Melt Flow Properties During Capillary Extrusion of Linear Low-Density Polyethylene

Abstract

The melt flow properties of a linear low-density polyethylene (LLDPE) were measured by means of a capillary rheometer under the experimental conditions of temperatures from 220° to 260°C and apparent shear rates varying from 12 to 120 s^?1. The end pressure drop (ΔP _end) was determined by employing the Bagley's plotting method. The results showed that ΔP _end increased nonlinearly with increasing shear stress. The end pressure fluctuation phenomenon was observed at lower shear stress level, and several plateau regions were generated in the end pressure drop-shear stress curves, suggesting onset of the wall-slip phenomenon during die extrusion of the resin melt. The critical shear stress with onset end pressure fluctuation phenomenon increased with a rise of temperature. Furthermore, the melt shear flow did not strictly obey the power law. The melt shear viscosity decreased nonlinearly with increasing shear stress and with a rise of temperature, whereas the dependence of the melt shear viscosity on the test temperature accorded with a formula similar to the Arrhenius expression.     

Crystalline structure and morphology of poly(L‐lactide) formed under high pressure

The poly(l ‐lactide) (PLLA) samples were prepared by the annealing under 100 MPa at 75–145^°C and 200 MPa at 105–145^°C for 6 h, respectively. The crystalline structures, thermal properties and morphology were investigated using differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), and scanning electron microscopy (SEM). On the basis of the DSC and WAXD results, it can be seen that the α′ form was formed by the annealing under 100 MPa at 85–95°C but not found under 200 MPa at 105–145°C. A phase diagram of PLLA crystal form under high pressure was constructed under the given experimental conditions, which displayed the α′ form was formed at limited temperature and pressure range. Besides, SEM suggested that the PLLA samples annealed under 100 MPa crystallize to form lamellar‐like crystals due to the low growth rate and the confined crystallization behavior under high pressure. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40637.     

Cellulose–poly(acrylamide–acrylic acid) interpenetrating polymer network membranes for the pervaporation of water–ethanol mixtures. II. Effect of ionic group contents and cellulose matrix modification

The separation properties in the dehydration of a water–ethanol mixture and the swelling behavior of interpenetrating polymer network (IPN) pervaporation membranes based on a cellulose or cellulose–hydroxyethyl cellulose (HEC) matrix and poly(acrylamide and/or acrylic acid) were investigated depending on the ionic acrylate groups content (γ) in synthetic polymer chains (0–100 mol %), the HEC content in the matrix (0–50 wt %), and the temperature (25–60°C). The separation factor (α), permeation rate (P), and separation index (αP) significantly improved with increasing γ values only for the separation of concentrated ethanol solutions (～86 wt %). For more dilute solutions of ethanol (～46 wt %), the P and αP values also increased but no considerable increase in α was observed. All types of membranes based on the cellulose matrix were characterized by a drastic decrease in the values of P at [EtOH] ≥90 wt % and, as a result, a decrease in the separation index (kg m^?2 h^?1) from ～2000 (for 86 wt % EtOH, 50°C) to ～240 (for 95 wt % EtOH, 50°C), which correlates with a decrease in the degree of membrane swelling. The modification of the cellulose matrix by introducing HEC into it makes it possible to increase considerably the membrane swelling in concentrated EtOH solutions and, hence, the αP value to ～760 (95 wt % EtOH, 50°C). All types of IPN membranes exhibit a marked increase in both α and P when the temperature increases from 25 to 60°C. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1452–1460, 2001     

The specific volume of poly(tetrafluoroethylene) as a function of temperature (30°–372°C) and pressure (0–2000 kg/cm2)

Experimental data on the specific volume of a 50% crystalline sample of poly(tetrafluorethylene) are presented and discussed. Data points were taken along 22 isotherms spaced 5 to 30°C apart (up to 372°C) in pressure increments of 100 kg/cm² up to 2000 kg/cm². In addition to the melting transition and the first-order solid–solid transition near room temperature, a previously reported second-order transition near 140°C at P = 0 is observed. This transition shifts to higher temperatures with increasing pressure by about 0.015°C per kg/cm². The melt data are discussed in detail. They can be fitted to both the empirical Tait equation, with the usual exponential temperature dependence of the Tait parameter, and to the Simha-Somcynsky hole theory (with the reducing parameters V^* = 0.424 cm³/g, T^* = 7906°K, and P^* = 7100 kg/cm² = 6960 bars), thus providing a test for this theory at high reduced temperatures near T? = 0.08.     

