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A range of powdered ethyl vinyl acetate (EVA) copolymers and polyvinyl chloride (PVC) formulations were compounded at PVC:EVA ratios 100:0, 60:40, 50:50, 40:60 and 0:100 respectively. Two grades of EVA with 20% and 27% vinyl acetate (VAc) (EVA I and EVA II) and two grades of PVC with K-values 56 and 71 (PVC I and PVC II) were used in the investigation. Mechanical analysis was performed on injection moulded samples of these blends and the results showed that the tensile and flexural modulus decreased significantly with increasing EVA concentration. Rheological analysis was performed using dual capillary rheometry and the results showed only slight changes in shear viscosity with increasing EVA content even at lower shear rates. Dynamic mechanical thermal analysis showed partial miscibility of the PVC and EVA over the range of concentrations studied.
Rheological studies were performed on polymer blends of different grades of commercial ethlene-octene copolymers (EOCs) and polypropylene (PP). The oscillatory flow properties of EOC, PP and EOCs/PP blends were analysed using a Rheometrics Dynamic Stress rheometer, SR 200. The results showed that the systems with different grades of elastomers presented different rheological behaviors. This fact probably is related to the differences in molecular weight and long chain branch present in the copolymers.
The objective of this work is to measure the rheological properties of some engineering polyesters based in terephthalates. These polyesters were poly(ethylene terephthalate)(PET), poly(trimethyl terephthalate)(PTT) and poly(butylene terephthalate)(PBT). Materials behaviors in steady, oscillatory and transient flows were studied at different temperatures from 250 to 310°C. Cone-plate and capillary rheometry were used to measure the rheological properties. No significant variation of the power law index was observed when the temperature was increased for the PET and PBT. The relaxation spectrum of the polymers did not show any significant variation for the PET and PBT, but for the PTT a small variation was observed. PET had the highest elasticity in all the experiments, as shown by the normal force (shear), the storage moduli (oscillatory), the elastic recovering (creep) and the stress overshot. PBT was the most sensitive to degradation at the tests conditions, due its longer aliphatic sequence in the chain. This sensibility was the main experimental obstacle to perform reliable measurements.
The rheological behavior of a material is important when mixing, melting, extruding, pumping, pressing, etc... Rheology is used to predict a material's response to differing modes of flow and deformation at any point from the processing step through its final end use. In the pressure sensitive adhesive (PSA) field, three terms are generally used to describe its performance: Shear Resistance, Tack and Peel Strength. These properties are directly related to the PSA's response to the application of stress and therefore its rheological behavior.The property of tack describes the ability of a PSA to spontaneously form a bond to another material under light pressures within a short application time. As the contact time increases, higher shear resistance and peel strength properties are found, related to a materials long time flow behavior. It is found that a single rheological test is able to directly determine the response of a PSA to varying deformation times, related directly to its shear resistance, tack and peel strength behavior.
The rheological behavior of blends of PMMA and epoxy is investigated. Time-temperature and time-concentration superposition is found to be valid in all cases as long as a homogenous solution is present. During curing of these blends phase separation occurs so that superposability is lost. As soon as the thermoset-rich phase gelates it dominates the mechanical behavior because of the co-continuous morphology, which is obtained with a 50/50 blend composition. The incorporation of reactive solvents in thermoplastic polymers leads to a dramatic reduction of viscosity until phase separation sets in. This makes such blends interesting systems for low-pressure processing for electronic applications.
The rheological properties of HDPE-maple wood composite resins were studied. The blends studied ranged from 0% (pure HDPE) - 50% 40-mesh size maple wood flour. Shear viscosity measurements and Bagley entrance corrections were performed in a capillary rheometer. It was found that the wood composite resins displayed yield stress behaviour especially at high percentages of wood content. Attempts were made to measure the yield stress using steady shear experiments in a rotational rheometer. Preliminary studies were also done on the extrusion parameters such as melting profiles, pressure profiles and outputs for the virgin HDPE and 50% HDPE-wood resins. Two Brampton Engineering single-stage compression screws with two compression ratios, 2 and 3.8, were used.
The effects of plasticizing acrylic copolymers, in particular a 90% (molar) polyacrylonitrile/ 10% (molar) methyl acrylate (PAN/MA) copolymer, with carbon dioxide (CO2) are studied. Differential scanning calorimetry (DSC) is used to evaluate the resulting shift in the glass transition temperature (Tg) following plasticization. Pressurized capillary rheometry is used to evaluate the melt rheology prior to and after plasticization. Dynamic and steady shear rheology data are used to evaluate the thermal stability of the copolymer. An estimated 20°C decrease in processing temperature can be obtained upon CO2 plasticization, which slows the kinetics of the copolymer degradation (crosslinking).
