Rolling and roll-drawing of ultrahigh molecular weight polyethylene reactor powders

Ultrahigh molecular weight polyethylene (UHMWPE) reactor powders have been found to be processable in the solid state by the techniques of rolling and roll-drawing. Plates of compacted UHMWPE reactor powder were prepared below their melting points. These plates were then rolled at 124°C. The maximum uniaxial draw ratio (DR) obtained by multiple rolling was about 10. In additional experiments, rolled plates of a DR of 6 were further drawn by tensile stretching at a temperature of 135°C. The specimens prepared by rolling and by the two-stage draw were characterized by tensile measurements, differential scanning calorimetry (DSC), and X-ray diffraction. Results show that, on rolling alone, the tensile modulus and tensile strength achieved were 3 GPa and 42 MPa, respectively, at a DR of 9.6. The rolled plates were effectively drawn further to a total DR of 86. Such highly drawn films exhibited tensile moduli and tensile strength up to 81 and 1.3 GPa, respectively. A high crystallinity and high crystal orientation were also obtained by the two-stage draw.     

High-performance polypropylene film prepared from reactor powders having different characteristics

Ultra-high molecular weight isotactic polypropylene (UHMW-iPP) reactor powders have been successfully ultra drawn below melting temperature (T_m) by a combination of calendar rolling and tensile drawing techniques. Two UHMW-iPP reactor powders having different MWs were synthesized by using the same Ziegler-Natta catalyst system at 70 °C in hexane. The resultant tensile properties increased with increasing draw ratio, due to orientation-crystallization during tensile draw, which was indicated by DSC and WAXD measurements. The film drawn under optimum conditions exhibited the maximum tensile modulus of ∼25 GPa, independent of sample MW, corresponding to 70% of the ultimate modulus of iPP crystal. However, the higher maximum tensile strength of ∼1.0 GPa was achieved for the reactor powder having the higher MW, which is three times as high as those of commercial high-strength iPP tapes. Such a fact that high performances have been achieved by processing from reactor powder state below T_m implies that crystallization with less entanglement occurs during polymerization. When drawability and resultant properties were compared among different iPP reactor powders prepared under different conditions, it was clarified that they were predominantly affected by not only MW but also by the reactor powder morphology, especially surface smoothness.     

Transparent,Lightweight, and High Strength Polyethylene Films by a Scalable Continuous Extrusion and Solid‐State Drawing Process

The continuous production of transparent high strength ultra‐drawn high‐density polyethylene films or tapes is explored using a cast film extrusion and solid‐state drawing line. Two methodologies are explored to achieve such high strength transparent polyethylene films; i) the use of suitable additives like 2‐(2H‐benzotriazol‐2‐yl)‐4,6‐ditertpentylphenol (BZT) and ii) solid‐state drawing at an optimal temperature of 105 °C (without additives). Both methodologies result in highly oriented films of high transparency (≈91%) in the far field. Maximum attainable modulus (≈33 GPa) and tensile strength (≈900 MPa) of both types of solid‐state drawn films are similar and are an order of magnitude higher than traditional transparent plastics such as polycarbonate (PC) and poly(methyl methacrylate). Special emphasis is devoted to the effect of draw down and pre‐orientation in the as‐extruded films prior to solid‐state drawing. It is shown that pre‐orientation is beneficial in improving mechanical properties of the films at equal draw ratios. However, pre‐orientation lowers the maximum attainable draw ratio and as such the ultimate modulus and tensile strength of the films. Potential applications of these high strength transparent flexible films lie in composite laminates, automotive or aircraft glazing, high impact windows, safety glass, and displays.     

