Function Of Draw Ratio Research Articles

Improvements in the Use of Attenuated Total Reflection Fourier Transform Infrared Dichroism for Measuring Surface Orientation in Polymers

Improvements in the use of attenuated total reflection (ATR) Fourier transform infrared (FT-IR) dichroism for measuring surface orientation in polymer films are described, with poly(ethylene terephthalate) (PET) as an example material. It is shown that normalizing band intensities relative to a nondichroic band, prior to calculating dichroic ratios, eliminates the need to maintain identical contact areas/pressures when removing, rotating, and reclamping samples to the ATR element, which has been a major historical drawback to this technique. The normalization is vital; it makes the calculated dichroic ratios largely insensitive to variations in sample/prism contact area, and less sensitive to uncertainties in the refractive indices and birefringence of the polymer. For PET, it is shown that the birefringence can be neglected in the analysis, and a single approximate refractive index used. This is a significant benefit since the birefringence will vary as a function of orientation and crystallinity. Polymers that are much more birefringent than PET can also be analyzed by using the formalism described in this paper, provided that the three independent indices are known. This paper is presented in two parts; first, equations are derived which allow the calculation of all second-order orientation parameters ( P200, P220, P202, and P222), and the averaged squared direction cosines, from the normalized ATR dichroic ratios. Second, we show how a single-reflection diamond ATR unit is an ideal tool for this work, since it allows small, hard, or irregularly shaped samples to be examined without fear of damaging the ATR element. We illustrate the technique using data obtained from a series of uniaxially drawn films, and one biaxially drawn film, using a commercially available accessory. From these data, orientation parameters were calculated as a function of draw ratio and compared with those obtained from specular-reflectance FT-IR and birefringence analysis of the same samples. The method should be applicable to any polymer provided that (1) a suitable nondichroic band is available for normalization and (2) the largest polymer refractive index lies well below that of the ATR element (2.4 in the case of diamond). It must be realized that condition 1 is not trivial; careful investigation is required to identify truly nondichroic bands (if any exist for the polymer of interest).

Prepregs and laminates of polyetherimide-reinforced by a thermotropic LCP

Unidirectional sheets (prepregs) of blends of polyetherimide (PEI) with a liquid crystalline polymer (LCP) are prepared. The mechanical properties of prepregs at directions of 0°, 45°, and 90° to the machine direction are investigated as a function of draw ratio and LCP concentration. The results show that drawing significantly increases the tensile strength and modulus of prepregs in the machine direction and only slightly decreases these properties in the transverse direction. An increase in the LCP content greatly enhances the tensile strength and modulus in the machine direction but decreases these properties in the 45° and 90° directions. The strain at break of prepregs decreases with LCP content in all directions tested. An abrupt drop in the tensile strength, modulus, and strain at break of prepregs occurs in the 45° and 90° directions when LCP content reaches 40%. Prepregs are used to manufacture unidirectional and quasi-isotropic laminates. Unidirectional laminates show mechanical properties close to those of the corresponding prepregs. The tensile modulus of quasi-isotropic laminates exhibits a continuous increase with increasing LCP content while the tensile strength increases with an LCP content up to 30%, then it decreases rapidly. The morphology of LCP in prepregs is observed to change from disperse to continuous at LCP contents of 40 and 50%. This effect is found to be responsible for the large decrease in tensile strength of prepregs in the 45° and 90° directions and quasi-isotropic laminates at higher LCP concentration. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:329–340, 1997

Orientation in uniaxially drawn poly(ethylene terephthalate) (PET) film by two-dimensional 13C n.m.r. and FTi.r. spectroscopy

Two-dimensional magic angle spinning (2D-MAS) 13C n.m.r. spectroscopy and FTi.r. microscopy have been used to measure the orientation in uniaxially drawn film as a function of draw ratio. Results obtained agree well with those obtained by optical birefringence measurements. FTi.r. microscopy is a powerful method for mapping the orientation across the film thickness with quick data collection and analysis. The strength of the 2D-MAS n.m.r. method lies in its chemical and phase selectivity while its weakness lies in the time-consuming data acquisition and analysis coupled with the lack of knowledge about the orientation of the chemical shift tensor in the molecular frame.

