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Aligned, uniform fiber matrixes are highly desirable in numerous engineering and physical science applications. Here, modified electrospinning (ES) deposition substrates (paired and in parallel) are explored to achieve rapid preparation of multiple topographies. Three ES substrates with well-defined geometries (rectangular, concave, and E-shaped) were investigated (arranged in parallel) for their impact on fiber size, morphology, orientation, and cell behavior. The results indicate fiber alignment and orientation can be improved and modulated based on the substrate geometry. In addition, altering the interdistance space between various parallel substrates has a clear impact on fiber diameter size and alignment (random, aligned, and perpendicular orientation). Electric field simulations based on substrate geometries show greater probable regions of aligned electric field vectors and distribution, which indicates the most likely deposition attributes of electrospun PCL fibers. Fibrous PCL membranes were biocompatible, and cell growth and guidance were along the fiber path, with evidence of branching at intersecting fibers for multiaxial fibrous topographies. These findings show that the substrate geometry can be optimized to effectively assemble multiaxial layered and well-aligned fibers in a controlled fashion, which is ideal to support several application developments dependent on fiber topography, integrity, and morphology. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 133, 44823.

The effect of accumulated deformation and deformation routes in the course of equal-channel multiple angular extrusion (ECMAE) on physical and mechanical properties of polyethylene (PE) differed in molecular mass (MM) has been studied. As deformation routes, route C (shear planes are parallel, and the simple shear direction of every deformation zone is changed through 180°) and route E (shear planes are turned through ±45° around the extrusion axis and the normal to the axis, and simple shear direction is changed through 180° or ±90° with respect to the deformation zone) were selected. It has been shown that ECMAE provides the increase of microhardness H, modulus of elasticity E, and tensile strength σT up to 4.5 times with strain at break eb staying practically at the level of eb of the initial material. The value of the effects achieved depends on MM, accumulated deformation and the selected deformation route. The best set of physical and mechanical characteristics was observed in the case of route E. The observed effects are related to the formation of a special orientation order and increased degree of crystallinity of extrudates. According to SEM data, route C results in mostly uniaxial orientation of macrofibrils at an angle of 35° to the direction of extrusion, and formation of a part of tie fibrils and macrofibrils oriented perpendicularly to the main orientation. The route E produces biaxial orientation of macrofibrils. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Chemiresistive polymer composite ribbons that function as chemical detectors were produced from solution-cast films of polymers and carbon composites. An array with multiple polymer sensor threads was exposed to dimethyl methyl phosphonate, a nerve agent simulant, and different interferents in the vapor phase. Principal component analysis was used to differentiate between the analytes. The response of the ribbon sensors as a function of the carbon composite and the host polymer source was investigated. The freestanding threads/sensors were mounted into a cell perpendicular to the gas flow to provide little pressure drop and were imbedded into fabrics to provide an example of a small, low-cost, wearable chemical sensor. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

The detaching process of two parallel surfaces glued together by a single polyethylene chain in vacuo was investigated with a steered molecular dynamics method. Various statistical properties were analyzed in detail, including the mean-square end-to-end distance; parallel and perpendicular mean-square radii of gyration; shape factor; segment density distribution; average percentages of the microstructure of the chain of the tail, train, bridge, and loop; average surface adsorption energy; average total energy; and average pulling force (〈f〉). All these properties depended strongly on the pulling velocity (v). There existed a peak in the curve of 〈f〉 as a function of the detaching distance. Further, the relation between the maximum value of 〈f〉 and v showed three distinctive regions: a region of weak dependence at v 6.50 A/ps. These investigations may provide some insight into the microcosmic principle of the failure process of polymeric adhesives. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

The effect of ultrasonic oscillations on the weld line strength of amorphous polystyrene (PS), polymethyl methacrylate (PMMA), and PS/PMMA (20/80, 50/50, 80/20) blends at various temperatures was investigated. By facilitating the molecular diffusion across the weld line, the introduction of ultrasonic oscillations could evidently improve the weld line strength of PS, PMMA, and their blends. The different effects on the weld line strength of PS/PMMA (20/80, 50/50, 80/20) blends were investigated. The ultrasonic oscillations could greatly increase the weld line strength of PS/PMMA (80/20) by ∼ 70%, but was less efficient to PS/PMMA (50/50, 20/80) blends, due to the great difference of weld line morphologies of these blends. The dispersed phase of PS/PMMA (80/20) in the weld line was spherical while two different morphologies in the weld line of PS/PMMA (50/50) were observed. And the stripe-like morphology of PS perpendicular to the flow direction in the weld line of PS/PMMA (20/80) is responsible for the little effect of ultrasonic oscillations. The fractured surfaces of PS, PMMA, and PS/PMMA (80/20) with weld line became much rougher due to the introduction of ultrasonic oscillations. The morphology study of PS/PMMA (80/20) showed that the spherical dispersed phase of PS/PMMA at the skin turned smaller under ultrasonic oscillations. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2990–2997, 2006

