Extrudate swell and flow analysis of polystyrene melt flowing in an electro‐magnetized die in a single screw extruder

An electro‐magnetized capillary die via a parallel co‐extrusion technique was used to study the changes in the overall and radial extrudate swell ratio of polystyrene (PS) melt flowing in a single screw extruder. The effects of magnetic flux density, wall shear rate (screw rotating speed) and die temperature were studied. The results suggested that, in the case of non‐magnetic die the average overall swell ratio of the melt ranged from 1.25 to 1.55. The swelling ratio increased with increasing wall shear rate up to 8.5 sec^?1 and then decreased at 17.1 sec^?1. Increasing die temperature caused a reduction of extrudate swell ratio. The changes in extrudate swell ratio can be explained using the simultaneously measured velocity profiles during the flow in the die, and the swell ratio decreased with increasing radial position. Melt contraction of the melt layer near the die wall was observed. The die temperature was found to have no effect on the change of the radial extrudate swell profiles. When an electro‐magnetized die was used, the average overall swell ratio was found to increase with increasing magnetic flux density to a maximum value and then decreased at higher flux densities. The magnetic flux density of the maximum swell was changed by the wall shear rate. It was associated with a balance of elastic and magnetic energies during the flow. The magnetic energy was thought to have a pronounced effect on the swell ratio at low shear rate and low die temperature. Considering the radial position, the highest swell ratio occurred at the duct center, in the range 2.4–3.3. There was no extrudate contraction of the melt layer near the die wall. Copyright © 2005 John Wiley & Sons, Ltd.     

Melt flow behavior of polypropylene composites filled with multi-walled carbon nanotubes during extrusion

Polypropylene (PP) composites filled with multi-walled carbon nanotubes (MWCNTs) were prepared using a twin-screw extruder. The melt flow properties of the composites were measured with a capillary rheometer in a temperature range from 180 to 230 °C and at various apparent shear rates varying from 100 to 4000 s⁻¹. The results showed that the melt shear stress increased almost linearly while the melt shear viscosity decreased almost linearly with increasing shear rates in a bi-logarithmic coordinate system. The melt shear flow followed the power law relationship and the dependence of the melt shear viscosity on temperature obeyed the Arrhenius equation. The relationship between the melt shear viscosity and the MWCNT weight fraction was roughly linear under the investigated range of temperature or shear rate.     

The melt elastic behavior of polypropylene/glass bead composites in capillary flow

The melt extrudate swell and entry pressure losses are important characteristics of elastic properties during die extrusion of polymeric fluids. They are usually expressed with die-swell ratio (B) and entry pressure drop (ΔP_o). In the present paper, the die-swell behavior and entrance pressure drop of a polypropylene (PP) filled with A-glass beads were investigated by using a Rosand capillary rheometer to identify the effects of the filler contents and extrusion rate on the elastic behavior of the sample melts. The experiments were carried out under the conditions with an apparent shear rate range of 50–10⁴ s⁻¹ and a temperature of 190 °C. The results showed that B increased nonlinearly with increasing shear rate at the wall (γ_w), and increased linearly with the increase of shear stress at the wall (τ_w). With the increase of the volume fraction of the fillers B decreased nonlinearly. Similarly, the entry pressure drop increased linearly with the increase of τ_w, whereas the influence of the filler concentration on ΔP_o was insignificant in this case. Furthermore, B increased as a linear function of ΔP_o, and extension stress (σ_e) increased nonlinearly with increasing γ_w.     

RHEOLOGICAL PROPERTIES OF LIQUID CRYSTALLINE COPOLY (ρ-HYDR0XYBENZ0ATE/BISPHENOL A TEREPHTHALATE)

Various aspects of the rheological behaviour of liquid crystalline copolyesters, i.e.,samples of copoly (p-hydroxybenzoate / bisphenol A terephthalate), were explored by usingInstron capillary rheometer. The experimental results indicated that the apparent viscositywas affected significantly by shear rate, melt temperature and p-hydroxybenzoate unit con-tent. The flow activation energies △E_η are in the range of 205.1 to 74.5 kJ/mol, dependingon the shear rate of 10-1000 s~(-1), at temperature 568-603K. These copolyesters exhibit ayield phenomenon in the shear flow, and the values of yield stress decrease with increasingtemperature. It is quite unusual that the extrudate of the copolyester shows the smallerswelling ratio even than unity at the lower temperature and lower shear rates.     

