Glass fiber reinforced polymer composites are becoming widely used in industry. With this increase in production, an in-situ method of quality control for the curing of the polymer is desirable. This would allow for the production of high-quality parts having more uniform properties.' Recently, in-situ fiber optic monitoring of polymer curing has primarily focused on epoxy resins and has been performed by Raman or fluorescence methods. In addition, some infrared (IR) investigations have been performed using transmission or ATR cells. An alternate IR approach involves using optical fibers as a sensor by utilizing evanescent wave spectroscopy

Cossins, Sheryl

Kellar, Jon J.

Winter, Robb M.

English

NASA Technical Reports Server

IN-SITU CURE MONITORING OF THE IMMIDIZATION REACTION
OF PMR-15*
SHERYL COSSINS
South Dakota School of Mines and Technology
Rapid City, South Dakota
and
Dr. Jon J. Kellar
Department of Metallurgical Engineering
Dr. Robb M. Winter
Department of Chemical Engineering
South Dakota School of Mines and Technology
Rapid City, South Dakota
Glass fiber reinforced polymer composites are becoming widely used in
industry. With this increase in production, an in-situ method of quality control for
the curing of the polymer is desirable. This would allow for the production of
high-quality parts having more uniform properties. 1 Recently, in-situ fiber optic
monitoring of polymer curing has primarily focused on epoxy resins and has
been performed by Raman or fluorescence methods. 2"s In addition, some
infrared (IR) investigations have been performed using transmission or ATR
cells. 7.e An alternate IR approach involves using optical fibers as a sensor by
utilizing evanescent wave spectroscopy.
Initial work at South Dakota School of Mines and Technology (SDSM&T)
concerning the curing of epoxy adjacent an embedded silica optical fiber has
been monitored in-situ by evanescent wave spectroscopy. 1° The epoxy studied
was partially fluorinated and therefore had a refractive index lower than that of
the silica optical fiber. The lower refractive index of the partially fluorinated
epoxy allowed the fiber to be used as a waveguide for the internal reflection of
IR light. This evanescent wave samples the polymer at the fiber/polymer
interface. This combination of epoxy/silica served as a model composite system.
The bands used to monitor the cure of the epoxy were as follows: the C-N
overtone absorbance band at 4725 cm _ and the NH2 combination band of the
hardener at approximately 4925 cm_. It was found that the C-N band increased
and the NH2 band decreased over time. This result was expected, as epoxies
react with the NH2 in the curing agent to form C-N bonds while curing.
This method of cure monitoring has been applied to a PMR-15 composite
system. Optical grade sapphire fiber has been chosen as the sensor due to its
* Work funded under NASA Grant NGT3-52312
] Paper 3
https://ntrs.nasa.gov/search.jsp?R=19970024958 2020-06-18T00:18:13+00:00Z
wide transmission range, high refractive index, and strength. The system will be
used to determine the end of the immidization reaction or =gel point'. It is
important to know when the gel point has been reached because it is at this
point that the Lewis Research Center Group increases the temperature and
pressure applied in order to crosslink the polymer. Before the final product is
made, PMR-15 can go through undesired temperature cycling simply through
shipping and storing. This causes the polymerization reaction to be at different
stages for different batches or lots of PMR-15. Because of this batch to batch
variation, the time to reach the gel point can vary. By monitoring the reaction in-
situ, the gel point can be found for each batch and variation in the quality of the
final product may be reduced.
in order to monitor the PMR-15 reaction, we must first identify the bands
present and determine which will be changing during the reaction. Spectra of
the raw products of PMR-15 were collected using diffuse reflectance infrared
Fourier transform (DRIFT) Spectroscopy. Spectra were also collected for the
cured and uncured PMR-15 polymer. During the immidization reaction primary
amines are converted to tertiary amines. Therefore, the reaction is complete
when the primary and secondary amine bands have disappeared or stopped
decreasing. Some examples of near-lR bands for the raw materials are as
follows: 4,4'-methylene dianiline (MDA): amine stretching and bending
combination 5000-5050 cm 1, aromatic primary amines 6550-6850 cm'l;
3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA): aromatic CH stretch
5900-6100 cm 1, carboxylic acid stretch 5300-5400 cml; 5-norbornene-2,3-
dicarboxylic anhydride (Nadic): carboxylic acid stretch 5300-5400 cm1.
