Extrusion Draw Research Articles

Highly thermally conductive and mechanically robust composite of linear ultrahigh molecular weight polyethylene and boron nitride via constructing nacre-like structure

With the rapid development of modern electronic, developing highly thermally conductive and mechanically strong composites for achieving efficient and reliable thermal management has become an urgent task. In this work, boron nitride/linear-ultrahigh molecular weight polyethylene (LUHMWPE) composites with strong mechanical performance and high thermal conductivity (23.03 W/(mK) were fabricated by solid-state extrusion (SSE) method. The thermal conductivity achieved in this work is the highest for bulk polymer so far. The effects of extrusion draw ratio (EDR) on the morphology, structure, and thermal properties were also investigated. With increase in EDR, the original isotropic structure gradually transforms into nacre-like structure due to the extensive elongational flow field during SSE, accompanied by the augment of thermal conduction performance and mechanical properties. We attribute the high thermal conductivity and mechanical properties to the construction of nacre-like structure, where the h-BN platelets and LUHMWPE molecular chains are highly oriented. Our bioinspired composites have potential applications in thermal management field for modern electronics.

High thermal conductivity of chain-aligned bulk linear ultra-high molecular weight polyethylene

It is difficult for bulk polymers to be used in the thermal management field because of their low thermal conductivity (TC). Considering that there have been few studies on the enhancement of TC for bulk polymers, we, in this work, used linear ultrahigh molecular weight polyethylene (LUHMWPE), which has a reduced number of branching, rather than conventional UHMWPE to successfully produce a high TC bulk polymer via utilizing solid state extrusion (SSE) to obtain a highly oriented structure. The high orientation of polymer backbone chains parallel to the extrusion direction and the increased crystallinity were responsible for the greatly improved TC. The oriented bulk LUHMWPE's thermal conductivity reached 4.7 W/mK, approximately 13 times that of its compression-molded sample, is also higher than the conventional UHMWPE prepared by SSE (3.0 W/mK). Moreover, it is found that the final thermal conduction performance of bulk LUHMWPE had a positive correlation with the extrusion draw ratio. The result of scanning electron microscopy shows that a number of nanofiberlike structures were formed during SSE, accounting for the super high tensile strength (120.4 MPa) of the bulks. The enhanced thermal conduction performance and high tensile strength make neat LUHMWPE a highly potential candidate to be used in electronic packaging areas.

Toward biomimetic porous poly(ε-caprolactone) scaffolds: Structural evolution and morphological control during solid phase extrusion

Two-dimensional oriented scaffolds bear spatial limitation to regenerate three-dimensional (3D) tissues despite showing the ability to guide cell alignment and elongation. By combining solid phase extrusion (SPE) of co-continuous blends with phase removal, we prepared an interconnected 3D porous poly(ε-caprolactone) (PCL) scaffold with oriented pores. To better regulate structure of these distinctive scaffolds, structural evolution of co-continuous blends in the convergent die during SPE was investigated in this study. Morphological observation manifested that the elongation deformation of co-continuous blends proceeded along the extrusion direction in the converging die continuously. Due to the extrusion temperature below the melting point of the matrices, the aligned co-continuous phase was maintained to form the uniformly oriented pores after phase extraction. Unlike consecutive deformation of phase morphology, the change in the crystalline structure of PCL involved two stages divided by the critical deformation distance (∼10 mm). At stage I (<10 mm), spherical crystals of PCL transformed into ellipsoidal shape owing to plastic deformation. At stage II (>10 mm), organized PCL lamellae formed along the extrusion direction as a result of crystal fragmentation and rearrangement. On the basis of anterior cognition, effects of processing parameters on porous morphology were further explored. It was revealed that extrusion draw ratio and annealing time were more effective to regulate pore orientation and size of aligned porous scaffolds than extrusion temperature. The tunable morphological structure of biomimetic scaffolds is of vital importance to broaden their applications for tissue repair.

