SPE Library

The reaction of styrene-maleic anhydride (SMA) with polyethylene/methyl acrylate/glycidyl methacrylate (E-MA-GMA) was studied in a batch mixer and in a corotatmg twin screw extruder. Also, the mixing of a nonreactive blend of SMA with polyethylene/methyl acrylate (E-MA), with similar rheological properties to E-MAGMA, was studied under the same processing conditions. The mixing products of reactive and nonreactive systems exhibited drastically different properties. Reactive blends showed higher tensile modulus, tensile strength, strain at break and complex viscosity in comparison to non-reactive blends. The reactive blends had also finer morphology than the non-reactive ones.

The rheological properties of conventional PET resins are not particularly suitable for low density extrusion foaming with physical blowing agents and as a result modified resins with higher melt viscosity and elasticity are often used. In this work parameters affecting the monolayer flat sheet extrusion of foams having variable densities (from about 1.2 to 0.2 g/cc) are presented. Unmodified and chemically modified resins with different melt viscoelastic properties are used. The effects of variables such as type and concentration of atmospheric gases, resin rheology and choice of process conditions are related to product characteristics including density, crystallinity and thermoformability.

Blends of polypropylene and polystyrene compatibilized with styrene-butadiene-styrene (SBS) and styrene-ethylene/butylene-styrene (SEBS) copolymers were studied. The morphology was studied by Scanning Electron Microscopy. Emulsion curves relating the average radius of the dispersed phase to the concentration of compatibilizer added to the blend were obtained. The rheological behavior of the blends was studied by small amplitude oscillatory shear, and correlated to the morphological observations. The interfacial tension between the components of the blends was evaluated from the rheological data.

The influence of molecular structure on the rheology and processability of HDPE blow molding resins is studied. Experiments were conducted using capillary and extensional rheometers, a melt indexer and a blow molder unit. Twenty four resins were analyzed in terms of their shear flow and extensional properties, extrudate swell characteristics, and melt strength. The studied samples were produced using a variety of manufacturing technologies and had varying molecular weight characteristics. From the results, the influence of molecular structure on the rheological properties was determined. Furthermore, to assess resin processability, pillow mold (blow molding) experiments were performed. The implications of rheology on processability (parison sag and weight swell) are also discussed.

For a resin to be successful in a blow moulding application, it has to comply with a set of characteristics known as a whole as the material's blow mouldability". This concept includes the parison swelling behaviour (both in diameter and thickness) and the resistance of the melt to extension (melt strength). This paper outlines a new methodology geared towards the establishment of relationships between relevant rheological properties and key processing material behaviour parameters (swell and sag) governing the blow moulding process. The technique has been applied to the intermittent extrusion of a PC/ABS blend (PULSE™
). Several processing parameters such as drop time extrusion temperature and die gap were studied."

As Metallocene Catalysed Polyethylenes ( mPE's ) become more commercially available they are finding ever increasing application in the blown film industry. However, it is becoming apparent that no two mPE resins behave in exactly the same manner. This paper examines the rheological properties of a range of mPE's with different densities and MFI's. These resins were then blended with a conventional low density polyethylene ( LDPE ) to form monolayer films. The mechanical properties of these films were compared to three layer coextruded films of A:B:A structure, where A is LDPE and B is mPE.

The wall section of medical press-through blisters may reduce the stability of the packed medicine. A homogeneous wall thickness over the entire capsule chamber enables the manufacturer use a thinner starting foil without a lack of quality, which leads to the saving of raw material and other expenditures. Three thermoforming methods are tested on an industrial form-fill-seal" line. the temperature profile of the raw film before forming the friction coefficient between films and molds or plugs and the biaxial rheological properties of the foil influence the resulting wall thickness distribution."

During the cure of a thermoset-thermoplastic blend two-phase morphologies may be formed. The phase separation process can be controlled by manipulation of the rate of polymerization of the thermoset system. In this work, the effect of the addition of different amounts of polycarbonate (PC) on the rheokinetics of an epoxy thermoset system is presented. The reactive system used was diglycidyl ether of bisphenol-A cured with 4-4 diaminodiphenylsulfone. The blends of the PC and the epoxy resin were prepared using two different procedures: (a) hot melt blending and (b) dissolution in a common solvent. The kinetics was followed by differential scanning calorimetry and the change in the rheological properties during the curing by dynamic rheometry.