When a short fiber of a thermotropic liquid- crystalline polymer retracts in a quiescent, flexible polymer matrix, the polydomain texture inside the fiber evolves si- multaneously. We have demonstrated experimentally that the two processes are coupled. The dynamic interfacial ten- sion, determined from the retraction of the short fiber, de- creases with time. On the other hand, we have determined the aspect ratio of the polydomains inside the fiber through the power spectra of two-dimensional discrete Fourier trans- formations of polarized optical microscopy images. The polydomains are initially elongated and aligned with the fiber axis. As the fiber retracts into a spherical drop, the polydomains first retract into a circular shape and then are squeezed into elongated shapes perpendicular to the origi- nal fiber axis. An exponential function correlates the evolu- tion of the dynamic interfacial tension with that of the aspect ratio of the textures. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3114 -3120, 2006

Tensile properties are important basic characteristics of materials and influence their end-use and performance. More importantly, in the case of leather due to end-use applications such as shoe uppers, automotive and furniture upholstery, mechanical properties such as tenacity are of extreme importance. Therefore, fundamental studies on the tensile properties of leather are needed. In this study, an attempt has been made to examine the effect of gauge length (GL) on the tensile properties of shoe upper leather. Two different specimens in the form of rectangular and dumbbell shapes have been cut from parallel and perpendicular directions to the body axis of the leather and have been tested. Results showed that the maximum breaking load and the percentage extension at break decreased with the increase in GL. Rectangular specimens showed a 30% decrease in maximum breaking load and a 13% decrease in percentage extension at break, while dumbbell specimens showed reductions in the order of 28 and 6%, respectively, as the GL increased from 9.53 cm to 23.5 cm. Highly varying supramolecular architecture of the collagen matrix and the frictional slippage caused by the free ends present in the collagen fibrils, which induce a weak-link effect similar to the one found in cotton fibers and yarns, are considered to be the probable reasons for this behavior. A limited scanning electron microscopic study has been undertaken to pictorially represent the breakage of leather at different GLs. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1202–1209, 2006

A triblock copolymer consisting of hole-transport, electron-transport, and nanocluster-binding moieties was used in the fabrication of photovoltaic test devices. Depending on the casting solvent used in the device fabrication process, the morphology of the block copolymer in the devices was either an ordered, perpendicular cylindrical phase or a uniformly mixed homogeneous material. The photovoltaic action spectra of these two device types revealed clearly that the charge collection efficiency was influenced favorably by the microphase separation of the ordered system. Underlying mechanisms for these observations are discussed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3362–3368, 2004

The effect of fiber orientation on the tough- ening of polymers by short glass fibers generally below their critical length was investigated using specimens with either well-aligned or randomly oriented fibers. The fibers were aligned by an electric field in a photopolymerizable mono- mer, which was polymerized while the field was still being applied. These materials were fractured with the aligned fibers in three orientations with respect to the crack plane and propagation direction. Specimens with fibers aligned normal to the fracture plane were the most tough, those with randomly oriented fibers were less tough, and those with fibers aligned within the fracture plane were the least tough. The fracture behaviors compared favorably with predictions based on observed processes accounting for fiber orienta- tion. The processes considered were fiber pull-out (includ- ing snubbing), fiber breakage, fiber-matrix debonding, and localized matrix-yielding adjacent to fibers bridging the frac- ture plane. Fibers not quite perpendicular to the fracture plane provided the greatest toughening; these fibers pulled out completely and gave a significant contribution from snubbing. Fibers at higher angles provided less toughening, involving nearly equal contributions from pull-out, break- age, and debonding. Fibers within the fracture plane pro- vided the least toughening, involving debonding alone. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2740 -2751, 2003

The microstructure of compacted woven polypropylene cloths prepared at their optimum compaction temperature of 184°C has been examined. Details of transverse and longitudinal cross-sections have been revealed by permanganic etching and observed with scanning electron microscopy. The original cloth was found to contain perpendicular cracks and biconical defects reported previously in other systems. After compaction, the cloth bonded together to form a thick solid sheet, with a melting point raised for the residual material but reduced for the recrystallized component. The higher melting regions form a continuous three-dimensional network with linear traces in a longitudinal section, in agreement with recent observations of fiber structure. Recrystallization occurs both within and externally from tapes: where parallel tapes meet, transcrystalline layers emanate from tape surfaces, with a distinct line where the two growth fronts meet. In some more extensive recrystallized regions row structures are formed, probably indicating local flow during compaction. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 787–793, 2000

