Effect Of Drawing Temperature Research Articles

Effect of draw temperature and flame polishing on birefringence of silica glass fiber

AbstractRecently developed methods for high resolution birefringence measurement have been applied to distinguish between the surface and interior birefringence of silica glass fibers as a function of drawing temperature and initial surface condition for two types of silica glass with different water contents. Fibers were drawn in a water‐free argon environment using graphite heating elements. It was found that fibers drawn at lower temperatures resulted in greater, interior birefringence, in agreement with previous reports. Additionally, it was found that in the case of low‐water silica glass, flame polishing via oxygen–hydrogen mixture and drawn into fibers at lower temperature resulted in significant surface compressive stress upon drawing. This compressive stress may be the result of surface stress relaxation in silica glass that occurs in the presence of water during fiber drawing. In silica glass that contains greater internal hydroxyl impurity concentrations, the interior birefringence as well as the surface stress relaxation was significantly reduced under the same fiber drawing conditions. Characterization of such stress responses provides insight into the effects of common processing techniques as well as impresses the significance of preform processing for consistent fiber production.

Fast, Light-Responsive, Metal-Like Polymer Actuators Generating High Stresses at Low Strain

Summary Producing lightweight polymeric actuators able to generate high stresses typical of hard metals and/or ceramics remains challenging. The photo-mechanical responses of ultra-drawn ultra-high molecular weight polyethylene (UHMWPE) actuators containing azobenzene photo-switches with symmetrically attached polyethylene (PE) side chains are reported. Long PE side chains promote dispersion within the apolar UHMWPE matrix, and the ultra-drawn films are highly aligned. The ultra-drawn azobenzene-doped UHMWPE films have high Young's moduli (∼100 GPa) and are viscoelastic at room temperature at strains below 1%. The photo-mechanical response of the films is fast ( 6 × 104 Pa (kg m−3)−1) to UV or visible light at a low strain (∼0.06%). The actuator responds to rotating linearly polarized light, causing a photo-induced stress wave response. Such rapid, high-stress, low-strain, photo-mechanical responses are unique in soft polymer systems with physical values approaching hard metals/ceramics.

Preparation of High Modulus Poly(Ethylene Terephthalate): Influence of Molecular Weight, Extrusion, and Drawing Parameters

Poly(ethylene terephthalate) (PET) which is one of the most commercially important polymers, has for many years been an interesting candidate for the production of high performance fibres and tapes. In current study, we focus on investigating the effects of the various processing variables on the mechanical properties of PET produced by a distinctive process of melt spinning and uniaxial two-stage solid-state drawing (SSD). These processing variables include screw rotation speed during extrusion, fibre take-up speed, molecular weight, draw-ratio, and drawing temperature. As-spun PET production using a single-screw extrusion process was first optimized to induce an optimal polymer microstructure for subsequent drawing processes. It was found that less crystallization which occurred during this process would lead to better drawability, higher draw-ratio, and mechanical properties in the subsequent SSD process. Then the effect of drawing temperature (DT) in uniaxial two-stage SSD process was studied to understand how DT (<Tg or close to Tg or close to Trec) would affect the crystallization, draw-ratio, and final mechanical properties of PET. The designed process in current work is simulated to an industrial production process for PET fibres; therefore, results and analysis in this paper have significant importance for industrial production.

Effect of conformation on the properties of uniaxially drawn polylacide films upon drawing temperature

Polylactide(PLA) films were drawn at various drawing temperature of 65, 90 and 120 °C. The effects of drawing temperature on structural conformation and properties of PLA films were investigated. It was confirmed that the PLA films at drawing temperature of 65 and 90 °C were composed of α′ phase crystal form. The strain-induced crystallization and molecular orientation increased with increasing the draw ratio, which result in improving the mechanical and thermal properties of α′ phase PLA films. However, at drawing temperature of 120 °C, the strain-induced crystallization and molecular orientation of PLA films were not distinctly detected. It was supposed that the rate of the chain relaxation was faster than chain orientation and strain-induced crystallization during uniaxial drawing process.

Orientation and structural development of semicrystalline poly(lactic acid) under uniaxial drawing assessed by infrared spectroscopy and X-ray diffraction

The effects of drawing temperature (Td) and draw strain on the orientation and structure of semicrystalline poly(lactic acid) (PLA) films were investigated by wide angle X-ray diffraction and polarized Fourier transform infrared spectroscopy. Semicrystalline PLA samples with two initial levels of crystallinity, Xc = 1% and 11%, were prepared by cold crystallization at 80 °C. Whatever Xc and Td, the total amount of the ordered phases (i.e. crystalline + mesophase) increased with draw strain, which could be ascribed to the formation of strain-induced mesophase at Td = 60 or 70 °C but crystalline at 80 °C. Also, the molecular orientation of both the amorphous and ordered phases increased with draw strain. Whatever Xc, the orientation of the ordered phases was insensitive to Td, whereas higher orientation in the amorphous phase was achieved at lower Td, and the trend was more significant for Xc = 1% compared with 11%.

