Crystalline Orientation Function Research Articles

Correlation of crystal alignment with interphase content in oriented high density polyethylene cast films

The microstructure and crystalline morphology of high density polyethylene (HDPE) cast films prepared in a wide range of draw ratios (1.6 to 148.8) were investigated. The flow-induced orientation of crystalline and amorphous phases was characterized using Fourier transform infrared spectroscopy (FTIR). The results showed that the draw ratio has a crucial role on the orientation state of the cast films. Scanning electron microscopy (SEM) images also confirmed this influence. The crystallinity of the films was examined using both differential scanning calorimetry (DSC) and Raman spectroscopy. Moreover, considering a three-phase structure (i.e. crystal, amorphous and interphase) for semi-crystalline polyethylene, Raman spectroscopy was also employed to estimate the amount of the so-called interphase in the HDPE cast films. As a result, the interphase content was found to decrease by increasing the applied draw ratio. The origin of this dependency was suggested to be due to a coil–stretch transition during elongation flow and the subsequent disentanglement. On the other hand, remarkable differences were observed in the CH2 bending vibration features of the Raman spectra of the cast films which were correlated with the applied draw ratios and with the calculated crystalline orientation functions.

Rheology of PP/PP-g-MA and PP/PP-g-AA Blends and Incidence on Orientation and Crystalline Structure of Their Cast Films

The intrinsic hydrophobic character of polypropylene limits its performance in many porous membrane applications. This can be improved by hydrophilic modification of the film surface through blending with hydrophilic polymers. For producing the precursor films and, consequently, microporous membranes with the appropriate crystalline lamellar morphology, the polypropylene chains should preserve their elongated form to serve as initial nuclei for the later development of lamellar crystals. The relaxation time of the chains is the most important factor for this stage. Commercial maleic anhydride and acrylic acid grafted polypropylenes were melt blended with a polypropylene at different weight ratios. The results showed that the modifiers lowered the crystalline orientation of the blends as compared to neat polypropylene films. The effect of the modifier on the melt relaxation spectra of the blends was investigated, and a linear relationship was found between the characteristic relaxation time of the blends and their crystalline orientation function.

The effect of hot multistage drawing on molecular structure and optical properties of polyethylene terephthalate fibers

In this work, mechanical and structural parameters related to the optical properties of polyethylene terephthalate (PET) fibers drawn at hot multistage have been investigated. The changes in optical parameters upon changing draw ratio are used to obtain the mechanical orientation factors and , various orientation functions f 2 (θ), f 4 (θ) and f 6 (θ), and amorphous and crystalline orientation functions (f a and f c ). Also, the numbers of random links between the network junction points (N 1 ), the average optical orientation (F av ), and the distribution function of segment ω(cos θ) were calculated. In addition, an empirical formula was suggested to correlate changes in the birefringence with the draw ratio and its constants were determined. The study demonstrated change on the molecular orientation functions and structural parameters upon hot multistage drawing. Significant variations in the characteristic properties of the drawn PET fibers were due to reorientation of the molecules caused by applied heat and external tension.

Determination of intrinsic birefringence values of polycaprolactone filaments

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

Ultradrawing above the static melting temperature of ultra-high molecular weight isotactic poly(1-butene) having low ductility in the crystalline state

Ultra-high molecular weight isotactic poly(1-butene) (UHMW-PB1) melt-grown crystal (MGC) films were drawn using the PIN drawing technique. Although the UHMW-PB1 MGC films had poor ductility in the crystalline state, they were ultradrawable in the molten state above the static melting temperature (Tm). The drawability of the MGC films was strongly influenced by the draw temperature, the sample thickness, and the contact time between the metal heater and sample, and it increased with decreasing sample thickness. The maximum draw ratio (DRmax) was nearly constant when the sample thickness was less than 100μm at a given draw temperature. The contact time between the metal heater and sample needed to draw continuously in the molten state was at least 0.1s. The ductility increased rapidly above 130°C, reaching a maximum at 200°C, and decreased at higher temperatures. A DRmax of 170 was achieved at 200°C under optimum conditions. The efficiency of the drawing, based on the Herman crystalline orientation function (fc) and tensile properties versus DR, was lower for films drawn at higher temperatures. The highest fc of 0.996, tensile modulus of 14GPa, and strength of 900MPa were obtained by ultradrawing with DR=50 at 155°C. This modulus corresponded to 58% of the X-ray crystal modulus (24GPa), whereas the modulus of PB1 films drawn in the crystalline state corresponded to only 12–13% (3GPa) of the theoretical crystal modulus.

