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Hydrothermo degradation of polydicyclopentadiene

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Hydrothermo degradation of polydicyclopentadiene

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Content HYDROTHERMO DEGRADATION OF POLYDICYCLOPENTADIENE
by
Xiaochen Li
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
Master of Science
(CHEMICAL ENGINEERING)
May 2014
Copyright 2014 Xiaochen Li
Table of Contents

Acknowledgements ............................................................................................................. 1

Abstract ................................................................................................................................ 2

Introduction ......................................................................................................................... 2

Experiments ......................................................................................................................... 6
2.1 Experiment Materials and Aging Conditions ............................................................ 6
2.2 Mass Evolution .......................................................................................................... 6
2.3 Raman spectroscopic testing ..................................................................................... 7
2.4 DMA .......................................................................................................................... 8
2.5 Nanoindentation ........................................................................................................ 8
2.6 SEM-EDS .................................................................................................................. 8

Results and Discussion ........................................................................................................ 9
3.1 Weight Change .......................................................................................................... 9
3.2 Micro-Raman Spectroscopy .................................................................................... 11
3.2.1 Choosing Proper Excitation Laser Light .......................................................... 11
3.2.2 Comparison of Aged and Unaged PDCPD Neat Resin .................................... 13
3.3 DMA ........................................................................................................................ 23
3.4 Elastic Modulus And Hardness ............................................................................... 24
3.5 SEM-EDS ................................................................................................................ 25

Conclusions ....................................................................................................................... 29

References ......................................................................................................................... 31

1

Acknowledgements
I would like to say thank you to my advisor Professor Steven Nutt. I am grateful
to have worked with Prof. Nutt in these years. He offered me lots of opportunities to do
research projects, presentations, teaching assistant, grader, and various students
programs. He is always supportive to his students. He gave me a lot of advice and
guidance for my research, which was really helpful to me. What I learnt from him is not
only knowledge, experience and skills, but also how to be a better person. By being hard
working, clean, responsible, efficient and very well organized, he sets me a great model
for my life and career.
I also want to acknowledge my colleagues in USC Composites Center. They gave
me so much help in these years. I benefit a lot by talking with them about my research.
They generously taught me how to do test, shared their experience, and gave hands when
I need. I want particularly thank Bo Jin, Lessa Grunenfelder, Yinghui Hu, and Yuzheng
Zhang. I was luck to have all these nice people working with me.
For funding and material support, I would like to acknowledge Materia and
Nycote. Materia provided funding and all the materials I need for my research. It’s a very
generous help. Nycote provided research funding and brought a new interesting project
for my last semester.
Finally but most importantly, I want to thank my parents. They always offer me
generous financial support and endless love. They always cheer me up when I’m down.
And they always give me confidence to overcome difficulties.
2
ABSTRACT
Polydicyclopentadiene (PDCPD) is a novel resin synthetized by ring-opening reaction
of dicyclopentadiene catalyzed by Grubbs’ catalyst. Except for high toughness, low
density and cost, PDCPD and its monomer have significantly low viscosity which allows
for 10 times faster infusion rates than traditional resins. PDCPD-based composites are
now applied in industries such as wind energy, oil and gas transportation and automotive.
In these applications, PDCPD often serves under hot wet and saline environment.
PDCPD’s resistance to hydrothermal and saline hydrothermal environment becomes a
key research property. In this work, long-term water & salt water (35% NaCl solution)
accelerated aging effect on PDCPD was studied from the standpoint of chemical
composition change and dynamic mechanical property. PDCPD neat resin, PDCPD/glass
composites systems were aged in 60°C deionized water and 60°C 35% NaCl solution for
180 days. DMA, Micro-Raman spectra, SEM-EDS data were analyzed and discussed for
future research references.
1 INTRODUCTION
Wind power is a thriving new energy industry. Average growth in new wind power
generating equipment installations is 27.6 percent each year for the last five years [1].
3

Figure 1. Composite Wind Blades in Offshore Environment.

