Rheological behavior of ultrahigh molecular weight polyethylene semidilute solutions. I. Solvent effect

The rheological behavior of ultrahigh molecular weight polyethylene (UHMWPE) semidilute solutions with different solvents has been studied. In a temperature range of 150–185°C, the viscosity of a UHMWPE semidilute solution with paraffin oil as solvent (soln 1) is more temperature-independent and viscosity-stable than that with decalin as solvent (soln 2). Usually the reduction of the molecular entanglement density in solution causes a rapid reduction in viscosity. Apparently soln 1 has a different entanglement density compared with soln 2. The activation energy of UHMWPE semidilute solutions changes with both shear stress and shear rate. The regressive equations for both solutions in between E_σ and σ or E_? and $ {\dot \gamma } $ have been obtained from a least-squares method. Finally, there is a discontinuity in the non-Newtonian flow region of η vs. $ \dot \gamma ^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} $ curve, no matter which temperature or solvent was used. The discontinuity occurs at a shear rate of about 70 s^?1, where a transformation from a qualitative change in entanglement in the solution takes place.     

Characterization of the rheological behavior of UHMWPE gels using parallel plate rheometry

The effects of shear flow, temperature, and gel concentration on the rheological behavior of the ultrahigh-molecular-weight polyethylene (UHMWPE) gel in gel spinning process were investigated. The gel point was determined using parallel plate rheometry in rotation mode with controlled stress. Likewise, the flow curves at various temperatures were determined with controlled shear rate from 10⁻² to 10 s⁻¹. Whereas the shear storage modulus (G′) was obtained in oscillation mode with controlled strain from 1 to 100%. The result shows that the gel point of the UHMWPE gel increases with increasing gel concentration. The result from the strain sweep indicates that G′ of the gel is 1.5 × 10³ Pa, and it exhibits a plateau at low strain, but it is reduced with increasing strain. At low shear rates, for temperatures above gel point, all flow curves exhibit a plateau, then go down with increasing shear rate. Studying contributions from UHMWPE gel concentration, temperature, and shear rate for rheological view, we found that spinning at 6% UHMWPE (MW : 1.4 × 10⁶ g/mol) gel and 140°C gives the best effect on formation of fiber structure. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1009–1016, 1998     

Ultradrawing properties of ultrahigh‐molecular weight polyethylene/functionalized carbon nanotube fibers and transmittance properties of their gel solutions

The influences of the dispersion level of carbon nanotubes (CNTs) and functionalized CNTs on the transmittance properties of ultrahigh‐molecular weight polyethylene (UHMWPE) gel solutions and on ultradrawing properties of their as‐prepared fibers are reported. The transmittance properties suggest that the dispersion level of functionalized CNTs in UHMWPE/functionalized CNTs gel solution is significantly better than plain CNTs in UHMWPE/CNTs gel solutions. The orientation factors, achievable draw ratios, tensile strength (σ_f), and modulus (E) values of UHMWPE/CNTs (F_xC_y) and UHMWPE/functionalized CNTs (F_xC_f‐y) as‐prepared fiber specimens reached a maximum value as their CNT and functionalized CNT contents approached optimum contents at 0.00015 and 0.0001 wt%, respectively. The σ_f and E values of both F_xC_0.0012 and F_xC_f‐0.001 series fiber specimens prepared at their optimum CNT and functionalized CNT contents reached another maximum as their UHMWPE approached optimum UHMWPE concentration of 1.7 wt%. Possible reasons accounting for these interesting properties are proposed. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Rheological properties of UHMWPE/HDPE blend gels and morphology and mechanical properties of gel-spun fibers

