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RP026
- Cure Monitoring: A Comparison of Dielectric and Thermal
Analysis; Micromet Instruments, Inc., Dr. David R. Day and
David D. Shepard
ABSTRACT
In the science
of thermoset curing, which ranges from adhesives to complex
composite structures, there is a constant need to monitor and
analyze cure reactions. Wheras both thermal and dielectric
analysis play a major role in laboratory analysis, dielectric
analysis is best suited for in-process application. While dielectric
analysis has been in use for over 50 years, only in recent
years has the technology been advanced far enough to make in-process
feasible. Microelectronic technology now enables the fabrication
of integrated circuit dielectric sensors which are extremely
sensitive and which function down to frequencies characteristic
of mechanical measurements (less than 1 Hz.) The work presented
in this paper was undertaken to investigate the relationship
of the dielectric response to thermal response during curing
of thermosetting resins.
Log conductivity
data extracted from multifrequency loss factor data using microdielectric
sensors exhibit changes long after heat of reaction data can
be measured by thermal analysis. This most likely due to the
long reaction times involved and the low amounts of heat produced
at the end of cure. Changes in Tg as measured by thermal analysis
and changes in log conductivity correlate well over the entire
course of the cure.
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RP077
- The Relation of Polymer Viscosity and Ion Viscosity; Micromet
Instruments, Inc., Dr. David R. Day
ABSTRACT
Dielectric sensors
are now finding their way into various polymeric process environments
to monitor electrical properties that are closely tied to mechanical
properties of the material. One such relation is that between
traditional mechanically measured viscosity (by cone and plate,
by oscillating plates, or by spindle) and the Ion viscosity
(derived from the dielectric Loss Factor.)
This relation
arises from the fact that the Ion viscosity is really a measure
of ion mobility, i.e., how easily ions (such as Na+ of Cl-)
can move through the polymer system. This mobility is a function
of polymer chain segment mobility and free volume. On the other
hand, mechanical viscosity is a measure of how easily polymer
chain segments can move past each other. This is also dependent
upon chain segment mobility and free volume.
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RP107
- Theory and Applications of Dielectric Analysis in Industry,
Micromet Instruments, Inc. Nathaniel Smith and David Shepard
ABSTRACT
In the past,
dielectric analysis (DEA) has been used as an important measurement
component in the overall analysis of polymer resins systems.
Much of this work has been done at the research level in determining
viscosity behavior, rate of cure, and cure endpoint. In the
areas where DEA has been used in the production environment,
it has been in the low volume applications of aerospace composites.
Within the last
several years there has been an expansion of the applications
where dielectric cure analysis has been used. This growth in
the applications of dielectric cure analysis has expanded beyond
the traditional areas of monitoring the cure of composites
to include such applications as factory floor control of molding
operations, monitoring resin synthesis, reduction and/or elimination
of physical testing, diffusion monitoring, and SQC analysis.
These applications and other techniques will be presented.
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RP104
- In-Situ Characterization of Epoxy Polymerization Reactions
by Microdielectric Analysis., The Glidden Company, C.M.Neag,
A.Rohn and D.Bode
ABSTRACT
Dielectric Analysis
(DEA) techniques represent a group of convenient non-destructive
tests that can be used to relate molecular motions observed
in an electrical field to a variety of polymeric properties.
Nearly all the published work in dielectric analysis has focused
on solid materials or monitoring the crosslinking process in
thermoset materials, especially epoxies. This work focuses
on monitoring batch polymerization processes in-situ. The principle
goals of this research center on correlating changes in the
dielectric characteristics of a polymerizing epoxy polymer
with changes in temperaturea and typically measured properties
like viscosity, molecular weight and oxirane level.
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RP075
- Correlation of Viscosity and Conductivity Using a Free
Volume Model, Georgia Institute of Technology, Joycelyn Simpson
and Sue Ann Bidstrup
ABSTRACT
Viscosity and
conductivity are measured over a 100C temperature range for
a homologous series of non-curing epoxy resins. The free volume
model successfully predicts the temperature dependence of viscosity
and conductivity for these polymers. (This is the preliminary
work for RP078, RP079, and RP080)
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RP078
- Rheological and Dielectric Changes During Isothermal Epoxy-Amine
Cure, Georgia Institute of Technology, Joycelyn Simpson and
Sue Ann Bidstrup
ABSTRACT
Dynamic viscosity
and ionic conductivity have been measured simultaneously during
the cure of a diglycidyl ether of bisphenol-A (DGEBA) epoxy
resin with diamino-diphenyl sulfone (DDS) by mounting a microdielectric
sensor into the plates of a rheometer. Two different cure temperatures
were examined. Periodically, throughout the cure, samples were
removed from the plates of the rheometer, quenched, and analysed
for the glass transition temperature and epoxide conversion.
The relationship between conductivity and viscosity appeared
to be independent of cure temperature. A linear relation with
a slope of -1 was observed between the natural logarithms of
conductivity and viscosity during the cure up to approximately
85% cure conversion. It was hypothesized that the reaction
rate was hindered by diffusion at this stage in the polymerization.
A free volume relationship was used to successfully correlate
conductivity with viscosity up to the diffusion limited region.
