Research Interests

Selected References

Research Projects

Group Members



Research Projects








Research Plan

Since I started my appointment in 2002, my focus has been on Polymer Materials. High quality research recognized by the international community, training of highly qualified personnel, and relevant interaction with industry has been the goal of this program.


The scope of my research program includes four theme areas.


Hybrid Polymer Nanocomposites

This area of research was initiated in the Department of Chemical Engineering by the candidate. Polymer nanocomposites have the phase distribution at the nanoscale level. Commercially available nanofillers (nanopowders) or materials with potential to provide nanostructures (clays) are added to the polymerization reactor. This is called in situ polymerization method.


Polyolefins are among the major commodities used in our modern lives. To improve the properties and to extend the applicability of such materials, our research group is developing hybrid nanocomposites of polyolefins and inorganic particles. These hybrid materials have excellent compatibility between the organic phase and the inorganic phase because the polyolefin is covalently bonded to the inorganic phase. Among a large universe of inorganic phases, we are currently investigating layered silicates, such as montmorillonite, and metal oxide nanopowders, such as aluminum oxide, titanium oxide and silica. The nanocomposites are produced inside the polymerization reactor. During the polymerization process, the polymer chain is chemically connected to the surface of the inorganic phase. We are paying special attention to the polymerization of olefins and polar comonomers catalyzed by transition metal complexes.


From this point of view, polymer chains are grown from the bottom-up on the surface of nanoparticles. Hybrid nanostructures that have polymer chains covalently bonded to the surface on nanoparticles have several advantages: a) there is a better control over the phase distribution at the nanoscale; b) re-aggregation of nanoparticles during materials processing is prevented; c) distinct polymer structures, that can be obtained by copolymerization or using different polymerization mechanisms simultaneous, have the potential to self-assemble on the surface of nanoparticles.


Although several inorganic nanoparticles are readily available commercially, their proper incorporation in polymer systems is still a challenge; the use of convention blending methods generally leads to aggregation of nanoparticles within the polymer matrix and little or none improvement on final properties is obtained. More importantly, some properties are only achieved by the proper control of the nanostructures.


To achieve the desired properties for an application, a method of producing polymer nanocomposites capable of controlling the interface is quite important. Several methods have recently been employed ranging from simply mixing polymer with fillers to more elaborated approaches. A key challenge in the preparation of nanocomposite materials is the establishment of good dispersion of nanosize inorganic phase into the polymer matrix and the efficiency to prevent re-aggregation of nanoparticles


Our research group in the Department of Chemical Engineering, at the University of Waterloo, has investigated new methods to produce a nano-filler well dispersed into the polyolefin matrix and the effect on the physicochemical properties. We have focused on the study of the chemical modification of nanopowders their interaction with the polymerization mechanism to create hybrid materials. This new class of materials has polyolefin chains covalently bonded to the surface of nanopowders during the polymerization reaction. 


Polyolefin-layered silicate (clay) nanocomposites

We have been actively developing the area of polyolefin-clay nanocomposites. The scope of our research includes: a) developing a drop-in technology for supporting coordination catalysts that can be implemented at industrial scale; b) use of organic modifiers on the clay to allow growing polymer chains to bond to the clay surface during polymerization (hybrid nanocomposites); and obtaining a product where clay is separated into nanolayers (exfoliation). Control of molecular weight and branching in hybrid nanocomposites has already been demonstrated. We are currently working in collaboration with General Motors Canada, on a research contract, for the development of hybrid polypropylene-clay thermoplastics nanocomposites.


Polymer-nanopowder nanocomposites

Conventional polymer composites, usually reinforced by micrometer-scale fillers into polymer matrices, have found large-scale applications for decades in automobile, construction, electronics, and consumer products.  Composites gain enhanced properties such as higher strength and stiffness compared with neat polymer. However, properties achieved by these traditional composites involve compromises. For example, stiffness is obtained at cost of toughness, which is also traded for optical clarity. Recently, nanoscale filled polymer composites give a new way to overcome the limitations of traditional counterparts.