Effect of drawing temperature on the structure and free volume of semicrystalline polyester yarns

Supercritical carbon dioxide (scCO2), an environmentally friendly solvent, can change the fine structure of fibers depending on treatment temperature and pressure. This article presents the results of an investigation into the effects of drawing temperature, scCO2 exposure and tension on structural changes, and mesomorphic transitions in partially oriented yarn (POY) and oriented poly(ethylene terephthalate) (PET) yarns. Samples of POY and PET yarns were uniaxially drawn at different temperatures to obtain filaments with different structures for subsequent exposure to scCO2 in the presence and absence of tension at a temperature of 80oC and under a pressure of 220 bar. Structural investigation of the samples was performed by combining the results obtained from differential scanning calorimetry, Fourier transform infrared, mechanical deformation, and density and birefringence measurements, all of which exhibited a good correlation. The fractional free volume in the PET samples was considered for interpreting structure–property relations. Results showed that the development of a transient structure strongly depends on process temperature and that for an identical draw ratio, PET yarns drawn at 23oC are significantly more oriented than those drawn at 68oC. Two crystallization mechanisms, that is strain-induced and thermal-induced crystallization, are involved that are frequently used to explain the structural changes during yarn deformation at different temperatures. The degree of crystallinity and orientation factors for PET yarns does not proportionally increase with increasing temperature of the drawing process; indeed, the highest value is obtained at a temperature of 100oC, whereas the lowest is observed at a temperature of 68oC, which is near the glass transition temperature. Tension under scCO2 exposure also produces significant effects in term of causing structural changes. POLYM. ENG. SCI., 55:2030–2041, 2015. © 2014 Society of Plastics Engineers

Deformation temperature and lamellar thickness dependency of Form I to Form III phase transition in syndiotactic polypropylene during tensile stretching

Phase transition from form I to form III in syndiotactic polypropylene crystallized at different conditions during tensile deformation at different temperatures was investigated by using in situ synchrotron wide angle X-ray diffraction technique. In all cases, the occurrence of this phase transition was observed. The onset strain of this transition was found to be crystalline thickness decided by crystallization temperature and drawing temperature dependent. The effect of drawing temperature on this phase transition is understood by the changes in mechanical properties with temperature. Moreover, crystalline thickness dependency of the phase transition reveals that this form I to from III phase transition occurs first in those lamellae with their normal along the stretching direction which have not experienced stress induced melting and recrystallization.

Microstructure and properties of porous nanocomposite films: effects of composition and process parameters

AbstractPorous nanocomposite films based on polypropylene (PP) and titanium dioxide (TiO2) nanoparticles were prepared by melt extrusion followed by uniaxial stretching. The effects of drawing temperature, extension rate, stretching ratio and composition of the base films on the final properties and microstructure of the stretched films were studied. Water vapor permeability (WVP) results showed a significant decrease in permeability of the films stretched at temperatures higher than 60 °C. Porosity, pore size and water vapor transmission rate in the porous nanocomposite films had a direct relation with nanoparticle content, extension rate and stretching ratio. Study of the morphology of the stretched films, using SEM, revealed that the pores form due to PP/TiO2 interfacial debonding at low stretching ratios. Higher stretching ratios cause an enlargement of the pores and the formation of a PP fibril structure parallel to the stretching direction. Quantification of dye adsorption revealed that the quantity of adsorbed dye increased with porosity and surface area of the pores. © 2014 Society of Chemical Industry

Study of microstructure of oriented PET fibres exposed to supercritical carbon dioxide

Samples of partially oriented yarn (POY) PET fibers were uniaxially drawn at temperatures below, near, and above the glass transition temperature at a constant draw ratio before exposure to supercritical carbon dioxide (scCO2) in the presence of tension at a temperature of 80 °C and a pressure of 220 bar. The effects of drawing temperature and scCO2 exposure on structural changes and on mesomorphic transitions, in particular, were investigated using differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and birefringence and density measurements. A good correlation was obtained among the results obtained from various techniques. Results indicated that the development of a transient mesophase structure depended strongly on process temperature. By drawing PET fibers in the samples at temperatures below the glass transition (cold-drawing), a mesophase structure developed in which the highly extended chains played a key role in structural changes incurred. Meanwhile, exposure to scCO2 led to the plasticization of the samples accompanied by their reduced glass transition and cold crystallization temperatures. This process also gave rise to the appearance of a second melting peak at about 135 °C that is related to the melting of imperfect and thin crystals, thereby inducing structural changes in the treated fibers. In the case of samples subjected to cold drawing and to scCO2 exposure, the transformation of the mesophase structure into the crystalline phase was found to be strongly affected by scCO2 exposure, while this same effect was negligible in the case of hot drawn samples.

