Increasing Draw Ratio Research Articles

Extreme Toughness Exhibited in Electrospun Polystyrene Fibers

Polystyrene (PS) commonly exhibits brittle behavior and poor mechanical properties due to the presence of structural heterogeneities promoting localized failure. The removal of this localized failure is shown here by processing PS into fibers with a range of diameters using electrospinning. Mechanical properties of individual electrospun fibers were quantified with atomic force microscopy based nanomechanical tensile testing. The resultant stress–strain behavior of PS fibers highlights considerable enhancement of mechanical properties when fiber diameter decreases below 600 nm such that polystyrene toughness increases significantly by over two orders of magnitude compared to the bulk. Consideration of the network properties of polystyrene is used to demonstrate the increase of draw ratio toward a theoretical limit and is potentially applicable to a range of glassy polymeric materials. image

Effect of Draw Ratio on the Microstructure of Silk Fibroin/Graphene Oxide Hybrid Fibers

In order to fabricate high performance artificial silk, hybrid fibers were dry spun from regenerated silk fibroin (RSF) aqueous solution mixed with graphene oxide (GO) nanosheets. The influence of draw ratio on the microstructure and mechanical properties of RSF/GO hybrid fibers was studied through Fourier transform infrared spectroscopy (FT-IR), synchrotron radiation wide-angle X-ray diffraction, Raman spectroscopy and mechanical testing. The results showed that with increasing draw ratio, both amorphous phase and mesophase of the dry-spun artificial fiber gradually converted to crystals. The orientation of crystals and mesophase changed slightly at low draw ratio, but increased significantly at draw ratios of 3 and 4X. The β-sheet content of silk fibroin and the disorder degree of GO sheets in the fibers also increased with the increase of draw ratio. The initial modulus, breaking strength and breaking energy of the hybrid fibers achieved great improvement at a draw ratio of 4X. The structure evolution of the RSF/GO hybrid fibers may benefit the understanding of the structure-property relationship of other composite fibers.

Structure and biocompatibility of highly oriented poly(lactic acid) film produced by biaxial solid hot stretching

Abstract Highly oriented long-chain-branched poly(lactic acid) (LCB-PLA) film was fabricated through biaxial hot stretching in solid state. Compared with neat PLA, more homogeneous film with higher draw ratio can be obtained for LCB-PLA. With increasing draw ratio, the long period, lamellae thickness and grain size of LCB-PLA decreased, while the crystallinity increased. For LCB-PLA with draw ratio of 6*6, the tensile strength and elongation at break can reach up to 208 ± 6 MPa and 85% respectively. After drawing, the increasing content of CH3 and C O group on the surface of LCB-PLA film was beneficial for cell adhesion and growth on it.

무어링 로프용 메탈로센 촉매 고밀도 폴리에틸렌 모노 필라멘트의 물성에 미치는 연신비의 영향

This study examined the effect of draw ratio on the properties of high density polyethylene (m-HDPE) prepared using a metallocene catalyst as mooring rope material for 20,000-30,000 ton ships (small and medium class ships). The density, crystallinity, crystallite size, crystalline orientation, melting enthalpy, and tensile modulus increased with increasing draw ratio from 8 to 14; however, the elongation at break decreased. The tensile strength of the m-HDPE filament increased significantly with increasing draw ratio up to 12 and then decreased a little. The reduction in tensile strength for the filament with draw ratio of 14 might be due to stress whitening. The various properties of the m-HDPE mono-filament with draw ratio of 14 prepared in this study (tensile strength: 8.0 g/d, elongation at break: 10.0%, tensile modulus: 104.5 g/d, water absorption: 0.19%, color fastness to sea water (grade): 4-5, chemical resistance: 82-94%) were found to pass the mooring rope material criteria for 20,000-30,000 ton ships (tensile strength: > 8 g/d, elongation at break: 10% <, tensile modulus: > 100 g/d, water absorption: 0.7% <, color fastness to sea water (grade): > 4, chemical resistance: > 80%).