Polyester-glass, Epoxy-glass and Epoxy-carbon composites have been designed for
manufacture rotor blades for wind turbines. With lower density, lower viscosity and
greater toughness, Polydicyclopentadiene (PDCPD) may lead to lighter, larger diameter
and more durable blades in wind blade composite technology (Figure 1). Since wind
turbine blades are often installed on offshore locations, PDCPD resin and PDCPD-based
fiber reinforced composite’s durability in seawater environment is an important concern.
PDCPD is formed by a ring-opening metathesis polymerization (ROMP) of
dicyclopentadiene (DCPD) and Grubbs’ catalyst. The reaction scheme for ROMP of
DCPD and Grubb’s catalyst is depicted in Figure 2. DCPD is a tricyclic monomer with
two C=C double bonds. Bis(tricyclohexylpho-sphine)benzylidine ruthenium (IV)
dicholride (known as Grubbs’ catalyst) initiates this polymerization and produces a
tough, highly cross-linked polymer. This reaction shows high metathesis activity, which
enables room-temperature polymerization in the presence of oxygen, water and a wide
range of functional group [1]. This reaction is widely used in building microcapsule self-
4
Figure 2. Reaction scheme for ROMP of DCPD and Grubb's catalyst [1].
healing systems, where resins are incorporated with microencapsulated DCPD that is
released by crack rupture. DCPD is then reacted with embedded Grubbs’ catalyst to bond
the crack faces [1].
Fourier-transform infrared spectroscopy (FTIR), dynamic mechanical analysis
(DMA), thermo gravimetric analysis (TGA), and Raman spectroscopy are widely used to
study chemical changes associated with matrix degradation. However, these methods
challenge with respect to sample preparation, because for both neat resin and composite
laminates, degree of degradation and water absorption vary with subsurface depth, where
near-surface material tend to exhibit greater degradation. When using the methods above,
one can only determine the approximate relationship between degradation of the testing
point and its depth away from material surface. For composite laminates with high fiber
5
volume fraction, it’s even harder to determine chemical changes using the above
techniques.
In this study, hydrothermal effect on mechanical properties of PDCPD resin was
studied by Nanoindenter. Nanoindentation is often used on polymers to investigate their
mechanical properties below the micron level. The elastic modulus and the hardness H
are obtained from cycles of loading and unloading. In our work, we also choose Micro-
Raman spectroscopy and SEM-EDS (Scanning Electron Microscope-Energy Dispersive
x-ray Spectroscopy) to get chemical composition information of precise locations on
aged neat resin and aged composite laminates.
Micro-Raman spectroscopy integrates a Raman spectrometer with a Raman
microscope, enabling a respectively very small volume’s (diameter<1 µm) identification
of chemical composition species from the volume’s microscopic region spectra
information. SEM-EDS, whose capabilities are due in large part to the fundamental
principle that each element has a unique atomic structure allowing unique set of peaks on
its X-ray spectrum, is used to analyze the concentration and the chemical characterization
of precise locations inside material samples.
In this work, durability of PDCPD in offshore environment was evaluated and
accelerated aging tests were performed on PDCPD and Epoxy in seawater like solution at
temperature of 60oC under hydrostatic pressure for durations up to 180 days. The
evolutions of chemical and mechanical properties have been investigated in order to
assess the aging mechanisms. Detailed results from Raman spectroscopic tests, DMA and
SEM-EDS tests were discussed. Evaluating the durability of PDCPD for offshore
6
applications is possible using the results in this work.
2 EXPERIMENTS
2.1 Experiment Materials and Aging Conditions
Accelerated aging was conducted on two groups of samples. First group is 4 layers
Epoxy (Momentive EPIKOTE Resin MGS RIMR 135) laminates and PDCPD (Proxima,
Materia, Pasadena, CA) laminates. The other group is 3cm*1cm Epoxy laminates and
PDCPD laminates.
Two aging conditions, as shown below, were used. Both conditions were at 60oC
which is lower than PDCPD neat resin’s Tg: 140oC. The aging period was 180 days for
all samples.
(a) 35% NaCl solution,
(b) Deionized water.
2.2 Mass Evolution
Weight change was monitored as a function of time for the following materials:
(a) PDCPD neat resin,
(b) PDCPD composite laminates,
7
(c) Epoxy neat resin,
(d) Epoxy composite laminates.
All above materials were submerged in both 60°C deionized water and 60°C 35%
NaCl solution.
Specimens were periodically removed from the aging tanks and were placed in the
specimen bags, which were sealed to allow the specimens to come to the laboratory
ambient temperature. Specimens were then removed from the bags and wiped free of
surface moisture with an absorbent paper towel [1] before measuring their weight. We
weighed the specimen immediately (within 30min) and recorded the weight as Wa. The
weight changes of all specimens were calculated accordingly:
!
!
!!
!
!
!
×100% (1)
where Wi is specimen’s initial weight, and Wa is the weight after aging.
2.3 Raman Spectroscopic Testing
The Raman spectra are collected by a Renishaw spectrometer with 532nm green light
laser and 633nm red light laser through a 100× objective lens Leica microscope. The
grading was 1800 l/mm (vis). For the 532nm green light laser, the laser power was set to
8
10%. For the 633nm red light laser, power of the laser is chosen accordingly that
providing relatively good spectra. The spectra recorded range was from 0 to 3200cm-1.
2.4 DMA
Dynamic mechanical analysis (DMA) data were obtained with a TA instrument DMA
2980. Single-cantilever-beam clamp was used to get the Tg. The ramp rate was set as
5oC/min for all unaged and aged samples. DMA tests were conducted according to
ASTM D7028.
2.5 Nanoindentation
Nanoindentation measurements were performed on PDCPD thin film specimens
(thickness~50µm) using a 100 nm Berkovich indenter (TriboIndenter, q=65.3˚, Hysitron,
Minneapolis, MN). The thin film specimens were sticked on a polished Epoxy base. The
tested specimens were water aged at 65°C for 0h, 120h, 240h, 360h and 480h. The
maximum indentation depth was 1000 nm. The loading rate was 1000µN/s and the
maximum load was 5000µm.
2.6 SEM-EDS
9
EDS characterization was performed with a JEOL JSM-6610LV scanning electron
microscope (SEM). Line scan mode was chosen, with the accelerate voltage at 15kV.
3 RESULTS AND DISCUSSION
3.1 Weight Change
The weight change verses aging time data for both PDCPD neat resin and PDCPD
laminates were documented and shown in Figure 3 for aging in 35% NaCl solution
(60°C, 180 days), and in Figure 4 for aging in deionized water (60°C, 180 days). The
following phenomena of the aging experiments were observed:
(a) For two types of specimens, the moisture uptake increased with time.
(b) For both deionized water and 35% NaCl solution aging, the moisture uptake rate of
neat resin is greater than composite laminate’s.
(c) For PDCPD neat resin, PDCPD laminates and PDCPD laminates with defects, weight
gaining rates in deionized water immersion are all slightly faster than in 35% NaCl
solution immersion.
10
0 500 1000 1500 2000 2500 3000 3500 4000
-‐0.2
-‐0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
Weight
change
(%)
Time
(hour)

