Lignin, matrix

Barsberg, S. and Thygesen, L.G. (1999). Spectroscopic properties of oxidation species generated in the lignin of wood fibres by a laccase catalysed treatment electronic hole state migration and stabilization in the lignin matrix. Biochimica et Biophysica Acta, 1472, 625-642. 

The high value for the quenching of 3,4-dimethoxyacetophenone by phenol suggests that it is probable that within the lignin structure hydroxyl groups are able to quench carbonyls by a static mechanism to yield phenoxy-ketyl radical pairs which decay on a timescales faster than the time resolution of our laser flash photolysis apparatus. Intersystem crossing rate constants for triplet radical pairs in the restricted environments of micelles have been demonstrated to be of the order of 2 -5 x 106 s-1 (25, 24). However, in the lignin matrix where diffusional processes are likely to be... 

A conclusion must be drawn from these experiments, The concentration of reactive species generated at dose rates as high as 3000 krad/h is sufficiently high so that they recombine with one another and do not have the time to diffuse and react with die surrounding lignin matrix. This is not the case when the dose rate is lower, the concentration of these reactive species is such that they have the time to diffuse and react with the lignin matrix. The result is an increase in the pulp ISO brightness. To compare our results with those used in literature (8-10-12), a 2.S Mrad dose was chosen. 

Wood can be considered as a biological composite of hollow tubes of cellulose fibers held together by a lignin matrix gluing material. Liquids are transported up and down the trees through the tubular plumbing system. About 90 percent of the wood tissue of softwood trees consists of fiber tracheid cells for liquid conduction and support. The hardwood trees evolved after the softwoods and have specialized water conduction cells called vessels. 

The application of C NMR techniques to the characterization of soda lignin confirmed that formaldehyde was released from the y-hydroxymethyl groups of C9 units during pulping via reverse aldol reactions with subsequent formation of vinyl ether structures in the lignin matrix [387]. Furthermore, in the same study, it was confirmed... 

In ARP pretreatment of hybrid poplar, deUgnification is increased with the treatment severity, but xylan removal occurs only to a certain extent. Increase of temperature from 175 to 195 °C in ARP does not affect xylan/lignin removal in hybrid poplar, yet the glucan digestibility of treated solid is increased. This is caused by an increase of cellulase accessibility to cellulose created by breakage of certain bonds and reconfiguration of the components in hemicellulose-lignin matrix. Crystallinity index of hybrid poplar increases after the ARP treatment. It is primarily caused by the removal of amorphous components,... 

Although the internal cell wall structures of diflFerent woods are not well understood, a variety of models have been proposed (4). These models vary in detail, but all have the cellulose fibrils surrounded by hemicellulose, which in turn is embedded within a lignin matrix. Hemicellulose apparently occurs as an interface between lignin and cellulose, but is covalently bonded only to lignin (2). Apparently cellulose and hemicellulose form before lignin is added in a space-filling manner (4). 

Wood is a composite material made up of cellulose fibres embedded in a relatively hydrophobic lignin matrix (Fig 3.10). For a complete breakdown of wood the lignin matrix has to be removed ore at least made hydrophilic. 

Lignin Matrix Composites from Natural Resources - ARBOFORM ... 

Optical microscopy shows that a higher amount of hardwood can be integrated into the lignin matrix whereas the fibres of softwood need more lignin to be fully covered (Figures 5.7 and 5.8). Therefore, better mechanical properties are already obtained at lower fibre contents and cannot be further increased by higher amounts of fibres than 45-50%. 

Figure 5.23 gives an illustration for two fittings from the lignin matrix composites meeting... 

---