Mississippi
Polymer Institute
Research Report
ACS Report
Graphs
AccuCure Setup
Gel Setup
Measurement
of the Extent of Reaction During Polymerization Using DSC,
Gel Time and a Newly Discovered Electrical Phenomena
Tracy
Wyatt and Tison Wyatt
Tison Technologies, LLC
PO Box 1268
Skyland, N.C. 28776-1268
Phone: 828-684-0050
E-mail: info@tison.com
Kenneth
T. Posey and Richard D. Sudduth
Mississippi Polymer Institute
University of Southern Mississippi
Box 10003
Hattiesburg,
Ms. 39406
Phone
601-266-4607
As
announced at :
American
Chemical Society
49th Southern Regional Meeting
Roanoke, Virginia
October
19-22, 1997
The
Discovery
Most
chemical reactions produce a voltage that can be detected
passively utilizing a patented electrode.
- This
technique has been called AccuCure™
What
is AccuCureTM
-
Electrodes must be adequately shielded and grounded from
spurious voltages.
AccuCure™,
using techniques which are patented, measures voltage produced
by a chemical reaction, i.e. polymerization, etc.
- Voltage
apparently indicative of the state of electrons being transferred
during a reaction
- Domains
of Cathodic and Anodic regions
need
to be large enough to detect measurement
- Domains must not be too random (good for Thermosets).
Materials Evaluated
Epoxy (Polycondensation Polymerization)
-
EPON Resin 828
-
EPI-CURE 3140 Polyamide Curing Agent
Urethane (Polycondensation Polymerization)
-
Smooth-On Crystal Clear 200 Part A
-
Smooth-On Crystal Clear 200 Part B
Unsaturated Polyester (Free Radical Polymerization)
-
Bondo (Unsaturated Polyester/Styrene Monomer)
-
Benzoyl Peroxide
Formulated
Reaction Rate
Considerations
Gel-Times
approximately 8 hrs. at room temperature
Long
gel time has the advantage of minimizing weighting and mixing
time errors
Gel-Time
approximately ten minutes at 150 F or 180 F depending on reacting
medium.
Short
gel times are advantageous for study simply because the rate
of electron transfer is increased
Experimental
Techniques
(Isothermal)
-
AccuCure™ Process
- DSC
Measurements (Isothermal)
-
Perkin-Elmer Model # DSC-7
- Gel-Time
Measurement (Isothermal)
-
Sunshine Gel Checker 22-B
AccuCure™
Measurement Results
- AccuCure™
measurement reproducible and consistent
- AccuCure™
produced mirror voltage curves for urethane and epoxy
- Did
not get mirror voltage curve for unsaturated polyester polymerization
- Maximum
for polyester polymerization appeared to occurred at gel-time
- Location
of gel-time for epoxy and urethane consistent relative to
AccuCure™ curve
Comparison
of Reaction Types
·
Condensation or step wise reactions evaluated
- Polyurethane reaction
- Epoxy reaction
· Condensation or step wise crosslinking characteristics.
- Early in the reaction monomer or low molecular weight units
disappear rapidly.
>> Reaction becomes ordered quickly.
- Since each step in the polymerization proceeds by approximately
the same rate, as reactive sites are used up the polymerization
rate decreases
· Free radical reaction evaluated
- Unsaturated polyester reaction free radical crosslinking
characteristics
- Chain polymerization reaction process is very complex with
many reactive processes occurring simultaneously.
>> Initiation Stage
>> Propagation Stage
>> Termination Stage
- At any instance in reaction the mixture could contain monomer,
high MW polymer, and growing chains
DSC
Measurement Compared
to
Identical Electrodes Measurement
- DSC
exothermic energy assumed to be one measure of rate at which
electrons are being transferred during a reaction
- Since
the AccuCure™ process is also believed
to involve the transfer of electrons some correlation with
the DSC results were expected
Conclusions
- AccuCure™
and DSC indicate a minimum of one corresponding peak for
polyurethane and epoxy reactions
- AccuCure
TM and DSC did not indicate a corresponding peak
for the polyester reaction
- AccuCure
appears to be able to distinguish a different reaction spectrum
for each reaction type
- Gel-Time
is indicated differently by AccuCure for the three different
reactions
- AccuCure™
is a measurement tool with great potential to measure reaction
progress
- AccuCure™
shows remarkable consistency, even with mirror image results
- Phenomena
measured using the AccuCure™ process
is not yet fully understood.
