High Molecular Orientation Research Articles

Enhanced Mechanical Performance of Self‐Bundled Electrospun Fiber Yarns via Post‐Treatments

AbstractA new route to high‐performance electrospun polymer fibers was developed using a self‐bundling electrospinning technique combined with post‐treatments such as stretching and annealing under conditions similar to those used for conventional fibers. Self‐bundled electrospun PAN fiber yarns were characterized by SEM, mechanical tests, polarized FT‐IR spectroscopy and WAXD. The obtained results revealed that the PAN nanofiber yarns possessed enhanced alignment, a higher degree of crystallinity and higher molecular orientation after treatments, resulting in a remarkable improvement in mechanical performance, approaching the strength value of the corresponding conventional fibers.magnified image

Development of Bicomponent Spunbond Nonwoven Webs Consisting of Ultra-fine Splitted Fibers

Abstract Development of bicomponent spunbond nonwoven consisting of ultra-fine splitted polypropylene (PP) and polyethylene (PE) fibers was described. The morphological structures developed in bicomponent spinning of PP/PE fibers with the cross-sectional configuration of “sixteen-segment hollow pie” were investigated in relation to molecular properties as well as the resulting fiber splittability. Structure developed in each component in the melt spinning process was found to depend not only on its molecular properties but also on those of the other component. Results showed that the PP/PE pair exhibiting good splittability possesses high molecular orientation in both components.

Effect of orientation and crystallinity on the photodegradation of poly(ethylene terephthalate) fibers

AbstractIn this research, photodegradation of poly(ethylene terephthalate) (PET) fibers was investigated with emphasis on the morphological state of yarns. Two kinds of yarns, FDY (Fully Drawn Yarn) and POY (Partially Oriented Yarn), with different molecular orientation and crystallinity were applied in this research. FDY is spun in the same way as POY and subsequently drawn at high speed and then entangled before winding up. This sample has higher molecular orientation and crystallinity than the POY sample. Several analytical methods were applied in this study: viscometry, X‐ray diffraction, FTIR spectroscopy, UV–Visible spectrophotometry, and mechanical testing. Viscometry was used to determine molecular weight as a monitoring factor for degradation. X‐ray diagrams showed higher crystallinity for FDY samples during weathering process by irradiation. Results of mechanical testing indicated that the tenacity of the FDY fibers had less deterioration in comparison with the POY ones. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

Preparation and characterization of biaxially oriented polypropylene film with high molecular orientation in the machine direction by sequential biaxial stretching

AbstractNovel approach of applying the ternary polymer blend of long‐chain branched polypropylene (LCB‐PP), conventional polypropylene (PP), and hydrogenated polydicyclopentadiene (hDCPD) has been employed to tensilize biaxially oriented polypropylene (BOPP) film in the machine direction (MD) by successive sequential biaxial stretching method. It is found that the addition of LCB‐PP improves the MD stretchability of the BOPP film of PP/hDCPD blend. Depending on the content of LCB‐PP, LCB‐PP/PP/hDCPD ternary blend could be biaxially stretched up to the MD stretching ratio (MDX) of 12 without film breakage whereas that of PP (conventional BOPP film) resulted in the MDX up to 6. This excellent MD stretchability enabled to tensilize the BOPP film in the MD, where Young's modulus in the MD could be increased up to 4.9 GPa, twice higher than that of conventional BOPP film. The orientation of total molecular chains and that of crystalline molecular chains were evaluated by in‐plane distribution of refractive indices and wide‐angle X‐ray diffraction, respectively. The results are discussed from the viewpoint of deformation behavior during stretching process. Moreover, the resultant film had a dimensional stability substantially equivalent to that of conventional one, in spite of the higher stretching ratio, and an improved moisture barrier property. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Effect of silicon on the formation of silk fibroin/calcium phosphate composite

The silk fibroin/calcium phosphate composites were prepared by adding the different amount of Na(2)SiO(3) to assess the effect of silicon on the HA (hydroxyapatite) formation in the composites. FTIR and XRD results suggested that the inorganic phase was constituted mainly by the amorphous DCPD (dicalcium phosphate dehydrate), a precursor of HA in the bone mineral, when the composites were prepared at the final Na(2)SiO(3) concentration lower than 0.008%. Otherwise, HA was formed as the predominant one in the as-prepared composite, accompanied with a conformational transition in the organic phase of silk fibroin protein from silk I (alpha-helix and/or polyglycine II (3(1)-helix) conformations) to silk II (antiparallel beta-sheet conformation). SEM images showed the different morphologies with the samples, i.e., sheet-like crystals in the composites prepared at a low Na(2)SiO(3) concentration and rod-like bundles in other composites. The rod-like bundles were connected together to form the porous network, due to the fact that the HA crystals grew with the aggregation of silk fibroin, and further accreted onto the silk fibroin fibrils. TG curves indicated that the composites prepared with a certain amount of additional SiO (3) (2-) had the higher thermal stability because of its high molecular orientation and crystallinity, and high water-holding capacity due to the porous microstructure.