Enhancement of the dimensional stability of poly(ethylene‐2,6‐naphthalene dicarboxylate) filament by multistep zone annealing spinning

Both good tensile properties and good resistance to thermal shrinkage are prerequisites for tire cord applications. For these purposes, poly(ethylene‐2,6‐naphthalene dicarboxylate) (PEN) filaments were prepared by multistep zone annealing (MSZA) spinning with a specially devised system. The melting temperature of the PEN filaments so obtained was slightly increased with an increasing total draw ratio. All the filaments exhibited a sharp melting peak around 270°C, but glass‐transition behavior was barely visible via differential scanning calorimetry. Rheovibron experiments showed α relaxation in the vicinity of 175°C. Increasing the draw ratio above 4 did not increase the birefringence value much, but it did lead to increases in the tensile properties. The PEN filaments consisted exclusively of α‐form crystals. The PEN filaments showed excellent resistance to thermal shrinkage, which was less than 1% even with heating to 140°C. In the MSZA spinning process, increasing the degree of hot drawing proved more effective than increasing the degree of cold drawing for obtaining PEN filaments with better dimensional stability at elevated temperatures. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 916–922, 2002     

Spinning and drawing properties of ultrahigh‐molecular‐weight polyethylene fibers prepared at varying concentrations and temperatures

The concentrations and temperatures of ultrahigh‐molecular‐weight polyethylene (UHMWPE) gel solutions exhibited a significant influence on their rheological and spinning properties. The shear viscosities of UHMWPE solutions increased consistently with increasing concentrations at a constant temperature above 80°C. Tremendously high shear viscosities of UHMWPE gel solutions were found as the temperatures reached 120–140°C, at which their shear viscosity values approached the maximum. The spinnable solutions are those gel solutions with optimum shear viscosities and relatively good homogeneity in nature. Moreover, the gel solution concentrations and spinning temperatures exhibited a significant influence on the drawability and microstructure of the as‐spun fibers. At each spinning temperature, the achievable draw ratios obtained for as‐spun fibers prepared near the optimum concentration are significantly higher than those of as‐spun fibers prepared at other concentrations. The critical draw ratio of the as‐spun fiber prepared at the optimum concentration approached a maximum value, as the spinning temperature reached the optimum value of 150°C. Further investigations indicated that the best orientation of the precursors of shish‐kebab‐like entities, birefringence, crystallinity, thermal and tensile properties were always accompanied with the as‐spun fiber prepared at the optimum concentration and temperature. Similar to those found for the as‐spun fibers, the birefringence and tensile properties of the draw fibers prepared at the optimum condition were always higher than those of drawn fibers prepared at other conditions but stretched to the same draw ratio. Possible mechanisms accounting for these interesting phenomena are proposed.     

Solid‐state polymerization of melt‐spun poly(ethylene terephthalate) fibers and their tensile properties

The production of high modulus and high strength poly(ethylene terephthalate) fibers was examined by using commercially available melt‐spun fibers with normal molecular weight (intrinsic viscosity = 0.6 dL/g). First, molecular weight of as‐spun fibers was increased up to 2.20 dL/g by a solid‐state polymerization, keeping the original shape of as‐spun fibers. Second, the polymerized as‐spun fibers were drawn by a conventional tensile drawing. The achieved tensile modulus and strength of as‐drawn fibers (without heat setting) were 20.0 and 1.1 GPa, respectively. A heat setting was carried out for the as‐drawn fibers. Tensile properties of the treated fibers were greatly affected by the condition of the heat setting. This was related to the increase of sample crystallinity and molecular degradation during the treatments. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1791–1797, 2007     

Ultradrawing properties of ultrahigh‐ molecular‐weight polyethylene/carbon nanotube fibers prepared at various formation temperatures

