Apparent Melt Viscosity Research Articles

Formulating calcium carbonate masterbatches

Abstract The effects of filler content, filler particle size and surface coating, as well as the natures of the wax and metal stearate lubricants on the properties of calcium carbonate-filled linear low-density polyethylene compounds were investigated. The elongation at break decreased exponentially with filler loading irrespective of whether the filler was surface coated or not. The corresponding decline in the impact strength was more gradual but it dropped abruptly on reaching a filler loading of 70 wt%. The effect of shear rate on the apparent melt viscosity followed an empirically modified Carreau–Yasuda model which included the effect of filler content. It features the zero-shear viscosity and the flow consistency index as adjustable parameters. These characterize the viscosity trends at low- and high-shear rates, respectively. In the absence of additives, the melt viscosity at 60 wt% filler exceeded that of the neat polymer by a factor of three. Adding 3 wt% wax and 1.0 wt% zinc stearate returned the melt viscosity to levels just above that of the neat polymer. Calcium stearate and magnesium stearate were less effective at reducing the apparent melt viscosity but a blend of the latter with zinc stearate performed particularly well.

Melt rheology and extrudate swell properties of talc filled polyethylene compounds

An experimental study of high-density polyethylene (HDPE) composites filled with talc (0–15 wt.%) was carried out to investigate the rheological properties. The apparent melt viscosity, melt density, and die-swell ratio (B) of the composites were measured at constant shear stress and constant shear rate by using a melt flow indexer and capillary rheometer. The experimental conditions were set to a temperature range from 190 to 220 °C for both apparatuses whereas a load range from 5 to 12.16 kg was selected for melt flow indexer and shear rate range from 1 to 10000 s−1 for capillary rheometer. The initial study showed that the talc particulates did not influence the melt viscosity compared with the neat HDPE but decreased the elasticity of the polymer system. The HDPE/talc systems obeyed power-law model in shear stress–shear rate variations and were shear thinning, meanwhile, the die-swell increased with an increased wall shear rate and shear stress. The melt density of the composites increased linearly with an increase of the filler weight fraction and decreased with the increase of the testing temperature. The talc-HDPE composites showed compressible in the molten state.

Design and Synthesis of Polysiloxane Based Side Chain Liquid Crystal Polymer for Improving the Processability and Toughness of Magnesium Hydrate/Linear Low-Density Polyethylene Composites.

In this study, a polysiloxane grafted by thermotropic liquid crystal polymer (PSCTLCP) is designed and synthesized to effectively improve the processability and toughness of magnesium hydroxide (MH)/linear low-density polyethylene (LLDPE) composites. The obtained PSCTLCP is a nematic liquid crystal polymer; the liquid crystal phase exists in a temperature range of 170 to 275 °C, and its initial thermal decomposition temperature is as high as 279.6 °C, which matches the processing temperature of MH/LLDPE composites. With the increase of PSCTLCP loading, the balance melt torque of MH/LLDPE/PSCTLCP composites is gradually decreased by 42% at 5 wt % PSCTLCP loading. Moreover, the power law index of MH/LLDPE/PSCTLCP composite melt is smaller than 1, but gradually increased with PSCTLCP, the flowing activation energy of PSCTLCP-1.0 is lower than that of MH/LLDPE at the same shear rate, indicating that the sensitivity of apparent melt viscosity of the composites to shear rate and to temperature is decreased with the increase of PSCTLCP, and the processing window is broadened by the addition of PSCTLCP. Besides, the elongation at break of MH/LLDPE/PSCTLCP composites increases from 6.85% of the baseline MH/LLDPE to 17.66% at 3 wt % PSCTLCP loading. All the results indicate that PSCTLCP can significantly improve the processability and toughness of MH/LLDPE composites.

THERMOPLASTIC VULCANIZATES BASED ON DYNAMICALLY VULCANIZED POLYPROPYLENE/CARBOXYLATED NITRILE RUBBER BLENDS

ABSTRACT Thermoplastic vulcanizates (TPVs) based on polypropylene (PP) and carboxylated nitrile rubber (XNBR) with improved mechanical properties were prepared by dynamic vulcanization using dicumyl peroxide (DCP) in combination with N,N′-m-phenylene-bis-maleimide (BMI) as a cross-linking system. The effect of PP grafted with maleic anhydride (PP-g-MA) or with glycidyl methacrylate (PP-g-GMA) and triethylene-tetramine (TETA) as the compatibilizing systems on the mechanical, morphological, and dynamic mechanical properties of PP/XNBR blends was investigated. Experimental results revealed that PP-g-GMA has a better compatibilizing efficiency. Tensile strength and elongation at break presented a significant improvement with the addition of 2.5 to 7.5 phr of this functionalized PP. The improvement of the tensile properties was observed for all blend compositions studied. Also the tensile properties of the blends did not change considerably after three reprocessing cycles, confirming the efficiency of this system as a TPV. The presence of PP-g-GMA also resulted in an increase of the apparent melt viscosity of the corresponding TPVs, confirming the reactive compatibilization. A decrease in rubber particle size with the presence of PP-g-GMA was also observed by scanning electron microscopy.