Recent progress in microfiltration polypropylene membrane fabrication by stretching method

Microfiltration polypropylene (MF-PP) membrane has been widely used in many industries due to their excellent combination of good separation performances and low production cost. In addition to membrane configuration, the structure of MF-PP membrane also plays an important role in separation performance. MF-PP membrane is commonly produced by thermal induced phase separation (TIPS) and stretching. TIPS is the simplest one where the polymer is dissolved in a solvent at a decent temperature and then cooled to induce phase separation which leads to the formation of microporous structure. However, this method is limited by the nature of PP that is difficult to dissolve in organic solvents and the solvent-contaminated effluent produced during the fabrication process. Therefore, the stretching method is more favorably used. The Stretching method involves four processing stages in sequence (i.e. melt-extrusion, annealing, stretching, and heat setting). Polymer composition, extrusion draw ratio, as well as stretching rate and temperature, are important parameters that significantly affect the pore structures evolved and thus the properties as well as the performances of MF-PP membrane. In this paper, the recent development of MF-PP fabrication by stretching methods as well as the parameters involved in each method will be reviewed and discussed comprehensively.

Polypropylene-Based Porous Membranes: Influence of Polymer Composition, Extrusion Draw Ratio and Uniaxial Strain.

Several commercial grades of homo-polymer and its blends were selected to prepare microporous membranes through melt extrusion-annealing-uniaxial stretching technique (MEAUS). Branched or very fluid polypropylene was employed to modify the polymeric composition. In some blends, micro-sized calcium carbonate was added. We analysed the influence of sample composition, extrusion draw ratio, and we performed a deep study concerning the uniaxial strain rate, using in some cases extreme strain rates and strain extents. The crystalline features were studied by Differential Scanning Calorimetry (DSC), and the morphology of porous structure was analyzed through Scanning Electron Microscopy (SEM). Thermal stability and thermomechanical performance was measured by thermogravimetric analysis (TGA) and dynamic-mechanical-thermal (DTMA) study. A close relationship was found between crystalline characteristics, porous morphology and the trends registered for permeability.

Effects of extrusion draw ratio on the morphology, structure and mechanical properties of poly(l-lactic acid) fabricated using solid state ram extrusion

The utilization of an SSRE technique induced highly oriented PLLA.

Stereocomplex Crystal Formation and Development of Morphology and Mechanical Property upon Drawing of a Blend of High Molecular Weight Poly(L-lactic acid)/Poly(D-lactic acid)

The structural changes and development of morphology, crystal structure and mechanical property upon uniaxial drawing of an equimolar blend of high-molecular weight poly(L-lactic acid)/poly(D-lactic acid) (PLLA/PDLA) were investigated. Solvent-cast film of the blend were drawn by a tensile force and solid-state coextrusion. The initial film was consisted predominantly of α-form crystals and a small amount of stereocomplex (SC) crystals. Although the amount of SC did not increase upon annealing the solvent-cast film at 200°C, it increased (with draw ratio) upon drawing by either of the draw techniques when the draw was performed in the temperature range between the melting temperature of α-form crystals (Tmα = 170-180°C) and SC (TmSC = 220 °C). Upon drawing at a given temperature, SC formed significantly more rapidly with draw ratio for the solid-state coextrusion than for the tensile drawing. Thus, an oriented product consisting of only SC was obtained by the solid-state coextrusion at Te = 200 °C to an extrusion draw ratio of 16, even for a high-molecular weight PLLA/PDLA blend, although the formation of SC in such a blend has been shown to be difficult in bulk from melt or in solution. The dynamic Young's moduli of SC samples above Tg (∼60 °C) was significantly higher than that of an α-form sample.

Crystal Transformation and Development of Tensile Properties upon Drawing of Poly(L‐lactic acid) by Solid‐State Coextrusion: Effects of Molecular Weight

AbstractMelt‐crystallized films of poly(L‐lactic acid) (PLLA) with Mv in the range of 3.8 ∼ 46 × 104 consisting of α‐form crystals were uniaxially drawn by solid‐state coextrusion. The effects of Mv, extrusion draw ratio (EDR), and extrusion temperature (Text) on the crystal/crystal transformation from α‐ to β‐form crystals and the resultant tensile properties of drawn products were studied. The crystal transformation proceeded with EDR and more rapidly for the higher Mv's. Furthermore, the crystal transformation proceeded most rapidly with EDR at a Text around 130 °C, independently of the Mv's. As a result of the optimum combination of processing variables influencing the the crystal transformation (Mv, Text, and drawability), highly oriented films consisting of β‐form crystals alone were obtained by coextrusion of higher Mv samples at Text's slightly below the melting temperature (150 ∼ 170 °C) and at higher EDR's &gt; 11. Both the tensile modulus and strength increased rapidly with EDR. The modulus at a given EDR was slightly higher for the samples with higher Mv's. In contrast, the strength at a given EDR was remarkably higher for the higher M v's. The highest tensile modulus of 8.0 GPa and strength of 500 MPa were obtained with the sample of the highest Mv of 46 × 104 coextruded at 170 °C to the highest EDR of 14.