Enhanced electroactive β phase in three phase PVDF/CaCO3/nanoclay composites: Effect of micro‐CaCO3 and uniaxial stretching

ABSTRACTIn this study, electroactive polar phase transformation and crystallinity of poly(vinylidene fluoride) (PVDF)‐based composites, such as PVDF/CaCO3/nanoclay, is explored as a function of micro‐CaCO3 fraction and draw ratio (R) of uniaxial stretching. Composites including PVDF/clay, PVDF/CaCO3 and most importantly PVDF/CaCO3/clay with varying fraction of micro‐CaCO3 were extruded into homogenous and flexible cast films. Characterization via Fourier transform infrared spectroscopy, X‐ray diffraction, and differential scanning calorimetry (DSC) confirmed the presence of β phase in all the composites incorporated with micro‐CaCO3 and nanoclay either individually (i.e., PVDF/CaCO3 and PVDF/clay films, respectively) or together (i.e., PVDF/CaCO3/nanoclay composites). Interestingly, a gradual but significant improvement in this electroactive phase (β phase) was obtained with successive increment in CaCO3 content into a fixed composition of PVDF and nanoclay (PVDF/CaCO3/clay composites). Further increment in β phase content was obtained via uniaxial stretching to different draw ratios and at a temperature of 90 °C, where for PVDF/CaCO3/clay (especially, 100–35‐3 and 100–40‐3) samples almost no α phase was observed irrespective of R. Conversely, the crystallinity of melt extruded samples decreased gradually all the way with CaCO3 concentration in PVDF/CaCO3/clay composites compared to the neat PVDF while increased gradually with increasing draw ratio. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44940.

Spectroscopic elucidation of structure-property relations in filaments melt-spun from amorphous polymers

Melt spinning and drawing of amorphous cyclo-olefin and co-polyamide polymeric materials were performed to develop mono-component continuous filaments. Raman spectroscopy was employed to assess the effect of a static bending deformation on the microstructure of the filaments. Spectra stemming from the fiber regions under tensile and compressive loading do not show any appreciable shift of their vibrational bands as a function of applied strain. The bent filaments manage to redistribute strains without any stretching or buckling of polymer chains associated with peak shifting in the Raman spectrum. The influence of fiber draw ratio on the degree of molecular ordering was demonstrated by means of polarized Raman spectroscopy. An increase in draw ratio leads to a variation of the polarization ratio for spectroscopic bands located along the polymer backbone. We observed a correlation between the polarization ratio of these vibrational bands and the macroscopic tensile modulus of the material.

Influence of the draw ratio on the mechanical properties and electrical conductivity of nanofilled thermoplastic polyurethane fibers

Electrically conducting textile fibers were produced by wet-spinning under various volume fractions using thermoplastic polyurethane (TPU) as a polymer and carbon black (CB), Ag-powder, multi-walled carbon nanotubes (MWCNTs), which are widely used as electrically conducting nanofillers. After applying the fiber to the heat drawing process at different draw ratios, the filler volume fraction, linear density, breaking to strength, and electrical conductivity according to each draw ratio and volume fraction. In addition, scanning electron microscopy (SEM) images were taken. The breaking to strength of the TPU fiber containing the nanofillers increased with increasing draw ratio. At a draw ratio of 2.5, the breaking to strength of the TPU fiber increased by 105 % for neat-TPU, 88 % for CB, 86 % for Ag-powder, and 127 % for MWCNT compared to the undrawn fiber. The breaking to strength of the TPU fiber containing CB decreased gradually with increasing volume fraction, and in case of Ag-powder, it decreased sharply owing to its specific gravity. The electrical conductivity of the TPU fiber containing CB and Ag-powder decreased with increasing draw ratio, but the electrical conductivity of the TPU fiber containing MWCNT increased rapidly after the addition of 1.34 vol. % or over. The moment when the aggregation of MWCNT occurred and its breaking to strength started to decrease was determined to be the percolation threshold of the electrical conductivity. The heat drawing process of the fiber-form material containing the anisotropic electrical conductivity nanofillers make the percolation threshold of the electrical conductivity and the maximum breaking to strength appear at a lower volume fraction. This is effective in the development of a breaking to strength and electrical conductivity.