To produce polyethylene (PE) fibers with relatively high tensile strength but low cost, ultra-high-molecular-weight polyethylene (UHMWPE)/high-density polyethylene (HDPE) (UH) blend gels were prepared from paraffin oil and further fabricated into UH blend fibers by gel spinning. This research focused on the rheological properties of UH blend gels with high solid contents (SCs) ranging from 25 to 100 g/L, as well as morphology and mechanical properties of resultant gel-spun UH blend fibers. The rheological measurements indicated that the apparent viscosity, shear storage, and loss moduli of the UH blend gels were not markedly increased compared with those of the UHMWPE gel with much less SC. No obvious solid–liquid phase separation occurred in UH blend gels at a temperature above the sol–gel transition temperature. UH blend fibers were prepared by drawing as-spun fibers (draw ratio [λ] = 3) at 110°C to λ = 15, 45, 60, and 80, respectively. The orientation degree of fibril structure in UH blend fibers increased with increasing λ but the length of fibrils (L_fibril) showed a complex change. The L_fibril of UH blend fibers became larger due to chain arrangement in company with the transformation of the kebab structure to the extended shish structure when the λ was less than 45 but decreased during further elongation (λ = 60 and 80) because of fibril breakage and recrystallization. The change in morphological behavior led to the corresponding change in mechanical properties of resultant gel-spun UH blend fibers. The tensile strength of gel-spun UH55-45 blend fiber (UHMWPE/HDPE = 5/5 and λ = 45) reached 15.6 cN/dtex, which could fulfill the requirement of mechanical properties in common application.     

Utilization of supercritical CO2 as a processing aid for preparation of ultrahigh molecular weight polyethylene/functionalized activated nanocarbon fibers

This is the first investigation to report the processing and properties of ultrahigh molecular weight polyethylene (UHMWPE)/functionalized activated nanocarbon (FANC) gel solutions with the aid of supercritical carbon dioxide (scCO₂). The ultradrawing and ultimate tensile properties of scCO₂UHMWPE and scCO₂UHMWPE/FANC fibers were found to improve considerably compared to those of UHMWPE and UHMWPE/FANC fibers prepared in the conventional way. The maximum achievable draw ratio obtained for the optimal scCO₂UHMWPE/FANC fibers drawn at 95°C reached 445. The highest tensile tenacity (σ_f) of the fully drawn scCO₂UHMWPE/FANC fiber reached an extraordinary high value of 104 g/d, which is about 3.2 and 1.1 times of that of the optimal UHMWPE and UHMWPE/FANC fully drawn fibers, respectively. The σ_f obtained for the optimally fully drawn scCO₂UHMWPE/FANC fiber is about 25 times of those of steel fibers and is the highest tensile tenacity ever reported for single‐stage drawn polymeric fibers. Considerably lower dynamic transition temperatures and evaluated thinner crystal lamellae nucleated off of extended chains or FANC nucleants were found for as‐prepared scCO₂UHMWPE and scCO₂UHMWPE/FANC fibers compared with UHMWPE and UHMWPE/FANC fibers, respectively. Specific surface area, morphological, and Fourier transform infrared analyses of the activated nanocarbon (ANC), acid‐treated activated nanocarbon (ATANC) and FANC nanofillers and investigation of thermal, morphological, and orientation factor properties of the as‐prepared and drawn UHMWPE, UHMWPE/FANC, scCO₂UHMWPE, and scCO₂UHMWPE/FANC fibers were performed to understand the remarkable ultradrawing, dynamic transition, and ultimate tensile properties obtained for scCO₂UHMWPE and scCO₂UHMWPE/FANC fibers. POLYM. ENG. SCI., 59:1462–1471 2019. © 2019 Society of Plastics Engineers     

Research on the molecular entanglement and disentanglement in the dry spinning process of UHMWPE/decalin solution

The macromolecular entanglement and disentanglement in the dry spinning process of ultrahigh molecular weight polyethylene (UHMWPE)/decalin solution were investigated. By the fitting results of the theoretical model to the experimental data, it is found that the variation tendency of the N_skT value, which reflects the chain slippage at the slip links in the extensional deformation on spinning line of draw‐down process, is in accordance with the fact that each of the relationship curves between the tensile strength, modulus of the UHMWPE fibers through maximized solid state drawing and the draw‐down ratio showed a peak, thus discovering the molecular movement mechanism of “disentanglement on spinning line.” When the entanglements were included in the flow units, their apparent quantity would decrease. Based on this result, the optimum draw‐down ratio can be determined directly by measuring the draw‐down stress at the exit of the spinning duct. The molecular entanglements numbers, which are derived from the theoretical fitting to the experimental data of predrawing and after‐drawing process, abruptly increased in large amounts. It may be concluded that these are mainly not attributed to the topological entanglements, but attributed to the agglomerate entanglements. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 864–875, 2006     