Crystallisation kinetics of novel branched poly(ethylene terephthalate): a small‐angle X‐ray scattering study

Three types of poly(ethylene terephthalate) (PET) were investigated: linear (unprocessed) bottle‐grade PET (intrinsic viscosity, IV ～ 0.82 dL g^?1); a branched PET produced from linear PET by reactive extrusion with 0.4% w/w pyromellitic dianhydride and pentaerythritol in 5:1 molar ratio (IV ～ 0.97 dL g^?1); and a control sample produced from the same linear PET by extrusion under the same conditions without the reactive agents (IV ～ 0.71 dL g^?1). A key finding is that the reactive extrusion process, presumably as a consequence of branching and branch distribution, significantly modifies the crystallisation kinetics and changes the final morphology. Using small‐angle X‐ray scattering (SAXS) and differential scanning calorimetry (DSC), the crystallisation kinetics of PET was monitored from the melt (270 °C) to a crystallisation temperature of either 205 or 210 °C. The IV of the branched PET was ～ 21% greater than that of the unprocessed PET, and the rate of melt crystallisation (from DSC measurements) was 510 s for the branched, 528 s for the control, and 640 s for the unprocessed PET. The lamellae spacings measured from the equilibrium SAXS patterns were ～160 ± 10 Å for the branched PET and ～180 ± 10 Å for the unprocessed PET. Such properties offer the potential for new applications requiring high‐melt‐strength PET. Copyright © 2006 Society of Chemical Industry     

Order-Disorder Conformation Change of Succinoglycan in Aqueous Sodium Chloride as Studied by Static and Dynamic Light Scattering

Summary Static and dynamic light scattering measurements have been made on a sodium salt sample of succinoglycan in 0.01 M aqueous NaCl at different temperatures between 25 and 75°C where the polysaccharide undergoes a thermally induced change from an ordered (helical) to disordered conformation with raising temperature T. The weight-average molecular weight M _w, the z-average radius of gyration, and the hydrodynamic radius sharply decrease in a relatively narrow T range (around 55°C) in which the specific rotation was previously found to change sigmoidally with T. In particular, the value of M _w (4.55 × 10⁵) in the ordered state at 25°C is twice as large as that (2.27 × 10⁵) in the disordered state at 75°C, giving decisive evidence that the helical structure of the polysaccharide in aqueous NaCl is composed of paired chains. It is concluded that this structure is a double-stranded helix and breaks directly into two disordered chains with increasing T. Received: 6 July 2001 / Accepted: 24 July 2001     

Effect of die temperature on the morphology of microcellular foams

A study on the extrusion of microcellular polystyrene foams at different foaming temperatures was carried out using CO₂ as the foaming agent. The contraction flow in the extrusion die was simulated with FLUENT computational fluid dynamics code at two temperatures (150°C and 175°C) to predict pressure and temperature profiles in the die. The location of nucleation onset was determined based on the pressure profile and equilibrium solubility. The relative importance of pressure and temperature in determining the nucleation rate was compared using calculations based on classical homogeneous nucleation theory. Experimentally, the effects of die temperature (i.e., the foaming temperature) on the pressure profile in the die, cell size, cell density, and cell morphology were investigated at different screw rotation speeds (10 ～ 30 rpm). Experimental results were compared with simulations to gain insight into the foaming process. Although the foaming temperature was found to be less significant than the pressure drop or the pressure drop rate in deciding the cell size and cell density, it affects the cell morphology dramatically. Open and closed cell structures can be generated by changing the foaming temperature. Microcellular foams of PS (with cell sizes smaller than 10 μm and cell densities greater than 10 cells/cm³) are created experimentally when the die temperature is 160°C, the pressure drop through the die is greater than 16 MPa, and the pressure drop rate is higher than 10⁹ Pa/sec.     

Effect of entrance geometry on the capillary flow of cellulose acetate–acetone solution

Capillary flow data were obtained for a 27.5% solution of cellulose acetate in acetone. The solution temperature was 50°C, and the range of apparent shear rates investigated was 1.7 × 10⁵ to 1.7 × 10⁶ sec^?1. Capillaries having tapered entrance angles of 37.88° to 120.63° were used. A power-law model was adequate to describe the shear stress at the wall (τ_w) and the corrected shear rate \documentclass{article}\pagestyle{empty}\begin{document}$(\dot \gamma )$\end{document} relationship. Entrance angle affected the entrance pressure drop corrected for kinetic energy, (ΔP_0,c); ΔP_0,c increased as the angle widened. Treating the entrance flow as an elongational flow situation facilitated superposition of the Delta;P_0,c data on a single curve. Estimated elongational viscosities decreased with increasing applied stress.     

