Solid-state Coextrusion Research Articles

Uniaxial Draw of Poly(ether ether ketone)/Poly(ether imide) Blends by Solid-State Coextrusion

Amorphous and crystalline blends of poly(ether ether ketone) (PEEK) and poly(ether imide) (PEI) have been drawn uniaxially by solid-state coextrusion over the whole composition range. The amorphous blends have been drawn at 125 o C which is below the T g s of these compatible blends, and the crystalline blends have been drawn at 125 o C and also at 225 o C, which is above the single T g . Reported are the effect of draw on T g , PEEK crystallization, and the respective orientations of PEEK and PEI in the drawn blends. The T g s of the miscible amorphous PEEK/PEI blends are depressed up to 6 o C by draw, but their densities are slightly increased, contrary to conventional free volume theory. The density of the crystalline PEEK drawn at 125 o C exhibits a minimum at an extrusion draw ratio (EDR) of about 2.0, whereas that of the crystalline PEEK drawn at 225 o C increases monotonically with EDR. The densities of the crystalline blends drawn at both 125 and 225 o C decrease monotonically with EDR. These observations are attributable to the interplay between the destruction of the lower-melting PEEK crystals and the increasing packing in the amorphous regions on drawing. The effect of draw on the crystallization kinetics of PEEK and in PEEK/EI blends has been evaluated by DSC. PEEK in the drawn blends crystallizes faster on cold crystallization. On the other hand, when the samples were annealed in the melt followed by crystallization (melt crystallization), the drawn PEEK crystallizes slower than the undrawn PEEK. The orientations of PEEK and PEI in the amorphous drawn blends were studied by infrared dichroism. It is found that the orientations of both PEEK and PEI at a given draw ratio increase with increasing PEEK content in the blends

Property opportunities with polyolefins: a review. Preparations and applications of high stiffness and strength by uniaxial draw

Abstract Major progress has been made in preparation of high-modulus and high-strength fibres and films by uniaxial drawing of semicrystalline polyolefins. Solid-state coextrusion followed by tensile drawing on ultra-high molecular weight polyethylene (UHMWPE) and polypropylene (UHMWPP), and poly(4-methyl-1-pentene) starting from single-crystal mats, prepared from dilute solutions, produces superdrawn films with tensile moduli approaching the theoretical values reported for the crystal for each of these three polyolefins. For PE, a modulus of 220 GPa and strength of 6 GPa have been achieved. For PP, the corresponding maximum values are 37 and 2.2 GPa. This two-stage drawing technique has also been successfully applied for ultradrawing PE reactor powders. Films of compacted powder, prepared below the melting point of the powder, have been solid-state coextruded at 110°C to a draw ratio of 6, followed by tensile drawing at 120–135°C. The drawability and the uniformity of the resultant fibres and films are sensitively affected by the drawing temperatures and rates, and also by the choice of reactor powder. The maximum draw ratio achieved directly for reactor powder is ∼85, with a corresponding tensile modulus of ⩽ 130 GPa. For special conditions, high uniaxial draw and high modulus for selected reactor powders have been achieved simply by direct compaction plus calendering. In none of these processes is the polyolefin melting point exceeded. Applications of the oriented polyolefins are cited in terms of use as tapes, yarn and fabrics.

Effects of draw conditions on deformability and draw efficiency of high molecular weight poly(ethylene terephthalate) fibres

The effects of draw conditions on the deformability and efficiency of uniaxial draw were studied for solution-spun fibres from high molecular weight poly(ethylene terephthalate) (intrinsic viscosity = 2.6 dl g −1). The fibres could be drawn up to a draw ratio of 16.4 by three stages of draw (tensile draw at 80° C + solid-state coextrusion at 90° C + tensile draw at 200°C). During the solid-state coextrusion, crystal destruction and orientation of non-crystalline segments in the predrawn fibres took place, leading to further deformation at the third stage of draw. The tensile modulus and strength of the resultant highly drawn fibres reached 39 and 2.3 GPa, respectively. The improved ductility and efficiency of draw developed as a result of changes in supermolecular structure and in the number of net points due to entanglements and stress-induced crystals during deformation.

Deformation mechanism of amorphous poly(ethylene terephthalate) as a function of molecular weight and entanglements

The deformation mechanism of amorphous poly(ethylene terephthalate)(PET) has been studied as a function of molecular weight and entanglement density in predrawn films. PET chips (intrinsic viscosity = 0.6–4.9 dl g –1) were dissolved in mixed solvent of 1,1,1,3,3,3-hexafluoro-2-propanol and dichloromethane. The polymer solutions (polymer conc. = 2–40 wt%) were frozen at −30°C and then most of the solvent was removed at −30°C under vacuum, resulting in amorphous films with various entanglement densities. The films were drawn by solid-state coextrusion at 70°C. It was found that the initial polymer concentration used for film preparation had a marked effect on the maximum achievable extrusion draw ratio ( EDR max) of the films, especially for higher molecular weights. The optimum concentration decreased and the highest EDR max increased with increasing molecular weight. The deformability was also affected by the stress-induced crystals, which might act as net points. The tensile modulus and strength of drawn films were related to draw ratio and molecular weight. The higher the draw ratio and molecular weight, the higher were the tensile properties of drawn samples. The improved efficiency of draw with higher molecular weight was explained by the suppression of disentanglement and relaxation of oriented amorphous molecules during deformation; both are important in the development of structural anisotropy and continuity along the draw direction.