Weight
change
of
PDCPD
laminates
in
salt
water

Weight
change
of
PDCPD
neat
resin
in
salt
water
Figure 3. Weight change V.S. aging time for PDCPD resin and PDCPD
composites laminates in 35% NaCl solution.
0 500 1000 1500 2000 2500 3000 3500 4000
-‐0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
Weight
change
(%)
Time
(hour)

Weight
change
of
PDCPD
laminates
in
water

Weight
change
of
PDCPD
neat
resin
in
water
Figure 4. Weight change v.s. aging time for PDCPD resin and PDCPD
composites laminates in pure water.
11
3.2 Micro-Raman Spectroscopy
One of the advantages of Micro-Raman spectroscopy is the function of a small
volume’s (diameter<1 µm) fixed-point identification, which allows accurate positioning
and precise detection of the chemical composition information on a specific small
location of the testing specimen.
3.2.1 Choosing Proper Excitation Laser Light
Peaks of Raman spectrum are theoretically independent from wavelength of
excitation light. Sometimes, for conjugated polymer samples, strong fluorescence signal
may be excited by lights some excitation wavelengths. The fluorescence signal
sometimes become too strong and thus covers the sample’s signal. On the other hand,
according to Rayleigh’s law, intensity of light scattered is inversely proportional to λ4 (λ
is the wavelength of excitation light), which means Raman peaks’ intensity decreases
when larger λ is used. So for different samples, different excitation wavelength should be
chosen properly, in order to provide stronger sample signal when having weaker
fluorescence influence.
We chose 532nm green excitation light laser and 633nm red excitation light laser for
both PDCPD and Epoxy samples. The Raman shift V.S. intensity data were shown in
Figure 5 and Figure 6.
12
0 500 1000 1500 2000 2500 3000 3500
0
2000
4000
6000
8000
10000
12000
Intensity
Raman
shift
(cm
-‐1
)
A