Studies on melt flow properties during capillary extrusion of PP/Al(OH)3/Mg(OH)2 flame retardant composites

The apparent melt shear viscosity of polypropylene (PP) composites filled with aluminium hydroxide (Al(OH)₃) and magnesium hydroxide (Mg(OH)₂) was measured by means of a melt flow rate instrument under experimental conditions of temperature ranging from 170 to 195 °C and load varying from 2.16 to 12.5 kg, to identify the effects of particle size and content. The results showed that the melt shear flow of the composites obeyed the power law under the experimental conditions, the dependence of the melt apparent shear viscosity (η_a) on temperature was consistent with the Arrhenius equation, and the sensitivity of the η_a for the composite melts to temperature increased with addition of flame retardant. The η_a of the composites decreased with increasing apparent shear rate. The η_a increased with an increase of the content of flame retardant, but this rate of increase decreased with a rise of temperature or load. When the particle size of flame retardant was smaller than 5 μm, the η_a of the composites increased with increase of particle size of flame retardant, and then reduced with a further increase of particle size of flame retardant.     

Extrudate swell behavior of PS and LLDPE melts in a dual die with mixed circular/slit flow channels in an extrusion rheometer

Extrudate swell behaviors of polystyrene (PS) and linear low‐density polyethylene (LLDPE) melts in a dual channel die, having mixed circular/slit flow channels, in a constant shear rate rheometer were examined. The extrudate swell ratio for PS melt was observed to be higher than that for LLDPE melt for all cases, this being associated with the differences in molecular structures that could be described in terms of power law indexes and secondary flows near the die entrance. In single channel die, the extrudate swell of both PS and LLDPE melts in circular flow channel die was greater than that in slit flow channel, whereas, in dual channel die the slit channel exhibited a higher extrudate swell ratio, the results being explained by revealing the flow patterns of the melt in the barrel and die of the rheometer. It was found that the dimensionless size of the vortex flows near the entrance, and the extent of disentanglement of molecular chains on entering the die were the important factors for the differences in the extrudate swell ratios of the melts at the die exit influenced by the die designs used. Copyright © 2003 John Wiley & Sons, Ltd.     

Melt flow behavior in capillary extrusion of nanometer calcium carbonate filled PCL bio-composites

Nanosized calcium carbonate (nano-CaCO₃) filled polycaprolactone (PCL) bio-composites were prepared by using a twin-screw extruder. The melt flow behavior of the composites, including the entry pressure drop, melt shear flow curves and melt shear viscosity, were measured through a capillary rheometer operated in a temperature range of 170∼200 °C and shear rates varying from 50 to 10³ s⁻¹. The entry pressure drop showed a non-linear increase with increasing shear stress when the filler weight fraction was less than 3%, while it decreased slightly with an increase of shear stress at a filler weight fraction of 4%. The melt shear flow roughly followed a power law, while the effect of temperature on the melt shear viscosity was estimated by using the Arrhenius equation. Moreover, the influence of the nano-CaCO₃ on the melt shear viscosity of the PCL composite was not significant at low filler levels.     

Die swell ratio of polystyrene melt from an electro‐magnetized capillary die in an extrusion rheometer: effects of barrel diameter,shear rate and die temperature

A constant shear‐rate extrusion rheometer with an electro‐magnetized capillary die was utilized to investigate die swell behavior and flow properties of a polystyrene melt as the application of an electro‐magnetic field to the capillary die was relatively novel in polymer processing. The test conditions such as magnetic flux density, barrel diameter, extrusion rate and die temperature were studied. The results suggest that the maximum swelling of the polystyrene melt with application of the electro‐magnetic field could be enhanced up to 2.6 times (260%) whereas that without the electro‐magnetic field was 1.9 times (190%). The barrel diameter of 30 mm was found to be a critical value in the case of the die swell ratio and flow properties of the polystyrene melt were significantly affected by the magnetic flux density. This involved the number and angle of magnetic flux lines around the barrel part. Under the electro‐magnetic field, there were two mechanical forces influencing the die swell ratio and the flow properties; magnetic torque and shearing force. The die swell at wall shear rates less than 11.2 sec^?1 was caused by the magnetic torque, whereas at higher wall shear rates it was dependent on the shearing force. For a given magnetic flux density, the maximum increase in the die swell ratio as a result of the magnetic torque was calculated to be approximately 20%. Increasing the die temperature from 180 to 200°C reduced the overall die swell ratio and suppressed the effect of the magnetic flux density. Copyright © 2004 John Wiley & Sons, Ltd.     

