Production,properties and impact toughness of die‐drawn toughened polypropylenes

We report the solid‐state die‐drawing of polypropylene and blends of polypropylene with a polyethylene elastomer to produce highly oriented products with enhanced mechanical properties. The blends showed an improvement in the drawability compared to the polypropylene homopolymer. The tensile modulus of the polypropylene homopolymer and the blends, along the draw direction, increased with draw ratio. In the transverse direction, the modulus of the homopolymer and the blends decreased with draw ratio as a result of anisotropy along the draw direction. The impact fracture behavior of the isotropic and the oriented samples was evaluated from noteched Charpy tests at 1 m/s over a wide range of temperatures. Linear elastic fracture mechanics were used to characterize the brittle fracture and the J‐integral approach was used to characterize the semi‐brittle and ductile fracture. In the isotropic state, the inclusion of the elastomer phase in the polypropylene matrix increased the toughness and also decreased the brittle‐ductile transition temperature. The oriented sheets, drawn at 110°C to a draw ratio of 4, were tested with the initial notch parallel and perpendicular to the draw direction. When tested with the initial notch parallel to the draw direction, the toughness of the homopolymer and the blends decreased when compared with the isotropic material. The brittle‐ductile transition temperature increased as a result of anisotropy. When tested with the initial notch perpendicular to the draw direction, the blends and the homopolymer showed considerable improvement in toughness compared to the isotropic state. Fracture along this direction is complicated, with subsidiary cracks propagating perpendicular to the main crack direction (which is parallel to the draw direction).     

Fracture behavior of die‐drawn toughened polypropylenes

The Leeds die‐drawing process has been used to make oriented sheets of toughened polypropylenes. Die‐drawn oriented sheets were produced by drawing at 110°C to draw ratios of 4, 6, and 10. Comparative measurements have been undertaken of the plane stress fracture toughness at room temperature using the essential work of fracture method for isotropic and oriented polypropylene homopolymer and the two polypropylene blends containing 10 and 25% of a polyethylene‐based elastomer. In the isotropic state, the blend containing 25% elastomer exhibited higher fracture toughness than the homopolymer and the 10% blend. The oriented sheets were tested both parallel (cracks perpendicular to the draw direction) and perpendicular (cracks parallel to the draw direction). For the latter case of cracks parallel to the draw direction, the fracture toughness of all the materials decreased with increasing draw ratio and up to a draw ratio of 4 the 25% blend exhibited higher fracture toughness than the other two materials. At higher draw ratios, however, the unfilled polypropylene was tougher than the blends. When tested parallel to the draw direction, all three materials failed with the cracks growing slowly initially followed by sudden rupture. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1336–1345, 2003     

Morphological changes of wide polyoxymethylene rod during a microwave heating drawing process

The microwave heating drawing process for producing a polyoxymethylene (POM) rod (2.5 mm in diameter) with a sonic modulus of 40 GPa has been analysed by investigating the changes in both orientation and thermal properties during drawing. During the initial crystalline deformation in the necking region, the lamellae are oriented perpendicular to the draw direction and are then unfolded into microfibrils. The crystalline orientation function reaches a high value (0.988) at a draw ratio of 6 immediately after necking. In the advanced ultra-drawing stage, the Young modulus increases gradually with increasing amorphous orientation. At the same time, the orientation distribution in the radial direction is caused by the temperature distribution induced in the radial direction of the rod. It is noted that fine adjustments of ambient temperature and microwave power are required to get ultra-high-modulus POM rods over 40 GPa with large crosssections.     

Structure and mechanical properties of uniaxially oriented films of syndiotactic polystyrene and poly(2,6‐dimethyl‐1,4‐phenylene oxide) blends

The structure and mechanical properties of highly oriented films of a miscible blend of syndiotactic polystyrene and poly(2,6‐dimethylphenylene‐1,4‐oxide) (sPS/PPO) were studied in the composition range of sPS/PPO = 10/0 to 5/5. The oriented films were prepared by stretching the amorphous films of the blends. Wide‐angle X‐ray diffraction and polarized FTIR spectroscopy were used to analyze the amount of mesophase and molecular orientation. Drawing of the amorphous films of sPS and sPS/PPO blend induced a highly oriented mesophase. The mesophase content increases with increasing draw ratio and becomes nearly constant above a draw ratio of 3. Under the same draw ratio, the mesophase content decreases with increasing PPO content. The orientation function in the mesophase is as high as 0.95–0.99 irrespective of the composition and draw ratio. On the other hand, the orientation of molecular chains in the amorphous phase and mesophase increases with increasing draw ratio, and it decreases with increasing PPO content. The drawn films of pure sPS show high strength and high modulus in the drawing direction, but exhibit low strength in the direction perpendicular to the drawing. In the case of sPS/PPO = 7/3 blend, however, the ultimate strength in the perpendicular direction was dramatically improved compared with that of pure sPS and the ultimate strength in the parallel direction was similar to that for the oriented pure sPS. The improved mechanical properties in the sPS/PPO blends were discussed in relation to the structural characteristics of the sPS/PPO blend system. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91:2789–2797, 2004     

