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Applied Rheology

SPE Library content related to rheology

MELT RHEOLOGY AND X-RAY ANALYSIS OF GRADIENT COPOLYMERS: SEQUENCE DESIGN FOR PROCESSIBILITY

Michelle M. Mok , Soyoung Kim , Wesley R. Burghardt , John M. Torkelson, May 2010

Gradient copolymers have great versatility in terms ofsequence distribution of monomers along the polymerbackbone for control over their level of nanophaseheterogeneity and flow properties. Using a gradientcomposition rather than a block-type distribution, it ispossible to design longer chains which undergonanophase segregation at lower temperatures yet becomemore homogeneous and melt processible at accessibletemperatures. These behaviors are investigated for a rangeof block and gradient architectures using melt rheologyand small-angle x-ray scattering.

CORRELATION OF FILM CASTING BEHAVIOR WITH NON-LINEAR RHEOLOGY FOR A SERIES OF HDPE’S WITH DIFFERENT DEGREES OF SPARSE LONG CHAIN BRANCHING

Donald G. Baird, May 2010

The degree of film-width reduction or necking during film-casting is analyzed for several metallocene-catalyzed high density polyethylenes HDPE with varying degrees of sparse long-chain branching LCB. It is found that the addition of sparse LCB reduces the degree of necking to a greater degree than broadening the MWD. Analysis of the uniaxial extensional and dynamic shear rheology with the pom-pom constitutive model reveals that a distribution of branches along shorter relaxation time modes is important in reducing necking at higher drawdown ratios.

CORRELATION OF FILM CASTING BEHAVIOR WITH NON-LINEAR RHEOLOGY FOR A SERIES OF HDPE'S WITH DIFFERENT DEGREES OF SPARSE LONG CHAIN BRANCHING

Donald G. Baird, May 2010

The degree of film-width reduction or necking during film-casting is analyzed for several metallocene-catalyzed high density polyethylenes, HDPE, with varying degrees of sparse long-chain branching, LCB. It is found that the addition of sparse LCB reduces the degree of necking to a greater degree than broadening the MWD. Analysis of the uniaxial extensional and dynamic shear rheology with the pom-pom constitutive model reveals that a distribution of branches along shorter relaxation time modes is important in reducing necking at higher drawdown ratios.

TRACKING PHASE SEPARATION KINETICS OF BLOCK COPOLYMER SOLUTIONS USING DYNAMIC MECHANICAL MEASUREMENTS

Vandita Pai-Paranjape, André Van Zyl, Jan Pleun Lens, Dake Shen, May 2010

Rheology is used to track the phase separation kinetics of block copolymer solutions during processing and then modeled using the Avrami equation. Previous studies dealt explicitly with disorder-order transitions following shallow temperature quenches. To make this work applicable to the processing of solution-cast films, styrenic block copolymers in solvents of varying selectivity are cast as thin, dilute samples and dried isothermally so that various constant-concentration kinetics can be tracked. Rheology proves to be useful in tracking both rapid and slow kinetics of diblock and triblock styrenic copolymers in toluene. It is found that the diblock copolymer undergoes faster ordering than a triblock copolymer of comparable molecular weight. A competition between thermodynamic driving forces and kinetic suppression of the phase separation exists as concentration changes. AFM images are provided to confirm the kinetic data and to understand the meaning of the Avrami exponent values determined for the different systems studied.

THE RELATIONSHIP BETWEEN TUBULAR LOW-DENSITY POLYETHYLENE (LDPE) BLOWN-FILM OPTICS AND MOLECULAR STRUCTURE

Jaap den Doelder , Teresa Karjala , Mehmet Demirors, May 2010

LDPE product development is accelerated by understanding the relationships between process, structure, rheology, fabrication, and end-use properties. This paper describes the data analysis of a large set of tubular LDPEs.Focus is put on film optics in relation to structure, including fabrication condition effects. It is found that haze, gloss, and clarity are largely independent in the good-optics range. Good optics is found to be related to narrow molecular weight distribution, whereas melt index and density play a secondary role. It is advised to use topology-generating models to further quantify structural features in relation to optics.

