Crystalline Orientation Factors Research Articles

Injection Molding Simulation of Polyoxymethylene Using Crystallization Kinetics Data and Comparison with the Experimental Process

It is well known that the processing conditions in polymer processing have a high impact on the resulting material morphology and consequently the component’s mechanical behavior. However, especially for semicrystalline polymers, the tools available for predicting the final morphology of injection molding parts still have significant limitations. In order to investigate the potential of injection molding simulation for the prediction of the morphology, POM homopolymer specimens were injection molded. The crystallization kinetics data were measured, and simulations in 3D and 2.5D with and without crystallization analysis were conducted in Autodesk Moldflow. The simulations are found to be good accordance with the experiments. Predicted spherulite size and crystalline orientation factor reveal a good qualitative correlation with optical micrographs. Also, the evolution of these parameters along the flow path is plausible. The simulation is found to be a powerful tool for morphology prediction in polymeric parts. Its applicability, however, is still limited to 2.5D models in Autodesk Moldflow, which, of course, is insufficient for complex, thick-walled 3-dimensional parts.

Fiber Formation and Structural Development of HBA/HNA Thermotropic Liquid Crystalline Polymer in High-Speed Melt Spinning.

High-speed melt spinning of thermotropic liquid crystalline polymer (TLCP) resin composed of 4-hydroxybenzoic acid (HBA) and 2-hydroxy-6-napthoic acid (HNA) monomers in a molar ratio of 73/27 was conducted to investigate the characteristic structure development of the fibers under industrial spinning conditions, and the obtained as-spun TLCP fibers were analyzed in detail. The tensile strength and modulus of the fibers increased with shear rate in nozzle hole, draft in spin-line and spinning temperature and exhibited the high values of approximately 1.1 and 63 GPa, respectively, comparable to those of industrial as-spun TLCP fibers, at a shear rate of 70,000 s−1 and a draft of 25. X-ray diffraction demonstrated that the mechanical properties of the fibers increased with the crystalline orientation factor (fc) and the fractions of highly oriented crystalline and non-crystalline anisotropic phases. The results of structure analysis indicated that a characteristic skin-core structure developed at high drafts (i.e., spinning velocity) and low spinning temperatures, which contributed to weakening the mechanical properties of the TLCP fibers. It is supposed that this heterogeneous structure in the cross-section of the fibers was induced by differences in the cooling rates of the skin and core of the fiber in the spin-line.

Melt spinning of high-strength fiber from low-molecular-weight polypropylene

Polypropylene (PP) with high melt flow index (MFI) or low molecular weight, although desired in melt spinning for enhanced productivity, is difficult to be spun into high-strength fiber using the standard process where extensive jet stretching is applied. In this work, a processing route involving minimal jet stretch has been explored. A two-stage hot drawing procedure in the solid state was found to be suitable for producing high-strength fiber from low-molecular-weight PP with an ultrahigh MFI of 115 g/10 min. Fibers produced achieve a maximum tensile strength and Young's modulus of approximately 600 MPa and 12 GPa, respectively. The melt temperature of the fiber reached 170.8°C, approximately 5°C higher than that of the original resin. Wide-angle X-ray diffraction (WAXD) study shows that the stable α-monoclinic crystalline structure is developed during the drawing process. A well-oriented crystalline structure along the fiber axis is generated, having a crystalline orientation factor as high as 0.84. POLYM. ENG. SCI., 2015. © 2015 Society of Plastics Engineers

Experimental study on the thermostable property of aramid fiber reinforced PE-RT pipes

