SPE Library

The flow of melt in runner systems of injection molds takes place in channels whose cross section can be either circular, square, rectangular or of any other geometrical form. In order to obtain a uniform distribution of the melt at low pressures, knowledge of the pressure drop along the flow path is important. Based on the modern developments in rheology, this paper presents easily applicable relationships for calculating pressure drop in the flow channels of different geometry taking flow rate, resin type and melt temperature into account. Worked-out examples illustrate the use of the equations presented, which were found to agree well with the results in the practice.

Applications of nanometer-sized particles can facilitate the formation of microcellular foams in the continuous extrusion foaming process. Both intercalated and exfoliated polystyrene/nanoclay composites were foamed using CO2 as the foaming agent. The resulting foam structure is compared with that of pure polystyrene and polystyrene/talc composite. It is found that unique foam structure can be created by changing the content and the dispersion of nanoclay particles. The effects of nanoclay dispersion on the polymer melt rheology and the foaming process are discussed. Combining nanoclay compounding with microcellular foaming provides a new technique for the design and control of foam structure.

In order to develop a polycarbonate (PC)/ acrylonitrile-butadiene-styrene (ABS) product with a high content of recycled PC, a low molecular weight virgin PC was added to recycled PC to minimize batch-to-batch property variations in the compounded product. Six PC/ABS blends were prepared on a twin screw extruder by mixing 50 wt% virgin ABS and 0-25 wt% low molecular weight virgin PC with 25-50 wt% high purity recycled PC recovered from end-of-life electronics. These blends were characterized rheologically and mechanically. Results showed that this strategy could yield consistent quality resin blends with a high recycle content.

Ethylene-1-butene, ethylene-1-pentene, ethylene-1-hexene, ethylene-1-heptene, ethylene-octene and ethylene-1-nonene random copolymers were prepared by Ziegler-Natta catalyst system and their rheological and thermal properties were determined. The rheological properties (zero shear viscosity, zero shear first normal stress coefficient, steady state viscosities and components of complex modulus are decreasing with the increase of co-unit size because the entanglement density decreases with the increase of co unit side group length. The melting point, heat of fusion also decrease with the increase of co-unit side group length because of the decrease of crystallinity.

This works tries to correlate the influence of the thermal and deformation histories that the polymer blend undergoes during its manufacturing on its microstructure. This is done by using a rheological model for polymer blends in the numerical simulation of this deformational field. The applied model is a modification of Bousmina et al in the Grmela's [1] model for two immiscible viscoelastic fluids and allows to obtain the size and shape of the dispersed particle of these heterogeneous systems through the deformational parameters, as shear rate and physical properties, as interfacial tension and viscosity of the polymers.

Low molecular weight polypropylene (Eastman, Epolene N-15) has been chemically modified during reactive processing using a catalytic hydrosilylation reaction in a batch mixer under various processing conditions (1,2). The hydrosilylated PP (Si-PP) has been blended with a commodity polypropylene resin (Montell, KF 6100) in a batch mixer at concentrations ranging from 5-20 wt%. This PP blends have been characterized in terms of their rheological properties as well as their thermal and impact properties. Addition of the hydrosilylated PP reduces the processing torque and the shear viscosity, while the impact properties depend on the crystallinity, Si-PP content and dispersed phase morphology.

Melt blending of polypropylene (PP) with a low molecular weight unsaturated polyester (UP) was studied in a batch mixer in the presence of peroxide free radical initiator. Competing degradation and crosslinking reactions of the peroxide with the blend components resulted in a finer and more uniform morphology for this immiscible blend system. The blends were characterized by FTIR, DSC, microscopy and rheology in order to examine the possibility of the formation of block" or "graft" PP-UP structures which would enhance phase interaction and promote compatibility. The batch data were used to define the process requirements for the continuous modification by reactive extrusion."

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.

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."

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.

The National Institute of Standards and Technology (NIST) develops Standard Reference Materials® for calibration, quality assurance and for research into improved measurements. Two fluids that demonstrate shear thinning and normal stresses typical of polymeric fluids have been developed as standards for rheological measurements. SRM 2490 is a solution of polyisobutylene dissolved in 2,6,10,14-tetramethylpentadecane. SRM 2491 is a poly(dimethylsiloxane) melt, with less temperature dependence than SRM 2490. NIST certifies 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.

The effect of stearic acid on the particles and the effect of the particle shape on the shear/dynamic viscosity have been investigated using uncoated and coated talc, calcite and mixed talc/calcite filled polypropylene composites. The viscosity of the stearic acid coated filler particles exhibited much less than the uncoated fillers. In addition, the effect of stearic acid was more significant on coated calcite than the coated talc system. The real yield value measured using a sandwich creep measurement exhibited lower than obtained from the extrapolation. The isotropic calcite seems to give less interfacial force and hydrodynamic resistance between the filler and the polypropylene matrix than the anisotropic talc at low shear rate/stress. The Cox-Merz relation fails between the complex and shear viscosity for the both uncoated and coated compounds.

LDPE, HDPEs and metallocene polyethylenes (MPOs) were grafted with vinyl triethoxy silane in co-rotating twin screw-extruders. Afterwards, the materials were crosslinked in water. Peroxide modified materials were also made. Degrees of crosslinking were measured by determining their gel contents after extraction of the soluble component in xylene and orto-dichlorobenzene. Dynamic rheological experiments were carried out for all materials at different temperatures. Five different catalysts were studied. The degree of crosslinking achieved for the PEs employed after curing follows the order HDPE1 > HDPE2 > LDPE. The degree of crosslinking achieved for the MPOs used after 24 hours of curing time was very similar. The crystallinities of modified HDPEs and LDPE are greatly affected by the crosslinking processes. However, the lamellar thickness distribution of the silane-crosslinking MPO materials is less affected.

Activities in MEMS and biomedical applications are placing increasing demands on industry for product miniaturisation. In turn, this is leading to developments in materials processing. In this context the micro-injection moulding ( micromoulding ) of polymers and composites has evolved as a technology for the manufacture of intricate components of mass less than 0.001g. However, some fundamental issues need addressing for the process, and especially its products, to gain wider acceptance by the manufacturing sector. In particular, during the injection process polymers and composites are often exposed to severe processing conditions. For example, simple analysis of the injection rates reveals that melts can be subjected to shear rates > 1*106 s-1 on flow through the feed system in micromould tools. Such severe processing conditions may have a detrimental affect on the polymer properties and adversely affect the functionality and longevity of the final component. Studies conducted within our laboratory are focused on enhancing the understanding of polymer processing-property interaction, and especially the effects of micro-scale processing on the rheological and mechanical properties of polymers and composites. Our studies will investigate the effects of micro-scale processing on engineering and commodity polymers, nanocomposites, metal and ceramic injection moulded feedstock and biomaterials. In this paper we present the findings of some initial studies on moulded rectangular plaques of a miniature moulding scale. Surface micro-morphology and mechanical properties of mouldings are investigated using SEM and atomic force microscopy using contact and tapping modes.