Polyethylene, crystalline Morphology

FIG. 48 Variation of the tensile modulus of superdrawn polyethylene crystalline morphologies of different molecular weight... 

Southern and Porter (29) and Kwei et ah (30, 31) have reported the production of transparent polyethylene from normally translucent polyethylene by a variety of deformation processes. The deformation process results in crystalline entities with dimensions less than the wavelength of light in size, thereby not causing light scattering and consequently the resultant transparency. Similar changes in crystalline morphological dimensions may be responsible for the transformation in optical proper-... 

Reprinted by permission of John Wiley Sons, Inc. from (a) Holland, V. F. and Lindenmeyer, P. H., Morphology and crystal growth rate of polyethylene crystalline complexes J. Polymer Sci. 57, 589 (1962) (b) Blundell, D. J., Keller, A. and Kovacs, A. I., A new self-nucleation phenomenon and its application to the growing of polymer crystals from solution , J. Polymer Sci. B 4, 481 (1966). Copyright 1962, 1966 John WUey Sons, Inc. 

Similar to polyethylenes the morphology of these polymers is also described as a lamellar stack of crystalline and non-crystalline layers. This so-called two phase model is applied for the interpretation of X-ray diffraction data as well as for heat of fusion or density measurements. However, it is well known that several mechanical properties, as well as the relaxation strength at the glass transition temperature, cannot be described by such a simplistic two-phase approach, as discussed by Gupta [59]. Prom standard DSC measurements [60], dielectric spectroscopy, shear spectroscopy [61], NMR [62], and other techniques probing molecular dynamics at the glass transition (a-relaxation) temperature, the measured relaxation strength is always smaller than expected... 

Some polymers used as adhesives, for example, polyethylene, and Ethylene-vinyl acetate copolymers, are crystalline and their properties will be altered by altering the degree of crystallinity or the crystalline morphology. Cooling rates, annealing treatments and the use of nucleating agents are process variables, which it may be possible to exploit to determine adhesive joint performance. 

Abo El Maaty MI, Olley RH, Bassett DC (1999) On the internal morphologies of high-modulus polyethylene and polypropylene fibres. J Mater Sci 34 1975-1989 A1 Raheil lAM (1987) Development of crystalline morphology in polyethylene and PEEK. PhD Thesis, University of Reading... 

Holland V, Lindenmeyer P (1962) Morphology and crystal growth rate of polyethylene crystalline complexes. J Polym Sci 57(165) 589-608... 

In this chapter, the crystallization of these two engineering polymers, namely, polyethylene terephthalate (PET) and polyphenylene suffide (PPS), will be discussed with reference to the various aspects of crystallization. The effects of various parameters on the crystallization process and crystalline morphology of these polymers will also be discussed. 

Turning to analogy about mediiuns with crystalline morphology of polymer matrices, let us note, that semicrystalline polymers (e.g., high-molecular polyethylenes) large strains, making 1000 2000%, are realized owing to... 

Sakurai T, Nagakura H, Gondo S, Nojima S. Crystallization of poly(e-caprolactone) blocks confined in crystallized lamellar morphology of poly(c-caprolactone)-Wock-polyethylene copolymers effects of polyethylene crystallinity and confinement size. Polym J 2013 45 436-443. 

White, J.L., Dharod, K.C., Clark, E.S., 1974. Interaction of melt spinning and drawing variables on the crystalline morphology and mechanical properties of high-density and low-density polyethylene fiber. Journal of Applied Polymer Science 18, 2539—2568. 

Polyethylene/PolypropyleneBlends Blends of polyolefins represent one of the most studied polymer systems in the field of immiscible blends. Studies on blends of iPP with crystallizable and/or amorphous polyolefins, such as polyethylenes (PEs) of various density (HD PE, ED PE, LLDPE), atactic PP, propylene-etylene elastomers, and polyisobutylene, have shown that their properties depend strongly on the crystalline morphology, crystallization conditions, and composition... 

Figure 15.31 Model for the description of crystalline morphologies in a polyethylene film with an equibiaxial texture [94].

---