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RP079
- The Correlation Between Chain Segment and Ion Mobility
in an Epoxy Resin System, Georgia Institute of Technology,
Joycelyn Simpson and Sue Ann Bidstrup
ABSTRACT
Steady-sheer
viscosity and ionic conductivity have been measured for nine
commercial diglycidyl ether of bisphenol-A (DGEBA) epoxy resins
with molecular weights ranging from 340 to 14,200. The temperature
dependence of viscosity and ionic conductivity was modeled
using free volume viscosity and ionic conductivity relationships,
which correlate the fractional free volume required for polymer
chain segment motion (B) and fractional free volume required
for ion motion (B') with polymer structure. The fractional
free volume required for polymer chain segment mobility was
observed to increase systematically with the molecular weight
of the resins. The fractional free volume required for ion
mobility did not vary for the resin series. The stoichiometric
mixture of a low molecular weight DGEBA resin and a 4,4'-diaminodiphenyl
sulfone cross-linker was partially polymerized to extents of
reaction ranging from 0% to 49%. The fractional free volume
required for polymer segment mobility for these partially polymerized
samples was consistent with results for the neat resins.
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RP080
- The Effect of Stoichiometry on Chain Segment and Ion Mobility
in Partially Polymerized Epoxy Systems, Georgia Institute
of Technology, Joycelyn Simpson and Sue Ann Bidstrup
ABSTRACT
The temperature
dependence of steady-sheer viscosity and ionic conductivity
were measured for a series of unreacted mixtures and partially
cured, ungelled samples of diglycidyl ether of bisphenol-A
(DGEBA) and an amine cross-linking agent, diamino diphenyl
sulfone (DDS). Six stoichiometric ratios of epoxide groups
to amine hydrogens were examined. Free volume expressions were
used to model the temperature dependence of the conductivity
and viscosity for the unreacted DGEBA-DDS mixtures. In addition,
these expressions were combined to successfully correlate changes
in viscosity and conductivity during the DGEBA-DDS polymerization
prior to gelation. It was also demonstrated that the change
in weight average molecular weight during polymerization could
be interpreted from the dielectric data. Through studying variations
in the stoichiometry, it was possible to examine the effects
of changes in chemical structure and ion concentration on the
fitted parameters in the free volume models. The inherent ion
transport factor was found to be inversely proportional to
the concentration of ions in the test samples. The fractional
free volume for segmental motion (B) was found to increase
with an increase in the glass transition temperature and to
be a function of the rigidity of the polymer.
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RP071
- - The Curing of Epoxy/Amine Systems Viewed Through Microdielectrometry;
University of Lyon, C.Mathieu, G.Boiteux, G.Seytre, Laboratory
of Macromolecular Materials, INSA, M.Feve, J.P.Pascault,
Technical University of Lodz, Poland, J.Ulanski, and Aerospatiale,
P.Dublineau
ABSTRACT
Aim of this
article is to show how microdielectrometry can improve the
curing of epoxy resins by detecting in real-time critical events
like gelation or vitrification. The isothermal curing of DGEBA/3DCM
in stoichiometric proportions is followed with: electrical
techniques of microdielectrometry and DC measurements, analysis
of insolubles, dynamic mechanical analysis and viscosimetry.
Electrical techniques have evidenced their own efficiency to
detect chemical phenomena with parameters sensitive to the
modification of the system during the network formation.
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RP053
- Microdielectrometry - a New Technique for Measuring the
Viscosity of Polymers; University of Liege, J.Denoel, J.M.Liegeois,
P.Landuyt (this is a French language paper)
ABSTRACT
During the cure
of thermosets in autoclaves, the final properties of the composite
are directly conditionned by the evolution of the resin viscosity.
Microdielectrometry, a new technique recently developed at
M.I.T. is able to monitor the cure by measureing ionic viscosity
which is proportional to mechanical viscosity measured by other
means. This technique is successfully applied in other fields
of study of polymers (R.I.M., thermoplastics, moisture absorption,
aging, etc.) in the laboratory as well as in industrial production
processes.
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RP094
- Relaxation Processes in the Electrorheological Response,
P.Katsikupoulos and C.Zukoski, Dept. of Chemical Engineering,
University of Illinois, Urbana
ABSTRACT
In this paper
we report on studies of the frequency dependent behavior of
the ER response. We find that insulated electrodes will produce
an ER response when an oscillating electric field is applied.
In DC fields no ER response is observed. The results reported
here suggest that the stress transfer properties of ER suspensions
can be altered both through variations of field strength and
through frequency modulation.
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RP127
- Dielectric and Thermal Cure Characterization of Resins
Used in Pultrusion, University of Mississippi, Reshma Shanku,
James G. Vaughan, Jeffrey A. Roux
ABSTRACT
The ability
to conduct on-line measurements of a resin's degree of cure
is important to a pultruder for setting optimum pultrusion
processing parameters. In this study, in-situ dielectric measurements
were conducted to determine the degree of cure as a function
of the pultrusion die axial position. Dielectric analysis utilizes
a sensor which is inserted at the center of the impregnated
fibers and travels along with the fibers through the heated
die. The conductivity due to ionic movement in the resin is
measured and a cure index is calculated from this data. The
purpose of this study was to determine degrees of cure for
pultruded epoxy/graphite, epoxy/glass and polyester/glass composites
using dielectric measurements and to compare the on-line measured
values with values obtained using differential scanning calorimetry
(DSC) and with values predicted using a numerical heat transfer/chemical
kinetic pultrusion model. A 2.54cm x 0.32cm profile was produced
at a pull speed of 30.5cm/min for the epoxy composites and
at 61cm/min for the polyester composite. DSC samples were taken
from the composite close to the location of the embedded sensor
to verify the values of degrees of cure obtained from the dielectric
measurements.
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