Constant Draw Ratio Research Articles

Porous Membranes Based on Polypropylene-Ethylene Copolymers. Influence of Temperature on Extrusion, Annealing and Uniaxial Strain Stages.

In this study, block and random copolymers of polypropylene–ethylene are selected to prepare porous membranes through the melt extrusion-annealing-uniaxial stretching technique (MEAUS), at a constant draw ratio. In some cases, these copolymers were blended with a homopolymer grade. The variation of temperature in the stages of extrusion, annealing and uniaxial strain was analysed. Several characterisation techniques were employed to study this influence. The crystalline orientation was analysed by polarised infrared spectroscopy (FT-IR), and crystalline features were studied by differential scanning calorimetry (DSC). The thermal stability of the membranes was checked by thermogravimetric analysis (TGA). Tensile tests were performed to ascertain the stiffness and ductility of the produced samples. The results were correlated with the porous morphology, global porosity, and permeability to air. A close relationship was found between crystalline characteristics, porous morphology and the trends registered. An improved pore distribution along the membrane surface was found when copolymers were employed.

Determination of draw resonance onsets in tension-controlled viscoelastic spinning process using transient frequency response method

Draw resonance onsets of actual viscoelastic spinning processes with secondary forces operated by constant draw ratio are determined via transient frequency response simulations under a constant tension or force boundary condition, which causes the system to be always stable. Transfer function data between the spinline velocity and the tension at the take-up position in the frequency domain, which are transformed from the transient responses of the take-up velocity with respect to a step change of the take-up force, play a key role in the determination of the onset points for various spinning cases. It is confirmed that the critical draw ratios established in this study are almost the same as those decided by linear stability or direct transient simulation methods for velocity-controlled spinning systems. The transfer function data for the stability analysis can be readily and beneficially applied to an analysis of sensitivity of a spinning process with respect to a sinusoidal disturbance.

Effect of thermal modification on rheological properties of polyethylene blends

We examined the effects of thermal modification under flow field on the rheological properties of linear low-density polyethylene (LLDPE) with high molecular weight, low-density polyethylene (LDPE), and their blends, without thermal stabilizer. Although structural changes during processing are not detected by size extrusion chromatography or nuclear magnetic resonance spectroscopy, linear viscoelastic properties changed greatly, especially for the LLDPE. A cross-linking reaction took place, leading to, presumably, star-shaped long-chain branches. Consequently, the modified LLDPE, having high zero-shear viscosity, became a thermorheologically complex melt. Moreover, it should be noted that the drawdown force, defined as the uniaxial elongational force at a constant draw ratio, was significantly enhanced for the blends. Enhancement of elongational viscosity was also detected. The drawdown force and elongational viscosity are marked for the thermally modified blend as compared with those for the blend of thermally modified pure components. Intermolecular cross-linking reactions between LDPE and LLDPE, yielding polymers with more than two branch points per chain, result in marked strain-hardening in the elongational viscosity behavior even at small strain. The recovery curve of the oscillatory modulus after the shear modification is further evidence of a branched structure.

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.

Analysis of regenerated cellulose fibers with ionic liquids as a solvent as spinning speed is increased

In order to improve the spinning efficiency, the spinning experiments with cellulose/1-butyl-3-methylimidazolium chloride solution were done whilst increasing spinning speed. It was found that the tenacity and initial modulus of regenerated cellulose fibers increased but the elongation at break decreased slightly with increasing spinning speed at constant draw ratio. Further, the synchrotron wide-angle X-ray diffraction and small-angle X-ray scattering were carried out to illustrate the relationship between the structure and the mechanical properties. It was shown that the crystal orientation, crystallinity, amorphous orientation factor as well as orientation of the microvoids along the fiber increased with the spinning speed as the diameter of the microvoids in the fiber decreased. From the analysis of the spinline stress, it is clear that the spinline stress increased when both extruding and draw speed increased at constant draw ratio. This resulted in the improvement of supramolecular structure and mechanical properties of the regenerated cellulose fibers.

