Amorphous Orientation Research Articles

Dichroism of an ideally oriented polymer chain

AbstractVisible dichroism can be utilized as a measure of the degree of orientation of an amorphous region in a polymer. But the relations between dichroism and states of dyes in polymer must be elucidated before dichroism can be used more widely as a reliable means for study of amorphous orientation. To calculate the orientation factor for visible dichroism, it is necessary to decide the dichroism of an ideally oriented polymer chain. For this purpose, a single crystal of Congo Red was prepared and the dichroic spectrum of the crystal was measured. It was found that the dichroism of the Congo Red molecule itself is unity in a suitable wavelength region. As a result, a simple means for the treatment of dichroic spectra was given. The angle between the polymer chain axis and the principal axis of the absorbed dye molecule was discussed.

Simultaneous Measurements of Stress and Infrared Dichroism on Polymers I. Stress Relaxation of Vulcanized Natural Rubber

Abstract A method for simultaneous measurements of stress and infrared dichroism as time-dependent behavior of polymer films was devised using a double beam infrared spectrometer. The film sample held between clamps of a stretching device was placed just in front of the entrance slit of the spectrometer where the sample and reference beams came alternately. Two polarizers were used, one in the sample beam and the other in the reference beam. Thus the sample and reference beams were polarized to have the electric vectors parallel and perpendicular to the stretching direction of the sample, respectively. With this arrangement the spectrometer responded only to the difference in the transmittance of the two beams. Setting the spectrometer at one of the wavenumbers of the absorption band maxima, we could record continuously the change in its dichroism during mechanical treatments which gave rise to molecular orientation in the sample. The stress was recorded automatically by means of a pair of strain gauges pasted on the cantilever beam of the stretching device. By theoretical considerations, a simple relationship was found to exist between the quantity recorded on the spectrometer by this method and the orientation function of transition moment of a vibrational absorption band with respect to the stretching direction. The method was applied to the stress relaxation experiments of vulcanized natural rubber carried out at different elongations less than 600 per cent and at room temperature. Changes of infrared dichroism were measured for five absorption bands at 1664, 1380, 1361, 1129, and 844 cm−1, of which the last one is a crystalline band. From the results of this study, the stress relaxation observed was ascribed mainly to the amorphous orientation rather than to the crystalline orientation, which was completed almost immediately after elongation.

THE RELATIONSHIP BETWEEN YOUNG'S MODULUS AND DEGREE OF ORIENTAION FOR POLYETHYLENE TEREPHTHALATE FIBRES

In the previous report, relationship between Young's modulus and birefringence for drawn and heat-treated PET fibres was discussed.In this report, the mechanism of small deformation of PET fibres below glass transition temperature is discussed and a new theoretical approach between Young's modulus and molecular orientation is proposed under the following assumptions: a) A segment transforms in accordance with “affindeformation” theory: b) Intersegmental force during the affin transformation of the segment is proportional to the rotational angle of the segment.Then, Young's moduli of PET fibres heat-treated at constant length after drawing and ones drawn after crystallization are measured and compared with the theory. The results obtained are as follows:1. The rotational angle ω of a segment due to the deformation of a sample and Young's modulus E may be expressed by following equations; where υ is Poisson ratio of the sample; θ is the angle between the fiber axis and the segmental axis; ez is tensile strain of the bulk sample; E0 and G0 are constants.2. The relationship between Young's modulus and amorphous orientation factor may be represented in terms of the above equations. The values of E0 and G0 are 1700_??_1900kg/mm2, 80kg/mm2, respectively, for the samples drawn without heat-treatment, but these are a little smaller for the samples drawn after crystallization, Young's modulus of drawn PET fibres depends mainly upon amorphous orientation and the effect of crystallinity is rather small.3. The above results suggest that the force constant of the amorphous segment below glass transition temperature dose not much differ from that of the crystalline chain, but a part of intermolecular strain makes a series to intra-molecular strain and lowers much the Young's modulus of bulk sample; and that there may be more parts of fold structure in samples drawn after crystallization than in ones drawn without heat-treatment.