Superdrawing of polytetrafluoroethylene nascent powder by solid-state coextrusion

A film of nascent powder of polytetrafluoroethylene (PTFE), compacted below the ambient melting temperature (Tm, 335 °C), was drawn by two-stage draw techniques consisting of a first-stage solid-state coextrusion followed by a second-stage solid-state coextrusion or tensile draw. Although the ductility of extrudates was lost for the second-stage tensile draw at temperatures above 150 °C due to the rapid decrease in strength, as previously reported, the ductility of extrudates increased with temperature even above 150 °C when the second-stage draw was made by solid-state coextrusion, reflecting the different deformation flow fields in a free space for the former and in an extrusion die for the latter. Thus, a powder film initially coextruded to a low extrusion draw ratio (EDR) of 6–20 at 325 °C was further drawn by coextrusion to EDRs up to ∼︁400 at 325–340 °C, near the Tm. Extremely high chain orientation (fc = 0.998 ± 0.001), crystallinity (96.5 ± 0.5)%, and tensile modulus (115 ± 5 GPa at 24 °C, corresponding to 73% of the X-ray crystal modulus) were achieved at high EDRs. Despite such a morphological perfection and a high modulus, the tensile strength of a superdrawn tape, 0.48 ± 0.03 GPa, was significantly low when compared with those (1.4–2.3 GPa) previously reported by tensile drawing above the Tm. Such a low strength of a superdrawn, high-modulus PTFE tape was ascribed to the low intermolecular interaction of PTFE and the lack of intercrystalline links along the fiber axis, reflecting the initial chain-extended morphology of the nascent powder combined with the fairly high chain mobility associated with the crystal/crystal transitions at around room temperature. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3369–3377, 2006

Preparation of Oriented β-Form Poly(l-lactic acid) by Solid-State Coextrusion: Effect of Extrusion Variables

A film of melt-crystallized poly(l-lactic acid) (PLLA) consisting of α-form crystals was uniaxially drawn by solid-state coextrusion at 110−170 °C using split billets of different polymers. The effects of extrusion variables, including the extrusion draw ratio (EDR), temperature (Text), and pressure (Pext), on the crystal transformation from the initial α-form to the oriented β-form crystals were studied. The crystal transformation proceeded rapidly with EDR. It was found that when coextrusion was made at a constant Pext and EDR but at different Text's, there was a Text (130 °C) where the crystal transformation proceeded most efficiently. Furtheremore, when coextrusion was made at a constant Text and EDR but at different Pext's, the transformation proceeded more efficiently at a higher Pext. These results show that crystal transformation proceeds with the EDR most efficiently for the coextrusion at a Text of 130 °C and a higher Pext. As a result of the specific effect for each of the extrusion variables o...

Structural Defects Generated upon Two-Stage Solid-State Coextrusion Drawing of Ultrahigh Molecular Weight Polyethylene Reactor Powder.

A film of ultrahigh molecular weight polyethylene reactor powder, prepared by compaction below the melting point, was drawn by two-stage coextrusion at 110-130°C to a total extrusion draw ratio (EDRt) of 24. EDRt is a product of the EDRs of the two stages. Two kinds of flaws were observed; kink bands running at an angle of 30-60° to the fiber axis and periodic variations in the sample thickness along the fiber axis. The effects of extrusion variables on the formation of these flaws were studied by polarized light microscopy, atomic force microscopy (AFM) and wide-angle X-ray diffraction recorded with normal beam (diameter; φ = 0.5mm) and micro-beam (φ = 10 or 100μm). The number of flaws of both types increased with decreasing coextrusion temperature and/or decreasing die EDR used for the second-stage coextrusion. It was found that the kink bands were generated by the spring back associated with the die swell. In contrast, the thickness variation along the draw axis was found to form within an extrusion die during the second-stage draw. The effect of each of the two kinds of flaws on the stress/strain behavior is also discussed.

