Disentanglement Control to enhance Plastic Processing Lecture # 37 (Applications) by J-P IbarPLASTICS: PLASTICS: “Thermoplastics Thermoplastics” Generally processed by heating and pressurizing the Generally processed by heating and pressurizing the material material Heating softens the material. Heating softens the material. To Reduce Viscosity To Reduce Viscosity When the viscosity is reduced to When the viscosity is reduced to liquify liquify the resin, then the resin, then the material is forced into the desired shape using many the material is forced into the desired shape using many different processes. different processes. Platics Platics degrade at high temperature and degradation degrade at high temperature and degradation reduces strength and mechanical properties reduces strength and mechanical propertiesWhat if ? What if ? What if a plastic melt could flow 10 times better? What if a plastic melt could flow 10 times better? What if a plastic melt could be processed at What if a plastic melt could be processed at substantially lower temperature? substantially lower temperature? What if extrusion could be done with What if extrusion could be done with substantially lower pressure? substantially lower pressure? What if extrusion throughput could increase What if extrusion throughput could increase substantially ? substantially ? What is the key to make this happen? What is the key to make this happen? REDUCE VISCOSITY REDUCE VISCOSITYViscosity is defined as the ratio of Shear Stress to Shear rate Viscosity is defined as the ratio of Shear Stress to Shear rate Water = .001 Pascal Water = .001 Pascal-seconds seconds Honey = 10 Honey = 10-100 Pascal 100 Pascal-seconds seconds Molten Plastics = Molten Plastics = 100 100-1 million Pa 1 million Pa-s Viscosity decreases substantially with increasing shear rate Viscosity decreases substantially with increasing shear rate Viscosity decreases with higher temperature (this has been the Viscosity decreases with higher temperature (this has been the main technology available to work with). main technology available to work with). Viscoelastic fluid, has strain energy stored within, recovers Viscoelastic fluid, has strain energy stored within, recovers deformation, creates swell problems entering molds and cavities. deformation, creates swell problems entering molds and cavities. Melt micro Melt micro-fractures due to excessive shear friction, degrades. fractures due to excessive shear friction, degrades. Viscosity ViscosityENTANGLEMENTS are responsible for high Viscosity ENTANGLEMENTS are responsible for high Viscosity Length of the macromolecules is characterized by Molecular Length of the macromolecules is characterized by Molecular weight. weight. Resin producers offer various grades, with great difference in Resin producers offer various grades, with great difference in chain lengths: chain lengths: LDPE magnified 100 million X: extended length is15m LDPE magnified 100 million X: extended length is15m UHMWPE magnified 100 million X: length is between 3 UHMWPE magnified 100 million X: length is between 3 km km --8 km 8 km The macromolecules are very long when fully extended , The macromolecules are very long when fully extended , but but with no stress, they coil up in spherical macro with no stress, they coil up in spherical macro--coils that coils that entangle one another, entangle one another, creating a tangled web. creating a tangled web. a polymer melt is a network of these a polymer melt is a network of these ENTANGLED coiled chains. ENTANGLED coiled chains. Can a melt be Can a melt be “disentangled disentangled”?Shear Induced Vibration Boosted Shear Induced Vibration Boosted Disentanglement: Disentanglement: “Dynamic Shear Dynamic Shear-Refinement Refinement” Dynamic Shear Dynamic Shear-Refinement produces Refinement produces “disentanglement disentanglement” of macromolecules and makes of macromolecules and makes melts of long chain molecules flow like shorter melts of long chain molecules flow like shorter chain molecules: chain molecules: the disentangled melt enhances mixing with the disentangled melt enhances mixing with additives, such as additives, such as nanocomposites nanocomposites. REFERENCES: REFERENCES: Thesis of Sylvain Thesis of Sylvain Bourigaud Bourigaud at UPPA (2005) Polyethylene (branched). at UPPA (2005) Polyethylene (branched). Thesis of Steffen Berger (2006) Polypropylene (high Mw). Prof. Thesis of Steffen Berger (2006) Polypropylene (high Mw). Prof. Munstedt Munstedt, University Erlangen. , University Erlangen. Extensive Investigation