However,
if AccuCure™ produces consistent, reproducible
and usable results, a detailed understanding of the voltage
phenomena is not required.
Potential
Applications for
AccuCureTM
- Unstirred
chemical reactions after initial mixing
-
Thermosets (Composites)
- Rubbers / Elastomers
- Reaction
identification or reaction spectrum
- Measurement
of critical reaction phases
-
Reaction Onset
- Reaction Rate
-
Gel Time
- Completion of Multiple Reaction Scheme
-
Cure Cycle
Major
Advantages of AccuCure's
Passive
Feature
- Process
itself determines process completion
- Data
Collection can be easily achieved during actual production
runs without disturbing finished product
- Since
AccuCure™ is a passive monitoring system, potentially
dangerous and/or explosive reactions can be monitored with
minimal safety concerns
Potential
Production Advantages
of
AccuCureTM
- Reduction
of lost production due to incorrect processing
- Ability
for corrective action during processing
Real time indication of stage of reaction
- Any
combination of the above leads to
Increased profitability
Acknowledgments
- George
A. Fowles -- Retired Vice President of B.F. Goodrich Chemical
Company
-
Significant Contribution to Product Concept
- Karl
Oestreich -- B.S. Chemical Engineering
-
Significant Contribution on Identifying Applications in
the Private Sector
- Dr.
Robert A van Brederode -- Director, Polymer Extension Program,
N.C.
State University
-
Significant Contribution in Process Implementation
- Dr.
Joseph Bassett -- Retired Professor of Chemistry, Western
Carolina University
-
Significant Assistance with Experimental Implementation
- Dr.
Roger Bacon -- Dept. Head of Chemistry, Western Carolina
University
-
Significant Assistance with Experimental Implementation
AccuCure™
Availability
Tison
Technologies, LLC has developed a totally automated package,
available in a NEMA 4 Stainless steel inclosure using AccuCure™
technology adaptable to different processes.
Exclusive
and nonexclusive licenses are available.
CONTACT
INFORMATION
AccuCure™
invented by : W. Tison Wyatt, President of Tison Technologies,
LLC
AccuCure™
Setup
Gel
Checker Setup
Mississippi Polymer
Institute, Research Paper
Abstract
This study introduces
a new technique to follow the extent of selected polymer reactions
using the voltage produced from such reactions. This new measurement
process, designated as AccuCure™, uses patented electrodes
well shielded from spurious electrical voltages to measure
polymerization voltages. In this study, three different types
of polymerization reactions were investigated in the evaluation
of this new technique. They included one cross-linking free
radical reaction, an unsaturated polyester, and two crosslinking
polycondensation or step growth reactions that included a
polyurethane and an epoxy. The voltages from these reactions
were also correlated to the extent of the reactions as indicated
from differential scanning calorimeter (DSC) measurements
and gel time measurements. This newly discovered electrical
phenomenon and the isothermal DSC measurements appeared to
closely follow the reaction process for the urethane reaction.
In addition, one mirror image AccuCure™ curve was also
generated for the urethane reaction consistent with the mechanism
proposed for this new electrical phenomenon. The location
of the gel time was repeatable and consistent for the urethane
reaction relative to the AccuCure measurements. In general,
all three polymerization reactions evaluated using the AccuCure™
appeared to have a unique reaction spectrum, and were found
to have repeatable and consistent gel time and isothermal
DSC measurements. While the cause of this newly discovered
electrical phenomenon is not yet fully understood, significant
practical commercial implications for monitoring chemical
reactions have been demonstrated for the AccuCure™ process.
Introduction
Previous studies
performed by Nathaniel Smith and David Shepard (1,2) have
followed the cure of thermosetting resins by measuring the
dielectric change from an applied voltage (1,2). The dielectric
technique is based on the principle that molecular dipoles
will align themselves with an applied electrical field. The
changes in the measured dielectric properties have been found
to be a function of the mobility of the polar groups within
a reaction (1,2).
