Relaxation of Chain Extension of Amorphous PET Fiber Above the Glass Transition Temperature

The average relaxation time for segmental orientation is considerably shorter than that for chain extension1,2, due to the difference of the ability to move between segments and chains. So in certain time intervals, an almost total relaxation of the segmental orientation can take place with little relaxation of global chain extension. Under the controlled conditions1,3, high global chain orientation but nearly random segmental orientation (GOLR) state can be achieved. Through the hot shrinka…     

Thermal shrinkage stress in high‐speed‐spun,high molecular weight poly(ethylene terephthalate) filaments

High‐speed spinning of poly(ethylene terephthalate) with an intrinsic viscosity of 0.98 dL/g was performed at a take‐up velocity of 2.5–5.5 km/min, and the effects of the fiber structure on the isothermal and nonisothermal shrinkage‐stress evolution in as‐spun filaments were investigated. In isothermal measurements, the peak shrinkage stress was consistent with the degree of amorphous orientation, whereas the so‐called frozen stress relaxation was rather constant with respect to the take‐up velocity. The maximum shrinkage stress in nonisothermal testing was also consistent with an amorphous orientation. A spontaneous elongation phenomenon took place for filaments spun at 2.5 and 3 km/min that resulted in the lowering of shrinkage stresses in both experiments. A simple calculation showed that the inertial force in the spin line was about half of the resultant shrinkage force. Filaments spun at 5.5 km/min had markedly lower shrinkage stresses and shrinkage with respect to the degree of amorphous orientation. This was attributed to the fiber structure, which gave a much lower loss‐tangent maximum for these filaments. In addition, a hypothetical model is proposed suggesting the possibility that filaments spun at 5.5 km/min may have narrow tie‐chain‐length distributions that provide relatively longer shortest tie molecules. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 964–972, 2001     

涤纶工业丝等温收缩中的结构变化

采用广角X 射线衍射、密度梯度、声速和差示扫描量热等实验方法对 145 5dtex/ 110f成品涤纶工业丝等温收缩的结构变化进行了表征 ,外加张力为 0 3N ,测定温度范围 375～ 494K .结果表明 ,涤纶工业丝的热收缩在宏观上表现为速率不同的两个过程 ,对应两种不同机理 .其中快过程对应非晶区的解取向 ,对收缩的贡献是主要的 ;慢过程对应晶区的变化 ,包含了晶粒的增长 ,新的不完善晶粒的形成和晶区的完善 .晶粒的增长在较短的时间内基本完成 ,再结晶则存在于整个收缩过程 .随温度的升高 ,晶区变化速度明显加快 ,对非晶区解取向的抑制效应因此变大 .     

超临界二氧化碳处理对聚酯纤维结构及其性能的影响

用DSC、扫描电镜、X射线衍射、萨那蒙法对超临界二氧化碳处理聚酯纤维的熔点、表面形态结构、聚集态结构进行测定,并对处理后织物的收缩性能进行了分析探讨。实验结果表明：随着超临界二氧化碳处理温度、压力的提高,聚酯纤维的熔点、熔融热略有增加,纤维表面的低聚物增多,纤维的结晶度增加,取向度略有下降,同时聚酯织物的收缩率增加。预定型处理有助于提高聚酯纤维的热稳定性,降低二氧化碳处理对聚酯织物收缩率的影响。     

Anisotropy in the thermal shrinkage of polyimide film

Anisotropy in a polyimide film was investigated in a quantitative manner by a nonlinear regression of the thermal shrinkage data obtained from thermomechanical analysis. The thermally induced shrinkage of this pyromellitic dianhydride–oxydianiline polyimide film at 573 K was directionally anisotropic in the film plane by as much as about 0.4%. The direction of maximum thermal shrinkage was inclined by about π/6 rad from the machine direction of the film. The thermal shrinkage behavior of the polyimide films in the vicinity of the glass‐transition temperature (T_g) showed an unusual anisotropic response. On the basis of a correlation between the anisotropy in the thermal shrinkage of the films and the molecular orientation of the polyimide, this characteristic thermal shrinkage behavior around T_g is suggested to be due to a recovery of the free volume lost by a physical aging process. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3222–3229, 2000     

Study of molecular orientation in poly(ethylene terephthalate) fibers by fluorescence polarization

Molecular orientation in poly(ethylene terephthalate) (PET) fibers was studied by polarized fluorescence. The observed amorphous orientation of the spun as fiber was not random but uniaxial along the fiber axis. This orientation increased with draw ratio up to about 2 and then remained fairly constant. The amorphous regions of PET fibers were disoriented when the fibers were heated while unconstrained. The fluorescence data obtained were correlated with shrinkage measurements. Fluorescence data indicated that spin drawing had more effect upon orientation than subsequent drawing of the fiber, whereas birefringence data indicated the opposite. The reason for this behavior is discussed.     

