Fibrillization mechanisms

The film is fibrillated mechanically by mbbing or bmshing. Immiscible polymers, such as polyethylene or polystyrene (PS), may be added to polypropylene to promote fibrillation. Many common fiber-texturing techniques such as stuffer-box, false-twist, or knife-edge treatments improve the textile characteristics of slit-film fibers. 

Such information offers an opportunity to study details of the fibrillation mechanism. The fibers formed by stretching the spherulitic polymer representing nothing other than ribbon formations plastically deformed and oriented towards the mechanical stress that is released by comparatively weak mutual interconditions existing in an earlier formation (Figure 3). This behavior points to the existence of some weak surfaces in the crystalline polymers. Elements of the super-molecular structure detached by action of the external mechanical forces can slide on the weak surfaces. Evidence for the strain-destruction relationship must come from studies of the modification of the contact surfaces of two neighboring spherulites under mechanical stress. 

The second generation model comprised more refined flow analysis, two mechanisms of dispersion (the fibrillation mechanism and a drop splitting mechanism for low supercritical capillary numbers, with the choice of break-up mechanism based on locally computed microrheological criteria), as well as coalescence effects [Huneault et al., 1995a]. The latter effects were taken into account by determining the coalescence constant in Equation 7.117 from the plot shown in Figure 7.18. Thus, the developed model was self-consistent, fully predictive, without any adjustable parameters. 

Wang and Cakmak (52) studied the development of structure hierarchy in tubular film blown dynamically vulcanized PP/EPDM blend. The blown films were found to exhibit an unusual asymmetric structure. The PP phase was found to fibriUate at all the outside surface, while the inner surface remained relatively featureless. This was attributed to disproportionally rapid cooling of the outside surface by the air steam blown externally onto the film being extruded. This, in turn, resulted in sohdification of very thin PP surface layers that caused their fibrillation under the heavy stress they had to endure. Increase in the blow-up ratio was found to expand this web-like surface texture. As a result of this fibrillation mechanism, the increase of both the blow-up ratio and draw-down ratios was found to reduce the mechanical properties. 

Introduction Mechanism of Fibrillation Mechanism of Defibrillation Clinical Defibrillators Electrodes Synchronization Defibrillator Safety ... 

Warfarin has been the mainstay of oral anticoagulant therapy for many years, principally for atrial fibrillation, mechanical heart valves, or venous thromboembolism. Adverse-effects profile of patients on warfarin therapy parallel what would be seen in vitamin K deficiency. Dne to its inhibitory effect on VKOR in the liver, warfarin affects the fnnction of the MGP and has been associated with vascular calcification in various animal and human studies. 

Wu Y, Wang S, Zhou D, Zhang Y, Wang X, Yang R (2013) Biodegradable poly(vinyl alcohol) nanocomposites made from rice straw fibrils mechanical and thermal properties. J Compos Mater 47 1449-1459... 

A scaffold design based on nanofibers can successfully mimic the stmc-ture and components of ECM component in the body and therefore properties of other native tissues. Specifically, the ECM consists of a cross-linked network of collagen and elastin fibrils (mechanical fiamework), interspersed with glycosaminoglycans (biochemical interactions). In spite of its remarkable diversity due to the presence of various biomacromolecules and... 

Two mechanisms for spherulite growth have been proposed one by Keith and Padden [106], the fibrillation mechanism, and the other by Bassett [107], the splaying and branching mechanism. 

Y. Suzuki, NMR Study of Bomb) Mori Silk Fibroin for Understanding the Fibrillation Mechanism, Sen i Gakkaishi, 2012, 68, P382. 

Fibrillated Fibers. Instead of extmding cellulose acetate into a continuous fiber, discrete, pulp-like agglomerates of fine, individual fibrils, called fibrets or fibrids, can be produced by rapid precipitation with an attenuating coagulation fluid. The individual fibers have diameters of 0.5 to 5.0 ]lni and lengths of 20 to 200 )Jm (Fig. 10). The surface area of the fibrillated fibers are about 20 m /g, about 60—80 times that of standard textile fibers. These materials are very hydrophilic an 85% moisture content has the appearance of a dry soHd (72). One appHcation is in a paper stmcture where their fine fiber size and branched stmcture allows mechanical entrapment of small particles. The fibers can also be loaded with particles to enhance some desired performance such as enhanced opacity for papers. When filled with metal particles it was suggested they be used as a radar screen in aerial warfare (73). 