The micro-voltage
produced by a chemical reaction is a phenomenon proposed in
this study to be a useful analytical tool for observing the
progression of a chemical reaction. This technique differs
from dielectric analysis in that voltage analysis does not
induce a voltage into the reaction medium, it measures the
voltage produced from the reaction. The technique uses a patented
electrode which is placed into a reaction medium, where the
voltage is measured (3).
Tison Wyatt (3)
has previously found that as a polymerization reaction proceeds
to completion that distinctive changes in potential occur
between electrode. In an attempt to increase the understanding
of this phenomenon three polymerization reactions were investigated
in this study.
1) One cross-linking
free radical reaction (Unsaturated Polyester)
2) Two cross-linking
polycondensation reaction
One that is moisture
sensitive (Polyurethane) One that doesn't generate water (Epoxy)
Recently several
articles have appeared in the literature describing isothermal
differential scanning calorimeter (DSC) studies of polyurethanes
(4), epoxies (5), and polyesters (6). The isothermal DSC study
by Rodriguez (6) on unsaturated polyester resins addressed
the conversion of double bond functionalities into the single
bond matrix of a cross-linked resin. The rate of energy generated
by the heat of reaction as measured by an isothermal DSC measurement
can then be assumed to be one measure of the rate at which
electrons are being transferred during a reaction. Since the
new voltage technique is believed to involve the transfer
of electrons, then some correlation with the DSC results would
be expected. Consequently, isothermal DSC measurements were
chosen as a comparison measurement tool for the new voltage
evaluation technique.
In this study,
polarization reactions involving an unsaturated polyester,
a polyurethane and an epoxy were studied for the purpose of
correlating the phenomenon of reaction voltage to the reaction's
gel time and isothermal DSC curve.
According to Bagotzky
and Kisin (7) a battery is an electrochemical device that
has two electrodes in contact with an ion-conducting electrolyte.
When the electrodes are of two dissimilar materials a potential
will exist between the electrodes such that a significant
amount of voltage can be produced from the cell. One electrode
is termed an anode, the oxidizing electrode where electrons
are released and the other electrode is termed a cathode,
the reducing electrode where the electrons are absorbed. The
anode electrode has a negative polarity and the cathode electrode
has a positive polarity. The potential difference between
the two electrodes is termed the open circuit voltage (o.c.v.).
The o.c.v. is determined by the equation: o.c.v = E(.) - E(-)
. Electrochemical principles state that if the two electrodes
are of similar materials then the o.c.v. is effectively zero
(7). This principle is a key point in the method of measuring
the voltage of a reaction. With identical electrodes, one
should eliminate the o.c.v. . However, using an AccuCure™
electrode, Tison Wyatt(3) has discovered that a voltage does
appear to be produced during many chemical reactions.
Bagotzky and Kisin
(7) also indicate that any chemical reaction in which there
is a reducer being oxidized, releasing electrons, and an oxidizer
that gains electrons has the potential to produce a current.
If the oxidizer and reducer are mixed together thoroughly
then no electrical energy should be produced. For this case,
the electron transfer within the reaction is so randomly spaced
that the reaction energy is liberated as heat. A battery,
then, produces current because it is able to order the reaction
so that a controlled potential is created (7).
Organic
Cathodes and Anodes
Cahoon and Heise
(8) describe an electrochemical model of organic cathodes
and anodes for batteries, in which organic compounds and organic
reactions are used to produce electrical current. Cahoon and
Fleise (8,9) further classified organic electrodes into the
following organic reaction types (9):
1. Oxidations
and reductions, including irreversible and redox processes.
2. Substitutions,
aliphatic and aromatic, nucleophilic, electrophilic, free
radical, etc. in which an atom or group attached to a carbon
atom is removed and another enters its place. No change in
degree of unsaturation of reactive carbon occurs.
3. Additions of
molecules, atoms, or ions to carbon-carbon, and to carbon-hetero
multiple bonds to other element unsaturated groups, and ions.
These involve an increase in number of groups attached to
carbon thus increasing the degree of saturation.
4. Eliminations,
which involve a decrease in the number of groups, bound to
carbon. The degree of unsaturation increases.
5. Rearrangements,
condensations, inversions in which the carbon skeleton of
the molecule is internally rearranged.
