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SPE Library content related to rheology
A COMPREHENSIVE STUDY OF LOW-DENSITY POLYETHYLENE IN CAPILLARY FLOW
The capillary flow of a commercial LDPE melt was studied both experimentally and numerically. The excess pressure drop due to entry (Bagley correction), the compressibility, the effect of pressure on viscosity and the possible slip effects on the capillary data analysis have been examined. Using a series of capillary dies having different diameters, D and length-to-diameter L/D ratios, a full rheological characterization has been carried out, and the experimental data have been fitted both with a viscous model (Carreau-Yasuda) and a viscoelastic one (K-BKZ/PSM model). Particular emphasis has been given on the pressure-dependence of viscosity, with a pressure-dependent coefficient βp. For the viscous model, the viscosity is a function of both temperature and pressure. For the viscoelastic K-BKZ model, the time-temperature shifting concept has been used for the non-isothermal calculations, while the time-pressure shifting concept has been used to shift the relaxation moduli for the pressure-dependence effect. It was found that only the viscoelastic simulations were capable of reproducing the experimental data well, while any viscous modeling always underestimates the pressures, especially at the higher apparent shear rates and L/D ratios.
COMPLEX INVESTIGATION OF INJECTION MOULD FILLING
Thin wall injection moulding is a difficult process. High viscosity polymeric material is injected into a mould by high speed and high pressure. A special instrumented injection mould was designed for the investigation of the cavity filling of injection mould. Rheological measurement can be carried out with different wall thickness slit die inserts. The pressure can be measured during the filling, the packing and the cooling stages as well. The pressure drop during the filling can be used for determination the flow properties of the material. The measured cavity pressure of the injection cycle is proper for the validation if thin wall injection moulding simulation. The filling of the dies was simulated by Moldex3D software.
RHEOLOGICAL CHARACTERIZATION OF MELT MIXED PCL - MWCNT NANOCOMPOSITES PREPARED AT DIFFERENT MIXING SPEEDS
Composites of poly(caprolactone) (PCL) and multiwalled carbon nanotubes (MWCNTs) were produced by melt-mixing in a small scale compounder by varying the screw speed between 25 and 400 rpm at a constant mixing time of two minutes. By that, different levels of dispersions, as assessed by quantitative analysis of area ratio of remaining primary agglomerates from light microscopy, were achieved. With increasing screw speed the state of dispersion increases and levels off starting at about 100 rpm. Melt rheological properties were measured in frequency sweeps. Interestingly, distinct differences in the complex viscosity * and the storage modulus G’ were found in dependence on the agglomerate area ratio, whereas the loss modulus G’’ was not much influenced. The storage modulus at 0.1 rad/s initially increased with decreasing area ratios, showing that especially the storage modulus is very sensitive to the nanotubes dispersion state. It increased up to a mixing speed of about 75 rpm illustrating improved dispersion followed by a decrease when further increasing the speed. As GPC investigation showed no significant differences in the degradation of the PCL matrix depending on the rotation speed, the effect of decreasing rheological parameter was assigned to nanotube shortening. Both effects improved dispersion and nanotube shortening are also reflected in the electrical resistivity values of compression molded samples. Here, up to 75 rpm a decrease in resistivity due to the better dispersion was observed, whereas above 75 rpm, where dispersion had leveled off, again an increase was found reflecting the reduction in nanotube aspect ratio. Thus, it could be shown that rheological measurements are suitable to detect differences in the dispersion state in composites with a fixed type of CNTs and concentration but also the effect of nanotube shortening reflected in lower aspect ratios.
EFFECT OF COMMON STABILIZERS IN THE LONG-TERM HEAT AGEING PERFORMANCE OF POLYETHERIMIDES
A fast method was develop to predict the macroscopic properties of molded resin specimens tested in the Underwriting Laboratories (UL®) Relative Thermal Index (RTI) test (tensile strength retention) with microscopic properties that can be easily measured (molecular weight). By using higher temperatures than employed in the UL RTI protocol, accelerated ageing can be achieved in pellets. Polyetherimide (PEI) resin was spiked during extrusion with common stabilizers. The analysis focused on melt stability, rheology and long-term heat ageing performance. Hindered phenol stabilizers were detrimental under accelerated thermo-oxidative ageing of PEI. The use of new stabilizers should be carefully considered.
Enhancing Properties of PP-Impact Copolymers by Chemical Modification
Polypropylene impact copolymers are widely used in automotive applications. They are required to comply with many criteria. Customers demand high-performance materials which also exhibit good aesthetical properties. The challenge is to balance properties as high impact strength, good flow ability and absence of surface defects, like tiger stripes. It is known that peroxide modification whilst increasing the flow ability of polypropylene impact copolymers deteriorates the basic mechanical and aesthetical properties. Work was performed in which a PP-impact copolymer was subjected to peroxide aided chain-scission under simultaneous presence of the co-agent 1,4- butanedioldimethacrylate (1,4-BDDMA). Results show that samples made with 1,4- BDDMA exhibit superior cold impact resistance and tiger stripe performance compared to the materials made with only peroxide. In addition, morphology, molecular weight distribution, and rheological behaviour of the continuous and dispersed phases of the modified PP impact copolymer were studied.