Preparation of PAN@PU coaxial electrostatic spun nanofibers for oil/water separation

Coaxial electrostatic spinning (co-electrostatic spinning) technology has greatly expanded the versatility of the preparation of core–shell polymer nanofibers and has found a wide range of applications in the environmental and biological fields. Here we present a method for the preparation of coaxial nanofibers using polyacrylonitrile (PAN) and polyurethane (PU) as raw materials. It was found that the tensile strength ranges from 2.14 to 4.07 MPa with the increasing spinning speed of the nucleated PU layer, and the elongation at break was up to 95.09% for M_6:4, which was three times higher than that of the original M_PAN (30.54%), and the toughness of the nanofiber film was also significantly improved. Finally, the oil/water separation capacity of the coaxial nanofiber membrane was investigated, and the results showed that the separation fluxes for various oil compounds ranged from 2380.18 to 3130.17 L·m⁻²·h⁻¹, with separation efficiencies above 99%. This study not only investigates the effect of different flow rates of core (PU)/shell (PAN) on the performance of coaxial electrostatic spun nanofiber membranes, but also provides a new insight into the coaxial electrostatic spinning process.     

Cellulose-based fibers from liquid crystalline solutions. III. Processing and morphology of cellulose and cellulose hexanoate esters

Cellulose and a cellulose hexanoate ester (DS 0.69) exhibited liquid crystalline behavior in dimethylacetamide/lithium chloride and dimethylacetamide, respectively. The experimentally observed critical volume fraction (V^c_p) of cellulose was lower than that predicted by Flory's theory, whereas the experimental and theoretical values of V^c_p were within 70% of prediction for cellulose hexanoate. The V^c_p value obtained for cellulose hexanoate was lower than that previously reported for cellulose acetate butyrate with a maximum degree of butyration (CAB-3). This indicates that bulky substituents may lower V^c_p values. Fibers were spun from isotropic and anisotropic solutions of cellulose and cellulose hexanoate by a dry jet/wet spinning method. There was an increase in mechanical properties through the isotropic to anisotropic transition with moduli reaching 152 g/d (20.8 GPa) for cellulose fibers. The formation of cellulose fibers with high modulus at large extrusion rates and large takeup speeds (draw ratio) is explained with molecular organization prior to coagulation. This unexpected enhancement is attributed to the air gap that exists in the dry jet/wet spinning process. Similar improvements were not observed for cellulose hexanoate fibers. This is explained with incomplete development of liquid crystalline structure at the solution concentrations from which the fibers were spun. © 1993 John Wiley & Sons, Inc.     

Numerical investigation of spinneret geometric effect on spinning dynamics of dry‐jet wet‐spinning of cellulose/[BMIM]Cl solution

In this study, the effect of spinneret geometry, including the entrance angle α of the entrance channel, the length L_s, and the diameter D₀ of the exit channel, on the spinning dynamics of dry‐jet wet‐spinning of cellulose/1‐butyl‐3‐methylimidazolium chloride ([BMIM]Cl) solution was simulated by using finite element method. Based on the mathematical model of dry‐jet wet‐spinning established in our previous work (Xia et al., Cellulose 2015, 22, 1963) the radial and axial profiles of velocity, pressure, and shear rate in the spinneret and the profiles of diameter, temperature, and tensile stress in the air‐gap region were obtained. From the simulated profiles, the effect of spinneret geometric parameters on the flow behavior and the pressure drop of polymer solution in the spinneret and the die‐swell ratio near the spinneret was discussed. The entrance angle α of the entrance channel mainly influences the flow behavior of polymer solution in the spinneret and the die‐swell effect near the spinneret. As the decrease of the entrance angle α of the entrance channel, the vortices in the spinneret could be removed and the die‐swell ratio decreases. The increase of the length L_s of the exit channel results in the increase of pressure drop in the spinneret and the decrease of the die‐swell ratio. It is also found that the increase of the diameter D₀ of the exit channel reduces the flow velocity of polymer solution and decreases the pressure drop in the spinneret at a constant mass flow rate. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43962.     

