Protocol for characterizing the molar mass distribution and oxidized functionality profiles of aged transformer papers by gel permeation chromatography (GPC)

Abstract

Oil-immersed paper insulation and paper pressboards for structural support are widely used in electrical power transformers. Cellulose thus fulfills an essential task for the smooth power supply of our societies. However, the prevailing temperatures in such equipment, combined with a targeted service life of several decades, pose a serious challenge to the long-term integrity of cellulosic paper insulation. Therefore, numerous studies have been conducted to obtain kinetic data on the degradation processes that contribute to the thermally induced decomposition of cellulose. These studies usually rely on the assessment of the average degree of polymerization by viscosity measurements. In this work, we applied and optimized more advanced methods for the characterization of cellulosic materials based on gel permeation chromatography for the special case of thermally stressed unbleached Kraft paper samples. This allowed studying the molar mass distributions of paper polymers upon exposure to heat, as well as the investigation of changes in their conformation in solution and the observation of thermally induced cross-linking. In combination with group-selective fluorescence labeling, it was possible to track over time the changes in molar mass-dependent profiles of carbonyl and carboxyl groups of authentic Kraft insulator paper samples under thermal stress. In addition, changes of the hemicellulose composition were quantified. We hope that this analytical approach to the in-depth characterization of thermally stressed insulator paper will prove useful for future studies of this important cellulose product, and that our findings will contribute to a better understanding of the thermal decomposition of paper in general. Graphical abstract

Impact of residual extractives on the thermal stability of softwood Kraft pulp

“…These findings suggest that the arabinoxylan fraction of softwood Kraft pulp is thermally less stable than the galactoglucomannan fraction. This is in accordance with recently published results obtained by the analysis of paper strips made of Kraft pulp aged in transformer oil at 170 °C (Jusner et al 2022a(Jusner et al , 2022b. In general, the presence of extractives facilitates the pyrolytic decomposition of the hemicellulose fraction in softwood Kraft pulps.…”

“…The motivation for this study was to explore whether these extractive residues, and extractives in general, also affect the thermal stability of pulp fibers, in connection to our previous studies on the thermal stability of papers in power transformers and the analysis of the thermal effects (Jusner et al 2021(Jusner et al , 2022a(Jusner et al , 2022b. It has been proposed that extractives found in wood are likely to have a deteriorating effect on the thermal stability of wood fibers (Shebani et al 2008(Shebani et al , 2009Poletto et al 2012;Chen et al 2014;Poletto 2016;Hamada et al 2017).…”

Synthesis by carbonate aminolysis and chiral recognition ability of cellulose 2,3-bis(3,5-dimethylphenyl carbamate)-6-(α-phenylethyl carbamate) selectors

“…Elemental analyses were carried out at the microanalytical laboratory of the University of Vienna with a EURO EA 3000 CHNS-O instrument (HEKAtech, Wegberg, Germany), and halide contents were determined by argentometry. GPC analyses were performed according to standard procedures (Jusner et al 2022). An Agilent Technologies, Inc. (Santa Clara, CA, USA) 1100 HPLC apparatus equipped with a quaternary pump (G1311A), autosampler (G1313A), and DAD (G1315A) was used to evaluate the enantioseparation performance of the chiral columns.…”

Immobilization of a cellulose carbamate-type chiral selector onto silica gel by alkyne-azide click chemistry for the preparation of chiral stationary chromatography phases

“…GPC analyses were performed according to standard procedures. For details about GPC procedures see (Henniges et al 2011;Jusner et al 2022). An Agilent Technologies, Inc. (Santa Clara, CA, USA) 1100 HPLC apparatus equipped with a degasser (G1322A), quaternary pump (G1311A), autosampler (G1313A), thermostatted column compartment (G1316A), and DAD (G1315A) was used to evaluate the enantioseparation performance of the chiral columns.…”