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SPE Library content related to rheology
Molecular Structure and Rheology Relationship of Polyethylenes
The structure-rheology relationship is investigated in three polyethylenes namely high density polyethylene (HDPE), a metallocene linear low density polyethylene with no chain branching (mLLDPE) and a metallocene polyethylene containing long chain branching (mLLDPE-LCB). Shear and extensional rheology measurements were carried out in the linear viscoelastic regime and correlated to the molecular weight, molecular weight distribution and long chain branching. Shear rheology showed that HDPE exhibits a viscosity profile whereby the Newtonian behavior is not completely attained as shown by the slope of the storage modulus in the terminal region. mLLDPE was found to possess the longest and well-defined Newtonian region and the highest transition to the non-Newtonian region. In the presence of long chain branching (LCB), the terminal region is not apparent while the onset of shear thinning is decreased. Such behavior can be related to the effects of MWD and LCB and was corroborated using extensional viscosity measurements, which showed slight deviation from the LVE envelope for broader molecular weight distribution and strain hardening in the presence of long chain branching.
Optimization of Acrylic Components in Extruded Rigid PVC
In this study the effect of acrylic-based components, including process aids (PPA), on the rheological properties of rigid PVC formulation is investigated. A statistically designed experiment was set up to cover the effect of composition on the melt viscosity and the melt strength of the compound as a function of temperature. The effect of the acrylic components was studied in relation to the rheological properties such as capillary rheometry and melt strength. In the absence of an acrylic process aid, the PVC compound showed a loss of adhesion at the wall caused by a change in the microstructure and characterized by pressure oscillations and a dip in the melt strength trace. As the temperature is increased, the slippage appears to be minimized and the head pressure stabilized.
Practical Applications of Polyethylene with Excellent Easy Processability
The melt rheological properties of an ethylene/alpha-olefin copolymer polymerized by a supported metallocene catalyst, which have been developed as the easy processing polyethylene by Sumitomo Chemical, were evaluated and compared with conventional polyethylenes. The melt viscoelastic properties of the copolymer exhibit a shear rate dependence similar to that of high-pressure low density polyethylene that is considered to be caused by the wide molecular weight distribution and long chain branched molecular structure.In the latter part of this presentation, we have focused on the performance of the above copolymer. This copolymer exhibited superior processability in the fabrication of blown film such as low temperature and high output processing, leading to the production of a clean film without any additives and with low odor and taste.
Flash, a common injection molding defect, arises when melt flows from the cavity into thin gaps between parting surfaces. Besides rules of thumb for eliminating flash, there are few fundamental papers on flash analysis. Understanding flash as a transport phenomenon provides a systematic basis for solving flash problems. The governing equations for the gap flow are established and solved for an isothermal power law fluid, under constant pressure along the parting line where flash begins. Two shapes are investigated, rectangular and ring slits that respectively correspond to modeling flash from straight and curved parting lines. Our equation for flash length, the distance to which the melt penetrates the gap developed between the parting surfaces, is our main result. Further, adimensionalizing not only unifies the results for straight and curved parting lines, but also provides insight into how rheology, pressure and geometry govern flash. Our approach avoids tedious numerical simulation and mold structural analysis. The theory is validated by our polycarbonate flash experiments.
Characteristics of PP/PS/Clay Nanocomposite Produced by High-Intensity Ultrasonic Process
Polymer-clay nanocomposites of various concentrations were prepared by ultrasonically assisted melt blend process. The ultrasonic blend process using high intensity ultrasonic wave was employed to enhance nano-scale dispersion during melt mixing of polymer blend and organically modified clay. The materials studied were linear polypropylene and polystyrene reinforced with organophilic montmorillonite clay (nanoclay) at 3-5 wt% loadings. The effectiveness of the proposed ultrasonic processing technique on polypropylene matrix nanocomposites was evaluated by XRD, rheological measurements and thermal properties. We expected enhanced breakup of layered silicate bundle and further reduction in the size of dispersed phase with better homogeneity compared to the different immiscible blend pairs.Also, it was expected that generation of macroradicals in polymer mixture can lead to in-situ copolymer formation by their mutual combination, which should be an efficient path to compatibilize immiscible polymer blends and stabilize their phase morphology in the absence of other chemical agents.
Ultrasonic Assisted Extrusion of HDPE/Clay Nanocomposites
High density polyethylene (HDPE) /clay (Cloisite-20-A) nanocomposites were prepared by using single screw compounding extruder with continuous treatment of ultrasound at different amplitude up to 10?m. The die pressure and power consumption due to ultrasound were measured at different feed rates of materials of various clay concentrations up to 10 wt%. Rheological, mechanical and thermal properties of ultrasonically treated and untreated nanocomposites were studied. X-ray diffraction (XRD) and transmitted electron microscope (TEM) were used to investigate the dispersion of clay and nanocrostructure of composites. The experimental results showed that sonication enhanced the dispersion during melt mixing of HDPE and clay.
