Uniaxially oriented material

It is particularly important to note that this equation is valid for films with orthorhombic symmetry, as well as for uniaxially oriented materials. Moreover it is independent of xtrans, the fraction of trans material. 

The most common examples of uniaxially oriented materials include fibers, films, and sheets hot-stretched in one direction and composites containing fibers all aligned in one direction. Some injection-molded objects are also primarily uniaxially oriented, but most injection-molded objects have a complex anisotropy that varies from point to point and is a combination of uniaxial and biaxial orientation. 

Anisotropic materials will have a more complicated force pattern. Uniaxially oriented materials will split rather than pimcture imder puncturing loading. To improve the puncture resistance materials are needed with high tensile strength. In addition, the material should have a high compression modulus to resist the point penetration into the material. Resistance to notch loading is also important. 

Any extended part of a linear polymer molecule exhibits a strong anisotropy of many properties since its atoms and atomic groups are oriented and the macromolecule is actually a one-dimensional crystal . The parallel packing of these parts during the formation of a uniaxially oriented polymer substance imparts the anisotropie properties of a single molecule to the whole polymeric material. 

Fairly recently, another method for obtaining polymer materials with uniaxial orientation has been developed. It is the directed polymerization i.e. the synthesis of polymers under conditions at which the material attains instanteneously the oriented structure. The formation of crystals from the macromolecules in an extended conformation occurs in those polymerizing systems simultaneously with polymerization22. ... 

One of the aims of the present research at Leeds University, of which the spectroscopic studies form a major part, has been to gain an understanding of mechanical behaviour. Both the uniaxially oriented and the biaxially oriented materials discussed in this review have also been the subject of studies of mechanical anisotropy and deformation. It is therefore of some interest to indicate the key guidelines which are emerging from these related studies. 

The multidimensional chord distribution function (CDF) for oriented materials (in particular useful for the study of materials with uniaxial orientation, i.e., fibers) (Sect. 8.5.5)... 

As are the other multipole-expansion coefficients, the uniaxial orientation parameter is computed from Eq. (9.6). For materials with fiber symmetry the relation simplifies4 and... 

Of highest practical relevance is the case in which the scattering pattern, the structural entities, and even the orientation distribution g(uniaxial symmetry (F3-materials). If the structure is ruled by polydispersity and the material is uniaxially oriented, F3 is most frequently fulfilled. In this case the mathematical relations are considerably simplified. Suitably the orientation distribution is normal-ized... 

Straining of isotropic materials is a common method of testing or processing. During such treatment uniaxial orientation is frequently growing (Fig. 10.1). 

A few examples of the moduli of systems with simple symmetry will be discussed. Figure 1A illustrates one type of anisotropic system, known as uniaxial orthotropic. The lines in the figure could represent oriented segments of polymer chains, or they could be fibers in a composite material. This uniaxially oriented system has five independent elastic moduli if the lines (or fibers) ara randomly spaced when viewed from the end. Uniaxial systems have six moduli if the ends of the fibers arc packed in a pattern such as cubic or hexagonal packing. The five engineering moduli are il-... 

Figure 1 (A) Uniaxially oriented anisotropic material. (B) The elastic moduli of uniaxiaUy oriented materials.

Between the uniaxially oriented, non-crystalline specimens and the oriented polycrystalline materials, there is a whole range of ordering which yields different types of diffraction patterns in terms of detailed structures (3). 

Orientation of styrene-based copolymers is usually carried out at temperatures just above T. BiaxiaUy oriented films and sheet are of particular interest. Such orientation increases tensile properties, flexibility, toughness, and shrinkability. PS produces particularly clear and sparkling film after being oriented biaxiaHy for envelope windows, decoration tapes, etc. Oriented films and sheet of styrene-based polymers are made by the bubble process and by the flat-sheet or tentering process. Eibers and films can be produced by uniaxial orientation (237) (see Eilmand SHEETING materials). 

Does the weak interchain coupling imply poor mechanical properties The answer is No for films with = 15, Young s modulus reaches 50 GPa and the tensile strength approaches 1 GPa, mechanical properties which are characteristic of high performance materials. More importantly, the data in Fig. VI-2 demonstrates a direct correlation between the electrical conductivity and the mechanical properties. The linear relationship implies that the increase in both the conductivity and the modulus (or tensile strength) with draw ratio result from increased uniaxial orientation, improved lateral packing and enhanced interchain interaction. 

The effects of uniaxial and biaxial orientation can be quite different. Although many commercial processing techniques impose a biaxial strain on the polymer melt, we will deal here primarily with uniaxially deformed materials. 

Presently, the amount of data on transport in uniaxially oriented amorphous polymers is small in comparison with that of semicrystalline materials. The transport properties of oriented natural rubber (22), polystyrene (i3.,ii), polycarbonate (22.), and polyvinyl chloride (22,22) among others have been reported. One of the more complete descriptions of the effects of uniaxial orientation on gas transport properties of an amorphous polymer is that by Wang and Porter (34) for polystyrene. 

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