Mechanical Evaluation of Thermal Transitions in Polymer Nanofibres Using SPM

AbstractPolymer nanofibres produced by electrospinning techniques have unique mechanical properties due to their large surface area to volume ratio and potentially high molecular orientation. The effects of temperature on mechanical properties is challenging to measure due to the small fibre diameters produced. In this paper, scanning probe microscopy (SPM) is successfully used to elucidate the mechanical performance of individual electrospun polyvinyl alcohol (PVA) nanofibres over a range of temperatures. As observed in the results, thermal transitions have a dramatic effect on the mechanical behaviour of the nanofibres and are highlighted using SPM techniques analogous to dynamic mechanical thermal analysis but at the nanoscale. Interestingly, nanofibre thermal transitions are shown to be mediated by fibre diameter and the driving force of reducing the surface area of the nanofibre.

Does fountain flow influence molecular orientation in injection moulded parts?

Simulations of the isothermal and non-isothermal filling of a rectangular cavity were carried out for polystyrene using a Giesekus viscoelastic constitutive equation, whereby in the non-isothermal case the thermal resistance at the mould wall was modelled with different heat transfer coefficients to investigate the effect of the thermal resistance on the development of the molecular orientation. Results for stress development along the flow front and the cold wall were compared showing that the principal stress differences in the middle of the flow front are lower than those at the mould wall. In case of the non-isothermal filling, the latter one will increase further while the melt is gradually cooling down, which is especially true if the thermal resistance at the mould wall has been properly considered. Consequently, the high molecular orientation at the wall seems to be rather a result of the non-isothermal shear flow than of the extension at the advancing front as usually assumed.

Modeling of Flow-Induced Crystallization of Particle-Filled Polymers

We present a study on flow-induced crystallization of polymers filled with rigid particles. The numerical simulations reveal the interplay between filler particles, the polymer melt, flow, and flow-induced crystallization. Both crystallization kinetics and the resulting crystal orientation are affected, and they are crucial for the material properties that are created during flow. In the analysis of the problem, first a direct 2D numerical simulation technique for viscoelastic particle suspensions is applied to determine the local molecular conformation during the flow. Subsequently, we use this conformation as the driving force for flow-induced crystallization. Local anisotropic crystalline structures are formed due to high molecular orientation, especially near the particles. Because of the presence of the same particles, regions of the melt are shielded from the flow, and therefore, hardly any effect of the flow is seen in these regions. Both coupled and decoupled simulations were performed. In the last approximation the flow problem is solved using a generalized Newtonian viscous fluid model, and the velocity gradients obtained are plugged into a viscoelastic constitutive model that provides the molecular conformation. It is found that the decoupled method gives incorrect results, especially with respect to the molecular and crystalline structure orientation.

Fabrication and photoresponse of novel carboxymethylcellulose (CMC) based bacteriorhodopsin (bR) sensor

A single-pixel dry-type reconstituted bacteriorhodopsin (bR) sensor (Au/CMC + bR/ITO) incorporating carboxymethylcellulose (CMC) as the artificial membrane is fabricated according to a protocol developed to investigate signal acquisition from the proposed biosensor. Droplets of reconstituted purple membrane (PM) containing bR applied onto a gel-like solution of CMC placed on gold electrodes (anode) are allowed to dry under an electric field, utilising the PM fragment’s net negative charge and electric dipole moment. The resulting bR matrix thin film with high molecular orientation is finally sandwiched together with a semi-transparent indium titanium oxide (ITO) counter electrode and proper electrical connections made to form a single pixel bR-CMC photosensor. Efficient and reproducible photoresponse observed upon illumination clearly exhibits the potential of the proposed biosensor for future photosensing works.

