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Applied Rheology

SPE Library content related to rheology
EFFECTS OF LONG-CHAIN BRANCHING CONCENTRATION OF SUPERCRITICAL CO2 AND PRESSURE ON THE VISCOSITY OF LINEAR AND BRANCHED POLYPROPYLENES
Hee Eon Park , John M. Dealy, May 2008

Supercritical carbon dioxide (CO2) is of interest as a physical blowing agent in the manufacture of plastic foam and as a plasticizer to reduce melt viscosity during processing. The combined effects of concentration (C) of dissolved CO2 pressure (P) and temperature (T) on the rheological properties of the melt were determined to achieve optimum processing conditions. Linear and branched polypropylenes and their blends were chosen. A high-pressure sliding plate rheometer in which the shear deformation T P and C are all uniform was used. It was possible to use shift factors for T P and C to obtain a master curve.

STRACTURE AND INTERFACIAL ADHESION OF PP/PBS SANDWICH INJECTION MOLDINGS
Yuji Fujita , Toshihiro Yoshida , Hironari Sano , Naoya Aoki , Masaya Kotaki , Hiroyuki Hamada, May 2008

Polypropylene (PP) based sandwich injection moldings with biomass based polymers (PBS) in the core were studied. In order to obtain superior surface properties such as high chemical resistance and anti-scratch resistnce improvement of interfacial strength between skin and core parts is important which can be controlled by the additional PP component in the PBS core part. The selection of additional PP and injection conditions were found to be important to improve the interfacial strength of which phenomena was understood by the melt rheology at the injection condition.Scratch tests according to ASTM method was performed to investigate the relationship between scratch behavior and skin/core adhesion. Poor skin/core adhesion caused the skin/core delamination upon the scratch tests.

STRACTURE AND INTERFACIAL ADHESION OF PP/PBS SANDWICH INJECTION MOLDINGS
Yuji Fujita , Toshihiro Yoshida , Hironari Sano , Naoya Aoki , Masaya Kotaki , Hiroyuki Hamada, May 2008

Polypropylene (PP) based sandwich injection moldings with biomass based polymers (PBS) in the core were studied. In order to obtain superior surface properties such as high chemical resistance and anti-scratch resistnce, improvement of interfacial strength between skin and core parts is important, which can be controlled by the additional PP component in the PBS core part. The selection of additional PP and injection conditions were found to be important to improve the interfacial strength, of which phenomena was understood by the melt rheology at the injection condition. Scratch tests according to ASTM method was performed to investigate the relationship between scratch behavior and skin/core adhesion. Poor skin/core adhesion caused the skin/core delamination upon the scratch tests.

ON-LINE OPTICAL MONITORING OF NANOCOMPOSITE COMPOUNDING
Marion McAfee , Wai-Chow Chang, May 2008

On-line monitoring of compounding of PA6 with nanoclay is examined to investigate the level of exfoliation and degradation under a variety of conditions in real-time. On-line rheological and optical reflectance measurements are compared with off-line analyses of compounded samples to investigate the relationship between these readings and exfoliation/intercalation and/or degradation of the nanocomposite. The effect of the processing (twinscrew/ single-screw temperature and screw speed) on the resulting melt quality and the ability to assess this quality in real-time is discussed.

RHEOLOGICAL PROPETIES OF BRANCHED POLYSTYRENE PREPARED BY AN ULTRASOUND ASSISTED INTENSIVE MIXER
Hee Jung Kim , Hyungsu Kim , Hooseok Lee , Jae Wook Lee, May 2008

By combining ultrasonic energy which can cause chain scission of polymer molecules and a multifunctional agent (MFA) having double bonds at its ends we were able to modify the molecular structure of polystyrene (PS) from linear to a branched structure during melt processing. The three double bonds in chain ends of MFA were expected to act as sites for trapping macroradicals of PS during the course of ultrasound- assisted mixing process. The transformation of molecular structure of PS was confirmed by the measurements of rheological properties of the modified PS. After the ultrasonic irradiation of PS together with MFA increase in complex viscosities and shear-thinning behavior were observed. The Cole-Cole plot revealed the characteristic features of branched structure.