Solid-State Extrusion of Poly(tetrafluoroethylene) Nascent Powder.

Poly (tetrafluoroethylene) (PTFE) nascent powder was drawn by solid-state extrusion to extrusion draw ratios (EDR) ≤ 100 in the temperature (Te) range of 100~340°C, which covers the Tg(125 °C) and the ambient Tm(334°C). At a given Te, the maximum achievable EDR (EDRmax) increased with increasing shear rate (γ) and hence extrusion rate (Ve), reaching a maximum at a γ of 1 ˜ 4×104/min (V e of 300 ˜ 600 cm/minjdepending on the Te, and at yet higher γ's, the EDRmax decreased rapidly due to the formation of flaws. At a given γ, the EDRmax increased with increasing Te up to a Te =340°C. At Te's >340°C, the drawability was lost due to melting. The structure and properties of extruded products were complexly affected by the extrusion variables. Thus, the oriented rods having crystalline chain orientation function fc of 0.75˜0.96 and flexural modulus Ef of 7.5 ˜ 15 GPa at 24°C could be obtained by extrusion at an optimum Te of 340°C and a Ve of 1˜1000 cm/min (γ of 1×10˜1×105/min). These results show that nascent PTFE powder could be solid-state extruded at remarkably higher Ve's than other polymers, reflecting the less entangled morphology of the nascent powder and the high ductility of a PTFE crystal due to the week intermolecular interaction.

Preparation of oriented β‐form poly(L‐lactic acid) by solid‐state extrusion

AbstractMelt‐crystallized, low molecular weight poly(L‐lactic acid) (PLLA) consisting of α crystals was uniaxially drawn by solid‐state extrusion at an extrusion temperature (Text) of 130–170 °C. A series of extrusion‐drawn samples were prepared at an optimum Text value of 170 °C, slightly below the melting temperature (Tm) of α crystals (∼180 °C). The drawn products were characterized by deformation flow profiles, differential scanning calorimetry (DSC) melting thermograms, wide‐angle X‐ray scattering (WAXD), and small‐angle X‐ray scattering as a function of the extrusion draw ratio (EDR). The deformation mode in the solid‐state extrusion of semicrystalline PLLA was more variable and complex than that in the extensional deformation expected in tensile drawing, which generally gave a mixture of α and β crystals. The deformation profile was extensional at a low EDR and transformed to a parabolic shear pattern at a higher EDR. At a given EDR, the central portion of an extrudate showed extensional deformation and the shear component became progressively more significant, moving from the center to the surface region. The WAXD intensities of the (0010)α and (003)β reflections on the meridian as well as the DSC melting thermograms showed that the crystal transformation from the initial α form to the oriented β form proceeded rapidly with increasing EDR at an EDR greater than 4. Furthermore, WAXD showed that the crystal transformation proceeded slightly more rapidly at the sheath region than at the core region. This fact, combined with the deformation profiles (shear at the sheath and extensional at the core), indicated that the crystal transformation was promoted by shear deformation under a high pressure rather than by extensional deformation. Thus, a highly oriented rod consisting of only β crystals was obtained by solid‐state extrusion of melt‐crystallized, low molecular weight PLLA slightly below Tm. The structure and properties of the α‐ and β‐form crystals were also studied. © 2001 John Wiley &amp; Sons, Inc. J Polym Sci Part B: Polym Phys 40: 95–104, 2002

Development of oriented structure and properties on drawing of poly(vinylidene fluoride) by solid‐state coextrusion

