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SPE Library content related to rheology
Can the Nanoindentor Become a Rheological Tool?
The Nanoindentor is a modern version of the hardness tester designed for metals and ceramics. Recently, it has been proposed as a technique to measure rheological properties of soft time-dependant polymeric materials. This technique offers the promise of micron scale spatially resolved rheological information. Additionally, the theoretical foundation and historical development of the working equations for nanoindentation and traditional rheological instrumentation will be presented and discussed. The major difference between nanoindentation and the more classical rheological instrumentation is in the treatment of the instrument-sample interface. To illustrate how the treatment of the instrument-sample interface affects the data a series of measurements was preformed on poly(methyl methacrylate), (PMMA), and poly(dimethyl siloxane) (PDMS) samples.
Development of Lubricious Compound for Biomedical Applications Using Hydrophilic Polymers
An attempt was made to develop blends having self-lubricating properties. The approach was to melt blend various base polymers used in the medical industry with hydrophilic polymers known to impart lubricity when applied on the surface as coatings.Different base polymers used were nylon based elastomers and nylons. Hydrophilic polymers used were polyethyl oxazoline and polyvinyl pyrrolidone.These polymers were melt-blended at concentrations of 25% and 50% using a twin-screw extruder. Rheology, coefficient of friction and mechanical properties were studied.
Extrusion Foaming Behavior of PBT Resins
An investigation of the foaming behavior of polybutylene terephthalate (PBT) resins in extrusion was performed. Commercial grades of PBT with different molecular weights and rheological characteristics were chosen. PBT’s with a high temperature chemical blowing agent were extruded under different material and operational conditions (e.g. amount of blowing agent, set temperature at the die, screw rpm, etc.) to allow the understanding of the effects of those conditions on product characteristics. The foamed extrudates were analyzed for density, morphology, and crystallinity. It is shown that the foaming behavior and the foam quality of PBT are functions of the characteristic properties of the resins including rheological and crystallization behavior.
Rheology of Heat-Induced Gelation of Chitosan Solutions
Heat-induced gelation was observed above 80°C on a chitosan solution neutralized with a weak base, ? - glycerophosphate. Urea, a hydrogen bonding decomposing agent, was also used in some of these solutions to investigate the presence of hydrogen bonds in the resulting gels. The solution behaviour and gelation process were investigated using linear viscoelasticity.In solution state, the addition of urea decreased the rheological properties due to the reduction of hydrogen bonding interactions. During the gelation tests, the evolution of the storage and loss moduli was monitored as a function of temperature. Heating resulted in sol-gel transition at a critical temperature, the so-called gelation temperature Tgel. It was found that adding urea decreased the resulting gel strength and increased Tgel, corresponding to the retardation of the gelation process. These results indicate that hydrogen bonding is an important parameter in the chitosan physical gels formed, even at high temperature, which is not the usual belief. In parallel, pH and conductivity measurements revealed that gelation was also caused by polymer-polymer hydrophobic associations enhanced at high temperature, due to increased ionic strength.
New Developments in Micro-Compounding of Polymeric Materials
This paper presents the most recent development in microscale compounding technology in material science. The equipment consists of a 6-inch conical twin-screw extruder co- and counter-rotating and housed in a vertical clamp shell barrel, which can be operated in batch and continuous modes. The design and versatility of this equipment allows the evaluation of a myriad of materials ranging from polymer blends to filled systems and Nano-composites with 5 to 15 grams of sample. It is also possible to monitor changes in the rheological properties of the materials during processing allowing a better assessment of mechanisms such as polymer degradation and stability, reactive extrusion and crosslinking. Comparative analysis with other processing equipment such as mixing bowl and twin screw extruders on model systems and in terms of extent of dispersion and mixing is achieved.
