The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
The National Institute of Standards and Technology (NIST) develops Standard Reference Materials® for calibration, quality assurance and for research into improved measurements. Two fluid standards are being developed to exhibit shear thinning and normal stresses typical of polymeric fluids. SRM 2490 is a solution of polyisobutylene dissolved in 2,6,10,14-tetramethylpenta-decane. SRM 2491 will be a poly(dimethylsiloxane) melt, giving less temperature dependence than SRM 2490. NIST will certify the shear-rate dependence of the viscosity and first normal stress difference at 0 °C, 25 °C and 50 °C, and the linear viscoelastic behavior over the same temperature range. A round robin with the fluids will investigate variability in rheological measurements.
This paper reports the results of an investigation of the effects of purity level and nature of impurities on the properties of recycled polycarbonate and recycled acrylonitrile-butadiene-styrene polymers blended with the corresponding virgin resins. The relevant thermal, mechanical and flow properties were measured. It is concluded that properties of recycled polymers depend not only on the amount of impurity present but also on the kind of impurities and contaminants that are present. The latter factor even plays an important part in relation to compatibility of polymers. However, polymer melt rheology seems less sensitive to impurities than some mechanical properties such as impact strength. More than 99% purity is needed for recycling these polymers back into their original, high-value applications.
In order to find the right combination of material properties and processing conditions (blow moldability) for the production of a molded part that has a set of predetermined final properties, it is necessary to characterise the material behaviour under the actual processing conditions. Relating this to the rheological properties (under controlled experimental conditions) of the material, it is possible to design the molecular characteristics of the material in such a way as to attain the desired processing characteristics. This paper presents the results of a study examining the relationships between some basic rheological properties and the key processing material behavior parameters (swell and sag) governing the blow molding process. The technique has been applied to the intermittent extrusion of three HDPE LPBM resins manufactured using three different catalyst and process technologies.
It is well known that secondary flow will occur in the stagnant area near the die entrance of an extrusion die. The secondary flow may produce large-scale waviness on the extrudate surface if it propagates into the die land. For polymers that exhibit well-defined stick-slip transitions, propagation of the entry flow into the die is usually facilitated by slip flow. In this paper we show how the entry flow can quicken the sharkskin dynamics while only having a subtle effect on the rheology. This phenomenon is observed first hand using a flow birefringence technique. It is also shown how the effect of the die entry angle changes the slip behavior.
Several sizes of calcium carbonate were investigated because of their extensive use in the polymer industry as fillers. The investigation focused on developing an analytical tool which would lead to understanding and predicting the flow characteristics of slurries which have a Newtonian continuous phase but have high enough filler concentration to exhibit shear thinning or power law characteristics. We focus on concentrations where the initial yield behavior in not dominant A new function was found which linearly correlates the power law constant, n, to the concentration of the filler. The behavior of this function suggests that the Newtonian to Power-law behavior may be dominated by percolation processes.
During the extrusion of pigmented blown film products, film quality can sometimes be affected by inadequate pigment dispersion and in some cases excessive melt build-up around the die lips during extended production runs. These problems are particularly evident during the extrusion of white (TiO2) pigmented films. The rheological characteristics of a range of commercially available titanium dioxide based masterbatches, with different polyethylene carrier polymer melt flow indices, were investigated using a dual capillary rheometer over the temperature range of 190°C to 230°C. Scanning electron microscope studies were performed on the individual masterbatches to determine pigment particle size and the degree of pigment agglomeration. Blown film extrusion trials, using a Killion blown film line, were carried out to determine film quality. The results showed that the masterbatches containing relatively large individual particle size caused more difficulties during film extrusion. Rheological analysis showed that the pigment masterbatch with the higher shear viscosities gave improved pigment dispersion in the film, and improved agglomerate breakdown during the extrusion process.
Rheological tests measure melt-state polymer flow, delineating molecular structure and predicting extrudability. Rheology of compounds used in fiber optic (FO) cable jackets and in the conduits that contain such cables will be our focus. Polyolefin-based jackets strengthen the FO cable and protect internal components, while the conduit provides long-term strength and protects the cables against environmental stresses. High density polyethylene use in these applications is growing rapidly, spurred by FO cable growth. Important properties in both applications include melt-state processability, stress crack resistance and solid-state stiffness. Melt rheology directly influences processability, combining with crystallization behavior to dictate final solid-state properties.
Polyamide 6 (PA-6) homopolymer and copolymers have been chain extended from a low molecular weight feedstock into high molecular weight, high melt viscosity nylon products via a reactive extrusion process using a novel chain extender viz., triscaprolactamyl phosphite (TCP). The chain extension process involves an 'activated' polycondensation reaction between the endgroups of the nylon. In this paper we will discuss the effect of the chain extender concentration and the extruder process conditions on the chain extension efficiency with respect to molecular weight and rheological property benefits achieved.