Orientation of HDPE inclusions within solid-state drawn rubber-modified isotactic polypropylene: DSC insight

Effect of drawing temperature on the melting behavior of oriented isotactic polypropylene (PP) modified with ethylene-propylene-diene monomer rubber with a small amount of high-density polyethylene (HDPE) is explored in this study. Injection-molded specimens both neat and 8 vol % modified PP were solid-state drawn to natural drawing ratio and characterized by X-ray diffraction, dynamic mechanical analysis (DMA), Charpy impact test and differential scanning calorimetry (DSC). A synergy of orientation and embedding rubber particles caused a significant increase of low-temperature notched impact strength of oriented blends. It was shown, that the DSC method can be used successfully for the indirect but very sensitive characterization of orientation on a nanometre scale. At the drawing temperature of 120°C, the DSC data indicated an incomplete transition of the PP crystalline structure: This is reflected by splitting and shifting of the melting peak of PP. An increase of the melting temperature of the HDPE inclusions by 3.5°C reflects the high orientation. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Deformation-induced morphology evolution during uniaxial stretching of isotactic polypropylene: effect of temperature

The effects of draw temperature on the deformation-induced morphology evolution of isotactic polypropylene in terms of crystal orientation, degree of crystallinity, crystal size in the direction normal to chain axis, long spacing, and the deformation behavior at the crystal lattice and lamellae scale were investigated using differential scanning calorimetry, two-dimensional wide-angle X-ray diffraction, and small-angle X-ray scattering, respectively. The results revealed that the thermal behaviors are associated with the deformation-induced morphology evolution, and the morphology evolution is strongly temperature dependent. At low strain, crystal fragmentation takes place at all the draw temperature range studied; at high strain, after crystal fragmentation the draw temperature shows different effects on the morphology evolution: at low temperature (25 °C), fragmentation of the crystal blocks continues; at medium temperatures (80 and 110 °C), the broken crystal blocks remain stable and the unfolded chains and disentangled chains in amorphous region crystallize into crystal blocks with crystal size almost identical to that of the original broken ones; at high temperatures (130 and 140 °C), not only the unfolded chains and disentangled chains in amorphous region crystallize into crystal blocks, but also these small broken crystal blocks melt and recrystallize and the new crystal blocks formed possess larger crystal size than those of the original broken ones.

Effect of drawing temperature on mesomorphic transitions of oriented poly(ethylene terephthalate) fibers exposed to supercritical CO2

Samples of partially oriented yarn (POY) PET fibers were uniaxially drawn at 23, 68 °C (cold drawing) and 100 °C (hot drawing) and then exposed to the supercritical carbon dioxide (scCO2) without tension at a temperature of 80 °C and a pressure of 220 bar. The effect of drawing temperature on the evolution of mesomorphic phases and the structural changes under exposure to scCO2 were investigated by differential scanning calorimetry (DSC), Fourier transform infrared (FTIR), and wide-angle X-ray diffraction. The orientation factor of the samples was measured using a polarizing microscope. A good correlation was obtained between the results of various analyses. The results illustrate that evolution of structure strongly depends on both process temperature and post-treatment by scCO2 exposure. The latter process leads to plasticization and reduced glass transition temperature of the samples, thus inducing structural changes in the fibers.

Properties of uniaxially stretched polypropylene films: effect of drawing temperature and random copolymer content