Rheo‐optical studies of the deformation of crystalline polymers

AbstractThe deformation of a polycrystalline polymer must be examined in terms of the changes in morphology, texture, crystalline structure, and chain conformation. The understanding of the dynamic mechanical properties requires the specification of the rates of these changes. Optical techniques may be employed for this purpose. Dynamic x‐ray and dynamic infrared dichroism diffraction serve to define the rate of crystal orientation. Dynamic light scattering characterizes changes in the crystalline superstructure while dynamic birefringence characterizes the total orientation of crystalline and amorphous regions. A direct measure of amorphous orientation rate may be attempted by introducing a dye or chromophoric group into the amorphous regions and measuring its dynamic dichroism. In general, each of these dynamic observables may be resolved into a real and imaginary part (in and out‐of‐phase with strain). The results of measurements of these along with dynamic modulus measurements are discussed in an effort to present a consistent molecular and structural interpretation of mechanical behavior.

ORIENTATION BEHAVIOR OF THE AMORPHOUS REGION OF THE HEAT-TREATED POLYETHYLENE TELEPHTHALATE FILAMENT WITH HIGH ORIENTATION

Undrawn Tetron polyester filament of low crystallinity was stretched by 6.6 fold and heat-treated at 205°C in an oil bath, where the filament shrank by 25%. The filament was further stretched at 100°C to the original length, and again heat-treated at 200°C allowing shrinkage. This stretching and shrinking cycles were repeated twice. The final length was 80% of the original length. The parameters of the fine structure are expressed: X(X-ray crystallinity)=0.346, fx (X-ray orientation degree)=0.931, f0 (over-all orientation degree)=0.571 and fa (amorphous orientation degree)=0.664.This stabilized filament was stretched toward the original length at 100°C and the fine structure was investigated at each stretching stage and the following results were obtained.(1) The crystalline region is stable (X and fx were kept unchanged during the stretching), while f0 and fa increase remarkably. The fa_??_elongation ratio curve is convex to the draw axis saturating before it reaches the original length.(2) The stretching degree of amorphous chains, r/nl, was estimated from the filament length.The curve fa_??_r/nl agrees well with the one calculated by the Treloar's rubber theory, where r is the end-to-end distance of the chain between net points, the crystallites nl the value of r at the fully stretched state, and_??_-1 the inverse Langevin function. So the behavior of the amorphous chains within the polyester filament at 100°C or above may be considered to be nearly rubberlike.

Simultaneous measurements of stress and infrared dichroism on polymers

A method for simultaneous measurements of stress and infrared dichroism as time-dependent behavior of polymer films was devised by using a double beam infrared spectrometer. The film sample held between clamps of a stretching device was placed just in front of the entrance slit of the spectrometer where the sample and reference beams came alternately. Two polarizers were used, one in the sample beam and the other in the reference beam. Thus the sample and reference beams were polarized to have the electric vectors parallel and perpendicular to the stretching direction of the sample, respectively. With this arrangement the spectrometer responded only to the difference in the transmittance of the two beams. Setting the spectrometer at one of the wavenumbers of the absorption band maxima, we could record continuously the change in its dichroism during mechanical treatments which gave rise to the molecular orientation in the sample. The stress was recorded automatically by means of a couple of strain gages pasted on the cantilever beam of the stretching device. By theoretical considerations, a simple relationship was found to exist between the quantity recorded on the spectrometer by this method and the orientation function of transition moment of a vibrational absorption band with respect to the stretching direction. The method was applied to the stress relaxation experiments of vulcanized natural rubber carried out at different elongations less than 600% and at the room temperature. Changes of infrared dichroism were measured for five absorption bands at 1664, 1380, 1361, 1129, and 844 cm−1, of which the last one is a crystalline band. From the results of this study, it was concluded that the stress relaxation observed was ascribed mainly to the amorphous orientation rather than to the crystalline orientation, which was completed almost immediately after elongation.

