Polyethylene, considered drawing

Acetylene (ethyne), C2H2, can be polymerized, (a) Draw the Lewis structure for acetylene and draw a Lewis structure for the polymer that results when acetylene is polymerized. The polymer has formula (CH), where n is large, (b) Consider the polymers polyacetylene and polyethylene. The latter has the formula (CH2)W and is an insulating material (plastic wrap is made of polyethylene), whereas polyacetylene is a darkly colored material that can conduct electricity when properly treated. On the basis of your answer to part (a), suggest an explanation for the difference in the two polymers. 

In drawing this plot, the mean of the 3 lowest estimates of the number of branches per molecule given by Long (89) has been preferred to his highest estimate, and the data of Mendelson and co-workers (56) have been omitted, as their estimate of the number of branches depends on the assumption g = g, which is considered to be doubtful for polyethylenes (see Section 10). The line drawn corresponds to the equation ... 

A propylene molecule can be considered to be an ethylene molecule with one hydrogen replaced by a methyl radical. Using R for CH3, draw a representation of pxrlypiropylene like that of polyethylene shown in Section 20.4. 

It was considered initially that because there is no net tensile stress in a hydrostatic extrusion process it might be possible to impose very large plastic deformations without incurring fracture. It was indeed shown that Rj, of 30 can be imposed in polyethylene comparable to the draw ratios of 30 adiieved in a tensile drawing process, and that both processes are limited by the strain hardening behaviour of the material, which is determined solely by the total plastic strain imposed. This led to an important... 

From a mechanical point of view, high density polyethylene (HDPE)/isotactic polypropylene (iPP) blend have generally been considered as very unsatisfactory materials In particular, they show very poor ultimate mechanical properties at room temperature in comparison with those of the blend constituents. This fact precludes their use for most commercial purposes. In previous papers we found that it is possible to improve the mechanical tensile performance of these blends by appropriately varying the testing conditions such as the temperature and the drawing rate. 

Now consider the case of a uniaxially oriented polyethylene film or fibre, with full orientation, where the chain axes are. parallel to the draw direction or fibre axis and consider only the proton pair interaction arising from the CH2 groups. The CH2 groups are now such that the proton pairs lie in a plane perpendicular to the fibre axis. Figure 3 illustrates the situation. The intemuclear vector r makes an angle P with Ho, and an angle <(> with a chosen direction in the plane normal to the fibre axis. The angle between the fibre axis and Ho is y. 

An explanation was proposed for the PET results which has since been shown to apply equally to oriented polypropylene, high density polyethylene and nylon. The polymer sheet is considered as an oriented continuum characterised by three principal extension ratios Xi, X2, A3). If the isotropic sheet is considered as the state of zero strain, then the oriented polymer has extension ratios A3 in the draw or orientation direction (IDD) and it is convenient to take Ai in the direction of the sheet normal. Thus A3 and A2 define the projection of the strain ellipsoid in the plane of the sheet. When a deformation band forms in the oriented polymer the deformation can be described in terms of two shear... 

Yoda and Kuriyama have considered the structural changes associated with the hot rolling of polyethylene. As the draw ratio increases, the angle of the chain axis to the roll direction decreases until the chain coincides with the draw... 

Kolbeck and Uhlmann have considered the effect of high stress extrusion on the properties of several polymers - polypropylene, poly(vinylidene fluoride) and polyethylene. There was no substantial heating on deformation up to twenty-five times. Polypropylene and poly(vinylidene fluoride) could not be continuously extruded below the melting point and brittle fracture and necking was observed, while the tensile properties depend on draw ratio with yielding. Above 373 K annealing occurs but the product has a lower elongation to break. The properties of oriented nylon-6, > polyfethylene terephthalate)," - polypropylene, and polyethylene " have been widely studied. 

Tubular linear low-density polyethylene (LLDPE) film of thickness equal to 34.1 qm is produced (Kanai and White, 1984) by a blown film operation with draw ratio equal to 4. The annular die has an inner diameter 1.387 cm and outer diameter 1.496 cm. Calculate the pressure of the air to blow a bubble (i.e., the internal overpressure) of the given specifications and the axial tension to draw such a bubble. Consider that LLDPE is Newtonian with viscosity 720 Pa s, the process is isothermal at 180 °C, and LLDPE freezes at an axial distance of 15 cm. The mass fiow rate of the polymer is 0.21 g/s, and its density is 0.919 g/cm-. 

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