Melt rheology and morphology of thermoplastic elastomers from polyethylene/nitrile‐rubber blends: The effect of blend ratio,reactive compatibilization,and dynamic vulcanization

A study of the melt‐rheological behavior of thermoplastic elastomers from high‐density polyethylene and acrylonitrile butadiene rubber (NBR) blends was carried out in a capillary rheometer. The effect of the blend ratio and shear rate on the melt viscosity reveals that the viscosity decreases with the shear rate but increases with NBR content. Compatibilization by maleic anhydride modified polyethylene has no significant effect on the blend viscosity, but a finer dispersion of the rubber is obtained, as is evident from scanning electron micrographs. The melt‐elasticity parameters, such as the die swell, principal normal stress difference, recoverable shear strain, and elastic shear modulus of the blends, were also evaluated. The effect of annealing on the morphology of the extrudate reveals that annealing in the extruder barrel results in the coalescence of rubber particles in the case of the incompatible blends, whereas the tendency toward agglomeration is somewhat suppressed in the compatibilized blends. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1104–1122, 2000     

Flow behaviour of gas-containing LDPE/i-PP melts

An experimental study was conducted to investigate the rheological behaviour and extrudate swell of polyolefin blends based on two grades of low-density polyethylene (LDPE) and an isotactic polypropylene (i-PP). Blending was carried out on a twin-screw extruder “Brabender” at different composition ratios in the temperature range from 140 to 190°C. The LDPE/i-PP blends mixed with 0.5 wt.% blowing agent were extruded by means of “Brabender” extrusiograph at melt temperature of 200°C and different extrusion rates. The influence of composition content on the viscosity and extrudate swell was considered. The foam structure and morphology are discussed in terms of shear rate, molecular characteristics and composition content. The presence of layered structure was observed: an outer smectic layer and an inner partially crystalline layer. The thickness of smectic layer and size of spherulites were determined.     

Melt elongation flow behaviour of LDPE/LLDPE blends

The extensional rheological properties of low density polyethylene (LDPE)/linear low density polyethylene (LLDPE) blend melts were measured using a melt spinning technique under temperatures ranging from 160 to 200 °C and die extrusion velocities varying from 9 to 36 mm/s. The results showed that the melt elongation stress decreased with a rise of temperature while it increased with increasing extensional strain rate and the LDPE weight fraction. The dependence of the melt elongation viscosity on temperature roughly obeyed the Arrhenius equation, it increased with increasing extensional strain rate and the LDPE weight fraction when the extensional strain rate was lower than 0.5 s⁻¹, and it reached a maximum when the extensional strain rate was about 0.5 s⁻¹, which can be attributed to the stress hardening effect.     

Effect of electron beam-cross-linked gels on the rheological properties of raw natural rubber

Electron beam (EB)-cross-linked natural rubber (NR) gels were prepared from latex and characterized by various techniques. The addition of a small amount of these gels to raw NR was found to reduce the apparent shear viscosity and die swell remarkably. This effect was further enhanced with the addition of butyl acrylate as a sensitizer. The apparent shear viscosity first decreased up to 8 phr of gel loading and then increased. However, the percent die swell value decreased steadily upon gel loading. These were explained by calculating principal normal stress difference, the activation energy of melt flow and characteristics of EB-cross-linked gels. These effects were also reflected in the changes of mechanical and dynamic mechanical properties of gel-filled raw NR. Tailoring of the above properties could be done with the help of these gels.     

Apparent shear strength of hybrid glass fibre reinforced composite joints

The incorporation of nano or micro ceramic particles into fibre reinforced composites (FRC) to enhance their stiffness and durability has been widely investigated. This mechanism has been attributed to the increase in stiffness of the polymeric matrix phase and shear strength of FRCs due to the presence of particles at the interlaminar regions. In order to elucidate such effect, hybrid single-lap joints consisted of ceramic particles and glass fibre reinforced composites were evaluated to better assess the mechanical interlocking effect provided by silica and cement inclusions. A full factorial design (2³) was performed to identify the effect of the type of particle (silica and cement), particle weight fraction (2.5 and 5 wt%) and glass fibre grammage (200 and 600 g/m²) on the apparent shear strength and adherent strength of single-lap joints under tensile loading. The ceramic particle inclusions led to increased apparent shear strength and adherent strength. The inclusion of 5 wt% ceramic particles into 600 g/m² cross-ply glass fibre composites enhanced both adherent and apparent shear strengths.     

