Mechanical properties and microstructure of poly(ethylene terephthalate) microfiber prepared by carbon dioxide laser heating

We determined that a poly(ethylene terephthalate) microfiber was easily obtained by irradiating a carbon dioxide laser to an annealed fiber. The annealed fiber was prepared by zone drawing and zone annealing. First, an original fiber was zone drawn at a drawing temperature of 90°C under an applied tension of 4.9 MPa, and the zone‐drawn fiber was subsequently zone annealed at 150°C under 50.9 MPa. The zone‐annealed fiber had a degree of crystallinity of 48%, a birefringence of 218.9 × 10^?3, tensile modulus of 18.8 GPa, and tensile strength of 0.88 GPa. The microfiber prepared by laser heating the zone‐annealed fiber had a diameter of 1.5 μm, birefringence of 172.8 × 10^?3, tensile modulus of 17.6 GPa, and tensile strength of 1.01 GPa. The draw ratio estimated from the diameter was 9165 times; such a high draw ratio has thus far not been achievable by any conventional drawing method. Microfibers may be made more easily by laser heating than by conventional technologies such as conjugate spinning. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1955–1958, 2003     

Process–structure–property relationship of melt spun poly(lactic acid) fibers produced in the spunbond process

We report on the process–structure–property relationships for Poly(lactic acid) (PLA) filaments produced through the spunbond process. The influence of spinning speed, polymer throughput, and draw ratio on crystallinity and birefringence of fibers were evaluated. We established that increasing spinning speed increases crystallinity and birefringence of fibers. We also investigate the role of fiber structures on fiber tensile properties—breaking tensile strength, strain at break, initial modulus, and natural draw ratio. An increase in spinning speed leads to a higher breaking tensile strength, higher initial modulus and lower strain at break. We have shown an almost linear relationship between breaking tensile strength of PLA fibers and birefringence. This indicates that improved tensile properties at high spinning speeds can be attributed to enhanced molecular orientation. The dependency of fiber breaking tensile strength and strain at break on spun orientation were explained with natural draw ratio, as a measure of spun orientation. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44225.     

Ultradrawing of polystyrene by solid-state coextrusion: Shear-induced crystallization in isotactic polystyrene

Polystyrene with a 60% isotactic dyad content (iPS) was subjected to two-stage solid-state coextrusion at 124 and 160°C. It was shown that only shear-induced crystallization occurred with the amount of crystallinity strongly dependent on draw ratio. The steep increase in crystallinity from 0 to 29% is accompanied by a marked increase in the absolute total birefringence from 0 to 30 × 10^?3 and the tensile properties, from 2.5 GPa to 4.5 GPa, giving strong evidence for the necessity of a crystalline phase to achieve higher tensile moduli. Wide-angle X-ray scattering showed a higher crystal orientation for the extrudate produced at 124°C than for the one produced at 160°C. Thermal shrinkage experiments support a partial dissipation of orientation after extrusion at 160°C and on reextrusion in general. Electron microscopy revealed a fibrous nature for the solid-state coextrudates produced at both temperatures.     

Effect of tensile strain rate on the mechanical properties of constrained-uniaxially and simultaneous-biaxially drawn poly(ethylene terephthalate) sheets

The dependency of the mechanical properties (Young's modulus, yield strength, breaking strain, and breaking energy) of preoriented poly(ethylene terephthalate) (PET) sheets on the tensile deformation speeds was examined and discussed in relation to changes of density and birefringence. The procedures for preorientation were constrained-uniaxially (CU) and simultaneous-biaxially (SB) drawings at 65°C. The performance characteristics of the present tensile testing at room temperature were obtained over a wide range of extension rates (1.7 × 10^?4?13.1 m/s = 0.29–2.3 × 10⁴%/s) without changing the mode of deformation and the shape of the test pieces. The CU drawn PET is strain-rate-independent and mechanically superior in structure in the preextended direction with draw ratio λ > 2.5. In the SB drawn PET such a structure comes into existence at λ > 3, which has, furthermore, no dependency on draw direction (mechanically isotropic). The draw ratio of the latter case corresponded to the birefringence (?Δn/d) of about 5 × 10^?2. These results imply a possibility of producing the strain rate (from low to impact speeds) independent, anisotropy-free, and mechanically superior molded products of PET if adequate extrusion or blow molding methods which induce multiaxial orientation with ?Δn/d > 5 × 10^?2 are developed.     

