RESUMO
In order to improve lignin-based materials' utilization, the grafting mechanism of lignin was studied by investigating hydrogen peroxide (H2O2) initiator's effect on the structure of eucalyptus lignosulfonate calcium (HLS). HLS was treated by low content of H2O2 (H2O2/HLS(wt)=1%, 2%, 4%) under various reaction temperature and time. Changes in HLS structure were investigated by difference UV, UV, FTIR, (1)H NMR, GPC and intrinsic viscosity. The results showed that though phenolic hydroxyl group (Ph-OH) of HLS was not oxidated to the quinoid structure, its content still decreased after treated by H2O2 initiator. Meanwhile, the new aryl-alkyl ether structures and increased average molecular weight were observed. A radical coupling mechanism for the decreasing Ph-OH group's content was proposed, which radicals may terminate between phenoxy and benzyl radicals. In addition, the cleavage of methoxyl-aryl ether made a decline in the content of syringyl units, while that of guaiacyl, p-hydroxyphenyl units and free aromatic C-5 hydrogen increased when HLS reacted with H2O2.