Theoretical and experimental studies of anisotropic shrinkage in injection moldings of various polyesters

AbstractA novel approach to predict anisotropic shrinkage of slow crystallizing polymers in injection moldings was proposed, using the flow‐induced crystallization, frozen‐in molecular orientation, elastic recovery, and PVT equation of state. In the present study, three different polyesters, polyethylene terephthalate, polybutylene terephthalate, and polyethylene‐2,6‐naphthalate (PEN), are used. The anisotropic thermal expansion and compressibility affected by the frozen‐in orientation function and the elastic recovery that was not frozen during moldings were introduced to obtain the in‐plane anisotropic shrinkages. The frozen‐in orientation function was calculated from the amorphous contribution based on the frozen‐in and intrinsic amorphous birefringence and crystalline contribution based on the crystalline orientation function determined from the elastic recovery and intrinsic crystalline birefringence. To model the elastic recovery and frozen‐in stresses related to birefringence during molding process, a nonlinear viscoelastic constitutive equation was used with the temperature‐dependent viscosity and relaxation time. Occurrence of the flow‐induced crystallization was introduced through the elevation of melting temperature affected by entropy production during flow of the viscoelastic melt. Kinetics of the crystallization was modeled using Nakamura and Hoffman‐Lauritzen equations with the rate constant affected by the elevated melting temperature. Numerous injection molding runs were carried out by varying the packing time, packing pressure, flow rate, melt and mold temperature, and anisotropic shrinkage of moldings were measured. The experimental results were compared with the simulated data and found in a fair agreement. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3526–3544, 2006

Theoretical and experimental studies of anisotropic shrinkage in injection moldings of semicrystalline polymers

AbstractA novel approach to predict anisotropic shrinkage of semicrystalline polymers in injection moldings was proposed using flow‐induced crystallization, frozen‐in molecular orientation, elastic recovery, and PVT equation of state. The anisotropic thermal expansion and compressibility affected by the frozen‐in orientation function and the elastic recovery that was not frozen during moldings were introduced to obtain the in‐plane anisotropic shrinkages. The frozen‐in orientation function was calculated from amorphous and crystalline contributions. The amorphous contribution was based on the frozen‐in and intrinsic amorphous birefringence, whereas the crystalline contribution was based on the crystalline orientation function, which was determined from the elastic recovery and intrinsic crystalline birefringence. To model the elastic recovery and frozen‐in stresses related to birefringence during molding process, a nonlinear viscoelastic constitutive equation was used with temperature‐ and crystallinity‐dependent viscosity and relaxation time. Occurrence of the flow‐induced crystallization was introduced through the elevation of melting temperature affected by entropy production during flow of the viscoelastic melt. Kinetics of the crystallization was modeled using Nakamura and Hoffman‐Lauritzen equations with the rate constant affected by the elevated melting temperature. Numerous injection molding runs on polypropylene of various molecular weights were carried out by varying the packing time, flow rate, melt temperature, and mold temperature. The anisotropic shrinkage of the moldings was measured. Comparison of the experimental and simulated results indicated a good predictive capability of the proposed approach. POLYM. ENG. SCI., 46:712–728, 2006. © 2006 Society of Plastics Engineers

Simulation and Experimental Verification of Crystallization and Birefringence in Melt Spinning of PET

Abstract A novel approach for the numerical simulation of the development of crystallinity and birefringence on the spinline was proposed. The approach was based on the calculation of elastic recovery and crystalline and amorphous orientation functions without making any assumption about freezing. To model crystallization, the amorphous orientation function and the flow effect on the equilibrium melting temperature elevation due to the entropy reduction between the oriented and unoriented melts were incorporated. The crystalline orientation function was calculated from the frozen-in elastic recovery. The entropy change and frozen-in elastic recovery calculation were based on a nonlinear viscoelastic constitutive Eq. with the crystallinity and temperature dependent viscosity and relaxation time. The crystalline and amorphous contributions to the overall birefringence were obtained from the crystalline orientation function and the flow birefringence, respectively. The temperature, diameter, density, and birefringence profile in both low- and high-speed spun PET fibers were predicted and compared with the experimental data from literature. Theoretical predictions were found to be in agreement with the published experimental data.