Biaxial orientation characterization on-line and off-line and structure properties correlations in films

In this paper, biaxial orientation characterization techniques are briefly reviewed. Results obtained using birefringence and Fourier Transform Infrared Spectroscopy (FTIR) techniques are presented for different applications: On-line monitoring of birefringence for an amorphous polymer (polystyrene); On-line and off-line determination of orientation (birefringence) of polyethylene terephthalate (PET) and finally off-line measurement of orientation on polyethylene (LDPE) films using FTIR. Some typical morphologies of blown LDPE films are reported and discussed. Finally, correlations between orientation on one hand and shrinkage and tear strength on the other are attempted.     

Study of thermomechanical properties of hybrid tire cord

Thermomechanical properties of tire cords, which have a considerable influence on tire functions, were investigated in the current research. The nylon and polyester cords are the most commonly used polymers in the tire. Many efforts have been made to produce a new tire cord having the capability of integrating the desired properties of these two polymers into one cord. In this study, a new cord structure was developed using nylon 6,6 and polyester tire yarns. The effect of thermal treatment was studied at the temperatures of 180°C, 200°C, and 220°C under two different loads of 600 and 1800gf on thermomechanical properties of the nylon 6,6/polyester hybrid tire cord. Shrinkage and shrinkage force as thermal properties, as well as static and dynamic mechanical properties, were investigated. The relationship between the aforementioned properties and variation in the crystal structure and fiber orientation obtained from Differential scanning calorimetry (DSC) and Wide‐Angle X‐Ray Scattering (WAXS) analysis were examined too. The results showed that the higher tension leads to the higher initial modulus and storage modulus due to the crystallization of polymers during heat treatment. The shrinkage and shrinkage force also increased, as the tension increased. In addition, a decrease in residual shrinkage and shrinkage force were acquired because of an enhancement in the temperature.     

Bulk properties of synthetic polymer-inorganic salt systems. V. Mechanical properties of oriented poly(caproamide)

Single filaments of nylon-6 and of its mixtures with KCl, LiCl, and LiBr (salt content up to 5% w/w) were prepared by extrusion at 265°C. As-spun filaments with a varying degree of orientation were obtained by altering the take-up velocity a t constant outflow velocity. These as-spun filaments were further subjected to controlled thermal and mechanical treatments. Determinations of the elastic modulus, of birefringence, of wide-angle x-ray scattering, and of shrinkage were carried out for the as-spun and for the treated filaments. While KCl caused no detectable alteration of the properties of nylon-6, lithium halides caused a considerable increase of the elastic modulus of the polymer. Under the conditions adopted, moduli up to 14 GPa were obtained. The birefringence of as-spun fibers was, however, lower when lithium salt was present. Greater shrinkage a t 170°C was exhibited by the salted than by the pure polymer. The body of results has been interpreted in terms of a more efficient orientation of the extruded polymer when lithium salt is present. The latter effect is associated with the role of these salts in reducing the crystallization rate and in increasing the melt viscosity of the polyamide as characterized in preceding papers of this series. Lithium salts also favor the α → γ transformation between the two crystalline forms of nylon-6. The transformation was, however, reversed under sufficiently high applied stress.     

Study of heat treatment on the behaviour towards shrinkage,orientation and molecular order of stretched poly(vinyl chloride) fibres

The behaviour of stretched PVC fibres during thermomechanical treatments between 110–160°C has been studied. As far as shrinkage is concerned, three ranges of temperature have been characterized. Within the range 100–140°C the poly(vinyl chloride) undergoes a plastic deformation and has an elastoplastic behaviour. From 140 up to 170°C a creep phenomenon superimposes the elastic behaviour and then the polymer has a viscoplastic behaviour. As the temperature increases above 170°C there is flowing of polymer chains and the fibres break rapidly. Annealings carried out between 100 and 150°C cause the formation of ordered domains which are responsible for the formation of a temporary physical crosslinking network which hinders the shrinkage to such a temperature lower than their melting temperature. The loss of orientation of the amorphous phase is a rapid process which takes place as the temperature rises above 100°C even if the applied stress counterbalances the overall strain resulting from the potential shrinkage.     