Extraction of Total Phenolics of Sour Cherry Pomace by High Pressure Solvent and Subcritical Fluid and Determination of the Antioxidant Activities of the Extracts

Abstract

High pressure liquid extraction (HPE) and subcritical fluid (CO₂+ethanol) extraction (SCE) were used for the extraction of total phenolic compounds (TPC) from sour cherry pomace. Antiradical efficiency (AE) of the extracts was also determined. Ethanol was the solvent for HPE and co‐solvent for SCE. Combinations of pressure (50, 125, 200 MPa), temperature (20, 40, 60°C), solid/solvent ratio (0.05, 0.15, 0.25 g/ml) and extraction time (10, 25, 40 min) were variables for HPE according to the Box‐Behnken experimental design. The variables used for SCE were pressure (20, 40, 60 MPa), temperature (40, 50, 60°C), ethanol concentration (14, 17, 20 wt%) and extraction time (10, 25, 40 min). For HPE, TPC, and AE at the optimum conditions (176–193 MPa, 60°C, 0.06–0.07 g solid/ml solvent, 25 min) were found as 3.80 mg gae/g sample and 22 mg DPPH^?/g sample, respectively. TPC and AE at the optimum conditions (54.8–59 MPa, 50.6–54.4°C, 20 wt% ethanol, 40 min) for SCE were determined as 0.60 mg gae/g sample and 2.30 mg DPPH^?/g sample for sour cherry pomace, respectively.     

Thermal effects in polytetrafluoroethylene at high hydrostatic pressures

The temperature changes as a result of rapid hydrostatic pressure applications are reported for polytetrafluroethylene (PTFE, Teflon) in the reference temperature range from 294° to 381°K and in the pressure range from 13.8 to 200 MN/m². The thermal effects were found to be higher at the reference temperature approximating the transition temperatures of 19° and 30°C than at higher reference temperature. The data were analyzed by determining the predicted thermoelastic coefficients derived from the Thomson equation (?T/?P = αT/ρC_p). A curvefitting analysis showed that the empirical curve, (?T/?P) = ab(ΔP)^b?1, described the experimental thermoelastic coefficients obtained from the experiments. The fact that no agreement was found between the predicted and the experimental coefficients is due to the physical changes in PTFE at the transition temperatures. The relationship between the thermal effects and the chain molecular motion is discussed by including dynamic mechanical analysis and differential scanning calorimetry DSC measurements for the PTFE samples.     

The optimum taper angle for ethanol fermentation in a packed-bed column reactor

In ethanol fermentation, tapered columns facilitate the liberation of CO₂ and, since the bed expands through a larger cross-sectional area, smaller pressure drops occur. In this work, 0°, 2°, and 4° tapered columns, containing Saccharomyces cerevisiae entrapped in beads of K-carrageenan, were operated for continuous production of ethanol from glucose. The column inlet diameters and the bead volume were maintained constant for the three columns. With decreasing taper angle, increasing feed glucose concentration, increasing feed flow rate and increasing bead volume in the reactor, the pressure drop across the bed increased. There was no significant difference between the ethanol productivities obtained in the 0°, 2°, and 4° tapered columns when a packed volume of 52% of the total volume was examined. Increasing the packed volume to 84% of the total caused the cylindrical column to become inoperable due to pressure buildup and bead compression. When the columns were packed to 84% capacity, the productivity and pressure drop values obtained on the 2° and 4° tapered columns did not significantly differ. For a feed concentration of 150 g glucose dm^?3 and a residence time range of 5.4–15.94 h, the pressure drop varied between 4.5 × 10³ and 1.28 × 10⁴ Pa in the 2° and between 4 × 10³ and 7.98 × 10³ Pa in the 4° tapered column. Conversion in the 2° tapered column varied from 94% to 78.8% and in the 4° tapered column from 92.6% to 78.8%. Defining optimum taper angle as the smallest angle which allows for stable operation without any pressure buildup, the taper angle of 2° was selected as nearest to the optimum value.     