The comparative performance under repeated low mass pendulum impacts of glass–epoxy (G–E) composites, without and with the inclusion in the form of individual flexible foam sheet layer of either two numbers or three numbers at predetermined positions in the lay-up, is reported. Employing square cross-section test coupons, the orientation of the test specimen was changed with respect to the impact direction such that, in one case, the G–E part and the foam layers constituting the system was lying along the direction of impact in an edgewise manner; in the second case, the change was achieved by turning the specimen by 90° i.e., perpendicular (flatwise). The number of impacts causing specimen failure was noted in all the cases. While foam-free samples sustained a greater number of hits in the first set of experiments, foam-bearing ones performed better in the flatwise configuration. To interpret these observations, light macroscopic examination was conducted on the impacted samples. A correlation could be established between the macroscopic features and the impact results. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1565–1571, 1998

Films containing silver nanoclusters within a lamellar morphology were obtained via postprocessing reduction of the silver-containing regions of block copolymers synthesized by ring opening metathesis polymerization. Solution-cast films (0.1 mm thickness) of the block copolymer exhibited an oriented lamellar morphology with lamellar normals perpendicular to the film plane. The slightly anisotropic dielectric properties, perpendicular and parallel to the film plane, were investigated by direct measurement and by model calculations. The conductivity was highly anisotropic, differing by at least four orders of magnitude in directions parallel and perpendicular to the film plane. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 723–729, 1997

Mathematical modelling of physical and mechanical properties of plastic foam as well as numerous practical applications requires knowledge of foam structural characteristics. A necessity exists to determine the characteristics of the spatial structure of inhomogeneous materials comprising inclusions of other material, e.g., polyurethane foam without destructing the material and analysis of each element. A methodology is elaborated for preparing highly porous plastic foam specimens and investigation of foam strut-like structure with light microscopy (LM) by taking images in three mutually perpendicular planes. A mathematical model is developed for highly porous plastic foam for the determination of probability density functions of its building elements—polymeric struts': (a) length and (b) angles, using LM images in three mutually perpendicular planes. Computer codes are created and parameters of distribution functions for strut's length and angles are calculated using experimental data for verification. A good correspondence of the modelling results with experimental data is proved to exist. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39477.

The circular notch tip damage zone in biaxially oriented polypropylene has been analyzed using a thickness correction to the elastic stress distribution for a sharp-notched tension specimen. The size and shape of the damage zone as a function of applied stress followed a critical mean stress criterion, independent of specimen thickness. Also, the damage zone only grew while σ3 was greater than zero. Close observations of sections through the damage zone revealed that the circular zone, which consisted of many delamination crazes, had a distinctive pattern when viewed across the thickness difection. Large crazes grew into a triangular pattern with smaller crazes in between them. The shape developement of the triangular profile as well as the smaller crazes was explained using a stress-redistribution argument. The growth path of the delamination crazes in the x-z plane appeared to be in a direction perpendicular to the direction of σ3. © 1994 John Wiley & Sons, Inc.

Average residual stresses in polypropylene fibers, produced in a full-scale short-spin line, are estimated from the shift of the IR absorption peak at 975 cm-1. Linearly polarized incident IR radiation is used to separate between stress components parallel and perpendicular to the fiber axis. For all the fibers in this study, the axial stress component is larger than the average stress perpendicular to the fiber axis. Axial and perpendicular stresses are correlated with draw ratio and polydispersity index. For narrow molecular weight distributions (Mw/Mn < 4–5), the axial stress increases with increasing draw ratio. Average stress perpendicular to the fiber axis decreases with increasing draw ratio for all the molecular weight distributions in this study (Mw/Mn = 3–6). Measurements of residual stresses are consistent with other results characterizing molecular structure and mobility. An expression for estimating the stored deformation energy is discussed. © 1993 John Wiley & Sons, Inc.

