Polyethylene cold-drawn

The polyethylene samples examined are shown in Table III slowly cooled or quenched from melt, original monofilament, annealed, over drawn, cold drawn, single crystal, cast film, extended chain crystal, etc. The sample-probe distance can be chosen from TO to 260 mm. The setting angle is defined as the angle between the molecular plane and the be plane according to Bunn (1 1) as shown in Figure 12. 

Information on how orientation during melt crystallization affects the transport properties of polymers is sparse however, increases in the permeability have been attributed to the "shish kebab" morphology (ill). Most of the work involving barrier properties of oriented semicrystalline polymers has dealt with materials drawn at temperatures well below the melting point. The transport properties of cold-drawn polyethylene (34f 42-46), polypropylene (42,42), poly(ethylene terephthalate) (12,42-4 9), and nylon 66 (22) among others have been reported. 

As an example, fig. 11.8 shows a comparison of experimental and predicted moduli for cold-drawn low-density polyethylene. The theoretical curves are calculated using the Reuss averaging scheme and the values of (/ 2(cos0)) and P4(cos0) are derived from NMR data for the crystalline regions only. The fit is now quite good. 

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

Investigation of cold drawn specimens of low density polyethylene by low angle X-ray scattering indicates that there is little clearly defined lamellar structure in this material, in contrast with the strongly lamellar... 

Fig. 3. Low density polyethylene. Variation o f modulus with draw ratio/or samples cut from cold drawn dteet examined at —125 C. Compare with Fig. I. (Adapted from...

Fig. 4. Low density polyethylene. Angular rariotion of modulus at several temperatures for samples cut from cold drawn dteet. (Adapted from Gupta and iVard. )...

Fig. 8. Low density polyethylene. Effect of draw ratio on temperature variation of tan 0 for samples from cold drawn. sheet. (Adapted from Stachurski and Ward. i...

Gupta et al. investigated Rigidex 9 in parallel with the studies of low density polyethylene already reviewed. X-ray observations were interpreted as showing a structure after annealing of crystalline lamellae at about 45° to the stretch direction. The lamellae are poorly defined in cold-drawn specimens, which showed also some orientation of noncrystalline material. 

The relaxation associated with interlamellar shear has been further investigated by Stachurski and Ward, who confirmed and extended Takayanagi s earlier measurements. The anisotropy of the a peak in annealed samples, with tan 5q > tan 45 > tan 9o, was similar to that of the P relaxation in low density polyethylene, being attributed to an inter-lamellar shear mechanism. Evidence of this process was present also in cold drawn samples, but was less clearly defined. 

Neither in cold drawn nor annealed high density samples did Stachurski and Ward see any evidence for the c/c shear mechanism observed in low density material. It was noticed that for a range of low density polyethylenes the activation energy of this process increased with density. Provided that the molecular processes were similar in Rigidex an activation energy of about 400 kJ mol was predicted, which implied that the relaxation would not be observed below the melting point at the lowest accessible frequency of 10" Hz. 

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. ... 

Unordered regions in cold drawn polyethylene are partially oriented, and are probably traversed by strained tie molecules linking crystallites together. 

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. ... 

Hinton and Rider extended the notion of c-slip to a study of homogeneous plastic deformation in cold-drawn high density polyethylene. They noted that the direction of maximum refractive index (which they labelled as the current c-axis) swung round towards the tensile axis during the tensile deformation of specimens cut at a range of angles 0 to the IDD. 

X-ray diffraction study of cold-drawn high density polyethylene samples, J. Mater. Sci., 11, 2036-2044. 

Mobility of the reactants and reaction products of the oxidative kinetic chain reaction, of stabilisers and of the polymer molecules themselves affects the kinetics of the radical reactions. Morphology of a polymer material and its physical state, e g. stress, strain and orientation, has an effect on the mobility and therefore on the process of oxidative degradation. Fibres or slit films of polyethylene or pol ropylene are cold-drawn in the production. The orientation of the cold-drawn polymer material produced here has a particularly strong repercussion on oxidation stability. 

Figure 7.7 The variation of Eq, 45 and 90 with draw ratio in cold-drawn sheets of low-density polyethylene. Modulus measurements taken at room temperature (Reproduced with permission from Raumann and Saunders, Proc. Phys. Soc., 11, 1028 (1961))...

Figure 7.8 The variation of E, and E with draw ratio in cold-drawn sheets of low-density polyethylene. Modulus measurements taken at —125 °C.

Arai et al. have studied the effect of rolling and drawing on structure of polyethylene. A gradual decrease with temperature of the second moment of cold-drawn samples, absent in undeformed and hot-drawn samples, was attributed to intermediate regions less mobile than amorphous polymer. 

Rg. 16-19. Pscudoequilibrium Young s modulus parallel ( o) and perpendicular ( 90) to draw direction for cold-drawn sheets of low-density polyethylene, at — 125 C. (Gupta and Ward. ) Reproduced by permission, from Reference 105, p. 382, by courtesy of Marcel Dekker, Inc. 

Figure 7.6 Dichroic ratio D vs. draw ratio for cold drawn linear polyethylene [I]...

Figure 8.27 Comparison of experimental (—) variation in Eo and Ego for cold-drawn low-density polyethylene with those predicted by the aggregate model using orientation functions...

The aggregate model predicts only that the elastic constants should lie between the Reuss and Voigt average values. In polyethylene terephthalate, it is clear that the experimental compliances lie approximately midway between the two bounds. For cold-drawn fibres, it has been shown that this median condition applies almost exactly [87]. 

Figure 10.10 Temperature dependence of tan S in a cold-drawn and annealed HDPE sheet in different directions at 50 Hz. (Reproduced from Stachurski, Z.H. and Ward, I.M. (1969) Mechanical relaxations in polyethylene. J. Macromol. Sci. Phys. B, 3, 445. Copyright (1969) Taylor and Francis.)...

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