Thermal oxidation kinetics for a poly(bismaleimide)

The thermal oxidation of poly(bismaleimide) of the F655‐2 type, supplied by Hexcel‐Genin, was studied by isothermal gravimetry at 180, 210, and 240°C and various oxygen pressures ranging from 0 to 1.2 bar. Comparison of various sample thicknesses and visible microscopy observations on bulk aged samples shows that the whole oxidized layer has a depth of about 75 μm at 240°C, 138 μm at 210°C, and 229 μm at 180°C. An attempt was made to build a kinetic model to predict this depth. It is based on a differential equation in which O₂ diffusion and its consumption rate, r(C), are coupled, C being the O₂ concentration. Its resolution needs two sets of experiments: the first one to determine the O₂ diffusivity and solubility in the polymer, and the second one to determine r(C). The mathematical form of r(C) is derived from a mechanistic scheme of radical chain oxidation in which initiation is mainly due to POOH decomposition. This expression contains two kinetic parameters, α and β, the values of which are determined from the experimental curves of mass loss rate against O₂ pressure (in the stationary state). The theoretical predictions, at each temperature under consideration, are in excellent agreement with experimental results. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3418–3430, 2001     

Thermodynamic properties of methanol–benzene mixtures at elevated temperatures

The total pressure and the compositions of the vapour and liquid phases of the methanol–benzene system have been determined under equilibrium conditions at 100°, 120°, 140°, 160°, 180°, 200° and 220° for ten levels of concentration. The corresponding activity coefficients of methanol and benzene are reported; their values indicate that the equilibrium data are thermodynamically consistent. An azeotrope is found at all temperatures, its methanol content increasing as the temperature is increased. The relationship log P_az = 6·5098—(1,766/T) expresses the interdependence of the azeotrope vapour pressure P_az(lb/in² abs.) and temperature T(°K). Estimates of integral heat of mixing (H^E) and entropy change due to mixing (S^E) as functions of liquid composition (x_meth) have been made from the excess free energy of mixing G^E,(T) x_meth functions. Both H^E and S^E at a given x are positive increasing functions of temperature. These phenomena are discussed in terms of the dissociation of methanol ‘polymer’ and the formation of benzene–methanol ‘complexes’.     

Thermo-responsive mixed-matrix hollow fiber membranes

Up to date, preparation of thermo-responsive mixed-matrix membranes (MMM) has only be described as small scale flat membranes or multi-step processes for hollow fiber membranes. In this work, the development of thermo-responsive MMM hollow fibers composed of polyethersulfone as membrane polymer and poly(N-isopropylacrylamide) (PNIPAM) microgel particles via the wet spinning process is presented. PNIPAM particles are synthesized with (NP-S, z_{avg 20°C} = 105 nm) and without (NP-L, z_{avg 20°C} = 250 nm) sodium dodecyl sulfate and their thermo-responsive behavior is characterized by dynamic light scattering. Particle size (NP-S, NP-L), particle content (10%, 15%) and the extrusion pressure in the wet spinning process (1.0–3.0 bar) are investigated as experimental parameters. Reversible thermo-responsive behavior of the hollow fibers is demonstrated by water permeability measurements at different temperatures (20 and 50°C). The largest switching factors (R) are observed for the hollow fibers containing NP-L. For 15% NP-L and 1 bar extrusion pressure, water permeances between 0.5 and 6.0 L m⁻² h⁻¹ bar⁻¹ are observed, corresponding to R = 12 and a dextran (500 kDa) rejection of 91% at 25°C.     

Influence of processing parameters on the degradation of poly(L‐lactide) during extrusion

The influence of processing conditions during melt extrusion on the degradation of poly(L ‐lactide) (PLLA) has been investigated. PLLA polymer was processed by melt extrusion in a double screw extruder at 210 and 240°C. For each extrusion temperature, two screw rotation speeds, 20 and 120 rpm, were used. To investigate the influence of moisture on the thermal degradation during processing, the PLLA granules were dried at 100°C for 5 h and then either extruded directly or conditioned at 65% RH, 20°C for 24 h prior to extrusion. The results show that a decrease in molecular weight measured as number‐average (M_n) molecular weight occurs for all combinations of process parameters used. At processing temperature of 210°C, the change in molecular weight for the dry granules was shown to be dependent on the residence time (i.e., screw rotation speed) in the melt. By changing the screw rotation speed from 120 to 20 rpm at 210°C, M_n decreased from 33,600 to 30,200 g/mol. When the processing temperature was increased to 240°C, the dry granules showed an M_n of 25,600 and 13,600 g/mol when extruded at 120 and 20 rpm, respectively. M_n for the conditioned specimens extruded at 210°C was 18,400 g/mol when processed at 120 rpm and 12,300 g/mol at 20 rpm. When processed at 240°C, 20 rpm, M_n is independent of whether the granules were dry or moist prior to extrusion. It is probably due to the fact that the degradation at 240°C is so extensive that the presence of moisture in the polymer does not contribute further to the degradation process. The stress and strain at break decreased due to degradation and were dependent on the molecular weight of the samples. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2128–2135, 2001     