Flexible composite pipes are advantageous in ultra high strength, high modulus, pH and corrosion resistance and light weight, but there are still some hidden safety troubles because they are poorer in thermostable capacity. Therefore, test samples of flexible composite pipes were prepared with high-temperature polythene (PE-RT) as the neck bush and aramid fiber as the reinforcement layer. Experimental study was conducted by using HPHT vessel and differential thermal scanner for different working conditions, different temperatures, whole-pipe pressure-bearing capacity and 1000 h viability. It is shown by the environmental compatibility test that high temperature has little effect on the weight, Vicat softening temperature, mechanical properties and structures of neck bush PE-RT, but exerts an obvious effect on the tensility and whole-pipe water pressure blasting of the reinforcement aramid fiber. Besides, the drop of whole-pipe pressure-bearing capacity is caused by deformation and breaking of aramid fibers when the reinforcement layer is under the force of internal pressure. Finally, disorientation and crystallization of molecular thermal motion occur with the rise of temperature, so amorphous orientation reduces, crystallinity factor and crystalline orientation factor increase gradually, thus, disorientation of macromolecular chains increases and tensile strength decreases. It is concluded that this type of flexible composite pipe can smoothly pass 1000 h viability test. And it is recommended that it be used in the situations with temperature not higher than 95 °C and internal pressure not higher than 4 MPa.

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

Fiber making directly from poly(tetrafluoroethylene) emulsion

Poly(tetrafluoroethylene) (PTFE) fiber with a superior mechanical property was prepared directly from its emulsion by the novel manufacturing process. The PTFE emulsion turned into a paste when a high shear flow was applied and the paste was extruded through a nozzle into a strand consisting of fine PTFE particles. The diameter of the strand was reduced stepwise by applying the die-drawing process through a conical die at a low temperature. The strand was further die-drawn down at elevated temperatures into fine PTFE fibers with a highly oriented crystalline structure. The crystalline orientation factor of the PTFE fiber reached very close to unity. Although the fibers obtained have a very high tensile modulus, the tensile strength was not as high as that expected from the crystalline orientation, suggesting that the presence of some defects in the PTFE fiber formed in the instantaneous deformation.

Improvement of tensile properties of ramie yarns by applying a winding machine with heat treatment

AbstractA winding machine with heat treatment was newly developed to strengthen ramie yarns. During the treatment process, ramie yarn in normal or wet state was wound on a winding machine and passed continuously through a heater at 100 and 150°C, respectively, with different winding speeds and tensions. Higher tensile strength and stiffness of ramie yarn was achieved after heat treatment on wet yarn and winding speed had a significant influence on the tensile properties of yarns. However, a little decline in tensile strength was found for ramie yarns after heat treatment in normal state. This implies that the water‐swollened structure of ramie yarn during the heat treatment is crucial in strengthening yarns. In the case of heat treatment on wet yarns, the effect of winding tension on the tensile properties of yarns was studied. It was found that the tensile strengths and Young's moduli of ramie yarns first increased and then reached equilibrium as the winding tension was increased. The crystallinity calculated from X‐ray diffraction diagrams showed a slight decrease in heat‐treated ramie yarns whereas the crystalline orientation factors had no appreciable change. It was considered that the improved effect was related to the more oriented molecular chains in amorphous region and optimized yarn structure. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Preface: Phys. Status Solidi C 7/3‐4

Preface: Phys. Status Solidi C 7/3‐4

Polypropylene-Clay Nanocomposites Fibers Structure and Performance

Abstract Fibers from Polypropylene (PP) and polypropylene nanocomposite (PNC) were produced using a fiber spinning process. Various amounts of different clays were added to the PP matrix. The structure of PP and PNC fibers was evaluated using field emission scanning electron microscopy (FE-SEM) and X-ray diffraction. The crystalline axes orientation factors were determined from wide-angle X-ray diffraction pole figures of (110) and (040) reflections for PP and of (001) for clay. The d-spacing of the (001) clay crystalline plane, indicative of the clay dispersion, was determined from the intensity −2 θ plots superimposed on the two dimensional X-ray diagrams. The results obtained for the d-spacing at small angles indicated that the clay in the PNC maintained its intercalated distance at low loadings whereas at higher loadings, some aggregation was observed. Results on orientation of the clay (001) axis (normal to the clay platelets plane) indicated that it was oriented perpendicular to the machine direction, which is expected. Its orientation in the normal and transverse directions was different, suggesting that clay platelets were not randomly distributed in the transverse plane, which was confirmed from SEM observations. The orientation of PP c-axis in the fibers was slightly higher for the nano-composite that the pure resin. Tensile modulus, strength and elongation at break for both PP and PNC fibers increased with increasing draw ratio. Flexural modulus and strength of laminates made by consolidation of the PNC fibers were higher than those of consolidated pure PP fibers as well as those of bulk PP or PNC.