Investigating the production and properties of Ag/TiO2/PP antibacterial nanocomposite filament yarns

In this research, investigating the possibility of producing, processing and also characterization of antibacterial organic/inorganic nanocomposite polypropylene fiber has been presented. For this purpose, PP powder and inorganic nanocomposite filler were mixed using a twin screw extruder and modified granule was produced. After producing as-spun filament yarns by a pilot plant melt spinning machine at the take-up speed of 2000 m/min, samples were drawn, textured and finally weft knitted. Physical and structural properties of as-spun and drawn yarns with constant and variable draw ratios were investigated. The experimental results revealed that the crystallinity reduction of modified as-spun yarns could be compensated by drawing process. Tensile properties of modified drawn yarns with the variable draw ratio were higher than the pure PP, whereas the inverse observation was noticed in the case of constant draw ratio. The investigation of antimicrobial activity showed a high percentage of biostatic efficiency on the modified samples.

Comparing the effect of three processing methods for modification of filament yarns with inorganic nanocomposite filler and their bioactivity against staphylococcus aureus

This research compared three methods for producing and processing nanocomposite polypropylene filament yarns with permanent antimicrobial efficiency. The three methods used to mix antimicrobial agents based on silver nano particles with PP were as follows: 1) mixing of PP powder and inorganic nanocomposite filler with the appropriate concentration using a twin-screw extruder and preparing granules, 2) method 1 with a singlerather than twin-screw extruder, and 3) producing the masterbatch by a twin-screw extruder and blending it with PP in the melt spinning process. All pure polypropylene samples and other combined samples had an acceptable spinnability at the spinning temperature of 240 °C and take-up speed of 2,000 m/min. After producing as-spun filament yarns by a pilot plant, melt spinning machine, the samples were drawn, textured and finally weft knitted. The physical and structural properties (e.g., linear density, tenacity, breaking elongation, initial modulus, rupture work, shrinkage and crystallinity) of the as-spun and drawn yarns with constant and variable draw ratios (the variable draw ratio was used to gain a constant breaking elongation of 50%) were investigated and compared, while DSC, SEM and FTIR techniques were used to characterize the samples. Finally, the antibacterial efficiency of the knitted samples was evaluated. The experimental results revealed that the crystallinity reduction of the as-spun yarn obtained from method 1 (5%) was more than that of method 2 (3%), while the crystallinity of the modified as-spun yarns obtained with method 3 remained unchanged compared to pure yarn. However, the drawing procedure compensated for this difference. By applying methods 2 and 3, the drawing generally improved the tenacity and modulus of the modified fibers, whereas method 1 degraded the constant draw ratio. Although the biostatic efficiency of the nanocomposite yarns was excellent with all three methods, the modified fabrics obtained from methods 1 and 2 showed a higher bioactivity.

Processing and Properties of Nanocomposite Filament Yarns with Various Filler Concentrations from Two Different Modification Methods

AbstractIn this research, the possibility of producing and processing nanocomposite polypropylene filament yarns with permanent antimicrobial efficiency has been assessed by comparing two different methods. Therefore two approaches were used to mix various blending contents of antimicrobial agents based on silver/TiO2 nano particles with PP: 1) mixing of PP powder and inorganic nanocomposite powder as an antibacterial agent with the appropriate concentration in a twin screw extruder, preparing modified granules and feeding them to the melt spinning machine, 2) producing masterbatch by a twin screw extruder and blending it with PP in the melt spinning process. In both methods, pure PP and all other combined samples had an acceptable spinnability at the spinning temperature of 240 °C and take‐up speed of 2000 m/min. After producing as‐spun filament yarns by a pilot plant melt spinning machine, samples were drawn, textured and finally weft knitted. Physical and structural properties of as‐spun and drawn yarns with constant and variable draw ratios were investigated and compared. Moreover, the DSC, SEM and FTIR techniques have been used for samples characterization. Finally antibacterial efficiency of knitted samples was evaluated. The experimental results indicated that the maximum crystallinity reduction of modified as‐spun yarns reached 5%. But by applying method 2 (masterbatch), crystallinity of modified as‐spun yarns remained unchanged compared to pure yarn. However, drawing procedure has compensated this difference. By applying the second method, the drawing generally improved the increase of tenacity and modulus of modified fibers, whereas in method 1 the opposite effect was noticed in the case of constant draw ratio. Although the biostatic efficiency of nanocomposite fibers was excellent in both methods, modified fabrics obtained from method 1 showed higher bioactivity.