Use of Polarized Resonance Raman Spectroscopy of a Polyene Probe, and FT-IR Dichroism, to Probe Amorphous-Phase Orientation in Uniaxially Drawn Poly(Ethylene)

The linear diphenyl polyene Φ–(C=C–)4Φ has been investigated as a resonant Raman-active probe for molecular orientation, suitable for incorporation into polymers prior to melt extrusion and drawing. By examination of the polarization properties of the Raman scattered radiation, it is possible to determine the P200 and P400 orientation parameters for the dye molecule as a function of draw ratio. Assuming that the dye resides only in amorphous polymer regions, it is expected that the data will give insight into the orienting forces present in the amorphous phase during processing. Expressions were derived relating P200 and P400 to the polarized Raman intensities. An expression for Hermans' orientation parameter was also derived—it was shown that f was always slightly higher than P200 when evaluated from the same Raman data. These Raman measurements were illustrated by using the example of uniaxially drawn poly(ethylene) (PE) tubing. As an alternative approach, FT-IR dichroic ratios of bands due to the PE itself were used to determine the orientation ( P200) of the crystalline phase and also of gauche conformers present only in the amorphous phase; these results were compared with the Raman measurements on the dye probe. The orientation was examined as a function of draw ratio and subsequent thermal annealing. In general, both crystalline and amorphous phases oriented increasingly with draw ratio, but whereas annealing the samples only slightly relaxed the crystal orientation, the amorphous orientation decreased dramatically when measured by using either the probe molecule or the gauche conformer as a probe of the amorphous phase. This result support the assumption that the dye is localized in amorphous regions. This work is important since it shows how a cheap, commercially available probe molecule may be used to probe the amorphous-phase orientation of a polymer without requiring any chemical synthesis; simple melt-mixing is sufficient to dope the amorphous network. This capability will be useful for systems where convenient vibrational band: specific to the polymer amorphous phase are absent.

Tensile drawing of poly(aryl ether ether ketone): 2. Analysis of the stress-strain-orientation relationships through the Brown and Windle model

The deformation behaviour of amorphous poly(aryl ether ether ketone) films above the glass transition temperature is studied by analysing the amorphous orientation function and shrinkage stress variations versus draw ratio in the framework of the two component model of Brown and Windle which considers separate orientational and extensional contributions to the overall strain. This analysis is in line with our previous conclusion of the existence of two regimes dominated by orientation of rigid structural units and extension of the chains before and after the threshold of the strain-induced crystallization, respectively. Also supported is the disentanglement trend of the chains prior to the crystallization which brings about a physical crosslinking effect to the macromolecular network. The identification of the rigid structural unit with a single monomer unit is remarkably consistent with our previous determination of the size of the random link. The study of isothermally-crystallized samples supports the conclusion about the efficiency of the crystallites for preventing chain slippage. The estimation of the molecular weight between entanglements as a function of draw ratio for both amorphous and crystallized samples suggests that the physical crosslinking effect of the crystallites is much more efficient than the intertwining of the chains.

Elastic moduli of a liquid crystalline polymer and its in‐situ composites

AbstractThe elastic moduli of a liquid crystalline polyesteramide (LCP) and polycarbonate/LCP in‐situ composites with 10 to 80 wt% of LCP have been measured as functions of draw ratio λ from 1 to 15 by an ultrasonic method. For the LCP, the sharp rise of the axial Young's modulus E3 and the slight decreases of the transverse Young's modulus E1 and the axial (C44) and transverse (C66) shear modulus with increasing λ result from the alignment of chains along the draw direction. E1, C44, and C66 follow the lower bounds calculated using the series coupling scheme of the aggregate model. Although E3 lies close to the lower bound at low λ, it follows the upper bound calculated according to the parallel coupling scheme at λ > 3. The elastic moduli of the composites have similar draw ratio dependences as those of the LCP. The strong increase in E3 with increasing λ arises from the higher aspect ratio of the LCP domains in the composites and the improved molecular orientation within the domains. The reinforcement effect on the other moduli is much weaker, with E1 and C44 of the composites only 5 to 30% higher than those of polycarbonate at λ = 15. Since C66 of the LCP decreases to a value below that of polycarbonate at λ > 2, there is a positive reinforcement effect at low λ but a negative effect at high λ.