Effect of draw ratio on fiber structure development of polyethylene terephthalate

Fiber properties are decided by its structure, and the structure are mainly formed in the fiber drawing process. In this study, the effects of the draw ratio on the fiber structure development of polyethylene terephthalate after continuous neck-drawing were investigated using simultaneous WAXD/SAXS measurements. Low-oriented amorphous as-spun fibers were drawn to a draw ratio of 3.0–4.5, at which the fiber can be stably neck drawn. WAXD and SAXS images were obtained up to 2.0 ms when the structure was mainly developed. The smectic (001′) diffraction intensity and long period increased with increasing draw ratio up to 4.2, and a larger (001′) diffraction d-spacing was observed at a draw ratio of 4.5. The results suggest that more fibrillar structures were formed with increasing draw ratio up to 4.2, and more constrained molecular bundles were formed at a draw ratio of 4.5. A larger amount of constrained fibrillar structures can bear a greater tensile force in tensile tests, therefore the drawn fibers have higher tensile strengths.

Poly(L-lactic acid) scaffold with oriented micro-valley surface and superior properties fabricated by solid-state drawing for blood-contact biomaterials

Most biomaterials composed of biodegradable polymers will contact either accidentally or consistently with blood and this commonly requires both good mechanical strength and blood compatibility. Despite this demand, current processing methods still make it difficult and complex to simultaneously improve the two properties. To overcome present limitations, the aim of this work is to develop a solid-state drawing which is a novel method for blood-contact biomaterials that can simultaneously improve the two essential factors of mechanical strength and blood compatibility, as well as induce a micro-patterned surface. Solid-state drawn (SSD) poly(L-lactic acid) (PLLA) film significantly maximally increased tensile strength and elastic modulus about ninefold and sixfold, respectively, compared to undrawn film. Furthermore, it was determined that SSD-PLLA film had highly developed molecular orientation, higher crystallinity and surface hydrophobicity. Additionally, the SSD method could greatly reduce roughness of the surface and induce the formation of aligned valleys, forming microstructures on the film surface. The topographical cue delayed hydrolytic degradation and prevented damage on the surface by NaOH of alkali compounds are compared with undrawn film. In energy-dispersive x-ray spectroscopy analysis, the surface of SSD film treated by NaOH was not detected on any ions whereas undrawn film held foreign ions on surface defects. The hemolysis rate of SSD film was considerably decreased with an increase of draw ratio up to 0.2% maximally and SSD film has shown greatly lower platelet adhesion compared to undrawn film in blood-compatibility analysis. Interestingly, one-directional alignment of micro-valley structure on SSD film could promote initial adhesion of human umbilical vein endothelial cells (HUVEC) compared with undrawn film and guide the direction of HUVEC. In conclusion, the newly designed SSD method has shown potential for developing blood-contact biomaterials simply due to great mechanical properties, blood compatibility and an aligned micro-patterned surface.

Structure–Properties Relationship of a Novel Multilayer Film/Foam Material Produced through Co-extrusion and Orientation

The PP multilayer film/foams prepared by the multilayer coextrusion technique possess a unique solid/porous alternating horizontal architecture, in which the film layers can effectively suppress the premature rupture of cells in foam layers. This paper introduces a strong and lightweight layered cellular structure developed through optimized uniaxial drawing of the coextruded PP multilayer film/foams. Moreover, systematic study reveals the effects of orientation on the structure and properties of the oriented PP multilayer film/foams. Formation of subcellular interconnected porous structure decreases the bulk density with increasing draw ratio (DR) up to DR = 3.5. In addition, strain induced increase in the orientation of α crystals and crystallinity of PP during uniaxial drawing improves the tensile strength and modulus of the oriented multilayer film/foam significantly. The oriented PP multilayer film/foam with the lowest density and improved tensile properties can be obtained at DR = 4 at the optimized...

Preparation, mechanical properties and microstructure of polyoxymethylene fiber through melt spinning and hot drawing by using injection-molding grade resins

