THE ROLE OF WOOD PECTINS IN CHEMIMECHANICAL PULPING
In alkaline conditions, such as in chemithermomechical pulping (CTMP) and peroxide bleaching of mechanical pulps, wood pectins undergo two parallel reactions: methyl de-esterification and ^elimination. Alkali-induced ^-elimination of pectins cleaves the polymeric chain into smaller fragments that are able to diffuse out of wood and fibres. As a result of both de-esterification and β-elimination reactions highly charged anionic poly- and oligomeric pectic acids are released into the process water. These pectic acid fragments constitute a substantial part of so-called anionic trash, which is disturbing in papermaking. Here we studied the pectin reactions in alkaline conditions and found that the temperature is a key parameter controlling the chain cleavage of pectin by β-elimination and consequently the formation of anionic trash. Higher temperatures result in extensive cleavage to smaller fragments. However, once pectin is de-esterified, extended treatment does not result in additional cleavage because the cleavage by β-elimination depends on the presence of a methyl ester group on the adjacent galacturonic acid unit in the polymer chain. Consequently, when the deesterification is complete, the β-elimination reaction will stop. Alkali-induced cleavage of pectin is a very fast reaction: once it has happened, extended alkaline treatment does not give any additional cleavage of the pectin. By promoting methyl de-esterification in alkaline treatment of mechanical pulps, achieved by decreasing the initial treatment temperature from 90~100°C to 30~40°C, the amount of released anionic trash from suspension can be decreased with more than 50％.
pectins chemimechanical pulping anionic trash De-esterification, β-elimination
Andrey V. Pranovich Jonas N. Konn Bjarne R. Holmbom
Laboratory of Wood and Paper Chemistry, Process Chemistry Centre, Abo Akademi University, Porthansga Kemira Oyj, R&D and Technology, Finland
国际会议
16th International Symposium on Wood,Fiber and Pulping Chemistry(第十六届木材、纤维及制浆化学国际会议)
天津
英文
750-755
2011-06-08（万方平台首次上网日期，不代表论文的发表时间）