Abstract
An electron microscopy investigation was performed to understand the relationship between the microstructure and properties of carbonized cellulose and lignin (softwood kraft lignin) relative to the structure of the original biomass components. Structure details at micro- and molecular levels were investigated by scanning transmission electron microscopy. Atomic-resolution images revealed the presence of random disordered carbon in carbonized cellulose (C-CNC) and of large domains of well-ordered carbon with graphite sheet structure in carbonized lignin (C-Lignin). These structural differences explain why C-CNC exhibits higher surface area and porosity than C-Lignin. The presence of certain well-ordered carbon in carbonized lignin indicates some of the carbon in lignin are graphitized with heat treatment temperature up to 950 °C. This result is encouraging for future endeavors of attaining acceptable modulus of carbon fiber from lignin given suitable modifications to the chemistry and structure of lignin. The results of this research contribute to an improved understanding of the carbonization mechanism of the key cellulose and lignin components of biomass materials.
Highlights
By converting biomass into fuels, power, materials and chemicals, biorefining is gradually making contributions to sustainable industrial development (Ragauskas et al 2006; Aarum et al 2019)
The N2 adsorption–desorption isotherms of carbon in carbonized cellulose (C-cellulose nanocrystals (CNCs)) and C-Lignin feature typical type-II curves combined with H4-type hysteresis loop (Sing et al 1985)
For C-CNC, the adsorption amount undergoes a steep increase at relative pressure (p/p0) of ~ 0.1, indicating the completion of the first monolayer and transition to multilayer adsorption
Summary
By converting biomass into fuels, power, materials and chemicals, biorefining is gradually making contributions to sustainable industrial development (Ragauskas et al 2006; Aarum et al 2019). Biomass is a combination of three major biopolymers. Cellulose is an aggregate of linear chains of glucopyranose units linked by β-(1,4) glycosidic bonds to varying degrees of polymerization. The chains held together in parallel stacks by intra- and intermolecular hydrogen bonds form shortrange nanocrystalline regions. The cellulose nanocrystals (CNCs) alternate with amorphous regions and form microfibrils held by weak van der Waals forces Extended author information available on the last page of the article. Wood Science and Technology (2021) 55:587–606 et al 2011; Wu et al 2013; Trache et al 2017; Risnasari et al 2018; Wang et al 2020). Lignin is a complex polymer of aromatic alcohols (monolignols) composed mainly of three phenylpropane monomers: p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol
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