633
nm

532
nm
Figure 5. Raman spectra of aged PDCPD neat resin with 532nm green light laser (too
strong baseline) and 633nm red light laser.
0 500 1000 1500 2000 2500 3000 3500
0
5000
10000
15000
20000
25000
30000
35000
Intensity
Raman
shift(cm
-‐1
)
633
nm
532
nm
Figure 6. Raman spectra of aged Epoxy neat resin with 633nm red light laser (too
strong baseline) and 532nm green light laser.
13
(a) For PDCPD neat resin samples: we discovered that a 633nm red light laser is proper
for all aged PDCPD neat resin samples (Figure 5), while using a 532nm green light
laser would cause a strong baseline which makes PDCPD’s Raman peaks too weak to
be observed.
(b) For Epoxy samples, different from PDCPD, the 633nm red light laser caused a too
strong baseline in the Raman spectra. We chose 532nm green light laser for Epoxy
samples. (Figure 6)
Therefore, we chose the 633nm red light as a proper laser for PDCPD samples, and
the 532nm green light laser for Epoxy samples.
3.2.2 Comparison of aged and unaged PDCPD neat resin
3.2.2.1 Experimental observation
Optical microscope picture (Figure 7) shows the near surface area of the cross-section
of 3 months 35% NaCl solution aged PDCPD neat resin. We observed obvious color
change near all edges of the aged samples.
14
Figure 7. Polished cross section of 3 months 35% NaCl solution aged PDCPD neat
resin under 20× microscopic lens.
To investigate the chemical composition of multiple positions within the color
changed part between the surface and the center of the aged PDCPD samples, we
conducted Micro-Raman spectroscopic study using 633nm red excitation light laser.
Figure 8 shows the comparison of multiple testing points’ Raman spectra between unaged
PDCPD neat resin and deionized water aged PDCPD neat resin. Figure 9 shows the
comparison of multiple testing points’ Raman spectra between unaged PDCPD neat resin
and 35% NaCl solution aged PDCPD neat resin.
15
0 500 1000 1500 2000 2500 3000 3500
0
10000
20000
30000
40000
50000
60000
70000
80000

unaged

d=100µm

d=200µm

d=300µm

d=500µm
Intensity
Raman
shift
(cm
-‐1
)
Figure 8. Raman spectra of 3 months deionized water aged PDCPD neat resin (d is
the distance between tested point and the surface).
0 500 1000 1500 2000 2500 3000 3500
0
5000
10000
15000
20000
25000
30000
35000
40000
45000

unaged

d=100µm

d=200µm

d=300µm

d=500µm
Intensity
Raman
shift
(cm
-‐1
)
Figure 9. Raman spectra of 3months 35% NaCl solution aged PDCPD neat resin (d is the
distance between tested point and the surface)
16
The parameter d in both figures is the distance from the tested points to the sample’s
surfaces which were exposed to submerging environment. Decreasing in d meaning
closer of the Raman testing points are from the surface of the specimen.
3.2.2.2 The fluorescence phenomenon in PDCPD Raman spectra
The Raman spectra of multiple tested points on unaged PDCPD sample had slight
shape and intensity change, while spectra of multiple tested points for aged samples in
both environments are compared and observed in Figures 8 and 9:
(a) With d decreasing (meaning the tested points are getting away from the center of the
sample and getting closer to the sample surface), the intensity of the Raman spectra’s
baselines are increasing.
(b) With d decreasing, the shape of the Raman spectra are changing from flat to gradually
bumped shape. The Raman shift of the bumps centers were all measured and all
documented at around 1700cm-1.
(c) The intensity of each peak, or wide bump in every spectrum, is termed as I in our
work, and is increasing (also the baselines) with the decreasing of d.
(d) The intensity I is measured as the intensity of the main peaks within the whole
spectrum, e.g. for spectrum of d=100µm in Figure 10, the main peaks are at Raman
shift=1700 cm-1, thus for the spectrum at d=100µm, I =32500.
17