6. Proton-transfer.
7. Reordering
in which one reactant contributes an unshared pair electron
to another leaving an empty orbital available. This is simply
a Lewis acid-base reaction.
8. Single cleavage.
From the above
classifications, one might conclude that the mechanism by
which a polymerization would produce a voltage would have
many levels of complexity and would vary from one type of
polymerization to the next. This would make it very difficult
to develop one mechanism that could be used to predict the
extent of voltage a reaction would produce for every type
of polymerization.
Experimental
- Materials
This study utilized
three different polymerization reactions including a free
radical vinyl ester reaction, an epoxy reaction, and a urethane
reaction for the purpose of correlating the phenomenon of
reaction voltage to the reaction's gel time and isothermal
DSC curve.
These three cross-linking
reactions were supplied in a two-part system and mixed together
in the required amounts as indicated in their appropriate
formulation tables below. Each formulation was formulated
to give a room temperature gel time of about eight hours and
a gel time of approximately 10 minutes at the elevated isothermal
condition of the evaluation in this study.
The unsaturated
Polyester reaction involved an oxidative free radical reaction
that consists of an unsaturated polyester resin and methyl
ethyl ketone peroxide as the initiator. This mixture was evaluated
at an isothermal temperature of 65.5 'C or 150 'F. Chemicals
are from Bondo Corp., Atlanta, GA (1-404-699-0073).
| Polyester
Resin |
98.8%
|
| Methyl
Ethyl Ketone Peroxide |
1.2% |
The Urethane reaction
was a polycondensation cross-linking reaction and was moisture
sensitive. Chemicals were from Smooth-On Inc. in Gillette,
New Jersey 07933 (1-800-762-0744). This mixture was evaluated
at an isothermal temperature of 65.5 'C or 150 'F.
| Smooth-On
Crystal Clear 200 Part A |
52.63% |
| Smooth-On
Crystal Clear 200 Part B |
47.37% |
The Epoxy reaction
was a polycondensation or stepwise reaction that does not
generate a by-product (i.e. water). The epoxy reaction involved
is of bisphenol A/epichlorohydrin based epoxy resin cross-linking
with a polyamide curing agent (10). This mixture was evaluated
at the isothermal temperature of 82.22 'C or 180 'F. Chemicals
were supplied from Shell Chemical Company (I -800-TEC-EPON).
| Eopn
Resin 828 |
52.63% |
| EPI-Cure
3140 Polyamide Curing Agent |
47.37% |
Experimental
- Method
The electrode
used for evaluation was built by Tison Wyatt made from Teflon
insulated AccuCure™ electrodes. The probes were submerged
into a 10 ml reaction mixture, in a test tube as indicated
in Figure 1. These probes were connected to an IBM PC, with
a 386 or better CPU, via shielded alligator clips. The computer
used utilized a Vernier universal lab interface module capable
of measuring +/- 0.1 millivolt and sampled the voltage once
per second. Each reaction was run separately to measure the
voltage as the reaction progresses. Extra care was required
in this study to minimize all possible external sources of
voltage from being introduced into the reaction. Shielding
was accomplished by removing all electrical sources away from
the immediate area of the reaction.
A Sunshine gel checker time meter 22B as shown in Figure 2
was used to determine the gel time of the various cross-linking
reactions using the same test tube heating bath as used for
the voltage measurements. Each reaction was run separately
on the Sunshine gel checker to determine gel time.
The extent of
the reaction and the accumulated heat of the reaction were
measured versus time using an isothermal Perkin-Elmer DSC-7
measurement method. A 10 mg sample of each reaction was run
at the eventual isothermal temperature evaluated on the DSC.
The isothermal temperatures of the polymerization reactions
were 65.5 'C or 150 'F for the polyurethane and polyester
reactions and 82.22 'C or 180 'F for the epoxy reaction. The
reaction sample was placed into the DSC at room temperature
and raised to 20 'C below the eventual temperature at 40 'C/min.
then the DSC acquisition program was started and raised to
the isothermal reaction temperature at 40 'C/min. Similar
to the procedure used by Rodreiquez (6), the baseline for
the cure exothermal was then determined at the isothermal
temperature by running the DSC again on the very same sample
that was previously used in the DSC isothermal rate.