The effect of molecular orientation on the conductivity of iodine intercalates of 1,4-trans-polybutadiene

Of three polybutadienes, 1,4-cis-PB, 1,2-syndio-PB and 1,4-tarns-PB, only the latter forms an intercalate with iodine. Maximum conductivity of 1,4-trans-PB/I2 is 0.9.102 cm 1 in ambient atmosphere. Intercalation in stretch-oriented samples, obtained via calendering or solid state coextrusion is impaired leading to markedly lower conductivities. The effect of enhanced molecular orientation with respect to conductivity is adverse. These results undermine a conclusion reached by A.J. Thakur in a study of iodine intercalates of polydienes, implying that a conjugated backbone is not a necessary prerequisite for an effective organic conductor.

Effect of molecular weight on drawing poly(vinyl alcohol) from solution-grown crystal mats

Solution-grown crystal (SGC) mats of poly(vinyl alcohol) (PVA) with different degrees of polymerization ( DP = 3 500–18 200), precipitated from dilute solutions in ethylene glycol, were drawn by solid state coextrusion followed by tensile drawing at elevated temperatures (two-stage drawing). The SGC mats exhibited significant strain hardening during the second-stage tensile drawing. The draw stress at a given draw ratio ( DR) was higher for higher DP samples. Although the draw stress decreased and the maximum achievable DR increased with increasing drawing temperature, the practically highest temperature was limited to ⩽220°C, due to thermal degradation at higher temperatures. The maximum DR thus achieved at 220°C, as well as the efficiency of draw evaluated by the thermal elastic shrinkage, was not significantly affected by the sample DP in the range studied in this work. The ambient tensile modulus and strength increased rapidly with DR up to 50 and 1.3 GPa, respectively, at the highest achieved DR of 20 for each DP, showing no significant effect of sample DP on either the drawability or the resultant tensile properties of drawn films. Thus, among several properties examined, only the draw and fracture stresses at elevated temperatures and the differential scanning calorimetry melting temperature of drawn samples were significantly affected by DP, being markedly higher for higher DP samples. These features in drawing SGC mats of PVA are markedly different from those previously observed in superdrawing of SGC mats of polyethylenes with different molecular weights.

Electrical conductivity of iodine doped poly(butadiene-co-2-vinyl pyridine) diblock copolymers

Well defined AB poly(butadiene-co-2-vinyl pyridine) block copolymers with various compositions were prepared by anionic polymerization. The morphologies of solution-cast films of these diblock copolymers were investigated with electron microscopy. Semiconducting materials with conductivities as high as 10 −3 Scm −1 were obtained upon exposure of films of these block copolymers to iodine vapour. A specimen with lamellar morphology was subjected to solid state co-extrusion at 150°; good orientation of lamellae was achieved, but this sample, upon exposure to iodine vapour, did not show electrical anisotropy.

Conversion of single crystal mats to ultrahigh modulus polyethylene: the formation of a continuous crystalline phase

A series of ultrahigh modulus and strength polyethylene films of variable draw ratios (6–250), formed by the solid state coextrusion and post-drawing (SSE/PD of single crystal mats, were analysed by transmission electron microscopy (TEM). The high performance mechanical properties of these materials were attributed to the formation of ‘protofibrils’. Protofibrils are defined as long, highly crystalline fibrils which constitute a basic structural unit in ultradrawn polyethylene. The protofibrils observed here were made up of a series arrangement of ca. 8 nm thick ‘kebabs’ and crystalline ‘bridges’, were hundreds of nanometres long (along the chain direction), and were up to 10nm wide. Darkfield TEM, which yields a lower bound of crystal size, revealed crystalline regions with a protofibril substructure which were at least 3 microns long. The observed evolution of morphology with draw suggested that protofibrils formed via a stress-induced rearrangement of the original single crystal mat morphology and subsequent strain-induced crystallization.