Structure and performance of impact modified and oriented sPS/SEBS blens

Blends of syndiotactic styrene/p‐methyl styrene copolymer (SPMS) and poly (styrene)‐block ‐ploy(ethene‐co‐butylene)‐block‐polystyrene (SEBS) as well as theiruniaxial drwing behavior andd performance were investigated. Mixing was performed using a batch mixer at 280°C. Morphology was evaluted using scanning electron microscopy (SEM).Thermal properties, orientation and tensile properties were determined using differential scanning calorimetry (DSC), the spectrographic birefringence technique, and a tensile testing machine, respectively. The blends of SPMS/SEBS, 90/10 and 80/20 showed a two‐phase structure with an SEBS disperse phase in SPMS matrix. The average sizes of the SEBS paticles and tensile properties of the blends were affected by blending time and compositions. No significant effects on the modulus and strength were observed for the blends containing 10%SEBS or below. The quenched SPMS and SPMS/SEBS (90/10) blends were drawn at 110°C. and their crystallinity and orientation development compared. These were similar for both samples at low draw rations (<3.2), but were much faster for SPMS at higher draw ratios. The orientation process is shown to substantially invrease the strength and modulus in the drawing direction for SPMS and the blends. The toughness (energy under the stress‐strain curve) increased upon addition of SEBS and orientation, with a marked effect of the latter. SEM observation reveals that the dispersed SEBS has been extended to about the same draw ratio as the bulk blend in the drawn blends, indicating effcient stress transfer at the interface.     

Roll-drawing and die-drawing of toughened poly(ethylene terephthalate). Part 2. Fracture behaviour

Orientation of polymers in the solid-state has been used for a long time in enhancing the properties of the products and the die-drawing process at Leeds University (UK) and the roll-drawing process at IMI (Canada) have been used to produce oriented polymer products in a wide variety of shape and sizes. In this work, we explore the fracture behaviour of isotropic and oriented toughened poly(ethylene terephthalate) (PET) in order to improve the toughness of the oriented products in a direction other than the principal draw direction.The fracture behaviour of isotropic and oriented PET homopolymer and the two PET blends (containing 10% polyethylene elastomer and 10% compatibilized elastomer) was studied using the multi-specimen J-integral approach. In the isotropic case, the compatibilized blend had higher toughness than the homopolymer and the non-compatibilized blend. The oriented sheets from the die-drawing and roll-drawing process, drawn to a draw ratio of 3.2 at 170 °C were tested with the initial notch both parallel and perpendicular to the draw direction. For the former case, the compatibilized blend was tougher and in the other direction the drawn homopolymer was tougher than the blends. At similar draw ratios, the fracture behaviour and the toughness of the oriented sheets from the die-drawing and roll-drawing processes were identical.     

Post extrusion hot drawing of polycarbonate/liquid crystalline polymer blends

The post extrusion hot drawing of polycarbonate/liquid crystalline polymer (PC/LCP) blends, over the entire composition range, was studied. The extruded filament morphology and elastic modulus were followed as a function of blends composition, initial phase morphology, and draw ratio (DR). Hot drawing was found to cause further orientation to the already existing partially oriented LCP phase at the die exit, as reflected by the increased blends modulus. The additional orientation depends on the initial filaments structure, the blend composition, and the DR. Moreover, the orientability of the LCP phase is much higher, similar to that of neat LCP, for blends in which the LCP forms the continuous phase. In low LCP content blends, a critical DR was identified, beyond which the LCP fibrils undergo fragmentation and voids at the fibrils/matrix interface are formed, resulting in a decrease in the drawn filament modulus.     