Effect of shearing stress on reflective properties of cholesteric liquid crystal films is studied in this article. Heating up a glassy siloxane cyclic side-chain oligomer within the temperature range of the cholesteric (Ch) phase leads to the availability of its planar texture. Then, the received cholesteric liquid crystalline with planar texture is reoriented by shearing force quickly after it is taken off from the heater. The pitches change, and a pitch difference is induced by inhomogeneous distribution of stress. The SEM image indicates the pitch difference perpendicular to the substrates, and the results of transmission spectra show that the reflection bandwidth of the film obtained is broadened, and the central reflection wavelength of the reflective film moves. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

The density and pressure fields of a dilute polymer solution are nonuniform at the surface of a small sphere even when there is no fluid motion. The polymer solution is modeled by an ensemble of Hookean dumbbells. A hard core potential is assumed as the only interaction between the sphere and the macromolecules. The pressure field about the sphere is transversely isotropic. The perpendicular component of the pressure at the interface is greater than the isotropic pressure in the bulk of the fluid. The parallel component of the pressure at the interface is less than the bulk isotropic pressure. The surface adsorption (cf., surface pressure) and the film thickness vary with a parameter that is the ratio of the sphere radius, a, to the root mean square extension of the dumbbells, R0. The spherical results coincide with the plane wall results for a/R0 greater than approximately 100.

Optical anisotropy of polyimide films prepared from polyamic acid solutions was investigated by conoscopic observation and refractive index measurements. The conoscopic figure (crossed pattern) characteristic of a negative uniaxial crystal with its optic axis perpendicular to the film plane was observed for samples imidized on substrates. Uniaxial drawing of a polyamic acid cast film with 40 wt % solvent gave a highly oriented sample with an elongation of more than 80%. This sample had a conoscopic figure characteristic of a positive uniaxial crystal with its optic axis equivalent to the molecular c axis (parallel to the film plane). A large optical anisotropy (bire-fringence 0.18) was observed in the film plane. The TE-mode refractive index (parallel to the film plane) ranged from 1.64 to 1.82 at a wavelength of 633 nm according to the sample rotation. These values corresponded to the refractive indices perpendicular and parallel to the c axis, respectively. The optical system change of the polyimide film was explained in terms of the uniaxial orientation of the in-plane oriented molecular c axis.

Three experimental poly(ethylene terephthalate) fibers have been spun and then drawn at three different temperatures(70°C, 90°C, and 110°C) in such a way that the drawn fibers possess different orientations and crystallinities but retain the same diameters. Wide angle X-ray diffraction and birefringence measurements have been used to characterize orientation and crystallinities of the fibers. The influence of fine structure on the torsional fatigue behavior of the melt spun and drawn PET fibers has been studied by subjecting them to 1.7 Hz torsional cyclic deformation at various amplitudes. Fracture morphology was found to be strongly influenced by the degree of orientation and crystallinity. Highly oriented and crystalline structures tended to separate into a highly fibrillated structure. Fibers of low draw ratio exhibited initial deterioration of the surface structure with the generation of transverse cracks (perpendicular to the fiber axis). Subsequent torsional loading of the structure generated an increase in longitudinal cracks which finally resulted in the catastrophic failure of the fiber. The extent of fibrillation was found to be a function of draw ratio (orientation) and crystallinity. The amplitude of torsional strain was also found to have an effect on the intensity of fibrillation and the number of cycles to fiber failure.

For polytetrafluoroethylene (PTFE) films drawn uniaxially at 100, 150, 250, and 350°C, the morphology and degree of crystalline orientation were investigated by electron scanning microscopy and wide-angle X-ray diffraction, respectively. On the surface of the PTFE films which were heat-treated at 350°C for 2 h before the drawing, granules with a diameter of about 2 μm and bands with a width of about 0.3 μm were observed. By the drawing below the melting point, the bands are transformed into fibrils and a porous structure is formed by the drawing above the draw ratio (λ) of about 1.3. By drawing above the melting point, striations appear perpendicularly to the draw direction, and the collapse of the granules is observed. The orientation of the crystallites increases rapidly with increasing the draw ratio and approaches a plateau at λ ≈ 1.5 for the films drawn above the melting point and at λ ≈ 2.0 for that below it.

The manner in which diethyl phthalate (DEP) is absorbed into nitrocellulose (NC) fibers has been observed microscopically. The movement of pure DEP into dry fibers proceeds by capillary motion up the central canal (lumen) and through microcracks between fibrils. Attack, measured by a large change in birefringence, spreads from these foci, and within the time scale of the experiment there is little interaction with the primary (outer) wall of the fiber. If, however, the lumen and other capillary passages are blocked by water or other liquid, then attack proceeds evenly from the outer wall and a sharp boundary between swollen and unswollen material moves at a uniform speed towards the center of the fiber and appears to be unaffected by the fibrillar structure (Case II swelling). If the supply of DEP to the surface is interrupted, this boundary becomes immobile, and the concentration of DEP in the swollen layer is that which is just sufficient to saturate residual un-nitrated hydroxyl groups on the NC. Reducing the activity of the DEP by admixture with benzene results in similar sharp boundaries, presumably because capillaries become blocked with spent diluent. Apart from capillary action, movement is always perpendicular to the fiber axis.