Rheological behavior of semisolid hypereutectic Al–Si alloys

Abstract

Numerical comparison on the influence of geometric size on melt viscosity for conventional and gas-assisted extrusion of plastic micro-tube

We studied the effects of the geometric size on the viscosity of melt for plastic micro-tubes with different radius or L/D ratios by using the finite element method in this paper. Meanwhile, the Bird-Carreau constitutive model was used to describe the rheological properties of non-Newtonian melt. Two of geometric models were used in this study. For the geometric model with same L/D ratio but different radius, the same inlet pressure value was imposed on the inlet face of geometric model. For the geometric model with the same radius but different L/D ratios, the same inlet volume flow rate of melt were imposed on the inlet face of geometric model. Numerical results show that, for the conventional extrusion of plastic micro-tubes with same L/D ratio but different radius, the apparent viscosity of melt decreases with the decreasing of the radius. For the plastic micro-tubes with same radius but different L/D ratios, the apparent viscosity of melt is nearly not changed with the decreasing of the L/D ratio. However, for the gas-assisted extrusion of plastic micro-tube, the geometric size doesn’t seem to affect the melt viscosity.

Rheological and spinning properties of polystyrene/nano aluminum composites

PS/AlNPs composite fibers were prepared by adding AlNPs into PS to finish the simulation study of conductive matrix materials for Z-pinch: deuterated polystyrene/nano-aluminum (DPS/AlNPs). The effects of temperature and shear rate on the rheological properties, the relationship between the structural changes, the flow condition of composites melt and the properties of PS/AlNPs, as well as the morphology, thermal stability and mechanical properties of PS/AlNPs fiber were investigated. The results show that the PS/AlNPs melt is a typical shear thinning non-Newtonian fluid, and the apparent viscosity of the melt is negatively correlated with the temperature. The composite possesses non-Newtonian index of between 0.462 and 0.546 at 240-260 ℃, the coefficient of viscosity of about 1.8 to 2.1, and the activation energy of viscous flow sitting between 77.2 and 104.6 kJ mol-1, showing its good spinnability. The PS shows its ability to coat AlNPs very well and prohibits the AlNPs being oxided, giving birth to a PS/AlNPs fiber possessing smooth surface. The fiber has the biggest elongation at break and the highest breaking strength when the content of AlNPs is 1% and 5%, respectively.

Validation of an In-Mold Multivariate Sensor for Measurement of Melt Temperature, Pressure, Velocity, and Viscosity

Abstract A multivariate sensor (MVS) is described for measurement of melt temperature, melt pressure, melt velocity, and melt viscosity. Melt pressure and temperature are respectively obtained through the incorporation of a piezo-ceramic element and infrared thermopile. Melt velocity is derived from the initial response of the melt temperature as the polymer melt flows across the sensor lens. The apparent melt viscosity is then derived based on the melt velocity and the time derivative of the increasing melt pressure. The response of the MVS is analyzed using an instrumented mold including piezoelectric pressure sensors, an infrared pyrometer, and thermocouples. A 12-run, blocked half-fractional design of experiments (DOE) was run to characterize the effect of melt temperature, mold temperature, packing pressure, and ram velocity. The results show that the MVS provides excellent measurement of melt temperature and pressure. The accuracy of the melt velocity estimations depended on the ram velocity set-point, yielding a coefficient of determination of 0.91 for the lower ram velocities, and reaching saturation for melt velocities about 450 mm/s. The apparent melt viscosity estimated by the MVS are close to those predicted by the Cross-WLF model, exhibiting appropriate shear thinning but behavior but inconsistent temperature dependence.