3D FORMING OF GENUINE WOOD VENEER AND IN-MOLD LAMINATION WITH WOOD-PLASTIC-COMPOSITES (WPC) IN ONE INJECTION MOLDING CYCLE

C. Funke , H. Potente , V. Schöppner, May 2010

This paper covers the development of an innovative composite material together with a specialized process for 3D formed parts made of Wood-Plastic-Composites (WPC) with genuine wooden surface. Special preprocessed veneers are 3D formed and in-mold laminated with polypropylene-based WPC simultaneously. Questions relating to adhesive strength and warpage of the two components and the injection molding of WPC are analysed and discussed. Another key issue is the scientific derivation of the rheological behaviour of WPC, the optimization of the injection molding process for WPC and the analysis of the warpage between the two materials veneer and WPC

ENHANCING PROPERTIES OF PP-IMPACT COPOLYMERS BY CHEMICAL MODIFICATION

Peter Neuteboom, May 2010

Polypropylene impact copolymers are widely used in automotive applications. They are required to comply with many criteria. Customers demand high-performance materials which also exhibit good aesthetical properties. The challenge is to balance properties as high impact strength, good flow ability and absence of surface defects, like tiger stripes. It is known that peroxide modification whilst increasing the flow ability of polypropylene impact copolymers deteriorates the basic mechanical and aesthetical properties. Work was performed in which a PP-impact copolymer was subjected to peroxide aided chain-scission under simultaneous presence of the co-agent 1,4- butanedioldimethacrylate (1,4-BDDMA). Results show that samples made with 1,4- BDDMA exhibit superior cold impact resistance and tiger stripe performance compared to the materials made with only peroxide. In addition, morphology, molecular weight distribution, and rheological behaviour of the continuous and dispersed phases of the modified PP impact copolymer were studied.

ENHANCING PROPERTIES OF PP-IMPACT COPOLYMERS BY CHEMICAL MODIFICATION

Peter Neuteboom, May 2010

Polypropylene impact copolymers are widely used in automotive applications. They are required to comply with many criteria. Customers demand high-performance materials which also exhibit good aesthetical properties. The challenge is to balance properties as high impact strength, good flow ability and absence of surface defects, like tiger stripes. It is known that peroxide modification whilst increasing the flow ability of polypropylene impact copolymers deteriorates the basic mechanical and aesthetical properties. Work was performed in which a PP-impact copolymer was subjected to peroxide aided chain-scission under simultaneous presence of the co-agent 1,4-butanedioldimethacrylate (1,4-BDDMA). Results show that samples made with 1,4- BDDMA exhibit superior cold impact resistance and tiger stripe performance compared to the materials made with only peroxide. In addition, morphology, molecular weight distribution, and rheological behaviour of the continuous and dispersed phases of the modified PP impact copolymer were studied.

DEFORMATION AND FRACTURE MECHANISMS IN POLYETHYLENE / CLAY NANOCOMPOSITES

Walter Michaeli, Micha Scharf, May 2010

Polyethylene/montmorillonite nanocomposites based on LDPE, HDPE and LLDPE of similar rheological properties were prepared and mechanically tested in tension mode. It was shown that nanocomposites based on LLDPE exhibit a very peculiar behavior, with a significant improvement in toughness (elongation at break). The microstructural features of the various nanocomposites were investigated through scanning and/or transmission electron microscopy. Based on those observations, an explanation for the deformation and fracture mechanisms in LLDPE/montmorillonite nanocomposites was proposed.

COMPLEX THERMAL HOT-RUNNER BALANCING – A METHOD TO OPTIMIZE FILLING PATTERN AND PRODUCT QUALITY

Florian Petzold , Marco Thornagel , Kaushik Manek, May 2010

Depending on the material and process parameters geometrically balanced runners can show rheological imbalances. In hot runner systems these imbalances are handled by controlling the nozzle tempering. However this balancing method leads to high polymer temperatures and causes a product quality that differs from part to part. This paper presents and discusses the preferential polymer flow paths inside hot-runner systems and their dependency on the plastic system as simulated and analyzed by SIGMASOFT. It will be shown that a complex thermal hot-runner tempering layout tweaked by simulation reduces the imbalances and improves the product quality at the same time.