Higher order structural analysis of stereocomplex‐type poly(lactic acid) melt‐spun fibers

AbstractThe higher order structure of stereocomplex‐type poly(lactic acid) melt‐spun fibers of an equimolar blend of poly(L‐lactic acid) and poly(D‐lactic acid) was analyzed with wide‐angle X‐ray diffraction (WAXD) and birefringence measurements. Two different crystalline structures were observed in the fibers: α‐form homocrystals and stereocomplex crystals. The weight fractions of the two crystals were estimated with the WAXD integrated intensity data. The crystalline orientation factors were obtained from the WAXD measurements. Well‐oriented homocrystals formed during a drawing process at the crystallization temperature of the homocrystal. Drawing above this temperature caused the stereocomplex crystal to be formed. The crystalline orientation tended to be lower with increasing drawing temperatures. Through the combination of the intrinsic birefringence and the fractions of the α‐form homocrystals and stereocomplex crystals, the birefringence of the amorphous phase was evaluated. The amorphous birefringence stayed positive and decreased with increasing drawing temperature. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 218–228, 2007

Morphology of PET Cords at Different Stages of Simulated Tire Building

The effect of simulated tire-building steps on morphological characteristics of polyethylene terephthalate (PET) cords and their final dimensional stability is reported. Twisted single-ply cords were sequentially processed for mimicking dip coating (without real latex treatment), thermal curing (without embedding them in rubber matrix), and creep deformation. The degree of crystallinity and crystalline orientation factor ( fc) of the samples remained essentially unchanged in the course of the simulated manufacturing steps. As measured by birefringence, overall orientation of the cords increased in the coating step but decreased during simulated curing. Overall orientation again increased after creep testing. As measured by wide-angle X-ray diffraction, the cords having higher oriented amorphous (mesophase) content displayed the least variation in overall orientation during processing steps and the best dimensional stability.

Biaxial orientation in LLDPE films: Comparison of infrared spectroscopy, X‐ray pole figures, and birefringence techniques

AbstractIn this study, linear low‐density polyethylene films were produced using different processes (film blowing and biaxial orientation) and processing conditions. The orientation of the films was characterized in terms of their biaxial crystalline, amorphous, and global orientation factors using birefringence, tilted incidence polarized Fourier Transform Infrared Spectroscopy (FTIR), and X‐ray diffraction pole figures. Evaluation of a simplified FTIR procedure without the use of the tilted method for the determination of crystalline orientation factors proposed in the literature is also evaluated and assessed. The results indicate that FTIR overestimate the crystalline orientation factors, particularly for the crystalline a‐axis. Significant discrepancies are also observed for the b‐axis orientation, which may be due to an overlap of the amorphous phase contribution. Those differences are larger for films with low orientation, such as blown films. Amorphous phase orientation from FTIR depends on the band used and is not necessarily in agreement with that determined from the combination of X‐ray and birefringence. The simplified FTIR procedure is proven to be inadequate in the case of linear low‐density polyethylene blown films studied having a random lamellar crystalline morphology. POLYM. ENG. SCI. 46:1182–1189, 2006. © 2006 Society of Plastics Engineers.

Biaxial orientation in HDPE films: comparison of infrared spectroscopy, X-ray pole figures and birefringence techniques

In this study, high-density polyethylene films (HDPE) were produced using different processes (film blowing and biaxial orientation) and processing conditions. The orientation of the films was characterized in terms of their biaxial crystalline, amorphous and global orientation factors using birefringence, Fourier transform infrared spectroscopy (FTIR) using a tilted incidence technique and X-ray pole figures. Evaluation of a simplified FTIR procedure without using the tilted method for the determination of crystalline orientation factors proposed in the literature is also evaluated and assessed. The results indicate that FTIR overestimate the crystalline orientation factors, particularly for the crystalline a-axis. Significant discrepancies are also observed for the b-axis orientation, which may be due to an overlap of the amorphous contribution and/or saturation of FTIR bands. Those differences are larger for films with low orientation, such as blown films. Amorphous phase orientation from FTIR depends on the band used and is not necessarily in agreement with that determined from combination of X-ray and birefringence.

