Polymer oriented chains

The stretching properties of polymers are investigated by examining the effect of polymer orientation, polymer chain length, stretching rate, and temperature. Homogeneity of polymer films and consistency between lots of polymer films also are investigated. Statistical analysis of data includes Q-tests and f-tests. 

For the transformation of the macrocomposite model to a molecular composite model for the ultimate strength of the fibre the following assumptions are made (1) the rods in the macrocomposite are replaced by the parallel-oriented polymer chains or by larger entities like bundles of chains forming fibrils and (2) the function of the matrix in the composite, in particular the rod-matrix interface, is taken over by the intermolecular bonds between the chains or fibrils. In order to evaluate the effect of the chain length distribution on the ultimate strength the monodisperse distribution, the Flory distribution, the half-Gauss and the uniform distribution are considered. 

The oriented polymer chains provide a moderate level of rigidity to the substrate. 

As the laser beam can be focused to a small diameter, the Raman technique can be used to analyze materials as small as one micron in diameter. This technique has been often used with high performance fibers for composite applications in recent years. This technique is proven to be a powerful tool to probe the deformation behavior of high molecular polymer fibers (e.g. aramid and polyphenylene benzobisthiazole (PBT) fibers) at the molecular level (Robinson et al., 1986 Day et al., 1987). This work stems from the principle established earlier by Tuinstra and Koenig (1970) that the peak frequencies of the Raman-active bands of certain fibers are sensitive to the level of applied stress or strain. The rate of frequency shift is found to be proportional to the fiber modulus, which is a direct reflection of the high degree of stress experienced by the longitudinally oriented polymer chains in the stiff fibers. 

Birefringence can also be used to analyze polymer samples after melt processing. As we will see in the next chapter, the shear produced in certain molding techniques, such as injection molding, can orient polymer chains in certain parts of the mold, especially near the mold walls, whereas the chains in low-shear regions, such as in the middle of the mold, are not as oriented. Figure 6.104 shows the variation in birefringence, as... 

When polymer melts are accelerated during the manufacturing processes such as injection molding and afterwards cooled down quickly, the stretched molecular chains cannot relax, which leads to orientations in the direction of melt flow. These oriented polymer chains act differently toward ESC influences as compared to nonoriented molecules. Orientation perpendicular to the crack propagation direction may result in a higher ESCR, as will be shown in the following discussion. 

The solubility of the electrically conductive form, the protonated EM salt, is poor in common solvents, and so, initially, EM base was used to form films from NMP solution before conversion to the salt with HC1. Attempts to increase solubility by incorporating pendent alkyl chains were counterproductive as such polymers had significantly lower electrical conductivity. Better solubility is obtained for salts produced with sulphonic acids. Thus the camphor sulphonic acid salt dissolves in m-cresol and the 2-acrylamido-2-methyl-l-propanesulphonic acid salt dissolves in dichloro-acetic acid. The use of these systems, and polymer synthesised below room temperature, has facilitated the spinning of fibres with oriented polymer chains and conductivity along the fibre as high as 2x 105f2-Im-1 (Pomfret et ai, 1998). 

It has been observed that in these particular samples the crack is followed by the craze. The microhardness increases rapidly in this region (see Fig. 3.15). Table 3.3 shows the bulk microhardness values of the polymers investigated. In Table 3.4 the H values of the craze fibrils are listed. The data of Table 3.4 show that the microhardness of the fibrils is at least twice that of the bulk polymer. This is consistent with the concept of highly oriented polymer chains within craze fibrils (Bin Ahmad Ashby, 1988). It is noteworthy that the microhardness of craze fibrils in amorphous polymers is of the same order of magnitude as the microhardness of... 

Figure 11.6. Schematic illustrations of brittle fracture, (a) Idealized limiting case of perfectly uniaxially oriented polymer chains (horizontal lines), with a fracture surface (thick vertical line) resulting from the scission of the chain backbone bonds crossing these chains and perpendicular to them. This limit is approached, but not reached, in fracture transverse to the direction of orientation of highly oriented fibers, (b) Isotropic amorphous polymer with a typical random coil type of chain structure. Much fewer bonds cross the fracture surface (thick vertical line), and therefore much fewer bonds have to break, than for the brittle fracture of a polymer whose chains are perfectly aligned and perpendicular to the fracture surface, (c) Illustration of a defect, such as a tiny dust particle (shown as a filled circle), incorporated into the specimen during fabrication, which can act as a stress concentrator facilitating brittle fracture.

