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SPE Library content related to rheology
Properties of Thermoplastic Polyurethanes Derived from H12MDI
Thermoplastic polyurethanes (TPU) based on aliphatic diisocyanates such as 4,4'-dicyclohexylmethane diisocyanate (H12MDI) are indispensable in a variety of industrial, optical, and medical device applications. Relative to 4,4'-diphenylmethane diisocyanate (MDI) based TPUs, H12MDI based TPUs exhibit superior aesthetics, light stability, and biocompatibility. However, the use of H12MDI as a diisocyanate has a major impact on other properties of the final TPU. In this study, the thermal, mechanical, and rheological properties of a typical H12MDI based TPU were characterized and compared to an analogous MDI based TPU.
Analysis of Viscous Heating Effects in a Pressure Slit Rheometer Using Radial Functions Method (RFM)
A pressure rheometer was built to measure rheological properties of polymers at elevated pressures and temperatures. However the viscosity at high deformation rates decreases more than the predicted theoretical value represented by the Cross-WLF model. This paper studies the role of viscous heating in the resulting viscosity deviations by means of simulation using the Radial Functions Method (RFM).
Nitroxide-Mediated Controlled Degradation of Polypropylene
The purpose of this work is to evaluate a new polypropylene (PP)–based nitroxyl radical generator (NOR) and offer comparisons with a commonly used peroxide in the production of controlled-rheology polypropylene (CRPP) resins. CRPP resins are produced by reactive processing in a batch mixer by using different amounts of either the NOR or a peroxide initiator at different temperatures. Molecular weight and rheological properties are determined for all CRPP produced and a comparison between the effectiveness of the NOR and the peroxide initiator is provided.
Effect of Die Geometry and Extensional Rheological Properties on Vortex Development in Rectangular Dies
The vortex development of a low-density polyethylene in different flat dies under various processing conditions has been analyzed by the Finite Element Method employing the modified White-Metzner model as constitutive equation. The theoretical results are compared with the velocity distributions measured by Laser-Doppler Velocimetry (LDV).
Fundamental Structure-Property Relationship of Polymer Nanocomposites
The structure-property relationship of a set of model polymer nanocomposite systems has been investigated. The findings suggest that degree of exfoliation and aspect ratio of nanoplatelets in polymer matrices can greatly influence physical, mechanical and rheological behaviors of polymers. Most importantly, there appears to be a limit to which polymer nanocomposites can be applied for structural applications.
The Role of Chain Branching in Extrusion Blow Molding of Polyvinylidene Fluoride
The effect of long chain branching in polyvinylidene fluoride in extrusion blow molding is investigated in light of the enhanced rheological properties. The presence of long chain branching increased the melt strength; melt elasticity and strain hardening of the branched samples as opposed to their linear counterparts. These enhanced properties suggest better sag resistance during blow molding and higher blow-up ratio while achieving uniform wall thickness.
Determination of Uniaxial Extensional Viscosity for Polyolefins by Improved Entrance Pressure Drop Measurements
In this work, specially designed zero-length dies were used for the entrance pressure drop measurements with the aim to determine uniaxial extensional viscosity of polyolefin melts by using effective entry length correction and Cogswell/Binding models and the results were compared with the extensional rheology determined with the Sentmanat extensional rheometer. Reasonable agreement between these two techniques has been obtained.
High Heat Ductile (HHD) Copolymers by Reactive Extrusion
A blend of two polycarbonate copolymers, high-heat poly(ester-carbonate) (PEC) and polycarbonate-polydimethylsiloxane copolymer (PC-PDMS) provided an opaque, pearlescent blend. However, when a transesterification catalyst was used, the blend becomes miscible and translucent/transparent. The high-heat, ductile (HHD) materials were analyzed for a range of properties including optics, rheology, heat performance, flame retardance, and mechanical properties. The hydrolytic stability of the HHD materials was also measured by comparing the ductility of the blends before and after autoclaving.
Rheology of Heterogeneous Polymer Melts
Heterogeneous polymers represent an important class of plastics that comprise polymer blends, alloys, and fiber or mineral filled plastics. The rheology of these melts is dominated by the transient morphology that is produced during fabrication into finished products. Standard laboratory rheological tests do not take into account morphology. Combined measurements of a capillary viscometer and controlled stress rotational rheometer can provide a better understanding of the processing behavior of these complex rheological plastics
Effects of Molecular Weight Distribution on the Formation of Fibers of Electrospun Polystyrene
It is widely recognized that molecular weight distribution (MWD) is an important factor affecting the rheological behavior of polymer solutions. In this contribution, the effects of MWD on the formation of electrospun polystyrene fibers in THF have been studied. The results are compared with the monodisperse system. The importance of chain entanglements attributed to high molecular weight component within the polydisperse system has been acknowledged. Concentrations for the incipient as well as stable fiber formation in a polydisperse system may be predicted.
Rheological and Degradation Properties of Renewable Resource Polymer Blends
Over the past decade, considerable interest has emerged in replacing conventional fossil fuel-based polymers with bio-derived polymers. Two bio-derived polymers that have garnered significant interest are PHA and PLA. In this study, shear and extensional rheology, coupled with degradation studies using GPC, are used to investigate the flow properties of blends of these two polymers. The development of blends with tailored flow and thermal/mechanical properties is pursued.
