Uniaxially drawn sample

Fig. 10.3.1 [Hepl] F chemical-shift spectra of PTFE. The dipole-dipole interaction has been removed by M V8 multi-pulse excitation, (a) Isotropic molecular orientation, (b) Uniaxially drawn sample. The drawing direction is parallel to the magnetic field.

It should be noted here that in the Kratky scheme the sample orientation was modelled by the orientation (at constant volume) of rod-like units whose symmetry axes rotated on drawing in an identical manner to the lines joining pairs of points in the uniaxially drawn sample, without any change of length of the rotating units. 

It is known that the dipole moment associated with a particular infrared absorption in a polymer makes an angle of 15° with the chain axis. A particular uniaxially drawn sample of the polymer is found to transmit 25% of incident infrared radiation at the wavelength corresponding to this absorption when the incident beam is polarised parallel to the draw direction. If the sample has a birefringence 0.85 times that of a perfectly oriented sample, estimate the corresponding percentage infrared transmission for an incident beam polarised perpendicular to the draw direction. State clearly the assumptions made. 

The variation of birefringence with draw ratio for a set of uniaxially drawn samples of a certain polymer is found to be consistent with the simplest version of the affine rubber model when the draw ratio is less than 3.5. If the birefringence is 7.65 x 10 for draw ratio 3.0, calculate its value for a sample of draw ratio 1.5. If the birefringence for a very highly oriented sample is 0.045, what is the effective number of random links per chain ... 

C. The oriented films were finally annealed at 120 C for 0.5 hr. In order to control the degree of molecular orientation, the uniaxially drawn samples were annealed to shrink at 160 C. Aluminum electrodes for electric measurements were evaporated onto both film surfaces. The poling condition used for this experiment was 25 MV/m at 120°C for 2hrs. 

The molecular orientation induced during the processing of polymers by the preferential alignment of macromolecular chains or segments has an impact on the macroscopic physical properties. FTIR methods have been developed in order to measure this induced orientation. The FTIR technique determines the orientation-distribution function,/(0), which, in the case of a uniaxially drawn sample, relates the number of chain elements lying in one direction to the angle they make with respect to the draw direction. 

We give here a derivation of Eqs. (8.17) and (8.18) which relate the birefringence, An = nc — na, of an uniaxially drawn sample to the orientational order parameter of the monomers, S. Two coordinate systems are introduced. The first one, with coordinates x, y, z, is fixed on the sample, with the -axis oriented in drawing direction. The second, with coordinates x, y z is anchored on a monomer unit and varies in orientation between different monomers. We choose the latter local coordinate system so that the polarizibility tensor per monomer, /3 , has a diagonal form... 

P2 is widely used to describe the orientation in uniaxially drawn samples, such as fibers. Generalized spherical harmonics, of which Legendre polynomials are a subset, are required to describe orientation in samples without cylindrical symmetry [66]. 

An appropriate measure for the degree of orientation in an uniaxially drawn sample is the orientational order parameter of the monomeric units, S, de-... 

Figure 9 shows the result by Fukada, Date, and Hirai (1966) for uniaxially drawn poly(y-methyl L-glutamate) film (PMLG). The conformation of the chains is predominantly the a-helix. The sample was drawn twice as the original length and the frequency of stress was 20 Hz. The observed anisotropy is well expressed by the tensor (59) which leads to the d-constant of the film for elongational stress in the film plane (yz-plane),... 

In Figure 6, one can see, as with amorphous materials, that the more unbalanced the biaxial orientation is the greater are the reductions in permeability. Interpretations of the transport data for biaxially and uniaxially drawn PET samples can be explained by observing conformational changes in the polymer backbone itself. Apparently, the chain packing efficiency of the amorphous phase improves as the number of trans isomers in the ethylene glycol unit increases. Polarized infrared analysis of uniaxially and biaxially oriented systems indicates that the fraction of... 

The molecular orientation of the polymer matrix is described by means of a vector field n(x,y,z), with n being the unit vector (director) oriented along the mean molecular orientation direction. The molecular orientation of uniaxially drawn homogeneous polymers might be approximated, if one neglects the influence of the outer shape of the sample, to the cylindrical symmetry described by the orientation distribution function of the form ... 

Fig. 10.8 Birefringences for three sets of uniaxially drawn PVC samples plotted against the draw ratio ...

The birefringence An for a uniaxially oriented sample with draw ratio X = 3.5 was found to be 8.1 x 10 . Assuming that the orientation of the polymer molecules is adequately described by equation (11.6) using only the first term on the RHS, deduce An for a similarly drawn sample with X = 2.0. 