The voltage from
each reaction was then correlated with the extent of the reaction
from the DSC and the gel time of the reaction. Each group
was repeated three times on each apparatus to determine repeatability.
Results
AccuCure™
and Gel Time Comparison
The AccuCure™
and gel time results for this study are summarized in Figures
3-6 for the polymerizations of the polyurethane, epoxy and
polyester respectively. In general, it was found that the
results for these three different types of polymerization
reactions were very repeatable and consistent.
The results for
the AccuCure™ measurements for the three different polyurethane
polymerizations in Figure 3 were found to be particularly
consistent and reproducible, Note that the second (42) and
the third (#3) polymerizations in Figure 3 were found to produce
a positive maximum peak at approximately 150 seconds into
the reaction at an isothermal temperature of 150 'F. The third
polyurethane polymerization (#I) in Figure 3 was found to
give a negative peak at approximately 150 seconds into the
reaction. This third polyurethane polymerization (#I) was
basically a mirror image of the other two positive reaction
plots. This result indicates that the polarity of each electrode
in a polyurethane reaction was capable of assuming either
a positive or a negative charge. All three reactions produced
a peak at approximately 150 seconds into the reaction and
had a peak width of approximately 400 seconds. Also note that
as the AccuCure™ voltage appeared to approach a neutral
value asymptotically slightly after 400 seconds. The average
of three gel time measurements for the polyurethane reaction
was 497 seconds, which is very close to the asymptotic value
of time required to achieve the neutral value. Therefore,
the gel time appears to be estimable from the time to reach
this asymptotic neutral value.
The results in
Figure 4 show that the AccuCure™ measurements for the
three epoxy polymerizations were again very reproducible and
consistent. Mirror image plots, indicative of the passive
electrodes switching polarity, were also obtained for the
epoxy reaction. The epoxy reaction spectrum as Indicated in
Figure 4 appeared to produce at least four reasonably well
defined peaks. The first peak was at approximately 75 seconds,
the second peak at approximately 375 seconds, the third peak
at approximately 500 seconds and the last peak at approximately
600 seconds. The second peak appears to be the predominate
peak of the four. The average of three gel times for the epoxy
polymerizations was at 563 seconds and was at the approximate
location of the fourth peak of the AccuCure™ reaction
spectrum.
The first two
reactions, polyurethane and epoxy reactions, were condensation
or a step wise cross-linking reactions. Odian(10) indicates
that these reactions are typically characterized as having
monomer or low molecular weight units disappears rapidly at
the start of each reaction with each step in the polymerization
proceeding by approximately the same rate. Thus as reactive
sites are used up the polymerization rate slows down. This
suggests that as the reaction mechanism proceeds that the
reaction becomes ordered quickly and is able to develop anodic
and cathodic domains that are detectable by AccuCure™
as voltage.
Figures 5 and
6 show the results of the AccuCure™ measurements for
the polyester polymerization. The polyester polymerizations
were somewhat less consistent than the previous polyurethane
and epoxy reactions. There appears to be a negative peak in
Figure 5 at the start of the plot around 50 seconds,
but the rest of the results seem to be less predictable in
the short time frame of this evaluation. To check this hypothesis
an extended polyester polyrneri2,ation was generated and the
results from this run are shown in Figure 6. The average of
three get times for the polyester reactions was 597 seconds.
As indicated in Figure 6 the average gel time and the peak
of the extended run were apparently near the same time frame.
This suggests that the evaluation of the polyester polymerization
using the AccuCure™ process may be more effective if
the results for this material were taken over a longer period
of time to follow the effectiveness of the reaction process.
This last polyester
reaction was also a free radical cross-linking reaction, Salla
and Ramis(11) indicate that this reaction is typically characterized
as having a very complex reaction process with many reactive
processes occurring simultaneously (i.e. Initiation, propagation,
and termination). At any instance the reaction mixture could
contain monomer, high molecular weight polymer or growing
chains. Given this reaction mechanism one might conclude that
a free radical cross-linking reaction might not order as quickly
as a step polymerization, thus requiring a longer time frame
for consistent voltage measurements.
