Fibers extensibility

Silk type Function Proteins (ratio )a Predicted structure from sequence Amino acid (%Y Structure in solution Conformational change in solutione Fiber degree of crystallinity mf Fiber extensibility (%)e... 

Fibers extensibility MA (Vollrath, 1999), MI (Vollrath unpublished), FLAG (Gosline et at., 1999a,b), CYL (Dicko et at., 2004b), Acinous (Hayashi et al, 2004), Bombyx mori, Antheraea pemyi, Galleria mellonella (Denny, 1980). 

Photochromic control of the polymer properties leads to potential applications involving the mechanical properties of a solution (viscosity, photogelation), polymer fiber (extensibility, photomuscle ), or membrane (porosity). More important, however, the ability to control the activity of enzymes and other biologically important macromolecules leads to potential applications in clinical phototherapy. 

Researchers have examined the creep and creep recovery of textile fibers extensively (13-21). For example, Hunt and Darlington (16, 17) studied the effects of temperature, humidity, and previous thermal history on the creep properties of Nylon 6,6. They were able to explain the shift in creep curves with changes in temperature and humidity. Lead-erman (19) studied the time dependence of creep at different temperatures and humidities. Shifts in creep curves due to changes in temperature and humidity were explained with simple equations and convenient shift factors. Morton and Hearle (21) also examined the dependence of fiber creep on temperature and humidity. Meredith (20) studied many mechanical properties, including creep of several generic fiber types. Phenomenological theory of linear viscoelasticity of semicrystalline polymers has been tested with creep measurements performed on textile fibers (18). From these works one can readily appreciate that creep behavior is affected by many factors on both practical and theoretical levels. 

Figure 8-19. Both hair fibers extension cycled 200 times to 20% extension at 10% RH, put into water, and knotted. Fiber on the right treated with 3% cystine poly-siloxane prior to knotting. Note the lack of scale lifting from the polysiloxane-treated fiber. Reprinted with permission of the Journal of Cosmetic Science [67].

The standard requires specimens whose elongation at break is less than 8% to be extended at a rate of 50% per minute. The normal nominal gauge length is 20 mm. Consequently if the fiber extension at break is, say, 3.5% to 4%, the cross-head traverse speed will be lOmm. min. This would result in a time to break of 4.5s, The standard alternatively specifies that if the extension at break is equal to or greater than 8% the elongation rate shall be 100%/minute. Therefore in this case if the extension at break were, say, 10%, the cross-head traverse speed would be 20 mm,/min and the time to break would be 6 s. 

Abstract. The viscosity is a physical parameter which controls not only the melting and fining of melts, but also the stress relaxation and the nucleation and crystallization phenomena. Here the basis of viscous flow is presented and discussed. Rheological models and some measurement methods fiber extension, beam bending and indentation are described. 

Viscous Flow of Glass Forming Liquids 147 7.4.1 Fiber Extension and Cylinder Compression... 

The modified series model shown in Fig. 21 has been extended to include the viscoelastic behaviour. To this end the simple assumption is made that the time-dependent part of the creep strain arises solely from the rotation of the chains towards the direction of the fibre axis as a result of the shear deformation of the crystallites. This yields for the fiber extension as a function of the time t during creep caused by a stress CTq... 

Hartness [100], working with XAS and HMS fibers in a PEEK matrix showed similar behavior. The similarities between PEEK and PP are probably greater than the differences in their crystalline structure. Beaumont [101] has shown that with HMS (treated) fiber, there is almost no pull-out, whereas with HMU (untreated) fiber, extensive debonding and pull-out take place. The pull-out lengths can be measured and using an analytical technique outlined by Phillips [102], values can be obtained for the nylon/fiber interfacial bond strength and fracture energies. 

While not changing the chemical composition of the fiber extensively, physical treatments cause variations in structural and surface properties of the fiber and consequently affect the mechanical bonding to the polymer matrix. Thermal treatment, corona and plasma treatments can be given as examples to physical treatments applied on plant fibers [3]. Ragoubi et al. [33] reported an increase in mechanical and thermal properties of reed fiber-reinforced PLA and PP composites upon corona discharge treatment of fibers. 

On the basis on the carried out structural investigations of amorphous PET fibers simultaneous heat - mechanically modified at isothermal conditions and constant strain stress values it can be make the following conclusions The mechanical strain force applied simultaneously with the linear heating of the studied PET yarns affects significantly the deformation behaviour and samples crystallization kinetics. Moreover in contrast to the results obtained in the first experiment, all of the so treated specimens are partially crystaUine. The role of the tensile stress in the adjustment of the interacting processes of the fluid like deformation and stress-induced crystallization clearly reveals in the ultimate samples deformation. At stress values from 1.56 MPa to 2.16 MPa predominates the fluid like fibers extension, while the further stress increasing leads to the earlier crystallization start and thereby to decrease of the final fibers length. 

Fiber extension may occur under high tensile stress during draping. However, this mechanism is not as common as the other three listed previously due to the high stiffness (modulus of elasticity) of fiber materials. 

The skin-core structure is a macroscopic analogue of the partitioned structure within the fiber. Since fiber stresses become concentrated in the oriented regions, there is a loss of participation of some of the interior molecules to resist subsequent strains. Under fiber extension, the taut molecules will break first, triggering rupture of the fiber before the unoriented molecules contribute much resistance. A loss of overall fiber strength and tenacity results. 

Chen CJ, Kwak BM, Rim K, Falsetti HL (1980) A model for an active left ventricle deformation -formulation of a nonlinear quasi-steady finite-element analysis for orthotropic, three-dimensional myocardium. Int Conf Finite Elements in Biomechanics 2 639-655 Feit TS (1979) Diastolic pressure-volume relations and distribution of pressure and fiber extension across the wall of a model left ventricle. Biophys J 28 143-166 Ghista ND, Sandler HD (1968) An elastic viscoelastic model for the shape and the forces in the left ventricle. J Biomechanics 2 35-47... 

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