Orientation Of Crystalline Phase Research Articles

ORIENTATION BEHAVIOR OF POLYETHYLENE CRYSTALLITES IN THE FIXED-WIDTH-STRETCHING OF TUBULAR EXTRUDED POLYETHYLENE FILM

The orientation of Crystalline phase in a tubular extruded polyethylene film during constant width-stretching was studied quantitatively by means of X-ray pole figure technique and biaxial orientation functions.The experimental results shows that, in the lamellar texture, the b-axis lies prependicular to the screw axis and takes a circular arc-distribution, centering around the screw axis, in the initial stage of a deformation process owing to constant width-stretching. It then becomes, on the average, elliptic-distribution, whose major axis is lying in the transverse direction. The b-axis further orients gradually from the elliptic-distribution to a preferred orientation parallel to the transverse direction as the deformation increases. It is recongnized along with this that the c-axis orientation in the stretching direction proceeds through the (100)[001] plastic slipping and a rotation of the (100) slip-plane around the b-axis.

Mechanical anisotropy of regenerated cellulose films in relation to orientations of crystalline and noncrystalline phases

AbstractThe mechanical anisotropy of regenerated cellulose films is investigated, first, on the basis of the theory of infinitesimal elasticity. Fairly good agreement of calculated with observed results is obtained on the basis of orthogonal anisotropy with respect to the machine direction and the transverse and thickness directions of the films. The shear modulus G23 along the film plane and the Poisson ratio v32 are 1.5 times; 102 kg/mm2 and about 0.4, respectively, in the standard dry state. Second, the mechanical anisotropy in three different dry states is analyzed in terms of the degree of biaxial orientation of two kinds of structural units, cellulose II crystallites and noncrystalline chain segments, and their mechanical anisotropy. The calculation for averaging the mechanical anisotropies of these structural units on the basis of the homogeneous strain hypothesis gives results much higher than the experimental data, whereas the calculation on the basis on the homogeneous stress hypothesis gives results rather lower than experiment. As a modification of the two extreme calculations, a different averaging gives considerably better agreement between the calculated and observed results. The mechanical anisotropy in the wet state is further analyzed primarily in terms of the degree of biaxial orientation of noncrystalline chains by a modification of Krigbaum treatment, based on application of the kinetic theory of entropy elasticity for semicrystalline polymers, to anisotropic systems. The calculation gives results, however, much lower than those obtained experimentally, unless the ratio of the end‐to‐end distance of the noncrystalline chain to its fully stretched length is taken as unusually large. This may be due to underestimation of the contribution of the crystalline phase to terms of the same type as appear in the Krigbaum treatment.

Dimensional stability of regenerated cellulose film in relation to orientations of crystalline and noncrystalline phases

AbstractThe dimensional stability of regenerated cellulose film on swelling with water is discussed in relation to the biaxial orientation of the two kinds of structural units, cellulose II crystallites and noncrystalline chain segments, and their anisotropic swelling (anisotropic absorption of water). Considerable dimensional stability in the plane of the film but enormous instability of thickness on swelling in water of some commercial cellophanes is qualitatively interpreted in terms of the planar orientation of crystal (101) planes along the film surface and the orientation of the noncrystalline chain segments parallel to the film surface. The dimensional changes on swelling from the completely dry state to 10% moisture regain were further interpreted quantitatively in terms of the degrees of biaxial orientation of the two kinds of structural units and their degrees of anisotropic swelling by modifying the Hermans monophase model for crystalline and noncrystalline biphase structures. The following degrees of anisotropic swelling of the structural units were thus obtained: qc, [101] = 0.40%, qc, [101] = −0.33%, and qa = 2.42%.