Thermal Transitions and Rheology of Propylene-Ethylene-Based Terpolymers
We report on the thermal and the flow characteristics of newly developed propylene-ethylenediene terpolymers. These propylene-rich products were made using single site metallocene catalyst Exxpol™ technology and cover a broad range of chemical composition. The thermal transitions were determined using thermal scanning calorimetry (DSC). The glass transition temperature decreased from about -18 to -28 °C as the ethylene content was increased from 8 to 16 wt%. The crystallinity and the crystallization rate were also strongly affected by the composition. The linear viscoelastic behavior of the different polymers was measured with small amplitude oscillatory shear at various temperatures. The modulus and the viscosity are characteristic of linear polymers and are, for similar molecular weight, independent of chemical composition. The incorporation of un-saturation makes these polymers easily cross-linkable using various chemical or radiation techniques. The crosslinking helps extend their end-use application to elevated temperatures, much higher than their uncrosslinked copolymer counterparts, as demonstrated by dynamic mechanical thermal analysis measurements.
Fundamental Processing Characteristics in Polymer Micro/Nano Molding
Recent advances have created a need to understand processing characteristics, e.g. shear effects and the velocity field, during micro/nano molding. Polymers can be used to study these characteristics in shear thinning and viscoelastic systems. Here, we present results for the processing of non-Newtonian polymeric fluids in micro/nano channels during multi-phase penetrating flow. The dynamics of bubble flow (e.g. bubble shape, amount of coating and the flow field in front of and around the advancing bubble) will be investigated in conjunction with the effects of non-Newtonian rheology on coating.
Soft Thermoplastic Vulcanizates for Long Term Elastic Recovery Applications
Soft Thermoplastic Vulcanizates (soft-TPVs) have been developed for soft touch and elastic recovery applications. These low durometer, 15~30 Shore A materials were compared with soft non-crosslinked styrenic thermoplastic elastomers (TPEs). The mechanical properties, compression set, solvent resistance, rheological properties and dynamic mechanical properties were investigated. It was observed that these soft TPVs have excellent elastic recovery properties at 70°C and 100°C when compared to comparable TPEs. Specifically, long term compression set at 70°C for 1400 hours showed soft-TPVs to be 50% lower than that of similar TPEs. The tensile properties were lower for these soft-TPVs relative to the non-crosslinked TPEs. These “Soft Thermoplastic Vulcanizates” are ideal for applications in which lower compression set, higher elasticity and softness are required.
Analysis of EBeam Irradiated Polyporpylene
Polypropylene (PP) was irradiated with an E Beam with doses of 2.5 Mega Rads (MR), 5 MR, 10 MR, 15 MR, and 20 MR. The un-irradiated and the irradiated material was analyzed using a parallel plate rheometer, capillary rheometer and gel permeation chromatograph (GPC). The objective of this effort was to probe the structural changes in the polymer using aforementioned analytical techniques and determine the utility of the E Beam technique for rheology control. Of interest was the ability to narrow the molecular weight distribution of the material to achieve better process-ability and repeatability. The scope is limited to the results from the previously mentioned analytical techniques. Behavior of the material in actual processes such as injection molding and extrusion is beyond the scope of this study.
The Physical Property Advantages Gained when Alloying/Blending of Polycarbonate with Polymethyl Methacrylate
Blends of Polymethyl Methacrylate and Polycarbonate (20/80 & 50/50) were made. This was accomplished using a Dual TekFlow Processor which has already demonstrated its ability not only to blend and intimately alloy polymers, but also offers the advantage to reduce the viscosity of the new blend by disentanglement. The result is usually a new blend, with properties closer to a theoretical mix, i.e. with a more predictable performance level than what has been possible by more conventional methods of blend preparation. Rheological and thermal testing shows that the blends have very little degradation and about 40% disentanglement, meaning an improved fluidity by 40% when compared to the compounded contribution of the individual components. The 20/80 PC/PMMA blends look white, extremely well dispersed, and could be mistaken, at first glance, with Polypropylene. Injection molded specimens were made for the blends and both virgin resins, which allowed for investigation of their comparative tensile, flexural, impact and thermal properties. Mechanical test results indicate that the properties of the 20/80 PC/PMMA blend are slightly better than the Virgin PMMA, whereas the 50/50 PC/PMMA blend has intermediary properties compared to both resins.