热处理过程中聚酯长丝的形态变化

在自制的红外三因素处理机上~[1],用红外加热在定张力下对聚对苯二甲酸乙二酯(PET)成品长丝进行热处理(二次定型)。用X-光衍射(WAXS)、X-光小角散射(DAXS)、红外光谱(IR)和双折射方法,测定样品的热收缩、结晶度、晶粒尺寸和取向、非晶取向、长周期和链折叠带强度。所得形态参数的变化表明,处理温度在200℃以上时,张力不再阻碍链折叠。不同定张力样品的形态研究表明,存在阻碍链折叠的某个张力转折值。本文条件下,这个张力值为f_(critical)=0.066g/dtex 。张力大于此值,链折叠过程受阻。     

Structure and properties of poly(ethylene terephthalate) crystallized by converging flow and high pressure

The structure and properties of a poly(ethylene terephthalate) extrudate, prepared by converging flow and high pressure, were examined. Relatively high levels of crystallinity and orientation were produced by the combination of an orienting flow and high-pressure quench. The fine structure was examined in detail by x-ray diffraction, negative staining–transmission electron microscopy, and amine etching–gel permeation chromatography. The morphology was directly relatable to this unique preparative technique. Modulus was determined by a compressive Rheovibron technique. Low shrinkage and the compressive modulus were related to the structure in the development of a structural model.     

Caracterisation par analyse enthalpique differentielle du poly(ethylene-terephthalate) deforme

This study has been undertaken in order to establish an experimental method to characterize strained PET samples by Differential Scanning Calorimetry. We propose a method for sealing the samples to avoid the shrinkage at the glass transition temperature of the polymer. This method allowed characterization of the influence of the polymer chain orientation on the glass transition temperature and correlation of the endo-exotherm exchanges with the semi-crystalline structure of strained PET samples.     

Physical and mechanical properties of ultra-oriented high-density polyethylene fibers

Ultra-oriented high-density polyethylene fibers (HDPE) have been prepared by solid-state extrusion over 60–140°C range using capillary draw ratios up to 52 and extrusion pressures of 0.12 to 0.49 GPa. The properties of the fibers have been assessed by birefringence, thermal expansivity, differential scanning calorimetry, x-ray analysis, and mechanical testing. A maximum birefringence of 0.0637 ± 0.0015 was obtained, greater than the calculated value of 0.059 for the intrinsic birefringence of the orthorhombic crystal phase. The maximum modulus obtained was 70 GPa. The melting point, density, crystallinity, and negative thermal expansion coefficient parallel to the fiber axis all increase rapidly with draw ratio and at draw ratios of 20–30 attain limiting values comparable with those of a polyethylene single crystal. The properties of the fibers have been analyzed using the simple rule of mixtures, assuming a two-phase model of crystalline and noncrystalline microstructure. The orientation of the noncrystalline phase with draw ratio was determined by birefringence and x-ray measurements. Solid-state extrusion of HDPE near the ambient melting point produced a c-axis orientation of 0.996 and a noncrystalline orientation function of 0.36. Extrusion 50°C below the ambient melting point produced a decrease in crystallinity, c-axis orientation, melting point, and birefringence, but the noncrystalline orientation increased at low draw ratios and was responsible for the increased thermal shrinkage of the fibers.     

Morphology and mechanical properties of blown films of a low‐density polyethylene/linear low‐density polyethylene blend

The morphologies of films blown from a low‐density polyethylene (LDPE), a linear low‐density polyethylene (LLDPE), and their blend have been characterized and compared using transmission electron microscopy, small‐angle X‐ray scattering, infrared dichroism, and thermal shrinkage techniques. The blending has a significant effect on film morphology. Under similar processing conditions, the LLDPE film has a relatively random crystal orientation. The film made from the LDPE/LLDPE blend possesses the highest degree of crystal orientation. However, the LDPE film has the greatest amorphous phase orientation. A mechanism is proposed to account for this unusual phenomenon. Cocrystallization between LDPE and LLDPE occurs in the blowing process of the LDPE and LLDPE blend. The structure–property relationship is also discussed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 507–518, 2002; DOI 10.1002/polb.10115     

Effects of thermal treatment on biaxially oriented poly(ethylene terephthalate). II. The anisotropic glass temperature

Thermal properties of an anisotropic biaxially oriented Poly(ethylene terephthalate) (PET) were determined before and after further deformation of the Mylar film. Film shrinkage in different planar directions was monitored during and following initial heating. After stabilization for three days at 140°C, glass temperatures T_g were determined from the decrease in length of film strips and were found to vary in the different in-plane directions. An increase in anisotropy brought about by additional deformation in the direction of the greatest orientation enhanced the T_g difference from 8 to 16°C. T_g is highest in the direction of greatest orientation.     