To realize the novel properties of polymer nanocomposites, synthetic methods which have effect on controlling particle size distribution, dispersion, and interfacial interactions are critical. Synthetic techniques for nanocomposites are quite different from those for conventional microscale-filled composites and creating one universal technique for developing polymer nanocomposites is impossible due to the physiochemical differences between each system. Each polymer system may require a special set of processing conditions to be formed and different synthetic techniques in general could yield non-equivalent results.



Polymer Reaction Engineering

Mathematical Modeling of Polymerization Mechanisms

Coordination catalysts are extensively used for polymerization of olefins in industry. Good control of polymer molecular weigh and chemical composition are the most attractive features in this process. Because not all polymer chains have the same molecular weight, a distribution of molecular weights is obtained after polymerization. The same is valid for the chemical composition in copolymers or branched polymers. Through understanding the catalytic mechanism it is possible to predict what types of structures will be formed for a certain polymerization condition. To advance this knowledge in this area, we have been developing stochastic models to simulate the polymerization mechanism. Monte Carlo models are programmed in C + + language and used to predict with great detail the composition of polymer structures for a given reactor condition.


Synthesis and Characterization of Thermoplastic Elastomers

Thermoplastic elastomers are materials that have the elasticity of elastomers combined with the easy processability of thermoplastics. Instead of chemical crosslink, thermoplastic elastomers have a network of amorphous chains cross linked by physical domains of crystalline material. We have been working on the synthesis and characterization of polypropylene thermoplastics produced using two coordination catalysts. In a first stage, one catalyst produced isotactic polypropylene chains terminated by vinyl groups. In a second stage, another catalyst produces atactic polypropylene chains and also incorporates those vinyl terminated chains produces in the first stage. The final product is a mixture of chains with different composition, including long chains atactic polypropylene with long branches of isotactic polypropylene. This approach has also been extended to other polyolefins as well.



Polymer Materials

Characterization of Polymer and Properties

The final engineering properties of any polymer are a consequence of its molecular structure and its morphology in the solid state. Distribution of amorphous and crystalline phases, interfacial content between these phases, presence of fillers, blends of immiscible polymers can dramatically affect thermal and mechanical properties. We are interested in understanding thermal, mechanical, and degradation properties of polymer materials and macromolecules. The rational is to understand the structure of materials well enough to a point where the properties and the behaviour can be predicted. Ultimately, the development of structure-properties relationships is desired.


Currently we have been working on the characterization of degradation of membrane electrolyte assemblies (the core polymeric membrane used in hydrogen fuel cells, degradation of silicone rubber filled with nanopowders (material used in high voltage insulators), characterization of hydration in oriented polypropylene filled with Portland cement, characterization of protein immobilized in sol-gel thin films, and mechanism of creep in glass fibre polypropylene composites.




Research grants were recently obtained. Two areas that we are active include the application of wood and agricultural fibres in polymer bioproducts and the preparation of polymer materials based on renewable resources, which in some instances can be biodegradable.


High-impact wood-thermoplastics

Wood fibre filled thermoplastics have found several application in building, furniture and transportation industry. The objective of our research is to improve the impact properties of thermoplastics filled with wood fibres. The approach that we have been working on is to use in situ polymerization on the surface of the fibres. By controlling the interfacial adhesion and the stiffness of the polymer on the surface of the wood fibre we expect to significantly improve impact properties without affecting the overall stiffness and strength of the thermoplastic composites.


Application of wood and agricultural fibre in polymer bioproducts

Crop-based materials are becoming more prominent in a growing range of products, including packaging, automotive parts, and building materials such as panel-board, siding, window frames, and decking. Such materials include fibres from crops and thermoplastics. The rational is to increase the use of renewable materials as functional fillers for polymer matrices or the creation of polymer based materials completely from renewable sources. 


Biodegradable polymer films

This is a more recent project that started in January 2007. Protein films can be prepared from a variety of plant proteins by solution casting, spray drying or flash drying. In general, protein films present good barriers to oxygen and aromas at low to intermediate relative humidity. They are resistant to fats and oils, but they are not good barriers to water. This project will focus on understanding how physical and chemical parameters affect film preparation, how films interact with water and how to control final thermal and mechanical properties. Important parameters on film structure will be correlated to their effects on processing and final film properties such as colour, brittleness, water permeability and strength.