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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. 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. 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. |
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