The microstructure of a polyethylene terephthalate matrix near to a void under uniaxial draw

Under the appropriate conditions, a void can generate within a polymer matrix, when it is subjected to large strains. In this work, the local microstructure of a polyethylene terephthalate (PET) matrix near to such a void was studied through the use of a model system. The approach adopted was to mimic the void growth as a function of uniaxial stretching using a macroscopic sample of PET film, and evidence suggests that the PET matrix around the model void does possess structural features similar to those of a PET matrix which surrounds a microscopic void. Two separate but complementary methods, namely numerical prediction and direct measurement, were employed to characterise the matrix immediately adjacent to the void. The structure of the PET matrix was predicted by combining a previously established relationship between strain and molecular orientation, and strain distribution measured on the model sample, while direct measurements were performed using infrared and Raman spectroscopy. The results obtained demonstrated that a very varied and complicated structure exists in the material immediately surrounding a void, which is formed as a result of stretching. Uneven deformation due to expansion of the void results in a shell of polymer of high molecular orientation and crystallinity at its boundary. On continued drawing, the shell resists further deformation leading to a slower rate of void growth.

External Calibration in PA12 Tube Extrusion

AbstractIn polyamide 12 (PA12) tube extrusion, calibration is crucial for the major final properties such as elongation at break or burst pressure. In external calibration, the extruded tube is pulled through a cylindrical calibrator located in a water tank under vacuum. A water flow rate is applied at the calibrator inner side, creating a lubricating water layer at the polymer outer surface. A combination of a quenching and a mechanical drawing was highlighted during calibration by on-line measurements. A subsequent high molecular orientation in the outer tube layers was also featured by X-Ray diffraction and birefringence evaluation in light microscopy. Besides, influence of lubrication level in the sizing-sleeve was investigated by an estimate of the lubricating water layer and a characterization of the tube final surface state in different calibration conditions. Firstly, we quantitatively showed that rising the water layer thickness leads to a diminution of the draw ratio in the calibration tank, DrCAL (ratio between line velocity and velocity at the calibrator entrance). Excellent correlation has been found between tube superficial orientation and DrCAL: a reduced elongation of the polymer in the calibrator leads to a lower level of superficial orientation. Secondly, two kinds of surface defects were detected on the tubes by light microscopy and microtopography. At last, several correlations were featured with mechanical properties. Elongation at break was found to strongly depend on the molecular orientation resulting from calibration. Moreover, origin of rupture was investigated during tensile testing in light microscopy. We emphasized that surface defects alignments perpendicular to the extrusion initiate the rupture by creating a significant crack via coalescence of initial defects. Thus, microstructure, surface state and tensile properties can be controlled by fitting the calibration parameters to improve lubrication and reduce the draw ratio in calibrator.

External Calibration in PA12 Tube Extrusion

In polyamide 12 (PA12) tube extrusion, calibration is crucial for the major final properties such as elongation at break or burst pressure. In external calibration, the extruded tube is pulled through a cylindrical calibrator located in a water tank under vacuum. A water flow rate is applied at the calibrator inner side, creating a lubricating water layer at the polymer outer surface. A combination of a quenching and a mechanical drawing was highlighted during calibration by on-line measurements. A subsequent high molecular orientation in the outer tube layers was also featured by X-Ray diffraction and birefringence evaluation in light microscopy. Besides, influence of lubrication level in the sizing-sleeve was investigated by an estimate of the lubricating water layer and a characterization of the tube final surface state in different calibration conditions. Firstly, we quantitatively showed that rising the water layer thickness leads to a diminution of the draw ratio in the calibration tank, DrCAL (rati...

Molecular Orientation Distributions in the Crystalline and Amorphous Regions of Uniaxially Oriented Isotactic Polypropylene Films Determined by Polarized Raman Spectroscopy

Molecular orientation distributions in both the crystalline and amorphous regions of uniaxially oriented isotactic polypropylene (it.PP) films were determined by polarized Raman spectroscopy. By comparing polarized Raman scattering intensities of a highly oriented film for different polarization scattering geometries, the form of Raman tensor was determined for the Raman bands of it.PP. Orientation distribution coefficients, P l00, for the Raman bands were combined with the results of wide angle x‐ray diffraction (WAXD) and birefringence measurements in order to determine their tilt angle, Ω, which is the angle between the principal axis of a Raman tensor and the molecular chain axis. The angles, Ω, were determined for the first time for Raman bands assigned to both the crystalline and amorphous regions. It was shown that the molecular orientation distributions in the crystalline regions and in the amorphous regions can be determined fully by polarized Raman spectroscopy, once the tilt angle, Ω, was obtained first for a Raman band assigned to the crystalline regions only and then for one assigned to both the crystalline and amorphous regions. The study of uniaxially oriented it.PP films with different sample draw ratios (DR) revealed that the development of high molecular orientation in the crystalline regions took place up to DR=7.5. Compared to the crystalline regions, a lower degree of molecular orientation was observed in the amorphous regions, and there was a slight increase of molecular orientation above DR=7.5. Dedicated to Professor John L. Stanford on the occasion of his 60th birthday.

