Measurement and simulation of low‐density polyethylene extrudate swell through a circular die

BACKGROUND: Extrudate swell is a common phenomenon in polymer processing. The investigation of its mechanism is of both scientific and industrial interest. RESULTS: The rheological parameters of a material described by the viscoelastic PTT (Phan‐Thien–Tanner) constitutive model are obtained by fitting the distributions of material functions detected with a strain‐controlled rheometer. The swelling ratios of low‐density polyethylene (LDPE) under different volume flow rates are indirectly obtained using a photographic technique. A mathematical model of extrudate swell is established and its finite element model is derived. A penalty method is employed to solve the extrudate swell problem with a decoupled algorithm. Computation stability is improved by using the discrete elastic‐viscous split stress algorithm incorporating the inconsistent streamline‐upwind scheme. CONCLUSION: The swell phenomenon of LDPE through a circular die is investigated using both experimental measurement and numerical simulation. The swelling ratios obtained from the simulation are compared with those measured: they agree well with each other. The essential flow characteristics of polymer melts are predicted and the mechanism of the swell phenomenon is further discussed. Copyright © 2009 Society of Chemical Industry     

The influence of state-of-mix on the extrudate swell of a carbon black-filled styrene–butadiene rubber compound

The factors which govern the extrudate swell of a styrene–butadiene rubber compound filled with 30 phr of N330 carbon black at various states-of-mix were investigated. The state-of-mix is quantified by an effective filler volume fraction, based on an estimate of the amount of rubber immobilized in the carbon black agglomerates. The swell has been found to be dominated by recoverable strain and relaxation time, which are both controlled by the effective filler volume fraction. In contrast, shear rate, wall slip, and the rubber–carbon black network have not been found to have a significant effect on the extrudate swell. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:305–315, 1997     

A three-dimensional finite element analysis of the effect of reynolds number on extrudate swell of newtonian liquids from square dies

The effect of Reynolds number upon the extrusion of a Newtonian fluid exiting a square die is examined. It is shown that the extrudate swells at low Reynolds number but contracts at high ones. At zero Reynolds number, the maximum die swell ratio of 1.2 occurs. A swell ratio of one occurs at a Reynolds number of about 24. At large Reynolds numbers, the extrudate contracts to a circular cross-section with a swell ratio of 0.9611.     

聚合物熔体动态黏弹特性微尺度效应实验研究

针对聚合物熔体在微流道内,因拉伸/压缩作用导致的黏弹特性受物理尺度影响的问题,通过动态剪切流动实验系统研究了四种聚合物材料的黏弹特性,以及黏弹特性随物理尺度的变化规律。结果表明,在角频率1~100 rad/s的范围内,聚酰胺、聚氨酯、聚乳酸均表现出耗能模量大于储能模量的黏性占优特征,聚丙烯在高频区时表现出弹性占优特征。储能模量与耗能模量均随着物理特征尺度的减小而降低。物理特征尺度从1000 μm减小到250 μm的变化过程中,聚氨酯、聚酰胺和聚丙烯三种熔体的弹性效应对微尺度变化的敏感性比黏性效应强烈,储能模量变化率与耗能模量变化率的差值分别为5.8%、4.2%和2.6%。聚乳酸熔体的黏性效应对微尺度变化的敏感性与弹性效应基本一致,其储能模量变化率与耗能模量变化率的差值为-0.3%。材料分子链特征的差异导致储能模量与耗能模量随物理特征尺度减小的变化率不同。熔体黏弹特性对微尺度变化敏感性的强弱依次为聚氨酯、聚酰胺、聚丙烯和聚乳酸,其黏弹性特征参量的变化率分别为28.6%、22.6%、20.6%和19.45%。     

Viscoelastic behavior of polymer tape in a wound roll

A viscoelastic computational model is developed that uses experimentally determined viscoelastic material properties as input and can be used to predict the behavior of a tape material in a wound roll as stresses relax over time. Experimental creep test results are used to find best‐fit creep‐compliance parameters to describe two high density data storage tape media. The two tapes used in the analysis are a developmental tape with a poly(ethylenenaphthalate) (PEN) substrate and metal particle (MP) front coat similar to linear tape open (LTO4) (referred to in this work as “Tape C”), and LTO3, a commercially available tape with a PEN substrate and MP front coat. Sets of best‐fit creep‐compliance parameters are determined for both tapes. The differences between the predicted behavior using three‐, five‐, and seven‐parameter Kelvin–Voigt models are evaluated, both for a benchmark case and in a viscoelastic wound roll model. The choice of material model is found to significantly influence the predictions of the wound roll model. The differences between different material models for the same material are on the order of the differences found between the two different materials. A material model with a higher number of creep‐compliance parameters, although more computationally expensive, produces better results, particularly over long spans of time. The relative differences between the three‐, five‐, and seven‐parameter models are shown to be qualitatively consistent for several variations in the computational model setup, allowing predictions to be made based on simple benchmarks. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of chain disentanglement on melt crystallization behavior of isotactic polypropylene

