of a (stabilized) material to oxidative decomposition. Oxidative-Induction Temperature (dynamic OIT) or Oxidative-Onset Temperature (OOT) is a relative measure of the resistance of a (stabilized) material to oxidative decomposition.OIT) was determined by evaluating the extrapolated onset of OxidationOxidation can describe different processes in the context of thermal analysis.oxidation in measurements with different IsothermalTests at controlled and constant temperature are called isothermal.isothermal segments. A clear increase in OIT was observed with decreasing temperatures of the IsothermalTests at controlled and constant temperature are called isothermal.isothermal segment: 9.1 min at 225°C, 13.5 min at 220°C, 20.3 min at 215°C, 31.7 min at 210°C, 48.7 min at 205°C, and 74.1 min at 200°C. This trend exhibits slower OxidationOxidation can describe different processes in the context of thermal analysis.oxidation at lower temperatures.
Kinetic Analysis OIT Measurements
The Kinetics Neo software is used for determination of the kinetic parameters for predicting the IsothermalTests at controlled and constant temperature are called isothermal.isothermal lifetime.
The kinetic analysis measurements are conducted at various IsothermalTests at controlled and constant temperature are called isothermal.isothermal temperatures, as illustrated in figure 1.
Figure 2 presents a Time-to-Event chart illustrating the Oxidative Induction Time (OIT) of a black HDPE pipe as a function of temperature. The OIT values are typically derived from Differential Scanning Calorimetry (DSC) tests (figure 1).
A kinetic analysis of OIT measurements on HDPE black pipe samples for molten polymers under different IsothermalTests at controlled and constant temperature are called isothermal.isothermal conditions was performed using the model-free IsothermalTests at controlled and constant temperature are called isothermal.Isothermal Arrhenius according to method E from ASTM E 2070-23 [4] (figure 3). The analysis produced a plot of Log(time-to-event) versus the inverse of the temperature with a linear fit curve.
For the determination of kinetic parameters, the activation energy and pre-exponential factor were derived from the slope and intercept of the linear fit. The calculation of the pre-exponential factor assumes a first-order reaction and that the event occurs at a conversion of 5%. Kinetic parameters were determined by the Kinetics Neo software for the OxidationOxidation can describe different processes in the context of thermal analysis.Oxidation Induction Time (OIT).
Kinetic parameters (table 2) were determined by the Kinetics Neo software for the OxidationOxidation can describe different processes in the context of thermal analysis.Oxidation Induction Time (OIT).
Table 2: Kinetic parameters
| Log (Pre-exponential factor) | 13.3 Log (1/s) |
|---|---|
| Ea (Activation energy) | 165 kJ/mol |
| Coefficient of determination (R²) | 0.9999 |
The application of these kinetic results facilitates the prediction of the lifetime for a liquid phase at different temperatures.
This prediction is based on the extrapolation of the Arrhenius plot (figure 3), where the straight line is extended to lower temperatures, corresponding to an increase in the 1/T value.
Simulation Prediction of the Isothermal Lifetime
Figure 4 depicts the Arrhenius plot results. This curve is an extrapolated plot for different IsothermalTests at controlled and constant temperature are called isothermal.isothermal temperatures for HDPE black pipe samples. The measurements were conducted at temperatures above the polymer Melting Temperatures and EnthalpiesThe enthalpy of fusion of a substance, also known as latent heat, is a measure of the energy input, typically heat, which is necessary to convert a substance from solid to liquid state. The melting point of a substance is the temperature at which it changes state from solid (crystalline) to liquid (isotropic melt).melting temperature. Consequently, the prediction was calculated for molten polymers. However, an extrapolation of the Arrhenius plot to lower temperatures can facilitate a comparison of the polymer’s behavior, based on the estimation of the Thermal StabilityA material is thermally stable if it does not decompose under the influence of temperature. One way to determine the thermal stability of a substance is to use a TGA (thermogravimetric analyzer). thermal stability, when the same stabilizer system is utilized [5].
Conclusion
The OIT test provides a quick and effective method for characterizing the oxidative stability of polymers and comparing their thermo-oxidative performance. A comprehensive kinetic analysis is achieved through the combination of NETZSCH DSC measurements with the NETZSCH Kinetics Neo software for the determination of kinetic parameters using the IsothermalTests at controlled and constant temperature are called isothermal.isothermal Arrhenius.
Furthermore, a comparison of the Arrhenius plots of various polymers that contain the same stabilizer can facilitate determination of the polymer that exhibits high stability under the same conditions.