Origin of furanic compounds in thermal degradation of cellulosic insulating paper

Abstract

The chemical components of cellulosic insulation (i.e., Kraft paper, cellulose, lignin, pentosans) used in electrical transformers were aged in transformer oil to determine the relative yield of furanic degradation products. The results show that the pentosans component of the paper give, by far, the highest yield of 2-furfural followed by cellulose, levoglucosan, and lignin. However, the pentosans did not produce any detectable quantities of either 5-hydroxymethyl-2-furfuraldehyde or 2-furfurol, both of which are known to be produced by the degradation of Kraft paper. a-Cellulose was found to give 3 times as much 2-furfural as levoglucosan, which is a degradation product of cellulose, suggesting another pathway to 2-furfural production from cellulose than exclusively through the commonly quoted mechanism in which levoglucosan is the intermediate. It was also found that the production of 2-furfural from levoglucosan appears to be accelerated by acidic conditions in oxidized oil.

Controlled thermo-catalytic modification of regenerated cellulosic fibres using magnesium chloride Lewis acid

“…3a does not involve free-water, which could also react with the carbocation formed following the rupture of the glycosidic link. The laevoglucosan end group has been identified as an intermediate resulting from thermal pyrolysis (Sheirs et al 1998) and seems to be a more likely product, which could be formed following rupture at any point in the polymer chain accessible to the catalyst. Some recrystallisation does occur as a result of the baking treatment with magnesium chloride which may be evidence of increased thermal motion of the polymer chains, especially likely if larger numbers of more flexible chain ends are created by the scission reaction.…”

“…With this knowledge it is hoped that new Lewis acid treatment methods may be developed for lyocell, allowing faster soft-touch processing but with minimized loss of fabric strength. Information has also been gained concerning other Lewis acid catalysed reactions which take part in the degradation of cellulose at elevated temperatures (Kandola et al 1996;Sheirs et al 1998;Scheirs et al 2001).…”

Identification of a chemical indicator of the rupture of 1,4-β-glycosidic bonds of cellulose in an oil-impregnated insulating paper system

“…In addition, the results in Table 4 indicate that 1-butanol is mostly associated with the softwood hemicelluloses and not with a-cellulose, which makes this molecule of lesser interest as an indicator of paper damage. Finally, it is interesting to note that the relative yields measured for 2-FAL (last column in Table 4) are in conformity with data reported by Scheirs et al (1998), showing the highest amount from the hardwood hemicelluloses (xylan), followed by a moderate contribution from a-cellulose and a weak contribution from lignin. It is also significant that 2-FAL is in large part produced from D-(+)-glucose whereas this is not the case for CH 3 OH, though both appear to be formed in relatively small amounts from 1,6-anhydro-b-D-glucopyranose.…”

Controlled accessibility Lewis acid catalysed thermal reactions of regenerated cellulosic fibres

“…These agents are believed to act by catalysing dehydration and cross-linking reactions within the cellulose material structure, which suppress the formation of volatile tar products and induce the formation of a nonflammable protective char . The mechanisms of such reactions have been studied by a number of workers (Sheirs et al 1998(Sheirs et al , 2001Khelfa et al 2008;Emsley et al 1994). These same reactions are important in the deliberate thermal conversion of cellulosic fibres to carbon fibres and absorbent carbon materials, where the addition of metal salts or other acid catalysts encourages the thermally induced formation of an aromatic char (Di Blasi et al 2008;Kim et al 2001;Greinke et al 1992].…”

“…Lewis acid catalysed thermal reactions using metal salts have also been proposed for the heterogeneous depolymerisation of cellulose, to produce porous cellulosic fibre and micro-fibrillar products, for absorbency or filtration (Afanasiev et al 1989;Sarybaeva et al 1991). The mechanism of the depolymerisation reaction is believed to involve attack and bond rupture at the glyosidic oxygen and the formation of a carbo-cation, which can then react with water or the cellulose C6 hydroxyl group (Sarybaeva et al 1991;Sheirs et al 1998) This paper is concerned with Lewis acid treatments used to catalyse the partial depolymerisation of lyocell solvent-spun regenerated cellulosic fibre (Fink et al 2001), in order to create desirable fabric finishes. Controlled thermal-catalytic processing has been found to induce a partial degradation of the internal structure of lyocell fibre, which then increases its susceptibility towards surface abrasion, or fibrillation (Taylor and Collins 2007).…”