Polyethylene (PE) pipes, particularly cross-linked polyethylene (PE-Xb), are widely used in hot-water heating systems due to their durability and thermal resistance. However, prolonged exposure to elevated temperatures can cause gradual deterioration of both the polymer structure and its stabilizing additives. These chemical changes are often invisible but can significantly impact long-term performance and safety.
This technical note demonstrates how Evolved Gas Analysis–Mass Spectrometry (EGA-MS) can be effectively applied to evaluate aged deterioration in PE-Xb pipes, using only a minute sample amount, and focusing on both polymer structure and additive depletion.
[Background]
To understand the deterioration mechanism of polymeric products, it is necessary to evaluate the chemical changes in the polymers and additives. Evolved gas analysis (EGA) and thermogravimetry are complementary techniques. Both provide information about the thermal properties of polymeric materials. This note describes the analytical results obtained by EGA-MS of deteriorated cross-linked polyethylene (PE-Xb) pipes used in a hot-water heating system.
[Experimental]
EGA-MS measurements were done by a Multi-Shot Pyrolyzer (EGA/PY-3030D, Frontier Labs) interfaced directly to the split/splitless injection port of a GC/MS system. PE-Xb samples were collected by scraping the surfaces of the inner wall of “new” and “used” pipes. 0.2 mg of the sample was placed in a deactivated stainless sample cup.
[Results]
EGA-MS thermograms of “new” and “used” PE-Xb pipes are shown in Fig. 1. A single peak due to the thermal decomposition of PE is observed in both thermograms. A slight decrease in the peak top temperature of the “used” sample suggests some structural differences in the polymer.
To focus on the additive analysis, the sample weight was increased to 1 mg, and the split ratio and furnace maximum temperature were set to 1/10 and 400ºC, respectively. The EGA thermograms are shown in Fig. 2. The “new” sample shows small peaks (300–350ºC) prior to the PE decomposition in the extracted ion chromatograms (EICs) of a fragment ion of Irgafos 168 (m/z 441) and of Irganox 1076 (m/z 530), compared to the “used” one.
To learn more about how EGA-MS can be used to evaluate aged deterioration, antioxidant depletion, and additive behavior in polyethylene pipes used for hot-water heating systems, simply connect with us.
References: This technical note was developed by Frontier Laboratories Ltd. 4-16-20 Saikon, Koriyama, Fukushima, 963-8862 JAPAN. www.frontier-lab.com