Cellulose microfibrils and macrofibrils

Mechanical and Thermal Properties of Cellulose Microfibrils and Macrofibrils 1121... 

Supramolecular level (nm). The aggregation of the cellulose macromolecules into elementary fibrils, microfibrils and macrofibrils are described in this level. Its intermolecular interactions and crystal lattice are also discussed. 

Morphological level (nm to um). This level describes the organization of the microfibrils and macrofibrils into layers and walls the existence of distinct cell wall layers in native cellulose libers or in skin core structures in man-made cel-lulosic fibers are discussed. 

Figure 12.5 AFM images of (a) microfibrils coated with non-cellulosic polymer and (b) the primary wall structure showing microfibrils aligned parallel to one another and the macrofibrils. ...

From the nano scale to the macroscopic aspect, wood is structured in a hierarchical way. The molecules of cellulose (40-50%) are arranged first in microfibrils, then in macrofibrils and finally they constitute the layers of the wall of every cell in the wood (Figure 5.4). 

The annealed surface layer may be stabilized by lateral association with those hemicelluloses that bond strongly to the microfibrils. Also in the G-layer, which is mostly cellulose, the presence of any (uncertain) hemicelluloses and the layer s strongly hydrated nature (gelatinous implies a gel) must prevent strong lateral bonding of the individual microfibrils to form larger macrofibrils. 

Thirty to one hundred strands of cellulose aggregate into so-called elemental fibrils (cross section approximately 2 mn) via H-bridges, which in turn aggregate into microfibrils (cross section approximately 10 30 mn) and these into macrofibrils (cross section approximately 500 nm). The orientation of the cellulose fibrils in the wood cell wall differs. The strongest cell wall layer, for example, shows a constitution parallel to the axis which accounts for the high tensile strength of wood. ... 

The secondary cell wall contains about 94% cellulose and only grows when the primary cell wall is formed. In it, the cellulose molecules are highly oriented. With decreasing diameter, the following structural types can be distinguished fibers (0.06-0.28 mm), cell walls, macrofibrils (400 nm), microfibrils (20-30 nm), and elementary fibrils (3.5 nm). Lignin deposits as a cement in interfibrillar spaces of 5-10 nm in width. In fact, the inter-micellar spaces of 1 nm in width that occur between the elementary fibrils are accessible to H2O, ZnCl2, or I2, but not to dyestuffs. 

The elementary cellulose component of wood cell walls is represented by microfibrils which form lamellas or bundles, namely macrofibrils. Under the degradation process, wood first generates macrofibrils, then well-defined, homogeneous microfibrils (MFC) and finally, fibrils [19-21]. The defibrillation of the wood cell wall is obtained using a homogenous mechanical treatment in combination with some appropriate pretreatment, such as enzymatic treatment [22,23], carboxymethylation [21], or hydrolysis [24]. 

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