CONCENTRATIONS OF PHENOLIC HYDROXYL-GROUPS IN SECONDARY WALL AND MIDDLE LAMELLA OF SPRUCE (PICEA-ABIES)

A higher concentration of phenolic hydroxyl groups in the lignin of th e secondary wall (SW) as compared to the middle lamella (ML) has long been used to explain the topochemical effect observed when spruce is p ulped. However, a controversy exists as to whether or not there is a s ignificant difference in phenolic hydroxyl concentration between the t wo regions. Fractions rich in SW and ML materials were obtained from t hermomechanical pulps produced with high specific refining energies. A nalysis by periodate oxidation showed that the SW lignin contained app roximately 60% more phenolic hydroxyl groups than the ML lignin. Howev er, p-hydroxyphenylpropane units, believed to be concentrated in the M L, were not detected. If a correction factor is applied, then the diff erence is 37% in favor of the SW lignin. Neutral sulfite treatment gen erated phenolic hydroxyls at a higher rate in the ML lignin but still sulfonated the SW lignin to a greater extent.