Time: Thursday, May 15th, 11:00 a.m. & Friday, May 16th, 11:00 a.m.
Location: AGGARWAL LECTURE HALL, Room 130
Lectures Are Free And Open To The Public
Natural fibers are used in continuously increasing quantities as low-cost renewable fillers and reinforcements at very high loadings for decking, automotive and housing applications. The addition of fibers into a polymer matrix results in increase of melt viscosity and storage modulus, and the composite exhibits wall slip, surface tearing and other instability phenomena. The viscosity increase shows the same general trend predicted by theories for suspensions of neutral density spheres, but particles of different size and shape and interactions result in impossible to predict rheological behavior. Entrance pressure losses in capillaries also increase with loading and the relative increase depends strongly on polymer type and molecular weight. Surface tearing, which appears, like some sort of aggravated sharkskin, increases with loadings up to 50%, but can disappear completely at 60%. The surface appearance usually improves with increasing the shear rate, due to increased wall slip velocities. Lubricants are also beneficial. Die surface cooling improves surface appearance, it is widely used in industry and several techniques are described in the patent literature. Coupling agents are used for improvement of mechanical properties and they also influence the rheological behavior. They increase the resistance to shearing. For profile die design computer flow simulations for shear-thinning models are useful and, of course, good viscosity measurements are necessary.
Finite element and finite volume solutions of the mass, momentum and energy conservation equations (2-D or 3-D), for polymer melt flow, have led to significant improvements in die design for cast and blown film extrusion. The design criteria are: minimization of thickness variation at the die lip exit, avoidance of low wall shear rates to prevent degradation, reasonable pressure drops and avoidance of high wall shear stresses at the die lip walls to prevent the onset of sharkskin melt fracture. Repetitive sequences of computer simulations are necessary till satisfactory results are obtained for ‘routine’ design purposes. Numerical optimization of die design remains a challenge. Modeling of necking and draw resonance phenomena in cast film extrusion has received considerable attention in the literature usually on the basis of the thin membrane approximation. Edge beading has received less attention. These modeling efforts have had very limited impact on cast film production technology thus far. Modeling of blown film bubble shape has been the subject of numerous publications on the basis of thin membrane approximation and some publications have dealt with bubble instabilities. Again, there has been very little impact of the modeling efforts on blown film production technology. Cooling by multiple external and internal turbulent impinging air jets plays a very important role in determining bubble stability and production rate. It will be necessary that viscoelastic modeling of film extrusion be combined with the aerodynamics of cooling and heat transfer and studies in crystallinity, for the eventual prediction of film properties, for both blown film and cast film.
John Vlachopoulos was educated at NTU in Athens, Greece and at Washington University (St. Louis, MO) before joining the Department of Chemical Engineering at McMaster University in Hamilton, Ontario, Canada. He has been on sabbatical research leave at IKT, University of Stuttgart, Germany and at CEMEF, Paris Tech, in Sophia Antipolis, France. His research efforts are focused on various aspects of polymer processing and rheology including computer modeling of plasticating extrusion, die design, wood plastic composites extrusion, blown and cast film extrusion, rotational molding, injection molding and thermoforming. He has published some 300 papers in journals, conference proceedings and as book chapters. With his co-workers he has developed several commercially available computer software packages for melt flow simulation and licensed them to several hundred corporations in 31 countries, through his company Polydynamics Inc. He is the recipient of the Education Award of SPE, the Distinguished Achievement Award of the Extrusion Division of SPE and the S.G. Mason Award of the Canadian Society of Rheology. He has served as President of PPS 2005-2007. He is currently Professor Emeritus at McMaster University and active consultant and supplier of software to industry around the world. He has offered his short course on rheology and extrusion to polymer professionals, 73 times, in seven languages and in several countries around the world.