Procedure of isolating lignin
Two parallel samples were prepared from the extractive-free sawdust, and each
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sample had 1 g dry weight. The samples were placed in 100-ml beakers, and
also 15ml of cold (10 to 15℃) 72% sulfuric acid was added. Sulfuric acid was
added gradually in small increments while the material was stirred and
macerated with a glass rod. Each beaker was kept in a bath at 20±1℃ during
dispersion of the material. After the samples were dispersed, each beaker was
covered with a watch glass and they were kept in a bath at 20±1℃ for 2 hours.
The materials were stirred frequently during this time to ensure complete
dissolution.
Afterwards, the solid solutions were transferred from the beakers to the two
flasks separately, and about 300 ml of water was added to each flask. Then
more water was added to dilute the solution to a 3% concentration of sulfuric
acid. Then the solution was boiled for 4 hours by using a flask reactor with a
reflux condenser. After that, the lignin was transferred to the filter and hot water
was used to wash, and lignin was dried at room temperature. (TAPPI T222)