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Lignocellulose refers to plant dry matter (biomass), so called lignocellulosic biomass. It is the most abundantly available raw material on the Earth for the production of Biofuel. It is composed of two kinds of carbohydrate polymers, cellulose and hemicellulose, and an aromatic-rich polymer called lignin. Any biomass rich in cellulose, hemicelluloses, and lignin are commonly referred to as lignocellulosic biomass. Each component has a distinct chemical behavior. Being a composite of three very different components makes the processing of lignocellulose challenging. The evolved resistance to degradation or even separation is referred to as recalcitrance. Overcoming this recalcitrance to produce useful, high value products requires a combination of heat, chemicals, enzymes, and microorganisms. These carbohydrate-containing polymers contain different sugar monomers (six and five carbon sugars) and they are covalently bound to lignin.
Lignocellulosic biomass can be broadly classified as virgin biomass, waste biomass, and energy crops. Virgin biomass includes plants. Waste biomass is produced as a low value byproduct of various industrial sectors such as agriculture (corn stover, sugarcane bagasse, straw etc.) and forestry (saw mill and paper mill discards). Energy crops are crops with a high yield of lignocellulosic biomass produced as a raw material for the production of second-generation biofuel; examples include switchgrass ( Panicum virgatum) and elephant grass. The biofuels generated from these energy crops are sources of sustainable energy.
One barrier to the production of ethanol from biomass is that the sugars necessary for fermentation are trapped inside the lignocellulose. Lignocellulose has evolved to resist degradation and to confer hydrolysis stability and structural robustness to the cell walls of the plants. This robustness or "recalcitrance" is attributable to the crosslinking between the polysaccharides (cellulose and hemicellulose) and the lignin via ester and ether linkages. Ester linkages arise between oxidized sugars, the , and the phenols and phenylpropanols functionalities of the lignin. To extract the fermentable sugars, one must first disconnect the celluloses from the lignin, and then use acid or enzymatic methods to hydrolyze the newly freed celluloses to break them down into simple monosaccharides. Another challenge to biomass fermentation is the high percentage of pentoses in the hemicellulose, such as xylose, or wood sugar. Unlike hexoses such as glucose, pentoses are difficult to ferment. The problems presented by the lignin and hemicellulose fractions are the foci of much contemporary research.
A large sector of research into the exploitation of lignocellulosic biomass as a feedstock for bio-ethanol focuses particularly on the fungus Trichoderma reesei, known for its cellulolytic abilities. Multiple avenues are being explored including the design of an optimised cocktail of cellulases and hemicellulases isolated from T. reesei, as well as genetic-engineering-based strain improvement to allow the fungus to simply be placed in the presence of lignocellulosic biomass and break down the matter into Glucose monomer. Strain improvement methods have led to strains capable of producing significantly more cellulases than the original QM6a isolate; certain industrial strains are known to produce up to 100g of cellulase per litre of fungus, thus allowing for maximal extraction of sugars from lignocellulosic biomass. These sugars can then be fermented, leading to bio-ethanol.
Lignocellulosic biomasses has been considered in the production of biocomposites materials such as particle panels, wood-plastic composites, and cement/geopolymer wood composites. Even though the production of biocomposite materials rely mostly on wood resources, in less forest-covered countries or in countries where wood resources are already being overused, it is possible to utilize alternative sources of biomass such as invasive plants, agricultural and sawmills residues for the creation of new "green" composites. Biocomposites produced with lignocellulosic biomass as an alternative to conventional materials, are attracting attention because they are renewable and cheaper but also because they fit perfectly into the policy of the "cascade utilization" of the resources.
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