Oriented Polyethylene Terephthalate Sheet with Orthorhombic Symmetry

6 Oriented Polyethylene Terephthalate Sheet with Orthorhombic Symmetry 

All nine independent elastic constants have been determined for one-way drawn oriented polyethylene terephthalate sheet. The sheet was prepared by drawing isotropic sheet at constant width. It has been shown that there is then both a high degree of chain orientation in the draw direction and that the (100) crystal planes (which mainly reflect preferential orientation of the terephthalate residues in the chain) are preferentially oriented in the plane of the sheet. This type of orientation has been termed uniplanar axial. From the viewpoint of elastic anisotropy, the sheet possesses three orthogonal planes of symmetry and can be described as possessing orthorhombic symmetry. 

The anisotropy of the shear compliances is also very remarkable. Both 44 and see are large compared with S55 and reflect easy shear in the 23 and 12 planes respectively, presumably where the planar terephthalate chains are sliding over each other constrained only by weak dispersion forces. The compliance 55, which geometrically involves distortion of the plane of the polyester molecule, is of a similar order of magnitude to 5n and S22- 

It is interesting to apply the aggregate model to these data, calculating bounds for the elastic constants of an equivalent fibre by averaging the sheet constants in the plane normal to the sheet draw direction. This requires an extension of the mathematical treatment of Section 8.6.2 to deal with the case of a transversely isotropic aggregate of orthorhombic units. The basic equations have been given in detail elsewhere [99] so only the key results will be summarised here. If the orthorhombic unit constants are n, 13. 66 (Section 

the Reuss average fibre constants 5(3, plane are given by 

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Table 7. Full Set of Compliances for the Oriented Polyethylene Terephthalate Sheet with Orthorhombic Symmetry...

Table 8.9 Full set of compliances for the oriented polyethylene terephthalate sheet with orthorhombic symmetry [18].

Similar isochronous studies have been carried out on polyethylene terephthalate sheets with orthorhombic symmetry by Ladizesky and Ward, on cold-drawn Nylon 6 and 66 by Owen and Ward and on oriented polypropylene by Owen and Ward. ... 

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