Lignins physical properties

Wood is a composite material that is made, up basically of a mixture of three main constituents, cellulose, hemicellulose, and lignin (see Textbox 54), all of them biopolymers synthesized by the plants, which differ from one another in composition and structure (see Textbox 58). The physical properties of any type of wood are determined by the nature of the tree in which the wood grows, as well as on the environmental conditions in which the tree grows. Some of the properties, such as the density of wood from different types of trees, are extremely variable, as can be appreciated from the values listed in Table 71. No distinctions as to the nature of a wood, whether it is a hardwood or a softwood, for example, can be drawn from the value of its specific gravity. 

In woody gymnosperms, there are significant differences in the distribution, reactivity and physical properties of protolignins found in the compound middle lamella and the secondary wall (1-3). Additionally, variations between lignins in vessels and fibers have also been noted (3). All of these... 

The hydroxyl content of the lignin was incrementally eliminated by acetylation and ethylation according to previously described procedures (11). In addition, modification with propylene oxide was also used to alter the original lignin structure (12). Table I presents a summary of the hydroxy content, and pertinent physical properties, of the derivatized lignins. 

We have shown by our ISO brightness and Ak measurements that the lignin was attacked by the reactive species created by the y irradiation. The results indicate that the reactive species created attack indiscriminately the phenolic hydroxyl or coniferalde-hyde groups and the quinone groups. The decrease in physical properties is associated with die attack on the micro fibrils cellulose. However, at 3000 krad/h, the increase in the ISO brightness is smaller than the one observed around 300 krad/h for the TMP, while the physical properties of the pulp are affected more profoundly at 3000 krad/h than at 300 krad/h. The physical properties of the P-TMP behave similarly, while the increase in brightness is negligible at 3000 krad/h for P-TMP. 

The results imply a competition for the reaction sites between the lignin and the cellulose, and therefore a low specificity of the reaction between the reactive species and the surrounding pulp suspension has been observed. The intensity of the variation in the measured properties (die increase in ISO brightness or the decrease in physical properties) is proportional to the dose rate used, and therefore to the concentration of... 

Although ASPEN-Plus is widely used to simulate petrochemical processes, its uses for modeling biomass processes are limited owing to the limited availability of physical properties that best describe biomass components such as cellulose, xylan, and lignin. For example, Lynd et al. (1) used conventional methods to calculate the economic viability of a biom-ass-to-ethanol process. However, with the development by the National Renewable Energy Laboratory (NREL) of an ASPEN-Plus physical property database for biofuels components, modified versions of ASPEN-Plus software can now be used to model biomass processes (2). Wooley et al. (3) used ASPEN-Plus simulation software to calculate equipment and energy costs for an entire biomass-to-ethanol process that made use of dilute-H2S04 acid pretreatment. 

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