Availability of four energy crops assessing by the enzymatic hydrolysis and structural features of lignin before and after hydrothermal treatment

Unraveling the Fate of Lignin from Eucalyptus and Poplar during Integrated Delignification and Bleaching

“…[29] The signals of BE and A'g also disappeared in L HTPo ,i ndicating that these linkagesw ere cleaved under the given conditions. [29] Additionally,a st ypical units in spectra of poplar,P Ba nd Hc an also reflect the structural changes of lignin during the hydrothermalp rocess. In the aromatic region of the 2D-HSQC spectra of L HTEu and L HTPo ,s ome condensed signals occurred at the Su nits, suggesting that HTP can contributetot he condensation of lignin,w hich is in agreement with the literature.…”

“…[27,28] In the aliphatic oxygenateds ide-chain region of L HTEu and L HTPo ,t he relative abundance of b-O-4 linkages was decreased compared with that of L Eu and L Po .I na ddition, the disappearance of b-1 linkages and Ig groupsw as observed in L HTEu and L HTPo ,s uggesting that HTP resulted in the depolymerization and cleavage of thesek inds of linkages in lignin. [29] The signals of BE and A'g also disappeared in L HTPo ,i ndicating that these linkagesw ere cleaved under the given conditions. However, the signals of b-5 and b-b linkages still existedi nL HTEu and L HTPo ,i mplyingt hat the carbon-carbon (CÀC) linkages were relatively stable during the hydrothermalp rocess.…”

“…[29] With the implementation of [29,33] which was also verifiedi nt his study. [29] However,L HTPo contained al ower content of aliphatic OH groups than L Po ,w hichw as mainly caused by the oxidization of aliphatic OH groups during hydrothermalt reatment, and this could be confirmed by the increased contento fc arboxylic groups (Table 3). Furthermore, the S/G ratios of L HTEu and L HTPo were higher than those of L Eu and L Po ,w hich was likely owing to the preferentiald egradation of G-type units at high temperature.…”

“…For poplar lignin, the content of PB in L Po ,L HTPo ,a nd BL HTPo was gradually decreased (20.96, 5.63, and 3.86/100 Ar,r espectively) if HTP and Kraft pulpingw ere performed sequentially.H owever,t he content of Hu nits in poplar lignin was slightly increased after the integrated delignification process. [29] Moreover,t he abundance of S-type phenolic OH groupsw as highert han that of G-typei n L HTEu and L HTPo ,i mplying that the b-O-4 linkages in eucalyptus and poplar are preferentially composed of S-type lignin units. [6] Ta ble 3s ummarizes the contents and kinds of variousf unctional groupsi nt hose lignin fractions.…”

“…In the aromatic region of the 2D-HSQC spectra of L HTEu and L HTPo ,s ome condensed signals occurred at the Su nits, suggesting that HTP can contributetot he condensation of lignin,w hich is in agreement with the literature. [29] Additionally,a st ypical units in spectra of poplar,P Ba nd Hc an also reflect the structural changes of lignin during the hydrothermalp rocess. It was observedt hat the PB structure was still linked to lignin macromolecules eveni ft he signal intensity of PB was decreased, indicating that the ester bondsb etween PB and lignin were only partly cleaved under the given conditions.…”