HOW CAN POLYMER RHEOLOGY BE USEFUL TO GUIDE PROCESSING
Shi-Qing Wang , P. E. Boukany , S. Ravindranath , Y. Y. Wang, May 2008

This presentation discusses the latest developments in the field of nonlinear rheology of entangled polymeric liquids resulting from nearly two dozens of publications from the Polymer Dynamics Interface and Rheology Group at Akron. The essential findings are that a) entangled liquids respond to sudden startup flow elastically and undergo cohesive failure or yielding before subsequent flow is possible b) the flow field beyond the yield point is dictated by the characteristics of the yielding process that can be strongly inhomogeneous c) entangled liquids possess finite cohesion that can be overcome after flow cessation by internal elastic restoring forces.

HOW CAN POLYMER RHEOLOGY BE USEFUL TO GUIDE PROCESSING
Shi-Qing Wang , P. E. Boukany , S. Ravindranath , Y. Y. Wang, May 2008

This presentation discusses the latest developments in the field of nonlinear rheology of entangled polymeric liquids, resulting from nearly two dozens of publications from the Polymer Dynamics, Interface and Rheology Group at Akron. The essential findings are that a) entangled liquids respond to sudden startup flow elastically and undergo cohesive failure or yielding before subsequent flow is possible, b) the flow field beyond the yield point is dictated by the characteristics of the yielding process that can be strongly inhomogeneous, c) entangled liquids possess finite cohesion that can be overcome after flow cessation by internal elastic restoring forces.

RELATIONSHIP BETWEEN STRUCTURE AND RHEOLOGICAL PROPERTIES IN POLYMER/LAYERED SILICATE NANOCOMPOSITES
Hassan Eslami , Miroslav Grmela , Mosto Bousmina, May 2008

Poly[butylenes succinate-co-adipate] (PBSA) layered silicate nanocomposite was prepared by melt extrusion of PBSA and organically modified montmorillonite (OMMT). Nanocomposites were prepared at a single clay loading. Before taking rheological measurements the nanocomposites were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Stress growth experiments were performed for both pure polymer and nanocomposite. Flow reversal experiments were conducted for nanocomposites at different predetermined rest time after cessation of forward flow. The orientation state of silicate layers were also investigated by cooling down the sample in the rheometer before and after the forward flow and then by performing X-ray in the transmission mode.

RELATIONSHIP BETWEEN STRUCTURE AND RHEOLOGICAL PROPERTIES IN POLYMER/LAYERED SILICATE NANOCOMPOSITES
Hassan Eslami , Miroslav Grmela , Mosto Bousmina, May 2008

Poly[butylenes succinate-co-adipate] (PBSA) layered silicate nanocomposite was prepared by melt extrusion of PBSA and organically modified montmorillonite (OMMT). Nanocomposites were prepared at a single clay loading. Before taking rheological measurements, the nanocomposites were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Stress growth experiments were performed for both pure polymer and nanocomposite. Flow reversal experiments were conducted for nanocomposites at different predetermined rest time after cessation of forward flow. The orientation state of silicate layers were also investigated by cooling down the sample in the rheometer before and after the forward flow and then by performing X-ray in the transmission mode.

HIGH-PERFORMANCE-TIE-LAYER RESINS IN FLEXIBLE PACKAGING APPLICATIONS: STRUCTURE–PERFORMANCE RELATIONSHIPS
Chun Lee , William Podborny , Tim Schloemer, May 2008

Interlayer adhesion between tie and barrier layers in blown and cast film plays a major role in determining the performance of tie layer resins in barrier applications. In general tie-layer adhesion increases and film clarity decreases with increased maleic anhydride functionality (MAF). The tie resin employed for this investigation showed reduced adhesion to EVOH even with increased MAF. Understanding such unusual behavior is an important aspect of the structure of tie-layer resins to be used in industrial barrier packaging applications. We investigated structural factors of the tie resins using rheological measurements. It was found that dynamic shear rheological data does not provide useful information to understand tie layer performance. However extensional rheological data showed useful information to understand tie resin performance. The strain-hardening behavior of the tie-layer resin during the melt extensional process plays a major role in determining the interfacial adhesion between tie and EVOH layers and clarity regardless of a given range of MAF levels.