AbstractCast films of two linear polypropylenes (PP) having different molecular weights and their blends with 20 wt% random copolymer were prepared by extrusion. The produced cast films were then uniaxially hot drawn at T = 110 and 140°C under a draw ratio (DR) of 6 using a machine direction orientation (MDO) unit. The effects of drawing temperature and addition of random copolymer on the properties of the films were investigated. The type of crystals (spherulites or fibrils) was studied using differential scanning calorimetry (DSC). The drawing process generated a highly oriented fibrillar crystalline structure, resulting in an increase in the melting point of the films by about 10°C. The films drawn at 140°C revealed coexisting lamellae and fibrils whereas at 110°C mainly a fibrillar structure was observed. Tensile measurements showed a greater strength for the sample stretched at lower temperature (i.e., 110°C). The effect of drawing temperature and copolymer content on tear resistance was also explored. The medium‐molecular weight PP film stretched at 110°C showed greater tear resistance than at 140°C. The addition of the random copolymer into the medium‐molecular weight PP reduced the tear resistance significantly whereas the impact for the high‐molecular weight was not noticeable. Adding the random copolymer significantly decreased the haze for the films and hence drastically improved the clarity.Des feuilles coulées de deux polypropylènes (PP) linéaires avec des poids moléculaires différents et leurs mélanges avec 20% d'équivalent en poids de copolymère aléatoire ont été préparées par extrusion. Les feuilles coulées produites ont alors été étirées à chaud de façon uniaxiale à T = 110 et 140°C en vertu d'un rapport d'étirage de 6 à l'aide d'une unité d'orientation de sens machine. On a étudié les effets de la température d'étirage et l'ajout du copolymère aléatoire sur les propriétés des feuilles. Le type de cristaux (sphérulites ou fibrilles) a été étudié à l'aide de la calorimétrie à balayage différentiel (CBD). Le processus d'étirage a produit une structure cristalline fibrillaire fortement orientée, menant à une augmentation du point de fusion des feuilles d'environ 10°C. Les feuilles étirées à 140°C ont révélé des lamelles et fibrilles coexistantes, tandis qu'à 110°C, on a observé principalement une structure fibrillaire. Les mesures de la traction ont indiqué une résistance supérieure pour l'échantillon étiré à une température basse (c.‐à‐d., 110°C). On a également exploré l'effet de la température d'étirage et du contenu en copolymère sur la résistance au déchirement. La feuille de PP de poids moléculaire moyen étirée à 110°C a démontré une résistance au déchirement supérieur qu'à 140°C. L'ajout du copolymère aléatoire dans le PP de poids moléculaire moyen a réduit la résistance au déchirement de façon considérable, tandis que l'effet pour le poids moléculaire élevé n'était pas visible. L'ajout du copolymère aléatoire a considérablement réduit le trouble des feuilles et, par conséquent, a amélioré radicalement la clarté. Can. J. Chem. Eng. © 2010 Canadian Society for Chemical Engineering

Crystallization behavior of melt-spun poly(vinyl alcohol) fibers during drawing process

The crystallization behavior of melt-spun poly(vinyl alcohol) (PVA) fibers during hot drawing process was studied by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and computer controlled electronic universal testing machine. The effects of drawing temperature and drawing speed on the crystallinity and the stress induced crystallization of PVA fibers were discussed. The results showed that the crystallization process of PVA fibers during hot drawing presented three stages: initial stage, stress induced crystallization stage and slowly increasing stage. And PVA fibers with high crystallinity can be obtained by properly increasing the drawing temperature and drawing speed, especially when the drawing temperature and speed were 453 K and 100 mm/min respectively. The stress induced crystallinity of PVA fibers during drawing process was the difference between the crystallinity of PVA fibers after drawing and after only heat treatment. At the low drawing speed, i.e. 50 mm/min, due to the strong molecular movement and orientation relaxation under high temperature, the effect of stress induced crystallization weakens with the increase of drawing temperature, the ratio between stress induced crystallinity and thermal induced crystallinity changed from 8.7%:0%(393 K) to 1.7%:5% (453 K). While at the high drawing speeds, i.e. 100 mm/min and 500 mm/min, with the decrease of available orientation relaxation time, the stress induced crystallization plays an important role during the drawing process, the ratio between stress induced crystallinity and thermal induced crystallinity were 8%:2.9% and 10.2%:0.5% at 453 K respectively.

Feasibility and optimization of the hollow optical fiber drawing process

The drawing process for the fabrication of a hollow optical fiber involves the flow of glass, which is largely heated by thermal radiation, in an inert gas environment. It is critical to maintain the central core, which can collapse if the thermal conditions are not properly imposed and controlled. This paper presents the analysis and simulation of this complicated process. A numerical model is developed, validated, and applied to simulate the hollow optical fiber drawing process under a wide range of boundary conditions, particularly draw speed, tension, and temperature. A feasible domain of the drawing process is identified to give the range of the drawing parameters for which the geometry of the fiber is maintained and collapse of the core and viscous rupture of the fiber are avoided. The effects of drawing temperature and feeding speed, which are crucial factors in determining the geometry and quality of the fiber, are investigated in detail. A multi-variable unconstrained optimal design problem is posed and considered in terms of the feasible domain. An appropriate objective function, comprised of the maximum velocity lag, thermally induced defect concentration and draw tension, is proposed to quantify the quality of the hollow fiber. The univariate search method is then applied to obtain the optimal drawing temperature and feeding speed. This study provides a basis for the optimization of hollow fiber drawing process and indicates that a substantial improvement in fiber quality can be achieved.