Experimental Investigation of Effects of Spandex Brand and Tightness Factor on Dimensional and Physical Properties of Cotton/Spandex Single Jersey Fabrics

In this study, the effects of spandex brand, the tightness factor of the base, and spandex yarn on the dimensional and physical properties of cotton/spandex single jersey fabrics are investigated. In order to examine the effects of the tightness factor of cotton and spandex yarn, fabric samples were knitted by feeding both cotton and spandex yarns with three different adjustments of positive yarn feeding mechanisms so as to produce tight, medium, and loose cotton/spandex single jersey fabrics. Four different spandex yarns were used. The fabrics knitted with spandex yarns that have the largest tension values under a constant draw ratio give the highest weight, courses/cm, stitches/cm, thickness, and lowest air permeability values. Spandex yarns that have similar elongation % values affect the wale per cm values in a similar way. Because of the greater stretched structure of the spandex yarns that have shorter loop length values, the width of the fabric decreases and then the thickness of the fabric increases.

X-ray diffraction studies of poly(aryl ether ether ketone) fibers with different degrees of crystallinity and orientation

Structural studies of series of ‘as spun’ and drawn PEEK fibers have been carried out using X-ray diffraction and optical microscopy techniques. The analysis of results suggest that fibers produced at a constant draw ratio with increasing draw temperatures show enhanced orientation and crystalline behaviour. The resolved equatorial and meridional traces provide additional structural parameters in terms of crystallinity, crystallite size, and crystallite thickness. It is concluded that drawing at a temperature belowT g (i.e., 144 °C) results in poorly oriented non-crystalline materials, whereas drawing aboveT g results in highly oriented semicrystalline materials. Additional drawing proved to increase the overall orientation with slight improvements in lateral order of the chain molecules. Quantitative analysis revealed that the crystallite size increases with increasing drawing temperature. The results also revealed the increased crystallite size upon additional drawing. Crystalline orientation parameter, 〈P 2〉c, suggests almost perfect orientation. In all cases, the amorphous orientation is found to be lower than the overall orientation parameter obtained from the optical birefringence. As a result of additional drawing, crystalline orientation was found to increase slightly but the increase in the orientation of non-crystalline material was found to be substantial. An average crystalline density was determined from the orthorhombic unit cell dimensions. It was found to vary as a result of processing conditions. It was also found that the value of the maximum birefringence shows heavy dependence on the chain conformation.

Drawing properties of ultrahigh molecular weight polyethylene fibers prepared at varying formation temperatures

AbstractThe values of the percentage crystallinity, melting temperature, birefringence, and cross‐sectional area of ultrahigh molecular weight polyethylene (UHMWPE)/low MWPE (LMWPE) as‐prepared fiber specimens are reduced consistently as the formation temperatures decreased from 60 to 0°C. Much more sparse structures with significantly larger voids are found on the fractured surfaces of those as‐prepared fibers that were prepared at higher formation temperatures than those prepared at lower formation temperatures. The cross sections of the as‐prepared fiber specimens gradually change from an oblate to a nearly circular to an uneven circular shape as the formation temperatures are reduced from 60 to 10 to 0°C, respectively. It is worth noting that the achievable draw ratios (Dra) of the as‐prepared fibers reach maximum when they are prepared at an optimum formation temperature of 10°C. Moreover, the Dra values of the as‐prepared fiber (UL10) specimens can be further improved by using a two‐stage drawing process, wherein the temperature used in the second drawing stage (Tsec) is higher than 95°C. In fact, the optimum Tsec of the two‐stage drawn UL10 fiber specimens increases significantly from 105 to 115°C as the first‐stage draw ratio (Dlr) values increase from 20 to 40, respectively. The birefringence values, tensile strengths, and moduli of one‐ and two‐stage drawn UL10 fiber specimens increase consistently with increasing draw ratios, although the increasing rate of these values is gradually reduced as the draw ratios are greater than certain values. In contrast, at a constant draw ratio, the two‐stage drawn UL10 fiber specimens drawn at a higher Tsec always exhibit higher values of birefringence, tensile strengths, and moduli than those with the same Dlr but drawn at a lower Tsec. Moreover, at a constant draw ratio, the birefringence values, tensile strengths, and moduli of the fiber specimens drawn at a fixed optimum Tsec reach the maximum when they are first drawn up to an optimum Dlr of about 50. In fact, by using the proper optimum Tsec and Dlr, the tensile strengths and moduli of the two‐stage drawn UL10 fiber specimens can reach more than 11 and 155 GPa, respectively. The possible mechanisms accounting for these interesting properties are proposed in this study. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1559–1570, 2004

