Oriented high density polyethylene

The tensile creep behaviour of oriented high-density polyethylene has been studied by McCrum and coworkers " and by Ward and co-workers. " No creep curves as such are given, but the variation of isochronous modulus with temperature for specimens cut at various angles... 

Slip bands and kink bands were first studied in compression of oriented nylon 6,6 and 6,10 by Zaukelies, and subsequently in tensile specimens of oriented high density polyethylene (HOPE) by Kurakawa and Ban and Keller and Rider Zaukelies interpreted the angle between kink bands in oriented nylon and the compression axis in terms of Orowan s theory of crystal kinking, postulating dislocation mechanisms for the process. Keller and Rider ° and Kurakawa and Ban were impressed by the appearance of deformation bands in high density polyethylene in directions close to the IDD. In this polymer system the... 

Figure 3-7. Raman spectra in polarized light of stretch-oriented high density polyethylene. Experiments were taken in different scattering geometries. Porto s notation is used in the definition of the scattering geometries. Space group symmetry species are indicated (from f63]i.

For polymers, anisotropic friction 10) was observed on lamellar crystals II -13 as well as on extended-chain crystals obtained by friction transfer deposition 14). The anisotropic friction for lamellar crystals was explained by the occurrence of chain-folding oriented preferentially in planes parallel to the corresponding crystal face. For extended-chain crystals friction anisotropy observed parallel and perpendicular to the chain direction was interpreted by the interlocking asperity model. In this paper we give an overview regarding our nanotribological observations on oriented high density polyethylene (HDPE), poly(tetrafluoroethylene) (PTFE) and on crystals of polyethylene (PE) and transcrystallized poly(ethylene oxide) (PEO). 

Lv R, Xu W, Na B, Zhang Q and Fu Q (2008) Large tensile deformation behavior of oriented high-density polyethylene A correlation between cavitation and lamellar fragmentation, J Polym Sci Polym Phys 46 1202—1206. 

Young R J and Bowden P B (1974) Twinning and martensitic transformations in oriented high-density polyethylene, Phil Ma 29 1061-1073. 

Yan S, Katzenberg F, Petermann J. Epitaxial and graphoepitax-ial growth of isotactic polypropylene (iPP) from the melt on highly oriented high density polyethylene (HDPE) substrates. J Polym Sci B 1999 3 1893-1898. 

Fig. 19a, b. Curves of isometric heating a reference sample (curve 1) and sample obtained if molecular orientation exists and containing a spatial framework (curve 2) (schematic representation) b data for high density polyethylene (—A----------ordinary fiber, —O-------fiber obtained by... 

Fig. 20. Stress(er)-strain (ai) dependence for high density polyethylene samples. 1 reference sample, 2 sample obtained if molecular orientation exists, 3 super high tenacity fiber-fibril. Asterisks denote the points of fiber failure...

Figure 4 shows that the orientation of the two chains follow similar paths. The similarity suggests that the local environment is very much the same for both blend constituents. In contrast, a phase-separated binary mixture of polymer segments will exhibit a different orientation for each component. For example, high-density polyethylene and isotactic polypropylene form multiphase systems when blended together (16). When the incompatible blends are deformed, the component which constitutes the continuous phase always orients to a higher degree than... 

Thus, compared to other polymers, it is easier to obtain an extended and oriented chain structure in polyethylene. High density polyethylene (HDPE) is preferred to other types of polyethylene because HDPE has fewer branch points along its backbone and a high degree of crystallinity. These characteristics of linearity and crystallinity are important to obtain a high degree of orientational order and an extended chain structure in the final fiber. 

Fig. 3 Epitaxial growth of high-density polyethylene on oriented polypropylene. Polyethylene lamellae aligns at a 40° angle with the direction of orientation of the polypropylene. The orientation direction of polypropylene in the micrograph is along the horizontal. (From Ref...

Figure 3.66 shows the steady-shear viscosity for a polymer system at three molar masses. Note the plateau in viscosity at low shear rates (or the zero-shear viscosity). Also note how the zero-shear viscosity scales with to the power 3.4. (This is predicted by Rouse theory (Rouse, 1953).) Figure 3.67 shows the viscosity and first normal-stress difference for a high-density polyethylene at 200 C. Note the decrease in steady-shear viscosity with increasing shear rate. This is termed shear-thinning behaviour and is typical of polymer-melt flow, in which it is believed to be due to the polymer chain orientation and non-affine motion of polymer chains. Note also that the normal-stress difference increases with shear rate. This is also common for polymer melts, and is related to an increase in elasticity as the polymer chain motion becomes more restricted normal to flow at higher shearing rates. 

---