Journal of the Society of Materials Science, Japan
Online ISSN : 1880-7488
Print ISSN : 0514-5163
ISSN-L : 0514-5163
Viscoelastic Behavior of the Mat of Single Crystals of Polyethylene
Teruo ARAMAKIShunsuke MINAMIFumio NAGATOSHIMotowo TAKAYANAGI
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1964 Volume 13 Issue 128 Pages 394-398

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Abstract

In order to clarify the relaxation phenomena of crystalline phase in semicrystalline polymer, temperature dependence of complex dynamic modulus at frequencies of 3.5, 11 and 110c/s was measured for a mat of single crystals of polyethylene over a temperature range from -160°C to 120°C.
The single crystals prepared from 0.03% xylene solution of fractionated Marlex 9 (Mv=520000) were so laminated as to lay their surfaces in parallel to each other by rapid filtration, and pressed at room temperature to form a film of about 100μ thickness. The structure of a single crystal and the layered structure of single crystals within the film, which was used for the viscoelastic measurements, were examined by means of electron microscope and X-ray diffraction technique.
The temperature dependence of dynamic loss molulus E" at three different frequencies within the crystalline dispersion region, which was obtained by applying the stress in perpendicular direction to the molecular chain axis, were replotted as function of frequency at various temperatures. By making the curve at 80°C standard, and shifting the curves at various temperatures horizontally along the frequency axis, a master curve of E" as a function of angular frequency was obtained. The relaxation spectrum at 80°C was calculated from this master curve by using Alfrey's zeroth order approximation; Hl (log τ)=4.6/π-1 E" (log 1/ω). From the measurements on reproducibility of the temperature dependence of E" performed by repeating the cycles of heating and cooling, it is confirmed that the effect of the changes in crystalline structure on the relaxation spectrum for crystalline absorption is negligible below 110°C. The slope of the relaxation spectrum is about -1/5 at a longer time side and about 1/3.5 at a shorter time side, and both of them are broader than those observed for the primary dispersion region of non-crystalline phase.
The temperature dependence of the shift factor obtained for composing the master curve of E" is divided into two regions of different activation energies. This fact suggests that the relaxation mechanism of the crystalline dispersion can be classified into two different modes. Taking it into consideration that the activation energy of the crystalline dispersion below 70°C, 16.2Kcal/mole, is comparable to that of the secondary dispersion due to the local relaxation of the frozen main chains in the non-crystalline region and in the defective region within the crystal, the relaxation mechanism of this dispersion is reasonably ascribed to the occurence of the local torsional or twisting motion of main chains in the crystal lattice around their molecular axis. This dispersion is named here βc dispersion.
The activation energy of the crystalline dispersion above 70°C, 43.7Kacl/mole, is larger than that for βc dispersion. On the other hand, the fact that the lamella thickness of the single crystal of polyethylene thickens considerably above 110°C, suggests that the migrational motion of the molecular chains in the crystal lattice along the c-axis can occur in such a higher temperature region. Taking these facts into consideration, the relaxation mechanism of this dispersion can be ascribed to the large motion of the molecular chains in the crystal lattice, such as the migrational motion along the c-axis, and resembles that of the primary dispersion (αa dispersion) in respect to the occurence of large motion of molecular chains. This dispersion is named here αc dispersion.

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