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SPE Library content related to rheology
Long Chain Branching of Polypropylene via UV Radiation: Effect of Coagent and Other Radiation Variables on Continuous Modification
Continuous photomodification of polypropylene (PP) has been conducted in order to scale up a previously developed batch process for commercialization purposes. Utilizing this process PP rheological properties were modified by incorporation of long chain branches (LCBs).
Trimethylolpropane triacrylate (TMPTA) was employed as a coagent along with benzophenone (BPH), which was the photoinitiator. The effects of TMPTA presence, BPH concentration, and radiation duration on viscoelastic properties and gel content were studied. Gel permeation chromatography (GPC) was used to confirm formation of LCBs in the photomodified PP.
SPE Applied Rheology Division April 2015 Newsletter
Read the latest issue of the SPE Applied Rheology Division newsletter.
Innovative approach to the design of profile extrusion dies
Investigation of an extrusion die designed for the production of wood-plastic-composite decking profiles shows that numerical tools help to optimize flow balance.
Modeling multilayer film co-extrusion
Die plug analysis and chloroform washing validate a computational fluid dynamics model of polyester co-extrusion.
Microstructure and rheology of high-melt-strength poly-(propylene) impact copolymer
Separating a linear and a long chain branched impact polypropylene copolymer (ICP) into their subcomponent phases reveals the long chain branching and microgel content of each phase.
Controlled branching in propylene polymerization
A validated mechanistic kinetic model for a long-chain branched polypropylene system is proposed and optimized for controlled branching for the first time.
High-shear-rate capillary rheology of polymer melts
Investigation into the high-shear-rate rheology of polystyrene, polypropylene, and linear low-density polyethylene melts yields their true viscosities and sheds light on their rheological behavior.
Screw speed and nanocomposite rheology
Process conditions affect the intercalation, exfoliation, slippage of polymer chains, and relaxation times of polymer-clay nanocomposites.
Improving the scratch-resistance of acrylic glass
Nanoindentation studies show that incorporating functionalized multiwalled carbon nanotubes into polymethylmethacrylate hardens it and improves its elastic modulus.
High-performance compostable polymer biocomposites
Blending modified polylactic acid with hemp or jute fibers using hot melt extrusion improves its mechanical properties and compostability.
Characterization of glass fiber-reinforced high-density polyethylene
Glass fiber-reinforced high-density polyethylene composite increases in strength as the fiber orientation increases in anisotropy, which could lead to stronger composite materials.
Preparation and Rheological Properties of Epoxy-Based Liquids with Adjustable Viscosities
Epoxy-based liquids with adjustable viscosities were prepared by curing a two-component resin mixture at variable mixing ratios and their rheological properties were then characterized using a parallel plate rheometer. The viscosity was found to decrease as the portion of amine compound component decreased. Moreover, the rheological properties of such liquids were found to be highly thermally sensitive. At last, the authors proposed a possible mechanism to explain the viscosity change at different resin mixing ratios.
The Effect of Multilayer Rheology on the Flow Distribution in a Coathanger Style Die
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 the effect of experimentally measured multilayer rheology on the flow distribution in a coathanger style die.
Cyclic Olefine Copolymer (COC) Nanocomposites and Nanocomposite Foams: Preparation, Morphology and Properties
Cyclic olefin copolymers (COC)/ multi-wall carbon nanotubes (MWCNTs) composites of different carbon nanotubes (CNTs) concentration were prepared by melt blending. The dispersion of the CNTs in the polymer matrix was investigated by scanning electron microscopy (SEM). The rheological property and the electrical conductivity of the nanocomposites were studied. In addition, the nanocomposites were foamed by carbon dioxide, and the effects of the CNTs on the foam cell morphology were investigated.