Modeling and experimental study of birefringence in injection molding of semicrystalline polymers

The prediction of birefringence developed in injection moldings is very important in order to satisfy required specification of molded products. A novel approach for the numerical simulation of the flow-induced crystallization and frozen-in birefringence in moldings of semicrystalline polymers was proposed. The approach was based on the calculation of elastic recovery that becomes frozen when the flow-induced crystallization occurred. The flow effect on the equilibrium melting temperature elevation due to the entropy reduction between the oriented and unoriented melts was incorporated to model crystallization. To find the entropy reduction and the frozen-in elastic recovery during crystallization, a non-linear viscoelastic constitutive equation was used. From the ultimate elastic recovery the crystalline orientation function was calculated. The crystalline and amorphous contributions to the overall birefringence were obtained from the crystalline orientation function and the flow birefringence, respectively. The birefringence profiles were measured and predicted in moldings of polypropylenes of different molecular weights obtained at various melt temperatures, injection speeds, holding times and mold temperatures. The resulting predictions were in fair agreement with corresponding experimental data.

Development of macrostructural effects of cold drawing on nylon 6 fibers

AbstractThis work reports measurement of the molecular orientation by two techniques for nylon 6 fibers drawn at room temperature. The changes in the strain and optical parameters are used to obtain some macrostructural parameters to evaluate the cold‐drawing process values of the mechanical orientation functions, [P2(cos θ)], [P4(cos θ)], amorphous and crystalline orientation functions (Fc and Fa), and the molar number of chain segments per unit volume (Ne). Also the crosslink density (N0), the chain entanglement density (Ns), the average optical orientation Fav, the dielectric constant (ε), the dielectric susceptibility (η), the shrinkage stress (ks), and other parameters were calculated. Relationships between the calculated parameters are given. The present study demonstrates changes in the molecular reorientation factors and the obtained new physical properties resulting from cold‐drawing process. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 287–295, 2004

Structure and properties of injection‐molded polypropylenes with different molecular weight distribution and tacticity characteristics

AbstractTwo series of polypropylenes with different molecular weight distribution and tacticity characteristics were injection molded into flexural test specimens by varying cylinder temperature and the effects of the molecular weight distribution and tacticity on the structure and properties of the moldings were studied. Measured propertied were flexural modulus, flexural strength, heat distortion temperature, Izod impact strength, and mold shrinkage and structures studied were crystallinity, the thickness of skin layer, a*‐axis‐oriented component fraction and crystalline orientation functions. The relations between the structures and properties were also studied. It was found that the molecular weight distribution and tacticity characteristics affect the properties mainly through the molecular orientation and crystallinity, respectively. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2142–2156, 2002

Solid-State Extrusion of Poly(tetrafluoroethylene) Nascent Powder.

Poly (tetrafluoroethylene) (PTFE) nascent powder was drawn by solid-state extrusion to extrusion draw ratios (EDR) ≤ 100 in the temperature (Te) range of 100~340°C, which covers the Tg(125 °C) and the ambient Tm(334°C). At a given Te, the maximum achievable EDR (EDRmax) increased with increasing shear rate (γ) and hence extrusion rate (Ve), reaching a maximum at a γ of 1 ˜ 4×104/min (V e of 300 ˜ 600 cm/minjdepending on the Te, and at yet higher γ's, the EDRmax decreased rapidly due to the formation of flaws. At a given γ, the EDRmax increased with increasing Te up to a Te =340°C. At Te's >340°C, the drawability was lost due to melting. The structure and properties of extruded products were complexly affected by the extrusion variables. Thus, the oriented rods having crystalline chain orientation function fc of 0.75˜0.96 and flexural modulus Ef of 7.5 ˜ 15 GPa at 24°C could be obtained by extrusion at an optimum Te of 340°C and a Ve of 1˜1000 cm/min (γ of 1×10˜1×105/min). These results show that nascent PTFE powder could be solid-state extruded at remarkably higher Ve's than other polymers, reflecting the less entangled morphology of the nascent powder and the high ductility of a PTFE crystal due to the week intermolecular interaction.

Effects of molecular weight on the drawing and the draw efficiency of nylon-6

Tensile drawing was carried out on nylon-6 films of different viscosity average molecular weights (Mv=77 and 440×103) and crystalline forms (α- and γ-forms). The effects of Mv on the deformation behavior and the draw efficiency were discussed on the basis of the stress/strain curves recorded upon hot drawing, and wide-angle and small-angle X-ray diffraction, birefringence and tensile properties for the draw ratio (DR) series. The draw stress at a given strain and the fracture stress upon hot drawing were both higher for the higher Mv than for the low Mv, in either the α- or the γ-form sample. For a given Mv, the draw stress was lower for the γ-form than one with the α-form and the fracture stress was independent of the crystal forms, leading the former crystalline form to have a higher drawability than the latter, as previously reported. The Mv and the crystal form of predrawn samples had no effect on the crystalline chain orientation function (fc) measured as a function of DR. In contrast, the draw efficiency evaluated from the amorphous chain orientation function (fa) vs. DR and the tensile modulus and strength vs. DR was significantly higher for the higher Mv than for the low Mv. These drawing characteristics were discussed in terms of the entanglement effect and the deformability of the two crystal forms. The maximum achieved tensile modulus of 7.7GPa and a strength of 760MPa were thus obtained by the straight tensile drawing of the higher Mv sample that was initially a γ-form.