Oriented atactic polystyrene monofilaments show brittle-to-ductile transition in the vicinity of a degree of birefringence Δn = −2 × 10−3 (at a temperature of 20°C and at the stretching rate of 100%/min) independently of the various spinning conditions. The amorphous orientation of a cylindrically symmetric system was investigated by wide-angle x-ray scattering experiments. The orientation of polystyrene monofilaments in real space is denoted by P2(cos α) within the precision of measurement. The coefficient D2(r) of the second term in an expansion of cylindrical distribution function in spherical harmonics has two main peaks, near r = 1.6 A and r = 4 ∼ 5 A. The negative peak near r = 1.6 A indicates orientation of phenyl groups in a plane perpendicular to the fiber axis. The positive peak near r = 5 A (brittle region) or near r = 4 A (ductile region) indicates the piling up of phenyl groups for the direction of the fiber axis. It is most probable that the amorphous state of atactic polystyrene consists of an appropriate cohesion of planar zigzag chains of syndiotactic polystyrene. The lower spacing (r = 4 A) of the positive second peak in ductile region suggests that there are interchain phenyl groups near r = 5 ∼ 6 A in a plane perpendicular to the fiber axis and that the molecular chains are extended parallel to the direction of the fiber axis. This parallel packing of chain segments along the fiber axis suppresses the formation and growth of cracks of polystyrene monofilaments resulting in ductile fracture.

Wear behavior correlations with morphology and orientation directions have been established from commercially produced nylon 6 with different draw ratios between 1 and 7 approximately. The wear rate is least in a direction perpendicular to the draw direction for highly drawn samples. It correlates with surface microstructure and the inherent molecular characteristics induced by sample preparation. Well-characterized polymer specimens were used in this investigation.

A quantitative model for fitting infrared spectra of polyethyleneterephthalate samples over the region from 1100 to 720 cm−1 has been evaluated. The absorbance was described as the sum of a linear base line and a set of symmetrical bell-shaped Pearson VII curves. Using this model, experimental transmission spectra of yarns, measured with the electric vector parallel and perpendicular to the fiber axis, were fitted. It was found that each of the trans bands near 972 and 845 cm−1 consists of two components, a narrow and a broad one. These two components represent the crystalline and amorphous phases respectively. The band due to the out of plane benzene ring CH deformation vibration at about 875 cm−1 appeared also to be composed of two contributions. In this case, the narrow component was found to be due to molecules having interactions with direct neighbors. So this narrow component not only contains the molecules in the crystalline phase but also those forming part of bundles which are too small to be detected by x-ray diffraction. For a detailed insight into the molecular arrangement of the amorphous regions, the infrared detection of trans-guache transitions, fold content, detection of bundlelike structures, and molecular stress on tie molecules turned out to be of great practical importance. The structural details, which can be revealed by the infrared technique, cannot be obtained by other means. The potential of the method is illustrated with some practical examples.

The breaking mechanism of nylon-6 yarn is investigated, and the breakage of the yarn under simple tensile loading conditions is compared to that of a filament caused by the same loading. The simple model yarn consisting of seven filaments was prepared for this purpose. The yarn was ruptured at a low rate of extension, and the fracture morphologies of the filaments in the yarn were inspected by a scanning electron microscopy. These morphologies are clearly different from those of the filaments broken individually under the same testing conditions used for the yarn. Various kinds of appearances are obtained in the yarn, for example, a large V-shaped notch is observed, the controlled ductile tearing region is developed across the filament at a large angle to its axis, and the ruptured end is expanded into a plane which is perpendicular to its axis. These causes are discussed in detail to understand the breaking mechanism of the yarn.

The molecular orientation distribution of injection-molded polycarbonate discs is studied using birefringence and heat-shrinkage measurements and laser-Raman spectroscopy. Birefringence and heat shrinkage, which result from the molecular orientation, increase as the distance from the inflow gate decreases and as cylinder temperature decreases. Molecular orientation is reduced following annealing. Laser-Raman spectroscopy is used to measure the molecular orientation distribution along the disc cross-section perpendicular to the radial direction of disc. The relative intensity ratio for the 635 cm−1 and 703 cm−1 peaks in the Raman spectra correlate well with the degree of molecular orientation. The disk cross-section is found to consist of three different molecular orientation zones; a skin zone which is in contact with the mold, a core zone located at the center, and a shear zone between the skin and the core zones. Molecules in the skin zone are nonoriented while the orientation of molecules in the core zone is considerably relaxed. The shear zone consists of highly oriented molecules. The formation process of the molecular orientation distribution is discussed in relation to birefringence and heat shrinkage.