Molecular orientation of spider silks in the natural and supercontracted states

Two theoretical models are presented to predict average molecular orientation properties of spider silk which has unknown molecular orientation and chemical structure. Birefringence and elongation (or shrinkage) data are required for two distinct lengths of a sample in order to fit the data. The first model is based on the assumptions that each molecule behaves as the average and that the deformations are affine. The second model is based on a random distribution of the molecules as the fiber is first formed and that the molecular deformations are affine when the fiber is elongated to any length. Data were taken from spider silks in the natural state and in a shrunken state (due to water). The second model gives a much better fit of the data. The models are applicable to other systems.     

Weißbruchuntersuchungen an orientiertem Polypropylen

Summary On polypropylene sheets of increasing degrees of deformation and orientation, as obtained by cold rolling, stress whitening was investigated in a tensile tester with the aid of optical methods. The degrees of orientation were characterized with the aid of birefringence measurements and of shrinkage. The characteristic extentions in the tensile tester, at which stress whitening occurs, increase with increasing deformation and orientation from 3,6 up to a maximum of 8,0%.

---

Weißbruchuntersuchungen an orientiertem Polypropylen

Zusammenfassung Mit Hilfe einer optischen Meßmethode wurden im linearen Zugversuch Weißbruchmessungen an Polypropylen (PP)-Platten, die durch Kaltwalzen in zunehmendem Ausmaß deformiert und orientiert waren, durchgeführt. Der Orientierungsgrad wurde durch Messung der Doppelbrechung und der Schrumpfung charakterisiert. Die charakteristischen Dehnungsgrenzwerte nehmen mit zunehmender Deformation und Orientierung von 3,6 auf maximal 8,0 % zu.

Mit 5 Abbildungen und 2 Tabellen     

Solid-state extrusion of chain-extended polyethylene

Billets of chain-extended polyethylene were prepared from Alathon 7050 (M_w 59,000, M_n 19,000) in an Instron capillary rheometer by crystallization at a constant pressure of 460 MPa, at a series of teimperatures from 198 to 221°C corresponding to varying degrees of undercooling. This gives chain-extended morphologies with a range of crystallinites and lamellar thicknesses. The billets were then solid-state extruded at 100°C through a conical die with 20° entrance angle up to an extrusion draw ration 23.4. Thermal behavior was studied with differential scanning calorimetry. The orientation function measured by wide-angle x-ray diffraction showed higher orientation function measured by wide-angle x-ray diffraction showed higher orientation at equivalent draw ratio when the initial billets were crystallized at lower temperatures. Drawing efficiency, defined as the ratio of molecular draw ratio (from shrinkage) to extrusion draw ratio correspondingly increases, reaching a maximum of 0.71 in our solid-state extrusion. These studies show that highly chain-extended polyethylene, i.e., with few chain entanglements, draws poorly. Drawability was improved by increasing chain entanglements by lowering the crystallization temperature. Electron micrographs of fracture surface replicas of extrudates revealed the coexistence of undeformed, tilted, partially drawn lamellae and fibrillar structure consistent with the cahange of morphologies in Peterlin's model of plastic deformation.     

A STUDY OF STRUCTURE AND PROPERTY CHANGES OF BIODEGRADABLE POLYGLYCOLIDE AND POLY(GLYCOLIDE-co-LACTIDE)FIBERS DURING PROCESSING AND IN VITRO DEGRADATION*

Structure and properties of bioabsorbable polyglycolide (PGA) and poly(glycolide-co-lactide) (PGA-co-PLA)fibers were investigated during several industrial processing stages and in vitro degradation by means of wide-angle X-raydiffraction (WAXD), dynamic mechanical analysis (DMA) and mechanical property tests. In the orientation stage, the PGAfibers were found to have higher degrees of crystallinity than corresponding PGA-co-PLA samples produced under similarconditions. In the hot-stretching and post-annealing stages, after fibers were braided, PGA samples were found to gain morecrystallinity and higher T_g than PGA-co-PLA samples. The higher crystallinity in PGA fibers resulted in a slower rate ofdegradation. DMA results showed that a great deal of internal stress that was built during orientation and hot-stretchingstages was released in the post-annealing stage for a1l PGA and PGA-co-PLA samples. During earlier stages of in vitrodegradation, both PGA and PGA-co-PLA samples exhibited the typical cleavage-induced crystallization mechanism. Theheat shrinkage in the glass transition area was found to disappear after 6-8 days of degradation for all PGA and PGA-co-PLAsamples, indicating the amorphous portions of the polymers lost orientation after a short period in the buffer solution, mostlikely due to relaxation of the cleaved chains.