The transient, dynamic, steady shear and extensional properties of molten TLCPs (Vectra A950 and V300P) have been reported. The domain structure in quiescent and shearing conditions has been characterized by using a polishing technique and shearing/hot stage equipment. The steady state viscosity values of the TLCPs form the three-region flow curve at typical processing conditions, with an initial shear-thinning region, a plateau region, and a terminal shear-thinning region. The effective extensional viscosity of Vectra A950 is much higher than the steady shear viscosity and decreases with increasing extension rate (1 to 10 1/s). The trends of the dynamic moduli are different from those found in flexible-chain polymers, i.e., G' and G do not scale as ?2 and ?. A negative first normal stress difference N1 was found at low shear rates. A polydomain structure was found for the TLCPs with a domain size of ~ 10?m under quiescent condition. Under steady shearing at 10 1/s the domains first break up into smaller sizes and then coalesce."
Most engineering polymers are toughened by impact modifiers/rubbers and it is known that some inorganic fillers have to be used to enhance the toughness-stiffness balance. Recently, it is reported that toughness-stiffness balance of high-density polyethylene can be enhanced by blending with rigid particles such as calcium carbonate. The objective of this work is to examine the rigid toughening concept and its applications in polyolefins. The toughness stiffness balance of several HDPE/CaCO3 and PP/CaCO3 blends and the rigid toughening mechanisms in these systems are discussed.
Understanding the fatigue crack propagation (FCP) resistance of materials is of great importance because most materials exhibit crack growth below critical fracture loads under cyclic loading conditions. In this study, the FCP behavior of glass-filled epoxy composites was characterized using linear elastic fracture mechanics. The role of adhesion promoters in FCP behavior was determined by treating the glass fillers with silane-based adhesion promoters. Special attention was paid to the effect of moisture on FCP behavior. Epoxy composites reinforced with glass spheres showed improved resistance to FCP as compared to neat epoxy. FCP behavior was dependent on the type of the adhesion promoters used, especially in moisture treated specimens. Scanning electron microscope (SEM) studies revealed that the differences in FCP behavior was attributable to different toughening mechanisms present which in turn, depended on the type of adhesion promoter used.
While experience is a valuable asset, a novice failure analyst can solve even complicated plastics failures using a logical approach and utilizing the most appropriate analytical and test methods. By including old as well as state-of-the-art new methods, the test results often point right to the cause of failure. The eye, by itself, and with moderate magnification early in the investigation can provide information which helps point the way to solving the problem. Observations and test results are assessed as to which of the three major factors in plastics performance are involved - design, material, processing or combinations thereof.
Simulation and computer aided analysis of the injection moulded process is known to many, but rarely employed. Computer Aided Engineering (CAE) affords the opportunity to reduce costs.This is a case study of the rectification of the inconsistent surface finish concern involving rear mudguards used in automotive applications. The cause of the problem was difficult to diagnose accurately, and attempts to remove the problem by speculation guided by experience failed. CAE software was used as an instrument, to diagnose the cause of the problem via process simulation and analyses of the results. The information obtained was then applied to provide recommendations, which not only solved the problem but also improved the molding process. By showing the benefits CAE added to the final product design and process, it was concluded that process simulation and computer aided analysis is too important a tool for saving time, material, human resources, and consequently money, to remain under utilized.
The present research aims at examining the rotational molding characteristics of metallocene catalyzed Polyolefin Plastomers (POPs) and Thermoplastic Olefins (TPOs). The latter are blends of polypropylene with POPs. The rheological and thermal properties of two grades of POPs and a TPO in powder and micropellet form have been tested and their processability has been assessed by conducting sintering and rotomolding studies. Depending on their formulation, POPs can be successfully rotomolded and excellent properties can be obtained. Rotomoldable TPO resins should have low zero shear viscosity and low melt elasticity.
To date, powdered resins remain the main form of raw material used in the rotational moulding industry. However, in recent years interest has grown in the use of reactive liquid polymers as alternative materials. Reactive liquid systems offer the potential of engineering polymers which have previously proved difficult to rotomould in the powdered form, as well as significant reductions in cycle time. This paper investigates the potential of Dicyclopentadiene as a rotomoulding material. Rheological analysis and uniaxial moulding techniques, which have been used to develop a suitable material formulation for use in the rotational moulding process, are described.