An absorption band found at 974 cm−1 in the infrared spectra of “amorphous” nylon 6 films has been assigned to CH2 wagging or twisting vibrations in molecular chain folds. Annealing amorphous films in air at increasing temperatures up to 150°C has been shown to induce a steady increase in the intensity of the absorption band at 974 cm−1. Annealing at higher temperatures resulted in a sharp decrease in intensity up to an annealing temperature of 210°C. This sharp decrease coincided with a sharp increase in the long period determined by low-angle x-ray diffraction studies. Drawing amorphous films has been shown to induce a decrease in the intensity of the band at 974 cm−1. Polarized infrared investigations of amorphous drawn films revealed that the band at 974 cm−1 was strongly perpendicular in character. Treatment of amorphous films in water induced no frequency change in the band at 974 cm−1.

It is shown that in [η] = KMa there exists a relationship between K and a of the form log K = C − Ba. The parameters C and B are typical of each polymer and, under θ conditions, define a characteristic Kθ for the polymer. When plotted against m0/z, the molecular weight per backbone atom, the values of log Kθ cluster along three distinct lines. In a fashion similar to the observed dependence of number of atoms between chain entanglements on m0/z, the lines are associated with highly flexible polymers, intermediate flexibility polymers, and stiff chain polymers. Deviations from the intermediate flexibility line are explained on the basis of changes in the distribution of mass in the plane perpendicular to the overall direction of the backbone chain.

A study of the plastic zones created around the tips of cracks in glassy polymers, under small scale yielding, can be confronted by using the two well-known pressure-modified yield criteria and the elastic solution of the problem. There is particular interest in the case of a cracked body reinforced by another more resisting body under plane-strain conditions. The shapes of plastic zones developed around the tips of the crack subjected to opening mode loadinng conditons are examined as the crack approaches perpendicularly the bimaterial interface. For the study of plastic zones the exact solution derived from Muskhelishvili's complex potentials was used. Moreover, the plastic zones are confronted using either the exact solution or Sneddon's asymptotic expansion.

The local structure in the radius direction perpendicular to the fiber axis in nylon 6 gut yarn subjected to twisting and heat setting was investigated by the microbeam x-ray technique. The observations revealed that the b-axis (or chain axis) in a crystal gradually inclines within a tangential plane parallel to the fiber axis and away from it with increase of twist, not only in the outer region but also in the center region, i.e., in the vicinity of the center axis. This local behavior of the b-axis could not be distinguished in the previous work,1 when the usual collimator was employed in the WAXD technique.

Double oriented polyethylene and polypropylene specimens have been investigated for a wide range of draw ratios. Wear behavior was measured in three mutually perpendicular directions using specimens characterized mechanically and morphologically. Density, crystallinity and other correlations were established with draw ratio and wear behavior providing some novel results.

The refractive indices, birefringence, and cross-sectional area of cotton fibers was measured using interference polarizing microscope constructed by M. Pluta. A new technique was suggested by realizing the measurements at the perpendicular position of the duplicated image of fiber to the interference fringe. The proposed procedure is a combination of modification of Hamza method and Pluta dual wavelength method, and it was possible to measure at once the three mentioned features of single fiber at one time.

An experimental study of the spinnability and the variation in crystallinity and orientation in high-density and low-density polyethylene fibers with melt spinning and drawing conditions has been carried out. Three polymers (two high-density and one low-density) and eicosane (C20H42) were studied. The maximum spinnability was in the lower molecular weight high-density polyethylene. Hermans-Stein a, b, and c crystallographic axis orientation factors were computed from wide-angle x-ray scattering patterns. In the spun fiber, small take-up velocities cause the b axis to become perpendicular to the fiber axis in each fiber. The c axis increasingly orients itself parallel to the fiber axis as take-up velocity increases. The a axis orientation is different for each polymer. The results are interpreted in terms of modern theories of crystalline morphology, specifically the development of row structures. In the drawing experiments, the two high-density polyethylenes necked. A phenomenological theory of necking is discussed. The a, b, and c axis orientation factors were determined for different stages of drawing. In the necked regions and in completely drawn fibers, the c axis was parallel to the fiber axis and the a and b axes are perpendicular to the fiber axis. The tangent Young's modulus and tensile strength of the spun fibers increased with take-up velocity and in the drawn fibers were an order of magnitude higher than in the spun fiber. The mechanical properties of spun fiber may be correlated with the c axis (Hermans) orientation factor. The drawn fiber shows significant variations in Young's modulus and tensile strength at constant unit cell orientation.