800 1200 1600
0
3000
6000
Raman
shift
(cm
-‐1
)
Intensity

water

salt
water

unaged

Figure 10. Comparison of Micro-Raman spectra of 3 months water aged, 3 months
35% NaCl solution aged and unaged PDCPD neat resin.

These peaks (or wide bumps) that gradually appeared in the spectra with d decreasing
are fluorescence signals, and we recognized the phenomenon as fluorescence, which
often appears in Raman spectra with the existence of conjugate groups of chemical
compositions. With more SEM-EDS tests conducted and explained in later part of this
paper, the fluorescence phenomena and the fluorescence peaks are good signals of
detecting impurities’ existence in Raman spectroscopic data.

18
3.2.2.3 Chemical composition analysis from PDCPD Raman spectra
Two PDCPD aged sample’s spectra (aged in deionized water and 35% NaCl solution)
with high fluorescence peak (both at d=300µm) were investigated for comparison with
unaged sample’s spectra. Figure 11 shows the Raman spectra after their baselines and
fluorescence noise subtracted. Table 1 shows the corresponding bonds of the main
Raman peaks of PDCPD observed in Figure 10.
Table I. RAMAN PEAKS OF PDCPD NEAT RESIN CORRESPONDING TO FIGURE
We can see the Raman shift and relative intensity of all peaks have not changed after
aging, which leads to the following analyses:
Raman peaks of PDCPD
Raman shift-1 Bond
3054 C-H (1,2,6,7)
2940 C-H (4)
1659 C=C (1,2)
1616 C=C (6,7)
1454 C-H (6,7)
Poly-Dicyclopentadiene
19
(a) Comparing to unaged sample’s spectra peaks, the chemical composition of aged
PDCPD neat resin samples remain unchanged after 6 months submerging in 60oC
35% NaCl solution.
(b) Since there’s no chemical change of the polymer molecule in the aged samples, the
fluorescence phenomena suggested the existence of impurities in the form of
diffusion of small molecules which came from the experiments environment. This is
later explained in more detail in the SEM-EDS test part.
(c) The increase of I (intensity of fluorescence peaks) with decreasing d (distance from
tested points to sample’s surfaces) suggested that, the more closer the tested points
were to the surface of the specimen, the more impurities existed in the sample. More
detail explanation in the later SEM-EDS test part.
3.2.3 Comparison of aged and unaged Epoxy neat resin
3.2.3.1 Fluorescence in Epoxy Raman spectra
To investigate the different composition of the surface and center of the Epoxy neat
resin samples, we conducted Micro-Raman spectroscopic study using 532nm green
excitation light laser. The comparison of Raman spectra between unaged Epoxy neat
resin and 35% NaCl solution aged Epoxy neat resin is shown in Figure 11.
20
0 500 1000 1500 2000 2500 3000 3500
0
20000
40000
60000
80000
100000
Intensity
Raman
shift
(cm
-‐1
)