Crystal lattice deformation and the mesophase in poly(ethylene terephthalate) uniaxially drawn by solid-state coextrusion

The development of crystalline and mesophase structure on drawing of poly(ethylene terephthalate) (PET) has been studied. The uniaxial drawing has been done by solid-state coextrusion from 50 to 90°C. The unit-cell parameters of stress-induced crystallites in extrudates have been determined as a function of extrusion draw ratio ( EDR) up to 4.4 and at an extrusion temperature ( ET) above T g, at 70 and 90°C. The higher the EDR, the longer the c-axis chain direction, the shorter the a and b axes and the smaller the unit-cell volume. In comparison with the conventional lattice parameters obtained by Bunn and Fisher, the highest elongation of the c axis is near 10%. These features imply that the lattice of stress-induced crystallites is far from the closest packing. Coextrudates made below the T g of PET differ markedly from those made above T g. Wide-angle X-ray diffraction (WAXD) patterns of PET extruded at 50°C (below T g) even at high draw ratio exhibit small and/or imperfect crystallites. They appear much as a mesophase. The distance between macromolecular chains ranges from 3.2 to 5.4 Å. The shortest value in the mesophase approaches the interplanar crystal distance of 3.4 Å for the (100) crystal face, on which the benzene rings lie. The crystalline peak separation of the PET, WAXD curve has been evaluated to obtain absolute crystallinities and the content of mesophase and amorphous phase.

Uniaxial draw of poly(4-methyl-pentene-1) by solid-state coextrusion

By using solid-state coextrusion, poly(4-methyl-pentene-1) has been successfully drawn uniaxially to more than 30 times at 150°C. Wide-angle X-ray and infra-red dichroism reveal a highly oriented structure. The maximum tensile modulus obtained is 3.6 GPa comparable with that of the perfect crystal of this polymer of 6.7 GPa. Thermal analysis was used to follow the changes in morphology on draw, including the development of multiple melting points in the poly(4-methyl-pentene-1).

Solid-state co-extrusion of nylon-6 gel

A partially dried nylon-6 gel has been drawn at 150°C and to draw ratio 5.7 ×, by a split billet co-extrusion technique in an Instron capillary rheometer. The gel was prepared by dissolving nylon-6 in benzyl alcohol at 165°C and cooling to gel at room temperature. On removing solvent, preorientation was introduced into the gel with the b-chain axis weakly oriented perpendicular to the gel surface. Drawing produces double orientation. One population of the crystals is oriented with chain axes in the draw direction, as in the usual uniaxial drawing. The second population has its chain axes oriented perpendicular to draw direction. From birefringence, wide- and small-angle X-ray scattering studies, a deformation mechanism for the double orientation was proposed. Thermal and mechanical properties were also studied. Annealing at 190°C produced partial reorientation of the second crystals resulting in a more complex orientation.

Orientation in poly(ethylene terephthalate) drawn by solid state coextrusion

The development of uniaxial orientation by solid-state extrusion at 60 to 90° C has been evaluated for both the amorphous and crystalline components of a polyethylene terephthalate). Analyses involved X-ray diffraction, birefringence and visable dichroism. The dichroism was evalulated from a host dye molecule. The initial PET film for draw was amorphous and isotropic. Orientation functions for the amorphous and the developed crystalline phases are reported at a series of draw ratios up to 4.4.

A Deformation-Induced Phase Separation in the Solid State

AbstractAmorphous Polymethylmethacrylate/Polyethyleneoxide blends deformed by solid-state coextrusion exhibit anomalous anisotropic Small Angle Neutron scattering patterns in the low q range. It is shown that upon drawing the samples have undergone phase separation to some extent. The resulting structure of the system is characterized by combining scattering techniques with Differential Scanning Calorimetry.

Uniaxial draw of poly(ethylene oxide) by solid-state extrusion

Abstract : Ultradrawn filaments of poly (ethylene oxide) (PEO) have been prepared by a solid-state coextrusion in an Instron capillary rheometer. Two different molecular weights, 300,000 and 4,000,000 were evaluated. Properties have been examined as a function of uniaxial draw ratio. The drawn filaments of PEO exhibit extremes of melting point, percent crystallinity, birefringence, and tensile modulus. Features of a PEO filament with a draw ratio of 32 are a 72 deg C DSC melting point and a crystallinity of 94.0%, both measured at a scan 2.5 deg C/min. The corresponding birefringence is 0.035 and a Young's modulus of 3.5 GPa. (Author)

Extrusion drawn amorphous and semicrystalline poly(ethylene terephthalate): 3. Linear thermal expansion analysis