Digital holographic interferometry: Optomechanical properties of fibers

Studying polymer fiber's mechanical properties leads to an increased understanding of the behavior of polymeric structures. This will support the design of new synthetic fibers with improved properties. Thus, there is great interest in the exact knowledge of these properties. In this work, phase‐shifting digital holographic interferometry is used to investigate the variation of the optical properties of drawn polyvinylidene fluoride (PVDF) fiber. The study shows that the refractive index for light which is polarized in parallel direction to the fiber axis increases as the draw ratio increases. This implicates that the molecules become more oriented in this direction. However, the decrease in the values of the refractive index for light polarized perpendicular to the drawing direction reflects the reduced orientation of the molecules in this direction. This has been confirmed by studying the variation of the molecular orientation versus birefringence of the drawn PVDF fiber. Holograms and their relationship with the optomechanical parameters obtained are given for illustration. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Processing and properties of polyimide melt blends containing a thermotropic liquid crystalline polymer

Several polymer blend compositions of LaRC-TPI 1500 and New TPI 450 (Mitsui Toatsu) with Xydar SRT 900 LCP (Amoco Performance Products) were extrusion processed. In addition to binary blends containing one TPI with an LCP, ternary blends consisting of an alloy containing both TPIs as the matrix were also processed. By varying the ratio of the polyimides in the matrix, the blends' thermal behavior could be tailored. This paper addresses both processing issues and film properties of these blends. Rheological and thermal studies were conducted on both blends made in a torque rheometer and on biaxially oriented film produced with a counter-rotating annular die. These biaxial blend films were further characterized by measuring tensile and electrical properties. For 70/30 New TPI/Xydar equal biaxial films of 50 μm thickness, a modulus of 3.8 GPa and a stress at break of 100 MPa were measured. For near uniaxial blend films (±3°) a modulus of 14.5 GPa and a strength of 220 MPa in the machine direction (MD) were measured. The transverse direction (TD) properties were still higher than the neat New TPI. The electrical properties of these blends were outstanding. The dissipation factor was typically less than 0.01 for most blend compositions. Similarly, the dielectric constant was typically less than 3 up to temperatures as high as 300°C.     

Micro‐structure and characteristics of highly oriented polyoxymethylene obtained by press and biaxial drawing

The physical structure of oriented polyoxymethylene (POM) drawn in two steps by press drawing and subsequent simultaneous biaxial drawing was studied. The degree of crystallinity, the orientation, and the tensile modulus depending on draw ratio were analyzed. By the press drawing method, the draw ratio reached 6.0, the tensile modulus was 4.5 GPa, and the degree of crystallinity decreased from 70% to 65%. By the two‐step drawing of press drawing followed by subsequent simultaneous biaxial drawing, the tensile modulus reached 11 GPa when the draw ratio was 14 times, and the degree of crystallinity increased from 71% to 76–80%, but it did not depend on the draw ratio, and showed effectively a constant value (average 77%). The physical structural properties, such as the degree of crystallinity, the orientation of the crystal, and the lamella structure, were analyzed by SEM, X‐ray diffraction, and other methods. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 835–844, 2006     

Ultra-high modulus isotactic polypropylene. I. The influence of orientation drawing and initial morphology on the structure and properties of oriented samples

The influence of a number of factors (temperature–speed regime and the quantity of draw stages, molecular weight of a polymer, etc.) on the deformability of initial isotropic IPP and on mechanical characteristics of highly-oriented samples, obtained in the process of a two-stages isothermal orientation drawing, was studied. It was shown that the maximum achievable values of elastic modulus and draw ratio depended not only on the molecular weight of a polymer and the sizes of spherulites, constituting initial IPP, but on the structural organization of inner-and interspherulite regions. Upon physical aging of initial isotropic films, irreversible structural changes take place, which result in the formation of microvoids while being drawn and in the reduction of mechanical properties of obtained material. An extremal dependence of elastic modulus and draw ratio of maximum drawn IPP samples on draw speed was discovered. A structural model, which is supposed to possesstie molecules with various degrees of tautness in amorphous layers, was proposed. Higher effectiveness of two-stage drawing in comparison with one-stage drawing was established. The optimum temperature–speed regime of orientation drawing, which permits the reception of highly oriented, ultra-high modulus IPP with maximum high mechanical characteristics (elastic modulus ～ 30–35 GPa and tensile strength ～ 1,1 GPa), was determined.     