Instruments and techniques for measuring the shear and longitudinal ultrasound velocity through paper in the Z-direction (perpendicular to the plane of the sheet) are described. The fundamental problems in determining elastic properties with ultrasound on thin, rough, fibrous samples are analyzed. Limits are set on sample characteristics, which will assure that the Z-direction velocity measurements are reasonable indicators of Z-direction elastic properties. Data taken over a range of frequencies, pressures, and surface characteristics are presented and analyzed in terms of our concepts of Z-direction wave propagation in paper.

Deformation mechanism of poly(p-phenylene terephthalamide) (PPTA) fiber during axial compression was studied. PPTA fibers were embedded in resin and axialy compressed in a tensile machine. PPTA fibers were then taken out from resin at various stages of compression. Kink band formation was examined by means of polarizing microscopy, X-ray diffraction (WAXD), electron diffraction (ED), and electron microscopy. WAXD pattern of seriously compressed PPTA fiber shows that (200) reflection spots and arcs appear on the equator and meridian respectively. On the other hand, (110) reflection spots are confined to the equator. PPTA fiber could be splitted tangentially and radially into two kinds of thin fibrillar fragments (I and II) which reveal two distinct types of kink band and ED pattern. In fragment I obtained by tangential splitting, kink bands are formed at about 55° with respect to fibril axis, whereas in fragment II obtained by radial splitting kink bands are formed perpendicular to the fibril axis. These results were confirmed by ED studies. It was assumed that slip of (200) planes containing hydrogen bonded sheets as well as intermicrofibril slip plays an important role in the deformation of PPTA fiber during axial compression.

Chopped strand mat and glass-fabric-reinforced thin and thick laminates were made from phenolic and polyester laminating resins using three modifications of a hand lay-up method. Short-beam interlaminar shear strengths were determined in three-point bending at a span-to-depth ratio 3:1. Plane and perpendicular specimens were used. It was found that the perpendicular specimens were more useful. Interlaminar delamination energies were determined statically and dynamically. It was found that the results for the phenolic and polyester laminates cannot be simply compared because of differences in the fracture mechanism.

The machanical anisotropy of several thermoplastic polymers has been investigated, and the relationship with a practical dart drop impact measurement has been explored. It has been shown that the unnotched Izod impact strength of a specimen taken perpendicular to flow orientation can be correlated with the dart drop impact strength. Further, the effect of several dart drop test variables, such as drop height, dart tip radius, and specimen size, have been investigated and reported. It has been concluded that the conventional strength measurement of injection-molded specimens may lead to erroneous appraisal of the practical strength of a material. Testing at an orientation normal to flow or by multiaxial stressing as in a dart drop test is suggested.

A polypropylene film was stretched at 100–160°C., quenched to room temperature, and then restretched at the same temperature perpendicularly to the first stretching. The reorientation behavior was investigated by using optical and x-ray methods. During the restretching the monoaxial orientation caused by the stretching is converted into a new monoaxial orientation through a balanced state, where npp = nps < nss. The more or less parallel orientation to the film surface of the polypropylene molecules, brought about by the first stretching, proceeds further on restretching. nss is a linear function of the degree of stretching in area vA. The inclination of this line is independent of the type of deformation, stretching, or restretching, provided the temperature is kept constant. At 160°C. the plot of nss versus thickness is less steep than it is at 100 or 130°C. The overall reorientation apparently proceeds according to Kratky's first deformation law. The x-ray pattern of a restretched film is a four-point diagram which indicates the existence of a pair of reorientation axes inclined symmetrically against the stretching axis. The inclination grows larger with restretching, and the axes merge into the restretching axis at extreme restretching. This phenomenon is less pronounced when the restretching is carried out at higher temperatures. The density of the restretched film is determined mainly by the stretching temperature, but extreme restretching has a tendency to lower it very slightly.

Crystallization and orientation of isotactic polypropylene film by stretching were investigated. The specimen used was a film of thickness 0.03 mm. and had ca. 30% crystallinity in the initial state. It was observed both by x-ray examination and measurement of density that the crystallization of the stretched film increased proportionally to the stretching ratio. And it was confirmed that a quasi-crystalline structure was already developed in the low stretching ratio coexisting with the ordinary stable crystalline structures. This quasi-crystal structure can be easily transformed into the ordinary stable state at above 100°C., as well as the quasi-crystal structure in melt spinning filament, as described in a previous paper. It was also confirmed that the ordinary stable crystalline part was biaxially oriented by high stretching at room temperature, that is, (110) plane of the crystallite was preferentially oriented perpendicular to the surface plane of the film in the cross section perpendicular to the stretching axis. This phenomenon was elucidated from both the cohesive interactions between lattice planes and the compressive stress in the stretching process.