The influence of formation temperature on the ultradrawing properties of ultrahigh‐molecular‐weight polyethylene/carbon nanotube (UHMWPE/CNT) fiber specimens is investigated. Gel solutions of UHMWPE/CNT with various CNT contents were gel‐spun at the optimum concentration and temperature but were cooled at varying formation temperatures in order to improve the ultradrawing and tensile properties of the UHMWPE/CNT composite fibers. The achievable draw ratio (D_ra) values of UHMWPE/CNT as‐prepared fibers reach a maximum when they are prepared with the optimum CNT content and formation temperature. The D_ra value of UHMWPE/CNT as‐prepared fibers produced using the optimum CNT content and formation temperature is about 33% higher than that of UHMWPE as‐prepared fibers produced using the optimum concentration and formation temperature. The percentage crystallinity (W_c) and melting temperature (T_m) of UHMWPE/CNT as‐prepared fiber specimens increase significantly as the formation temperature increases. In contrast, W_c increases but T_m decreases significantly as the CNT content increases. Dynamic mechanical analysis of UHMWPE and UHMWPE/CNT fiber specimens exhibits particularly high α‐transition and low β‐transition, wherein the peak temperatures of α‐transition and β‐transition increase dramatically as the formation temperature increases and/or CNT content decreases. In order to understand these interesting drawing, thermal and dynamic mechanical properties of the UHMWPE and UHMWPE/CNT as‐prepared fiber specimens, birefringence, morphological and tensile studies of as‐prepared and drawn fibers were carried out. Possible mechanisms accounting for these interesting properties are proposed. Copyright © 2010 Society of Chemical Industry     

Drawing in high pressure CO2—a new route to high performance fibers in memory of late Roger Porter

In this paper, we introduce a new draw technique for polymer orientation and apply it to different polymer fibers: poly(ethylene terephthalate) or PET, nylon 6,6, and ultra‐high molecular polyethylene (UHMWPE). In this technique, a polymer is drawn uniaxially in supercritical CO₂ using a custom high‐pressure apparatus. This technique can be used in replacement of a traditional drawing process or as a post‐treatment process. With PET, the technique is not effective at temperatures at or below 130°. In contrast, the process is highly effective for nylon 6,6 where CO₂ drawn fibers show significantly higher crystallinity and orientation along with improved mechanical properties. While the fibers are plasticized, the drawability of the fibers is only slightly dependent on temperature. High pressure CO₂ drawing of ultrahigh molecular weight polyethylene (UHMWPE) fibers is equally effective. Commercial high performance fibers can be drawn up to a ratio of 1.9 in asecond stage, resulting in large increases in tensile modulus and small improvements in tensile strength.     

Correlation among powder morphology,compactability, and mechanical properties of consolidated nascent UHMWPE

The influence of the catalytic system and synthesis conditions on the reactor powder morphology and the molecular packing in the nascent UHMWPE is studied with the help of various electron microscopic methods. The potentiality of different morphologies for producing strong consolidated material by sintering at temperature lower than the melting temperature is considered. It is shown that the small catalytic particles of colloidal sizes (reactor powders of M‐series) produce homogeneous broccoli type morphology consisting of small nodules with the sizes less than 0.2–0.5 μm, which in turn, comprise crystalline domains and disordered regions. Comparison analysis of transmission electron microscopic data with the DSC and NMR results enabled to conclude that the disordered regions are predominantly comprised of tie molecules with low degree of coiling, taut tie molecules, and a number of tight folds. This type of morphology best fits for compaction and sintering. Reactor powder morphology arising upon synthesis lab‐scale and commercial UHMWPE on supported catalysts is not so homogeneous, and consists of miscellaneous morphological units, such as spirals, flakes, secondary fibrils, interconnecting the subparticles, large and small lamellae in depending of the catalyst system. The density of disordered regions in these reactor powders is less than that in the particles of M‐series. The tensile strength of the samples obtained by sintering of the M‐powders is higher than the strength of the other ones by a factor 2.5, which makes them good precursors for orientation drawing. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Structural Evolution of UHMWPE Fibers during Prestretching Far and Near Melting Temperature: An In Situ Synchrotron Radiation Small‐ and Wide‐Angle X‐Ray Scattering Study