Complete identification of the bands is ongoing. 11"12
Design of a curing cell to duplicate conditions at Lewis Research Center
has been completed. The requirements of this cell were to maintain a
temperature of 600 °F + 1 °F for 60 to 90 minutes, to accommodate up to three
150 _m diameter sapphire fibers, and be easily cleaned without damage to the
fibers. It was also designed to have a nitrogen blanket to prevent occurrence of
oxidation reactions. Experiments to monitor the immidization reaction are
currently being performed.
References
1. V. Kierman, Laser Focus World, August, 49 (1995).
= C. Sung and H. Nak, Materials Science and Engineering, A162, 241
(1993).
, K.E. Chike, M.L. Myrick, R.E. Lyon and S.M. Angel, Applied Spectroscopy
47,1631 (1993).
Paper 3 2
°°
.
.
8.
9.
10.
11.
12.
J.F. Maguire and P.L.Talley, Journal of Advanced Materials, 26, 1
(1995).
J.F. Aust, M.K. Higgins, P. Groner, S.L. Morgan, and M.L. Myrick,
Analytica Chimica Acta, 293, 119 (1994).
J.F. Aust, K.S. Booksh, and M.L. Myrick, Applied Spectroscopy, 50, 382
(1996).
L. Xu, J.H. Fu, and J.R. Schlup, J. Am. Chem. Soc, 116, 2821 (1994).
Jovan Mijovic and Sasa Andjelic, Macromolecules, 29, 2787 (1995).
Lisheng Xu and John R. Schlup, Applied Spectroscopy, 50, 109 (1996).
S. Cossins, M. Connell, W. Cross, R. Winter and J. Kellar, Applied
Spectroscopy, 50, 900 (1996).
B.G. Osborne and T. Fearn, Near Infrared Spectroscopy in Food Analysis
(Longman Scientific and Technical, New York, 1986), p. 28.
A. Garton,/nfrared Spectroscopy of Polymer Blends, Composites and
Surfaces (Oxford University Press, New York, 1992), p. 136.
3 Paper 3
In-situ Cure Monitoring of the Immidization Reaction of PMR-15
Presented by
Sheryl Cossins
South Dakota School of Mines and Technology
Under the direction of
Dr. Jon Kellar and Dr. Robb Winter
SDSM&T
and
Dr. Chris Johnston
Lewis Research Center
May1, 1997
Fig. I
OUTLINE
Objectives
Evanescent Wave Spectroscopy
Silica Fiber Sensor
PMR-15 Reaction
• IR Bands
Summary of Results
Conclusions
• Future Research
Fig. 2
Paper 3 4
OBJECTIVES
• Fiber selection
• Identification of PMR-15 IR bands
Curing cell design
Monitor immidization reaction of
PMR-15
Fig. 3
BULK MATRIX
POLYMER of
DIFFERENT
PROPERTIES
SIZINGS
ADSORBED
MATERIAL
FIBER CHEMISTRY
TOPOGRAPHY
RBER MORPHOLOGY
BULK RBER
FIBER-MATRIX INTERPHASE
P.J. Herrera-Franco and L.T. Drzal, Composites, 23, 1 (1992).
Fig. 4
5 Paper 3
FIBER OPTIC WAVEGUIDES
cladding buffer
core
nl >n2
Oc=sin-l(n21n 1)
O>Oe
112 _ * _ EVANESCENT
WAVE
SAMPLING
Fig. 5
SILICA FIBER SENSOR
Create I cm sensing region in
140 _m diameter silica fiber
• Embed in Epo-Tek 328
• Heat to 150 °C for I hour
• Collect spectra during cure
Fig. 6
Paper 3 6
1,7
1,5
1.3
A
b
s 1.1
O
r
0.9b
a
n 0.7
¢
e
O.5
0.3
0.1
5OOO
NIR Cure of Epo-Tek 328
27 C (fully cured)
150C
95C
83C
7O C
40C
4500 44OO4,900 4800 4700 4600 4300 4200
Wavenumber (cm-t)
Cossins, Connell, Cross, Winter, Ke]lar, Applied Spectroscopy, 50, 900 (1996),
Fig. 7
4100 4000
PMR-15 REACTION
NADIC O O O BTDA O
II II I! _i
o(C. C - C
/ -_/Ac/
It II iJ
O O O
INTERMEDIATE
MDA
0 0 0 0
Jl H '-_" H _'_' H II II I1fX-,:-"c-
PMR-15 BEFORE CROSSLINKING O O
0 0 0 0 0
IT II II I1 II
C. .C. C ..C
• k-x, / / \ /
II II II II
o O 0 0
Fig.
7 Paper 3
Infrared Fibers and Their Transmission Ranges.
Fiber Type (core material)
fused silica (ultra low -OH)
chalcogenide glass
zirconium fluoride
silver halide
sapphire
n]_l_qgg...(£_- 1)_
26000-4000
3333-1000
20000-2325
3000-625
12000-2200
Fig.9
Sapphire Fiber Background
0.6
0.6
R
e O.4
S
P o.,
o
n o.2
s
e
0.1
0
12600 11500 1_ _ 8800 "/1800 nO0 _ 4600 _00 2500
Wavenumber (cm-1)
Fig. io
Paper 3 8
BTDA DRIFT Spectrum
O.OO8
A o.oo7
b
o_
S
O o.o05
r
oAo4
b
a o.H3
n
o.oo2
C
• o.oot
o q i _ l + q i
10000 _ $000 8600 8N0 7MO ?_0 6S00
Wavenumbers (cm-1)
Fig,] 1
Nadic DRIFT Spectrum
0.12
A o.1
b
S oJ8
0
r o_
b
a 0.o4
C
o.112
e
$500 6000 5S00 SO00 4500 4000
Wavenumber (cm-1)
Fig.12
9 Paper 3
02S
A
b 0.2
S
O o.18
r
b
a o.1
n
C o,os
MDA DRIFT Spectrum
e
o J i i i r _ _ i i
75oo 7000 6soo SO00 5500 SO00 4600 4000 3500
Wavenumber (cm-1)
Fig. 13
PMR-15 DRIFT Spectrum
0.16
A 0.14
b o.12
S
0 o.1
r 0.o8
b
a o.o6
n
C
e o.o2
0
7OOO
I ! I I t
eSO0 6000 r_O0 5000 4500 4000
Wavenumber (cm-1)
38O0
Fig. 14
Paper 3 1o
SUMMARY OF RESULTS
Sapphire fiber chosen
Heating cell designed
Possible IR bands for cure monitoring
identified
Fig, 15
CONCLUSIONS
Monitoring of the immidization reaction
of PMR-15 Is possible
Fig. 16
I l Paper 3
FUTURE WORK
Obtain fiber spectrum and compare to
DRIFT
Identify and monitor IR bands
changing with cure
Q Develop correlation of band change to
gel point
Fig. 17
Paper 3 12


In-Situ Cure Monitoring of the Immidization Reaction of PMR-15

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