Measurement of surface orientation in uniaxial poly(ethylene terephthalate) films using polarised specular reflectance Fourier transform infrared microscopy

Abstract Polarised Fourier transform infrared (FT-IR) external-reflection spectroscopy has been used to measure molecular orientation at the surface of uniaxially drawn poly(ethylene terephthalate) (PET) films as a function of draw ratio. The spectra, which were obtained using an FT-IR microscope operating in the reflectance mode, were of high signal-to-noise ( S N ) ratio, and contained only the specular component of the reflected radiation. The dichroic ratio of the 1019 cm−1 ring stretching band was used to measure the PET orientation function, P200. Prior to quantifying band intensities, the reflectance spectra were either transformed using the Kramers-Kronig algorithm, or simply differentiated; it was found that the dichroic ratios obtained using either pretreatment were similar. It was shown that the P200 values obtained using the FT-IR method compared well with those obtained using surface refractive index measurements, provided that the intensity of the 1019 cm−1 band was normalised relative to a non-dichroic band in the spectrum prior to computing dichroic ratios. The use of a reflecting microscope to perform the analysis of surface orientation not only simplifies sample alignment compared with “macro” reflectance accessories, but also allows awkward-shaped or small samples to be examined with relative ease. Unfortunately, a significant current limitation is that samples must be sufficiently “optically thick” to prevent double-pass (“transflectance”) radiation reaching the detector and yielding non-specular features in the reflectance spectrum. For polyaromatics, this probably means thicknesses in excess of 50 μm to obtain good spectra in the fingerprint region. Polarised attenuated total reflectance microscopy may present an alternate approach for examining thinner films.

Theoretical Estimation of Segmental Orientation in Deformed Polymeric Networks Using a Lattice Model and Application to Orientation of Amorphous Chain Segments of Poly(ethylene terephthalate) and Oriented Crystallization of Polyethylene

The orientation distribution of chain segments in a uniaxially deformed polymer film has been estimated theoretically as a function of draw ratio using a lattice model similar to the one proposed by Erman et al. The model of Erman et al. was somewhat modified to compare the theoretical results with experimental ones. In doing so, the preferred axis associated with the orientation of segments was chosen along the direction between the two successive cross-link points, and the orientation of the preferred axis was assumed to behave in an affine fashion under elongation. The treatment was formulated in terms of the orientation distribution function with respect to the stretching direction by the application of the Legendre addition theorem. Numerical calculations were carried out to study the mechanism of the orientation of amorphous chain segments of poly(ethylene terephthalate) (PET) films, as well as oriented crystallization of polyethylene (PE) films. X-ray diffraction measurements were done to obtain the orientation distribution functions for PET and PE drawn films. The calculated orientation distribution functions were in good agreement with those observed experimentally.

Segmental Orientation Behavior of Poly(butyleneterephthalate-co-tetramethylene oxide) upon Uniaxial Deformation

The segmental orientation behavior of the thermoplastic elastomer [poly(butylene terephthalate-co-tetramethylene oxide)] has been studied with IR dichroism and polarizing microscopy. The orientation of hard segments as well as soft segments has been determined as a function of draw ratio. The difference in the orientation behavior of soft and hard segments has been associated with the respective T g 's. It has been also established that annealing significantly affects the deformation behavior. The segmental orientation has been observed to be strongly affected by the addition of small amount of the asymmetric chain extender

Orientation studies in polyacrylonitrile films uniaxially drawn in the solid state