Effect of melt spinning and cold drawing on structure and properties of poly (aryl ether ketone) (PAEK) fibers

The effects of melt spinning and cold drawing on structure development and resulting properties of poly (aryl ether ketone) (PAEK) have been investigated. Melt spun and subsequently cold drawn fibers were characterized by differential scanning calorimetry, wide angle X-ray diffraction, small angle X-ray diffraction, and birefringence techniques. At low take-up speeds, essentially amorphous fibers are produced. High take-up speeds result in development of crystallinity in the as-spun fibers. Cold drawing above the, T_g of PAEK causes further increase of crystallinity. Wide angle X-ray patterns indicate progressive alignment of chains along the fiber axis in as spun as well as in cold-drawn fibers with the draw down ratio and cold draw ratio. However, cold drawing was observed to broaden the WAXS peaks. SAXS patterns of cold drawn and fixed annealed fibers changed from two-point to four-point patterns indicating mosaic pattern formation of crystalline and amorphous regions. Mechanical properties including tensile strength, elongation at break, modulus, and yield strength were measured and correlated with fiber structure. Fracture surfaces of tensile tested fibers were observed using scanning electron microscopy and correlated with developed fiber structure.     

Structure development in melt‐spinning syndiotactic polystyrene and comparison to atactic polystyrene

Syndiotactic polystyrene (s‐PS) and atactic polystyrene (a‐PS) were melt‐spun into filaments. The s‐PS filaments exhibited increasing amounts of crystallinity and orientation with increasing drawdown ratio and spinline stress. The a‐PS filaments were amorphous but exhibited birefringence. The birefringence and Hermans orientation factors for a‐PS were proportional to this spinline stress. In ice water and at low drawdown ratios, the s‐PS is glassy or mesomorphic. At higher drawdown ratios and spinline stresses, it crystallized. The crystalline form was the zigzag TTTT hexagonal α‐form. The birefringence and orientation factors of the s‐PS filaments were higher than those of the a‐PS filaments and the difference of the birefringence increased with increasing spinline stress. Mechanical testing results showed that the Young's modulus and tensile strength generally increased with increasing spinline drawdown ratio for both a‐PS and s‐PS filaments. The elongation to break was enhanced for both materials by increased chain orientation. Polym. Eng. Sci. 44:2141–2147, 2004. © 2004 Society of Plastics Engineers.     

Effect of initial take-up speed on properties and structure of as-spun and drawn/heat-set poly(ethylene terephthalate) filaments

The effect of initial take-up speed on the properties and structure of both as-spun and drawn/heat-set poly(ethylene terephthalate) filaments was characterized through measurements of birefringence, percent crystallinity, tensile properties, high temperature shrinkage, loss tangent temperature dependence, DSC melting behavior, and wide-angle (WAXS) and small-angle X-ray scattering (SAXS). While a steady trend toward improved as-spun filament orientation and tensile properties occurred with increasing initial take-up speed, the reduced drawability of these more structured precursor filaments resulted in corresponding drawn/heat-set filaments that were of relatively lower overall orientation and tensile strength. The observed trends in tenacity, initial modulus, and high temperature shrinkage of the drawn/heat-set filaments appeared to be well correlated with the extent and distribution of amorphous phase rigidity as perceived through inferences made from the loss tangent temperature dependence. The WAXS patterns of the drawn/heat-set samples indicated that these filaments all possess a well-developed and highly oriented crystalline structure. Application of a simple two phase model allowed the determination of an amorphous orientation factor, which for the drawn/heat-set filaments was generally found to decrease as the draw ratio imposed in order to achieve comparable levels of elongation to break decreased. The SAXS patterns of the drawn/heat-set filaments indicated that comparable long period spacings exist in all cases and that a transition from a four-point pattern to a two-point bar-shaped pattern occurred when the precursor filament possessed some significant amount of as-spun crystallinity. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2115–2131, 1998     