Flow through porous media of a shear-thinning liquid with yield stress

Darcy's law for the laminar flow of Newtonian fluids through porous media has been modified to a more general form which will describe the flow through porous media of fluids whose flow behavior can be characterized by the Herschel-Bulkley model. The model covers the flow of homogeneous fluids with a yield value and a power law flow behavior. Experiments in packed beds of sand were carried out with solutions of paraffin wax in two oils and with a crude oil from the Peace River area of Canada. The model fitted the data well. A sensitivity analysis of the fitting parameters showed that the model fit was very sensitive to errors in the flow behavior index, n , of the Herschel-Bulkley model. A comparison of the “n” values calculated from viscometer measurements and from flow measurements agreed well. A more general Reynolds number for flow through porous media, which includes a fluid yield value, was developed. The data were fitted to a Kozeny-Carman type equation using this Reynolds number. The constant in the Kozeny-Carman equation was determined for the two packed beds studied using Newtonian oils. The data could all be represented, within the experimental error, by the relationship f^* = 150/Re^*. Since the mean volume to surface diameter of the packing was determined by the measurement of its permeability to a Newtonian oil, assuming C' = 150, the new definition of the Reynolds number allows the direct use of the Kozeny-Carman equation with Herschel-Bulkley type fluids.     

Camphene as a novel solvent for polypropylene: Comparison study based on viscous behavior of solutions

Polypropylene solutions were prepared using three solvents: paraffin oil, decalin, and a novel solvent—camphene. The effects of these solvents were evaluated based on the activation energy of flow and on their melting‐point depression. Experimental results indicate that the values of the viscosity of the resulting solutions were close to Newtonian behavior in the shear rates below 34 s⁻¹. The Arrhenius–Frenkel–Eyring equation was used to describe the dependence of the viscosity on the temperature. In addition, the viscosity increased with the polymer concentration, which can be described by a power‐law correlation. The activation energy of the flow of the polypropylene/camphene solution was the lowest and that of the paraffin oil solution was the highest. Correspondingly, the melting‐point depression of polypropylene solutions in camphene and decalin were substantially lower than that in paraffin oil (71, 61, and 33°C, respectively). These results indicate that lower activation energies of flow correspond to higher values of melting‐point depression. Moreover, analysis of variance indicated that the primary factor affecting the viscous behavior is the concentration, followed by the solvent and the temperature. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 2068–2074, 2000     

Study on hyperbranched polyesters as rheological modifier for Spandex spinning solution

The rheological behavior of polyurethane (PU)/N,N‐dimethylformamide (DMF) spinning solutions with various contents of hyperbranched polyesters was studied using a RS150L‐controlled stress rotational rheometer. The results showed that the viscosity of the spinning solutions could be greatly reduced by adding hyperbranched polyesters even at 0.5 wt% loading. The zero‐shear viscosity of solutions with hyperbranched polyesters was much lower than that of pure PU/DMF solution, which indicated a lower degree of entanglement when solutions were in a static state. The apparent activation energy of viscous flow and the critical shear rate for shear thinning of solutions with hyperbranched polyesters were much lower than that for pure PU/DMF solution, which indicated a weaker entanglement structure formed. In addition, the effect of hyperbranched polyesters on the mechanical properties of Spandex fiber was discussed. Copyright © 2006 Society of Chemical Industry     

Gel spinning of UHMWPE fibers with polybutene as a new spin solvent

Gel spinning of UHMWPE fibers using low molecular weight polybutene (PB) as a new spin solvent was investigated. A 98/2 wt% PB/UHMWPE gel exhibits a melting temperature around 115°C and shows large‐scale phase separation upon cooling the solution to room temperature. The resulting precursor fiber from this gel was hot‐drawn to a ratio of 120, yielding a fiber with tensile strength of 4 GPa and Young's modulus of over 150 GPa. Wide‐angle X‐ray diffraction indicates good molecular orientation along the fiber axis. The results also demonstrate the potential to further improve the mechanical properties. With respect to the gel spinning industry, this new solvent has a number of advantages over paraffin oil and decahydronaphthalene, and holds a promise of greatly improving the process efficiency. POLYM. ENG. SCI., 56:697–706, 2016. © 2016 Society of Plastics Engineers     