Dynamic Moduli and Elongation of Synthetic Fibers

The measurements have been made of the sonic moduli (pulse propagation moduli) and the tensile moduli simultaneously on the filaments produced from various polymers to investigate the orientation characteristics of molecules in the drawing process. The tensile moduli have been measured dynamically by giving the sample sinusoidal strain, whose amplitude is about 0.4% and frequency is 0.12cps, and by stress relaxation statically. These three moduli gives different information each on the behavior of polymer molecules during the elongation. The variance of pulse propagation time (ΔT) has also been measured when the sample is given dynamic strain (Δγ) or stress (ΔS) of the low frequency of 0.12cps. The physical meanings of the coefficients ΔT/Δγ and ΔT/ΔS are discussed from the point of molecular orientation.The measuring apparatus consists of pulse propagation viscoelastic meter, strain meter, stress meter, bias current part, drawing device and X-Y recorder. The dynamic tensile moduli have been measured by Lissajous method. Only the change of pulse propagation time has been amplified after the electric current corresponding to the propagation time of the sample, which was not dynamically strained, was cut off by the opposite bias current. The measurements have been made mainly on polypropylene filaments (1050d) at room temperature (about 30°C). The results are as follows:(1) The dynamic tensile moduli (E') and pulse propagation moduli (Es) do not change so much for polypropylene filaments of lower draw ratio, but increase much for that of higher draw ratio with the increase of static strain. E' increases monotonously with the increase of draw ratio. Es, however, has a minimum at the draw ratio of about 1.5. The reason why the Es curve passes the minimum seems to be found in the process of crystalline orientation which gives much influence upon the drawing process at the lower elongation. At the higher elongation, E' and Es increase in accordance with the increase of amorphous orientation.(2) The propagation moduli on polypropylene filaments were measured during the stress relaxation. The stress relaxation moduli (Er) decrease monotonously within the measured time. Because of increase of molecular orientation Es increases to about 100sec and reaches the constant value which corresponds to the strain. R. S. Stein et al. have reported that crystalline orientation is completed within 1sec from the observation of dynamic birefriengences and dynamic X-ray diffraction. Taking accounts of these results, it is considered that the change of Es within 100sec has been occasioned by the relaxation of the orientation of the amorphous parts though the orientation is usually complete within 100sec. The change of Es which is derived from crystalline orientation seems to be too fast to observe.(3) The change of pulse propagation time (ΔT) when a filament received dynamic strain (Δγ) or dynamic stress (ΔS) are recorded on the X-Y recorder with either of them. The coefficients ΔT/Δγ or ΔT/ΔS are defined as“strain-pulse propagation coefficient”or“stress-pulse propagation time coefficient”respectively. The strain-pulse propagation time coefficient is useful as a measure showing the degree of the allowance of molecular strain. The coefficients of polypropylene are positive for lower elongated filaments, negative for moderately elongated filaments, and zero for highly elongated filaments. The change of the coefficient with the increase of the static strain also shows this tendency.

The orientation of polyethylene

AbstractThe orientation of the crystals and the amorphouse regions of polyethylene occurring during stretching has been studied using the combined techniques of x‐ray diffraction, infrared dichroism, and birefringence. The state of orientation is expressed in terms of the position of a point on a triangular “orientation diagram.” It is found that the a and b crystallographic axes orient differently. The degree of crystalline orientation is greater at a given elongation for a sample oflower degree of crystallinity than higher. An appreciable amount of amorphous orientation occurs, and appears greater in the more crystalline samples. Orientation oflarger crystalline aggregates has been studied using the light scattering technique and is found to parrallel that of the crystallites. A model consistent with these various types of experimental studies is proposed.

The X‐ray diffraction, birefringence, and infrared dichroism of stretched polyethylene. II. Generalized uniaxial crystal orientation

AbstractA general method for describing the crystal orientation in a uniaxially oriented crystalline polymer is presented. It is shown that two orientation functions may be quantitatively evaluated from x‐ray diffraction data. The variation of these during mechanical and thermal treatment may be studied. These functions are sufficient to completely characterize the crystal contribution to birefringence and infrared dichrosim. By subtracting the crystal contribution from the total birefringence or dichroism, the amorphous orientation may be characterized.

The x‐ray diffraction, birefringence, and infrared dichroism of stretched polyethylene

AbstractThe results of a study of x‐ray diffraction, birefringence, and infrared dichroism on a series of polyethylene samples elongated between 0 and 400% are presented. It is shown that, by using any two of the three methods together, one may determine individually the orientation of the amorphous and crystalline portions of the polymer. The results of the third method may then be predicted. Both amorphous and crystalline regions orient appreciably upon stretching. The amorphous orientation is somewhat lower than that of the crystallites. Many of the amorphous chains appear to become completely stretched out. The results indicate that the degree of crystallinity remains constant during stretching and that the oscillator strength of the CH2 rocking vibration is also constant.

Crossed amorphous and crystalline chain orientation in polythene film.

Crossed amorphous and crystalline chain orientation in polythene film.