Research Areas
Research at CEPSE is conducted in a wide range of
areas that include
Polymer Rheology, Polymer
Processing, Polymerization Reaction Engineering,
Novel Polymer Systems and Characterization,
Polymer Synthesis, Rubber
Recycling, Solid State Formulation of
Powder Coatings, and Process Modeling,
Monitoring and Control. Brief descriptions of the activities
in each of these research areas are given below.
Polymer
Rheology
Polymeric
materials display complex rheological behavior that includes shear-rate-dependent
viscosities and large elastic (memory) effects. Whereas the flows
of simple Newtonian fluids are governed by the well-known Navier-Stokes
equation, polymeric materials are not. Rheology is the study of
relationships between flow fields and the stresses that arise
in order to learn the proper governing equations. CEPSE has focused
on the characterization of such advanced materials, and the understanding
of relationships between macromolecular constitution and macroscopic
flow behavior. Because of the complicated relationship between
structure and flow behavior, rheology also provides unique material
characterization tools.
A
combined experimental and theoretical collaboration between Professors
Schieber
and Venerus
has resulted in a full-chain reptation molecular model for entangled
linear polymers that quantitatively predicts non-linear rheological
behavior in a wide range of flows that includes single- and double
step strains, startup and cessation of constant strain rate and
exponentially increasing strain flows.
These and other flows are
also used to evaluate other rheological models such as single-segment
reptation and pom-pom models.
Other
experimental research involves the development of novel rheological
techniques for generating elongational flow fields, particularly
equibiaxial elongational flow. These techniques include a novel
lubricated squeezing flow method for which a US Patent
has been issued and bubble inflation. Data from these and other
flows are used in the formulation and evaluation of rheological
constitutive equations and to establish relationships between
chemical structure and flow behavior in linear and branched polymers.
One current project is focused on the rheology of metallocene-catalyzed
poly-ethylenes and poly-propylenes.
Additional
research at CEPSE has developed theoretical and numerical techniques
to relate nanoscale properties to macroscopic rheological properties.
For example, efficient stochastic simulations for rigid-rod-like
structures that lead to liquid crystalline materials have been
developed. These techniques have also been used in finite element
simulations to predict flow fields in complex geometries for a
wide variety of polymeric materials. Back to top
Polymer
Processing
Transport
models (for fluid flow, heat transfer and mass transfer) solved
on powerful computers are essential tools in modern process engineering
research. Process simulation allows for design and optimization
"experiments" to be carried out on computers before costly process
or machine modifications are tested in the laboratory or plant.
At CEPSE, process modeling and simulation research is carried
out on both in-house and commercial software using finite difference
and finite element techniques. Current problems of interest include
foamed 
polymer processing, blown-film processing and reactive
extrusion. This latter work is performed jointly with the Dow
Chemical Corporation.
While
a great deal of information can be gained from the rheology and
modeling approaches described above, the ultimate test of novel
process design and optimization ideas is on actual process equipment.
CEPSE's processing laboratories are furnished with lab-scale equipment
for single- and twin-screw extrusion, injection molding and compression
molding. This equipment can be used to produce test specimens
of solid, foamed or composite polymers for subsequent analysis
of various physical properties. In addition, results from lab-scale
processing studies can be used to verify theoretical models of
the process, which are useful for performing scale-up analyses.
Back to top
Polymerization
Reaction Engineering
Through
the use of mathematical modeling techniques and bench-scale experimentation,
CEPSE researchers under the direction of Prof. Teymour,
are investigating some of the problems inherent in nonlinear polymerization
processes. These processes are employed to an even greater extent
because branching and/or crosslinking of polymers can be used
to impart advantageous properties to specific polymers. This,
however, is accompanied by the possibility of gelation and of
the production of highly polydisperse materials, which most of
the time is undesirable. "Numerical Fractionation" 
theory
is used to explain these phenomena and to design benign processes
that can result in a tightly controlled polymer microstructure.
The development of gelation in batch and continuous reactors is
being investigated for a variety of branching and crosslinking
chemistries. Current efforts are aimed at the analysis of the
curing stages of crosslinked coatings to investigate the possible
relation of macroscopic defects to microscopic local phenomena.