Combining a homemade extension apparatus and the in situ synchrotron radiation small‐ and wide‐angle X‐ray scattering methods for measurement, the structural evolutions of gel‐spun ultrahigh molecular weight polyethylene (UHMWPE) fibers during prestretching at temperatures of 25 and 100 °C are investigated, respectively. Lamellar rotation toward the stretching direction occurs before strain hardening, while the folded‐chain crystal destruction and extended‐chain fibril formation processes occur in the strain hardening zone at 25 °C. While at 100 °C, stretching induced crystal melting before the stress plateau region and formation of fibrous crystals at the onset of the stress plateau are observed. Further stretching results in shear displacement of crystal blocks and, finally, destruction of the folded‐chain crystals and formation of extended‐chain fibrils. Prestretching UHMWPE fibers at 100 °C within a certain strain range can produce highly oriented fibrous crystals, which may provide an ideal precursor structure for the poststretching process.     

High‐strength regenerated cellulose fibers spun from 1‐butyl‐3‐methylimidazolium chloride solutions

High‐performance regenerated cellulose fibers were prepared from cellulose/1‐butyl‐3‐methylimidazolium chloride (BMIMCl) solutions via dry‐jet wet spinning. The spinnability of the solution was initially evaluated using the maximum winding speed of the solution spinning line under various ambient temperatures and relative humidities in the air gap. The subsequent spinning trials were conducted under various air gap conditions in a water coagulation bath. It was found that low temperature and low relative humidity in the air gap were important to obtain fibers with high tensile strength at a high draw ratio. From a 10 wt % cellulose/BMIMCl solution, regenerated fibers with tensile strength up to 886 MPa were prepared below 22 °C and relative humidity of 50%. High strengthening was also strongly linked with the fixation effect on fibers during washing and drying processes. Furthermore, an effective attempt to prepare higher performance fibers was conducted from a higher polymer concentration solution using a high molecular weight dissolving pulp. Eventually, fibers with a tensile strength of ～1 GPa and Young's modulus over 35 GPa were prepared. These tensile properties were ranked at the highest level for regenerated cellulose fibers prepared by an ionic liquid–based process. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45551.     

Investigation of the ultradrawing properties of gel spun fibers of ultra‐high molecular weight polyethylene/carbon nanotube blends

The carbon nanotubes (CNTs) contents, ultrahigh‐molecular‐weight polyethylene (UHMWPE) concentrations and temperatures of UHMWPE, and CNTs added gel solutions exhibited significant influence on their rheological and spinning properties and the drawability of the corresponding UHMWPE/CNTs as‐prepared fibers. Tremendously high shear viscosities (ηs) of UHMWPE gel solutions were found as the temperatures reached 140°C, at which their ηs values approached the maximum. After adding CNTs, the ηs values of UHMWPE/CNTs gel solutions increase significantly and reach a maximum value as the CNTs contents increase up to a specific value. At each spinning temperature, the achievable draw ratios obtained for UHMWPE as‐prepared fibers prepared near the optimum concentration are significantly higher than those of UHMWPE as‐prepared fibers prepared at other concentrations. After addition of CNTs, the achievable draw ratios of UHMWPE/CNTs as‐prepared fibers prepared near the optimum concentration improve consistently and reach a maximum value as their CNTs contents increase up to an optimum value. To understand these interesting drawing properties of the UHMWPE and UHMWPE/CNTs as‐prepared fibers, the birefringence, thermal, morphological, and tensile properties of the as‐prepared and drawn fibers were investigated. Possible mechanisms accounting for these interesting properties are proposed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The straight‐chain segment length distribution in xerogels of UHMWPE,which provide high drawability of gel‐derived fibers

A series of ultra‐high‐molecular‐weight reactor powders with different technological prehistory were utilized for obtaining fibers through the gel technology. The fibers prepared from some powders exhibited high draw ratios and good mechanical properties (Young's modulus and tensile stress) but other powders yielded fibers of very low drawability. The low‐frequency Raman study revealed that the straight‐chain‐segment (SCS) length distributions in dried gels prepared from powders of “drawable” group are bimodal, while the gels issued from powders unsuitable for fiber drawing have unimodal length distributions of SCS. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Novel aromatic polyimide fiber with biphenyl side‐groups: Dope synthesis and filament internal morphology control

