To understand structure change of lignin-carbohydrate complexes (LCCs) in kraft cooking process

it was separated firstly out from the powder of rise straw by Björkman procedure

into which coniferyl alcohol glucoside with 13C-label had been rejected

and its structure was determined by 13C NMR and FT-IR spectra.The result showed that lignin was linked to carbohydrate by benzyl ether

ester and α-ketal bonds

and β-O-4 structure was the main structure of lignin in LCC.Then

the LCC obtained with and without 13C-label was cooked by kraft method and isolated respectively

to get lignin-carbohydrate complex-kraft lignins(LCC-KLs).The LCC-KLs structures were determined by 13C NMR and FT-IR spectra

and the intensities of α-carbons increased markedly for the sample with α-13C-label.The result showed that most of benzyl ether bonds and ketal linkage between lignin and carbohydrate were broken in pulping

but there still were bits of ketal linkage.Main structures of LCC-KL were found to be β-O-4 units

with a small number of phenylcoumaran units

pinoresinol units and β-1 units.