Accessibility lignin

Aminolysis is a laborious procedure, e.g., for wood samples, a 6-7-h reaction period may be required for the aminolysis step alone. The accuracy of this method is critically dependent upon both a quantitative acetylation of phenolic hydroxyl groups and a selective deacetylation of phenolic acetyl groups. Although these requirements may not represent a serious concern in the analysis of soluble or reagent-accessible lignin preparations, they could present a problem in the case of lignocellulosic materials. 

Organosolv method uses volatile organic solvents namely acetone, methyl alcohol, ethyl alcohol or non-volatile solvent such as ethylene glycol. Biomass is soaked in solvent or combination of solvents at different ratios to produce enzymatic or microbial accessible lignin-free feedstock for fermentation (Harmsen et al., 2010). Solvents mostly are recovered and reused to reduce the cost (Behera et al., 2014). 

At low relative humidities, adsorption is due to interaction of water with accessible hydroxyl groups. These are present on the lignin and on the carbohydrates ia the noncrystalline or poorly crystalline regions. The high differential heat of adsorption by dry wood, - 1.09 kJ/g (469 Btu/lb) water. 

The above results appear consistent with a model for lignin proposed by Pepper ei al. (20) which consists of a core structure to which are attached the more readily accessible side-chain units. These units comprise that fragment of lignin which is easily degraded and released as low molecular weight identifiable products by any degradation procedure. 

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