Opto-thermal properties of fibers. XVI. Macrostructural and optical properties of cold-drawn, quenched PET fibers

In this article, the relation between the macrostructural changes in uniaxially stretched polyester (PET) fibers, caused by heat treatment, and quenched in coarse-grain ice were studied. The developing macrostructure was determined using double-beam interferometry. Application was carried out by two-beam interferometry to determine the optical parameters. Using a two-beam Pluta polarizing interference microscope connected to a device to dynamically study the draw ratio with birefringence changes. The relations of drawing changes with some optical parameters are given. The evaluation of density, the mean square density fluctuation, crystallinity, amorphous orientation, crystalline orientation functions, the mean square density fluctuation 〈η2〉, the number of chains per unit volume Nc, and the number of random links between the network junction points N(1) have been found. The results obtained clarify the effect of annealing time and temperature with different draw ratios on the structure of PET fibers. Also, the optical results were used to calculate an optical orientation function and an optical orientation angle of drawn, quenched PET fibers. Relations between the optical data, draw ratios, and other parameters with different quenching conditions are given for these fibers. The change of the refractive index profile of the quenched PET fibers with various conditions are given. Illustrations are given using graphs and microinterferograms. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1881–1894, 1999

Study of the structure development during the melt spinning of nylon 6 fiber by on-line wide-angle synchrotron X-ray scattering techniques

The melt spinning of nylon 6 has been studied with on-line wide-angle synchrotron X-ray scattering techniques. The apparatus consisted of a single screw extruder and a metering pump mounted on a horizontal platform that could be translated in the vertical direction allowing a range of distances to be sampled with the X-ray beam. The structure development, equatorial crystallinity index, and crystalline orientation were studied as a function of take-up speed and position along the spinline. For low-speed (50 mpm) situations, the nylon chains crystallize into independent hydrogen bonded sheets that start to interact with each other as their concentration starts to increase. For higher speed situations, the nylon chains crystallize directly into the interacting hydrogen-bonded sheet structure. Upon conditioning at room temperature for 24 h, this interacting hydrogen-bonded sheet structure transforms into the well-known three-dimensional alpha and gamma phases of nylon 6, probably existing in a shish-kabob structure. The equatorial crystallinity index increases as distance from the spinneret increases and as take-up speed decreases. The crystalline orientation function is constant along the spinline for a constant take-up speed, and increases as take-up speed is increased. Conditioning further increases both the crystallinity and crystalline orientation of the fibers. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1277–1287, 1999

Opto-mechanical properties of fibres. Part 2. Effect of stretching on some optical and structure parameters of PET fibres (woollen type)

The influence of cold drawing on the birefringence, orientation, crystallinity and other structural parameters is examined for polyester (Egyptian PET woollen type). A two-beam Pluta polarizing interference microscope connected to a device for dynamically studying the effect of the draw ratio on the refractive indices has been used. The optical data obtained the densities and crystallinities of the samples. The mean square density fluctuation 〈η2〉, crystalline orientation function, amorphous orientation function, the number of chains per unit volume Nc and the number of random links between the network junction points N1 are then calculated. Calculations are also carried out to determine the strain optical coefficient, the orientation factor, the orientations angle, the number of molecules per unit volume N, and the isotropic refractive index. In addition, Poisson's ratio over all strain ranges, the distribution of segment at an angle θ with respect to the draw ratio, the electric polarizability constant (Δα/3α0) and other structural parameters and constants are calculated. An empirical formula is suggested to correlate the change in Δ n, Fc , Fa , ω(cos θ), A and Nc , and its constants are determined. The refractive index profile is studied. Interferograms and curves are given for illustration. © 1999 Society of Chemical Industry

Effect of Crystalline and Amorphous Structures on Biodegradability of Poly(Tetramethylene Succinate)