AbstractGel films of poly(vinylidene fluoride) (PVDF) consisting of α‐form crystals were drawn uniaxially by solid‐state coextrusion to extrusion draw ratios (EDR) up to 9 at an optimum extrusion temperature of 160 °C, about 10°C below the melting temperature (Tm). The development of an oriented structure and mechanical and electrical properties on coextrusion drawing were studied as a function of EDR. Wide‐angle X‐ray diffraction patterns showed that the α crystals in the original gel films were progressively transformed into oriented β‐form crystals with increasing EDR. At the highest EDR of 9 achieved, the drawn product consisted of a highly oriented fibrous morphology with only β crystals even for the draw near the Tm. The dynamic Young's modulus along the draw direction also increased with EDR up to 10.5 GPa at the maximum EDR of 9. The electrical properties of ferroelectricity and piezoelectricity were also markedly enhanced on solid‐state coextrusion. The D–E square hysteresis loop became significantly sharper with EDR, and a remanent polarization Pr of 100 mC/m2 and electromechanical coupling factor along the thickness direction kt of 0.27 were achieved at the maximum EDR of 9. The crystallinity value of 73–80% for the EDR 9 film, estimated from these electrical properties, compares well with that calculated by the ratio of the crystallite size along the chain axis to the meridional small‐angle X‐ray scattering (SAXS) long period, showing the average thickness of the lamellae within the drawn β film. These results, as well as the appearance of a strong SAXS maximum, suggest that the oriented structure and properties of the β‐PVDF are better explained in terms of a crystal/amorphous series arrangement along the draw axis. Further, the mechanical and electrical properties obtained in this work are the highest among those ever reported for a β‐PVDF, and the latter approaches those observed for the vinylidene fluoride and trifluoroethylene copolymers. © 2001 John Wiley &amp; Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1371–1380, 2001

Superdrawing of polytetrafluoroethylene virgin powder above the static melting temperature

A new two-stage draw technique was successfully applied to the superdrawing of polytetrafluoroethylene (PTFE) virgin powder. A film, compression-molded from powder below the melting temperature (Tm = 335 °C), was initially solid-state coextruded to an extrusion draw ratio (EDR) of 6–20 at 325 °C, about 10 °C below the Tm. These extrudates from the first-stage draw were further drawn by a second-stage pin draw in the temperature (Td) range of 300–370 °C that covers the static Tm. The maximum achievable total draw ratio was ∼60 at a Td = 300 °C and increased rapidly with increasing Td, reaching a maximum of 100–160 at a temperature window between 340 and 360 °C, depending on the initial EDRs. At yet higher Td's, the ductility was lost as a result of melting. The high ductility of the PTFE extrudates at such high temperatures was ascribed to the improvement of interfacial adhesion and bonding between the deformed powder particles upon the first-stage extrusion combined with the rapid heating of only a portion of the extrudate followed by the elongation at a high rate. The highly drawn fibers were highly crystalline (χc ≤ 87%) and showed high chain orientation (fc ≤ 0.997) and a large crystallite size along the chain axis (D0015 ≤ 160 nm). The molecular draw ratio, estimated from the entropic shrinkage above the Tm, was close to the macroscopic deformation ratio independently of the initial EDRs. These results indicate that the draw was highly efficient in terms of chain extension, orientation, and crystallization. Thus, the maximum tensile modulus and strength achieved in this work were 102 ± 5 and 1.4 ± 0.2 GPa, respectively, at 24 °C. These tensile properties are among the highest ever reported on oriented PTFE. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1995–2004, 2001

Uniaxial Drawing of Isotactic Poly(acrylonitrile): Development of Oriented Structure and Tensile Properties

Uniaxial drawing of isotactic poly(acrylonitrile) (iso-PAN, isotactic triad fraction of 68%) and the resultant structure and tensile properties of drawn products were studied. The results were compared to those of atactic-PAN (at-PAN). Dried gel films prepared from 2 to 10 wt % solutions in N,N‘-dimethylformamide were initially drawn by solid-state coextrusion (first-stage draw) to an extrusion draw ratio of 16, followed by a further tensile draw at 100−200 °C (second-stage draw). The ductility of iso-PAN increased rapidly above 100 °C, due to the onset of molecular motion in crystalline regions, as found by WAXD at elevated temperatures. In contrast, the ductility of at-PAN increased above the first-order crystal/crystal transition at around 150 °C. Thus, the temperature for optimum second-stage draw of iso-PAN, 130−140 °C, was significantly lower than that (160−180 °C) of at-PAN, reflecting their crystal softening temperatures. The maximum achieved total draw ratios (DRt), after the two-stage draw, were...