Isotactic polypropylene (iPP) with “disentangled” chains was generated through crystallization of iPP from its mineral oil solution. TGA test assured complete removal of mineral oil from iPP precipitates. Time sweep rheological measurements showed the modulus build-up with time indicating the formation of “disentangled” chains in iPP after the sample disentanglement treatment. The “disentangled” chains could preserve for a certain time before completely re-entangled during melting. Crystallization kinetics of iPP with “disentangled” chains was studied by using polarized optical microscope. The growth rate of spherulites in “disentangled” iPP was faster than that in the entangled one.     

Flame retardation of polypropylene: Effect of organoantimony compounds on the melt flow behavior

The melt flow behaviour of polypropylene filled with organoantimony compounds, triphenylstibinedibromide and its derivatives with tribromo-, trichloro-, and pentachloro-phenols, as flame retardants has been studied in the temperature range of 180 to 220°C, and at shear rates of 29.5 to 588.8's^?1, using a capillary rheometer. A decrease in the melt viscosity at all shear rates and temperatures was noticed on addition of these flame retardants, The melt viscosity further decreased upon increasing the concentration (from 5 to 20 phr) of the flame retardants. The die swell was measured in order to determine the melt elasticity of the filled systems. The minimum melt viscosity of filled propylene was observed approximately where the maximum die swell (melt elasticity) occurred.     

静电场对CaCO3结晶过程的影响及与绿色阻垢剂的协同阻垢性能

使用非蒸发浓缩法研究了静电场对碳酸钙结晶过程及晶型的影响。研究发现经静电处理后,碳酸钙结晶过程初期晶体生长速度缓慢,存在一个稳定期,这个稳定期的长短受温度影响很大。60℃时稳定期可达3 h,当温度升高到80℃后,稳定期缩短到0.5 h内。SEM和IR分析结果表明,经静电处理后,水垢中文石型碳酸钙的含量增加。晶体稳定期和文石型碳酸钙的出现主要是因为,高压静电场导致水分子和HCO₃^-极化变形,使得二者的极性增加,反应活性增强。静态阻垢实验和动态阻垢实验结果表明,静电水处理和聚环氧琥珀酸(PESA)之间存在明显的协同阻垢效应。PESA在静电水中的静态阻垢率可达95.8%,比在配制水中的提高了18.9%;动态阻垢率为92.1%,阻垢率提高了14.5%。     

A study on the onset surface melt fracture of polypropylene materials with foaming additives

The melt fracture behaviors of linear and branched polypropylene resins with foaming additives were investigated. The effects of branching, processing temperature, additives, and blowing agent on the surface melt fracture of polypropylene materials were thoroughly studied. A CCD camera was installed at the die exit to precisely observe the onset of surface melt fracture of extruded foams. The critical wall shear stress was determined for various linear and branched polypropylene resins using a capillary die. It was found that the branching required to foam polypropylene resins also promotes melt fracture: the critical shear stress was decreased by 0.0175 MPa with an increase of 0.1 n/1000c in long‐chain branching. It was also observed that the dissolved blowing agent (butane) significantly suppressed the melt fracture of both linear and branched polypropylene resins. On the other hand, a noticeable increase in the critical shear stress of branched polypropylene materials was observed with the nucleating agent (talc) and the aging modifier (glycerol mono stearate), whereas almost negligible effect of the additives on the critical shear stress was observed for linear polypropylene materials. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of polypropylene fiber processing conditions on fiber mechanical behavior

An investigation into the mechanical behavior of melt‐spun isotactic polypropylene (iPP) fibers is reported. Two different iPP formulations, PH835 and Exxon3854, synthesized using Ziegler–Natta and metallocene catalysts, respectively, and spun at take‐up velocities ranging from 1000 to 3000 m min^?1 were subjected to uniaxial tensile loading, cyclic loading and creep tests. The strain rate sensitivity was determined by performing strain rate jumps. Injection molded specimens from the same iPP formulations were tested under the same conditions. The fiber birefringence increases slightly with increasing take‐up velocity, while the crystallinity is approximately insensitive to this process parameter in this range of velocities. Fibers from the two iPP samples behave differently at large plastic strains despite having the same birefringence and crystallinity. Differences are also seen in creep. The behavior of fibers is significantly different from that of the injection molded samples of the same iPP and same crystallinity. These have lower strain hardening rate, smaller failure strains, close to zero strain rate sensitivity and exhibit a yield point phenomenon. The difference is associated with the different nature and spatial organization of the crystals and inter‐crystalline amorphous and mesomorphic phases. © 2014 Society of Chemical Industry     