STUDIES ON THE RELATIONSHIP BETWEEN ORIENTATION MECHANISM AND MECHANICAL PROPERTIES OF ORIENTED POLYPROPYLENE

The orientation behavior of crystalline and non-crystalline phases of three kinds of polypropylene during uniaxial stretching and after annealing under a given degree of the stretching, were observed by means of simultaneous measurements of x-ray diffraction, infrared dichroic ratio and birefringence. The three kinds of polypropylene were different in isotacticity but almost same in viscosity average molecular weight with each other.The orientation behavior of crystallites differed with the degree of isotacticity of the polymers; i.e., for lowly isotactic polymers, the preferential orientation of the crystal c-axis but random orientation of crystal a′-and b-axis around the c-axis, both with stretching, while for highly isotactic polymers, more preferential negative orientation of crystal b-axis than a′-axis, especially at low degrees of stretching, were observed. This feature suggests that some super-structures of aggregated crystallites, such as spherulite structure, would be formed for the highly isotactic polymers, but not for the lowly isotactic ones.The orientation of crystalline and non-crystalline phases proceeded much more prominently as the increase of degree of isotacticity. This may be interpreted in terms of the effective orientation of the structural units, which should be governed by various structural factors being sensitive to the isotacticity, such as the degree of crystallinity, the size and perfection of crystallite, and the average length of non-crystalline chains.The changes of the degree of crystallinity and the orientation of crystallites and non-crystalline chain segments during annealing under a given degree of stretching, were much affected by the degree of stretching of molecular chains before the annealing. Little change of orientation of the structural units but considerable increase of degree of crystallinity occured at relatively low degrees of stretching, and vice versa at high degrees of stretching.

Change of orientation by thermal contraction of polyacrylonitrile fiber

AbstractPolyacrylonitrile polymer powder was dissolved in 70% nitric acid and spun into isotropic filament through a glass nozzle of 0.5 mm. diameter in a coagulating bath of 30% nitric acid. Stretching was carried out in two stages: the first stretching was done in water at 20°C. followed by drying, and the second stretching was done in a boiling saturated solution of ammonium sulfate. The total stretching ratio was 23. These filaments were shrunk freely in water at 70–180°C. The change in orientation factors was traced by x‐ray, infrared dichroism, visible dichroism, and sonic modulus methods. The relation between the reciprocal absolute temperature of thermal contraction and the logarithm of fiber length is a straight line which has two inflection points at 93 and 175°C. The orientation factors by x‐ray and infrared dichroism remain unchanged up to 175°C. On the contrary, the orientation factors by visible dichroism and sonic modulus drop suddenly at about 90°C. This indicates the occurrence of relaxation of the amorphous chain at the glass transition temperature and shows the polymer is not perfect single‐phase material. Orientation of crystalline and amorphous phases is stable from 100 to 170°C. in spite of considerable thermal contraction. The stability of orientation can be explained by the growth of a folded structure in the polymer.

Anisotropy in Mechanical Relaxations in Uniaxially Oriented Polymers

A new method for studying the anisotropy in mechanical relaxations of oriented polymers is proposed. The method consists of measuring velocicty and attenuation of ultrasonic shear waves propagating in the normal direction to the film as a function of the angle between draw direction and wave polarization. This method can separate the orientation of crystalline phase, amorphous phase and others in the polymer, because multiple relaxations in the temperature dispersion curve are ascribed to related phases, respectively. Preliminary results for low density polyethylene and polytetrafluoroethylene at 3 and 10 MHz in temperature -60° to 40°C are presented and the deformation mechanism of polyethylene is suggested.

X-Ray Study of Reactions Involving Accelerators. Orientation of Crystalline Phases on Stretching of Rubber Stocks

Abstract About a year ago, in the course of a systematic survey of the x-ray diffraction patterns of a number of routine rubber samples with different accelerators present, certain similarities were noted in the diffraction effects from the accelerators in these stocks. Close examination of these effects showed that they were identical. The stocks contained the accelerators tetramethylthiuram disulfide, tetramethylthiuram monosulfide and zinc dimethyldithiocarbamate, which are chemically similar (Table I); the first is the disulfide, the second, the monosulfide, and the third, the zinc salt. Thus, the diffraction patterns indicate that, on curing, the disulfide and the monosulfide in the presence of sulfur react with zinc oxide to form the zinc salt. This is not a new concept. The zinc salts have been extracted with solvents from stocks similar to the above, and it has been supposed that such reactions occur. However, the extraction method leaves some doubt as to whether the salt was originally present in the rubber matrix or whether it was formed in the solvent on extraction. Every crystalline material has its own characteristic x-ray diffraction pattern, which is different from that of every other crystalline material, just as the fingerprints of each person are different from those of every other person. Thus, with x-ray “fingerprint”patterns it is possible to identify positively the presence of these salts in the rubber matrix and show that they must have been formed in the rubber mix on curing. Further, it was noted that this crystalline salt is strongly oriented in the rubber matrix on stretching. It seemed advisable, then, to investigate other similar reactions by the x-ray method and to investigate the significance of the strong orientation of these reaction products in the rubber matrix.