Fig. 2 Scanning confocal microscopy images of blend films of ultra-high-molecular-weight polyethylene and 10 wt% EHO-OPPE (see Fig. 1). (a) As prepared film, (b) Uniaxially deformed sample drawn to a draw ratio of 80. Both images were acquired by detecting the polarization direction oriented parallel to the (eventual) deformation direction. Inset shows images acquired by detecting the orthogonal polarization direction. Adapted with permission from [35]. Copyright 2000 American Chemical Society...

Fig. 12. High density polyethylene. Variation of modulus with temperature for highly oriented samples from uniaxially drawn sheet. Note crossover in annealed samples. (Adaptedfrom Gupta and Ward. )...

The low temperature y relaxation has been examined by Buckley, Gray and McCrum in Rigidex 9 samples both uniaxially drawn and annealed and drawn at constant width to give bia.xial orientation. In each case the modulus parallel to the stretch relaxed more than that in the perpendicular direction. This was interpreted in terms of a series Takayanagi model as evidence for deformation of amorphous material in an inclined lamellar structure. The work by Stachurski and Ward already discussed did not throw any light on the nature of the y transition. 

Recently Wright et al. have obtained room temperature values of all five elastic constants for uniaxially drawn polymethylmethacrylate (Perspex) and polystyrene (Carinex) by measuring the critical angle for total reflection of an ultrasonic beam incident on immersed samples. The specimens were stretched by similar extents at different temperatures, with orientation assessed by measurements of optical birefringence. 

A quantitative treatment of the specular reflection spectra obtained from the surface of uniaxially drawn PETP samples was performed. A procedure for correcting for the effect of surface irregularities is presented, and an overall orientation function based on the orientation and content of trans-conformers is calculated. The results are correlated with mechanical modulus and crystallinity values. In addition, an unconventional dichroic ratio parameter based on a combination of two major bands is proposed. Results obtained from the Kramers-Kronig analysis and directly from the reflection spectra are discussed. Both are compared with the overall orientation function obtained before. 21 refs. 

A critical assessment was made of the use of ATR-IR spectroscopy for the study of the surface composition and orientation in uniaxially drawn PETP films. The use of reference bands commonly used in such analyses was examined, paying particular attention to the possible deleterious effects of sample orientation, incident polarisation and sample contact. The use of conventional sampling procedures to obtain in-plane surface dichroism measurements is shown. 25 refs. 

In order to clarify the intrinsic crystal piezoelectricity, it is very important to know how form I crystallites deform when strain is applied. The relationship between the external strain and the lattice strain for the uniaxially drawn film is shown in Figure 5, where (A) and (B) denote samples annealed at 175 C and 120°C for 2hr, respectively. The c axis strain of samples is as small as 0.8-1.5% of the external strain, as deduced from the large elastic constant along c axis. On the other hand, the a and b axes strains are very large (2.5-6.0%. The apparent Poisson s ratio of the form I crystallite is extremly large, which depends on the conditions of anealing = 4.0 (120 C)... 

Fig. 29a and b. Simultaneous stress-strain and FTIR measurements during uniaxial deformation and recovery of a primarily amorphous PTMT film, a stress-strain curve of the mechanical treatment b FTIR spectra in the 1500-1400 cm 8(CH2) region alongside the wide angle X-ray diagrams of the original and a 600% drawn sample... 

Sawai et al. studied the mechanical properties of a stereocomplex PLA film prepared by casting from a solution of an equimolar blend of PLLA and PDLA [35]. The film was uniaxially drawn by solid-state coextrusion and characterized by DMA. The optimum draw temperature resulting in the highest draw and mechanical properties was 200° C. The maximum achieved tensile modulus and strength, for the samples with an extrusion draw ratio of 16 and prepared by solid-state coextrusion of a highly crystalline stereocomplex film, were 9500 and 410 MPa, respectively. Furthermore, the PLA stereocomplex films with an extrusion draw ratio of 16 exhibited excellent thermomechanical stability as evaluated by the E measured as a function of temperature. The reported E values at room temperature, 100 and 200°C, were 9500, 7000, and 3000 MPa, respectively [35]. Equimolar amounts of PLLA and PDLA stereocomplex are therefore characterized, upon orientation, by the most relevant me-... 

Figure 4.15 Comparison of orientation in uniaxially drawn PET as a function of draw ratio, as measured by four independent techniques (see text for details). The residual orientation detected in the undrawn sample using IR dichroism is believed to arise as a result of microtome-induced...

Polarised confocal Raman microscopy was used to measure molecular orientation in uniaxially drawn PETP films, prepared with draw ratios from 1 to 3.5. The orientation of both polarised Raman microscopy and polarised attenuated total reflection IR spectroscopy. Crystallinity profiles were measured through the thickness of the film samples and compared with the orientation gradients existing in the films. This procedure was to determine whether the intuitive assumption that orientation and crystallinity would be positively correlated actually holds true on the microscopic scale for these samples. 18 refs. 

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