The plots for
the polyurethane, epoxy, and polyester reactions appear to
be unique for each reaction. This could suggest that the AccuCure™
technique might be a useful spectrum analysis tool for the
study of or identification of various types of reaction processes.
DSC Measurement
Compared to AccuCure™ Electrode Measurement
As discussed in
the introduction, the rate of energy generated by the heat
of reaction as measured by an isothermal DSC measurement can
be assumed to be one measure of the rate at which electrons
are being transferred during a reaction. Since the AccuCure™
process is believed to involve the transfer of electrons,
then some correlation with the DSC results would be expected.
Consequently, isothermal DSC measurements were chosen as a
comparison measurement tool for the new voltage evaluation
technique. The results summarizing the comparison between
the DSC measurements and the AccuCure™ electrode measurements
are summarized in Figures 7-9.
The isothermal
DSC curve for the polyurethane reactions as indicated in Figure
7 indicates that the maximum DSC peak and the maximum for
the AccuCure™ peak occur at approximately the same time.
With compensation for differences in sample heat up rates
to isothermal conditions and different sample sizes, timing
to the peak maximum could be considered identical for both
measurements. This result suggests that both techniques are
measuring the same polyurethane reaction characteristic.
The AccuCure™
curve for the epoxy reaction in Figure 8 suggests many different
reaction stages, where as the DSC curve only indicates one
reaction peak. However, the first peak of the AccuCure™
curve does appear to correspond with the maximum in the DSC
curve. This suggests at least one epoxy reaction component
appears to be similarly indicated by both the DSC and the
AccuCure™ results.
Finally, Figure
9 compares an isothermal DSC curve with the AccuCure™
curve for one of the polyester reactions evaluated. Apparently
the AccuCure™ and DSC techniques are measuring different
stages of the reaction, since the maximums are occurring at
different locations. This result suggests that the DSC and
the AccuCure™ results do not indicate a common reaction
process for the polyester reaction.
Discussion
of voltage Phenomenon in Polymer Reactions
It is proposed
that the following conditions would be expected to exist in-order
for voltage to be produced and measured from a polymerization
reaction with similar electrodes:
1. Anodic like
and cathodic like domains should exist within the reaction,
(a domain is considered to be a specific volume of the reaction
mixture)
2. The domains
would be significant enough in size to produce a measurable
voltage.
3. The domains
would be ordered such that a net potential difference is produced
(i.e. a non-random system).
4. It appears
that if the anodic and cathodic domains are too random and/or
insignificant in size that a voltage may not be detectable.
5. Thermodynamic
conditions should be conducive to the production of electrical
energy.
6. The reaction
and electrodes must be shielded from spurious electrical voltage
from equipment in the vicinity.
A possible explanation
of the observed voltages produced with AccuCure™ electrodes
is as follows. Polymerization starts out in a manner where
the reactants are possibly randomly ordered so that the reaction
does not produce an initial voltage and as the reaction proceeds,
if the reactants stay randomly oriented, the reaction would
only produce heat. However, as the reaction proceeds and produces
a polymer of significant mass, the reaction may become ordered
such that a voltage is produced. At this point the reaction
medium consists of a polymer mass, monomer, and other reactants.
It is proposed that the polymer mass possibly during the reaction
becomes ordered in such a way that a potential difference
is created and measurable by a voltmeter. As the polymerization
proceeds to completion the potential difference should disappear.
The above is proposed to explain how the phenomenon of voltage
produced by a reaction might occur. The critical point here
is even if we do not understand this phenomenon, the measurable
change in voltage during a reaction should have significant
application if it relates to a reaction consistently and repeatably.
It will be left to future researchers to determine the mechanisms
responsible for this phenomenon.
Conclusion
This study utilized
three different polymerization reactions included a free radical
vinyl ester reaction, an epoxy reaction, and a urethane reaction
for the purpose of correlating the phenomenon of reaction
voltage to the reaction's gel time and isothermal DSC curve.
A new technique was introduced to follow the extent of selected
polymer reactions using the voltage produced from such reactions.
This new measurement process, designated as AccuCure™
uses patented electrodes well shielded from spurious electrical
voltages to measure polymerization voltages.