The polyoxymethylene (POM) fiber was melt spun by use of different commercial grades of POM resin, and the effect of post-drawing on mechanical properties and microstructures was investigated extensively. The fiber obtained from the POM resin with a higher melt flow index (MFI) exhibits a better hot-drawing capability and also achieves a greater ultimate draw ratio. The mechanical evaluation reveals that the tensile strength and elastic modulus of POM fiber are improved significantly after post-drawing compared to the as-spun fibers. Although the greater draw ratios result in higher mechanical strength and modulus for the POM fiber, the fiber obtained from the POM resin with an MFI of 13.0 g/10 min achieves the optimal mechanical performance at the ultimate draw ratio. The morphologic and structural developments of POM fiber were studied by scanning electronic microscopy and X-ray powder diffraction. The results indicate that the POM fiber spun by the resin with an MFI of 13.0 g/10 min has a smooth lateral surface and a compact cross section after post-drawing. The fiber samples spun by the POM resins with low MFIs show some hollow disfigurements as well as a rough surface at the ultimate draw ratio, whereas the fiber obtained from the resin with a high MFI of 27.0 g/10 min presents the ununiformity of diameter after post-drawing. The POM fibers achieve a crystalline orientation during the hot-drawing process, which results in a transformation from the spherulitic crystals to the lamellar structure in the drawing direction. The level of crystalline orientation can be improved with an increase of draw ratio and thus results in a high modulus and strength for the resulting POM fiber samples. In addition, the thermal analysis indicates that the crystallinity of the as-spun fibers can be enhanced by post-drawing due to the orientation-induced crystallization.

Densifying and strengthening of electrospun polyacrylonitrile‐based nanofibers by uniaxial two‐step stretching

ABSTRACTThe effects of alignment of polyacrylonitrile (PAN) nanofibers and a two‐step drawing process on the mechanical properties of the fibers were evaluated in the current study. The alignment was achieved using a high‐speed collector in electrospinning synthesis of the nanofibers. Under optimal two‐step drawing conditions (e.g., hot‐water and hot‐air stretching), the PAN nanofiber felts exhibited large improvements in both alignment and molecular chain‐orientation. Large increase in crystallinity, crystallite size, and molecular chain orientation were observed with increasing draw ratio. Optimally, stretched PAN‐based nanofibers exhibited 5.3 times higher tensile strength and 6.7 times higher tensile modulus than those of the pristine one. In addition, bulk density of the drawn PAN nanofibers increased from 0.19 to 0.33 g/cm3. Our results show that fully extended and oriented polymer chains are critical in achieving the highest mechanical properties of the electrospun PAN nanofibers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43945.

Thermal oxidative aging behavior and stabilizing mechanism of highly oriented polyamide 6

Highly oriented polyamide 6 (PA6) was successfully fabricated through solid hot stretching technology. The effect of orientation on the structure and thermal oxidative stability of PA6 was investigated. It was found that the molecular orientation was incapable to change the degradation mechanism. Compared with the isotropic sample, a much slow drop of the intrinsic viscosity was observed for the oriented samples, and the degradation rate constant (k 1) decreased with the increase in draw ratio. The increasing trend of FTIR absorption assigned to different carbonyl groups was obviously slowed down by orientation, and the carbonyl index of the oriented PA6 was much lower than that of the isotropic sample during the whole aging process. The degradation temperature and char yield increased dramatically for the oriented sample of PA6, which displayed relatively high activation energy (E a) over the whole conversion degree. The enhancing mechanism of thermal oxidative stability of PA6 was explored, indicating that the relatively high crystallinity and orientation factor and the stable dense crystalline structure of α crystal formed by orientation were favorable for the improvement of the oxygen barrier property and slowing down the thermal oxidative degradation of PA6. This investigation clearly showed that molecular orientation can be an efficient way to enhance the thermal oxidative stability of PA6.

A study of ethylene vinyl alcohol copolymer fiber for the drawing process

This study investigates the effect of the drawing process of ethylene vinyl alcohol (EVOH) fibers on their physical properties. Three different ethylene contents, namely EV-32, EV-38 and EV-44, were used where the ethylene content has the order of EV-44 &gt; EV-38 &gt; EV-32. The result indicates that at the same drawing temperature and draw ratio, the online drawing stress of the fiber with high ethylene content is higher than that with low ethylene content. Moreover, the drawn EVOH fiber, at the drawing temperature of 80℃ and the draw ratio of 2.0, exhibits an optimal mechanical property. As the draw ratio increases, the online drawing stress, birefringence and initial modulus increase. Notably, unlike typical polymeric fibers, the glass transition temperature ( Tg) of the drawn EVOH fibers decreases with the draw ratio due to more water being absorbed by thinner fibers within the same number of samples. The draw ratio was found to have little effect on the melting temperature ( Tm). At the same draw ratio, the online drawing stress, birefringence, stress and initial modulus of the fiber EV-44, which has the highest ethylene content, is higher than those of EV-32 and EV-38. The creep strain of the drawn fibers EV-32 and EV-38 linearly increase with the drawing time when the applied stress maintains constant at 150 MPa, while an insignificant increase is observed for EV-44, suggesting that EV-44 is difficult to deform and has higher size stability. In the stress relaxation test, the elongation increases with the initial stress. At the same elongation percentage, the initial stress of the drawn fibers has the following trend: EV-44 &gt; EV-38 &gt; EV-32 and the stress relaxation time (τ) has the following trend: EV-44 &gt; EV-38 &gt; EV-32, indicating again that EV-44 is relatively difficult to deform during drawing. Finally, EV-44 fiber performed the best in the hot water resistance test.