Study on poly(ethylene terephthalate)/polypropylene microfibrillar composites. II. Solid‐state drawing behavior

AbstractA (20/80) blend of poly(ethylene terephthalate)/polypropylene (PET/PP) was solid‐state drawn to enhance the molecular orientation of the PET microfibers. Effects of drawing temperature (23–140°C) and drawing speed (max. 1000 mm/min) on the morphology and draw ratio of the blend were studied and discussed based on the drawing behaviors of the pure polymers. In cold drawing, there seemed to be a critical drawing speed below which the natural draw ratios of the polymers remained constant, but above which the draw ratios first decreased slightly because of suppression of molecular relaxation and then increased because of breakage of highly strained molecules and disintegration of lamellar crystals into finer mosaic blocks. Macroscopically, the pure PP and the PET/PP composite extrudates gave similar draw ratios at the same speeds. SEM showed that the PET microfibers suffered a smaller elongation than the PP matrix and severe voiding occurred at the PET/PP interface. Furthermore, substantial fiber breakage occurred during cold drawing at speeds above 200 mm/min. In comparison, drawing at 100°C caused no obvious interfacial voiding and fiber breakage. Furthermore, the natural draw ratio of the blend was lower than that of the pure PP extrudate, indicating that the PET microfibers had constrained the deformation of the PP matrix. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1989–2000, 2004

Simultaneous biaxial deformation behavior of isotactic polypropylene films

AbstractThe simultaneous biaxial deformation behavior of isotactic polypropylene films was investigated using a novel laboratory film stretcher. A detailed description of the apparatus and its measurement capabilities is presented. The effects of drawing temperature and ratio, strain rate, and deformation modes on the macroscopic equibiaxial deformation and its relation to film dimension uniformity were studied. The strain rate was found to have a large influence on biaxial deformation homogeneity. For temperatures 15°C to 5°C below the melting point, it could be concluded that a homogeneous biaxial deformation was achieved if the Hencky strain rate was higher than 0.1 s−1. Additionally, it was found that the nominal biaxial yield stresses were linearly dependent on temperature in the range under investigation.

Preparation and characterization of iodinated poly(vinyl alcohol) microfibril

Iodination of poly(vinyl alcohol) (PVA) microfibril, which was obtained from saponification of poly(vinyl pivalate), was conducted before and after zone drawing at various conditions. The resulting PVA microfibrils were characterized by differential scanning calorimeter and scanning electron microscopy. Surface morphologies of these PVA microfibrils showed some differences between PVA microfibril iodinated after and before drawing. Crude shapes of PVA microfibrils iodinated after drawing indicated that iodine decreased the structural regularity severely. On the other hand, PVA microfibrils iodinated before drawing showed relatively ordered surfaces. This was ascribed to the enhanced molecular ordering of PVA microfibrils due on zone drawing. Iodinated PVA microfibrils showed a decrease in crystal melting temperature of about 100 °C compared to the untreated sample. PVA microfibrils drawn after iodination showed relatively higher crystal melting temperature than those of microfibrils iodinated after drawing. These results were considered as the proofs of the changes in crystalline lattice of the PVA microfibrils. Effects of drawing temperature on sublimation of iodine were also evaluated.

Effects of Drawing Temperature on Phase Transition in Poly(Vinylidene Fluoride) Films

Poly(vinylidene fluoride)(PVDF) films from the melt were uniaxially drawn at different temperatures. The structure and properties of the drawn PVDF films were characterized by WAXD (Wide Angle X-ray Diffraction), IR (Infrared spectroscopy). The properties of the drawn films strongly depend on drawing conditions. At a given drawing ratio, however, the crystal form was remarkably different with drawing temperatures. The structural changes on the drawn PVDF films were discussed.

Effects of Drawing Temperature on Phase Transition in Poly(Vinylidene Fluoride) Films

Poly(vinylidene fluoride)(PVDF) films from the melt were uniaxially drawn at different temperatures. The structure and properties of the drawn PVDF films were characterized by WAXD ( Wide Angle X-ray Diffraction), IR (Infrared spectroscopy). The properties of the drawn films strongly depend on drawing conditions. At a given drawing ratio, however, the crystal form was remarkably different with drawing temperatures. The structural changes on the drawn PVDF films were discussed.