Continuous enzymatic synthesis of Z-kyotorphin amide in an enzyme-immobilized fixed-bed reactor

α-Chymotrypsin immobilized on natural and inexpensive supports such as diatomaceous earth was used as catalyst for Z-Tyr-Arg-NH₂ (Z-kyotorphin amide) synthesis. In order to obtain the optimal reaction conditions, a 2² factorial experimental design was used. The factors considered were cosolvent (dimethylformamide) concentration and temperature; optimal product yield was achieved at 40% (v/v) dimethylformamide and 25°C. A sequential kinetic model was considered which generally gave good agreement between experimental and theoretical data for continuous synthesis of Z-kyotorphin amide in a packed-bed immobilized reactor system. The activation energy for the synthesis was determined to be 48.0 ± 2.3 kJ mol^?1.     

Extension behavior and morphology in polypropylene extended under hydrostatic pressure

The effect of hydrostatic pressure on molecular deformation of polypropylene extended under hydrostatic pressure is investigated by using internal friction measurements, wide angle X-ray diffraction, and polarizing microscopy. A homogeneously transparent straight part is obtained by extending samples in the pressure range from 78 to 128 MPa. The overall mechanical properties of a sample extended under P = 102 MPa is significantly different from that of a sample extended under P = 128 MPa. The difference is related to the magnitude of hydrostatic pressure, the extension ratio, and the extent of transparency. The observed results on the β relaxation in the extended samples is found to be related to the morphological reorganization from a coarse spherulitic to a fine spherulitic structure. The cold-drawn sample at atmospheric pressure has the γ-peak at around °50°C, while the hydrostatically extruded samples and the extended samples have no γ-peak. Consequently, the hydrostatic pressure suppresses the formation of the molecular structure relevant to the γ relaxation.     

Pressure drop for single and two‐phase flow of non‐newtonian liquids in helical coils

New experimental results on pressure loss for the single and two‐phase gas‐liquid flow with non‐Newtonian liquids in helical coils are reported. For a constant value of the curvature ratio, the value of the helix angle of the coils is varied from 2.56° to 9.37°. For single phase flow, the effect of helix angle on pressure loss is found to be negligible in laminar flow regime but pressure loss increases with the increasing value of helix angle in turbulent flow conditions. On the other hand, for the two‐phase flow, the well‐known Lockhart‐Martinelli method correlates the present results for all values of helix angle (2.56‐9.37°) satisfactorily under turbulent/laminar and turbulent/turbulent conditions over the following ranges of variables as: 0.57 ≤ n′ ≤ 1; Re′ < 4000; Re_l < 4000; Re_g < 8000; 8 ≤ x ≤ 1000 and 0.2 ≤ De′ ≤ 1000.     

Melt rheology of nanometre‐calcium‐carbonate‐filled acrylonitrile–butadiene–styrene (ABS) copolymer composites during capillary extrusion

The melt flow properties during capillary extrusion of nanometre‐calcium‐carbonate‐filled acrylonitrile–butadiene–styrene (ABS) copolymer composites were measured by using a Rosand rheometer to identify the effects of the filler content and operation conditions on the rheological behaviour of the sample melts. The experiments were conducted under the following test conditions: temperature varied from 220 to 240 °C and shear rate ranged from 10 to 10⁴ s^?1. The filler volume fractions were 0, 10, 20, 30, 40 and 50%. The results showed that the shear flow did not strictly obey the power law under the test conditions, and that the entry pressure drop (ΔP_en) and the extension stress (σ_e) in entry flow increased nonlinearly, while the melt shear viscosity (η_s) and extension viscosity (η_e) decreased with increasing the wall shear stress (τ_w) at constant test temperature. The dependence of the melt shear viscosity on the test temperature was approximately consistent with the Arrhenius expression at fixed τ_w. When τ_w was constant, η_s and η_e increased while ΔP_en and σ_e decreased with the addition of the filler volume fraction. © 2002 Society of Chemical Industry