unaged
Epoxy

d=15µm

d=30µm

d=60µm

d=150µm

d=300µm

d=600µm
Figure 11. Raman spectra of 3 months 35% NaCl solution aged Epoxy resin (d is the
distance between the tested point and the surface).
The parameter d is the distance from the tested point to the sample’s surface, which
was exposed to submerging environment.
For aged Epoxy samples, Raman spectra of multiple tested points are compared and
observed in Figures 11:
(a) With distance d decreasing (tested points getting closer to the samples’ surfaces), the
intensity of the Raman spectra’s baselines are increasing.
(b) Fluorescence phenomena were observed. I, the intensity of fluorescence peaks, were
increasing from center to the surface of the samples (with decreasing of the distance
21
d). The Raman shift of the fluorescence peaks are measured as approximately
1600cm-1.
With more SEM-EDS tests conducted and explained in later part of this paper, the
fluorescence phenomena and the fluorescence peaks in Raman spectroscopic data are
good signals of detecting impurities’ existence.
3.2.3.2 Chemical composition analysis from Epoxy Raman spectra
We chose a spectrum (d=300µm) of 35% NaCl solution aged Epoxy neat resin with
high Raman fluorescence peak, had its baseline subtracted and noise eliminated before
comparing the spectrum with unaged Epoxy neat resin spectra. (Figure 12)
500 1000 1500 2000 2500 3000 3500
-‐3000
-‐2000
-‐1000
0
1000
2000
3000
4000
5000
6000
7000
Epoxy
in
salt
water
aged
Epoxy
laminates
Epoxy
in
unaged
Epoxy
laminates
Intensity
Raman
shift
(cm
-‐1
)
Figure 12 Comparison of Micro-Raman spectra of 3 months 35% NaCl solution aged
and unaged Epoxy neat resin.
22

Similar to the previous PDCPD neat resin spectra, the relative intensity of all peaks in
the Epoxy neat resin were observed as no change (Figure 12) after 6 months submerging
in 60oC 35% NaCl solution, which leaded to no change on chemical compositions of the
aged Epoxy neat resin.
The Epoxy’s fluorescence peaks were not caused by chemical change of the polymer
molecule but by impurities, or diffusion of small molecules coming from experiment
environment.

3.2.4 Conclusion of Micro-Raman spectra analysis

In this chapter, we found both aged PDCPD neat resin and Epoxy neat resin have
characteristic fluorescence peaks. For PDCPD neat resin, we chose 633nm red excitation
light laser, the characteristic fluorescence peaks were at ~1700cm-1. For Epoxy neat
resin, we chose 532nm green excitation light laser, the characteristic fluorescence peaks
were at ~1600cm-1.
We see a clear trend that in the Raman spectra, the characteristic fluorescence peak’s
fluorescence increased with decreasing d (the distance between tested point and sample
surfaces). These florescence peaks could have been caused by small foreign molecules
emigrated to the system or the change of the resin itself. The fluorescence phenomena
and the unidirectional growth of fluorescence peak’s intensity in Raman spectroscopic
23
data may serve as good signals of detecting impurities’ existence. Further studies such as
DMA and SEM-EDS were conducted to help sort out the cause.
3.3 DMA
Figure 13 and Figure 14 are the evolution of Tg of unaged and aged PDCPD neat
resin and laminates samples aged in both water and 35% NaCl solution aging at 60oC up
to 160 days. We observed that the Tg data had no significant change, which means
molecular structure of PDCPD neat resin and laminates had no change within the 6
months aging period. PDCPD neat resin and laminates showed good durability in both
35% NaCl solution and deionized water aging environment (60oC).
Figure 13. Tg change of PDCPD neat resin and PDCPD laminates in 35% NaCl solution.
-‐20 0 20 40 60 80 100 120 140 160
0
20
40
60
80
100
120
140
160
180
200
Tg(
o
C)

PDCPD
laminates

PDCPD
neat
resin
time
of
aging
in
60
o
C
salt
water
(day)
24
-‐20 0 20 40 60 80 100 120 140 160
0
20
40
60
80
100
120
140
160
180
200