COMPLEX THERMAL HOT-RUNNER BALANCING – A METHOD TO OPTIMIZE FILLING PATTERN AND PRODUCT QUALITY

Florian Petzold , Marco Thornagel, May 2010

Depending on the material and process parameters geometrically balanced runners can show rheological imbalances. In hot runner systems these imbalances are handled by controlling the nozzle tempering. However this balancing method leads to high polymer temperatures and causes a product quality that differs from part to part. This paper presents and discusses the preferential polymer flow paths inside hot-runner systems and their dependency on the plastic system, as simulated and analyzed by SIGMASOFT. It will be shown that a complex thermal hot-runner tempering layout tweaked by simulation reduces the imbalances and improves the product quality at the same time.

THE MECHANICAL PROPERTIES OF MEDIUM MOLECULAR WEIGHT HIGH DENSITY POLYETHYLENE FILMS: MAKING THE LINK BETWEEN ORIENTATION AND RHEOLOGY

T. Ishikawa, F. Nagano, T. Kajiwara, May 2010

This paper describes a study of the mechanical properties of films produced from five different medium molecular weight homopolymer high density polyethylene resins. The machine direction (MD) tear strength and dart impact strength of these films track together. This is due to the tendency of these films to fail during dart impact testing by tearing in the machine direction. The ratio of MD and transverse direction (TD) tear properties correlates with low frequency linear viscoelastic measurements. There is a straightforward relationship between melt index measurements and low frequency rheology for the resins in our study, which relates film properties directly to readily available resin properties and film processing conditions.

A GPC-Mx Approach Of Improving Rheology-Mwd Prediction For Polypropylene

Wallace W. Yau , Jian Wang , Rongjuan Cong , David Gillespie , Joe Huang, May 2010

A new GPC polydispersity parameter, MxR, was introduced in this study. The MxR value, based on the GPC-Mx concept originally proposed by Yau [1], was found to be more suitable to account for the effect of different parts of the polymer molecular weight distribution (MWD) on rheology measurements at different shear rates than do the traditional polydispersity index based on the ratio of Mz, Mw and Mn values. By using this Mx-approach on a set of polypropylene homopolymers, we show that a much improved correlation indeed exists and can be achieved between GPC measurement with the rheology polydispersity indices of PDI and ModSep. Also presented in the paper is the improved correlation between melt flow rate (MFR) and molecular weight (MW) by using this Mx approach.

TRANSIENT RHEOLOGY OF A POLYPROPYLENE MELT REINFORCED WITH LONG GLASS FIBERS

Hesam Ghasemi , Pierre J. Carreau, Musa R. Kamal, May 2010

The purpose of this research is to understand fiber orientation of long glass fibers (> 1mm) in polymer melts and the associated rheology in well-defined simple shear flow. Specifically, we are interested in associating the rheological behavior of glass fiber reinforced polypropylene with the transient evolution of fiber orientation in simple shear in an effort to ultimately model fiber orientation in complex flow. A sliding plate rheometer was designed to measure stress growth in the startup and cessation of steady shear flow. Results were confirmed by independent measurements on another sliding plate rheometer13. A fiber orientation model that accounts for the flexibility of long fibers, as opposed to rigid rod models commonly used for short fibers, was investigated and results are compared with experimentally measured values of orientation. The accuracy of this model, when used with the stress tensor predictions of Lipscomb, is evaluated by comparing against experimental stress growth data. Samples were prepared with random initial orientation and were sheared at different rates. Results show that fiber flexibility has the effect of retarding transient fiber orientation evolution. Additionally, it is shown that the stress growth measurements provide results that are not fully explained by the chosen models.

THE USE OF RHEOLOGICAL AND THERMAL FRACTIONATION METHODS FOR THE ASSESSMENT OF NUCLEATING AGENT EFFICIENCY IN POLYPROPYLENE

Eric Moskala, May 2010

The increasing diversity of commercial polypropylene products in recent years, related to the increase in the production volumes of PP, has led to a high number of studies dealing with structure-specific nucleating agents (NAƒ??s). Experiments on sorbitol-based NAƒ??s suggest that the nucleation function of this group of nucleating agents is a result of hydrogen bonding and self-assembly. So far, nucleation studies have been conducted in an indiscriminate manner with little reference to the exact effect of PP structure on nucleating behaviour of NAƒ??s. However, given the variety of commercial PP structures produced today, the question on the existence of synergy between polypropylene structure and nucleating efficiency of NAƒ??s remains open. The SIST (Stepwise Isothermal Segregation Technique) has been used in this study as a fast and efficient method to characterize a group of random PPƒ??s having different structures, giving the lamellar thickness distribution. In addition, temperature sweep measurements were performed to study the effect of flow on the interaction between NA and PP. In this way, small discrepancies between different materials can be pointed out to assess the nucleating efficiency of the nucleating agent.