Rheological analysis of multi-phase systems is very difficult because the morphology is strongly related to the flow history. The small amplitude oscillatory shear flow does not affect the morphology and is very useful to predict the viscoelastic behavior of immiscible blends. In this work we study the dynamic rheological properties of Polypropylene based ternary blends with linear low density polyethylene and ethylene/propylene terpolymers of different viscosities taking into account the effects of changing the composition and concentration of the dispersed phase. The predictions of a constitutive equation for emulsions of viscoelastic fluids are also included.

The effect of coupling agents and particle size on melt rheology of polyphenylene sulfide-bonded neodymium-iron- boron (Nd-Fe-B) alloy magnets was studied with oscillatory flow experiments to accelerate efforts to optimize their processing. The minimum viscosity of the polymer-bonded magnets near 290°C was obtained with Nd-Fe-B fillers (106-150 particle size range) that were coupled with a silane coupling agent. All the samples tested followed power-law fluid flow behavior. Morphological and dynamic mechanical analysis of the samples showed that the beneficial function of the coupling agent may be ascribed to enhanced wetting of the magnetic Nd-Fe-B powders by the polymer, improving the processability of the polymer bonded magnets.

Seemann Composite Resin Infusion Molding Process (SCRIMP) is a room temperature vacuum-assisted resin transfer molding technique developed in recent years for high strength composite fabrication. This process is being used for marine, civil infrastructure, transportation and defense applications. Unsaturated polyester and vinyl ester resins are the two major resins used in SCRIMP today. The objective of this study is to compare the resin moldability and properties of SCRIMP molded composites based on these two kinds of resins. Effects of resin type, initiator, promoter, inhibitor and retarder on the reaction kinetics, chemorheological changes and resin shrinkage were studied by using DSC, RDA and dilatometry respectively. The surface quality of the molded samples was measured by a profilometer. A kinetic model in conjunction with a heat transfer model was developed to simulate the SCRIMP process.

Rheological data obtained under the conditions of temperature and shear existing in conversion processes are required for the prediction of the performance of polymer resins in those processes. The capillary rheometer simulates the conditions seen in conversion processes and can be used to produce pertinent data. The ± 3 ? variation of the viscosity verses shear rate curves (over the range of shear rates seen in a process) for a resin or compound, can be used as a tool for monitoring consistency and predicting processability. When the measured viscosities for a material fall within the tube" formed by the upper and lower limits of the variation the product is consistent. If not the way the curve moves out of the "tube" will provide information on the root causes of the product variation. This talk discusses the application of the "tube" concept to a range of filled and unfilled resins using an automated capillary rheometer system that makes the "tube" concept practical for application in quality assurance and process control."

Rheological data obtained under the conditions of temperature and shear existing in conversion processes are required for the prediction of the performance of polymer resins in those processes. The capillary rheometer simulates the conditions seen in conversion processes and can be used to produce pertinent data. The ± 3 ? variation of the viscosity verses shear rate curves (over the range of shear rates seen in a process) for a resin or compound, can be used as a tool for monitoring consistency and predicting processability. When the measured viscosities for a material fall within the tube" formed by the upper and lower limits of the variation the product is consistent. If not the way the curve moves out of the "tube" will provide information on the root causes of the product variation. This talk discusses the application of the "tube" concept to a range of filled and unfilled resinsusing an automated capillary rheometer system that makes the "tube" concept practical for application in quality assurance and process control."

Poly Phenylene Sulfide (PPS) is a relatively new Polymer, which is now finding an increasing number of applications in industry. It couples good chemical and impact resistance with high temperatures. This material has been the focus of intensive research over the past few years. However, not much Rheological or Processing data has been published for PPS. This research provides an insight into the effect of molecular weight and its distribution by the rheological properties of PPS, as well as processing parameters like extruder output, die pressure and torque. It is found that a sample with a narrow molecular weight distribution and low molecular weights when compared to other samples is relatively easier to process with wider operating windows.

INSITE™ Technology has enabled the production of ethylene/styrene interpolymers (ESI), typically containing up to about 50 mole % styrene. These ESI show good filler acceptance, and this technology allows the engineering of novel materials. Materials have been produced by melt compounding based on a range of fillers, including calcium carbonate and aluminum trihydrate (ATH). The properties of filled ESI are presented and discussed, including solid state dynamic mechanical spectroscopy and ignition resistance. The toughness of highly filled materials, such as indicated by elongation at rupture from tensile stress/strain behavior is described. Melt rheological properties of filled ESI are related to processing operations. Some potential applications for filled ESI are introduced.