A new organic‐soluble aromatic polyimide with biphenyl side‐groups has been synthesized from 4,4′‐oxydiphthalic anhydride and 3,5‐diamino‐benzonic‐4′‐biphenyl ester (DABBE) via a one‐step polymerization in m‐cresol. A higher molecular weight polyimide has been obtained by the addition of chlorotrimethylsilane (TMSCl) in the solution of DABBE to form, in situ, silylated diamine. The optimum mole amount of TMSCl relative to the number of amino groups is 100%. This polyimide is soluble in m‐cresol, allowing fibers to be spun from isotropic solution using a dry‐jet wet spinning method. Based on a ternary phase diagram of m‐cresol, ethanol, and water, controlling of the internal morphology of as‐spun fibers has been achieved by varying the rate of polyimide coagulation through adjustment of nonsolvent/solvent miscibility in the coagulation bath. Scanning electron microscopic pictures show that filament internal morphologies ranged from porous‐like to fully solid. The solid as‐spun fibers can be drawn at high temperatures (>330°C) under tension to high drawn ratios (up to 6×), which produces a remarkable increase in tensile strength to about 1.0 GPa and an initial modulus higher than 60 GPa. POLYM. ENG. SCI. 46:123–128, 2006. © 2005 Society of Plastics Engineers     

Gel spinning of UHMWPE fibers with polybutene as a new spin solvent

Gel spinning of UHMWPE fibers using low molecular weight polybutene (PB) as a new spin solvent was investigated. A 98/2 wt% PB/UHMWPE gel exhibits a melting temperature around 115°C and shows large‐scale phase separation upon cooling the solution to room temperature. The resulting precursor fiber from this gel was hot‐drawn to a ratio of 120, yielding a fiber with tensile strength of 4 GPa and Young's modulus of over 150 GPa. Wide‐angle X‐ray diffraction indicates good molecular orientation along the fiber axis. The results also demonstrate the potential to further improve the mechanical properties. With respect to the gel spinning industry, this new solvent has a number of advantages over paraffin oil and decahydronaphthalene, and holds a promise of greatly improving the process efficiency. POLYM. ENG. SCI., 56:697–706, 2016. © 2016 Society of Plastics Engineers     

Gel‐spinning of partially saponificated poly(vinyl alcohol)

DMSO/water (80/20 volume ratio) solutions of commercial poly(vinyl alcohol)s (a‐PVA₉₉, a‐PVA₈₈) with degrees of saponification of 99.3 and 88 mol % were gel‐spun into methanol (−20 and −70°C). The dry filaments obtained were drawn at 200°C (a‐PVA₉₉) and 150–180°C (a‐PVA₈₈). The maximum draw ratio and Young's modulus were 26 and 34 GPa for a‐PVA₉₉ and 21 and 24 GPa for a‐PVA₈₈ (drawing temperature: 160°C). So, at first, the dry filaments obtained for a‐PVA₈₈ were drawn at 150–180°C until 10 times their original length. Moreover, the predrawn a‐PVA₈₈ filaments were perfectly saponificated under fixing at the both ends and then the filaments were redrawn at 200°C. The maximum draw ratio and Young's modulus for the filaments (a‐PVA_88→99) predrawn at 150°C were 28 and 39 GPa, respectively. The a‐PVA_88→99 filaments had two melting peaks (228 and 236°C). © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2872–2876, 2000     