Foaming of Nanoclay Reinforced PS/PMMA Polymer Blends
Nanoclay reinforced polymer blends exhibit high potential as a new material for CO2 foaming because they can provide higher CO2 solubility, lower gas diffusivity, and better mechanical properties than foams made of homopolymers. In this paper, a polystyrene (PS)/poly(methyl methacrylate) (PMMA)/nanoclay blend was selected to study the relationship among blend morphology, nanoparticle distribution, and foam structure. PMMA serves as the dispersed domain in PS. Blends with different morphology were obtained by changing the nanoclay content and the screw configuration, which were then foamed by using CO2 in a batch system. Effects of nanoclay content on the blendmorphology, rheological properties, and foam morphology were studied. It is found that the highest foam nucleation efficiency appears at the interface of PS/PMMA/nanoclay.
Removing the Mystery from Rotomoulding: New Insights into the Physiochemical Processes Involved Leading to Improved Quality Control
This paper presents a first report from a longterm collaborative programme between Matrix Polymers Limited and the Manchester Metropolitan University. The purpose of the programme is to examine physiochemical mechanisms of the rotational moulding process using a variety of analytical techniques.The effect on the performance of polyethylene (PE) caused by variation of the rotomoulding cooking cycle is investigated using a combination of infrared spectroscopy and melt rheology. Analytical results are correlated with large scale performance characteristics, measured by established industrial assessment techniques such as low temperature impact strength, brittleness, part density development and yellowness index.
Analyze Rheology of Polymer Thin Film by Nano-Rheometrics Simulation
This study has built up a nano-rheometrics simulation system to investigate the viscoelastic properties of polymer thin film. Experimental studies and traditional continuum mechanics are difficult to describe some critical nano-effects. By taking advantages of molecular dynamics simulation and the definitions of continuum mechanics, we could effectively analyze viscoelastic properties (i.e. viscosity, stress, elastic and viscous moduli…) on different condition in nano-scale. This proposed system includes a polymeric fluid modeled with the shifted Lennard-Jones potential, while the polymer bond stretching/bending/torsion is modeled with Hook-like model. All simulation results are in a good qualitative agreement with similar experiment.
Flame Retardant Polypropylene
To improve the fire retardant properties of polypropylene (PP), it was compounded with aluminum hydroxide (ATH) using two different compounding lines, a twin screw extruder and a co-kneader. Flame retardant, rheological and mechanical tests were performed. The effects of processing machines and process parameters on the properties of the compounds were investigated. The influence of the properties of filler and matrix material was also examined.To minimize the content of additives without loss of the flame retardant properties, modified layered silicates (Nanofil, Suedchemie) were dispersed within PP/ATH compounds and their influence on the processing and compound properties was studied.The present investigation demonstrates the possibility to use a polypropylene as matrix material for halogen free cable compounds.
Optimization of the Properties of Polymethylmethacrylate Nanocomposites for Optical Applications
Transparent plastics like polymethylmethacrylate are widely used for optical components. Some disadvantages of plastic components like low hardness and abrasion resistance may be optimized through the modification with nanomaterials. The application of nanoparticles in polymers can also increase its refractive index and thereby broaden the fields of application of optical components.Polymethylmethacrylate nanocomposites with different nanomaterials were prepared by melt extrusion. The distribution of nanoparticles in the polymer matrix and optical properties of nanocomposites were optimized by means of modifying the surface of the nanoparticles and by varying the process parameters. The influence of the particle type and content on the mechanical and rheological properties was studied.
Mono- and Multi-Layer Tubing Incorporating a Silver Based Antimicrobial
The occurrence of device related infection is a common and problematic issue in the medical healthcare industry. This paper examines the effect of antimicrobial content on the rheological, mechanical and bactericidal properties of a range of mono- and multi – layer medical tubing products. The incorporation of antimicrobial masterbatch was shown to have negligible effect on rheological and processing properties of the materials tested. Mechanical properties were altered to some extent, but more importantly the antimicrobial efficacy of all the tubing samples was shown to be acceptable.