Effect of water molecules on crystallization during unixial drawing of poly(ethylene terephthalate) films

The role played by sorbed water molecules present within poly(ethylene terephthalate) film at the moment of uniaxial drawing on the appearance and the percentage of the strain‐induced crystalline (SIC) phase is investigated by birefringence, X‐ray diffraction, and differential scanning calorimetry measurements. We show that, for law draw ratio, water play its traditional plasticizer effects. The SIC phase appears for a draw ratio, which depends weakly on the relative humidity. The water does not modify the degree of crystallinity of drawn films but impedes the growth of a part of the crystallites and modify their crystalline size. For high draw ratio, water impedes the orientation of the amorphous phase. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1056–1066, 2000     

The influence of annealing treatment on the molecular structure and the mechanical properties of isotactic polypropylene fibers

An investigation was carried out on the effects of annealing treatment on the molecular structure and the mechanical properties of isotactic polypropylene fibers annealed in an air heated environment at temperatures ranging from 60 to 140°C. Analysis of the equatorial X‐ray diffraction traces showed the presence of a three phase system of amorphous‐smectic‐monoclinic forms and revealed the transformation of the metastable smectic form to the highly stable monoclinic form as the annealing temperature is increased, resulting in an enhanced degree of crystallinity and the crystallite size. The improvements in the degree of crystallinity and the crystallite size became more remarkable above 120°C. Evaluation of the crystallinity was carried out using an analysis of density, infrared spectroscopy, and X‐ray diffraction methods whereas the state of the molecular orientation was evaluated using polarized infrared spectroscopy measurements only. Polarized infra‐red spectroscopy measurements after the curve fitting procedure showed a slight increase of the molecular orientation of the helical chain segments present in the crystalline phase represented by the IR bands at 841 and 998 cm^?1 whereas the amorphous structure represented by the IR band at 974 cm^?1 showed no significant change with increasing annealing temperature. The improvement in the molecular orientation of the crystalline phase became more remarkable above 120°C. Tensile strength of the annealed fibers increased with increasing annealing temperature but the elongation at break and the initial modulus were not affected as much as the tensile strength. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Correlation between different microstructural parameters and tensile modulus of various polyethylene blown films

The objective in this study is to establish a model for the prediction of tensile properties using various types of polyethylene films (LLDPE, HDPE, and LDPE). A series of blown films were produced by varying three process parameters: take‐up ratio, blow‐up ratio, and frost line height. The tensile properties of the resulting films were investigated in relation to their microstructural characteristics. The microstructural parameters were determined by differential scanning calorimetry, wide angle X‐ray diffraction (WAXD) pole figures, SAXS (small angle X‐ray diffraction), and birefringence measurements. The orientation parameters of the films were measured by WAXD and birefringence. They were determined for both crystalline and amorphous phases. The crystalline content, lamellar thickness, and crystal sizes were obtained from DSC and WAXD. The SAXS technique was used to find the average length of the crystalline and amorphous layers. A model for the tensile modulus is proposed and correlated to some structural parameters including crystallinity, orientation factors for crystalline c‐axis and amorphous phase, lamellar thickness, crystal size, the average length of the crystal layer, and long spacing period. The measured modulus and the calculated one were compared and a reasonable agreement was found between them for all series of films. POLYM. ENG. SCI., 47:1430–1440, 2007. © 2007 Society of Plastics Engineers     

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.     

