Abstract
Lignin, a natural biopolymer and abundant by-product, is a particularly promising feedstock for carbon-based materials and a potentially sustainable alternative to phenolic resins, which are typically derived from crude oil. The source and method used to isolate lignin have a large impact on the thermal properties of the polymer, and can affect resultant materials prepared from lignin. Previous investigations into lignin characterisation often utilise a variety of feedstocks and isolation methods, which can make robust comparisons challenging. We present a systematic investigation into the chemical composition of lignins extracted using an identical Organosolv isolation method but from different biomass feedstocks: hemp hurds, eucalyptus chips, flax straw, rice husk and pine. We show how the aromatic structure of lignin can affect the thermal behaviour of the polymer, which correlates to the structure of resulting carbons. Carbons from lignins with a high syringyl unit content display a pronounced foaming behaviour which, on activation, results in a high-surface area material with hierarchical porosity.
Highlights
Lignin is a natural biopolymer found in lignocellulosic biomass and is a major byproduct of the paper pulping and biofuel production processes
The highly aromatic structure of lignin makes it a good candidate for a sustainable replacement for phenolic resin, a crude oil-derived aromatic polymer used in the synthesis of polymeric carbons and as a thermal binder. [16,17,18,19] Native lignin is found in plant cell walls within a matrix of cellulose and hemicellulose. [20,21,22] The polymer has a highly complex structure that differs depending on its origin
Due to the complexity of the three-dimensional macromolecule the exact structure of lignin is unknown, [23] it is formed primarily from three aromatic monomers known as monolignols; p-coumaryl, coniferyl, and sinapyl alcohol
Summary
Lignin is a natural biopolymer found in lignocellulosic biomass and is a major byproduct of the paper pulping and biofuel production processes. Due to the complexity of the three-dimensional macromolecule the exact structure of lignin is unknown, [23] it is formed primarily from three aromatic monomers known as monolignols; p-coumaryl, coniferyl, and sinapyl alcohol. These result in the formation of p-hydroxyphenyl (H), guaiacyl (G) and sinapyl (S) residues respectively in the polymer. We show how the aromatic lignin structure impacts the thermal behaviour of the polymer, and the high-value application of these materials to produce products such as activated carbons with hierarchical porosity
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