Influence of DE-value on the physicochemical properties of maltodextrin for melt extrusion processes

In this study, five different types of maltodextrins (DE-2, DE-6, DE-12, DE-17 and DE-19) were characterized for the physico-chemical properties. TGA, DVS and SEC analyses were carried out and additionally apparent melt-viscosity (in a micro-extruder) and the glass transition temperature (analyzed by DMA) of maltodextrin/plasticizer mixtures were also measured in order to evaluate both the effect of plasticizer nature and content and the effect of the DE-value. For this, three plasticizing agents were compared: water, d-sorbitol and glycerin. The adsorption isotherms showed that depending on the DE-value and the relative humidity they were exposed to, different behavior could be obtained. For example, for relative humidities below 60% RH maltodextrin DE-2 was the least hygroscopic. And on the contrary for relative humidities above 75% RH maltodextrin DE-2 was the most hygroscopic. The rheology measurements showed that the viscosity decreased with the increase of the DE-value and with the plasticizer content, as expected. On the contrary, no direct correlation could be established between the DE-value and the glass transition temperature. These results demonstrated that to predict maltodextrins behavior and to better adapt the process conditions, combined analyses are mandatory as the DE-value alone is not sufficient. The most compelling evidence was obtained by size exclusion chromatography, which pointed out that maltodextrins had a bimodal molecular weight distribution composed of high and low molecular weight oligo-saccharides. Indeed, maltodextrins are highly polydisperse materials (i.e. polydispersity index ranging from 5 to 12) and that should be the reason why such distinct behaviors were observed in some of the physico-chemical analyses that were preformed.

In‐mold multivariate sensing of colored polystyrene

The role of colorant in polymer processing was investigated with respect to pressure and infrared (IR) sensing. Polystyrene was combined with blue, black, and purple color additives using twin‐screw extrusion. Injection molding was then conducted using these three materials with a mold instrumented with a suite of commercial sensors as well as a custom multivariate sensor (MVS) capable of sensing melt temperature, mold temperature, melt pressure, melt velocity, and melt viscosity. Melt pressure and melt temperature are, respectively, obtained through the incorporation of a piezoceramic element and IR thermopile within the sensor head. Melt velocity was derived from the initial response of the melt temperature as the melt flows across the sensor's lens. The apparent melt viscosity was then derived based on the melt velocity and the time derivative of the increasing melt pressure given the cavity thickness. The accuracy of the temperature, pressure, velocity, and viscosity results were evaluated. Results indicated that the velocity estimates obtained with the commercial sensors and MVS had a coefficient of determination, R2, of about 0.99 regardless of colorant. The temperature measurements and viscosity estimates were similarly and correctly found to be invariant of the colorant blend. POLYM. ENG. SCI., 55:2794–2800, 2015. © 2015 Society of Plastics Engineers

Vibration assisted extrusion of polypropylene

A new homemade apparatus, i.e. vibration assisted extrusion equipment, is employed to extrude polypropylene. Vibration assisted extrusion is based on the application of a specific macroscopic shear vibration field. Reduction of apparent melt viscosity as a function of vibration frequency is measured at different screw speeds and die temperatures. The effect of the process is investigated by performing mechanical tests, differential scanning calorimetry studies, polarized light microscopy and wide-angle X-ray diffraction. It is found that, compared with conventional extrusion, vibration assisted extrusion could effectively improve the rheological properties of PP melt by incorporating an extra shear vibration field. Both the tensile strength and elongation at break increased under the shear vibration field. For vibration assisted extrusion samples, both the melting temperature and crystallinity increased, accompanied by remarkable grain refinement. Vibration assisted extrusion induced a significantly enhanced bimodal orientation with a high fraction of a*-oriented α-crystallites, while only a limited improvement in the flow direction orientation. A structural model, i.e. bimodal c-axis and a*-axis orientation of PP macromolecular chains, was adopted to explain the experimental results.

Quality control using a multivariate injection molding sensor

Injection molding part quality is modeled using a multivariate sensor. Melt pressure and temperature are respectively obtained through the incorporation of a piezo-ceramic element and infrared thermopile within the sensor head. Melt velocity is derived from the transient response of the melt temperature as the polymer melt flows across the sensor’s lens. The apparent melt viscosity is then derived based on the melt velocity and the time derivative of the increasing melt pressure given the cavity thickness. Quality metrics taken into account are finished part thickness, width, length, weight, and tensile strength. A 12-run, blocked half-fractional design of experiments was performed to derive predictive models for part mass, dimensions, and structural properties. Several predictive part quality models were created using data from the machine, a suite of commercial sensors, the multivariate sensor, and combinations thereof. The results indicate that multiple orthogonal streams of process data yield higher-fidelity models with coefficients of determination approaching one. Furthermore, best subset analysis indicates that the most important process data are gathered from in-mold sensors, where the acquired information is closest to the states of the polymer forming the final product.