Properties of a Core-Sheath Conjugate Fiber Composed of Poly (butylene terephthalate) and Poly (L-lactic acid).

A new core-sheath conjugate fiber was developed by combining poly(L-lactic acid) (PLLA) as the sheath and poly(butylene terephthalate) (PBT) as the core. The tensile strength of the conjugate fiber was found to increase with increasing melt-draw ratio and PBT composition at a constant draw ratio. SEM observation of the conjugate fiber revealed that the PBT core fiber could be pulled out from the PLLA sheath to leave smooth surfaces on both sides. DSC and WAXS data of the drawn conjugate fiber suggested that only PBT had been crystallized in the core without crystallization of PLLA in the sheath. It was therefore considered that the crystallization of PLLA was hindered by a strong stress that was applied by the crystal orientation of PBT through the interface of the two polymers in contact. The PLLA sheath of the conjugate fiber was readily removed by alkali treatment to obtain the PBT core fiber although its strength became slightly lower than that of the original conjugate fiber. This alkali treatment of the conjugate fiber can give an environmentally friendly process for the denier-decreasing treatment of polyester fiber, because the hydrolysis product, that is L-lactic acid salt, can readily be assimilated into carbon dioxide and water in environment.

Properties and Degradability of the Fibers of Block Copoly(ester-ether) Comprising Poly(L-lactide) and Poly(oxyethylene-co-oxypropylene).

The A-B-A tribloc copoly (ester-ether) comprising poly (L-lactide) (A) and poly(oxyethylene-co-oxypropylene) (B) was prepared by copolymerization of L-lactide and a commercially available telechelic copolyether, PluronicrTM (PN) by the catalysis of tin octanoate. The copolymers were melt-spun by the conventional method. Then, the as-spun filament obtained was drawn to 2.5-12.5 times at 40 and 60°C. At a constant draw ratio the tensile modulus of the filament decreased with increasing composition of PN in the copolymer and with increasing draw ratio. Upon immersion in a phosphate buffer (pH=7.4), the filaments showed a time-dependent decrease in tensile strength with accompanying surface erosion. The degradability of the filaments with the same identical copolymer compositions was found to decrease with increasing draw ratio, because of the increased orientational crystallization of PLLA. The block copolymers comprising PLLA and PN, therefore, were shown to have high potentiality as the biodegradable polymers with improved flexibility and biodegradability.

Determination of the Axial Correlation Lengths and Paracrystalline Distortion for Aromatic Copolyimides of Random Monomer Sequence

X-ray methods have been used to investigate the structure of aromatic copolyimide fibers prepared from 3,3 , ,4,4'-biphenyltetracarboxylic dianhydride (BPDA), o-tolidine (OTOL), and p-phenylenediamine (PPD). The X-ray fiber diagrams of these copolymers contain nonperiodic layer lines that are indicative of a random comonomer sequence. The meridional peak positions are reproduced accurately in the predicted scattering for an infinite chain with random sequence and highly extended chain conformation. However, there is a less than adequate match between the observed and calculated peak profiles, which are predicted to be very much sharper than those observed. It is shown that the latter match is improved by consideration of chains of finite length with significant distortions from linearity. The results favor a sinuous chain conformation consisting of highly but not completely extended segments separated by less ordered regions or discontinuities. From analysis of the peak profiles, we have derived the correlation length in the chain axis direction, analogous to the axial crystallite size for homopolymers. This correlation length is 180 A for homopoly(BPDA-OTOL) but increases steadily with the introduction of PPD comonomer, reaching approximately 1000 A for the 60/40 BPDA-OTOL/BPDA-PPD copolymer at a x12 draw ratio. The results are compared to those for Kevlar 149 poly(p-phenylene terephthalamide) fibers, for which the observed axial crystallite width is 395 A, much less than for the copolyimides. The correlation length and sinuosity are independent of OTOL/PPD ratio at constant draw ratio. Hence the increasing linearity obtained at higher PPD content and higher draw ratio is simply due to the presence of the more flexible BPDA-PPD units.