Structure and property changes of polyamide 6 during the gel‐spinning process

Polyamide 6 (PA6) gels were prepared by the dissolution of PA6 powder in formic acid with CaCl₂ as a complexing agent. The concentration of the polymer was 16% w/v. PA6 fibers were obtained through gel‐spinning, drawing, decomplexation, and heat‐setting processes. The structure and properties of the fibers at different stages were characterized with differential scanning calorimetry, thermogravimetric analysis, X‐ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. The experiment results indicate that the melting transition of the as‐spun fibers obtained by the extrusion of the PA6/CaCl₂/HCOOH solution into a coagulation bath through a die disappeared. A porous structure existed in the as‐spun fibers, which led to poor mechanical properties. Compared with the as‐spun fibers, the melting and glass‐transition temperatures of the decomplexed and drawn fibers retained their original values from PA6, the degree of crystallinity increased, the porous structure disappeared, and the mechanical properties were improved. The maximum modulus and tensile strength obtained from the drawn fibers in this study were 32.3 GPa and 530.5 MPa, respectively, at the maximum draw ratio of 10. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4449–4456, 2013     

Lubrication of poly(vinyl alcohol) chain orientation by carbon nano‐chips in composite tapes

The extraordinary structural properties of graphene and carbon nanotube materials motivate the development of practical methods for their use in fabricating continuous, strong, and tough composite fibers. Poly(vinyl alcohol) (PVA)/carbon nano‐chip fiber (CNCF) composite tapes with 0.5 wt % loading show that Young's modulus, tensile strength, and toughness are increased by 585%, 653%, and 20%, respectively as compared to the control (PVA) tapes. Nano‐chips exfoliated from the CNCF during processing, lubricate polymer chain alignment, and orientation during drawing, where composite tapes could be drawn to higher draw ratios compared with the control tapes. As a result, the Herman's orientation factor (f) increased from 0.5 (control tape) to 0.8 (composite tape). Theoretical analysis shows ～ 16 vol % of the composite tapes consists of fully oriented PVA chains, which contributes to its exceptional mechanical performance. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Enhancing mechanical properties of gel‐spun polyvinyl alcohol fibers by iodine doping

High strength polyvinyl alcohol (PVA) fibers with a conventional degree of polymerization of 1500 were prepared by doping iodine with PVA spinning solution. The iodine‐doped PVA (I‐PVA) aqueous solution was extruded into cold methanol that provides dark purple PVA‐iodine complex gel fibers. Only a small amount of iodine was required to enhance drawability and molecular orientation by reducing the interaction between PVA chains. An increase of ca. 10% in the maximum draw ratio of the doped fibers compared with that of undoped PVA translated into values for the tensile strength, 2.2 Giga‐Pascal (GPa), and initial modulus (47 GPa) that were more than 30% higher than those of the neat PVA fiber. Easier chain slippage of molecules in the amorphous segments of the I‐PVA fiber during drawing leads to increased orientation in these segments, which is believed to be the source of the improvements in mechanical properties. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Influence of copolymer fraction composition in ultrahigh molecular weight polyethylene blends with ethylene/1‐hexene copolymers on material physical and tensile properties

The reactor blends (RBs) with bimodal molecular weight distribution on the base of ultrahigh molecular weight polyethylene (UHMWPE) and low molecular weight random ethylene/1‐hexene copolymers (CEH) were synthesized by two‐step processes including ethylene polymerization followed by ethylene/1‐hexene copolymerization over rac‐(CH₃)₂Si(Ind)₂ZrCl₂/methylaluminoxane catalyst. The four series of blends differed in a composition of copolymer fraction that was varied in a wide range (from 3.0 to 37.0 mol % of 1‐hexene). The differential scanning calorimetric study shows the double melting behavior of the net semicrystalline CEHs, which can be attributed to intramolecular heterogeneity in chain branch distribution. The introduction of CEHs leads to the modification of nascent RB crystalline and amorphous phases. Physical and tensile properties as well as melting indexes of the materials depend not only on the percentage of copolymer fraction that varied from 6.9 to 35.8 wt % but also on its composition. The increase of copolymer fraction with high content of 1‐hexene (≥11.0 mol %) in the blends leads to the change of the character of stress–strain curves; the materials behave as elastomers. Controlled regulation of copolymer fraction characteristics in the synthesis yields RBs combining the enough high strength, good plastic properties with enhanced melting indexes as compared with the net UHMWPE. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40151.