of Dynamic Disentanglement technology by Extensive Investigation of Dynamic Disentanglement technology by JP JP Ibar ( 1999 Ibar ( 1999-2006): linear polymers (PMMA, PC, PETG, EVOH, PP, 2006): linear polymers (PMMA, PC, PETG, EVOH, PP, LLDPE LLDPE…). ).Boosting of Disentanglement Boosting of Disentanglement To boost the disentanglement of macromolecules, To boost the disentanglement of macromolecules, JP Ibar had the idea of a combination of extensional JP Ibar had the idea of a combination of extensional flow, shear flow and vibration to exercise on a flow, shear flow and vibration to exercise on a molten plastic as it is continuously extruded to pass molten plastic as it is continuously extruded to pass through treatment stations at determined through treatment stations at determined temperature, frequency and amplitude of vibration, temperature, frequency and amplitude of vibration, during and under specific during and under specific shear and vibrating shear and vibrating conditions, to obtain a controlled progressive conditions, to obtain a controlled progressive decrease in the entanglements between decrease in the entanglements between macromolecules, in order to significantly and macromolecules, in order to significantly and controllably decrease the viscosity of the extruded controllably decrease the viscosity of the extruded melt. melt. Benefits of Disentangling Benefits of Disentangling Technologies Technologies Reduce viscosity of melt prior to another molding operation such Reduce viscosity of melt prior to another molding operation such as as mixing blends, additives, composites: new products, new process mixing blends, additives, composites: new products, new processes. es. Viscosity is lowered during processing, allowing preparation of Viscosity is lowered during processing, allowing preparation of higher higher concentrate concentrate masterbatches masterbatches for for nanocomposites nanocomposites. . With less viscosity for the plastic melts, With less viscosity for the plastic melts, nanocomposites nanocomposites and composites and composites have reduced energy to process. Some examples of applications: have reduced energy to process. Some examples of applications: Lower melt temperatures: 50 deg C reduction is not uncommon Lower melt temperatures: 50 deg C reduction is not uncommon Lower pressures during extrusion: factors of 10 to 20 Lower pressures during extrusion: factors of 10 to 20 Higher throughputs: more than 40% for film casting (faster coo Higher throughputs: more than 40% for film casting (faster cooling ling from lower T) from lower T) Improve quality of end product Improve quality of end product Better dispersion of Better dispersion of nano nano-particles in the final production resulting in particles in the final production resulting in Mechanical improvements Mechanical improvementsResearch Project Research Project Fundamental understanding of Shear Fundamental understanding of Shear-Refinement Refinement (rheology rheology, molecular origin) is missing. , molecular origin) is missing. Why? Why? Present knowledge is rather empirical: shear Present knowledge is rather empirical: shear--refinement refinement processing parameters vary with throughput, chemical processing parameters vary with throughput, chemical polymer etc. polymer etc. It costs too much to find the correct Shear It costs too much to find the correct Shear--Refinement Refinement processing window empirically processing window empirically Needs correct modeling from fundamental research. Needs correct modeling from fundamental research. Previous Disentangling machine was too costly, because of Previous Disentangling machine was too costly, because of the lack of understanding. the lack of understanding.What is the SESAME Project? JP Ibar has designed a 2nd generation apparatus to disentangle polymer melts and is leading a collaboration on this project between several universities across 3 continents, all dedicated to the improvement of polymer properties by melt manipulation (“smart processing”). J.P. Ibar: -Presently Fulbright Visiting Professor at IPREM. -Consultant for the Plastic Industry. -Has been awarded a 4 year Marie-Curie Grant. -Leader of the SESAME Consortium. --teaches courses on the internet on: -“smart processing” technologies (IM /extrusion under vibration). -Characterization of Polymers by Thermal Analysis: an industrial practice. -Non-Linear Viscoelasticity: application to processing. -The Instability of Entanglements of Polymer Melts: from theory to applications -The SESAME project