Preparation of antistatic high‐density polyethylene composites based on synergistic effect of graphene nanoplatelets and multi‐walled carbon nanotubes

Graphene nanoplatelets are promising candidates for enhancing the electrical conductivity of composites. However, because of their poor dispersion, graphene nanoplatelets must be added in large amounts to achieve the desired electrical properties, but such large amounts limit the industrial application of graphene nanoplatelets. Multi‐walled carbon nanotubes also possess high electrical conductivity accompanied by poor dispersion. Therefore, a synergistic effect was generated between graphene nanoplatelets and multi‐walled carbon nanotubes and used for the first time to prepare antistatic materials with high‐density polyethylene via 1‐step melt blending. The synergistic effect makes it possible to significantly improve the electrical properties by adding a small amount of untreated graphene nanoplatelets and multi‐walled carbon nanotubes and increases the possibility of using graphene nanoplatelets in industrial applications. When only 1 wt% graphene nanoplatelets and 0.5 wt% multi‐walled carbon nanotubes were added, the surface and volume resistivity values of the composites were much lower than those of the composites that were only added 3 wt% graphene nanoplatelets. Additionally, as a result of the synergistic effect of graphene nanoplatelets and multi‐walled carbon nanotubes, the composites met the requirements for antistatic materials.     

Thermal,crystallization, mechanical,and rheological characteristics of poly(trimethylene terephthalate)/poly(ethylene terephthalate) blends

Blends of poly(trimethylene terephthalate) (PTT) and poly(ethylene terephthalate) in the amorphous state were miscible in all of the blend compositions studied, as evidenced by a single, composition‐dependent glass‐transition temperature observed for each blend composition. The variation in the glass‐transition temperature with the blend composition was well predicted by the Gordon–Taylor equation, with the fitting parameter being 0.91. The cold‐crystallization (peak) temperature decreased with an increasing PTT content, whereas the melt‐crystallization (peak) temperature decreased with an increasing amount of the minor component. The subsequent melting behavior after both cold and melt crystallizations exhibited melting point depression behavior in which the observed melting temperatures decreased with an increasing amount of the minor component of the blends. During crystallization, the pure components crystallized simultaneously just to form their own crystals. The blend having 50 wt % of PTT showed the lowest apparent degree of crystallinity and the lowest tensile‐strength values. The steady shear viscosity values for the pure components and the blends decreased slightly with an increasing shear rate (within the shear rate range of 0.25–25 s^?1); those of the blends were lower than those of the pure components. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 676–686, 2004     

Experimental study on viscosity properties of cyclic olefin copolymer (COC) flowing through micro capillary dies

As an emerging polymer, COC has been commonly used to make microfluidic chips by microinjection molding; and in this process, COC melt flows in a trans-scale cavity in which macro and micro scales coexist. Thus, in such a circumstance, understanding viscosity property of COC melt would be helpful to mold design, parameter determination of injection molding and prediction of molding quality. In this paper, viscosity properties of COC melt flowing in three dies with different diameters (500 μm, 200 μm, 100 μm) were investigated at three different temperatures (240 °C, 260 °C, 280 °C) by a capillary rheometer. The results showed that viscosity of COC melt flowing in different micro dies can be reduced significantly by increasing temperature, and visco-temperature property of COC melt could be described by Vogel equation in a considerable accuracy. It was found that temperature sensitivity of viscosity of COC melt varies with shear rate. Besides, as die diameter decreased, viscosity of COC melt was also reduced greatly. Moreover, in 500 μm die, viscosity of COC decreased constantly with shear rate; however, in 200 μm and 100 μm dies, viscosity witnessed an increase within a certain shear rate range. It implies that behavior of COC molecular chains might varies in different micro-scales.     