Experimental studies on the relaxation behavior of commercial polymer melts

With a rotary rheometer, various methods were used to determine the characteristic relaxation times for a commercial polydimethylsiloxane (PDMS), and their consistency and relation to the linear relaxation spectrum were examined. The experimental damping functions of the step deformation of the PDMS, a polymethylvinylsiloxane, and a high‐density polyethylene were compared with predictions of the Doi–Edwards theory and Marrucci model; the effect of wall slip on the damping function data is discussed, and the appearance of stress peaks due to material instability as the strain increased above a critical value is detailed. Through the application of a previously proposed stress decomposition method to the data of large‐amplitude oscillatory shear for the PDMS sample, the relationship between the generalized elastic modulus [G(ω,γ)] and the shear relaxation modulus [G(γ,t)] was investigated. In the linear and initial nonlinear regimes, as the angular frequency (ω) increased, G(ω,γ) approached G(γ,t) on the timescale t = 1/ω, where t is the time. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of fillers on the relaxation behavior of chlorobutyl vulcanizates

The effect of addition of fillers (carbon black (CB), carbon silica dual phase filler (CSDPF), and nanoclays) on the relaxation behavior of chlorobutyl vulcanizates has been studied. The primary relaxation (α‐transition, the glass transition) was studied by dynamic mechanical analysis as a function of temperature (?60 to +100°C) and positron annihilation life time spectroscopy (?70 to +110°C). Irrespective of the filler and its loading, all the composites showed the glass transition temperature in the range of –29 to –33°C, which was explained on the basis of relaxation chain dynamics of polyisobutylene in the vicinity of fillers. The secondary relaxation (α* or β relaxation) was studied using dielectric relaxation spectra in the frequency range of 100–10⁶ Hz. Nanoclays had a profound influence on the secondary relaxation, whereas CSDPF and CB had a marginal effect. The nonlinear strain dependent dynamical parameters were also evaluated at double strain amplitudes of 0.07–5%. The nonlinearity in tan δ and storage modulus has been explained on the concept of filler–polymer interactions and the interaggregate attraction (filler networking). The “percolation limit” of the fillers in the composites has been studied by DC conductivity measurements. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3161–3173, 2006     

Effect of chain structure on the melt rheology of modified polypropylene

The effect of molecular structure of polypropylene (PP) on the melt rheological properties were investigated for electron irradiated polymer and di-2-ethylhexyl peroxy dicarbonate (EHPC)-treated polymer. The modifications were examined in terms of the rheological behaviors, molecular weight distribution, and the degree of branching. The high melt strength PP was obtained by irradiating with 50 and 80 kGy and adding EHPC. The modified PPs showed the strain hardening in the uniaxial elongational viscosity, though the linear elongational viscosity was lower than that of the unmodified PP. Low angle laser light-scattering measurements of the modified PPs showed the interesting results; high irradiation doses such as 50 and 80 kGy caused higher molecular weight chains branching. Nevertheless, the long branching chains were not detected for the EHPC modified PP, which also showed the strain hardening in uniaxial elongational flow. In this article, the relation between chain structure and rheological properties is discussed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1493–1500, 1999     

Flow visualization and extrudate swell of natural rubber in a capillary rheometer: Effect of die/barrel system

An investigation was carried out to examine the effect of die/barrel system on the flow patterns and extrudate swell of natural rubber in the barrel of a capillary rheometer, using a colored tracer as the visualization technique. The capillary rheometer used in this work had two dies located along the barrel, which is novel in rheometer design. The flow of the rubber in the upper barrel was dependent on the piston/barrel action and changed with piston displacement, whereas the complexity of the flow in the lower barrel was dependent not only on the piston displacement, but also on the geometry of the upper die design. The flow patterns that developed in the whole barrel were independent of the die located at the bottom of the barrel. In addition, the change in extrudate swell was associated with the flow occurring in the barrel, residence time, elastic characteristic, and the temperature rise during the flow. It was concluded that the general style of the flow patterns of natural rubber was greatly dependent on the die geometry that the material had previously moved past. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2525–2533, 2001     

Effect of molecular structure in branched polyethylene on adhesion properties with polypropylene