has received substantial interest from the industry. -Objective: understand and apply the rheology of Polymer Melt Entanglement to Processing The SESAME project deals with polymer physics and its application to melt processing, often described as « Plastic Processing ». Their high viscosity implies the use of large torque and pressure in the equipment used to process them (extruder, twin-screw, injection molding machine). The high viscosity is due to entanglements. Traditional remedy has been to reduce viscosity by raising temperature, but with the known limitations due to degradation. Several universities of world wide reputation on 3 continents (Europe, USA and China) will collaborate on this project to control the viscosity and elasticity of polymer melts and reduce them by “disentanglement of the macromolecules” induced by strong deformations. The theoretical challenge is to understand the stability of entanglement of melts with respect to deformation and produce useful applications in the area of processing, for instance for the compounding of masterbatches of well dispersed carbon nanotubes. J-P Ibar has recently explored the use of shear oscillation superposed to shear and extensional stresses to amplify the magnitude of viscosity and elasticity reduction obtained by shear-refinement in a modified lab dynamic rheometer. A new processing machine capable of modifying the stability of entanglements has been designed. This new generation “disentangler” will produce disentangled melts. The characterization of the properties of those melts and of the articles created from them is the object of the present international collaboration between several universities. The project is backed up by the industry, with many practical applications in the compounding of plastics with wood flour, nano-particles, thermally instable additives. Objective: understand and apply the rheology of Polymer Melt Entanglement to ProcessingDevelopment of Science & Technology of Melt Disentanglement. Part I: Equipment Manufacturing of a new Disentanglement Processor For conducting lab experiments, we must build a small lab demo machine which practices to control the melt visco-elasticity by thermal-mechanical treatment manipulation. Ideally, this machine should be small enough to be driven by low power electrical motors capable of combining the shear and oscillation to the melt. 1. Design and drawings (done). 2. Manufacturing costs: 2.1 Feeder: 2.2 Exit pumps: 2.3 on-line rheometer: 2.4 sensors, transducers, PC, interfaces, software: 2.5 Disentanglement Processor mechanical parts: 2.6 electrical drives and motors.
Description
It has been empirically demonstrated by experiments I conducted in the last 10 years that thermal-mechanical history of a polymer melt, in particular the use of mechanical oscillation superposed to shear and extensional flow (for instance in the gap of an extruder) boosts the magnitude of viscosity and elasticity reduction obtained by "disentanglement". At the same time, several universities of world wide reputation called “shear-refinement” the reduction of viscosity and elasticity of branched polymer melts by a pre-shearing treatment. Viscosity and melt elasticity play a crucial role during processing of plastic materials, being responsible for the high temperature required to produce flow, also responsible for thermal degradation, for the long cycle times and thus for the present productivity limitation in our industries. In the case of loaded polymers, which addresses more than 80% of the polymer resin used today, their high viscosity, aggravated by the presence of the concentrate, limits the maximum amount of dispersants allowed, such as for carbon nanotubes (“CNT”), as well as the quality of the mix.
The objective of this Lecture is to introduce the need of a collaboration between several universities and the industry (the SESAME project) to transform the “art” of Disentanglement/Shear-Refinement into a solid science, based on a fundamental understanding of the effect of molecular variables (such as chain molecular weight Mw, degree of branching, branch length), and processing variables (such as strain amplitude, strain rate, extension ratio, in other words melt thermal-mechanical history) on melt disentanglement and re-entanglement. The fundamental science is required to expand the shear-refinement technology from an art form to a rapidly expanding commercial platform. The understanding of disentanglement from a molecular and rheological aspect must be resolved and controlled. LECTURE available with audio.<