Orientation of amorphous poly(ethylene terephthalate) by tensile drawing,roll-drawing,and die-drawing

Orientation of initially amorphous poly(ethylene terephthalate) films and sheets was carried out by means of tensile drawing in a tensile tester, roll-drawing using a series of four rolling stations, and by die-drawing. The drawing temperature was 80 and 90°C and drawing rate ranged from 2 to 20 cm/min in the different processes. Crystallinity was observed to increase with draw ratio for all these processes. The onset of crystallinity development depends on the drawing rate. The glass transition temperature was essentially constant and crystallization temperature decreased with increasing draw ratio. The trans conformers content was observed to increase with draw ratio at the expense of the gauche conformers for the three processes. The orientation of the trans conformers increases readily from the beginning of draw and saturates rapidly. The orientation of the gauche conformers was negligible. Some differences are observed for the behavior of the 1020 and 730 cm^?1 benzene ring bands, which may be due to differences in the benzene ring configuration at the surface as a result of different deformation mechanisms for the die and roll-drawing. However, further investigations to elucidate this hypothesis are needed. The mechanical properties obtained in the longitudinal direction increased for all the processes. In the transverse direction, the roll and die-drawing processes induced a decrease in modulus and strength with increasing draw ratio, similar to that observed for uniaxial orientation. This indicates that these processes are mainly uniaxial, despite the plane strain nature of the deformation.     

Ultradrawing of amorphous polymers by coextrusion illustrated with atactic polystyrene

Films of pure and high-impact atactic polystyrene were prepared by the recently developed technique of solid-state coextrusion. The films were produced at extrusion rates ≥4 cm/min at 126°C with a maximum extrusion draw ratio (EDR) of 11.6. These ultradrawn films are fibrous, have a high birefringence of ?2.24 × 10^?2, and exhibit a 72% elastic recovery. The material has a tensile modulus of ～4–5 GPa and a tensile strength to break of 85 MPa. Thermal analysis suggests a constant T_g.     

Controlling of threadline dynamics via a novel method to develop ultra‐high performance polypropylene filaments

A detailed study was conducted to investigate the effects of horizontal isothermal bath (hIB) on the production of ultra‐high performance polypropylene filaments. Two different commercial PP polymers were used with the melt flow rate of 4.1 and 36 g/10 min. The optimum process conditions depended on polymer molecular weight. Fibers showed distinct precursor morphology for each at each optimum process condition. However, two sets of filaments demonstrated similar fiber tenacity and modulus of about 7 and 75 g d^?1, respectively, for as‐spun and more than 12 g d^?1 for tenacity and more than 190 g d^?1 for modulus values of drawn fibers after just 1.49 draw ratio. The mean value for the modulus after the drawing process for the high melt flow rate was 196 g d^?1. The theoretical modulus of PP is 35–42 GPa¹⁹, (275–330 g d^?1), shows the hIB fiber's modulus performance is approaching its theoretical maximum value. Fibers had greatly improved thermal properties, degree of crystallinity, crystalline and amorphous orientation factors. The hIB spinning system produced highly oriented and predominantly amorphous structure for as‐spun fibers and a well‐defined, highly oriented crystalline fibrillar and amorphous structure after drawing process with the draw ratios lower than 1.5. POLYM. ENG. SCI., 55:327–339, 2015. © 2014 Society of Plastics Engineers     

Determination of intrinsic physical constants of poly(trimethylene terephthalate) from drawn filament

The intrinsic lateral sonic moduli of the crystalline and amorphous regions of poly(trimethylene terephthalate) (3GT) (about 4.1504 ± 0.8396 GPa and 1.6096 ± 0.0368 GPa, respectively) were obtained from sonic moduli and crystallinities of unoriented 3GT filaments annealed under different conditions. Using the obtained intrinsic lateral sonic moduli of the crystalline and amorphous regions, the degree of orientation of the amorphous region of uniaxially drawn 3GT filaments could also be obtained from the crystallinity, sonic modulus, and the degree of crystalline orientation estimated from X‐ray azimuthal scan data. Thus, the intrinsic birefringences of the perfectly oriented crystalline and amorphous regions of the 3GT fibre (about 0.2057 ± 0.0160 and 0.2175 ± 0.0923, respectively) could be obtained from the appropriate combinations of birefringence, crystallinity, and the degree of orientation of the crystalline and amorphous regions. © 2003 Society of Chemical Industry     

