Plant cell walls form an organic complex composite material that fulfils various functions. The hierarchical structure of this material is generated from the integration of its elementary components. This review provides an overview of wood as a composite material followed by its deconstruction into fibres that can then be incorporated into biobased composites. Firstly, the fibres are defined, and their various origins are discussed. Then, the organisation of cell walls and their components are described. The emphasis is on the molecular interactions of the cellulose microfibrils, lignin and hemicelluloses in planta. Hemicelluloses of diverse species and cell walls are described. Details of their organisation in the primary cell wall are provided, as understanding of the role of hemicellulose has recently evolved and is likely to affect our perception and future study of their secondary cell wall homologs. The importance of the presence of water on wood mechanical properties is also discussed. These sections provide the basis for understanding the molecular arrangements and interactions of the components and how they influence changes in fibre properties once isolated. A range of pulping processes can be used to individualise wood fibres, but these can cause damage to the fibres. Therefore, issues relating to fibre production are discussed along with the dispersion of wood fibres during extrusion. The final section explores various ways to improve fibres obtained from wood.
Collapse-prone timbers such as species of Eucalyptus are poorly utilised due to low conversion rates that necessitate long pre-drying times. A supercritical CO 2 lumen water expulsion pre-treatment prior to kiln drying is proposed to bypass lengthy pre-drying. After drying (air, kiln or oven drying), shrinkage, collapse, washboard depression and checking of Eucalyptus nitens were determined using image analysis of 0.8 mm thick wafers and 5 mm thick biscuits. Lumen water expulsion-kiln drying reduced collapse by 75% and washboard depression by 71%, compared to drying from green. As water is removed from the water conductive tissue (vessels, rays, and fibre-tracheids) by lumen water expulsion, the water column is broken throughout the specimen, thereby disrupting the development of meniscus-induced water tension as subsequent drying occurs. Remaining water is proposed to reside in the non-water-conductive fibre tissue. If the process can be applied on large scale to Eucalyptus nitens, there is the opportunity for higher conversion rates to increase the commercial viability of solid wood products.Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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