Adhesion properties between branched polyethylene (PE) and isotactic polypropylene (PP) were studied by a peel test and scanning electron microscopy. In this study, two types of branched PEs were used; one is a linear low density polyethylene (LLDPE) and the other is a high pressure low density polyethylene (LDPE). The adhesive strength of the LLDPE/PP is much higher than that of LDPE/PP. Furthermore, the formation of PE influxes between PP spherulites has a small effect on the adhesion. The dynamic viscoelastic measurements for the binary blends composed of branched PE and PP were also carried out to estimate the interfacial tension by using a rheological emulsion model proposed by Palierne. The interfacial tension is 1.0 mN for LLDPE/PP and 2.1 mN for LDPE/PP, suggesting that the interfacial thickness of LLDPE/PP is about twice that of LDPE/PP. The adhesive strength between branched PE and PP will be determined by the interfacial thickness, which represents the entanglements between two polymers. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 457–463, 1998     

The effect of pressurized carbon dioxide as a plasticizer and foaming agent on the hot melt extrusion process and extrudate properties of pharmaceutical polymers

The aim of the current research project was to explore the possibilities of combining pressurized carbon dioxide with hot melt extrusion of polyvinylpyrrolidone-co-vinyl acetate 64, Eudragit^® E100 and ethylcellulose 20 cps, to evaluate the ability of the pressurized gas to act as a temporary plasticizer as well as to produce a foamed polymeric material. Pressurized carbon dioxide was injected into a Leistritz Micro 18 intermeshing co-rotating twin-screw melt extruder using an ISCO 260D syringe pump. The physicochemical characteristics of the polymers before and after injection of carbon dioxide were evaluated using MDSC, dissolution measurements, specific surface area measurements, porosity, dynamic vapour sorption and microscopy. An extruder set up and screw configuration were configured and optimized for injection of pressurized CO₂. Carbon dioxide acted as plasticizer for all three polymers, reducing the processing temperature during the hot melt extrusion process. The specific surface area and the porosity of the polymers was increased after treatment with carbon dioxide, resulting in enhanced dissolution. The macroscopic morphology was changed to a foam-like structure due to expansion of the carbon dioxide at the extrusion die. This resulted in improved milling efficiency.     

Effect of processing on the melt degradation of starch‐filled polypropylene

Compounded polypropylene powders with various concentrations of corn starch were processed in a Haake torque rheometer at constant temperature, 180 °C, for different times in a closed system. A scanning electron micrograph of 5‐min processed sample shows a fine dispersion of starch particles in the polypropylene (PP) matrix. A good distribution and interaction of the starch particles are seen with increasing processing time (up to 15 min). Infrared spectroscopy evidence on the extracted films shows that most interactions between PP and starch are obtained after about 10 min processing. The presence of 2–6 wt% starch in the PP has a melt‐stabilising effect by reducing melt flow index and increasing apparent viscosity with a good correlation. However, 6 wt% starch gives complete inhibition of the PP melt degradation up to 20 min processing. Carbonyl groups are not formed during processing of PP containing 6 wt% starch. This is also an indication of a starch stabilising effect on the PP chemical structure. An increase in elongation at break of PP films having 6 wt% starch, when compared with the controls, is observed, while their ultimate tensile strength remains almost the same. © 1999 Society of Chemical Industry     

电导法表征一种三元阻垢剂成分阻CaCO3垢协同效应的研究

采用电导法研究了羟基亚乙基二膦酸（HEDP）、多氨基多醚基甲叉膦酸（PAPEMP）、水解聚马来酸酐（HPMA）三种阻垢剂单组分时的阻垢性能和二元复配、三元复配后的协同效应。考察了pH、温度等条件对三元复配物阻垢性能的影响。实验表明,HEDP、PAPEMP、HPMA配比为5：3：2时阻垢性能最好,复配阻垢剂的性能在温度范围为40～90℃之间随着温度升高而下降,在pH为6～9之间随着pH的升高而下降。     

电导法表征一种三元阻垢剂成分阻CaCO3垢协同效应的研究

采用电导法研究了羟基亚乙基二膦酸（HEDP）、多氨基多醚基甲叉膦酸（PAPEMP）、水解聚马来酸酐（HPMA）三种阻垢剂单组分时的阻垢性能和二元复配、三元复配后的协同效应。考察了pH、温度等条件对三元复配物阻垢性能的影响。实验表明,HEDP、PAPEMP、HPMA配比为5：3：2时阻垢性能最好,复配阻垢剂的性能在温度范...     

Effect of swelling process on the thermoelastic temperature change of ethylene propylene diene rubber filled with carbon black

The effects of both dynamic cyclic extension and swelling on the thermoelastic behavior of ethylene propylene diene rubber loaded with different concentrations of carbon black have been studied. As the strain amplitude increases, the concentration of the ruptured bonds increases, leading to more enhanced friction between particles and consequently to the observed rise in temperature. Temperature change was found to be highly dependent on the swelling and also on carbon black concentration. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1890–1897, 1999