In the lamellar crystals of semicrystalline materials and the extended chain structure of oriented polymers, chain packing is usually much more efficient than in the amorphous, isotropic state. The efficiency of chain packing in the crystalline phase reduces the free volume available for transport to such an extent that, as a first approximation, the crystalline phase may be regarded as impermeable relative to the amorphous phase. 

The importance of the alignment of the polymer chains has been recently demonstrated in a study in which PPyCPFs) films have been stretched to 96% [102]. The conductivity parallel to the stretch was increased, while the strain perpendicular to the stretch increased from 1.45 to 2.65% (but with more creep) at the same time very little strain could then be produced parallel to the stretch. The suggestion made was that counter-ions migrated to locations between the oriented polymer chains, producing strain perpendicular to this direction. The nanoscale chain configuration has also been altered by rolling as well as... 

The results of measurements of intrinsic birefringence permit estimation of chain segment stifi iess in an oriented polymer chain. Birefringence is among the techniques used to evaluate molecular orientation in polymers. Figure 2.27 shows changes in birefrin-genee of PVC film on its extension at 90"C. Data in the paper show that the... 

The formation of banded textures in thin-film samples of solutions of hquid crystalline polymers (LCPs), subjected to shear, has been reported in the literature since 1979 [15]. Because of the symmetrical properties of the liquid crystal solutions, large domains of weU-oriented polymer chains are formed during shear flow, while defects are squeezed into small regions. The shear accounts for an additional energy stored in the solution. When the shear is stopped, the system will first relax with a characteristic time fb to a transient state. In this state the distortion energy is minimized, and the orientational order is kept, resulting in a banded stmcture. This behavior is observed only if two conditions are fulfilled [16] ... 

Orthotropic n. Having three mutually perpendicular planes of elastic symmetry, as in composites having fibers miming in two perpendicular directions, or biaxially oriented sheet. If the fibers or orientation are unidirectional, the material is still orthotropic but also isotropic in the two directions perpendicular to the fibers or oriented polymer chains. Complete textile glossary. Celanese Corporation, New York. Brandrup J, Immergut EH (eds) (1989) Polymer handbook, 3rd edn. Wiley-Interscience, New York. 

Other Thermoplastics. Polyoxymethylene (POM) was imaged by afm, revealing oriented polymer chains parallel with the machine axis of sample extrusion (Fig. 15). Atomic scale resolution of the chains demonstrated the helical nature of the polymer chains. Long-range correlation between poljuner chains was observed as well (97). Imaging of extended chain crystals of POM closely matched molecular models for this material, allowing for the molecular packing and order in the extended chain crystal to be well understood. The authors were able to describe the polymer chain orientations with respect to the crystal (98). 

Since networks with unique properties result from cross-linking highly axially oriented polymer chains, the question naturally arises as to what limits there are, if any, to the degree of intermolecular order required to observe these effects. Partially crystalline undeformed polymers possess a large amount of intermolecular order, since significant portions of the polymer molecules are constrained to lie parallel to one another in three-dimensional array. This order is only on a microscopic scale since the crystalline regions are randomly arranged relative to one another. The question as to whether the presence of such order influences the properties of the resultant isotropic network is a matter to be decided by experiment. 

The inequalities > 1 and (Omri < 1 hold for cis- and trans- K, respectively, therefore their Tj and T2 values can be calculated by using Eq. 8 and 9, respectively. Fig. 5 exhibits these parameters for solitons in trans-VA. with randomly oriented and with partly stretch-oriented polymer chains as a function of temperature and the angle / between the external magnetic field Bq and the stretching directions. Figure 5 shows the field sensitivity of the relaxation parameters of solitons that can be explained by the depinning of their motion in trans- A film. 

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