Amorphous lignin

The filaments of all plant fibers consist of several cells. These cells form crystalline microfibrils (cellulose), which are connected together into a complete layer by amorphous lignin and hemi-cellulose. Multiple layers stick together to form multiple layer composites, filaments. A single cell is subdivided into several concentric layers, one primary and three secondary layers. Figure 5 shows a jute cell. The cell walls differ in their composition and in the orientation of the cellulose microfibrils whereby the characteristic values change from one natural fiber to another. 

Figure 10. Scanning electron micrograph of a composite of cellulose powder-lignin powder mixture. The hig, fibrous cellulose particle (right) appears to be bonded to the big amorphous lignin particle (left). A split in the cellulose particle suggests that bonding between lignin and cellulose particles was stronger than the tensile strength of cdlulose perpendicular to the fiber axis (12A).

T Hatakeyama, H Hatakeyama. Temperature dependence of X-ray of amorphous lignin and polystyrenes. Polym 23 475 99, 1982. 

The combination of rigidity and stress resistance that is required in higher plants is provided by the structure of the various layers and lamellae of the cell wall that contain crystalline microfibrils, matrix polysaccharides, and amorphous lignin. According to an early interpretation by Freudenberg, the microfibrils in the cell wall act in the same way as the reinforcing rods in prestressed concrete. A better mathematical model is furnished by filament-wound, reinforced-plastic structures, such as pressure vessels. 

Hatakeyama, T., Hatakeyama, H. Temperature dependence of X-ray dilfactograms of amorphous lignins and polystyrenes. Polymer 23, 475 77 (1982)... 

Fibrillar fines obtained from cellulosic fibres are known for their unique structure, material characteristics, and potential applications (Hubbe et al. 2008). An amorphous lignin and hemicellulose matrix separates the elementary nanofibrils in natural vegetable fibres. Based on raw material sources, pretreatment and subsequent defibrillation procedures will produce a broad spectrum of fibril structures as well as nomenclatures used to describe them. Thus, we find various terms adopted in the field, such as nanoscale-fibrillated cellulose, cellulosic fibrillar fines, cellulose aggregate fibrils, and microfibrillar cellulose. 

Figure 5.21. Atomic force microscopy height image (A) shows the topographic features of the fiber, whereas the phase image shows the different components present in the material (B), notably the cellulose microfibrils and the amorphous lignin patches [84], Scale is 3pm on a side. (From Chernoff and Maganov [84], (2003) American Chemical Society used with permission.)...

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