PROCESSING AND CHARACTERIZATION OF BLENDS OF POLY LACTIC ACID (PLA) AND SAPINDUS TRIFOLIATUS.

A. Ambekar , A. Kadam , A. Bhoite, May 2010

We investigated thermal mechanical rheological properties of a binary blend of poly lactic acid (PLA) and Sapindus trifoliatus as additive in it. The blends with different percentages of Sapindus Trifoliatus were extruded and their molded properties were examined. DSC thermograms show improvement in the crystallization. Rheological properties changed drastically with increasing percentage of Sapindus Trifoliatus. Tensile strength and modulus increased by addition of Sapindus Trifoliatus. Immiscibility was measured with thermal data. It is also observed that thermal stability of blends was lower than the pure PLA.

EFFECT OF HEAT AND SHEAR ON THE GELATINIZATION OF THERMOPLASTIC STARCH WITH VARIOUS PLASTICIZERS

Avinash Baji, Shing-Chung Wong, Todd A Blackledge, Siwei Leng, May 2010

Different compositions of starch/water/plasticizer slurries are prepared in a batch mixer followed by an equilibration time. The slurries were then subjected to different thermal and shear treatments. A rheological technique has been developed to track the influence of shear on the gelatinization process and the results are also supported by DSC and polarized light microscopy for static systems. Shear has a dramatic effect on gelatinization and the dependence of the onset and conclusion temperatures with slurry composition vary widely depending on the type of plasticizer used.

ULTRASOUND AIDED EXTRUSION PROCESS FOR PREPARATION OF POLYOLEFIN-CLAY NANOCOMPOSITES

Sergey Lapshin , Sarat K. Swain , Avraam. I. Isayev, May 2010

A continuous ultrasound assisted process using a single screw compounding extruder with an ultrasonic attachment was developed to prepare polyolefin/clay nanocomposites. High density polyethylene (HDPE) and isotactic polypropylene (PP) were compared. The feed rate that controls the residence time of the polymer in the ultrasonic treatment zone was varied. Die pressure and power consumption were measured.Rheological properties morphology and mechanical properties of the untreated and ultrasonically treated nanocomposites were studied. Similarities and differences of obtained nanocomposites are discussed based on their properties and structural characteristics.

COMPLEX VISCOSITY OF LIQUID N-HEXADECANE UNDER OSCILLATORY SHEAR USING NON-EQUILIBRIUM MOLECULAR DYNAMICS SIMULATIONS

Henry Pawlowski, May 2010

Rheological computer experiments, involving small amplitude oscillatory shear flows for liquid n-hexadecane, are performed using non-equilibrium molecular dynamics methodology. In particular, the so-called Cox-Merz rule, which suggests that the magnitude of the complex viscosity with respect to frequency is equal to that of the steady shear viscosity with respect to shear rate, is validated. At different frequencies, the complex viscosity, including both dynamic and out-of-phase parts, varies significantly with respect to temperature. ?ÿ

RHEOLOGICAL BEHAVIOR OF POLY(1-BUTENE)/WOOD COMPOSITES

Yan-Chen Chiou, Ya-Yuen Chou, Hsien-Sen Chiu, Chau-Kai Yu, Chia-Hsiang Hsu, May 2010

The work deals with the influence of content of the untreated wood flour filler (natural pine wood) on rheological behavior of blends with poly(1-butene) matrix. Therefore the blends with 5, 10, 15, 20, 30 and 50 % of wood flour were prepared in microcompounder. The rheological behavior was studied in oscillatory shear regime. Cole-Cole plot was used for determination of differences in molecular weight and distribution. It was found that low content of the wood flour acts as a lubricant agent and decreases zero shear viscosity. On the contrary, increasing content of the wood flour has an opposite effect.