Biaxial Orientation Characterization in PE and PP Using WAXD X-Ray Pole Figures, FTIR Spectroscopy, and Birefringence

In this study, different polyethylene and polypropylene films (LDPE, LLDPE, HDPE, and PP) are produced using different processes (film blowing and biaxial orientation) and processing conditions. The orientation of the films is characterized in terms of their biaxial crystalline, amorphous, and global orientation factors using birefringence, Fourier transform infrared spectroscopy (FTIR) using a tilted incidence technique, and X-ray pole figures. The results indicate that FTIR overestimates the crystalline orientation factors, particularly for the crystalline a-axis. Significant discrepancies are also observed for the b-axis orientation, which may be due to an overlap of the amorphous contribution and/or saturation of FTIR bands. These differences are larger for films with low orientation, such as blown films. Amorphous phase orientation from FTIR depends on the band used and is not necessarily in agreement with that determined from the combination of X-ray and birefringence.

Wplyw grzania strefowego na strukture wlokien PET i dynamike procesu przedzenia ze stanu stopionego. Cz. I. krystalicznosc i orientacja molekularna

Effects of heating chamber temperature (TK) and take-up speed (VL) on crystallinity degree (XV), optical birefringence (Dn), crystalline orientation (fc), and amorphous orientation (fa) of PET fibers obtained in melt spinning with zone heating were investigated. Zone heating has been provided by thermostatic chamber with hot air in the temperature range 100-210 degrees C. Take-up speed of fibers varied dependently on the type of spinning: conventional or high speed one (>4000 m/min). Crystallinity degree has been determined from density measured using gradient column, crystalline orientation factor was determined from WAXS diffraction patterns while amorphous orientation factor was determined on the basis of birefringence measurements as well as of crystalline orientation factor and crystallinity degree. Measurements have been carried out for small and big VL values, 2600 or 4800 m/min respectively, at low (135 degrees C) or high (195 degrees C) chamber temperature. Lower TK value is in the middle of the range between glass transition temperature (Tg) and the temperature of maximal crystallization rate (Tmax). It has been found PET fibers showing high XV value can be obtained using conventional VL speed at temp. TK >135 degrees C (Figs. 1 and 2) while in case of high speed spinning XV increase requires high TK temperature close to Tmax ≈ 190 degrees C (Fig. 2). Molecular orientation is characterized by high values of crystalline orientation factor fc ≈ 0.9, independently on spinning conditions. It proves the constant critical level of fa orientation needed to oriented crystallization occurring. High amorphous orientation of the fibers is obtained during melt spinning with online crystallization induced in technological line (Fig. 1, 8). Zone heating is a factor inducing the crystallization in case of low take-up speeds while at high speed spinning high value of fa is this factor. Amorphous orientation is higher for low TK (Fig. 7). High TK leads to decrease in fa value because of relaxation. The fibers showing the highest values of birefringence were obtained at high chamber temperature (Fig. 6).

A comparison between the thermomechanical and structural changes in textured PET yarns after superheated steam and dry heat treatment

PET yarns textured at different texturing conditions were treated with superheated steam or dry heat at different temperatures for different times. The effects of the treatment conditions on the thermomechanical and structural changes of the yarn were examined by shrinkage, X-ray diffraction and birefringence measurements. With increase in superheated steam temperature, the crystalline orientation factor and birefringence decreased, whereas crystal size increased. Dry heat treatment had a smaller effect on shrinkage and structural properties in comparison with superheated steam treatment. The additional shrinkage after texturing process was investigated. The effect of heat-setting in both media was more significant at 200 °C. The time dependence of the properties was not linear.