The effect of draw ratio on the mechanical properties and crystalline structure of single polymer polypropylene composites

The properties of self-reinforced single polymer composites produced by the Leeds hot compaction process are highly dependent on the compaction temperature as well as the constituent oriented elements used to produce the compacted sheets. In this paper, the variation in tensile mechanical properties of uniaxial hot compacted sheets manufactured from drawn polypropylene (PP) tapes with change in compaction temperature have been investigated, for a range of different draw ratio tapes. It is shown that there is a measureable difference between the optimum compaction temperatures required for obtaining the highest modulus and strength in the compacted sheets. The compaction temperature required to achieve the maximum tensile modulus was seen to increase with increasing draw ratio. The compaction temperature to obtain the maximum tensile strength was found to be both independent of the draw ratio and a few degrees higher than that for obtaining the maximum modulus. Peak modulus and peak tensile strength was shown to be dependent on the draw ratio of the drawn tape.Differential scanning calorimetry measurements on the compacted sheets were also performed in order to investigate the change in crystalline structure with compaction temperature and draw ratio. This has shown that the changes in structure within the oriented phase (i.e. tapes) during the compaction process itself are directly related to the final properties of the hot compacted sheets.

Fabrication of Hollowed Polytrimethylene Terephthalate Fiber by Carbon Dioxide Laser Irradiation

ABSTRACTPolytrimethylene terephthalate hollowed fiber was fabricated by neck drawing process with carbon dioxide irradiation. Fiber diameter increased with increasing draw ratio, and the hollowed fiber of hollowness ratio 46.4% was formed with draw ratio 5.5. Scanning electron microscopy showed internal multiple hollows was formed in fiber cross-section. Drawing stress obtained from drawing tension in situ monitored during the drawing increased with draw ratio, and it corresponded to the increasing trend of hollowness ratio. Necking images showed that the fiber diameter decreased steeply with increasing draw ratio, and the drastic decrease with high draw ratio generated the multiple hollows.

High orientation of long chain branched poly (lactic acid) with enhanced blood compatibility and bionic structure.

Highly oriented poly (lactic acid) (PLA) with bionic microgrooves was fabricated through solid hot drawing technology for further improving the mechanical properties and blood biocompatibility of PLA. In order to enhance the melt strength and thus obtain high orientation degree, long chain branched PLA was prepared at first through a two-step ring-opening reaction during processing. Linear viscoelasticity combined with branch-on-branch model was used to predict probable compositions and chain topologies of the products, and it was found that the molecular weight of PLA increased and topological structures with star like chain with three arms and tree-like chain with two generations formed during reactive processing, and consequently draw ratio as high as1200% can be achieved during the subsequent hot stretching. With the increase of draw ratio, the tensile strength and orientation degree of PLA increased dramatically. Long chain branching and orientation could significantly enhance the blood compatibility of PLA by prolonging clotting time and decreasing platelet activation. Microgrooves can be observed on the surface of the oriented PLA which were similar to the intimal layer of blood vessel, and such bionic structure resulted from the formation of the oriented shish kebab-like crystals along the draw direction.