Thermal and Rheological Evaluation of Pharmaceutical Excipients for Hot Melt Extrusion
Hot melt extrusion (HME) technology is becoming more broadly practiced in the Pharmaceutical industry. It offers many advantages over alternative pharmaceutical processing technologies such as wet granulation, solution casting, etc. A thorough understanding of the thermal and rheological properties of the polymeric excipients used is an important consideration during the selection of the excipient and processing conditions. The purpose of this paper is to report an experimental study that characterizes the thermal and rheological properties of hydroxypropyl cellulose (HPMC), ethylcellulose (EC), and polyethylene oxide (PEO). Thermal characterization was performed via DSC and TGA to identify transition (Tg/Tm) and degradation temperatures. Rheological performance was characterized by torque rheometry on a batch mixer and on a slit-die rheometer supplied by a single-screw extruder.
Rheological Studies of Polymers under High Pressure Carbon Dioxide
The viscosities of carbon dioxide-impregnated polymers in the literature are currently limited to high shear rates using capillary or extrusion rheometers. This paper uses a rotational rheometer to report data on the zero-shear viscosity of carbon dioxide-saturated polymers. The viscosity drop of a polybutene oil is one and half orders of magnitude at 35°C and 6 MPa, while the zero-shear viscosity of poly(dimethylsiloxane) (PDMS) drops half of an order of magnitude at 30°C and 3 MPa. Efforts are ongoing to measure the CO2- plasticized viscosity of polystyrene melt.
A Magnetorheological Study of Multi-Walled Carbon Nanotube Dispersions
The magnetorheological properties of multi-walled carbon nanotube (MWCNT)/mineral oil dispersions were studied using a parallel plate rheometer. 0.5, 1.5 and 2.53 vol% nanotubes dispersions were investigated. Strain sweep, frequency sweep, magneto sweep and steady shear test were conducted in various magnetic fields. Storage modulus G', loss modulus G complex viscosity ?* and dynamic yield stress ?y increased with increasing magnetic field strength which was partially attributed to the increasing degree of alignment of nanotubes in a stronger magnetic field. The G' and G" of MWCNT/mineral oil dispersions were scaled with nanotube volume fraction ? by a power-law. The shear thinning behavior of MWCNT/mo dispersions followed the Ostwald-de Waele or power law."
Foaming Polystyrene with a Mixture of CO2 and Ethanol
Use of mixtures of blowing agents in thermoplastic foam extrusion has been an industrial practice for a long time. However it has gained renewed interest in the past few years due to the introduction of difficult-to-process alternative gases, targeted as potential replacement for the banned ozone-depleting blowing agents. Reasons for blending physical foaming agents (PFA) are numerous. The incentives may be economical, environmental or technical. With respect to that latter factor, blending suitable PFA’s is often regarded as providing a better control of processing conditions. For example, a specific PFA could be selected for its inflation performance and blended with other co-blowing agents chosen for their stabilizing role. Although considerable amount of work has been done in that area, very little information has been disclosed in open literature.Carbon dioxide (CO2) has been reported as an interesting candidate for low-density polystyrene (PS) foaming, although the required concentrations are associated with high processing pressure due to the low solubility of the gas. Thus stable processing conditions are difficult to achieve. This work studies the effect of blending CO2 with ethanol (EtOH) as a co-blowing agent for PS foaming. Extrusion foaming performance of this mixture will be discussed, with respect to its solubility (i.e. degassing conditions) and rheological behavior. The function of each blowing agent during the process will be analyzed with respect to the plasticization, nucleation, expansion and stabilization phases. Attention will also be paid to the interaction involving the two PFA components.
