Oriented biaxial

In addition to orientation in one direction (mono-axial orientation), biaxial orientation is possible. This is achieved when sheet is stretched in two directions resulting in layering of the molecules. This can increase the impact strength, tensile strength and solvent cracking resistance of polymers and with crystalline plastics the polymer clarity may also be improved. 

Experimental orientational data have been obtained from proton NMR spectra of 1,4-difluorobenzene, 1,4-dichlorobenzene, 1,4-diboromobenzene and naphthalene dissolved in several nematic solvents at different tempera-tures. The results indicate a relationship between the sign and magnitude of dielectric anisotropies of the nematic solvents and the temperature dependence of the orientational biaxiality ratio of the solutes dissolved in them. ... 

Orientation of styrene-based copolymers is usually carried out at temperatures just above T. Biaxially 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 biaxially 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. Fibers and films can be produced by uniaxial orientation (237) (see Film AND SHEETING materials). 

General Description Polypropylene is produced commercially in different forms, depending upon the desired properties. Polypropylene films can be stretched, or oriented, to modify the properties. Biaxially oriented polypropylene (BOPP), and oriented polypropylene (OPP) films are polypropylene films that have been oriented biaxially and uniaxially, re-spectively.f ]... 

Biaxial Orientation. Biaxial orientation substantially improves the physical properties of the film and increases its commercial value. Biaxially oriented films are produced by stretching polymers in directions perpendicular to each other in the melt or rubbery state. The improvement over uniaxially oriented films is due to the redistribution of c-axis chain orientation (36). This results in a film with enhanced physical properties in both directions. The direction perpendicular to the MD is defined as the transverse direction (TD). 

Property Cast film Monoaxiall y oriented Biaxially oriented... 

Uniaxially oriented (OPP-U) with maximum tensile strength of 103 MPa in the direction of orientation Biaxially oriented (OPP-X), such that both machine direction and transverse direction tensile strength exceed 103 MPa ... 

The film can be further oriented uniaxiaUy via a secondary heated roll stacks, or oriented biaxially via a combination of machine direction and transverse direction stretching, which can be accomplished simultaneously or as a two-stage process. Greater detail of cast film extrusion and film orientation process, effects, and mechanics can be found in the referenced texts [18,19]. 

Biaxial Orientation. Biaxial orientation in polymers can be represented in several ways, eg, by Euler s angles (60,68,75,76). This involves the angle (p with respect to the first symmetry axis and a second latitude. A different set of angles was proposed by Wilchinsky (77) in 1963 and later expanded (67,78) (Fig. 2). These (80-85) involve the above mentioned angle , denoted here by [Pg.891]

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