Non‐Solvent Fractionation of Lignin Enhances Carbon Fiber Performance

Abstract

Lignin is an abundantn atural polymer in plants next to cellulose, yet also am ajor industrial waste produced from both lignocellulosic biorefinery and the paper-making industry. [1] Annually,a pproximately 50 million tons of lignin waste are generated from pulping mills. [2] This lignin waste stream could be furthera dded up to 300 million tons if the billion-ton initiative for lignocellulosic biofuels is implemented. [3] Even though upgradingl ignin into value-added products has been extensively soughta fter for decades to enhance economic return for the paper-making industry,t he current commercial utilization of lignin is mainly to burn the black liquor for heat recovery. [2, 4] Converting lignin waste into high-value products thus represents one of the most challenging issues for both the papermaking industry and lignocellulosic biorefinery.The most challenging issue in upgrading lignin wastes lies in the inherent heterogeneity of lignin polymer because of its variousf unctional groups, diversei nterunitary linkages, different molecular weight, and polydispersity. [4c, 5] This heterogeneity could result from lignin biosynthesis during secondary cellwall thickening and be furtheraugmented by biomass process-Even though lignin carbon fiber has been soughta fter for several decades, the poor mechanicalp erformance remains to be am ajor barrier for commercial applications. The low mechanical performance is attributed to the heterogeneity of lignin polymer.R ecent advances in fractionation technologies showedt he great potential to reduce lignin heterogeneity,b ut current fractionationm ethods often depend on costly chemicals and materials such as enzymes, organic solvents, membranes, and dialysis tubes.H ere, an ew non-solvent strategy was developed to fractionate lignin by autohydrolysis. By using only water,l ignin was efficiently fractionated into watersoluble and -insoluble fractions. The latterf raction had increasedm olecular weight and uniformity and resulted in more b-O-4 interunitary linkages as analyzed by size-exclusion chromatography and 2D heteronuclear single quantumc oherence NMR spectroscopy,r espectively.I np articular, the water-insoluble fraction significantly enhanced the mechanical performances of the resultant carbon fibers. Mechanistic study by differential scanning calorimetry (DSC) revealed that the miscibility of lignin with guest polyacrylonitrile molecules was improved with the reduced lignin heterogeneity.C rystallite analysesb y XRD and Raman spectroscopy revealed that the crystallite size and content of the pre-graphitict urbostratic carbon structure were increased. The fundamentalu nderstanding revealed how lignin fractionation could modify lignin chemical features to enhancet he mechanical performance of resultant carbon fibers. The autohydrolysis fractionation thus represents a green, economic, and efficient methodology to process lignin waste andb oost lignin carbon fiber quality,w hich could open new horizons for lignin valorization.

Discovering Biomass Structural Determinants Defining the Properties of Plant-Derived Renewable Carbon Fiber

“…Likewise, the chemical features of polymer precursors in biomass feedstocks are likely to define the properties of resultant materials. This fundamental structure-property relationship between lignin chemical characteristics and carbon fiber properties was also evidenced by previous studies of manufacturing processes, where molecular weight, uniformity, linkage profile, and functional group all can potentially impact on carbon fiber properties ( Beaucamp et al., 2019 ; Culebras et al., 2018b ; Li et al., 2017a , 2017b , 2018a , 2019b ; Zhang et al., 2019 ). Despite the manufacturing process studies, it is still not clear if these chemical features can be achieved through feedstock improvement and how these chemical features are different in different feedstock cultivars, engineered lines, and growth conditions.…”

A Unique Bacterial Pelletized Cultivation Platform in Rhodococcus opacus PD630 Enhanced Lipid Productivity and Simplified Harvest for Lignin Bioconversion

“…The acidified medium was centrifuged at 8000 rpm for 20 min, which was followed by lyophilization for lignin powders. Lignin samples (30−50 mg) and the polymers extracted from the pellets were subjected to 2D HSQC NMR analysis as described by Mansfield et al 55 The frequencies of lignin linkages and lignin units were quantified as we reported previously, 56,57 and lignin linkages were expressed as per 100 aromatic rings. Analytical Methods and Statistical Analysis.…”

Molecular Engineering of Biorefining Lignin Waste for Solid-State Electrolyte

“…30–50 mg of lignin was dissolved in 0.6 mL of DMSO- d 6 and placed in the NMR tube. Adiabatic 2D 1 H– 13 C HSQC spectra were acquired on a Varian 500 MHz NMR spectrometer in the “gradient HSQCAD” mode, as reported before. , The parameters of HSQC were set at 1.0-s pulse delay, 64 scans, 1024 data points for 1 H, and 256 increments for 13 C. The central solvent peak at δC/δH = 39.5/2.49 ppm was used as the reference. For quantification of lignin linkages, the well-resolved contours of the linkages were integrated using the software MestReNova.…”