Probing the molecular dynamics in XLPE aged at different temperatures by 1H NMR relaxation time measurements

Fuzzy recognition of LDPE weathering risk based on environmental parameters

The environmental adaptabilities of low-density polyethylene (LDPE) play an important role for high-speed trains’ reliability and comfort. The weathering of LDPE depends on environment factors, while the complexity of the weathering processes inhibits the evaluation of environmental weathering risks. To elucidate the correlation between weathering and environmental factors, and to predict the weathering risk of target areas of interest, three-year-long natural weathering tests were conducted at twelve natural exposure stations in China. Properties of weathered LDPE were compared and analysed using factor analysis. The fuzzy recognition method based on analytic hierarchy process (AHP) was established and used to predict the weathering risk based on environmental database. The results indicate that the factor scores can partitioned the atmospheric environments into five weathering risk grades. This article used the accumulated cumulative temperature of the daily maximum temperature for weathering risk evaluation, which is more scientific than the annual average temperature widely used and is useful for revealing the difference in LDPE weathering in Turpan and Korla. A comparative chart of LDPE’s weathering risk in China was established by this fuzzy recognition method for the first time, which caters to the continuous extension of high-speed railway to new regions.

Non-destructive analysis of polymers and polymer-based materials by compact NMR

Low-field nuclear magnetic resonance (NMR) based on permanent magnet technologies is currently experiencing a considerable growth of popularity in studying polymer materials. Various bulk properties can be probed with compact NMR tabletop instruments by placing the sample of interest inside the magnet. Contrary to this, compact NMR sensors with open geometries give access to depth-dependent properties of polymer samples and objects of different sizes and shapes truly non-destructively by performing measurements in the inhomogeneous stray-field outside the magnet system. Some of the sensors are also portable being thus well suited for onsite measurements. The gain of both bulk and depth-dependent microscopic properties are important for establishing improved structure-property relationships needed for the rational design of new polymer formulations. Selected recent applications will be presented to illustrate this potential of compact NMR.

Single-sided Nuclear Magnetic Resonance for condition monitoring of cross-linked polyethylene exposed to aggressive media

The potential of single-sided Nuclear Magnetic Resonance (NMR) to monitor truly non-invasive changes in polymer materials during aging under aggressive media is for the first time evaluated. For this, the NMR method is used in combination with other condition monitoring methods including mechanical measurements, mass uptake, and differential scanning calorimetry. It is validated by studying for the first time the aging kinetics of silane cross-linked polyethylene (PEX) exposed to media used in oil and gas production and transportation, including aliphatic and aromatic hydrocarbons, sulphur solvents, and corrosion inhibitors in combination with CO2 and H2S. All investigated parameters changed, with the strongest effects detected for the NMR chain mobility and in the presence of hydrocarbons. Furthermore, a universal linear correlation curve could be established between the depression of the tensile strength and the chain mobility. This result represents a fundamental step towards establishing single-sided NMR as a new analytical tool for in situ condition monitoring of polyethylene working under sour conditions. The proposed approach can be easily extended to other polymer materials.