Development of the Fibrillar and Microfibrillar Structure During Biomimetic Mineralization of Wood

Abstract

Wood is a hierarchical composite, consisting at its lowest hierarchy level of crystalline cellulose elementary fibrils with diameters of 2–4 nm embedded in a matrix of hemicelluloses and lignin. At the micrometer scale, it has a cellular architecture resembling a honeycomb structure. The transformation of the hierarchical wood structure into a silica replica has been reported recently. Its formation process and structural details are studied in this contribution. First, a silica/biopolymer composite is prepared by wood delignification and cell‐wall modification, followed by silica precursor infiltration and condensation. The calcination process is monitored to gain insight into the structure development upon decomposition of the biopolymers. The material changes its architecture gradually from fibrillar structures of 10–20 nm in diameter with homogeneous electron density, into fibrils of 8–10 nm in diameter with inhomogeneous electron density, exhibiting internal sub‐fibrillar structures of about 2 nm in diameter. The steps of the successful replication of the cellulose elementary fibrils into nanopores of similar diameter and orientation in a fibrillar silica matrix are demonstrated. These nanopore replicas of the original cellulose are wound in a steep helix within the macropore walls. These advanced materials may have lightweight structural applications and the nanopores may be advantageous for molecular separation.

Chemistry and water-repelling properties of phenyl-incorporating wood composites

“…In its monomeric state, TEOS can penetrate into cell walls (Saka et al 1992), whereas this is not possible for prehydrolyzed and precondensed siloxane species due to their larger molecular dimensions (Unger et al 2012). The penetration of TEOS into cell wall pores down to a size of as low as 1 nm was recently described by means of a combined delignification and chemical functionalization approach (Van Opdenbosch et al 2011;Fritz-Popovski et al 2013). If the presence of water is limited to the cell wall, hydrolysis and condensation (as shown in Figure 1a and b) will mainly occur within the cell wall.…”

Hierarchical Architectures to Enhance Structural and Functional Properties of Brittle Materials

“…So far, the most successful route consists of partial delignification of the wood tissue followed by infiltration of a hydrophilic solution of tetraethyl orthosilicate (TEOS), which enters preferentially the swellable regions of hemicelluloses and amorphous cellulose, but not the crystalline cellulose fibrils. [116] Mechanical properties of the former cell walls, of this material, are entirely different from the one of wood charcoal. The smallest pores are needle like with only about 2 nm diameter, resembling the size, shape, and orientation of the former elementary cellulose fibrils.…”

“…The smallest pores are needle like with only about 2 nm diameter, resembling the size, shape, and orientation of the former elementary cellulose fibrils. [116] Mechanical properties of the former cell walls, of this material, are entirely different from the one of wood charcoal. While the Young's modulus and indentation hardness (after correction for porosity) are in the same order of magnitude as for charcoal, the indentation ductility index D suggests a considerable amount of plastic deformability of the silica material ( Table 2 and Figure 13c), quite similar to the original biological template.…”

Cellulose‐Based Biotemplated Silica Structuring

“…[244,245] and the aforementioned hybrid cellulose-silica aerogels, [131] but lower than obtained from dried isotropic silica gels. [192] The similarity between the true biogenic silica extracted from Equisetum hyemale and its artificial [219] analogues with respect to structural hierarchy, porosity, specific surface area and thermal properties is striking and illustrates the close replication of natural processes achievable by simplified means. [192] The similarity between the true biogenic silica extracted from Equisetum hyemale and its artificial [219] analogues with respect to structural hierarchy, porosity, specific surface area and thermal properties is striking and illustrates the close replication of natural processes achievable by simplified means.…”

“…This is due to the fact that the formed silicic acid has a high tendency to condense to polysilicic acids and ultimately undesired spherical silica. (a), [106,184,207] (b), [171][172][173] (c), [188,204,205,208] (d,e), [106,209,210] (f), [141] (g), [211,212] (h,i), [120,203] (j), [213] (k), [107,206] (l), [106,122,123,169,214] (m), [120,203,215] (n), [141,186,[216][217][218] (o), [134,186,208,219] (p). It is therefore of advantage that cellulose itself is a weak acid.…”