华南湿地松EMCC制浆过程中木素结构的变化(英文)

以华南湿地松为原料制备卡伯值为 16～ 32的常规硫酸盐浆和深化脱木素的改良硫酸盐 (EMCC)浆 .从木材和纸浆中分离木素 ,利用13C_NMR和31P_NMR技术表征木素样品的结构 ,研究制浆过程中木素结构的变化 .结果表明 ,从木材和纸浆中分离出来的木素结构是不同的 ;制浆方法影响纸浆残余木素的结构特征 ,包括脂肪羟基、酚羟基和羧基含量 ,β_O_4结构和缩合结构含量 .对常规硫酸盐浆和改良硫酸盐浆 ,卡伯值较低的纸浆残余木素脂肪羟基和 β_O_4结构含量较低 ,酚羟基、羧基和缩合结构含量较高 .当卡伯值相同时 ,EMCC木素的脂肪羟基和酚羟基含量较低 ,β_O_4结构和羧基含量较高 。

High Oxygen Nanocomposite Barrier Films Based on Xylan and Nanocrystalline Cellulose

The goal of this work is to produce nanocomposite film with low oxygen permeability by casting an aqueous solution containing xylan,sorbitol and nanocrystalline cellulose.The morphology of the resulting nanocomposite films was examined by scanning electron microscopy and atomic force microscopy which showed that control films containing xylan and sorbitol had a more open structure as compared to xylan-sorbitol films containing sulfonated nanocrystalline cellulose.The average pore diameter,bulk density,porosity and tortuosity factor measurements of control xylan films and nanocomposite xylan films were examined by mercury intrusion porosimetry techniques.Xylan films reinforced with nanocrystalline cellulose were denser and exhibited higher tortuosity factor than the control xylan films.Control xylan films had average pore diameter,bulk density,porosity and tortuosity factor of 0.1730 μm,0.6165 g/ml,53.0161% and 1.258,respectively as compared to xylan films reinforced with 50% nanocrystalline cellulose with average pore diameter of 0.0581 μm,bulk density of 1.1513 g/ml,porosity of 22.8906% and tortuosity factor of 2.005.Oxygen transmission rate tests demonstrated that films prepared with xylan,sorbitol and 5%,10%,25% and 50% sulfonated nanocrystalline cellulose exhibited a significantly reduced oxygen permeability of 1.1387,1.0933,0.8986 and 0.1799 cm^3×μm/m^2×d×k Pa respectively with respect to films prepared solely from xylan and sorbitol with a oxygen permeability of 189.1665 cm^3×μm/m^2×d×k Pa.These properties suggested these nanocomposite films have promising barrier properties.

Rigid polyurethane foam reinforced with cellulosewhiskers: Synthesis and characterization

A novel nanocomposite of rigid polyurethane foam was prepared by the polymerization of a sucrose-based polyol, a glycerol-based polyol and polymeric methylene diphenyl diisocyanate in the presence of cellulose whiskers. The cell morphology of the resulting foams was examined by scanning electron microscopy which showed both the pure foam and the nanocomposite foam had homogeneous cell dispersion and uniform cell size of approximately 200 μm. Analysis of the foams by Fourier transform infrared(FT-IR) spectroscopy indicated that both samples exhibited signals attributed to the polyurethane including the NH stretching and bending vibrations at 3320 cm^(-1) and 1530 cm^(-1), the OC=O vibration at 1730 cm^(-1) and the CO-NH vibration at 1600 cm^(-1). FT-IR analysis of the nanocomposite indicated that cellulose whiskers were crosslinked with the polyurethane matrix as the signal intensity of the OH stretch at 3500 cm^(-1) was significantly reduced in comparison to the spectral data acquired for a control sample prepared from the pure polyurethane foam mixed with cellulose whiskers. According to ASTM standard testing procedures, the tensile modulus, tensile strength and yield strength of the nanocomposite foam were found to be improved by 36.8%, 13.8% and 15.2%, and the compressive modulus and strength were enhanced by 179.9% and 143.4%, respectively. Dynamic mechanical analysis results testified the improvements of mechanical properties and showed a better thermal stability of the nanocomposite foam.