A set of experimental data is carried out on short fiber suspensions in viscoelastic fluids. Parameters such as fiber volume fraction, fiber length and pre-shearing are studied. Transient tests on pre-sheared samples showed that fiber orientation depends on both the strain and the rate-of-strain tensors. Increasing fiber concentration and aspect ratio increases rheological material functions in the low shear rate region. In the high shear rate region, the effect is less pronounced. The experimental data are compared to a rheological model based on the modified Jeffrey equation. The theoretical results are found to be in good agreement with most experimental data. Further changes to the original model were necessary to be able to predict the rate-of-strain-dependent fiber orientation and the observed behavior of the considered material functions.

Constrained geometry catalysts make it possible to control independently various molecular characteristics. The polymers produced with these catalysts are of great interest commercially and make possible the systematic study of the effects of various molecular characteristics on rheological behavior. Several constrained geometry catalyzed and metallocene polyethylenes were subjected to a comprehensive rheological evaluation including linear viscoelastic behavior and non-linear viscoelastic behavior in shear and extension. The effect of molecular weight, short chain branching and long chain branching on the rheology of these materials are described. Based on these results, a procedure was developed for quantifying LCB using linear viscoelastic data and backbone MWD.

Shear and compression rheometry of representative boronsilane (BSI) polymers and corresponding LDPEs demonstrates feasibility of modeling processing of the latter using BSIs at an ambient temperature. Industrial-range rheology of BSis was shown to be relevant for the performance in shock absorbers. Boronsilane polymers [BSI] constitute an unique class of polymers [1,2] of readily adjustable ratio of viscous and elastic components of their (Tab. 1) viscoelastic response. Level of the response at an ambient temperature is comparable with that of polymer melts at processing temperatures [3,4]. BSIs display also high and adjustable level of recoverable compressibility (resilience). These characteristics imply application in: • rheometry e.g. for identifying local stress distribution in the melt flow of o polymer using calibrated stress traces [5] embedded in 'rheoequivalent' BSI in an ambient temperature experiment; • technology such as • ambient temperature performance testing of the rapid prototype" [6] plastic molds and dies which are less expensive than these made of metals • high performance shock absorbers of readily adjstable resilience [7]. Here we aim at: • comparison of ambient temperature capillary rheometry of representative 'elastic' and 'viscous' BSI (designated as 'elastomer' and 'plastomer' resp.) with the melt rheometry of LLDPE a IUPAC melt rheology standard [7a]. In both cases technically significant range of stress was covered; • comparison of the volume viscosity and the time dependent compressibility of the 'elastomer' and the 'plastomer'. "

The shear and extensional rheology of three polyethylenes(PE's) synthesized using metallocene catalysts are compared. One of the PE's is linear i.e. no long-chain branches (LCB), while the other two have different amounts of long chain branching. The shear viscosity of the linear PE is reflective of the narrow molecular weight distribution of metallocene catalyzed PE's while the apparently branched PE's exhibit a higher viscosity and an earlier onset of shear thinning. The linear polymer exhibited lower activation energy than the branched PE with similar MW. The linear PE does not show stress-strain hyesteresis while the branched polymer does. All of them show supercooling behavior.

The curing process of an epoxy-fiber composite prepreg is a multistep process involving polymerization, gelation, crosslinking, and vitrification. Optimization of industrial processing requires knowledge of how each step is affected by time and temperature. This is usually facilitated by construction of a time-temperaturetransformation (TTT) diagram.1,2,3 Since the overall epoxy conversion reaction is exothermic, the rate and degree of conversion can be studied isothermally using differential scanning calorimetry (DSC), by comparing the change in enthalpy with the total change in enthalpy of the reaction4. An alternative method for determining the degree of conversion is by measuring the shift in Tg between Tg0 and Tg?, which will be proportional to the degree of conversion.3 The Tg can be measured by a variety of techniques, the most common being DSC, dynamic mechanical analysis (DMA) and thermomechanical analysis (TMA).5 Although DSC can detect both exothermic change and Tg, the two events are displayed on one signal and the two events are often found to overlap, making both signals difficult to quantify. Dynamic DSC allows the separation of reversing, in-phase events like glass transitions, from non-reversing, out-of-phase events like curing and enthalpic relaxations.6-12 However, both enthalpic change and Tg shift are unable to detect the gelation point, since it is not a rate effect. They can detect vitrification, since a drop in the rate of conversion occurs at this point. Gelation, being a molecular weight effect, is only seen in viscosity or chain mobility studies. The two most common techniques for determination of the gelation point are DMA (or rheology) and dielectric analysis (DEA). There are a variety of DMA techniques available for measuring the modulus and viscosity of epoxies, the most common being torsional braid analysis (TBA), parallel plate (or cone and plate), and three point bending. Several methods, most commonly DSC and DMA, can detect vitrif