Tsuneo Seto

Phase Transformation and Deformation Processes in Oriented Polyethylene

Plastic deformation processes in oriented polyethylene are investigated by the X-ray method, and changes in texture produced by transverse compression are interpreted in terms of twinning, slip and phase transformation. The crystal structure of the new form produced by the phase transformation is determined, and the unit cell is a monoclinic one with a=8.09, b=2.53, c=4.79 A and β=107.9°. The phase transformation is considered to be of diffusion-less type and a transition mechanism similar to that of twinning is proposed.

X-ray structure analysis of trans-1,4-polybutadiene

Abstract The crystal structure of trans-1,4-polybutadiene has been reported by Natta et al. to be pseudo-hexagonal below its solid-phase transition temperature. In the present X-ray structure analysis, it is revealed that the crystal belongs to the monoclinic system with the space group P21/a. The unit cell, with the lattice constants a = 8.63 A, b = 9.11 A, c = 4.83 A, and β = 114°, includes four molecular segments.

Observation of Kink Bands in Oriented Polyethylene

Kinking of fibrils in oriented polyethylene under stress was investigated and three kinds of kink band were found. They were studied with an optical and an electron microscope and by means of X-ray diffraction. From the relationship between the directions of the c-axis, the applied forces and the kink bands, two types of kinking are proposed. One is by crystalline slip along molecular chains accompanied by rotation of the c-axis and the other is by a mechanism similar to twinning induced by shear stress along the king boundary. The kink band formed by compression of an oriented plate along its fiber axis was always oriented in such a way that it appeared to be normal to the fiber axis in the flat surface of the plate and oblique to it in the lateral face. Thus it is suggested that grain boundaries play an important part in the formation of the kink band.

Melting and Solid-Solid Transition of Polyethylene under Pressure

The thermal behaviours of unfractionated polyethylene (PE) was observed up to 31.4 kb by differential thermal analysis, and its pressure-temperature phase diagram was obtained. The thermograms showed three signals, denoted I, II and III. Signal I, the melting of folded chain crystal, was observed up to 8 kb. Below 4 kb, signal II corresponded to the melting of orthorhombic solid; between 4~8 kb, it corresponded to the superposition of the melting of orthorhombic solid and orthorhombic-hexagonal transition; and above 8 kb, it corresponded to the orthorhombic-hexagonal transition alone. Above 4 kb, signal III had a newly-observed flat shape for a specimen crystallized at elevated pressure, but a peak shape for a specimen crystallized at 1 b. The flat signal corresponded to the continuous melting of hexagonal solid. The effect of the molecular weight distribution which makes PE behave as a multi-component system at high pressure is discussed.

Morphology and Growth Behaviour of Myelin Figures of Lecithin

Abstract Growth behaviour and morphological features of myelin figures in egg-yolk lecithin/hydrophilic liquid systems were investigated by microscopic observation at room temperature. The morphological features were conveniently classified into three steps according to the time of growth. In the first step, myelin figures with a simple rod-like form rapidly grew all together perpendicularly to the circumference of a lecithin block into the medium. In the second step, more complicated forms, such as helical and coiling ones, occurred. In the third step, the parts where a contact between surfaces of neighbouring rods had occurred wcre associated, fused and transformed into a mosaic structure. The representative growth mechanism of each of these three steps was dependent mainly on a diffusion of aggregates of lecithin molecules towards myelin figures near their roots, on a lateral diffusion in the bilayer along the long axis of a myelin figure and on a lateral diffusion in the bilayer around the long axis, ...

Structural Changes and Melting Behavior of γ-Irradiated Polyethylene

The structural changes and melting behavior of high density polyethylene irradiated at room temperature were studied by X-ray diffraction and differential scanning calorimetry up to about 4000 Mrad. The melting point and the heat of fusion were depressed by irradiation. A monotonic lattice expansion and an increase in overall specific volume with increasing dose, which lead to a decrease in the specific volume of the amorphous region, were also observed. These changes are thought to be caused by the formation of crosslinks near the surfaces of crystallites and in the amorphous region. The melting point depression can be explained by the effects of lattice distortion and crosslinks outside the crystallites introduced by irradiation. Above 1000 Mrad, a phase transformation into the hexagonal form was observed below the melting point.