PDCPD
laminates

PDCPD
neat
resin
Tg(
o
C)
Time
of
aging
in
60
o
C
water
(day)
Figure 14. Tg change of PDCPD neat resin and PDCPD laminates in deionized water.
3.4 Elastic Modulus and Hardness
In this study, the change of elastic modulus, E, and hardness, H, associated with
evolution of network oxidation in the aged layer was determined by nanoindentation.
Figure 15 indicates the evolution of elastic modulus and hardness as function of time.
Each point in this figure was the average of 20 sample points. For each sample point, data
of the plateau region, 300 nm to 800 nm depth, were used to calculate the average
modulus and hardness. Because the initial data got from depth<150 nm are artifact of the
imperfect surface contact.
25
From Figure15, we can observe an increase of Elastic modulus. This result indicates that
PDCPD is stiffer with water aging treatment. This phenomenon is also found in other
polymers, for example Epoxy and Polyimide. Water aging are understood as reduction in
molecular weight caused by chemical bond breakage. The chain secession will lead to an
increase in the packing density. Both polymer shrinkage and water gaining increase the
bulk density.
Figure 15. Change of PDCPD resin’s Modulus (a) and Hardness (b) with aging time
3.5 SEM-EDS
SEM-EDS scanning was conducted along the straight line consist of Raman
spectroscopic tested points, direction from the surface of the sample towards inside
(Figure 16).
0 100 200 300 400 500
2
3
4
Modulus
(GPa)
Aging
Time
(hour)
0 100 200 300 400 500
0.10
0.15
0.20
0.25
0.30
Hardness
(GPa)
Aging
Time
(hour)
26

Figure 16. EDS line scan of the transverse of the aged resin sample.

The EDS spectrum identifies elements of the specimen and gives the percentage by
weight (Wt%) and the percentage by number of atoms (At%). Line scanning mode was
chosen from cross-section edge of the aged PDCPD neat resin samples towards its center.
Only C (Carbon) and O (Oxygen) were observed in EDS spectra on the line
investigated (Figure 17). EDS data showed an obvious trend of decrease of O (At%) from
the surface of the aged sample to its center. In the aged sample, both 35% NaCl solution
aged and water aged, the concentration of O reached 15% to 50% in the surface (20 µm
away from edge). Even at the center part of the aged samples (d>>20 µm), the
concentration of O is about 15%, which is about 3% higher than the unaged sample’s
Oxygen concentration.

27
Figure 17. Concentration of Oxygen in aged PDCPD resin by EDS. Upper: 3mon water
aged; Lower: 3mon 35% NaCl aged
Only C (Carbon) and O (Oxygen) were observed in EDS spectra on the line
investigated (Figure 17). EDS data showed an obvious trend of decrease of O (At%) from
the surface of the aged sample to its center. In the aged sample, both 35% NaCl solution
aged and water aged, the concentration of O reached 15% to 50% in the surface (20 µm
away from edge). Even at the center part of the aged samples (d>>20 µm), the
concentration of O is about 15%, which is about 3% higher than the unaged sample’s
Oxygen concentration.
The EDS results agree with the previously Raman spectra’s unidirectional increase of
the fluorescence peaks intensity. We conclude that the strong fluorescence peaks in
0 20 40 60 80
5
10
15
20
25
30
35
Concentration
of
O2
in
salt
water
ZAF
of
O2
(At%)
Distance
(um)
0 20 40 60 80 100
0
6
12
18
24
30
36
42
48
54