Using Rheology to Understand Silcone Elastomers
Silicone thermoset elastomers are increasingly being used in over-molding or co-molding applications with thermoplastic polymers. Understanding the fundamental properties of silicone formulation components and the material property changes that occur during crosslinking is essential to successful molding and use. Rheological and dynamic mechanical characterization are outstanding tools for building an understanding of silicone thermal and elastic properties, as well as the cure reaction chemistry that takes place during silicone molding processes.
The Role of Rheology in Non-Pressurized Polymer Foaming Systems
This work explores the influence of rheological properties on polymer foam development in non-pressurized systems. To understand the complex contributions of rheology on different stages of the foam processing in such systems, visualization studies were conducted using a polymer-foaming microscopy setup. Morphological analysis was used to determine the rheological processing window in terms of shear viscosity, elastic modulus, melt strength and strain-hardening, intended for the production of foams with greater foam expansion and more uniform bubble size distribution.
Rheology and Slot Die Coating Technology
Slot die coating technology is a function of the coating process, auxiliary system and fundamental technique. The decision to utilize a coating technology needs to be analyzed against these functions to determine best fit. In the era of clean, thin and precise converting operations, a customized coating system is necessary to have a technical edge. Building the system from the material up to the process sets the stage for a high precision tool designed around the process needs. This material up building process begins with the rheology of the fluid. Rheology is the study of flow. When you talk about squeezing, spreading, or lubricating a fluid, you are talking rheology. When you apply a force that causes a fluid to move, rupture, or flow you are describing a rheological force. Understanding rheology is fundamental to building fluid coating processes and inparticular a slot die coating head. The dramatic increase in the expectations of coated products, in areas as diverse as optical films to battery technology, has put substantial pressure on the systems used to produce the next generation of coated products. With increased speeds, thinner coatings and increased functional performance, awareness of coating techniques and technologies is required. The world is changing and new tools are needed to compete in the changing world markets. An awareness of coating techniques, technologies and systems allow for novel adaptations and application to new market opportunities. Rheological understanding and an application to slot die technology provides innovative tools that will help coating companies improve precision, tackle new markets, and develop new processes.
Preventing Squeeze-Out of Sealant during Hot Bar Sealing: Modeling and Experimental Insights
Excessive pressure and temperature during hot bar sealing can result in poor seals due to squeezing out of the sealant. A model is developed that shows the amount of squeeze-out increases with increasing seal bar pressure, seal temperature (by lowering the viscosity of the sealant), sealing dwell time, film thickness and decreasing seal bar width. Photomicrographs of the seal area reveal the change in sealant thickness near the edge of the seal area which correlates with the model predictions. The study shows that differences in rheological behavior of sealants, such as that between linear and branched polyolefins, can impact squeeze-out. Practical guidelines are proposed from the work to prevent problems associated with excessive squeeze flow.
Effects of Temperature and Viscoelasticity on Film Die Flow Uniformity
This study shows the effect of die temperature distribution and resin viscoelacticity on the flow uniformity in a film die. The magnitude of the thermal affects can be significant enough to mask other rheological effects. Computational Fluid Dynamics (CFD) simulations predictions using temperature-dependent viscosity models and gradients in the die wall temperature boundary conditions agreed well with the experimental measurements of flow uniformity. When the die wall is more uniformly heated, the flow uniformity is improved in both the measurements and simulations, although the simulations showed more deviation from the experimental results as the elasticity and shear thinning of the resins increased.
Unique Rheological Properties of Polymer Melts with Flexible Nanofibers
Rheological response under elongational flow is studied using polymer melts with polymeric fine fibers composed of poly(butylene terephthalate) PBT and poly(4-methyl-1-pentene) PMP. Both fibers are prepared by hot-stretching of the blends with isotactic polypropylene PP or poly(L-lactic acid) PLA. The samples with 1 wt% of PBT fibers whose diameters are smaller than 1 µm show marked strain-hardening in elongational stress. On the contrary, the sample with PMP fibers with a diameter of approximately 2 ?m shows no strain-hardening, although the measured elongational stress is significantly higher than that calculated from the linear viscoelastic properties.
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