Effect of dope extrusion rate on morphology and performance of hollow fibers membrane for ultrafiltration

The objective of this study is to determine the effects of dope extrusion rate (DER) on polyethersulfone hollow fiber ultrafiltration membrane performance and morphology. The hollow fiber ultrafiltration membranes were produced by using a simple dry/wet spinning process with forced convection in the dry air gap. A newly developed dope solution consists of 20.6 wt.% polyethersulfone (PES), 63.6 wt.% 1-methyl-2-pyrrolidone (NMP), 9.3 wt.% polyethylene glycol (PEG) and a mixture of potassium acetate and water (20/80 wt.%) was used as a bore fluid in this study. This newly developed dope solution was designed to be very close to its cloud point (binodal line) in order to speed up the coagulation process so that the relaxation effect on molecular orientation can be reduced. The dope extrusion rate was varied from 2.0 to 4.0 cm 3/min with 0.5 cm 3/min increments in order to study the effect of DER on fiber performance and morphology. The experimental results showed that the flux of the hollow fiber ultrafiltration membranes decreases while the separation performance for particular solute increases with an increase in dope extrusion rate. This suggests that the outer skin layer of the membranes becomes apparently thicker and denser with increasing dope extrusion rate. Once the separation performance reaches maximum (critical point), the rejection decreases with increasing dope extrusion rate, observed possibly due to formation of less tighten outer skin structure at high dope extrusion rate. Plane-polarized Fourier transform infrared spectroscopy revealed that membrane spun at dope extrusion rate of 3.5 cm 3/min showed largest spectrum difference suggesting that higher molecular orientation is responsible for an enhanced separation performance. This study also indicated that ultrafiltration hollow fiber membrane produced has a high potential to be used for cyclodextrin separation.

An in depth study of crystallinity, crystallite size and orientation measurements of a selection of poly(ethylene terephthalate)fibers

A selection of commercially available poly(ethylene terephthalate) fibers with different degrees of molecular alignment and crystallinity have been investigated utilizing a wide range of techniques including optical microscopy, infrared spectroscopy together with thermal and wide-angle X-ray diffraction techniques. Annealing experiments showed increased molecular alignment and crystallinity as shown by the increased values of birefringence and melting enthalpies. Crystallinity values determined from thermal analysis, density, unpolarized infrared spectroscopy and X-ray diffraction are compared and discussed in terms of the inherent capabilities and limitations of each measurement technique. The birefringence and refractive index values obtained from optical microscopy are found to decrease with increasing wavelength of light used in the experiments. The wide-angle X-ray diffraction analysis shows that the samples with relatively low orientation possess oriented non-crystalline array of chains whereas those with high molecular orientation possess well defined and oriented crystalline array of chains along the fiber axis direction. X-ray analysis showed increasing crystallite size trend with increasing molecular orientation. SEM images showed micro-cracks on low oriented fiber surfaces becoming smooth on highly oriented fiber surfaces. Excellent bending characteristics were observed with knotted fibers implying relatively easy fabric formation.

Dry Jet-Wet Spinning of Cellulose/N-Methylmorpholine N-oxide Hydrate Solutions and Physical Properties of Lyocell Fibers

In dry jet-wet spinning of a cellulose/ N-methylmorpholine N-oxide hydrate solution, the effects of the hydration number n in NMMO hydrates and the concentration and molecular weight of cellulose are investigated in terms of the physical properties of the fibers. Dry jet-wet spinning of lyocell fibers is also investigated using three different set-ups; a piston type, an N2 gas pressure type, and spinning equipment with an extruder. The effects of spinning conditions such as the spin draw ratio, air gap distance, and composition of the coagulation bath are investigated. The physical properties of the fibers such as birefringence, initial modulus, and tensile strength increase with a decrease in n and an increase in the air gap distance and spin draw ratio. The relationship between the physical properties and the fiber denier is newly suggested in this spinning system. The tensile fracture morphology reveals that fibers from the NMMO hydrate containing less water have more fibrils due to their higher molecular orientation. Further, the orientation structure of the cellulose becomes more noticeable with the decreased hydration levels of the solvent because it produces thicker and longer fibrils when the cellulose fibers are treated with an ultrasonic generator. The crystallite size of the cellulose depends on the composition of NMMO in the coagulation bath. The crystallite size also decreases with the increased air gap distance.

