Fibre hierarchical

Additional information on fracture of fibres hierarchically. structured appears in the paper by Viney and in the paper by Hearle ( Fracture of Common Textile Fibres ). 

Fig. 10 (a-f) Hierarchical self-assembly model for chiral rod-like units A curly tape (c ), a twisted ribbon (d ), a fibril (e ) and a fibre (f). Adapted from Aggeli et al. [20], Copyright 2001 National Academy of Sciences, USA... 

Zhang, B.J., Davis, S.A., Mendelson, N. H. and Mann, S. (2000) Bacterial templating of zeolite fibres with hierarchical structure. Chemical Communications, 781-782. 

Figure 29. Fiuman osteoblast-like MG 63 cells in cultures on material surfaces modified with carbon nanoparticles. A fullerene Cgo layers deposited on carbon fibre-reinforced carbon composites (CFRC), B fullerene C o layers deposited on microscopic glass coverslips, C terpolymer of polytetrafluoroethylene, polyvinyldifluoride and polypropylene, mixed with 4% of single-wall carbon nanohorns, D the same terpolymer with high crystalline electric arc multi-wall nanotubes, E diamond layer with hierarchically organized micro- and nanostmcture deposited on a Si substrate, F nanocrystalline diamond layer on a Si substrate. Standard control cell culture substrates were represented by a PS culture dish (G) and microscopic glass coverslip (FI). Immunofluorescence staining on day 2 (A) or 3 (B-Fl) after seeding, Olympus epifluorescence microscope IX 50, digital camera DP 70, obj. 20x, bar 100 pm (A, C, D, G,H)or 200 pm (B, E, F) [16].

The common elements in the cited examples are the mechanical characteristics and the insulation properties. These advantages come, not only from macroscopic configuration of these materials (the hollow cylindrical structure of stubble for instance), but, mainly, from their microscopic structure. Most the vegetal fibres can be described by two models wood fibres and cotton fibres, which will be presented later. In order to better understand the mechanical properties of these fibres, let us first consider their molecular constitution, then their hierarchical structure. 

We are so used to food that has a fibrous texture that when it is homogeneous fibres have to be added. An example is Quorn , a mycoprotein produced from Fusarium, a mycelial fungus. The threads or hyphae are about 5 pm in diameter and very thin-walled. So they hardly register as giving texture. Since they can be given a variety of flavours, it makes sense to complete the illusion with texture. One way is to align the hyphae in a shear field, add some egg albumen and fix the structure with heat. Although this does not produce a hierarchical structure, and so is more similar to chicken or fish than mammalian muscle, it is nonetheless very acceptable. 

Silk is a fibrous protein produced by several insect species. Commercially, silk is produced from the cocoon stage larvae of the moth caterpillar Bombyx mori, as it has been, in China, for some 4500 years. A single cocoon produces a continuous thread up to 1 km in length, and the protein fibroin contains large amounts of glycine, alanine, tyrosine, proline and serine The peptide chains are arranged in anti-parallel P-sheets which make up the hierarchical structure of the crystalline silk fibres. A number of spiders also produce silk webs, although the fibroin structure is rather different to that from silk worms. 

The fibres possess a complex hierarchical microstructure, in which regions of well-ordered crystalline cellulose are interspersed with areas of random... 

Figure 5 Hierarchical microstructure of a linen fibre (a) from cellulose chains to the fibre and (b) a scanning electron micrograph showing the ultimate cells bundled in fibres...

As with other natural fibres, silk has a hierarchical microstructure - about five anti-parallel (f-sheets, each with around 12 chains, aggregate to form parallel, crystalline microfibrils (approximately 10 nm in diameter), bundles of which make up fibrillar elements (roughly 1 p,m across), which in turn associate to comprise the individual fibroin filaments (7-12 xm) at each level of organisation, the ordered elements are embedded within amorphous matrices derived from the non-crystalline components. Once again, then, the behaviour of the structural composite can be understood in terms of the semi-crystalline array of its component parts. 

Figure 3.2 Schematics of the hierarchical architecture of cortical bone. (A) Longitudinal section of femur. (B) Enlarged cross section of cortical bone showing cylindrical osteons. (C) Enlargement of an osteon showing the central Haversian canal with a blood vessel, the concentric lamellae and the radial canaliculi (see also J). A more detailed view of an osteon is shown in the inset in the bottom right. (D) Collagen fibre composed of hundreds of fibrils. The evenly spaced dark spirals are...

The cellulose fibre is organized in a cellular hierarchical structure and can be described as a multiphase system of concentric layers surrounding the lumen. The outermost layer is the primary wall (P), followed by the outer layer of the secondary wall (SI), the middle layer of the secondary wall (S2), and the inner layer of the secondary wall (S3), as shown in Figure 17.3. The middle lamella (ML) which is located outside the primary wall is not considered a cell wall layer. 

Nanofibrils can be extracted from natural resources, since many cellulosic fibres (such as cotton, hemp, flax) or protein fibres (such as wool, silk from silkworm or spider) have hierarchical structures composed of fibrils in nanoscale sizes. 

Cellulose, the base of all cellulosic fibres, is a complex composite material which structurally comprises three hierarchical levels ... 

Hierarchical structure using a carbon fibre reinforcement, testing element by ITV Denkendorf. 

Figure 19.10 Schematic diagram showing the hierarchical structure of a semi-crystalline cellulose fibre.

The chemical composition as well as the morphological microstmcture of vegetable fibres is extremely complex due to the hierarchical organisation of the different compounds present at various compositions. Depending on the type of fibre, the chemical composition of natural fibres varies. Primarily, fibres contain cellulose, hemicellulose and lignin. The property of each constituent contributes to the overall properties of the fibre. 

Juntaro J, Pommel M, Kalinka G, Mantalaris A, Shaffer MSP, Bismarck A et al (2008) Creating hierarchical structures in renewable composites by attaching bacterial cellulose onto sisal fibres. Adv Mater 20 3122-3126... 

A composite pigment-biopolymer structure with potential use in biocomposites can be formed by different techniques, such as precipitation, mixing, self-assembly, or hierarchical methods. There are many open questions about the production, use, and potential benefits of these filler-fibre complexes. In this chapter, we present some targeted work, which investigated biopolymer composites produced by in situ calcium carbonate precipitation and mixing techniques. 

Keywords Bacterial cellulose Hierarchical composites Mechanical properties Natural fibres Surface modification... 

The previous three sections involved the treatment of natural fibres by removing substances from the natural fibres. This section, however, describes a new modification that does not involve the removal but the addition of new material onto the surface of natural fibres. This type of modification involves the deposition of nanosized cellulosic materials onto the surface of natural fibres to enhance the interfacial adhesion between the fibres and the matrix [9,10,14,104]. By doing so, a hierarchical structure can be created. These works were inspired by nature. Nature maximises the efficiency of structural materials by creating hierarchical stmctures the arrangement of the constituents at every level, from the molecular level to the macroscopic level. By applying this concept, composites that possess a hierarchical structure with improved mechanical properties can be manufactured. 

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