Flow behavior of polyacrylamide solution. III. Mathematical treatment

The flow behavior of polyacrylamide solutions was systematically determined over a wide range of temperatures (20–50°C) and concentrations (20–50 ppm) by using a coaxial cylinder viscometer. The results indicated that the rheological behavior of low-concentration polyacrylamide solution behaves similar to non-Newtonian fluids at all these concentrations. The effect of temperature on the consistency coefficient and flow behavior index of polyacrylamide solution of the different concentrations followed an Arrhenius-type relationship. Moreover, the effect of concentration on consistency coefficient and flow behavior index followed an exponential-law relationship at the temperatures used. The rheological constants for the Arrhenius and exponential-law models were determined. The combined effect of temperature and concentration on the coefficient of dynamic shear stress can be represented by a single equation: shear stress = 2.446 × 10⁻⁷exp(0.0639C + 3613/RT)(shear rate)^{2.337 exp(−0.00707C−245/RT)}. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2784–2789, 2001     

Fluid elasticity measurements from hole pressure error data

A slit die of variable height H (0.135 in., 0.1975 in., or 0.2488 in.) width W 2.5 in., and variable length L_e (12.0 in., 12.5 in., or 13.5 in.) has been designed and constructed for measuring the wall shear stress σ_w and the hole pressure error P_H. Values of P_H and σ_w are obtained directly and rapidly on a chart recorder from three commercial pressure transducers by means of an electronic differencing technique. The reliability of P_H measurements is established by the excellent agreement between viscosity η values obtained from this apparatus and a rheogoniometer and by measuring negligible values of P_H for the New tonian fluid, glycerine, for σ_w < 800 dyn/cm² and values of P_H > 0 for σ_w ≥ 800 dyn/cm² and values of P_H < 0 for a low-elasticity solution of polystyrene in dioctyl phthalate (DOP). Values of P_H are found to be independent of the distance E of the transducers from the die exit and the die height which indicated that P_H is independent of the undisturbed wall pressure P_w for constant values of σ_w. Our values agree well with those measured by Higashitani for a similar Separan solution in a different slit die. Using this new slit die, it is shown the P_H is sensitive to changes in molecular weight (MW) for a series of solutions of polystyrene in DOP and that P_H could be used to monitor continuously the changes in molecular structure which occured during the mechanical degradation of a 2.0% aqueous poly(ethylene oxide) solution. The simple relation between P_H and N₁ (P_H = ?cN₁, where c is a constant) is verified for solutions of polystyrene in DOP and aqueous Separan solutions over a large range of flow conditions (? = 1000 sec^?1). Because c is found to vary slightly with polymer type, concentration, and molecular weight, a method is presented for obtaining N₁ directly from P_H data.     

Viscous behavior of ultrahigh molecular weight polyethylene solution

The viscous behavior of the decalin solution of ultrahigh molecular weight polyethylene (UHMEPE) was studied. The influence of the concentration of polymer as well as the temperature was investigated. The flow curve can be described by the power-law model. The dependence of the viscosity on the temperature can be described by the Arrhenius–Frenkel–Eyring equation. The dependence of viscosity on the concentration can also be described by a power-law correlation. The addition of aluminum stearate increased the activation energy of flow of the solution. The viscosity of UHMWPE solution was decreased at lower concentration and increased at higher concentration of UHMWPE. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:289–293, 1997     

The Softness Parameters of Ions. Prediction of the Occurrence of Miscibility Gaps in Molten Salt Mixtures