The Effect of Long-Chain Branching on Extensional Rheoelogy and its Correlation as a Predictor for Molecular Architecture
The effect of sparse long-chain branching on extensional rheology is analyzed for metallocene-catalyzed polyethylene resins with varying degrees of branching. The onset of extensional strain hardening distinguishes the degrees of branching while such distinctions are not apparent in shear flow behavior.
Investigation and Modification of the Melt Rheology of Olefin Block Copolymers
The melt rheology of novel Olefin Block Copolymers (OBCs), recently developed by The Dow Chemical Company, was investigated. The melt shear rheology of OBCs was found to be characteristic of linear random copolymers of ethylene and __olefins. Furthermore, the melt rheology can be modified to target certain specific application areas by chemical means or by blending with traditional polyolefins with broader molecular weight distributions or those containing long chain branching.
Shear Rheology of Highly Filled Polymeric Suspension
Highly filled polymeric materials exhibit complex rheological properties. In this study the rheological characteristics of highly filled suspension based on ethylene octane copolymer binder and Dechlorane filler were studied. Steady shear and thixotropic behaviors are discussed.
Viscoelastic Behavior of Sulfonated Polystyrene Ionomers
Sulfonated polystyrene ionomers (alkali metal salts) with molecular weight below the entanglement molecular weight of polystyrene were prepared. The rheological behavior of the ionomers was characterized by dynamic and steady-state shear experiments. In general, the viscosity of the ionomers increased with sulfonation level and as the size of the cation decreased. Whereas, the starting polystyrenes were Newtonian fluids, the ionomers were non-Newtonian and viscoelastic.
Rheological and Crystallization Behavior of Linear and Branched PBT
Rheological and thermal characteristics of PBT resins were investigated with potential applications in low density foaming. The branched PBT was produced by extrusion modification with a tri-functional modifier, whereas the linear PBT was processed under the same condition without the modifier. The presence of branched molecules resulted in increased elasticity and slower crystallization kinetics due to higher concentration of entanglements and/or increased interchain interactions. Degradation by processing for both resins produced shorter chains, and involved reduced shear viscosity and faster crystallization kinetics, in particular, at high temperature.
Influence of Polymer Matrix and Coupling Agents on Melt Flow Behavior of Wood Filled Polyethylene Composites
The influence of coupling agents on the melt rheological properties of HDPE/wood flour composites has been investigated in this work by means of a capillary rheometer. Scanning electron microscopy was also employed to supplement the rheological data. It was found that molecular weight and molecular weight distribution of the polymer matrix and coupling agent characteristics influence the melt flow properties of the filled composites. Generally, low molecular weight and narrow molecular weight distribution polyethylene matrix provides larger increase of the viscosity of the composites with respect to the unfilled resin. Coupling agents tend to increase the resistance to shearing, but wall slip effects may interfere with the measured values, especially at very high filler loadings.
Improving the Toughness of Poly(Lactic Acid)(PLA) through Co-Continuous, Immiscible, Biodegradable Blends with PHA
Poly(lactic acid) (PLA) and Polyhydroxy octanoate (PHO) were melt blended using a torque rheometer in the ratios of 80/20, 60/40, 50/50, 40/60, and 20/80. In this study, the rheological, thermal, and mechanical properties of the blends were investigated. Differential scanning calorimetry showed that the two components in these blends were found with two crystalline phases and two amorphous phases confirming the coexistence of two immiscible components. The addition of modified PHO in PLA increased the toughness of the PLA and increased the elongation to break more than 158%. Results obtained from rheological test indicated that the melt viscosities of PLA/modified PHO decreased as a function of modified PHO content.
Difference in Thermoforming Processability Observed for Three High Impact Polystyrenes
The difference in thermoforming processability of three STYRON* high-impact polystyrene (HIPS) resins was investigated. Experiments were performed on a moldbottle thermoformer as well as a step-case tool thermoformer. Disparities observed were analyzed in terms of differences in rheological properties of the resins. Conclusions were drawn as to which rheological characteristics the resins should possess in order to give the largest temperature processing window coupled with high quality thermoformed parts.
Mechanical Hole Burning Spectroscopy in the Vicinity of the ODT for an SIS Block Copolymer
We describe results for experiments in which a novel rheological technique is applied to a styrene-isoprene-styrene triblock copolymer in the vicinity of the order-disorder transition. Mechanical Hole Burning Spectroscopy (MSHB) was developed to probe dynamic heterogeneity in polymers. In this technique, a large amplitude oscillatory strain (LAOS) is imposed on a sample as a perturbation, and is followed by a small step strain. The relaxation response is then compared with that without the LAOS perturbation. It has been assumed that mechanical holes for heterogeneous systems. For homogeneous systems no hole would result. Here the heterogeneity of a tri-block copolymer was investigated in the vicinity of its order-disorder transition and it was found that the mechanical hole intensity gradually decreases as the phase boundary is approached from the ordered regime. At the one-phase or the disordered region, no apparent holes were observed.
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