Recent work in layered silicate nanocomposites has focused on the exfoliated morphology wherein the clay platelets are homogenously dispersed within the matrix polymer with no registry between silicates. The intercalated morphology, however, wherein individual platelets retain strong registry, is thought to have the potential for properties unavailable to the exfoliated morphology, including flame retardance, fracture toughness and true polymer-ceramic behavior. Routes to the manufacture of such hierarchical laminates and their potential property enhancements are discussed.
The impact of particle size, size distribution, and silica loading on film properties of UV-cured hybrid organic-inorganic thin composites was investigated in this work. Commercial silica organols of hexanediol diacrylate monomer (HDDA) containing high concentration of monodisperse silica nanospheres (13, 25 and 50 nanometers) were cured with a polyester tetraacrylate (PEA) to give transparent nanocomposites. Silica loading can be as high as 40% silica. The composite coatings can be efficiently used as topcoats to protect polymer substrates against scratch, abrasion and chemicals.Dynamic mechanical thermal analysis (DMTA) measurements showed that complex modulus (E*) increased and loss tangent (tan?) decreased with small particle size and high silica content, but the dynamic glass transition temperature (Tg) was unaffected by size and size distribution.Coatings with mixtures of 50 and 13 nm particles at 75/25 weight ratio obeyed to volume packing theory and gave the highest values of E* and tan?. Resistance to abrasion and friction were more effective with large particles, while gloss was highest with small ones. These properties were best seen when silica content is superior to 15 % where strong interactions at the silica-polymer interface and particle/particle were detected.AFM observation showed that the surface of the coating was well covered with silica particles, protecting it from aggressive physical and chemical attacks. Examples of transparent hard coatings protecting various plastic foils or sheets against scratch and abrasion will be shown during the presentation.
Grooved feed extruders (GFE) for quality production at lowest costs require screw and barrel designs capable of achieving gradual increases in pressure along the extruder and low friction in the feed section. Barrier-melting and mixing zones must be adapted to higher rates compared with smooth bore extruders (SBE). Because of reduced energy-losses new GFE-designs are no longer water cooled but use ceramic heating-/air-cooling-devices. Performance data of GFEs and SBEs represent differences in output and quality esp. at high speeds. Pros and Cons are discussed with respect to extruder downsizing, flexibility, regrind processing and vented extrusion, leading to preferred applications for GFEs and SBEs.
Metallocene plastomers are well known for providing superior toughness and excellent heat sealing performance in many high performance flexible packaging films. In a great many form-fill-seal applications it is also a requirement that the film continue to seal well even when the film surface is contaminated with product.This paper presents examples of the excellent sealing performance of plastomers, in particular of their performance when sealing through contaminants. Both laboratory heat sealing experiments and actual VFFS packaging tests are described.
Inorganic fillers such as calcined clay and wollastonite have been used to modify the properties of nylons for several years and glass fiber reinforced products are extensively used. The use of glass fibers, while offering many benefits, does lead to problems of anisotropy caused by fiber orientation. This can result in warpage and shrinkage, particulary in larger, thin sectioned mouldings. Calcined clay and wollastonite were introduced to minimize warpage, but still maintain rigidity.Silane coupling agents provide the ability to bond inorganic fillers to organic resins by establishing molecular bridges". Current technology utilises primarily ?-aminopropyltriethoxysilane as a coupling agent for improving interphase interactions in mineral-filled nylon systems. Although many mechanical properties are greatly improved by the use of ?-aminopropyl-triethoxysilane impact properties generally are not.This presentation covers mineral fillers and silanes and how to combine both in a successful way. N-nbutyl-?-aminopropyltrimethoxysilane is presented as a further aminosilane development that imparts not only excellent processability and rigidity to a composite but also increased impact strength due to its coupling and dispersion abilities."
Composites of high density polyethylene (HDPE) with hydroxyapatite (HA - the main inorganic constituent of the human bone) were produced by extrusion compounding and subsequently injection molded. Shear controlled orientation in injection molding (SCORIM) was used deliberately to induce a strong anisotropic character in the composite materials. Bi-composite moldings featuring a sandwich like morphology were also produced by mono-sandwich injection molding. These composites combine a HDPE/HA outer layer and HDPE/C fiber reinforced core. For all the cases, the mechanical performance of the produced composites was assessed and the structure developed investigated and related to the processing conditions.
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ANTEC 2016 - Indianapolis, Indiana, USA May 23-25, 2016. [On-line].
Society of Plastics Engineers
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