Fibres stretching

Pioneer newly acquired seed business specialising in corn and soya Polyesters staple and filament fibres for clothing, bedding and insulation polyester films for films and packaging resins for plastic containers Specialty Fibres stretch clothing based on Lycra non-woven products advanced fibres ... 

Oriented fibres, stretch-blow-moulded bottles and biaxially oriented film have also been demonstrated. 

Dissolution the dissolution of polymer in solvent. The molecular chains of the solid polymers may be entangled, and the entanglements will affect the molecular chain stretching. The dissolution of polymers in solvent can disentangle these entanglements to aid the gel fibre stretching. 

Both the anionic and the cationic surfactants have been found to improve the solution charge density that enhances the fibre stretching process. It appears that there is no difference between adding an anionic and a cationic surfactant into the polystyrene solution, because they both lead to bead-free and uniform fibres. However, when a surfactant molecule is able to associate with the polymer linkage in the solution, it gives rise to an improvement in fibre evenness, because this polymer-surfactant interaction tends to make... 

According to data /3/, the AE sources in the fibrous composites are plastic deformation and cracking of the die material, shift stratification on the fibre-die interphase border, fibre destmction and stretching fibres out of the die. 

In oriented systems (fibres or stretched films), the scattered image often appears as a two-bar or a four-point pattern with the scattering maximum at or near the meridian (fibre axis). The one-dimensional scattered intensity along the meridian must be calculated by the projection method using the following fonnalism... 

Many fibrous composites are made of strong, brittle fibres in a more ductile polymeric matrix. Then the stress-strain curve looks like the heavy line in Fig. 25.2. The figure largely explains itself. The stress-strain curve is linear, with slope E (eqn. 25.1) until the matrix yields. From there on, most of the extra load is carried by the fibres which continue to stretch elastically until they fracture. When they do, the stress drops to the yield strength of the matrix (though not as sharply as the figure shows because the fibres do not all break at once). When the matrix fractures, the composite fails completely. 

Flow is generally classified as shear flow and extensional flow [2]. Simple shear flow is further divided into two categories Steady and unsteady shear flow. Extensional flow also could be steady and unsteady however, it is very difficult to measure steady extensional flow. Unsteady flow conditions are quite often measured. Extensional flow differs from both steady and unsteady simple shear flows in that it is a shear free flow. In extensional flow, the volume of a fluid element must remain constant. Extensional flow can be visualized as occurring when a material is longitudinally stretched as, for example, in fibre spinning. When extension occurs in a single direction, the related flow is termed uniaxial extensional flow. Extension of polymers or fibers can occur in two directions simultaneously, and hence the flow is referred as biaxial extensional or planar extensional flow. 

The large diameter A/l-afferent fibre enters the dorsal horn of the spinal cord through the medial division of the dorsal root. It then descends through the medial region of lamina I or II, or alternatively, curves around the medial (central) edge of the dorsal horn down to the ventral horn. On reaching deeper laminae, laminae IV and V, the AjS-fibres ascend back up into laminae III and IV where they repeatedly subdivide and form a characteristic termination pattern. The densest arborisation appears to occur in lamina III. Axons originating from specialised muscle stretch receptors have collaterals that pass ventrally to make monosynaptic connections with neurons of laminae V, VI and VII. Some also extend to laminae VIII and IX of the ventral horn where they synapse directly onto motor neurons and form the basis of monosynaptic reflexes. 

Poly(trimethylene terephthalate) (PTT) is a polymer with very useful properties. As a textile fibre it has excellent softness, stretch and recovery. As a resin it has excellent barrier properties. Developed over 60 years ago, PTT has not been very widely used compared to poly(ethylene terephthalate) (PET) as one of the key monomers 1,3-propanediol (PDO) has been expensive. 

An increase in rod-like arrangement of the macromolecules can also arise by stretching a polymer either in its solid state, either in the melt or even in solution (for polymers leading to lyotropic liquid crystals such as aromatic polyamides). This is the basis of the development of synthetic fibres including high modulus polyethylene Dyneema , polyamide Nylons and Kevlar , polyester Tergal or Dacron fibres. 

The main application of spandex (e.g., Lycra ) is for stretched apparel clothing. It is used to make yarns when combined with other natural and synthetic fibres. 

This stretching, similar to the drawing of fibres, which promotes orientation and crystallite formation, is called biaxial orientation. It gives the film added strength and gas-barrier properties. In some processes, monoaxial (uniaxial) drawing is employed, e.g., polypropylene, which is then slit into thin strips and fabricated into heavy duty sacks, carpet backing, etc. The stenter process is used to make biaxial oriented poly(vinylidene dichloride) ("ding" film), polyester, polyamide and polypropylene films. 

A driven, fabric reinforced, beltlike component over which loosely formed textile fibres (slub) are drafted (orientated and drawn) to improve yam formation and consolidation. Two aprons work face to face, between which the yam being formed is drawn. The aprons separate two sets of cots and fluted steel rollers, revolving at different speeds to create the stretching required. 

The generic name given, in the USA, to stretch fibres based on elastomeric long-chain polyester polyurethanes. Trade names are, e.g., Lycra and Vyrene . 

Fig. 5 Schematic representation of the domain contributions to the tensile deformation of the fibre chain stretching and chain rotation due to shear deformation...

Chain stretching is governed by the covalent bonds in the chain and is therefore considered a purely elastic deformation, whereas the intermolecular secondary bonds govern the shear deformation. Hence, the time or frequency dependency of the tensile properties of a polymer fibre can be represented by introducing the time- or frequency-dependent internal shear modulus g(t) or g(v). According to the continuous chain model the fibre modulus is given by the formula... 

This simple fracture model has a major shortcoming. The exclusion of chain stretching in the model leads for small initial orientation angles to strength values that become infinite. It follows from Eq. 27 that the shear stress is a continuous function of the fibre stress and it increases asymptotically to the value of 2gtan . So for initial orientation angles... 

Asakura, T., and Yao, J. M. (2002). C-13 CP/MAS NMR study on structural heterogeneity in Bombyx mori silk fibre and their generation by stretching. Protein Sci. 11, 2706-2713. 

Attempts were made later on to prepare synthetic stretch fibres based on polyurethane. At present many such fibres are marketed as "Spandex", "Lycra , etc. 

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