Polyethylene terephthalate, drawing

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... 

Elenga, R., Seguela, R. and Rietsch, F., Thermal and mechanical behaviour of crystalline polyethylene terephthalate) effects of high temperature annealing and tensile drawing, Polymer, 32, 11, 1975-1981 (1991). 

Isothermal draw resonance is found to be independent of the flow rate. It occurs at a critical value of draw ratio (i.e., the ratio of the strand speed at the take-up rolls to that at the spinneret exit). For fluids that are almost Newtonian, such as polyethylene terephthalate (PET) and polysiloxane, the critical draw ratio is about 20. For polymer melts such as HDPE, polyethylene low density (LDPE), polystyrene (PS), and PP, which are all both shear thinning and viscoelastic, the critical draw ratio value can be as low as 3 (27). The maximum-to-minimum diameter ratio decreases with decreasing draw ratio and decreasing draw-down length. 

Fig. 19.11A,B presents, as an example, data of drawing series of nylon 6 and polyester filaments (Van der Meer, 1970). The additional data for the polyester (polyethylene terephthalate) are given in Table 19.8 by stretching the Young modulus increases by a factor 8 and the tensile strength by a factor 5.5 (Fig. 19.13).

Figure 4.3 Variation of modulus as a function of strain or draw ratio for polyethylene terephthalate (PET) and polypropylene (PP) in the axial and transverse directions (Hadley et al, 1969). Note the rather small effect in the transverse direction.

In the solid phase, support for a similar contention has come from the drawing of polyethylene terephthalate, combined with stress optical measurements, and also for the behaviour of craze fibrils in a range of glas polymers. 

Problem 30.16 Polyethylene terephthalate is also prepared by the transesterification of dimethyl terephthalate with ethylene glycol. Draw the mechanism for this nucleophilic acyl substitution. 

Poly(a, -dimethyl-j3-thiopropiolactone) has been melt-spun at 185°C to give a fiber which, after drawing, had a tenacity of 1.4 g/den. (polyethylene terephthalate, 4-7 g/den.) and an initial modulus of 12 g/den. (30-130 g/den.) (16). Tensile recovery at 10% elongation was 80%. No information is available about poly (thiol esters) with higher melting points, such as poly(hexamethylene dithiolterephthalate). 

Draw the structure of the monomer(s) employed to form each of the following polymers shown in Table 12.5 (a) polyvinyl chloride, (b) nylon 6,6, (c) polyethylene terephthalate. 

The idealised case of cold drawing which has been discussed, is typical of the behaviour of several major thermoplastics such as polyethylene, polypropylene, nylon and polyethylene terephthalate, which readily cold draw at ambient temperatures. Other thermoplastics, which... 

Fig. 4. CorO for the unique axes of fluorescent VPBO molecules dispersed in uniaxially oriented tapes of polyethylene terephthalate plotted against the birefringence — of the tapes. O, samples drawn at S(PC to draw ratios between 1 and 6 . samples drawn to draw ratio 2 7 at temperatures between 65° and 90°C. (Reproduced by permission from Ref. 18. Copyright I PC Business Press Ltd.)...

Fig. 7. Co O and co O plotted against draw ratio, /.. for chain a.xes in uniaxially oriented tapes of polyethylene terephthalate.. cos O and O. cos determined from Raman intensity measurements on the 1616 (vn line. Curves (a) pseudo-affine cyg regate deformation model, atrves (b) affine rubber elasticity model.

A qualitative fit to experimental data was found for polyethylene, and by later workers for nylon,polyethylene terephthalate, and polypropylene, but the predicted birefringence at small draw ratios tended to be low, with the approach to full orientation being more gradual than found experimentally (Fig. 1). 

Fie/. 3. Polyethylene terephthalate. Variation of increase in birefringence on drawing with draw ratio for filaments cold drawn at different temperatures. ( From Ref. 34.)... 

MEASURED VALUES OF EXTENSIONAL MODULI OF POLYETHYLENE TEREPHTHALATE FILAMENTS (IN ON ra -) FOR A RANGE OF NATURAL DRAW RATIOS (NDR) AND INITIAL BIREFRINGENCE (A/i) COMPARED WITH REUSS AND VOIGT PREDICTIONS FOR AN AGGREGATE MODEL. 

The variation of compliances with draw ratio for cold drawn polypropylene filaments examined at 20°C appeared very similar to that of high density polyethylene, with an increase in all compliances but Sii, which was insensitive to draw ratio. Ward aggregate theory was not applicable except for low draw ratios, implying that other processes intervened in addition to an orientation of pre-existing units. It was probable that even above the glass transition temperature increasing orientation led to a reduction in molecular mobility, as was known to occur in polyethylene terephthalate. ... 

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... 

Fig. 2. The variation of tensile yield stress with 0, the angle between the initial draw direction and the tensile axis. The material is oriented polyethylene terephthalate sheet, draw ratio 5 1. Equation (8) was used to construct the full-line and is a good fit to the available data (after Brown et...

Applied Spectroscopy 51, No.3, March 1997, p.346-9 AMPLITUDE SPECTRUM APPROACH IN DYNAMIC FT-IR SPECTROSCOPY OF UNIAXIALLY ORIENTED POLYETHYLENE TEREPHTHALATE FILMS. I. DRAW RATIO DEPENDENCE... 

The three-phase structures 12, 13, and 14 are of particular interest because of the even more severe violation of the phase rule. At constant pressure, in equilibrium, only one-phase areas should be stable. Drawn fibers of poly(ethylene terephthalate) (PET) are discussed as three-phase sttucture with Figs. 5.68-72 and 5.113-115. As in polyethylene, the drawing to fibers or films orients the amorphous nanophase and achieves an arrested mesophase order, proven with Fig. 5.72. Since the drawing of PET fibers is much less efficient in extending the molecules than gel-spinning, there remains a sizeable portion of the amorphous phase, as shown in Fig. 5.71. The mobile mesophase of PET has not been found as a stable phase, as in polyethylene. Copolymers of PET with stiffer repeating units, such as oxybenzoate, however, have stable mesophases (see Chap. 7). 

The postyield ductile fracture of polymers was extensively investigated (170-183), resulting in a conclusion that the crack is initiated from cavities growing from defects in the drawn material. These cavities have a rhombic shape with the long and short diagonals perpendicular and parallel to the draw direction. These cavities were observed in PVC, PE, polyethylene terephthalate (PET) at room temperature and in PC, PMMA, polyether sulfone (PES), and PS at elevated temperatures. At slow strain rates, the growth of these cavities in a plastically deformed material loaded in tension is stable until the critical size is reached resulting in an unstable catastrophic failure. 

For polyethylene terephthalate fibers, the point D in Fig. 3 corresponds to a draw ratio of about 8. 

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