Cold crystallization and thermal shrinkage of uniaxially drawn poly(ethylene 2,6‐naphthalate) by solid‐state coextrusion

AbstractSolid‐state coextrusion has been used to prepare uniaxially drawn films from isotropic poly(ethylene 2,6‐naphthalate) (PEN) of a minimum degree of crystallinity (ca. 5%) both below and above its glass transition temperature Tg. The onset of cold crystallization (Tc) of the drawn films has been studied as a function of the extrusion temperature (ET) and the draw ratio (EDR). It has been shown that Tc decreases markedly on draw, as much as 95°C, and, at constant draw ratio Tc goes through a minimum in the Tg region. For undrawn PEN, annealing below 153°C has no significant effect on Tc. To evaluate the crystallization rate constant (k) and the activation energy (Ea) of the drawn specimens, a nonisothermal DSC procedure has been used. With increasing EDR, k increases markedly and Ea goes down over threefold compared with the undrawn polymer. At high ET, strain‐induced crystallization has also been shown to play an important role in lowering Ea for cold crystallization. Thermal shrinkage above Tm indicates a high elastic recovery, underlining the efficiency of deformation, ca. 93%, achieved by solid‐state coextrusion.

Investigation of molecular orientation and conformational change upon drawing for various ethylene/1‐butene copolymers by IR spectroscopy

AbstractInfrared spectroscopy was used to investigate the molecular orientation and the conformational change upon drawing for various ethylene/1‐butene copolymers in a wide range of crystallinity (0 ≤ Xc ≤ 85% ). The degree of crystalline orientation at constant draw ratio decreases with increasing crystallinity. The orientation function for the amorphous CH2 sequence in the trans conformation, f(am), was calculated assuming additivity for the orientation functions of the trans bands. f(am) increases with drawing in a characteristical way for the different materials and reaches a value higher than that of the amorphous gauche bands. Furthermore, it was found that f(am) is strongly dependent on crystallinity. The relative concentration of the amorphous CH2 sequences in the trans conformation increases at the expense of that of the gauche sequences. The transformation from gauche to trans in the amorphous phase occurs simultaneously with the orientation of the amorphous CH2 sequences.

Significance of sample dimensions and other parameters for characterizing drawing process of polymer films

Uniaxial drawing of polymer samples by tensile testing, machines usually is characterized by drawing temperature, velocity and ratio. These data in general do not succeed in describing the drawing process completely, therefore different and/or additional parameters are necessary for characterization of drawing process. Striplike specimens of polyamide 6 and polyethylene terephthalate films were cut and drawn to a constant draw ratio. Especially sample dimensions, drawing velocity, drawing temperature and ambient medium were varied. Local draw ratio, birefringence and yield stresses were investigated.

UNFOLDING AND REFOLDING PHENOMENA IN DRAWING AND/OR ANNEALING PROCESSES

The fold content (Cf) of polyethylene, which varies with drawing and/or annealing, was evaluated by IR method described in the previous report.Polyethylene film having a-axis orientation was drawn to various draw ratios, draw directions and at various temperatures. In the drawing processes, Cf decreases abruptly in the region of draw ratio of 2-3 and gradually decreases with further drawing when drawn along the machine direction. The contents of remaining folds are quite different between the specimens drawn along the machine direction and those drawn transversely to this direction. Cf also decreases with increasing draw temperature when the film is drawn at constant draw ratio. These facts suggest the difference between the deformation processes of the slipping or rotation of lamellae and those of direct unfolding of chains from the lamellae.In the annealing process, Cf reflects the content of refolding and indicates the differences in the microstructures of the drawn specimen before and after heat treatment.