Effect of thermotropic liquid crystalline poly(ether ketone)arylates on the processibility and properties of poly(ether ether ketone)s fibers

ABSTRACTA series of composite fibers based on poly(ether ether ketone)s (PEEK) and a thermotropic liquid crystalline poly(ether ketone)arylates (PEKAR) have been prepared by melt spinning. The structure, compatibility, and properties of these composite fibers were investigated in detail by rheological measurements, differential scanning calorimetry, thermogravimetric analysis, wide‐angle X‐ray diffraction, scanning electron microscopy, orientation degree test, and mechanical properties test. The results showed that the addition of PEKAR could reduce the apparent melt viscosity of the blends obviously, which is beneficial in improving the processibility of PEEK at a relatively low temperature. After adding 1 wt % PEKAR to PEEK, the tensile strength of the post‐treatment fiber improved by 8.8%, whereas the crystallinity of the as‐spun fiber increased from 21.76% to 31.51%, and the orientation degree also increased with the addition of PEKAR. The result of morphology research suggested that PEKAR had a good compatibility with PEEK resin. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40595.

Compatibilization of starch–zein melt processed blends by an ionic liquid used as plasticizer

An ionic liquid (1-butyl-3-methyl imidazolium chloride [BMIM]Cl) was used as a plasticizer in starch, zein and their blends; and compared to glycerol, a classical plasticizer of starch. Thermoplastic plasticized biopolymer materials were obtained by melt processing using a twin screw microcompounder. Such a device allows simulating a twin screw extrusion process on small batches of a few grams, and to evaluate the necessary specific mechanical energy input for native starch destructurization; and the final apparent melt viscosity. Both were shown to be significantly reduced for starch in presence of [BMIM]Cl (compared to glycerol), while zein processing behavior was less sensitive to the plasticizer used. This induces significant starch/zein viscosity ratio differences, which affect melt mixing of the starch zein blends. In starch rich blends, this results in smaller zein aggregates in the case of [BMIM]Cl.The characterization of the materials indicates that, compared to glycerol, the use of [BMIM]Cl leads to less hygroscopicity, a more efficient plasticization of both starch and zein phases and a compatibilization of starch/zein blends.

Rheological Behavior of Blends of Poly(Phenylene Sulfide) with a Thermotropic Liquid Crystalline Aromatic Poly(Ether Ester)

A new type of thermotropic liquid crystalline aromatic poly(ether ester) (PEE) was prepared from 1,3-bis(4′-carboxyphenoxy)benzene, 1,4-diacetoxybenzene, and p-acetoxybenzoic acid through a melt transesterification process. The rheological behavior of blends of poly(phenylene sulfide) (PPS) with PEE was studied using a high-pressure capillary rheometer with the shear rate range of 50 s−1 to 3000 s−1. The results show that according to the range of shear rate, the flow curves of PEE/PPS blends can be divided into three zones: a first shear-thinning zone (n < 1, “n” represents non-Newtonian indexes), a shear-thickening zone (n > 1), and a second shear-thinning zone (n < 1), and the former two zones are more obvious with the increase of PEE content or elevated temperature. In the second shear-thinning zone, the PPS melt is close to a Newtonian fluid at high temperature and high shear rate; meanwhile the non-Newtonian behavior of the PPS melt at high temperature is enhanced with the addition of PEE. The apparent viscosity of PPS melts sharply dropped after adding PEE, especially at relatively low temperature and low shear rate. The curve of apparent viscosity vs. shear rate starts to flatten out after adding PEE, suggesting that the addition of PEE lowers the sensitivity of PPS to shear rate. As the content of PEE increases, the activation energy of the viscous flow, ΔEη, of PPS decreases, which means that adding PEE weakens the temperature sensitivity of the apparent viscosity of the PPS melt. It can clearly be seen that the addition of PEE is beneficial to the processing of PPS.

Rheology, Phase Morphology and Crystallization Properties of PA6/PP-g-MAH/POE Blends

The phase morphology, rheology, and crystallization properties of the PA6/PP-g-MAH/POE blends prepared by melt-blending method were studied by scanning electron microscopy (SEM), capillary rheometer and differential scanning calorimetry (DSC), respectively. The results suggest that the compatibility of PA6 and POE can be improved by the compatibilizer of PP-g-MAH and the 10% of PP-g-MAH is preferred. PP-g-MAH and PA6 can both serve as nucleating agents for each other, and improve their crystallization behaviors. All melts of PA6/PP-g-MAH/POE blends are pseudo-plastic fluids, and PP-g-MAH components can increase the melt apparent viscosity due to its inherent higher viscosity, and so the processing property of the blend will be controlled in much wider temperature range.