Determination of intrinsic birefringence values of polycaprolactone filaments

Intrinsic birefringences of polycaprolactone filaments are determined using the approach suggested by Samuels. First, intrinsic lateral moduli are determined from the values of crystallinity and sonic moduli of unoriented filaments. These values are found to be 3.473 GPa and 0.071 GPa, respectively, for crystalline and amorphous regions. The crystallinity, sonic moduli and crystalline orientation function of drawn and heat set filaments are used to evaluate amorphous orientation functions. Finally, Stein and Norris's equation along with birefringence data is used to obtain intrinsic birefringence values of crystalline and amorphous regions and these values are found to be 0.079 ± 0.002 for crystalline regions and 0.066 ± 0.008 for amorphous regions. Copyright © 2012 Society of Chemical Industry     

A correlation of Young's modulus with yield stress in oriented poly(vinyl chloride)

The variations of tensile and compressive yield stresses and of Young's modulus of oriented poly(vinyl chloride) sheet with direction and with degree of orientation, represented by birefringence, are shown. Young's modulus was calculated from elastic stiffness constants measured by an ultrasonic pulse method at 5MHz with estimated strain and strain rate amplitudes of 2 × 10^?5 and 100s^?1. Yield strains were about 5 × 10^?2 measured at strain rates of about 2 × 10^?2s^?1. Although the measuring conditions were so different there was found to be a close correlation between tensile yield stress and Young's modulus, the two quantities being connected by a simple linear relationship, as direction of measurement and degree of orientation were varied. Compressive yield stress did not correlate with Young's modulus, and changed little with direction or degree of orientation by comparison with tensile yield stress. The empirical linear relationship between tensile yield stress and Young's modulus, difficult to account for theoretically, might form the basis of a method for determining tensile yield stress ultrasonically.     

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.     

Roller drawing of polyoxymethylene

The roller drawing of polyoxymethylene (POM) sheets was carried out in the temperature range of 140–157°C. The mechanical properties, the molecular orientation, and the microstructure of the roller-drawn POM sheets were investigated by means of tensile test, dynamic viscoelasticity, wide-angle X-ray diffraction, small-angle X-ray scattering, visible dichroic spectrum, electron microscopy, and so on. The Young's modulus and the tensile strength increased with increasing draw ratio up to draw ratio, λ of 14–15. The improvement of the mechanical properties is concerned with structural changes, such as the increase in orientation function in the crystalline and amorphous regions and the formation of taut tie molecules and crystalline bridges in the intercrystallite and interfibrillar regions. In the higher draw ratio range (λ > 15), the increase in Young's modulus and tensile strength was restricted by the formation of interfibrillar microvoids.     

Determination of intrinsic birefringence of smectic phase in isotactic polypropylene

When isotactic polypropylene is quenched at 0°C from the molten state, a biphasic material, amorphous-smectic, is obtained. The smectic phase has an intermediate order between the amorphous and the crystalline. In this study the intrinsic birefringence of the smectic phase was determined. Tapes with different draw ratio were prepared at room temperature, at which the smectic phase does not transform into the crystalline phase. The amount of the smectic phase was determined with measurements of density and sorption of vapors of dichloromethane. The value of the intrinsic birefringence for the smectic phase is: δ°n_sm = 40 · 10⁻³. This value is in good agreement with the values proposed by Samuels for the intrinsic birefringence of the amorphous and the crystalline phases. © 1996 John Wiley & Sons, Inc.