John Vlachopoulos
Professor Emeritus, Chemical Engineering

Arriving at McMaster University after defending his doctoral dissertation (August 1968), John Vlachopoulos started teaching fluid mechanics, heat transfer, rheology and polymer processing courses, at both undergraduate and graduate level. He focused the research efforts with his graduate students, research staff and postdoctoral fellows on polymer processing and rheology. He founded and directed the Centre for Advanced Polymer Processing and Design CAPPA-D (1987-2017). His former graduate students and research coworkers are now university professors or occupy important positions in industry in Canada, USA, Latin America, Europe and the Far East. Special emphasis was placed on rheological characterization of polymers, on developing mathematical models and solving problems of industrial relevance, using finite element and finite difference methods. The most important research accomplishments and projects include:

1. POLYMER EXTRUSION INSTABILITIES: Relations involving molecular weight distribution and elucidation of the role of molecular disentanglements on extrudate swell and melt fracture phenomena.
SCREW EXTRUSION OF PLASTICS: Models of the entire plasticating single screw extrusion process from hopper to die exit and applications to screw design, as well in simulation of peroxide degradation for the production of controlled rheology PP.

2. EXTRUSION DIE FLOW SIMULATION AND DESIGN: Simulation of flow through dies for the production of cast film, sheet, blown film, profiles and development of computer assisted methodologies for design of flat, spiral and profile dies.
CALENDERING: Models with and without the hydrodynamic lubrication approximation involving wall slip and normal stress effects. Prediction of forces, pressures, torques and the existence of vortices in the melt bank.

3. FOUNTAIN FLOW IN INJECTION MOLDING: First ever published simulation of this phenomenon as well as elucidation of the role of kinematics, shear thinning and viscoelasticity. Explanation of the orientation phenomena behind an advancing flow front in cavity filling.

4. THERMOFORMING: Finite element simulation of polymer sheet inflation involving hyperelastic and viscoelastic constitutive equations with and without the membrane approximation.
PARTICLE COALESCENCE (SINTERING): Frenkel’s 1945 model, which was applicable to the very early stages of the process, was extended for the first time to full completion and inclusion of viscoelasticity. The extended model is currently being used in modeling sintering phenomena in selective laser sintering (SLS) and fused deposition modeling (FDM) by several research groups.

5. ROTATIONAL MOLDING: Development of rheological characterization techniques and observations of melt densification under a microscope for the determination of rotomoldability of resins including foams.
BLOWN FILM EXTRUSION: Elucidation of interactions between polymer rheology and the aerodynamics of cooling by turbulent impinging air jets, including the Venturi and Coanda effects. Studies of external single and dual orifice cooling jets and internal bubble cooling (IBC).

6. PLASTIC WOOD COMPOSITES EXTRUSION: First ever published studies of the surface tearing phenomenon that appears as some sort of exaggerated sharkskin. Study of the role of wall slip.
RHEOLOGY OF COMPOSITES AND RECYCLED PLASTICS: Rheological changes in plastics recycling, rheology of biodegradable polymers, rheology of composites including carbon nanotubes.