Polyethylene terephthalate anisotropy

Kashiwagi et al.10) determined the second moment anisotropy for the one-way drawn polyethylene terephthalate sheets discussed above. The three lattice sums S00, S2q and S4o were calculated from the crystal structure determination of Daubeny et al., the proton positions being calculated on the basis of known bond angles and lengths. The isotropic lattice sum S00 was adjusted to a value consistent with the measured isotropic second moment of 10.3G2. The values for P200, P220 etc. were then used to predict the optical anisotropy. The predicted refractive indices for the sheets of draw ratio 2 1 and 2.5 1 are shown in Fig. 10, together with the experimental... 

The sensitivity of the NMR anisotropy to the conformation of the glycol residue, which was a complication in polyethylene terephthalate, can be turned to advantage in 4GT, as shown by some recent research 36). The anisotropy of the second moment was determined for three cases, starting with a highly oriented tape ... 

When an initially isotropic polymer is drawn or extruded to a high deformation ratio under suitable conditions, it develops appreciable anisotropy which is apparent in mechanical tests at all stresses up to and beyond the yield stress. A typical example of the anisotropy of yield observed is shown in Fig. 2 in which the tensile yield stress of oriented polyethylene terephthalate (PET) sheets is shown as a fiinction of the an e 6 between the tensile axis (TA) and the initial draw direction (IDD). This large anisotropy is somewhat similar to that observed in cold-rolled metal sheets, for which theories of anisotropic plasticity were suggestedby Hill, Yoshimura and others. A modification of the theory... 

P.R. Pinnock and I.M. Ward, Mechanical and optical anisotropy in polyethylene terephthalate fibres. Brit. J. Appl. Phys. (1964), p. 1559. 

Table 7.6 compares the measured compliances for isotropic samples of five polymers with the Reuss and Voigt average compliances calculated from measurements on highly oriented specimens. For polyethylene terephthalate and low-density polyethylene the measured isotropic compliances fall between the calculated boimds, suggesting that here molecular orientation could well be the principal factor that determines mechanical anisotropy. For nylon 6 6 the... 

Polymers that do not crystallise, such as polymethyl methacrylate, show a good correlation between the (low) degree of mechanical anisotropy and molecular orientation determined from birefringence. There is so much disorder that it seems unlikely that a significant proportion of the chains can achieve the high alignment of a crystalline polymer such as polyethylene. Other polymers such as polyethylene terephthalate, which have a... 

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. 

Interlamellar shear in anisotropic polyethylene sheets. /. Macromol. Sci. B, 6, 215 Davies, G.R. and Ward, I.M. (1972) Anisotropy of mechanical and dielectric-relaxation in oriented poly(ethylene terephthalate). /. Polym. Sci. B, 6, 215. 

---