Effect of autohydrolysis on alkaline delignification of mixed hardwood chips and on lignin structure

International audienceAbstract Autohydrolysis (AH) prior to the kraft process is one way to valorize hemicelluloses. The presented results show that AH also has a beneficial effect insofar as kraft cooking can be substituted by soda cooking, and higher brightness levels can be achieved under the same bleaching conditions. The lignin has more free phenolic groups after AH, which is attributable to depolymerization, and which could partly explain the better pulping and bleaching results. Another explanation could be the lower amount of lignin involved in lignin carbohydrate complexes after an AH step

Characterisation of lignin and lignin-carbohydrate complexes (LCCs) in prehydrolysed wood chips

International audienceAbstract Isolation and analysis of lignin and lignin-carbohydrate complexes (LCCs) were performed to understand the better delignification ability of prehydrolysed wood chips. Lignin analysis showed that prehydrolysis led to a slight depolymerisation and an increase in free phenolic group content. The yield measurement and composition analysis of LCCs of mixed softwoods (SWs) and mixed hardwoods (HWs) revealed essential differences. In the case of SW, the amounts of lignin and xylan involved in LCCs were significantly lowered, whereas in the case of HW, less cellulose, glucomannans, and xylans were detectable in the residual LCCs. The molecular mass distributions of glucomannan-lignin and xylan-lignin fractions were not changed significantly

Characterisation of lignin and lignin-carbohydrate complexes (LCCs) in prehydrolysed wood chips

International audienceAbstract Isolation and analysis of lignin and lignin-carbohydrate complexes (LCCs) were performed to understand the better delignification ability of prehydrolysed wood chips. Lignin analysis showed that prehydrolysis led to a slight depolymerisation and an increase in free phenolic group content. The yield measurement and composition analysis of LCCs of mixed softwoods (SWs) and mixed hardwoods (HWs) revealed essential differences. In the case of SW, the amounts of lignin and xylan involved in LCCs were significantly lowered, whereas in the case of HW, less cellulose, glucomannans, and xylans were detectable in the residual LCCs. The molecular mass distributions of glucomannan-lignin and xylan-lignin fractions were not changed significantly

Effect of autohydrolysis on alkaline delignification of mixed hardwood chips and on lignin structure

International audienceAbstract Autohydrolysis (AH) prior to the kraft process is one way to valorize hemicelluloses. The presented results show that AH also has a beneficial effect insofar as kraft cooking can be substituted by soda cooking, and higher brightness levels can be achieved under the same bleaching conditions. The lignin has more free phenolic groups after AH, which is attributable to depolymerization, and which could partly explain the better pulping and bleaching results. Another explanation could be the lower amount of lignin involved in lignin carbohydrate complexes after an AH step

Lignin model compounds fluorobenzylation

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Study of the Reactivity of Lignin Model Compounds to Fluorobenzylation Using 13C and 19F NMR: Application to Lignin Phenolic Hydroxyl Group Quantification by 19F NMR

International audienceLignin is an aromatic biopolymer derived from lignocellulosic biomass. Providing a comprehensive structural analysis of lignin is the primary motivation for the quantification of various functional groups, with a view to valorizing lignin in a wide range of applications. This study investigated the lignin fluorobenzylation reaction and performed a subsequent 19F-NMR analysis to quantify hydroxyl groups, based on a work developed two decades ago by Barrelle et al. The objectives were to check the assignments proposed in this previous study and to examine the reactivity of various types of lignin hydroxyls with the derivatization agent. Selected lignin model compounds containing phenolic and aliphatic hydroxyls were subjected to the fluorobenzylation reaction, and the obtained reaction medium was analyzed by 13C and 19F NMR spectroscopy. The model compound results showed that phenolic hydroxyls were totally derivatized, whereas aliphatic hydroxyls underwent minimal conversion. They also confirmed that 19F NMR chemical shifts from −115 ppm to −117.3 ppm corresponded to phenolic groups. Then, a 19F NMR analysis was successfully applied to Organosolv commercial lignin after fluorobenzylation in order to quantify its phenolic group content; the values were found to be in the range of the reported values using other analytical techniques after lignin acetylation

Synthesis of cellulose triacetate-I from microfibrillated date seeds cellulose (Phoenix dactylifera L.)

International audienceCellulose triacetate (CTA) has successfully been synthesized from microfibrillated date seeds cellulose. The cellulosic material under study constituted 84.9% amorphous phase with a degree of polymerization of 950. Acetylation was conducted at 50 °C under optimized heterogeneous conditions by acetic anhydride as acetyl donor, acetic acid as solvent and sulfuric acid as catalyst. In this process, cellulose was acetylated without dissolving the material throughout. The acetylated cellulose chains on the surface were dissolved gradually in acetic acid, which created new accessible zones. The yield of cellulose triacetate was studied varying acetic acid, acetic anhydride and catalyst concentrations, as well as reaction times. The ratio between the intensity of the acetyl C=O stretching band at around 1740 cm−1 and the intensity of C–O stretching vibration of the cellulose backbone at 1020–1040 cm−1 was used to optimize the reaction time. The optimal reaction conditions of 8% concentration of sulfuric acid, acetic anhydride/cellulose weight ratio of 3:1, acetic acid/cellulose weight ratio of 7:1, reaction time of 3 h and reaction temperature of 50 °C have given highest yield of cellulose triacetate, of about 79%. The obtained date seeds-based cellulose triacetate was characterized thoroughly by Fourier transform infrared (FTIR), X-ray diffraction (XRD), nuclear magnetic resonance spectroscopy (NMR), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The synthesized product was identified as cellulose triacetate-I (CTA-I) characterized by a melting temperature of 217 °C and a decomposition temperature of 372 °C. These results demonstrated that date seeds can be used as potential source of microfibrillated cellulose which can be easily functionalized