Biobased Nanocomposites from Toughened Bacterial Bioplastic and Titanate Modified Layer Silicate: A Potential Replacement for Reinforced TPO
Biobased ‘green’ nanocomposites are the materials for the 21st century. Polyhydroxybutyrate (PHB) a bacterial bioplastic is recently highlighted because of its renewable resource based origin and its potential to replace/substitute petroleum derived non-biodegradable plastic like polypropylene (PP). The major drawback of PHB is its brittleness. This work investigates toughening mechanisms for PHB via incorporation of elastomeric components. Maleated polybutadiene with high grafting and low molecular weight was identified as the compatibilizer. The toughened PHB was characterized through their thermo-mechanical rheological and morphological analysis. The resulting toughened PHB showed ~440% improvement in impact strength over pure PHB with only 50% loss in modulus. The loss of modulus was recovered to permissible extent through incorporation of titanate modified montmorillonite clay. The hydrophilic clay was modified by titanate-based treatment to make it organophilic and compatible with the polymer matrix. The toughened PHB on reinforcement with 5 wt.% titanate based modified clay gave ~400% improvement in impact properties and 40% reduction in modulus over virgin PHB. The novel toughened bioplastic nanocomposites show potential as a green replacement/substitute of specific TPO for use in structural applications.
Influence of Curing Systems and Irradiation on Woodflour Filled EPDM Compounds
Rheological and mechanical behavior of EPDM rubber filled with woodflour was studied based on blend ratio and curing systems. Irradiation was also studied as an alternative crosslinking method. Results indicate that woodflour accelerates rubber vulcanization. When comparing curing systems, final overall vulcanizates properties did not deteriorate with the efficient system. Concerning irradiation, an optimum dose of 110 kGy was found, since lower doses do not promote crosslinking and higher doses tend to decrease overall properties.
The Dynamic Rheological Behaviors of PP Melt during Pulsatile Extruding Processing
A novel dynamic capillary rheometer (DCR) was designed to investigate the viscoelastic characteristic of polypropylene melt. The pulsatile flow of polymer melt could be got by parallel superposition of oscillation on steady shear flow in this novel DCR. The vibration frequency-dependent behavior of the phase angle and the shear stress vs. shear rate loops can be determined during pulsatile extruding processing. With the increase of the vibration frequency, the elastic characteristic of PP melt becomes more apparent.
Modeling the Interaction of Glass Yarns with Molten Plastic in the Cable Extrusion Process
We present a cable extrusion study that involves flow around a deformable moving fiberglass strand inside a cable extrusion die. In addition to non-Newtonian rheology, the fluid-structure interaction (FSI) between the polymer melt and the moving strand is highly non-linear. Using computational fluid dynamics (CFD), we have gained insight of our extrusion process by studying the strand deflection, the strand speed and the strand tension. The numerical results showed value in guiding the extrusion process.
Effect of Rheology and Die Design on Flow Balancing of Profile Extrusion Dies
A major challenge in profile extrusion die design is flow balancing at the die exit as an unbalanced flow causes distortion of the profile. This is especially true for complicated profile dies with uneven thicknesses in certain sections of the die. In this work, we demonstrate the use of a factorial statistical design of numerical experiments to study the effect of geometrical parameters and polymer shear thinning behavior on the optimum flow balancing of a profile die.
The Effect of Material Selection in Feed-Block Coextrusion of a Three Layer Film
This paper describes a case study dealing with the development of a three-layer product on a feedblock coextrusion system. The problems or phenomena that occurred during the product development experiments are explained via flow simulation and the rheological properties of the materials used. The results of the study are compared with real film samples produced during the development
A Comparative Rheological Study of Isotactic and Syndiotactic Polypropylene Resins with Similar MFI
A comparative rheological study of four pairs of isotactic and syndiotactic polypropylene resins with similar MFI was conducted. The rheological tests included double bore capillary rheometry, frequency sweeps and creep and recovery compliance. It was found that, for similar MFI, the viscoelastic behavior is significantly different between these two types of resins which suggest that stereoregularity has an important effect on the viscoelastic behavior of polypropylene melts.
Rheological, Mechanical and Thermal Behaviour of Radiopaque Filled Polymers
This work studied the effect of three radiopaque fillers (barium sulphate, bismuth trioxide and tungsten metal) on the rheological, mechanical and thermal properties of a range of medical grade polyurethanes and polyvinylchlorides. The results showed significant changes in the melt viscosity, mechanical properties and phase transitions (Tg and log E’) with different filler type.
Chemical Structure Effects on the Performance of TPUs
This work studied the effect of polyurethane chemical structure (i.e. polyester or polyether soft segments) on the rheological, mechanical and thermal properties of four commercial medical grade polyurethanes of similar Shore hardness. The results showed significant differences in melt viscosity, tensile properties and phase transition temperatures (tan ?) with particular polyurethane chemical structure.
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