Feasibility Analysis of an In-mold Multivariate Sensor

Abstract The initial design of a novel multivariate sensor is described for the measurement of melt temperature, melt pressure, melt velocity, melt viscosity, and mold temperature. Melt pressure and temperature are respectively obtained through the incorporation of a piezoceramic element and infrared photodetector within the sensor head. Melt velocity is derived from the initial response of the melt temperature as the polymer melt flows across the sensor's lens. The apparent melt viscosity is then derived from the melt velocity and the time derivative of the increasing melt pressure given the cavity thickness. The feasibility of the envisioned sensor is then analyzed using a production-grade mold that is instrumented with commercial piezoelectric pressure sensors, infrared pyrometer, and thermocouples. Several predictive models of part weight are developed using multiple regression of data obtained from a design of experiments to evaluate the capability of the envisioned multivariate sensor. The results indicate a correlation coefficient, R2, of 0.79 for a model based on the machine settings, 0.80 for a model based on a cavity pressure sensor, 0.90 for a model based on the multivariate sensor, and 0.98 for a non-linear model based on the multivariate sensor. The implication is that multiple orthogonal sensing streams with high fidelity models are necessary to provide automatic quality assurance sufficient for fully automated plastics manufacturing.

Rheological Behavior and Mechanical Properties of PVC/V-POSS Nanocomposites

The poly(vinylchloride) (PVC) nanocomposite was prepared by melt mixed of PVC with polyhedral oligomeric silsesquioxanes containing vinyl group (V-POSS). The rheological behavior of V-POSS/PVC nanocomposites was investigated by torque rheometer and capillary rheometer. The influences of composition of blends, shear rate, shear stress on melt apparent viscosity and non-Newtonian index (n) were discussed. The dynamic mechanical properties, mechanical properties and morphology were determined. The result shows that the plastic time of nanocomposites decreases while melt viscosity increases with increasing V-POSS content. V-POSS has a good compatibility with PVC. The nanocomposites have better impact strength with increasing V-POSS content. V-POSS can use as process aid and impact aid at appropriate contents.

The use of thermoplastic elastomers as polymer processing aids in processing of linear low density polyethylene

Commercially available thermoplastic elastomers based on block copolymers of diisocyanates and polyols and based on silicones have been reported by Kulikov et al. (2004 and 2006) to delay sharkskin in extrusion of Linear Low Density Polyethylene. In this work thermoplastic elastomers have been used as polymer processing additives in blown film extrusion of Linear Low Density Polyethylene. When a thermoplastic elastomer is added in small amounts to Linear Low Density Polyethylene it deposits at the die surface during extrusion and may postpone the onset of sharkskin enabling up to 20 times higher rate of extrusion. Many thermoplastic elastomers are certified for body and food contacts and could be a cost-effective substitution of fluorinated polymers in processing of Linear Low Density Polyethylene by extrusion. Oscillating and capillar rheometry have been used to reveal the mode of action of the additives. Results of capillar rheometry showed a decrease of apparent viscosity of the polymer melt when additive was added. Therefore Mooney method (Mooney, 1931) was applied to prove occurring slip inside of the die. Substantial delay of sharkskin was achieved also in conditions without slip of molten polyethylene inside the die by adding thermoplastic elastomer based on urethanes. Oscillating rheometry has been used to characterize elasticity of the materials. It could be shown that efficiency to delay sharkskin depends on elasticity of the specific thermoplastic elastomer at processing temperature. Surface tension of the solid materials was used to estimate the mutual affinity of the materials. Therefore a theoretical model of Rathod and Hatzikiriakos (2004) was used to evaluate the data. Finally a classification of polymer processing aids into “slip inducers” and “flow enhancers” by their mode of action was done. Ability of novel processing aids to postpone sharkskin was shown in blown film extrusion. Applicability of polymer processing aids in injection moulding could be proved by use of a mould with spiral cavity.

Rheological Properties of PTT/POE/OMMT Composites

Poly(ethylene-octene)(POE) and organic montmorillonite(OMMT) acting respectively as the toughening agents and reinforcing agents, were used to prepare nanocomposites with Poly(trimethylene terephthalate)(PTT) in order to modify PTT, and the rheological properties of these composites were investigated by using capillary rheometer instrument. The OMMT used in composite was prepared by intercalating triphenyl phosphate (TPP) into MMT by mixed solution method. PTT/POE/OMMT nanocomposites were prepared by melt blending in twin-screw corotating extruder. Rheological results show that PTT/POE/OMMT composite melt was pseudo-plastic liquid and the pseudo-plasticity of the melt was decreased with increasing OMMT content for the strong interface interactions between OMMT and polymer molecular chains. The melt apparent viscosity was increased with increasing OMMT content. The flow activation energy results suggested that the composite melt having more OMMT components is more sensitive to the change of temperature.