HIGH-PERFORMANCE TIE LAYER RESINS IN FLEXIBLE PACKAGING APPLICATIONS: STRUCTURE-PEROFRMANCE RELATIONSHIPS
Chun Lee , William Podborny , Tim Schloemer, May 2008

Interlayer adhesion between tie and barrier layers in blown and cast film plays a major role in determining the performance of tie layer resins in barrier applications. In general, tie-layer adhesion increases and film clarity decreases with increased maleic anhydride functionality (MAF). The tie resin employed for this investigation showed reduced adhesion to EVOH even with increased MAF. Understanding such unusual behavior is an important aspect of the structure of tie-layer resins to be used in industrial barrier packaging applications. We investigated structural factors of the tie resins using rheological measurements. It was found that dynamic shear rheological data does not provide useful information to understand tie layer performance. However, extensional rheological data showed useful information to understand tie resin performance. The strain-hardening behavior of the tie-layer resin during the melt extensional process plays a major role in determining the interfacial adhesion between tie and EVOH layers and clarity, regardless of a given range of MAF levels.

POLYMER-POLYMER INTERFACIAL SLIP MEASUREMENTS IN MULTILAYERED FILM
Patrick C. Lee , Hee Eon Park , Christopher W. Macosko , John M. Dealy, May 2008

Significant slip can occur during flow of twoimmiscible polymers due to reduced entanglements at theirinterface. The slip is of practical importance because of itseffect on morphology and adhesion of these multi-phasematerials such as disordered two-phase blends andmultilayer films. Using rheological technique we studiedthe interfacial slip in co-extruded multilayer films. Theviscosity drop of a multilayer sample below the averageviscosity of two neat components was observed for bothpolypropylene/polystyrene and polyethylene/fluoropolymer systems indicating interfacial slip.Furthermore the viscosity drop of a multilayer sampleincreased with the number of layers.

POLYMER-POLYMER INTERFACIAL SLIP MEASUREMENTS IN MULTILAYERED FILM
Patrick C. Lee , Hee Eon Park , Christopher W. Macosko , John M. Dealy, May 2008

Significant slip can occur during flow of two immiscible polymers due to reduced entanglements at their interface. The slip is of practical importance because of its effect on morphology and adhesion of these multi-phase materials, such as disordered two-phase blends and multilayer films. Using rheological technique, we studied the interfacial slip in co-extruded multilayer films. The viscosity drop of a multilayer sample below the average viscosity of two neat components was observed for both polypropylene/polystyrene and polyethylene /fluoropolymer systems, indicating interfacial slip. Furthermore, the viscosity drop of a multilayer sample increased with the number of layers.

RHEOLOGICAL PROPERTIES OF LONG CHAIN BRANCHED POLYETHYLENE MELTS AT HIGH SHEAR RATE
Jaejwan Kim , Dong Hak Kim , Younggon Son, May 2008

Capillary extrusion experiments involving a number of polyethylenes with emphasis on assessing the effect of long chain branching are performed. None of the metallocene catalyzed linear low density polyethylenes (mLLDPE) produced by Dow Chemicals which are believed to have some level of long chain branching show temperature dependence on the viscosity at the gross melt fracture regime. Furthermore these materials do not show spurt or stick-slip flow in contrast with most linear polyethylenes. LDPE and blends of LDPE with linear polyethylenes also show the absence of stick-slip flow but temperature dependence on the viscosity. From these observations we conclude that the stick-slip flow is very sensitive to the existence of long chain branching and the behavior of the stick-slip flow can be used as an indicator of LCB.