Mechanical performance of polymers improves with molecular weight (MW). Unfortunately, melt viscosity and thus lack of processability also increases with MW. Recently, a method to temporarily reduce the melt viscosity without changing MW has been proposed . The method uses processing windows such that shear oscillation superposed on extensional flow at gradually increasing shear thinning amplitude are created by imposing conditions of strain, frequency and temperature that bring the melt (G'/G*) close to 0.75-0.85. The purpose of the present communication is to report results of a two-year research and development effort aimed at reducing the viscosity of several commercial resins using a pilot stage disentanglement machinery. The paper explores the commercial implications and answers the following questions: is it possible to shear-disentangle a large quantity of commercial resin at fast throughput, is it possible to process the disentangled melt before it regains its normal entanglement, and is it possible to speed-up the re-entanglement process after forming to regain mechanical benefits? From a laboratory and low throughput extrusion scale, the answer to all these questions is positive. The technology is presently being tested at a pilot pre-production scale to quantify the answers from a commercial perspective.
The TPO (Polypropylene/Elastomer) market for injection molded automotive bumper fascia is driven by cost reduction, a balance of physical properties, ease of processability, and desirable aesthetics. Global volume for this application was approximately 740 MM lbs. in 1999, nearly half of which is electrostatically painted. Decreased application costs, increased productivity, and reduced environmental emissions can be realized through system optimization. This report describes the rheological and morphological phenomena governing the development of a conductive TPO (CTPO) for enhanced electrostatic painting.
The rheological characteristics of a range of pigmented polypropylene (iPP) was investigated using dual capillary rheometry techniques, over the temperature range 190°C to 230°C and shear rate range of 10s-1 to 800s-1. The iPP was compounded with pigment masterbatch concentrations ranging from 0.2% to 3.0%, using a 38mm Killion compounding line. The pigment masterbatches investigated were iron oxide, titanium dioxide and phthalocyanine blue. The rheological data, showed that there were considerable increases in apparent viscosity of pigmented iPP even at relatively low pigment loadings. The increase in apparent viscosity was particularly evident over the lower shear rate range. Activation energies (Ea) calculated from the rheological data showed large increases in Ea for pigmented iPP especially at lower shear rates, suggesting crystallization of the iPP melt.
Blends of ethylene-octene copolymer (EOC), Engage 8150, with Polypropylene (PP) were prepared using a Killion compounding extruder. The blends studied were in the range 1% - 30% EOC content. Rheological analysis of the various blends showed only slight increases in apparent viscosity with increasing EOC content. Mechanical analysis on injection moulded samples of these blends showed that tensile modulus and flexural modulus decreased and impact properties were improved significantly with increasing EOC content, especially at higher EOC concentrations. Dynamic mechanical thermal analysis (DMTA), and Differential Scanning Calorimetry analysis (DSC) would tend to indicate some degree of polymer miscibility especially at the higher EOC concentrations, with slight decreases in crystallinity and phase transition temperatures being recorded especially for the higher EOC concentrations.
This present work investigates the rheological properties and the effect of immersion in standard automotive fluids (an extension of SAE J2027) on the mechanical performance of a range of Nylons, Polypropylene Oxide/Polyamide (PPO/PA), and Polyetherimide (PEI). The rheological characteristics of Nylon 4.6., PPO/PA and PEI were investigated and the results showed significant decrease in shear viscosity at dwell times in excess of three minutes for Nylon 4.6. and PPO/PA. Injection moulded samples of the Nylon 4.6., impact modified Nylon 4.6., Nylon 12, PPO/PA and PEI were immersed in the standard automotive test fluids, Fuel C, zinc chloride solution and aggressive water. Subsequent mechanical analysis of the various specimens showed only slight decrease in the tensile modulus of the Nylon 4.6. after immersion in Fuel C, however significant weight gain and deterioration in tensile modulus were recorded after immersion in aggressive water. Dynamic Mechanical Thermal Analysis on the Nylon 4.6 showed only slight decrease in storage modulus (Log E') and Tg, after immersion in Fuel C. However a significant decrease in Tg by up to 80°C was recorded for samples immersed in aggressive water.
In this paper the linear viscoelastic properties of polypropylene (PP)/high-density polyethylene (HDPE) immiscible blends were measured as a function of frequency for different blend composition and temperatures. The morphology of the blends was studied by Scanning Electron Microscopy. The interfacial tension between the components of the blends was evaluated using small amplitude oscillatory shear analysis. The results seem to indicate that there is a range of compositions for which it is possible to use Gramespacher and Meissner analysis in order to calculate interfacial tension between polymers using small amplitude oscillatory shear measurements.