Fiber spinning from the nematic melt. II. Effect of thermal history on spinning of the copolyester of polyethylene terephthalate and p-oxybenzoate

Fibers were spun from the nematic phase of the copolymer of polyethylene terephthalate having 60 mol % of p-oxybenzoate units. A capillary rheometer was used for spinning with a shear rate at the wall of 6.4 sec^?1, and capillary (length/diameter) ratio of 14.1. The spinning temperature was varied from 250° to 300°C and, at each temperature, the spin-draw ratio was examined as a variable. Spinning was performed under two conditions. When spinning from the melt without preheating, the initial modulus of the fibers increased with spin-draw ratio and increased with increasing spinning temperature for a fixed spin-draw ratio. In the second case, the melt was preheated and then cooled to the desired temperature before spinning the fibers. The preheating temperature was 280°C for spinning at 250°C, and 300°C for spinning at 280°C. Preheating increased the fiber modulus to the value obtained by spinning at the preheating temperature. A reduction of the viscosity due to the melting of poly(p-hydroxybenzoic acid) (PHB) crystallites produces better orientation and higher modulus. However, with increasing spin-draw ratio, the modulus of the preheated fibers decreased to the values expected for the spinning temperature. This decrease in modulus is due to recrystallization of PHB in the threadline.     

Influence of chain extender on thermal properties and melt flow index of stereocomplex PLA

The effects of chain extension and melt blending temperature on the stereocomplex formation of 50/50 (w/w) poly(L-lactide) (PLLA)/poly(D-lactide) (PDLA) blends or stereocomplex polylactides (scPLAs) were investigated. Joncryl^® ADR 4368, a styrene-acrylic multifunctional oligomeric agent, was used as a chain extender. Differential scanning calorimetry and X-ray diffractometry were used to confirm the stereocomplex formation of the PLLA/PDLA blends. Melt flow indices (MFI) of the blends were also determined. The stereocomplex crystallinities gradually decreased with increasing blending temperature and Joncryl^® ADR 4368 ratio. The significant decrease in the MFI of scPLAs is believed to be attributed to chain extension at the blending temperatures of 170 °C and 200 °C. The MFI values of scPLAs decreased as the Joncryl^® ADR 4368 ratio and blending temperature increased. The results indicated that the chain extension has an effect on the stereocomplexation and it improved the melt strength of the scPLAs.     

Synthesis and characterization of poly1-hexene/silica nanocomposites

SiO₂ nano particles, with particle size of 12 nm, were first modified by substituting surface OH groups with O-hexyl moiety. Then, poly1-hexene/modified-SiO₂ composites with various nano-SiO₂ weight fractions were prepared by three different methods: in situ, solution, and melt methods and designated as PH-SiO₂/Insitu, PH-SiO₂/Sol and PH-SiO₂/Melt, respectively. PH-SiO₂/Insitu samples showed highly uniform particle dispersion up to 30 wt. % of silica while in PH-SiO₂/Sol and PH-SiO₂/Melt samples agglomeration of the silica nanoparticles occurred for filler contents ≥5 wt. % (i.e. 5, 10, 20 and 30 wt%). In the synthesized composites, the storage modulus significantly increased as high as 20.7 times when compared with neat poly1-hexene. Maximum decomposition temperature (T_max) and char yield at 600 °C increased with increasing silica level. Rheological results showed that G^ʹ> G^ʺ over the frequency range, illustrating the elastic behavior of the composite samples. In fact, samples showed the characteristic of a non-Newtonian fluid with a strong shear thinning effect in which η* increased with increasing filler weight fraction. From the results, it can be expected that modified silica could replace silica nanoparticles in polyolefin nanocomposite reinforcement.     

Determination of the Rheological Properties of Polypropylene Filled with Colemanite

Colemanite (Ca₂B₆O₁₁.H₂O) in powder form was filled to polypropylene (PP) at concentrations of 5, 7.5, 11.25, 16.875, and 25.312 wt%, and filled PP granules were obtained. To prevent oxidation, an antioxidant (Songnox 1010) was added to the colemanite‐filled polypropylene mixture at a ratio of 0.2 wt%. The rheological properties of the resulting composite material were determined using a Melt Flow Index testing device, at four separate pressure settings (298.2, 524, 689.5, and 987.4 kPa) and four separate temperature settings (190°C, 200°C, 210°C, and 220°C). The viscosity, shear rate, shear stress, and power law index (n) values of the colemanite‐filled PP were measured as part of the testing conducted. The study determined that viscosity values increased by approximately 60% in response to increasing colemanite content in the resulting filled material, while shear rate values decreased by 62%. The viscosity values were found to decrease with increasing temperature and pressure values, while shear rate values were found to increase. Additionally, Power Law Index value was found to vary between 0.561 and 0.687, with an average value of 0.608 based on the colemanite content used. Copyright © 2017 John Wiley & Sons, Ltd.