Crystallization and orientation behaviors in isotactic polystyrene and poly(2,6-dimethylphenylene oxide) blends

The crystallization and orientation behavior in the miscible iPS/PPO blends were studied aiming at producing oriented materials consisting of iPS crystals and amorphous PPO chains. Oriented films of iPS/PPO blends were prepared by drawing the melt-quenched blend films. The films were heat-treated under constraint at the drawing temperature so as to crystallize the molecular chains of iPS in the oriented state. The crystallinity and the crystal orientation in the drawn annealed films were studied by the wide-angle X-ray diffraction (WAXD), and the orientation behaviors of molecular chains were analyzed by polarized FTIR spectroscopy. WAXD diagrams show the presence of the highly oriented crystalline structure of iPS in the drawn annealed films of pure iPS and iPS/PPO=7/3 blend. The polarized FTIR spectra of drawn annealed films suggest that the molecular orientation of the amorphous chains of PPO and iPS is markedly relaxed by the heat treatment, although the orientation of iPS with 3₁ helical structure was retained during the oriented crystallization. It was concluded that the drawn annealed samples of the iPS/PPO=7/3 blend consist of highly oriented iPS crystals and nearly isotropic amorphous materials. The mechanical properties of the oriented iPS/PPO blends were measured not only in the stretching direction but also perpendicular to the stretching direction. It was shown that the ultimate strength in the perpendicular direction is 4-5 times higher in the drawn annealed film of iPS/PPO=7/3 blend than in the drawn annealed iPS. The improvement in the vertical strength in the blend is discussed in relation to the structural characteristics of the iPS/PPO blend.     

The effects of roll drawing on the structure and properties of oriented poly(ethylene terephthalate)

The effect of processing conditions on the structure and properties of roll drawn poly(ethylene terephthalate) (PET) was examined. It was found that, when roll drawing amorphous PET at temperatures just above the glass transition, only very low draw ratios were obtained. This is probably because there were no crystallites to lock in the applied extension. Roll drawing at high temperatures, above 130°C, where there was significant thermal crystallization, produced film of high strength. At temperatures between 130°C and 190°C, the properties were almost independent of processing temperature. Mechanical tests performed on roll drawn samples, processed in this temperature range, showed that the initial modulus and the yield stress increased linearly with draw ratio. The yield strain decreased with draw ratio up to λ = 4.0, and then became almost constant. The processing temperature that produced samples with the greatest strength was 170°C. This was because the highest draw ratios were obtained at this temperature while maintaining constant width deformation. At low draw ratios, the crystallinity increased with the processing, whereas at higher draw ratios, it was independent of temperature. This constant level of crystalline fraction may have produced the constant failure strain that was observed at high draw ratios. The orientation functions were similarly unaffected by the processing temperature, although birefringence measurements did suggest that lower processing temperatures may have produced higher levels of orientation. The orientation of the trans conformers was independent of the temperature, but the overall content was increased at higher processing temperatures.     

Structure–properties relations of the drawn poly(ethylene terephthalate) filament sewing thread

This article presents research into draw ratio influence on the structure–properties relationship of drawn PET filament threads. Structural modification influence due to the drawing conditions, i.e., the birefringence and filament crystallinity, on the mechanical properties was investigated, as well as the shrinkage and dynamic mechanical properties of the drawn threads. Increasing draw ratio causes a linear increase in the birefringence, degree of crystallinity, filament shrinkage, and a decrease in the loss modulus. In addition, loss tangent and glass transition temperature, determined at the loss modulus peak, were increased by drawing. The observed structural changes influence the thread's mechanical properties, i.e., the breaking tenacity, elasticity modulus, and tension at the yield point increase, while breaking extension decreases by a higher draw ratio. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Production and properties of highly oriented polypropylene by die drawing

A comprehensive examination of the die-drawing behavior of polypropylene has been carried out, examining the effects of draw temperature, haul-off speed, and initial billet size. A range of oriented products was obtained and characterized, primarily by the determination of Young's modulus at room temperature, the maximum modulus being 20 GPa for a draw ratio R_A of 23.2. Using a large-scale machine, it was found possible to produce drawn products at speeds up to 2 m min^?1 at a draw temperature of 155°C and R_A of 19.3. The dynamic mechanical behavior of several drawn materials was studied over the temperature range ?30 to +80°C. It was of particular interest that the β relaxation was found to be absent in samples of high draw ratio.     