Thermal expansion analysis of uniaxially-oriented poly(ethylene terephthalate) (PET) films has been carried out from 123 K up to the PET glass transition temperature, T g. The films are prepared by solidstate co-extrusion, from different premorphologies (amorphous, 33% and 50% crystalline), to draw ratios (EDR) up to 4.4, over a wide temperature range ( T ext). The coefficients of linear thermal expansion exhibit anisotropy: normal to the draw direction ( α ⊥) it increases, whereas along the draw direction ( α ∥) it always decreases with draw, independent of the initial morphology. Results are interpreted by treating PET as a simple two-phase composite structure. Tie-molecules occurring in the amorphous domains and bridging adjacent crystallites have a major influence. At EDR=4.4, a significant number of taut tiemolecules are developed, resulting in α ∥ becoming negative ( α max ∥=−1.0×10 −5°C −1) at temperatures below ambient. This appears to be the first report of a negative α for a polymer of relatively low crystallinity. Temperature for extrusion draw significantly affects α. Normal to the draw direction, α ⊥ decreases with T ext whereas α ∥ increases. The results show the thermal expansion of PET depends primarily on orientational effects. Only in the absence of anisotropy does per cent crystallinity have a dominant influence. In addition, the TMA thermograms display sharp transitions which are attributed to irreversible shrinkage of the oriented films. The shrinkage temperature ( T s) shows a strong dependence on both orientation and crystallinity, and it is discussed in association with T g.

Extrusion drawn amorphous poly(ethylene terephthalate): 4. Irreversible spontaneous elongation

Uniaxially-oriented poly(ethylene terephthalate) (PET) films prepared by solid-state co-extrusion exhibit irreversible spontaneous elongation (rather than shrinkage) under specific conditions. Results for these conditions show that marked elongation (up to 20%) can occur during annealing of unconstrained samples. This phenomenon, which is not commonly observed for polymers, depends strongly on the prior conditions of extrusion draw. There is significant increase in length for films prepared with extrusion draw ratio (EDR) at 2.0 in the extrusion draw temperature ( T ext) range 80–100°C. The extrusion rate is also significant. Lower extrusion rates favour spontaneous elongation on subsequent heating. In addition, the annealing temperature ( T a) also affects elongation. Samples extruded at T ext=80°C to EDR of 2.0 show maximum elongation at T a=180–190°C. However at higher temperatures, e.g. at 10°C below the melting temperature and higher, shrinkage occurs instead. Moreover, annealing at T a=90°C for different periods of time ( t a) shows that prior to the elongation a moderate amount of shrinkage occurs ( t a ⩽ 30 s). The results suggest a correlation between spontaneous elongation and crystallization during anealing.

The surface orientation of polystyrene measured by liquid contact angle

AbstractThe surface contact angle of glycerol and of water on polystyrene (PS) films has been found to depend on the extent of uniaxial draw for atactic PS. The contact angle depends on direction for the smooth films of PS drawn by solid state coextrusion. Results as a function of draw ratio to values over 4 on these noncrystalline PS samples, Mw = 6 × 105, have also been interrelated with other measures of orientation such as the anisotropy of surface and bulk properties measured, respectively, by dichroic reflectance infrared spectroscopy and by birefringence.

The effects of oxygen diffusion on the surface photooxidation of polystyrene

AbstractThis paper further illustrates the applicability of multiple internal reflectance infrared spectroscopy to the analysis of near‐surface photooxidation. The results are compared with transmission infrared spectra to evaluate compositional gradients resulting from photooxidation and the influence of oxygen diffusion. The sample was a solvent‐cast film of atactic, narrow distribution polystyrene, Mw of 100,000, that had been drawn to a ratio of 3.0 at 110°C by solid state coextrusion. Irradiation of these thin films, ∼25μm thickness, was performed on exposure to air at 35°C for periods of up to 6 h using a mercury source emitting at 254 nm. On photooxidation, a board peak appears at 3200–3500 cm−1, attributable to hydroperoxide formation. The most dramatic increase in the infrared spectra is found for a carbonyl band at 1730 cm−1. It appears to result from an aromatic acid group since it is shifted to 1660 cm−1 on immersion of the oxidized polystyrene films in aqueous ammonium hydroxide. It is confirmed that the photooxidation of polystyrene occurs preferentially at the surface and that this reaction rate is greatly reduced in the drawn polystyrene film.

Small-angle neutron scattering studies on amorphous polystyrene oriented by solid-state coextrusion

Small-angle neutron scattering studies on amorphous polystyrene oriented by solid-state coextrusion

The multistage ultradrawing of atactic polystyrene by solid-state coextrusion

Abstract Atactic polystyrene (PS) films have been highly drawn by solid-state coextrusion. The highest extrusion draw ratios, > 20, ever reported for PS were achieved by a two-stage coextrusion with high-density polyethylene as the coextrudate at 130°C. Nylon 66 billets also allowed coextrusions at the PS glass transition temperature and polypropylene billets at temperatures as high as 160°C. The coextruded amorphous PS films are fibrous, display a high degree of orientation by birefringence, and show enhanced tensile properties. Most significant, all films, including the most highly drawn ones, exhibit quantitative recovery upon rapid thermal shrinkage underlining the efficiency of deformation and thus energy storage achieved by the two-stage solid-state coextrusion.