Softness parameters σ_M for cations and σ_X for anions, have been calculated as dimensionless quantities for approx. 90 cations and 18 anions. They are given by σ_M = [σ_A (M^m+) - σ_A(H⁺)]/σ_A(H⁺) and σ_X = [σ_B(X^a?) - σ_B(OH^?)]/σ_A(H⁺) where σ_A = [σI_i(M) + ΔH⁰_h(M^m+)]/m and σ_B = [-E_a(X) + ΔH⁰_h(X^a?)]/a are Ahrland's parameters. The new normalized and comparative (to the test ions H⁺ and OH^?) softness parameters are positive for soft ions and negative for hard ones. These parameters, obtained independently, are used with a four-coefficient equation to calculate coordinate bond energies for metal halides with acceptable accuracy. Considerations of the average coordination in reciprocal molten salt mixture lead to an expression for the metathesis energy change as proportional to the product of the differences in softness parameters of the two cations and the two anions. An empirical one-coefficient equation involving the softness parameters is proposed to deal with next-nearest-neighbor interactions in binary common-ion molten salt mixtures. These relationships are then used with Blander and Topol's equation to predict the occurrence of irascibility gaps in uni-univalent reciprocal salt mixtures. The gaps found in other systems are also discussed in terms of the softness of the constituent ions.     

Crystallization and microporous membrane properties of ultrahigh molecular weight polyethylene with dibenzylidene sorbitol

Dibenzylidene sorbitol (DBS) was chosen as an in situ forming nucleating agent to study ultrahigh molecular weight polyethylene (UHMWPE) crystallization and microporous membrane. The experimental results indicated that DBS self‐assembled into fibrils first and the solution became a physical gel before UHMWPE crystallization during thermally induced phase separation (TIPS) of UHMWPE/liquid paraffin (LP)/DBS solution, and the temperature of DBS self‐assembly shows a strong dependence of DBS concentration. With decreasing temperature further, DBS fibrils as heterogeneous nucleating agent accelerated UHMWPE crystallization, which was showed more clearly in UHMWPE/LP/DBS phase diagram. UHMWPE microporous membranes were prepared through TIPS method with the control of DBS concentration. It was found that UHMWPE microporous membranes in the presence of DBS fibrils show small porous size and low water permeability, but relatively larger mechanical strength. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40706.     

Spoilage of coconut oil purification and properties of a fungal lipase that attacks coconut oil

A lipase was isolated from a strain ofAspergillus flavus which attacked coconut kernel and oil with the liberation of free fatty acids. The enzyme was purified 109-fold by ammonium sulphate precipitation, diethyl aminoethyl-cellulose and Sephadex G-200 chromatography. The optimum pH of the enzyme reaction was 6.2. The action of the enzyme on pure triglycerides was studied. The triglycerides of the shorter chain fatty acids were more rapidly hydrolyzed, while hydrolysis of tristearin was not detected under the conditions of assay. K _m for trilaurin and trimyristin were 9.09×10⁻⁴ and 1.42×10⁻³ M, respectively. Para-chloromercuricbenzoate was an inhibitor. Thin layer chromatography and gas liquid chromatography of the esterified products of enzymatic hydrolysis of coconut oil showed the presence of oleate, palmitate, myristate, laurate, caprate, caproate and caprylate but not stearate, although stearate was present in coconut oil.     

Studies on melt spinning. VI. Simulation of draw resonance using Newtonian and power law viscosities

Draw resonance, a periodic variation of spin line diameter in unstable melt spinning, was measured for its wave form under 34 different spinning conditions for PET and PP. In and attempt to simulate the measured wave form, the equations of continuity and momentum for the isothermal melt spinning of power law fluids were solved for their limit cycle solutions expressed in the time variations in the cross-sectional area at the take-up. Power law exponent p and draw down ratio ψ_w uniquely define the solution. Theoretical curves were superposed on the experimental amplitude-versus-ψ_w diagram and oscillation period-versus-ψ_w diagram to assign p value to each experimental point. Excellent agreement between theory and experiment was obtained with PET in that p values were nearly independent of ψ_w and of the diagram used in the determination of the p value, amplitude diagram, or oscillation period diagram. Motion pictures (16mm) of the side profiles of the pulsing spinline showed good agreement with the theoretical side profiles constructed from the corresponding limit cycle solution. It was proposed that the stability of melt spinning has no direct equivalence to the spinnability of fluids.