Reactive and non-reactive blends of polyamide 6 (PA6) with different styrenic based polymers [acrylonitrile-butadiene-styrene terpolymer (ABS) and styrene-acrylonitrile copolymer (SAN)] were made on a twin screw extruder under similar processing conditions and blend composition. Effect of reactive compatibilizer on thermal, morphological and rheological properties were studied using DSC, SEM and a parallel plate oscillation rheometer. It was found that the reactive blends have lower crystallization rate and nucleation ability but higher melt viscosity with co-continuous morphology, whereas the uncompatibilized blends have higher crystallization rate and nucleation ability but lower melt viscosity and form disperse and/or coarse co-continuous morphology.
Powder Injection Molding (PIM) is a manufacturing technology for the mass production of small and complex metal or ceramic parts. PIM is composed of mixing, injection molding, debinding and sintering processes. We have developed a numerical simulation program for the injection molding process of PIM parts, PIMflow, taking account of the peculiar rheological behavior of powder/binder mixture, most notably the apparent slip phenomena at the mold wall. The coupled analysis between the filling, packing and cooling stages was performed because the viscosity and slip phenomena of powder/binder mixture highly depend on temperature. Using the example of electronic package, this paper demonstrates the importance of this issue.
The addition of reinforcing fibres, or fillers, to liquid thermosets significantly alters the rheological behaviour of such resins, drastically increasing viscosity. In order to successfully mould these materials a good understanding of their rheological behaviour is required. A simple numerical model is developed, predicting evolution of the resin cure reaction, and resulting in-mould rheological, and flow behaviour. Qualitative comparisons are made to initial moulding experiments completed with neat, and wood fibre filled polyester resins. Moderate additions of fibre were found to improve part quality due to the increase in initial viscosity, while a practical limit was reached above which excessive fibre clustering occurred.
Polypropylene/clay nanocomposites have been prepared with a variety of hybrid structures by melt mixing a fixed amount of organically modified clay, different levels of a maleated polypropylene and polypropylene. The structure has been investigated with X-Ray diffraction and transmission electron microscopy. An optimum level of maleated polypropylene is found to yield the greatest degree of exfoliation in polypropylene. The relative viscosity curves reveal a systematic trend with the extent of exfoliation and show promise for quantifying the hybrid structure of the nanocomposites.
Multi-cavity hot runner injection molds have historically had problems with unbalanced and/or unrepeatable filling patterns sometimes related to thermal variations in the manifold which can typically result in a number of processing issues. Typically, if a scientific approach to identifying optimal filling patterns is utilized, the overall performance of a multi-cavity hot runner tool can be improved. Scientific processing techniques in addition to cavity pressure transducers can be an advantageous approach to identifying optimal filling patterns and any variations that may exist in these types of injection molds. The purpose of this study is to identify the effect of cavity pressure transducers on the overall performance of a 32- cavity hot runner injection mold. Typical scientific processing techniques such as short shot studies and on-machine rheology curves were used as the foundation of the study. Once the preliminary molding conditions were identified and the cavity pressure transducers strategically placed, a design of experiments (DOE) was conducted to determine the effects of varying process conditions (injection velocity, hold pressure, and hold time) on specific cavity pressures in the 32-cavity hot runner injection mold. The short shot study provided an idea of the mold filling imbalances and allowed for the cavity pressure transducers to be strategically placed, an end of fill transducer in each quadrant of the mold. The results showed that an injection velocity ranging from 35 to 95% resulted in adequate material viscosities during the fill stage. The DOE indicated that injection velocity and hold pressure had the most significant effect on the cycle integrals. Also, the hold time tended to have a significant effect on the cycle integral when increased from 1 to 3 seconds. Additionally, increased injection velocity tended to increase flash and decrease warpage.
An investigation of the transient, steady and dynamic flow properties of the thermotropic liquid crystalline polymer Vectra A950 (Ticona) is presented. The steady viscosity curve shows the typical three-region flow curve of LCPs. In the transient shear experiments, the shear stress grows during the start-up of constant shear rate flow and goes through a maximum at approximately ?=2. Dynamic mechanical experiments show the existence of a linear viscoelastic region at small strains, and that the onset of nonlinearity varies with frequency. In the linear viscoelastic region, the storage and loss modulus, G'(?) and G(?) do not display the typical dependence on ?2 and ? respectively. The results obtained for a frequency sweep using constant strain and constant stress instruments are qualitatively different."
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ANTEC 2016 - Indianapolis, Indiana, USA May 23-25, 2016. [On-line].
Society of Plastics Engineers
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