Fibrillar Breaks

In wet cotton the fluidity of the absorbed water between fibrils inhibits stress transfer, so that fibrils break independently. Fig. 6a. 

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Fif . 6. (a) Fibrillar break in wet cotton, (b) Multiple split break of Kevlar, (c.d) Single split break of Kevlar. For further e.xplanation. see Fig. 1. 

Menashi et al.153) could confirm the results of Privalov and Tiktopulo152 and inter-prete the described effects as follows In the case of native tropocollagen, the pyrrolidine residues are probably directed away from the fibrillar axis and are mostly coated by water which is structured in the immediate neighbourhood to the pyrrolidine residues. During the denaturation these pyrrolidine residues form hydrophobic bonds with each other or with other apolar residues within the same chain (endothermic interaction) while the structure of water breaks down (increase of entropy). 

Colchicine does not influence the renal excretion of uric acid or its concentration in blood. By virtue of its ability to bind to tubulin, colchicine interferes with the function of the mitotic spindles and causes depolymerization and disappearance of the fibrillar microtubules in granulocytes and other motile cells. This action is apparently the basis for the beneficial effect of colchicine, namely, the inhibition of the migration of granulocytes into the inflamed area and a decreased metabolic and phagocytic activity of granulocytes. This reduces the release of lactic acid and proinflammatory enzymes that occurs during phagocytosis and breaks the cycle that leads to the inflammatory response. 

The ubiquity of this power-law behaviour in SCG tests on PE has been the subject of considerable discussion, usually based on the assumption of a fibril creep failure mechanism [43, 45, 46, 47, 76, 79]. At high and intermediate K, after a certain induction period, steady-state crack advance is generally observed to occur by a stick-slip mechanism all or part of the fibrillar zone breaks down rapidly after an incubation time during which fibril creep takes place. The crack-tip then advances rapidly over a short distance and a new fibrillar zone stabilises, as sketched in Fig. 12. 

Much attention has been focused on the microstructure of crazes in PC 102,105 -112) in order to understand basic craze mechanisms such as craze initiation, growth and break down. Crazes I in PC, which are frequently produced in the presence of crazing agents, consist of approximately 50% voids and 50% fibrils, with fibril diameters generally in the range of 20-50 nm. Since the plastic deformation of virtually undeformed matrix material into the fibrillar craze structure occurs at approximately constant volume, the extension ratio of craze I fibrils, Xf , is given by... 

In terms of macrostructure, studies on the deformation of spherulites during biaxial orientation elucidated that spherulitic break-up occurs not only at their boundaries, but also at their centers. In either case and preferentially at higher temperatures, a fibrillar morphology was observed to develop at higher levels of stretching. Less data are available on direct methods to quantify the behavior of amorphous segments as they take part in these deformations. 

A number of electron optical observations furnish rather convincing indications that once in each fibrillar period there is a weak level at which protofibrillar continuity may be interrupted under sufficient stress. For example, fibrils have been observed to break off squarely, normal to... 

Xylogincan -Crystallite size of fibrils changed -Aggregation of fibrillar units into ribbon assemblies broke down -Lower stiffness or breaking stress -Increased extensibility in uniaxial tension... 

A striking feature of poly(p-benzamide) fibre is the extremely splintered nature of the broken end of the heat treated material (Fig. 10). The tendency of the fibres to break up into fibrillar or high aspect ratio particles and to show very poor mechanical properties in a direction perpendicular to the fibre axis must clearly be related to the extremely high axial orientation of the polymer molecules. One can envisage these fibrillar particles as built up of submicroscopic fibrils, themselves built up of the ultimate linear crystallites. 

Botanical polysaccharides exist as structural constituents of plant cell wall [64]. The main types of polysaccharides involved in cell wall are rigid fibrillar chitin (or cellulose) matrix-Uke (3-glucan, a-glucan, and glycoproteins [64-70]. Therefore, the selectirai of an effective extraction procedure for plant polysaccharides will have to depend on the cell wall structure [64]. In general, the basic theory of extraction of polysaccharides from botanical materials is to break the cell wall under certain conditions such as pH value, temperature, irradiation with microwave, and ultrasonic radiation [65,71]. 

Practical polymer processing operations, such as extrusion and injection, are complex processes highly dependent on the conditions of shear, extensional stress and temperature. It has now been realized that shear stress and extensional stress have different effects on the orientation of PLGs. Nematic PLCs have a polydomain texture and each domain consists of mesogens with the same local orientation. The directions of these domains are randomly aligned while in a quiescent state. Only if a stress is applied are the domains oriented in one direction. As Ide and Ophir [6] and Viola et ah [7] have pointed out, shear stress is related to rotational motion (torque), and its application will result in a tumbling flow of PLC domains. Only once the shear stress has reached a critical value will it break down the domains and lead to a uniform molecular orientation. In contrast, extensional stress tends to orient the domains in one direction without breaking down the domains even if the stress is low. Viola et ah [7] also considered that shear flow induces sheet-like textures while extensional flow induces fiber-like textures. Therefore there will be differences in the hierarchical and fibrillar structures acquired in different fibrication processes. 

Kuhfuss and Jackson s polyester containing 60mol% PHB (COP) [8-10] can serve as a PLC model. Pure COP kept under pressure in a mold shows small fibrillar structures at break (Figure 9.1). This diminishes quickly with an increasing amount of PC and is completely lost in that... 

The preparation of nano-scaled polymeric assemblies such as nanofibers is one of the most useful methods to practically utilize polymeric materials as observed in the case of cellulose (Abe at al., 2007, Saito et al., 2006, Saito et al., 2007). For example, self-assembled fibrillar nanostructures from cellulose are promising materials for the practical applications in bio-related research fields such as tissue engineering (Isogai et al., 2011, Abdul Khalil et al., 2012). The efficient methods have also been developed for the preparation of chitin nanofibers. The conventional approaches to the production of chitin nanofibers are mainly performed upon top-down procedures that break down the starting bulk materials from chitin resources (Figure 2). 

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