Unoriented polyethylene

Studies were performed also with unoriented polyethylene terephthalate (Eisner, Koch, Bordas and Zachmann Also with unoriented samples the long period decreased with increasing time. Such a decrease has been observed already with samples quenched to room temperature (Zachmann and Schmidt The present results show that the decrease is not an artificial effect caused by quenching, but... 

Fig. 46. Change of the small angle scattering during stepwise heating and cooling of unoriented polyethylene terephthalate...

Fig. 27. The variation of with for an unoriented polyethylene film. (From Stein. R. S.. Erhardt, P.,van Aartsen, J. J., dough, S. and Rhodes. M. (1966. J. Polymer Sci.,C, No. 13.)...

Hence, the extension of an isotropic unoriented partially crystalline polymer leads to the formation of a highly organized material with a characteristic fibrillar structure. The anisotropy of the sample as a whole is expressed by a higher modulus, tenacity and optical anisotropy. It would seem that the increase in strength in the drawing direction suggests that the oriented samples consist of completely extended chains. However, while the strength of such perfect structure for polyethylene has been evaluated as 13000 MPas), the observed values for an oriented sample are 50 to 30 MPa. 

Fig.36. Variation in electrical conductivity (o) with molecular weight for polyethylene composites filled with 4% by volume carbon black, demonstrating the effects of orientation (I), degradation (II) and flow-induced segregation of carbon black aggregates (III). ( ) injection moulded (O) compression moulded (unoriented) [181]...

The stretch induced transformation of initially unoriented orthorhombic polyethylene (Vestolen A) into the monoclinic modification was studied by Heise, Riekel and Stach for stretching velocities down to 0.26 mm s"T The coexistence of both modifications and the formation of two domains of monoclinic material was established by the Vidicon detector. 

The fibril orientation in Figure 6 indicates that they were formed from material piled up in front of stylus due to plowing. Since this material is anchored to the sides of the wear tracl it becomes stretched and oriented into long fibrils. These fibrils make a large contribution to the lateral force exerted on the stylus. The high strength of oriented polyethylene ensures that failure initiates in the relatively unoriented material where the fibril is anchored to the side of the wear track. One end of the fibril is essentially tom from fhe matrix. Catastrophic fibril failure produces a large, rapid drop in lateral force and allows the stylus to junq> forward. This results in the sharp current spike coincident with the load (bop. 

Thus for unoriented systems, the scattered intensity is independent of O but becomes Q dependent upon stretching as is illustrated with the experimental data for stretched polyethylene shown in Fig. 24. ... 

The mechanical relaxations occurring in unoriented low density polyethylene are indicated schematically in Fig. 7(a). Studies on unoriented... 

The initial published reports on high density polyethylene were dynamic mechanical studies, but before considering them it is necessary to compare the mechanical relaxations in isotropic material with those observed in unoriented low density polyethylene. From the schematic curve of tan S v. temperature f Fig. 7(b)] it can be seen that the p relaxation, which was ascribed to branch point mobility, is not present, and that the high temperature relaxation is frequently resolvable into a and a peaks. 

Difiradion pattern of drawn polyethylene, showing oriented crystals (110 and 200 refledions) and the unoriented amorphous halo. 

FIGURE 24.9. Stress relaxation curves—as explained in the text—for polyisoprene (natural rubber, 1), oriented low density polyethylene (LDPE) with the draw ratio A = 1.8 (curve 2), indium (3), unoriented LDPE (4), cadmium (5), polyisobutylene (6), and lead (7). 

Many pol3nners, including polyethylene terephthalate, also crystallize if they are cooled slowly from the melt. In this case we may say that they are crystalline but unoriented. Although such specimens are unoriented in the macroscopic sense, i.e. they possess isotropic bulk mechanical properties, they are not homogeneous in the microscopic sense and often show a spherulitic structure under a polarizing microscope. 

Figure 6.6 Tensile modulus and loss factor tand for unoriented amorphous polyethylene terephthalate (a) and unoriented crystalline polyethylene terephthalate (b) as a function of temperature at 1.2 Hz (x) modulus ( ) land. (Reproduced with permission from Thompson and Woods, Trans. Faraday Soc., 52, 1383 (1956))...

TABLE 15 Refractive indices of unoriented linear polyethylene films... 

Gel spinning is a two-stage process for the production of high performance linear polyethylene (HPPE) [45, 46]. The first stage is the formation of a substantially unoriented gel with a very low chain entanglement density. 

A flat-plate X-ray diffraction pattern was obtained from an unoriented sample of polyethylene using CuKa radiation. It consisted of three rings of radius 22.2 mm, 36.6 mm and 19.7 mm. The specimen-to-film distance was 50 mm. Calculate the d-spacing of the planes giving rise to these reflections. It is thought that these... 

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