Theoretical Consideration of Air Gap Effect on Fiber Formation During Water-Quenched Melt Spinning and Application of Air Gap Spinning to Characterization of Fluid Relaxation Time

Theoretical studies on the dynamics of water-quenched air gap melt spinning for poly(ethylene terephthalate) (PET) were done. Spinning tension in the air region increases rapidly with decreasing air gap length. Especially, in the case of air gap length less than 2 cm, high spinning tension can be obtained. It might be thought that high spinning tension during spinning process leads to high molecular orientation of super fibers such as Aramid fibers. Maximum deformation rate in the spinning process having narrow air gap appears at the interface of air and water, which is also related to high molecular orientation. Using air gap spinning, draw resonance experiments were performed to characterize the relaxation time of PET. Comparing the experimentally obtained draw resonance wave forms with those of computations for Maxwell fluid model, the relaxation time is estimated to be about 0.002 s. This value almost coincides with that obtained by other methods.

Theoretical Analysis of Water-Quenched Air Gap Melt Spinning and Air Gap Effect on Fiber Formation

Theoretical and experimental studies on the dynamics of water-quenched air gap melt spinning were performed. The calculated spinning tension in the air region increases rapidly with decreasing air gap length. In particular, in the case of air gap lengths less than 2cm, high spinning tension can be obtained. It might be thought that high spinning tension during the spinning process leads to high molecular orientation of super fibers such as Aramid fibers. The maximum deformation rate in spinning processes with narrow air gaps appears at the boundary between air and water, which may be also related to the development of high molecular orientation.Draw resonance experiments were performed using air gap melt spinning on Poly (ethylene terephthalate). With decreasing air gap length, the draw resonance instability was suppressed. This might be related to the results of numerical simulation in which larger Weissenberg numbers in the draw resonance analysis for the Maxwell fluid model and higher spinning tension in the air in the case of short air gap lengths lead to the stabilization of the spinning process.

Structure of polypropylene fibres coloured with a mixture of pigments with different nucleating ability

Investigations of the structure of polypropylene fibres coloured with a mixture of quinacridone and phthalocyanine pigments were carried out. The structure of the fibres, evaluated by wide-angle X-ray scattering and small-angle X-ray scattering methods, was compared to the structure of noncoloured fibres and the fibres coloured with particular pigments. It was stated, that pigments participate in the nucleation process at low take-up velocity. In the presence of pigments, nuclei of two polymorphic forms α and β are formed. In fibres coloured with the mixture of pigments the competition between formation of the α and β nuclei occurs. The β nuclei formed on the crystals of the quinacridone pigment dominate. The high number of the β nuclei, together with the higher growth rate of the β crystals, leads to the formation of a structure containing a large amount of the β form, only slightly lower in comparison to the fibres coloured with the quinacridone pigment. At higher take-up velocities under higher molecular orientation in the cooled stream of the fibre, the very effective row nuclei are produced. In the presence of such nuclei, pigments do not participate in the nucleation process and do not affect the fibre structure.

Method for Prediction the Distribution of Material Properties during Injection Molding (III)

There are many methods of molding plastic products. Injection molding is used widely because it can manufacture an intricately shaped product in a short period of time. However, one problem with injection-molded products is that they are apt to warp. Although warpage prediction by warp analysis provides qualitative agreement with actual warping, quantitative prediction accuracy is still insufficient. An investigation into the cause of that problem revealed that the thermal expansion coefficient of injection molded products was characterized by anisotropy and a large distribution in the layers along their thickness. However, it was found that the prediction method was not capable of analyzing that anisotropy and distribution with sufficient accuracy. Based on that result, it was assumed that prediction of the anisotropy and distribution of the thermal expansion coefficient was important for improving warp analysis accuracy, and a method of predicting that anisotropy and distribution was investigated.In this study, injection molding was used to form a plate made of Polystyrene (PS), an amorphous material, and the residual stress generated by the anisotropy and distribution of the thermal expansion coefficient was examined. It was found that flow and thermal factors were dominant in inducing residual stress in the surface layer and in the inner layer of the PS plate, respectively. The molecular orientation ratio of each layer was also measured. The surface layer where the flow factor was dominant had a high molecular orientation ratio and the inner layer where the thermal factor was dominant had a small molecular orientation ratio. The thickness of the plate was then sliced into six layers and measurements were made of the anisotropy and distribution of the thermal expansion coefficient in order to examine the relationship with the molecular orientation ratio. The results indicated that the thermal expansion coefficient had a wide distribution in each layer. Moreover, a correlation was observed between the thermal expansion coefficient and the molecular orientation. It was found that the anisotropy and distribution of the thermal expansion coefficient can be predicted from the molecular orientation.