Hardwood lignin content

Chemical charge, Hquor composition, time of heatup, and time at temperature of reaction are all functions of the wood species or species mix being digested and the intended use of the pulp. A typical set of conditions for southern pine chips in the production of bleachable-grade pulp for fine papers is active alkaH, 18% sulfidity, 25% and Hquor-to-wood ratio, 4 1. Time of heatup is 90 min to 170°C time at temperature of reaction, 90 min at 170°C. Hardwoods require less vigorous conditions primarily because of the lower initial lignin content. 

Hardwoods appear to have a much higher content of such aryl-glycerol-p,y-diaryl ethers because of the more restricted possibilities for condensations in the aromatic ring of sinapyl-type units owing to their two methoxyl groups. This is reflected in the greater susceptibility of hardwood lignins to mild hydrolysis (see Section I). 

Thermogravimetric weight loss for the OSL is similar to that of kraft lignin. Except for a slightly elevated methoxyl content, the NMR and degradation results in Table II are within the expected range for a hardwood lignin. 

We wish therefore to suggest that since all studies of lignin degradation have accounted for no more than about 50% and 25% of the initial lignin content of hardwoods and softwoods, respectively, that only the accessible side-chain portion of the lignin has been involved in such degradations. Indeed, little may be known about the chemical nature of the rest of the lignin substance in each case. Therefore it seems advisable to con-... 

Vinzant, T. B., Ehrman, C. I., and Himmel, M. E., SSF of pretreated hardwoods Effect of native lignin content. Appl Biochem Biotechnol 1997, 62, 97-102. 

The lignin content can be estimated from the spectrum by measuring the fractional area, A, of a band of signals between chemical shifts of 141 and 159 parts per million (ppm) relative to the total area of the spectrum. This band is assigned to C-3 and C-4 of guaiacyl units or C-3 and C-5 of syringyl units the fact that it is associated with just two carbon atoms of each structural unit means that the method can be used for both softwoods and hardwoods. 

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