RHEOLOGICAL PROPERTIES OF LONG CHAIN BRANCHED POLYETHYLENE MELTS AT HIGH SHEAR
Jaejwan Kim , Dong Hak Kim , Younggon Son, May 2008

Capillary extrusion experiments involving a number of polyethylenes with emphasis on assessing the effect of long chain branching are performed. None of the metallocene catalyzed linear low density polyethylenes (mLLDPE) produced by Dow Chemicals, which are believed to have some level of long chain branching, show temperature dependence on the viscosity at the gross melt fracture regime. Furthermore, these materials do not show spurt or stick-slip flow, in contrast with most linear polyethylenes. LDPE and blends of LDPE with linear polyethylenes also show the absence of stick-slip flow, but temperature dependence on the viscosity. From these observations, we conclude that the stick-slip flow is very sensitive to the existence of long chain branching, and the behavior of the stick-slip flow can be used as an indicator of LCB.

RHEOLOGY AND STRUCTURE OF FILLED PROPYLENE/ETHYLENE COPOLYMERS
Paula Wood-Adams , Arkady Fatseyeu , Cheng Huang , Teresa Karjala , Patricia Ansems, May 2008

We have studied a new family of propylene/ethylene(P/E) copolymers produced by The Dow ChemicalCompany which allow high filler loadings whilemaintaining good processability. Our goal was to providea fundamental understanding of the unexpectedly lowviscosity exhibited by these materials when filled withparticulates. We propose that in these copolymers interfacial slip (between the particles and the polymermelt) is enhanced by the presence of a thin layer of lowviscosity polymer around the particles. The formation ofthis layer is surface tension driven and can occur insystems such as these copolymers which are homogeneousin the bulk. Such behaviour has been observed with blockcopolymersand blends; this study is the first time it hasbeen observed in an industrial copolymer of this type.

Differentiated Compression Molding: A New Process Innovation Creates Dramatic Cost Savings & Product Improvements for Compression-Molded Applications
Harald Herbst, September 2007

Long glass fibre thermoplastics (LGFT) used in compression moulded applications has grown dramatically due to metal replacement by composites and the derived benefits in both cost and weight savings. In order to make thin walled parts from higher viscosity thermoplastic materials as opposed to thermosetting resins machine producers have been challenged in terms of clamp size and tooling. In this paper a revolutionary new process called differentiated compression moulding (DCM) is described and compared with traditional compression moulding. Using new tool designs the process allows for reductions in press sizes of up to 70%. This in turn allows for significant cost savings in machine investment tooling and energy consumption. Larger projected areas and thinner walled investment tooling and energy consumption. Larger projected areas and thinner walled parts can be made on smaller machines. The paper discusses the physics and rheological conditions that allow for this innovation and a test case is compared to current technology.

Physics of Amorphous Polymers
Gregory B. McKenna, May 2007

Amorphous polymers are of continuing great fundamental and practical interest. From the melt state through the glass transition these materials exhibit highly nonlinear properties that are readily interrogated using methods of both linear and nonlinear rheology and mechanics. Here we examine several novel methods developed by the author to investigate swelling in rubber, nonlinear behavior of polymer glasses and the behavior of materials at the nanoscale

Determining the Processability of Multilayer Coextruded Structures
Joseph Dooley, May 2007

Multilayer coextrusion is a process in which two or more polymers are extruded and joined together in a feedblock or die to form a single structure with multiple layers. This paper will discuss techniques for measuring experimental rheology data for monolayer and multilayer structures and how that data can be used for determining the processability of multilayer coextruded structures.

Analysis of Viscous Heating Effects in a Pressure Slit Rheometer Using Radial Functions Method (RFM)
Ivan D. Lopez, Fritz Klaiber, Tim A. Osswald, May 2007

A pressure rheometer was built to measure rheological properties of polymers at elevated pressures and temperatures. However the viscosity at high deformation rates decreases more than the predicted theoretical value represented by the Cross-WLF model. This paper studies the role of viscous heating in the resulting viscosity deviations by means of simulation using the Radial Functions Method (RFM).










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