In general, all
three polymerization reactions evaluated using the AccuCure™
appeared to have a unique reaction spectrum, and were found
to have repeatable and consistent get time and isothermal
DSC measurements.
This newly discovered
electrical phenomenon and the isothermal DSC measurements
appeared to closely follow the reaction process for the urethane
reaction. In addition, one mirror image AccuCure™ curve
was also generated for the urethane reaction. This result
indicates that the polarity of each electrode in a polyurethane
reaction was capable of assuming either a positive or a negative
charge. The average gel time for the polyurethane reaction
was very close to the asymptotic value of time required to
achieve the neutral value. Therefore, the gel time can be
estimated from the time to reach this asymptotic neutral value.
The isothermal DSC curve for the polyurethane reactions indicates
that the maximum DSC peak and the maximum for the AccuCure™
peak occur approximately the same time. With compensation
for differences in sample heat up rates to isothermal conditions
and different sample sizes, timing to the peak maximum could
be considered identical for both measurements. This result
suggests that both techniques are measuring the same polyurethane
reaction characteristic.
The results for
the epoxy polymerizations were again very reproducible and
consistent. Mirror image plots, indicative of the passive
electrodes switching polarity, were also obtained for the
epoxy reaction. The epoxy reaction spectrum appeared to produce
at least four reasonably well defined peaks. The average gel
time for the epoxy polymerizations was approximately identical
with the fourth peak of the AccuCure™ reaction spectrum.
The AccuCure™ curves for the epoxy suggests many different
reaction stages, where as the DSC curve only indicates one
reaction peak. However, the first peak of the AccuCure™
curve does appear to corresponds with the maximum in the DSC
curve. This suggests that at least one epoxy reaction component
appears to be similarly indicated by both the DSC and the
AccuCure™ results.
The polyurethane
and epoxy reactions, are condensation or step wise cross-linking
reactions which suggests that as the reaction mechanism proceeds
that the reaction becomes ordered quickly and is able to develop
anodic an cathodic domains that are detectable by AccuCure™
as voltage.
The polyester
polymerizations were somewhat less predictable in the short
time frame used for the other polymerization reactions. To
check this hypothesis all extended polyester polymerization
was generated and the average gel time and the peak of the
extended run were near the same time frame. This suggests
that the evaluation of the polyester polymerization using
the AccuCure™ process may be more effective if the results
for this material were taken over a longer period of time
to follow the effectiveness of the reaction process. The results
for the polyester reactions indicate that the AccuCure™
and DSC techniques are measuring different stages for the
polyester reaction since the maximums occurred at different
locations. This result suggests that the DSC and the AccuCure™
results do not indicate a common reaction process for the
polyester reaction.
This last polyester
reaction was also a free radical cross-linking reaction indicating
that this reaction is typically characterized as having a
very complex reaction process with many reactive processes
occurring simultaneously. Given this reaction mechanism one
might conclude that a free radical cross-linking reaction
might not order as quickly as a step polymerization, thus
requiring a longer time frame for a consistent voltage measurement.
The AccuCure™
process results obtained in this study suggest that this process
involves the detection of the transfer of electrons during
a polymerization reaction. In this process polymerizations,
in general, start out in a manner where the reactants are
possibly randomly ordered so that the reaction does not produce
a voltage. As the reaction proceeds, if the reactants stay
randomly oriented, the reaction would only produce heat. However,
as the reaction proceeds it is proposed that the polymer mass
possibly orders the reaction such that a potential difference
is created and measurable by a voltmeter. As the polymerization
proceeds to completion the potential difference should disappear.
In general, the plots for the polyurethane, epoxy, and polyester
reactions appear to be unique for each reaction. This would
suggest that the AccuCure™ technique might be a useful
spectrum analysis tool for the study of or identification
of various types of reaction processes.
While the cause
of this newly discovered electrical phenomenon is not yet
fully understood, significant practical commercial implications
for monitoring chemical reactions have been demonstrated for
the AccuCure™ process. It will be left to future researchers
to determine the mechanisms responsible for this phenomenon.
Reference
I . Nathaniel
Smith, and David Shepard, "Dielectric Cure Analysis:
Theory and Industrial Applications", Reprint from SENSORS,
October 1995.
2. John Lane,
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