مرکز منطقه ای اطلاع رساني علوم و فناوري -

چكيده لاتين :

Amild acidic dioxane extraction procedure was used to isolate lignin from hardwood bleached chemimechanical pulp (BCMP). The isolated lignin was impregnated on Whatman filter paper and irradiated with ultraviolet (UV) light under various exposure times. Then, photodegraded lignin was recovered and characterized by FTIR spectroscopy and high pressure size exclusion chromatography (HPSEC). Loss of lignin aromatic content induced by syringyl and guaiacyl nuclei degradation, reduction in Caryl-O ether bond caused by demethoxylation and ~-O-4 bond cleavages, and formation of carbonyl and/or carboxyl groups with slight increase in phenolic hydroxyl group, were some of structural changes observed by FTIR spectroscopy studies. Analysis of lignin samples with HPSEC indicated that formation of high molecular condensed structures by radical coupling during 4 h irradiation time, caused to increase lignin molecular weight. However, with continuing irradiation time of up to 120 h, the molecular weight of lignin decreased by 23% of its original value due to predominating photodegradation mechanisms. The results are discussed in relation to the reaction pathways leading to the breakdown of the lignin macromolecular structure.