Uniaxial drawing of polytetrafluoroethylene virgin powder by extrusion plus cold tensile draw

Uniaxial drawing of polytetrafluoroethylene virgin powder by extrusion plus cold tensile draw

Effects of crystalline forms on the deformation behaviour of nylon-6

Solid-state coextrusion draw was carried out for films of aggregates of solution- and melt-grown crystals of nylon-6 with α- and γ-forms. Under ordinal crystallization conditions, the crystal form was primarily a monoclinic α-form. Thus, α-crystals were converted to the γ-form by iodine treatment, followed by treatment with aqueous solution of sodium thiosulfate. The maximum extrusion draw ratio achieved (EDR max) at temperatures in the range of 100–180°C was greatly affected by both the crystal forms and the initial morphologies. At a given crystal morphology, the EDR max for the γ-crystals was higher than the α-crystals. Further, the efficiency of draw evaluated from the crystalline chain orientation was higher for γ-crystals than α-crystals. For films with α-crystals, the intercrystalline network has an important role in transmitting the stress on draw. On the other hand, for films with γ-crystals, the effect of intercrystalline network on the efficiency of draw was less prominent. These results were almost independent of the extrusion temperature studied. The effect of crystal form on the ductility is explained based on the difference in the interchain interactions due to hydrogen bonding in the crystalline regions.

Development of high ductility and tensile properties by a two-stage draw of poly(acrylonitrile): Effect of molecular weight

Ultradrawing of atactic poly(acrylonitrile) (PAN) was investigated for a Mv series, ranging 8.0 × 104–2.3 × 106. Samples for the draw were prepared from 0.5–30 wt % solutions of PAN in N,N′-dimethylformamide. The solutions were converted to a gel by quenching from 100 to 0°C. The dried gel films were initially drawn uniaxially by solid-state coextrusion (first-stage draw) to an extrusion draw ratio (EDR) of 16, followed by further tensile draw at 100–250°C (second-stage draw). The maximum total draw ratio (DRt,max) and tensile properties achieved by two-stage draw increased remarkably with sample Mv. Other factors affecting ductility were the solution concentration from which gel was made and the second-stage draw temperature. The effects of these variables became more prominent with increasing Mv. The temperature for optimum second-stage draw increased with sample Mv. Both the initial gel and the drawn products showed no small-angle X-ray long period scattering maximum, suggesting the absence of a chain-folded lamellae structure, which had been found in our previous study on the drawing of nascent PAN powder. The chain orientation function (fc) and sample density (ρs) increased rapidly with DRt in the lower range (DRt < 30) and approached constant values of fc = 0.980–0.996 and ρs = 1.177–1.181 g/cm3, respectively, at higher DRt > 30–100. The tensile modulus also showed a similar increase with DRt. The tensile strength increased linearly with DRt, reaching a maximum, and decreased slightly at yet higher DRt. The highest modulus of 28.5 GPa and strength of 1.6 GPa were achieved with the highest Mv of 2.3 × 106. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 629–640, 1998

Development of High Ductility and Tensile Properties upon Two-Stage Draw of Ultrahigh Molecular Weight Poly(acrylonitrile)

Solutions (1−5 wt %) of ultrahigh-molecular-weight atactic poly(acrylonitrile) (UHMW-PAN) in N,N‘-dimethylformamide were crystallized to gel by quenching from 100 to 0 °C. The dried gel films exhibited poor ductility on straight tensile draw. However, they were ductile on solid-state coextrusion to an extrusion draw ratio (EDR) of 8−16 (first-stage draw). Thus, the initially coextrusion drawn films were further drawn by a tensile force (second-stage draw). Drawability of the gel film was strongly influenced by several factors, including the solution concentration from which gel was made, first-stage EDR, and second-stage draw temperature. With increasing prior solution concentration, the ductility of a gel film decreased. The maximum achieved total draw ratio (DRt,max) by the two-stage draw and the uniformity of drawn products increased with first-stage EDR. Further, the ductility increased rapidly above ∼150 °C, reaching a maximum at ∼190 °C, and decreased at yet higher temperatures. A DRt,max of ∼110 wa...