X-ray study on egg-yolk lecithin: Unit cell data and electron density profile

The unit cell dimensions and space group of egg-yolk lecithin (l-α-phosphatidylcholine) in the crystalline state were obtained from a set of X-ray fibre diagrams recorded from specimens oriented in two different axes; a = 8.84 A ± 0.05 A, b = 10.07 A ± 0.05 A, c = 54.69 A ± 0.05 A, with space group P21212, and four molecules per unit cell. From the 00l reflexions up to the 25th order, an electron density profile is obtained which is consistent with a probable structure of the molecule.

Lyotropic phase transitions in single crystals of l- and dl-dipalmitoylglycerophosphocholines

Abstract Lyotropic phase transition behaviour of solution-grown mono-domain thin layered crystals of L- and DL-dipalmitoylglycerophosphocholines (dipalmitoyl-GPC) was investigated in a low hydration region at room temperature. X-Ray diffraction measurements and observations by a polarising microscope were performed on the same crystal. In the layer plane of the as-grown thin layered crystal of l - or dl -dipalmitoyl-GPC, which was considered to be dihydrated (phase II), an optical anisotropy was observed. Through a slight absorption of water, the dihydrated crystal showed a monotropic phase transition to a lyotropic mesophase (phase III), in which the optical axis was rotated by about 90° in the plane of the layer. Associated with this phase transition, anisotropic changes both in the unit cell and the crystal dimension occurred. Further absorption of water induced a second lyotropic phase transition for each of the two substances, where the optical anisotropy in the layer plane vanished (phase IV). Combined X-ray measurements suggested that the optical anisotropies observed in phase II and III were caused not only by the inclination of the long aliphatic chains but also by the arrangement of the polar groups of the molecules, and that the binding of water to dipalmitoyl-GPC slightly differed in the l - and dl -molecules in the thin layered crystals and also in as-received powder (phase 1) from as-grown crystals.

Electron diffraction study on single crystals of l-type and dl-type lecithins

An electron diffraction study was carried out on thin single micro-crystals of l-type and dl-type dipalmitoyl lecithins grown in xylene suspensions and fine net patterns were obtained and the mechanism of the thermotropic phase transitions of them was clarified. From the apparent structure of diffraction patterns in low temperature, it is confirmed that the two dimensional lattices have p mm symmetry in l-type and in dl-type lecithins. Lattice parameters from the [001] projection are d100 = 9.9 A and d010 = 8.8 A in l-type, and d100 = 17.2 A and d010 = 8.9 A in dl-type. With anisotropic variation of dimensions along a and b axes, i.e. contraction for a and expansion for b, induced by temperature rise by electron irradiation during the observation, these diffraction patterns of the lattices of l-type and dl-type were transformed into those characterized by the six diffraction spots having nearly the same spacings. Four of them are observed on slightly outer and two are slightly inner positions as compared with their mean spacings of about (4.1 A)−1 in l-type and about (4.2 A)−1 in dl-type. The changes in the patterns observed indicate that at low temperatures the hydrocarbon chains are nearly perpendicular to the layer in dl-type lipid, and tilted with a more complicated packing in l-type ones. The dimension along a in dl-type is twice as large as that in l-type.

Structure Change of Oriented Polyethylene by Redrawing

This work was made in order to examine the propriety of the structure model of oriented polyethylene proposed by the authors. Drawn and annealed plates of polyethylene showing four point patterns in small angle x-ray diffraction were redrawn along the fiber axis and studied by x-rays. By redrawing the c-axis was made parallel to the redrawing axis, while inclination of lamellae was not changed markedly. The long spacing calculated from the height of the four spots according to the Bragg equation was increased with draw ratio which exceeded slightly the macroscopic draw ratio of the specimen. At high redrawing horizontal streaks appeared in small angle patterns below the spots corresponding to the interlamellar distance. These results are interpreted by the structure model by considering that macroscopic elongation is produced by glide on grain boundaries and inhomogeneous elongation of amorphous layers accompanied with generation of microcracks.