Asbestos and other fibers in a wide variety of bundle sizes or even individual fibrils are in commercial usage. The handling of asbestos and other fibers causes degradation of the larger fiber bundles to fibers having diameters less than two micrometers that remain airborne for extended periods of time. These airborne fibers are prone to inhalation and lung entrapment. The exact definition of harmfiil fibers and the mechanism by which they affect the body is not accurately known. 

Cardiac arrhythmias are an important cause of morbidity and mortality approximately 400,000 people per year die from myocardial infarctions (MI) in the United States alone. Individuals with MI exhibit some form of dysrhythmia within 48 h. Post-mortem examinations of MI victims indicate that many die in spite of the fact that the mass of ventricular muscle deprived of its blood supply is often quite small. These data suggest that the cause of death is ventricular fibrillation and that the immediate availability of a safe and efficacious antiarrhythmic agent could have prolonged a number of Hves. The goals of antiarrhythmic therapy are to reduce the incidence of sudden death and to alleviate the symptoms of arrhythmias, such as palpitations and syncope. Several excellent reviews of the mechanisms of arrhythmias and the pharmacology of antiarrhythmic agents have been pubflshed (1,2). 

Reentry mechanism Intranodal (AV node) reentry Extranodal reentry Reentrant tachyarrhythmia Atrial flutter Atrial fibrillation Ventricular tachycardia Ventricular fibrillation Conduction B/ocks ... 

A brittleness associated with a tendency to crystallise cmd fibrillate during mechanical stressing. 

In recent years there has been a renewed appreciation of potential beneficial effects of roughness on a macroscale. For example Morris and Shanahan worked with sintered steel substrates bonded with a polyurethane adhesive [61]. They observed much higher fracture energy for joints with sintered steel compared with those with fully dense steel, and ascribed this to the mechanical interlocking of polymer within the pores. Extra energy was required to extend and break these polymer fibrils. 

As with block copolymers, the important parameters are the surface density and length of the copolymer chains. Toughening of the interface may occurs as a result of pull-out or scission of the connector chains, or of fibril or craze formation in matrix. This last mechanism gives the highest fracture toughness, F, and tends to occur at high surface density of chains. 

As one example, in thin films of Na or K salts of PS-based ionomers cast from a nonpolar solvent, THF, shear deformation is only present when the ion content is near to or above the critical ion content of about 6 mol% and the TEM scan of Fig. 3, for a sample of 8.2 mol% demonstrates this but, for a THF-cast sample of a divalent Ca-salt of an SPS ionomer, having only an ion content of 4.1 mol%, both shear deformation zones and crazes are developed upon tensile straining in contrast to only crazing for the monovalent K-salt. This is evident from the TEM scans of Fig. 5. For the Ca-salt, one sees both an unfibrillated shear deformation zone, and, within this zone, a typical fibrillated craze. The Ca-salt also develops a much more extended rubbery plateau region than Na or K salts in storage modulus versus temperature curves and this is another indication that a stronger and more stable ionic network is present when divalent ions replace monovalent ones. Still another indication that the presence of divalent counterions can enhance mechanical properties comes from... 

In the case of grinding, the cellulose fibers go over a state of fine fibrillation into a more or less powdery substance. This mechanical severance of cellulose may break main valence bonds and will, therefore, decrease its degree of polymerization. In addition, the crystal structure of cellulose fibers is nearly lost [32]. Grinding of the cellulose fibers also, appreciably increases its surface area. 

In addition, it was found that the blends with highly fibrillar structure exhibited a significantly lowered viscosity. Increased shear rate caused slight changes in the blend morphology but did not enhance the fiber formation. Thus, in addition to shear, elongational forces are needed to achieve a well-fibrillated blend structure and significant mechanical reinforcement. 

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