The complete orientation distribution of the a and b crystallographic directions have been measured for a series of tubular extruded polyethylene films as a function of blow ratio. The use of pole figures as a means of representing orientation is emphasized and it is shown that the usual technique of using flat plate x-ray diffraction photographs can lead to erroneous conclusions. Increasing the blow ratio has a distinctly different effect upon the orientation of high density polyethylene film in comparison with low density polyethylene film. In contrast with previously published information our results clearly indicate that the c axis does not orient preferentially perpendicular to the extrusion direction. In particular, it is shown that one cannot in general deduce the maximum in the orientation distribution of the c axis from qualitative estimates of the a and b axes distributions. The ultimate tensile strength, elongation, modulus and tear strengths of these films were measured and the results correlated with the orientation of the crystallo graphic directions.

A discussion of the methods for studying orientation of crystalline and amorphous regions in polyethylene films is given. Extruded polyethylene films and films after having been stretched approximately 200% were studied by the methods of x-ray diffraction and absorption of polarized infrared radiation. It is shown that in extruded polyethylene films the a-axes of the crystallites are oriented parallel to the extrusion direction. The amorphous regions in these are either not oriented or show only to a slight degree the orientation of chains perpendicular to the extrusion direction. When the polyethylene films are stretched, both the crystallites and the amorphous regions become oriented. In stretched films, the orientation of the crystallites is with c-axis parallel to the stretching direction, and the chains in the amorphous regions are also oriented parallel to the stretching direction. Two mechanisms by which a-axis orientation may arise during extrusion of polyethylene films, and a convenient method for determining the relative degree of a-axis orientation in polyethylene films are given. The relative degrees of a-axis orientation as determined by x-ray diffraction and dichroism of absorption at 13.70 μ are compared for a number of film samples.

The anisotropic characteristics of injection-molded flat rubber sheets were investigated. The shrinkage and mechanical properties were measured in two directions: parallel and perpendicular to the flow direction. The results showed that (1) the shrinkage in the parallel direction is larger than that in the perpendicular direction, (2) such anisotropic shrinkage increases with the increase of vulcanization temperature and flow distance, (3) similar anisotropy was also noticed in 300% modulus, tensile strength, and elongation. Two kinds of orientation, “shear orientation” and “expanded orientation,” were observed. The former occurs by plug flow, and the latter by the expansion of the materials. The shrinkage was independent of the expanded orientation but was strongly associated with the shear orientation, while the mechanical properties were affected by the expanded orientation.

Lattice spacings perpendicular to the molecular chain axes and crystallite orientation of dried and moist (boiled in water) bulk nylon 6 were determined by x-ray diffraction under tension of 30–300 kg./cm.2. The deformation of the specimen was also measured. The lattice spacings are changed reversibly by the presence of water in nylon 6, but the elastic moduli of the lattice are not affected. The lattice elastic modulus in the direction of the hydrogen bonds is approximately double its value in the direction normal to the hydrogen bonds. The elastic modulus of the dried nylon 6 approaches the value of the lattice elastic modulus in the direction normal to the molecular axes, while the modulus of the moist nylon 6 is several times lower. From these facts, and especially from the relations between the lattice deformation, crystallite orientation, and specimen deformation, the principal differences in the deformation mechanism of dried and moist nylon 6 were deduced. The results obtained have also made possible some general conclusions about the crystalline structure of nylon 6 and the deformation mechanism of linear polymers.

A description of methods available for the determination of structural parameters in nylon 66 is given for both wide- and small-angle x-ray diffraction. The methods are applied to a series of drawn nylon 66 fibers, and the results indicate that the drawing process is one of crystal slip. It is concluded that the methods of characterization give a great deal of information about the structure along the fiber axis but that methods for examining the structure perpendicular to the fiber axis give less quantitative information and new methods are desirable.

Low density rigid foams, reaction products of polyether polyols with tolylene diisocyanate, may transmit moisture vapor at rates from 0.3 to more than 8 perm-inches at 23°C. Analysis of experimental data provided conservative design correlations showing that rate constants could be predicted only when a foam's polymer composition and physical structure were considered jointly. Among commercially acceptable rigid foam systems, cell structure and polymer aromaticity dominated the control of permeability levels. Permeabilities were lowest when transfer was directed perpendicular to the rise of highly orthotropic closed-cell foams based on aromatic polyols of low equivalent weight. Permeabilities increased with effective cell diameter and also as foam density and closed-cell content were reduced.