In
a related project, mixed-mode polymerizaton is investigated to
provide an understanding of the property development of polymeric
materials in reactors where both free-radical and polycondensation
mechanism occur simultaneously. This technology can be used to
control the molecular weight distribution of the polymer and its
structure. Alternatively, it can provide a pathway for graft copolymerization
of incompatible monomers.
Further
efforts are aimed at understanding the development of molecular
structure in the thin polymeric shells of the microencapsulants
produced by interfacial polycondensation. This process is used
to minimize the impact of toxic organic substances, such as pesticides
and herbicides, on the global environment. A better understanding
of the structure of the polymer produced can be used to create
more effective time-release characteristics in these substances.
Additionally,
these same principles are used in the investigation of the electropolymerization
of conjugated monomers for the production of electronically conductive
polymers. Mechanistic models are used to predict the rates of
formation of these polymers at modified electrode surfaces, as
well as their properties. Back to top
Novel
Polymer Systems and Characterization
Despite
the fact that virtually all polymer processing flows are nonisothermal,
the effects of deformation on energy transport in polymeric liquids
is poorly understood. Professors Venerus
and Schieber
have developed a novel optical setup based on the technique of
Forced Rayleigh Scattering (FRS) that provides quantitative measurements
of anisotropic thermal conduction in deforming polymer systems.
This setup has been applied to two polymer
systems: a polymer melt subjected to step shear strain deformations
and a cross-linked elastomer in uniaxial elongation. These data,
in conjunction with stress and birefringence measurements have
been used to evaluate a recently proposed stress-thermal rule.
These novel results will be invaluable for the development theoretical
models for anisotropic thermal conduction in polymers and in the
formulation of non-isothermal flow models of polymer processes.
The FRS setup is also being used to investigate thermal and mass
diffusion in other polymer systems including glassy polymers and
proton conducting membranes (PEMs) for fuel cell applications
in collaboration with Professor Smotkin.
Research
on the use of polymers in food packaging applications is carried
out in cooperation with Professor Sadler of the National Center
for Food Science and Technology. Study of the compatibility of
food and packaging materials and shelf-life modeling of packaged
food are the focal points of this research. A current project
involving Professors Sadler and Venerus
focuses on the transport and fate of organic compounds in EVOH
and other polymers used in packaging films. Other important issues
include the investigation of the safety aspects of using recycled
polymers for packaging applications.
Professor
Perez-Luna's
research focuses on surface modification and characterization
of materials for biomedical applications. Surface modification
of polymers can improve their biocompatibility. Grafting of thermoresponsive
polymers within microfabricated structures will be undertaken
in the near future with the goal of growing cells in complex structures
resembling the complexity of living tissue. The purpose of using
a thermoresponsive polymer grafted to the microfabricated structure's
surface is that once the cells grow to confluency, they can be
detached with a simple change in temperature. This would allow
a retrieval of intact cellular structures for tissue engineering
applications. Back to top
Polymer
Synthesis
Polymer
synthesis research, conducted by Prof. Mandal's
group, is primarily focused on the development of novel nonlinear
optical (NLO) polymers for photonic and laser technologies. These
polymers have potential applications in fiber optic communication
signal switching, optical computing, pattern recognition, and
signal processing systems. They can also be used for the control
and conversion of laser beams and for the development of equipment
for the protection of eyes and sensors from laser hazards. Recently,
rapid progress has been made in the development of new materials
with third-order NLO effects. These materials have been prepared
at CEPSE by the axial modification of macrocyclic compounds such
as phthalocyanine, followed by a crosslinking reaction. This process
results in a high density of macrocyclic rings in the structure
(over 20% by weight) and allows for the fabrication of both thin
and thick polymeric films without the formation of microcrystallites
or phase segregation. Current research targets the alternative
development of similar compounds through the peripheral modification
of tetraphenylporphyrin. Additional research efforts are focused
on the achievement of highly stable optical nonlinearities in
second-order NLO materials.