Blends containing liquid crystalline polymers: Preparation and properties of melt-drawn fibers,unidirectional prepregs,and composite laminates

This paper discusses the effect of melt drawing on the mechanical properties and morphology of liquid crystalline polymer (LCP) and thermoplastic polymer blends. Extruded fibers and films of LCP/polymer blends were melt drawn to develop uniaxial orientation of the dispersed LCP phase. The longitudinal modulus increased with increasing draw. The increase in modulus was due to higher aspect ratio of the LCP fibrils and improved molecular orientation of the LCP chains within the fibrils. Laminated composites were prepared using the extruded sheets as prepregs. The mechanical properties and the coefficient of thermal expansion (CTE) of the prepreg and the laminates agreed well with predictions from conventional composite lamination theories.     

Ultrasonic measurements of the elastic stiffness constants of oriented polyethylene

High density polyethylene (Rigidex 9), a high density copolymer of polyethylene and poly(butene-1) (Rigidex 2000), and low density polyethylene (Alkathene WJG 11) were oriented by hot drawing. The crystalline texture, as determined by wide- and low-angle X-ray diffraction, was a highly oriented chain axis in the draw direction with random orientation transversely and with lamellae surfaces perpendicular to the draw direction. Elastic stiffness constants were measured by a contact-probe ultrasonic pulse technique at 2.5 MHz both before and after annealing in a temperature range which did not significantly alter the crystalline texture. Assuming orthorhombic symmetry the nine stiffness constants of Rigidex 2000 and the three longitudinal and three shear stiffness constants of Rigidex 9 were measured after drawing and after subsequent annealing. Only the longitudinal constants of Alkathene were measured, as shear waves could not be transmitted. The longitudinal stiffness in the draw direction was markedly affected by drawing and by annealing, while the crystalline texture remained substantially unchanged; by comparison the other stiffness constants showed little change. Drawn Rigidex 9 reached a tensile modulus in the draw direction of 69 GPa. The results are compared with ‘static’ and low frequency measurements reported in the literature.     

Syndiotacticity‐rich ultrahigh molecular‐weight poly(vinyl alcohol) film. I. Determination of optimum polymer concentration by zone‐drawing method in film preparation

A new method using a simple zone‐drawing technique has been suggested for determining the optimum initial concentration of a polymer solution that has suitable macromolecular entanglements. This method was developed to replace the incorrect inherent viscosity‐measuring method for syndiotacticity‐rich (syndiotactic diad content of 63.4%) ultrahigh molecular‐weight (number‐average degree of polymerization of 12,300) (UHMW) poly(vinyl alcohol) (PVA) solution. Syndiotacticity‐rich UHMW PVA films were prepared from dimethyl sulfoxide (DMSO) solutions with different initial concentrations: of 0.1, 0.2, 0.3, 0.4, and 0.5 g/dL. In order to investigate the drawing behavior of the syndiotacticity‐rich UHMW PVA films with different solution concentrations, the films were drawn under various zone‐drawing conditions. Through a series of experiments, it was discovered that the initial concentration of PVA solution in DMSO caused significant changes in the draw ratio of the syndiotacticity‐rich UHMW PVA film. That is, the one‐step and maximum zone draw ratios of the film at an initial concentration of 0.3 g/dL exhibited its maximum values and gradually decreased at higher or lower concentrations. Thus, it was disclosed that the initial concentration of 0.3 g/dL is the optimum polymer concentration to produce a maximum draw ratio in this work. Based on the above results, it may be concluded that the optimum concentration of the initial PVA solution can be determined directly by measuring the zone draw ratio. The draw ratio, birefringence, crystallinity, degree of crystal orientation, tensile strength, and tensile modulus of the maximum drawn PVA film were 32.9, 0.0449, 0.61, 0.991, 1.91, and 46.2 GPa, respectively. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 123–134, 2000     

Production and properties of biaxially oriented polyethylene tubes

A study of the production of biaxially oriented polyethylene tubes by the die-drawing process was carried out examining the effects of draw temperature, haul-off speed, and mandrel size. The effect of postmandrel cooling was also studied. A range of biaxially oriented tubes of various draw ratios and thicknesses were produced. The Young's modulus and the tensile strength of biaxially drawn samples show considerable enhancement in both directions over the isotropic material. Biaxially drawn samples show remarkable improvement in their impact strength over the isotropic material. The crystalline orientation and texture of these samples are characterized using wide-angle X-ray scattering pole figure analysis. © 1996 John Wiley & Sons, Inc.