AbstractPolyacrylonitrile (PAN) films were made by casting a dimethyl sulphoxide (DMSO) solution. After drying, the films were uniaxially drawn by an essentially solid‐state drawing procedure. Using polarised‐infrared (IR) spectroscopy, the dichroism of the nitrile‐stretching vibration was monitored as a function of draw ratio. The dichroism results were converted to plots of chain‐orientation factor versus draw ratio. For this, α, the transition‐moment angle of the vibration, has to be known. Though a value of 68–73° has been suggested in the literature, for the present samples α cannot be 70° or less, and 73° is the most appropriate. The meaning and nature of the transition‐moment angle in the context of a flexible‐chain polymer molecule is discussed. The IR spectrum also showed dichroism in the SO stretch and the CH3 rocking vibrations from the (residual) DMSO present in the film, indicating that the solvent molecules were also orientated. It is proposed that this occurred due to dipolar interactions between the SO and the CN groups, which led to solvent molecules being bound to the polymer chains. X‐ray diffraction studies indicated ‘lateral‐ordering’ consisting of hexagonally packed, rod‐like chains with no c‐axis order. The diffraction patterns obtained here were the ‘standard’ ones for PAN, in contrast to those observed previously in solvent‐containing PAN gels.

Processing of thermotropic liquid crystalline polymers and their blends—analysis of melt‐spinning TLCP fibers

AbstractIsothermal melt‐spinning of two thermotropic liquid crystalline polymers (TLCPs), a wholly aromatic copolyester KU‐9211 (also named K161 from Bayer AG) and an aliphatic containing TLCP, PET/PHB60 (Tennessee Eastman), was studied to analyze the effect of processing conditions on fiber properties. Fibers were melt‐spun from a capillary rheometer equipped with an isothermal chamber in which cross‐flowed air was used as the cooling medium. The processing variables studied included the extrusion temperature, the extrusion rate, the cooling conditions, and the draw ratio. As‐spun fibers were characterized by measuring storage moduli and molecular orientation parameters as a function of draw ratio under various processing conditions. Among the processing variables studied, the draw ratio was the primary factor in determining both the fiber modulus and the molecular orientation. The extrusion rate did not appear to affect the fiber properties within the range studied. The properties of K161 fibers were also dependent on the extrusion and cooling temperatures, while PET/PHB60 fibers were rather insensitive to the processing temperatures within data scatter and temperatures studied. A composite model based on a rigid‐rod rotation mechanism and the deformation of nematic domains in an elongational flow field was used to model the experimental results and was compared with other theories available. Conformance of data to the composite model was obtained by use of a single temperature dependent parameter n, suggesting that the rigid‐rod rotation mechanism could be used to predict the orientation development of TLCPs. The Halpin‐Tsai equations and the orthotropic equation for angular dependence were used to describe the elastic properties of the TLCP fibers.

Draw Texturing of Cationic Dyeable Polyester Yarn

We have studied the effect of texturing parameters such as draw ratio, ratio of disc surface speed to yarn surface speed (D/Y), first heater temperature, and heating contact time on various properties, including tensile strength, crimp characteristics, tight spots, and broken filaments. Dye uptake in terms of K/S and critical dissolution time are examined as a function of draw ratio and heater temperature. Cationic dyeable polyester (CDPET) is compared to normal polyester with respect to texturing behavior, and properties of the resultant yarns are reported.

CO2 permeability and amorphous fractional free‐volume in uniaxially drawn HDPE

AbstractThe CO2 permeability of uniaxially drawn high‐density polyethylene (HDPE) was investigated and drastic changes were observed as a function of draw ratio. An estimation of variations in both density and fractional free volume of the amorphous component in the drawn polymers was made on the basis of experimental data. The dramatic variations in permeability resulting from drawing were shown to be the consequence of changes of fractional free volume in the amorphous phase of the drawn polymer. Good correlation exists between measured solubility and diffusion coefficients of drawn samples and the estimated fractional free volume; this correlation agrees with the existing free volume theory for diffusion in polymers.

Deformation mechanisms during uniaxial drawing of melt-crystallized ultra-high molecular weight polyethylene

The crystal deformation mechanisms during solid-state uniaxial drawing of melt-crystallized ultra-high molecular weight polyethylene (UHMW-PE) film have been studied as a function of draw ratio. At higher draw ratios (λ≥3) the fine slip processes during uniaxial drawing of melt-crystallized UHMW-PE result in a single-erystal-like (1 0 0) [0 0 1] texture, whereas the normals to the lamellae are inclined by more than 45° with respect to the applied force. It is postulated that in melt-crystallized UHMW-PE the coarse slip process is predominantly restricted due to the fold plane restraints, preventing lamellae from breaking up and rotating with their normals towards the draw direction. The inclination of lamellar normals with respect to the draw direction prohibits further drawing because shear stresses act perpendicular instead of parallel to the lamellar normals.

