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Stretching polyethylene fibres

A clear example for the absence of Xe in crystalline polymers is shown in Figure 12.2 for highly stretched polyethylene (PE) fibres. [Pg.459]

During the last ten years there have been several notable advances in the development of ultra high modulus polyethylene and polypropylene. This has been achieved most simply by tensile drawing , but also by hydrostatic extrusion , ram extrusion and die drawing all of which are solid phase deformation processes. In polyethylene, an alternative approach has been the production of fine ultra high modulus fibres from dilute solution, either by crystallisation in an elongational flow field or by stretching fine fibres spun to form a gel from dilute or reasonably dilute solution, 13 ... [Pg.139]

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. [Pg.32]

The workhorse polyester is polyethylene terephthalate) (PET) which is used for packaging, stretch-blown bottles and for the production of fibre for textile products. The mechanism, catalysis and kinetics of PET polymerization are described in Chapter 2. Newer polymerization techniques involving the ring-opening of cyclic polyester oligomers is providing another route to the production of commercial thermoplastic polyesters (see Chapter 3). [Pg.775]

Polyethylene. The Raman spectrum of polyethylene has been known for some years and all the bands have been identified seemingly unambiguously. Recently the spectrum has been recorded using stretched large-diameter fibres as a sample. The spectra were recorded with the fibre bundled vertically, horizontally and end-on in a Cary 81 spectrometer. The arrangements are illustrated in Fig. 3. The electric vector of the helium-neon laser is set vertically and therefore in the first orientation (a), the fibre axis and electric vector are parallel. [Pg.157]

In 4.3 we have already seen that polymers, in the rubber or fluid condition, crystallize much more rapidly when their chains are oriented. Therefore a stretched rubber, if stereospecific in its molecular structure, is able to crystallize at a temperature considerably above its equilibrium thermodynamic melting point. Also a thermoplast such as polyethylene, when in the molten state or in solution, can crystallize spontaneously when the chains are being orientated in elongational flow. The latter case is utilized when polyethylene is spun from a diluted solution (gel spinning process), resulting in fibres of super-high strength and stiffness ( Dyneema fibres). [Pg.84]

The moduli of polymers cover a wider range than those of other materials (from 105 N/m2 for rubber to 1010 N/m2 = 10 GPa for rigid polymers), which is one of the reasons why polymers are so versatile in application. Absolute stiffness and strength of polymers are much lower than those of metals, but on the basis of equal weight polymers compare favourably due to their much lower density. The specific moduli, defined as the moduli divided by the density, of isotropic polymers are of the order of one tenth of those of the stronger metals. The hyper-strong and hyper-stiff polymeric fibres such as fully extended polyethylene, stretched poly-(p-phenylene terephthalic amide) and carbon,... [Pg.388]

Bicomponent films can also be made from two different polymers if sufficient adhesion between the layers can be achieved to prevent delamination during stretching and fibrillation. Mehta has pointed out that bicomponent films can be made from polypropylene and low density polyethylene. After stretching and fibrillation the fibres look like ordinary split fibres but on heating they develop a spiral crimp with the LDPE on the inside. These fibres have the important advantage that a carded fleece, when needle-punched and exposed to temperatures above the melting... [Pg.451]

These data show that the dissociation energy of the urethane-type bonds is lower than that of -C-C- bonds from polyethylene or polypropylene. It is also two times lower than the dissociation energy of the bond from the polyamide chain. In this last case, the energetic barrier that must be overtaken in order as a elementary craek to appear is higher due to the supplementary orientation of the amorphous domains of fibres, realised by forced orientation during stretching. [Pg.163]

The results of such calculations for semi-crystalline polyethylene have been reviewed elsewhere [37]. A rather wide range of predicted values is obtained, due to the choice of force constants and also to sensitivity to detailed assumptions on the unit cell structure. In spite of these limitations the principal predictions for the elastic anisotropy are clear. These include the anticipated high values for C33 and the very low values for the shear stiffnesses C44, C55 and cee, which reflect the major differences between bond stretching and bond bending forces that control C33 and the intermolecular dispersion forces that determine the shear stiffnesses. It is therefore of value to compare such theoretical results with those obtained experimentally. Table 7.3 shows results for polyethylene where data for the orthorhombic unit cell at 300 K are used to calculate these constants for an equivalent fibre (Voigt averaging procedure see Section 7.5.2 below) compared with ultrasonic data for a solid sheet made by hot compaction. It can be seen that... [Pg.140]


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See also in sourсe #XX -- [ Pg.459 , Pg.460 ]




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