Discoloration of cellulose solutions in N-methylmorpholine-N-oxide (Lyocell). Part 2: Isolation and identification of chromophores

Abstract

The Lyocell process is a modern 'green' industrial fiber-making technology, which employs N-methylmorpholine-N-oxide monohydrate (NMMO) to directly dissolve cellulose. One problem in Lyocell processing is the discoloration of the spinning dope due to chemical side reactions. Two different methods were elaborated to isolate chromophores, which are present in minute amounts only, from Lyocell fibers, the first one using hydrogen chloride in alcoholic solution, the second one employing boron trifluorideacetic acid complex. Several chromophores were unambiguously identified by a combination of analytical techniques and comparison to authentic samples. Carbohydrate condensation products, such as catechols, were shown to dominate in early phases of chromophore formation. In later stages, these initial chromophores undergo further condensation reactions with degradation products of NMMO and NMMO itself, leading to nitrogen-containing heterocycles and quinoid products, among others. The incorporation of nitrogen into the chromophores and thus the participation of the solvent in chromophore formation were proven.

Chromophores in lignin-free cellulosic materials belong to three compound classes. Chromophores in cellulosics, XII

“…The CRI method was applied as previously published (Rosenau et al 2004a(Rosenau et al , b, 2005a(Rosenau et al , b, 2007. In brief, cellulosic material is suspended in a bidistilled solvent in the presence of BF3 acetate complex/sodium sulfite as the catalyst.…”

“…Due to their extremely low concentrations in the ppm to ppb range, individual colored compounds-called chromophores which literally means ''carrier of color'' from Ancient Greek vqxla = color and /eqeim = to carry-eluded isolation and identification (Suess and Filho 2003). This situation changed with the advent of a suitable approach toward this very purpose, later accepted in pertinent literature as the CRI method (chromophore release and identification), when the chemical structures of chromophores in cellulosics became analytically accessible (Rosenau et al 2004a(Rosenau et al , b, 2005a.…”

Studies on DMSO-containing carbanilation mixtures: chemistry, oxidations and cellulose integrity

“…The C-6 hydroxymethyl groups are thus oxidized to the aldehyde stage only, but not further to glucuronic acid moieties. Similarly, C-2 or C-3 keto groups are introduced without any further cleavage of adjacent carbon-carbon bonds (as for instance in periodate or permanganate oxidations).3 The structure of this compound strongly resembles the naphthoquinones isolated as trace chromophores from cellulosic fiber material, seeRosenau et al (2004Rosenau et al ( , 2005.…”

Investigation of toxic factors affecting cells of rat brains exposed to 3-methylcatechol

“…Measurement of 3-methylcatechol autoxidation in a cell-free system Neutral aqueous solutions of 3MC, like other phenolic compounds, undergo spontaneous oxidative decomposition (Rosenau et al, 2005).…”