Plant cell walls as fibrous lignocellulosic composites: relations with lignin structure and function

Abstract

Cell wall might be considered as a composite material, made of fibre (cellulose), a matrix (lignin, hemicellulose) and fillers (water, simple organics, tannins). Its properties depend both on plant anatomy (heterogeneity and anisotropy of organs, tissues, cells and cell wall layers) and on the structure of the macromolecules, their orientational order, their associations and the resulting supramolecular structures as particularly discussed in the case of lignin networks. From selected examples, it is shown that natural or artificial lignocellulosic compounds such as woods, straws or reconstituted woods (fibre and particle boards) can be described as composite materials. Their most typical physico-chemico-mechanical properties are: shrinkage and water swelling behaviour, collapse in relation to extractive and tannin content, improvement of dimensional and biological stability by chemical modifications, anisotropic properties of orientated strand boards and fibre-reinforced polyester-based composites, and lastly, biological properties (digestibility, extensibility). As for synthetic composite materials, such an approach is a prerequisite for industrial production of competitive lignocellulosic products.