Real‐time orientation and crystallinity measurements during the isotactic polypropylene film‐casting process

AbstractA method based on Fourier transform infrared (FTIR) transmission spectra is proposed to measure the crystallinity of isotactic polypropylene (iPP) samples. The method parameters were tuned as compared with wide‐angle X‐ray scattering measurements performed on test samples characterized by different crystallinity values obtained by solidification of thin iPP films under several cooling rates in a homemade device. The FTIR dichroic ratio measurements were adopted to measure crystalline and average Hermans' orientation factors of iPP samples obtained by film casting. The crystalline orientation measurement method was validated as compared with the birefringence measurement. The techniques were successfully used in real time during some film‐casting runs with a suitably modified FTIR system made of a spectrometer equipped with two optical guidelines and an external detector. Real‐time measurements are reported and discussed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 998–1008, 2003

Improvement of Flexural Strengths of Poly(L‐lactic acid) by Solid‐State Extrusion, 2. Extrusion Through Rectangular Die

AbstractSolid‐state extrusion of poly (L‐lactic acid) (PLLA) through rectangular die was performed to produce high flexural strength plates that can be used as internal fixation devices. A single‐angle wedge‐shaped rectangular die was utilized having the die exit dimension of 4 mm × 1 mm. Billets were machined out from vacuum compression molded PLLA having different crystallinities to have various thicknesses and thus various imposed draw ratios. Solid‐state extrusion of billets was performed at various drawing rates at 130 °C, above glass transition and below melting temperature. Extruded plates had the width and thickness smaller than the die due to the further drawing outside the die. The decrease in width was larger than the decrease in thickness, and this became more prominent with increasing draw ratio and drawing rate, resulting in a significantly smaller aspect ratio. Contributions of die drawing and further drawing outside the die were estimated from the extruded plate dimensions, by which the drawing rate effect was attributed to the further drawing outside the die. As actual draw ratio increased, crystallinity, melting temperature, crystalline orientation factor, and birefringence increased. Throughout the whole process the decrease in molecular weight was largely suppressed to be about 10%. As billet crystallinity, draw ratio, and drawing rate increased, both flexural strength and flexural modulus increased up to the maxima of 202 MPa and 9.7 GPa, respectively. This enhancement in mechanical properties was correlated with structural developments. Changes in flexural strength of solid‐state extruded PLLA plates as a function of draw ratio (the effect of drawing rate is co‐plotted by hollow symbols at corresponding draw ratio.).magnified imageChanges in flexural strength of solid‐state extruded PLLA plates as a function of draw ratio (the effect of drawing rate is co‐plotted by hollow symbols at corresponding draw ratio.).

Correlations between Orientation and Some Properties of Polymer Films and Sheets

The orientation effects of biaxially stretched polystyrene (PS) sheets and polyethylene (PE) blown films were investigated. The study mainly focused on the relationships between orientation of amorphous PS and semicrystalline PE and their shrinkage, tensile properties and tear resistance. For low orientations, it was found that the stress and strain (shrinkage in films) can be simply related to birefringence for both PS and PE. For tear properties of PE films, better correlations were observed with crystalline orientation factors.

Effect of molecular orientation on the biodegradability of aliphatic polyester

AbstractThe effect of morphological microstructure on the biodegradability of aliphatic polyester, poly(ϵ ‐caprolactone) (PCL) was studied in terms of crystallite size, crystallinity and amorphous and crystalline orientation factors. Microstructural changes during hydrolysis/biodegradation of the drawn PCL films were investigated by the conventional small and wide angle X‐ray scattering methods. The lower was the draw ratio, the higher the hydrolytic degradability or biodegradability. With the increase of the hydrolysis time, the long period, at earlier stage, decreased; then slightly recovered and the crystallinity increased while the lamellar thickness remained unchanged. The amorphous orientation factors start to decrease at earlier stage and gradually go down to zero before the end of hydrolysis. In the case of crystalline orientation factor, although the values decrease with increasing hydrolysis time, they do not reach zero point. After the biodegradation for 60 days, crystallinity, crystal lateral size and lamellar thickness in all drawn PCL films decreased, and then it was confirmed that even crystalline regions were degraded for long term biodegradation test.