Clay's location affects flammability of polypropylene
A synergistic effect between flame retardant and clay depends on the clay being situated within the polymer matrix.
Blend membranes for ionic polymer-metal composite actuators
Larger actuation displacements and blocking forces at 2.5 and 3.0 DC voltages render the new composites superior to Nafion and useful for many applications.
Entangling additives enhance polypropylene foam quality
Combining clay and compatibilizer additives with linear polypropylene forms nanocomposites with a densely entangled inner structure able to produce quality foams upon extrusion.
Dynamic mechanical analysis of natural rubber crosslinking reaction kinetics
The reaction order and rate constant for the crosslinking of natural rubber have been determined by modeling and compared to experimental results.
Thin film nano-indentation: an elastic foundation model
Atomic force microscopy and theoretical modeling were combined to measure Young's modulus of a thin (<100nm) polymeric film.
Toughness of hydrogels
Combining digital image correlation with the essential-work-of-fracture technique offers a plausible alternative to conventional means of measuring the robustness of soft materials.
Practical Rheology and its Role in Polymer Processing
Powerpoint Presentation at Polyolefin Conference 2011
Practical Rheology and its Role in Polymer Processing
Rheology is the science of material flow behavior, which is a very complex and multi-dimensional science. Even though it is complex, it also is quintessential to understand in order to optimize the processing of polymers. Knowing the difference between amorphous and crystalline polymers, what Melt Index really tells, and the effects of melt temperature on melt fracture are all important elements in the understanding of rheology. A simple understanding of what polymer rheology is and how shear and temperature can affect the flow characteristic of a polymer may make a big difference in the P & L of a company.
Macroscopic evaluation of nanofiller dispersion
The degree of dispersion of lamellar nanofillers in a polymeric matrix is evaluated by rheological, mechanical, and permeability analysis.
SHEAR & EXTENSIONAL RHEOLOGY OF C18-CNT/LDPE NANOCOMPOSITES
Nanocomposites of low density polyethylene (LDPE) and C18 modified multi wall carbon nanotubes (C18-CNT) were prepared by melt blending. Previous research has shown that addition of carbon nanotubes (CNTs) increase the dynamic viscosity and reduce the extensional viscosity with increasing loading. This research work shows that C-18 modification of CNTs helps to keep low values of dynamic viscosity, maintain extensional viscosity and does not increase strain hardening even at 5.0 weight % loading.
PROCESS DEVELOPMENT OF THE PROJECTILE INJECTION TECHNIQUE (PIT)
The projectile injection technique is a new powerful process variant of the well established fluid injection technique for the production of hollow shaped polymer parts. For suitable part designs the PIT allows to increase the economical efficiency and process capability significantly. First research results show that it is possible to reproducibly form hollow shaped geometries independent from the rheological properties of the used polymers.
HYDROLYSIS RESISTANT - HIGH IMPACT POLYETHERIMIDE RESIN BLENDS
Injection moldable hydrolytically stable transparent thermoplastic Polyetherimide resin blends with high impact and thermal resistance have been developed for healthcare applications. The two-phase resin blends are capable of withstanding 2,500 autoclave cycles at 134 C and 50 ppm morpholine while maintaining clarity and ductility. Injection molding of the new steam resistant blends as well as their rheological and material properties are compared to polyetherimide.
PROPERTIES OF POLY (PROPYLENE CARBONATE) PRODUCED VIA SK ENERGY'S GREENPOL TECHNOLOGY
Polypropylene carbonate (PPC) is an amorphous polymer made by alternating copolymerization of carbon dioxide and propylene oxide. SK Energy developed its own proprietary technology with a highly active catalyst for this polymerization and has begun to produce PPC in its continuous process type pilot plant since late 2008 with a trade name GreenPolTM. In this paper, we are describing the typical properties of PPC such as general physical properties, barrier properties, thermal and UV stability, and smoke density along with some rheological properties.
UV-INITIATED REACTIVE EXTRUSION OF POLYPROPYLENE
A new reactive extrusion (REX) process for the production of controlled-rheology polypropylene (CRPP) has been developed using benzophonene (BP) as a photo-initiator and an ultraviolet (UV) lamp. Experiments have been carried out in a co-rotating intermeshing twin-screw extruder and the effects of initiator concentration, polymer flow rate and reaction temperature have been studied. The CRPP products have been characterized through rheological measurements, size exclusion chromatography (SEC), differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy.
RHEOLOGICAL STUDIES ON A NOVEL LIQUID CRYSTALLINE EPOXY THERMOSET
Liquid crystalline epoxy thermosets were prepared by adding 3,3',5,5'-Tetramethylbiphenyl-4,4'-diyl bis(4-(oxiran-2-ylmethoxy)benzoate) (M1) into diglycidylether of bisphenol A (DGEBA)/ 4,4'-diaminodiphenyl methane (DDM) blends. Rheological tests with constant temperature and time tests under constant mechanical shear load conditions were performed by using rheometry instrument.
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