Novel Green Nanocomposites from Toughened Polyhydroxyalkanoate and Titanate Modified Montmorillonite Clay
The environmental regulations, societal concerns, and a growing environmental awareness have triggered the search for new products and processes that are compatible with the environment. Polyhydroxybutyrate (PHB) is a biodegradable polymer that has created significant interest recently because of its renewable resource-based origin. PHB shows susceptibility to fracture when subjected to high rates of deformation. This work investigates toughening mechanisms for PHB via incorporation of functionalizede lastomeric components into the PHB matrix. A compatibilizer was investigated to improve the interfacial adhesion between the incompatible elastomer and plastic phases. The toughened PHB was characterized through their thermo-mechanical, rheological and morphological analysis. The resulting toughened PHB showed more than5 times improvement in impact strength over virgin PHB with around 60 % 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. Nanocomposites with this modified clay exhibited more than 275% improvement in impact properties with around 40% reduction in modulus in comparison with the virgin PHB bioplastic.
Comparision of Measurement Techniques and Methods to Evaluate Irradiated Polymers
Electron Beam irradiated high density polyethylene (HDPE) and ethylene tetra fluoro ethylene (ETFE) was studied using dynamic rheology. The objective of this work was to compare and critique different modes and methods of dynamic mechanical testing, determine the best method or test to characterize the structural changes, and verify the governing phenomenon for structural changes in irradiated injection molded HDPE and ETFE. The predominant response to radiation in HDPE and ETFE is that of cross-linking. The tests were conducted in tension, bending, and shear.This study is limited to comparing the response of electron beam irradiated materials to the aforementioned tests. Effects of radiation levels and aging are beyond the scope of this work.It was found that dynamic shear testing at temperatures above the melting point of the materials is the best mode and method to finger print the structural changes in radiated HDPE and ETFE. The flexure test modulus results were higher than that from the tensile test.
Thermal and Rheological Characterization of Feedstocks for Powder Injection Molding
The rheological and thermal behavior of a powder injection molding feedstock (highly filled polymer blend) was studied using rheometry, and thermal techniques. The feedstocks were prepared using two mixing schemes. In the first scheme, an internal mixer and a twin-screw extruder were used. In the second scheme the blends were prepared in a laboratory internal mixer. The filler material was stainless steel and its content in the samples is above 90 % by weight. The rheological behavior of the feedstock was studied in dynamic mode. The techniques used and the results obtained are presented.
Synthesis and Characterization of Polypropylene Nanocomposite Fibers
Nanocomposite fibers were produced by the melt spinning of a polypropylene/organoclay compound, maleated with maleic anhydride functionalised propylene oligomers. XRD and TEM analyses showed that the organoclay exfoliation associated with property improvement was enhanced significantly by the elongational melt deformation during the melt spinning process. SEM and FTIR results revealed the preservation of a homogeneous monodispersed phase in the nanocomposite fibers. In addition, there was an overall improvement in the mechanical properties, including tenacity, when the organoclay were optimally delaminated. Rheological analysis and polarizing optical microscopy study showed a significant enhancement in the melt spinability and optical birefringence of the nanocomposites. The DMA results suggested the fiber matrix was simultaneously reinforced and plasticized by the exfoliated organoclay layers. A simple model was also proposed to illustrate the organoclay exfoliation mechanism during the melt spinning process.
Soft TPO Formulations Containing Specialty Propylene Elastomers
Vistamaxx™ polymers are Specialty Propylene Elastomers (SPE) 1 containing isotactic propylene crystallinity. The presence of the iPP crystallinity renders these polymers very compatible with polypropylene (PP). When these polymers are blended with PP, the flexural modulus of the composition is substantially reduced at low weight fraction of SPE. This paper describes the physical, rheological and morphological characteristics of SPE/PP blends, comprising SPE resins of varying MFR and crystallinity. The SPE composition in blends with a 3 MFR PP homopolymer is varied from 20 wt. % to 90 wt. The performance data is analyzed using regression models, correlating the blend properties with SPE and PP type and content in the formulation. Our results indicate that the SPE type, particularly crystallinity, has a strong influence on the physical properties of the blend formulations.
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ANTEC 2016 - Indianapolis, Indiana, USA May 23-25, 2016. [On-line].
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