Other research efforts in Prof. Mandal's
group are directed to the synthesis of high performance composites
from renewable resources such as cellulose and from novel dianhydrides.
A number of cellulose derivatives that yield high mechanical strength
have been prepared, while research on the synthesis of novel dianhydride
monomers leading to polyimides is in progress. Professors Mandal
and Smotkin conduct collaborative
research on the synthesis and characteriztion of solid polymer
electrolytes, nonflammable liquid electrolytes and fuel cell membranes.
Back to top
Rubber
Recycling
Used tires represent one of the major solid waste streams. Approximately
250 million tires are discarded annually, in addition to about
2 billion scrap tires already stockpiled across the United States.
To recycle or dispose of the tires in a manner which is economically
feasible and environmentally acceptable has been a challenge that
requires further research and development. Incineration or pyrolysis
of tires (Tire Derived Fuel, TDF), although it is not a recycling
process, has been used extensively to prevent further stockpiling
of tires in large metropolitan areas. The major issue with incineration
is particulate air pollutants and CO2 emission, which, similar
to carbon and fossil fuel, affects climate change. Pyrolysis also
has limited commercial application due to economic and technical
barriers.
There are two major approaches to rubber recycling: one is devulcanization
of rubber waste using chemical compounds, which results in a rubber
mixture with low mechanical properties; the other one is size
reduction, which is usually achieved at cryogenic conditions to
produce powder to be reused in the manufacturing of rubber compounds.
This process is usually not economically feasible because of the
cost associated with the use of liquid nitrogen needed for cryogenic
processes.
Arastoopour
and co-workers developed a novel patented rubber recycling process
based on Single Screw Solid State Shear Extrusion (SSSE) pulverization
technology. SSSE process produces rubber powders at ambient temperatures
and, at the same time, partially devulcanizes the rubber particles
due to breakage of the majority of sulfur crosslinks under high
shear and compression. Thus, this process is not only expected
to be more economical than the cryogenic process, but also provides
produced rubber materials with similar properties to the original
rubber, since no chemical compounds are added during devulcanization.
The rubber particles may also be used as fillers in asphalt or
in the manufacturing of tires. Back to top
Solid
State Formulation of Powder Coatings
There is an essential need to reduce volatile organic compounds
(VOC) in solvent-based coatings due to the environmental concerns
and requirements. Powder coating technology has been considered
the major innovation to address the elimination of solvents in
coating applications. The financial incentives that make powder
coatings more economical than liquid-based paints/coatings include
savings in handling and evaporation of solvents which may be composed
of up to half of the liquid coating. Professors Teymour
and Arastoopour,
and their research groups are involved in the production of powder
coating formulations below melting condition by simultaneous pulverization
and homogenization of the coating resin , the crosslinker and
additives using the twin screw SSSE process. This is not only
expected to reduce energy requirements and formulation time, as
well as curing time and temperature, but also allows the use of
less expensive low-temperature crosslinkers. Furthermore, an electrostatic
fluidized bed is used to apply dry powders on the surface of substrates,
which are subsequently cooled in a temperature-controlled oven.
The extent of curing and crosslinking is examined using soxhlet
extraction, followed by gel permeation chromatography. We expect
that the findings of this research will provide more economical
powder coating technology, and shorten the overall processing
time and curing temperature. Back to top
Process
Modeling, Monitoring and Control
Professor Cinar's
research focuses on the development of methods and tools for empirical
modeling, monitoring and control for multivariable processes and
their applications to polymer manufacturing operations. Statistical
and empirical modeling techniques are used to provide dynamic
models of complex processes. These models are used in the design
of advanced control techniques for multivariable nonlinear processes,
in the statistical monitoring and faulty diagnosis of batch and
continuous processes and in the intelligent, fault-tolerant supervisory
control of these processes with real-time knowledge-based control
systems.
Professor Caracotsios'
research focuses on the development of numerical methods for process
dynamics and parameter estimation. This research, in collaboration
with Prof. W.E. Stewart, has led to a commercially available programing
environment called Athena
Visual Workbench. Back to top