ntration
of
O2
in
water
aged
PDCPD
ZAF
of
O2
(At%)
I
28
Raman spectra (1550cm-1) are caused by impurity substance containing Oxygen, which
were introduced during aging.
There are two possible mechanisms of adding Oxygen by diffusion of water in the
resin. First, the H
2
O or other oxygen impurities could be trapped between the polymer
chains. Second, the water absorbed in the polymer may cause hydrolysis leading to chain
scission:
~A-B~ + H2O = ~A-H + ~B-H
A and B represent chemical groups in the main chain [3]. There are three methods to
decide which mechanism is dominant:
(a) Use spectra to find whether there is –OH peak introduced by aging.
(b) Use DMA to see whether Tg has changed by chain scission.
(c) Use oven to dry the aged sample and weight the dried sample. Compare the weight of
the dried sample with its original weight before aging to see whether the weight
gaining is reversed.
Both (a) and (b) were done and the results (discussed previously in 3.3 and 3.4)
showed the chemical composition of the sample had no change by both deionized water
or 35% NaCl solution aging. Thus both the increase of the fluorescence peak and the high
Oxygen concentration were caused by diffusion of water.
29
4 CONCLUSION
In this work, long-term water & salt water (35% NaCl solution) accelerated aging
effect on PDCPD was studied from the standpoint of chemical composition change and
dynamic mechanical property. For this purpose, PDCPD neat resin, PDCPD/glass
composites systems were aged in 60°C deionized water and 60°C 35% NaCl solution for
180 days.
DMA and Micro Raman spectra both showed that: chemical composition of PDCPD
neat resin was not changed by 6 months 35% NaCl solution aging, which proves PDCPD
has good resistance to salt degradation in 60˚C.
We found via all experiments that testing from center to the edge of the sample, the
unidirectional growth of fluorescence peak’s intensity in Raman spectra has a positive
correlation with the content of water or other Oxygen impurity. SEM-EDS results also
showed that concentration of Oxygen on the surface (within 30µm) is much higher than
the further inside part towards sample center. And both surface and inside part have
higher Oxygen concentration than unaged PDCPD sample. The emigration of impurities
may lead to degradation of resin’s mechanical properties and damage of resin-fiber
interface.
30
Future work of this study may consist following:
(a) Conduct single fiber pull out experiments to study NaCl solution aging’s effect on
PDCPD-fiber interfacial bonding, which is a promising way of analyzing the
composites’ macro mechanical behavior from the micro mechanics of single fibers-
resin interface.
(b) Conducting Nanoindentation experiments to study water aging and NaCl solution
aging’s effect on the PDCPD resin’s fracture toughness and more mechanical
properties.
(c) Obtaining a quantitative relation between the content of impurity and intensity
increase of the fluorescence peaks. This relationship will be meaningful when
studying the diffusion activity and concentration of Oxygen.
31
REFERENCES
1. BTM Forecasts. 29 August 2010. “340-GW of Wind Energy.”
2. “Standard Test Method for Moisture Absorption Properties and Equilibrium.”
Conditioning of Polymer Matrix Composite Materials.
3. Xiao, G. Z., M.E.R. Shanahan. 1997. Journal of Polymer Science: Part B: Polymer
Physics, Vol. 35, 2659-2670.
4. John Wiley & Sons, Inc. 1997. “Water Absorption and Desorption in an Epoxy Resin
with Degradation.” CCC 0887-6266/97 / 162659-12.
5. Kessler, MR. 2002. “Characterization and Performance of a Self-healing Composite
Material.” PhD Dissertation. University of Illinois at Urbana-Champaign.
6. White, S.R., N. R. Sottos, P. H. Geubelle, J. S. Moore, M. R. Kessler, S. R. Sriram,
E. N. Brown, S. Viswanathan. 15 Feb 2001. “Autonomic Healing of Polymer
Composites.” NATURE, Vol 409.

Abstract (if available)

Abstract Polydicyclopentadiene (PDCPD) is a novel resin synthetized by ring‐opening reaction of dicyclopentadiene catalyzed by Grubbs’ catalyst. Except for high toughness, low density and cost, PDCPD and its monomer have significantly low viscosity which allows for 10 times faster infusion rates than traditional resins. PDCPD‐based composites are now applied in industries such as wind energy, oil and gas transportation and automotive. In these applications, PDCPD often serves under hot wet and saline environment. PDCPD’s resistance to hydrothermal and saline hydrothermal environment becomes a key research property. In this work, long‐term water & salt water (35% NaCl solution) accelerated aging effect on PDCPD was studied from the standpoint of chemical composition change and dynamic mechanical property. PDCPD neat resin, PDCPD/glass composites systems were aged in 60°C deionized water and 60°C 35% NaCl solution for 180 days. DMA, Micro‐Raman spectra, SEM-EDS data were analyzed and discussed for future research references.

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Asset Metadata

Creator Li, Xiaochen (author)

Core Title Hydrothermo degradation of polydicyclopentadiene

School Andrew and Erna Viterbi School of Engineering

Degree Master of Science

Degree Program Chemical Engineering

Publication Date 05/07/2014

Defense Date 03/27/2014

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag degradation,OAI-PMH Harvest,PDCPD,resin

Format application/pdf (imt)

Language English

Contributor Electronically uploaded by the author (provenance)

Advisor Nutt, Steven R. (committee chair), Armani, Andrea M. (committee member), Shing, Katherine (committee member)

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