Synthesis of Mg-K-biochar bimetallic catalyst and its evaluation of glucose isomerization

Highly efficient isomerization of glucose to fructose is essential for valorizing cellulose fraction of biomass to valueadded chemicals.This work provided an innovative method for preparing Mg-biochar and Mg-K-biochar catalysts by impregnating either MgCl_(2) alone or in combination with different K compounds(Ding et al.in Bioresour Technol 341:125835,2021,https://doi.org/10.1016/j.biort ech.2021.125835 and KHCO_(3))on cellulose-derived biochar,followed by hydrothermal carbonization and pyrolysis.Single active substance MgO existing in the _(10)Mg-C could give better catalytic effect on glucose isomerization than the synergy of MgO and KCl crystalline material present in _(10)Mg-KCl-C.But the catalytic effect of _(10)Mg-C was decreased when the basic site of MgO was overloaded.Compared to other carbon-based metal catalysts,_(10)Mg-KHCO_(3)-C with 10 wt%MgCl_(2) loading had excellent catalytic performance,which gave a higher fructose yield(36.7%)and selectivity(74.54%),and catalyzed excellent glucose conversion(53.99%)at 100℃ in 30 min.Scanning electron microscope-energy dispersive spectrometer and X-Ray diffraction revealed that the distribution of Mg^(Mg^(2+))and K^(+)in _(10)Mg-KHCO_(3)-C was uniform and the catalytic active substances(MgO,KCl and K_(2)CO_(3))were more than _(10)Mg-C(only MgO).The synergy effects of MgO and K_(2)CO_(3) active sites enhanced the pH of reaction system and induced H2O ionization to form considerable OH−ions,thus easily realizing a deprotonation of glucose and effectively catalyzing the isomerization of glucose.In this study,we developed a highly efficient Mg-K-biochar bimetallic catalyst for glucose isomerization and provided an efficient method for cellulose valorization.

In Situ Wood Delignification toward Sustainable Applications

CONSPECTUS:As one of the most abundant and versatile natural materials on Earth,recently wood has attracted tremendous attention from scientists and engineers due to its outstanding advantages,including hierarchically porous microstructure,high mechanical strength,environmental friendliness,renewability,and biodegradability.Wood’s hierarchically porous structure and chemical components(e.g.,cellulose,hemicelluloses,and lignin)enable its mechanical,ionic,optical,and thermal properties to be tuned via physical,chemical,and/or thermal modifications.Among these various approaches,the chemical delignification of bulk wood is the most fascinating,in which the majority of lignin and hemicelluloses is removed while leaving the cellulose intact,maintaining wood’s physical integrity and hierarchical structure.This delignified structure is unique,composed of hollow,aligned channels made up of cellulose microfibrils,and particularly attractive given its origin from a sustainable and renewable resource.As a result,delignified wood has attracted increasing attention for applications that go far beyond traditional wood utilization,such as lightweight yet strong structural materials,energy storage and conversion,environmental remediation,flexible electronics,and bioengineering.This Account reviews recent developments in bulk wood delignification strategies toward the achievement of such advanced wood technologies for sustainable applications,with a focus on the research in our group.Similar to chemical pulping and bleaching,wood delignification involves a series of nucleophilic reactions based on alkaline Na2SO3 or Na2S systems(i.e.,chemical pulping)or electrophilic,radical,and oxidation reactions based on H2O2,ClO2,or NaClO systems(i.e.,chemical bleaching)to deconstruct,fragment,and promote the hydrophilicity of lignin macromolecules,which finally make lignin easier to be removed.We discuss the structure and properties of partially and near-completely delignified wood,with a focus on process-structure−property relationships.The resulting delignified wood materials,with tunable structure and properties,demonstrate various advanced functions,in a wide range of advanced applications,such as building and construction,green energy,and electronics.Finally,the potential challenges and appealing perspectives of in situ wood delignification are discussed.In situ wood delignification,as a powerful modification strategy,has speeded up the development of advanced wood technologies and wood-based functional materials and products.