Shear properties of some dental and other polymers

The shear modulus and elastic limit in shear were determined for a number of polymers of clinical interest, using a static torsion method. In particular, ultra-high modulus polyethylene was studied as a function of draw ratio, and compared with corresponding Young's modulus data. Materials of high shear moduli of potential clinical value are described.

Tensile properties of biaxially drawn polyethylene

The tensile properties of simultaneously biaxially drawn solution-crystallized ultra-high molecular weight polyethylene (UHMWPE) films were investigated as a function of draw ratio and were related to the data obtained for uniaxially drawn tapes. The Young's modulus of a biaxially drawn polyethylene film with a random in-plane orientation appears to amount to 3 8 of the Young's modulus of a tape drawn to the same extent uniaxially. Furthermore, the tensile strength is found to depend solely upon the draw ratio and not upon the drawing geometry since at the point of fracture the orientation in the film has become approximately uniaxial. These relationships are only valid for draw ratios ⩽10, whereas for draw ratios >10 the tensile properties of the biaxially drawn film are not significantly improved in contrast to those of uniaxially drawn tape.

Development of anisotropy in ultra-high molecular weight polyethylene

We report experimental measurements on the drawing behaviour of a pre-swollen drawn sample of ultra-high molecular weight polyethylene (UHMWPE). X-ray information is expressed in terms of an orientation function P 2( θ), and the increase in both P 2 and the tensile modulus are determined as a function of draw ratio. Scanning electron microscopy is used to follow the structural changes in the material. The experimental results are compared with a numerical simulation of the deformation and from these we suggest that early stages of deformation involve crystal orientation followed by subsequent chain extension at higher draw ratios.

Anisotropic mechanical properties of uniaxially oriented electrically conducting poly( p-phenylene vinylene)

The mechanical properties of uniaxially oriented poly( p-phenylene vinylene) film prepared by simultaneous thermal elimination and uniaxial extension of the poly(sulphonium salt) precursor have been measured both in the machine and transverse directions. The mechanical properties are anisotropic and dependent upon the degree of molecular orientation. Young's modulus varies between 2.3 and 37 GPa as a function of draw ratio in the machine direction and between 2.3 and 0.5 GPa in the transverse direction. The effect of chemical doping on mechanical properties has also been determined. A comparison between mechanical and electrical anisotropy in oriented samples has been made.

Biaxial drawing of dried gels of ultra-high molecular weight polyethylene

The fine structure and properties of ultra-high molecular weight polyethylene (UHMW-PE) films prepared by simultaneous biaxial drawing of the dried gel at 135°C were studied as a function of draw ratio. Scanning electron microscopy showed that the drawn films comprise fibrils which are several tens of nanometres thick and endlessly long. The fibrils are not straight along their whole length but entangled with each other. This is the most important structural feature of biaxially drawn UHMW-PE film. The small angle X-ray scattering peak corresponding to the long spacing disappeared at a certain draw ratio ( λ = 10 × 10). The differential scanning calorimetry (d.s.c.) measurements indicated that extended chain type crystals increase with increasing draw ratio. The crystallinity estimated by density, d.s.c. and infrared absorption was much less than that of uniaxially drawn materials, although it slightly increased with increasing biaxial draw ratio.

Macroscopic and crystallographic density of solid-state extruded polyethylene

The influence of draw ratio on macroscopic and crystallographic density of polyethylene with different initial morphologies, has been investigated by solid-state extrusion. An initial drop followed by an increase in macroscopic density as a function of draw ratio has been observed. Since precision X-ray measurements of unit cell parameters showed no variation of crystallographic density, it was concluded that plastic deformation of polyethylene upon drawing proceeds with a decrease of the degree of crystallinity. This was confirmed by differential scanning calorimetry.