The effect of orientation in the amorphous and crystalline regions on the biodegradability of PTMS [poly(tetramethylene succinate)] was studied using the amorphous orientation function, birefringence, and crystallinity. The crystalline and amorphous intrinsic lateral sonic moduli, E t,c 0 and E t,am 0 , were 2.61 × 103 and 0.41 × 103 MPa, respectively. Using the data on birefringence, crystalline and amorphous orientation function (f ∈ and f am), crystallinity, and sonic modulus of the oriented PTMS fibers, the intrinsic birefringence of the crystalline (Δ c 0 ) and amorphous (Δ am 0 ) regions were evaluated to be 0.0561 and 0.0634, respectively. The biodegradabilities of oriented PTMS films were reduced as the elongation increased, i.e., the amorphous orientation increased. At low elongation (100 and 150%), however, biodegradabilities remained unchanged when the degradation test was performed in activated sludge, which was attributed to the amorphous orientation occurring even at 100% elongation, though the amorphous orientation direction was perpendicular to the fiber axis.

Opto-thermal properties of fibers. XI. The effect of thermal annealing of drawing behavior for Egyptian polyester fibers on the crystallinity and some optical parameters

The structure developed of annealed Egyptain poly(ethyleneterephthalate) (PET) fibers is studied interferometerically due to the drawing process. Using a two-beam Pluta polarizing interference microscope connected to a device to dynamically study the draw ratio with the birefringence changes, the relations of drawing changes with some optical parameters are given. The evaluation of density, the mean square density fluctuation η2, crystallinity, amorphous orientation, crystalline orientation functions, number of chains per unit volume Nc, and number of random links between the network junction points N has been found. The results obtained clarify the effect of annealing time and temperature with different draw ratios on the structure of PET fibers. Empirical formula is suggested to correlate the changes in fθ, θ, Δna, and A with the draw ratio. Microinterferograms and curves are given for illustration. © 1998 John Wiley & Sons, Inc. J Appl Polm Sci 68: 1371–1386, 1998

Properties and Structure of Ultra-High Speed Spun Nylon 66 Fibers.

Structure and properties of ultra-high speed spun nylon 66 [poly (hexamethylene adipamide)] fibers prepared at take-up speeds of 5 to 12km/min were investigated through the X-ray and thermal analyses and the measurements of mechanical properties. With an increase in the take-up speed, both Young's modulus and dynamic storage modulus increased monotonously, while tenacity reached a maximum at around 6km/min. Birefringence and amorphous orientation function also showed a maximum. In contrast with these results, density showed a tendency of saturation at high-speed region. The existence of void in the filament was also suggested by the smallangle X-ray scattering measurement. From the wide-angle X-ray diffraction analysis, the increase in the crystalline orientation function, crystal perfection index and the thickness of lamellar were observed with an increase in the take-up speed. Thus, it was concluded that highly ordered crystalline structure was formed in the high-speed spinning of nylon 66 fibers. The existence of peak in tenacity was related with the formation of the void in the filament and the increase of Young's modulus was related with the ordering of crystalline structure.

Solid-state deformation of polytetrafluoroethylene powder

Polytetrafluoroethylene (PTFE) powder of a high molecular weight (~ 107) was drawn by solid-state extrusion in the temperature range 100–340°C, which covers the glass transition temperature (125°C) and the ambient melting point (334°C). Draw was attainable only above 100°C. The maximum achievable extrusion draw ratio (EDRmax) was almost constant, ~ 10, from 100–280°C, yet increased rapidly with further increasing temperature, reaching a maximum of 60 at 330–340°C. At yet higher temperatures, the drawability was lost due to melting. The structure and properties of drawn products were found to be complexely affected by extrusion temperature and EDR. For extrusion at 330–340°C, near the melting point, an effective and high draw was achieved. The crystalline chain orientation function, crystallite sizes, both along and perpendicular to the chain axis, differential scanning calorimetry heat of fusion, and flexural modulus increased with EDR and approached a maximum at EDR of 30–40, depending on the extrusion temperatures. Above a specific EDR, the efficiency of draw decreased due to the formation of flaws. The highly oriented PTFE consisted of microfibrils of a significantly large lateral dimension (~ 45 nm) compared to those (6–20 nm) generally found in oriented polymers. The modulus of a drawn PTFE was sensitive to the test temperatures, reflecting the reversible crystal/crystal transitions at ~ 19 and 30°C. The optimization of the extrusion conditions resulted in the maximum achieved flexural modulus at 24°C of 20 GPa at an EDR 40 for extrusion at 340°C.