Concurrent collection and post-drawing of individual electrospun polymer nanofibers to enhance macromolecular alignment and mechanical properties

Abstract The study reports a nanomanufacturing method that facilitates post-drawing of electrospun polymer nanofibers. Post-drawing is critical in conventional microfiber processing to enhance mechanical strength, but has been difficult to implement with nanofibers. Here, a parallel automated track collector was designed to permit continuous processing of thousands of individual nanofibers per minute under highly controllable drawing conditions. Post-drawing systematically induced macromolecular alignment and altered the chemical bond composition of polycaprolactone nanofibers with increasing draw ratio. The strength and stiffness of fibers with a draw ratio of 4 were enhanced by 7 and 15 times respectively and their mechanical properties exceeded previously reported values for conventional and nanoscale polycaprolactone structures.

Thermal and barrier properties of stretched and annealed polylactide films

In this study, both stretched and annealed polylactide (PLA) films were prepared by a twin-screw extruder with different draw ratios, and the effects of the orientation, crystallization, ambient temperature and humidity on the barrier properties were evaluated. The wide-angle X-ray diffraction results revealed that the crystallinity increase with the increase of draw ratio, and the α'-crystal was produced by uniaxially stretching. Moreover, the α'-crystal was easy to form when the film was annealed at 90°C. Based on the scanning electron microscopy observation, the film surface cracks occurred at a certain draw ratio. Modulated differential scanning calorimetry (MDSC) results showed that the glass-transition temperature and crystallinity increased with the increase of draw ratio. The barrier behavior results showed that, both stretched and annealed PLA films exhibited much better oxygen and water vapor barrier than undrawn PLA at middle draw ratio. Upon further stretching, their barrier ability was reduced. The annealed PLA film had higher barrier ability than that of the stretched PLA film. With regard to the temperature and humidity, the oxygen permeability coefficient increased with the increase of temperature, however, the water vapor permeability coefficient reduced slightly. The oxygen and water vapor permeability coefficient were insensitive to humidity.

Solid-state 13C NMR and synchrotron SAXS/WAXS studies of uniaxially-oriented polyethylene

We report solid-state 13C NMR and synchrotron wide-and small-angle X-ray scattering experiments (WAXS, SAXS) on metallocene linear low density polyethylene films (e.g., Exceed™ 1018 mLLDPE; nominally 1MI, 0.918 density ethylene-hexene metallocene copolymer) as a function of uniaxial draw ratio, λ. Combined, these experiments provide an unambiguous, quantitative molecular view of the orientation of both the crystalline and amorphous phases in the samples as a function of draw. Together with previously reported differential scanning calorimetry (DSC), gas transport measurements, transmission electron microscopy (TEM), optical birefringence, small angle X-ray scattering (SAXS) as well as other characterization techniques, this study of the state of orientation in both phases provides insight concerning the development of unusually high barrier properties of the most oriented samples (λ=10). In this work, static (non-spinning) solid-state NMR measurements indicate that in the drawn ExceedTM films both the crystalline and amorphous regions are highly oriented. In particular, chemical shift data show the amorphous phase is comprised increasingly of so-called “taut tie chains” (or tie chains under any state of tautness) in the mLLDPE with increasing draw ratio – the resonance lines associated with the amorphous phase shift to where the crystalline peaks are observed. In the sample with highest total draw (λ=10), virtually all of the chains in the non-crystalline region have responded and aligned in the machine (draw) direction. Both monoclinic and orthorhombic crystalline peaks are observed in high-resolution, solid-state magic-angle spinning (MAS) NMR measurements of the oriented PE films. The orientation is comparable to that obtained for ultra-high molecular weight HDPE fibers described as “ultra-oriented” in the literature. Furthermore, the presence of a monoclinic peak in cold-drawn samples suggests that there is an appreciable internal stress associated with the LLDPE. The results are confirmed and independently quantified by Herman's Orientation Function values derived from the WAXS measurements. The degree of orientation approaches theoretically perfect alignment of chains along the draw direction. We deduce from this observation that a high fraction of the non-crystalline chains are either tie chains that directly connect adjacent lamellae or are interlocking loops from adjacent lamellae. In either case, the chains are load-bearing and are consistent with the idea of “taut tie chains”. We note that transmission electron micrographs recorded for the ultra-oriented Exceed showed the lamellae are often appreciably thinner and shorter than they are for cast or blown Exceed 1018. Combined with higher crystallinity, the thinner lamellae statistically favor more tie chains. Finally, the remarkably large decrease in permeability of the λ=10 film is primarily attributed to the high degree of orientation (and loss of entropy) of the amorphous phase.