polymer-ceramic composite film fabrication and characterization for harsh environment applications...
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Polymer-Ceramic Composite Film Fabrication and
Characterization for Harsh Environment Applications
Santiranjan Shannigrahi
OUTLINES:
Polymer-ceramics composites
Basic applications
Current pain
Case study
Conclusions
GRAPH OF MATERIALS PRODUCTION
Source: CES EduPack, University of Cambridge/Granta.
Polymer – ceramic composites
APPLICATIONS OF POLYMER COMPOSITES
CURRENT PAIN
Harsh environment:
• Light/heat
• Moisture,
• UV illumination.
Significant Impact on polymer matrices
CASE STUDY
Composites: 1. Epoxy matrixTemperatureMoistureReversibility
2. PE matrix
UV and temperature
COMPOSITE FILM FABRICATION
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UV-Chamber
UV-VIS characterization
UV-3101 PC
UV-VIS-NIR-spectrophotometer SHIMADZU, (90-2500 nm)
Mechanical testing
Flexural testing using three point bending set up
Humidity chamber (90% Rh & 90oC
Specimens
HARSH ENVIRONMENTS AND CHARACTERIZATIONS
The total UV energy is 84.30 W/m2
EXPERIMENTAL DESIGN (EPOXY)
• Three factors can affect the properties of the epoxy in hygrothermal environment
1. Elevated temperature •Relaxation of polymer matrix
2. Moisture ingression• Changed interchain hydrogen bonding force & plasticization
3. Chemical reaction • Bond scission on main chains (backbones)
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0 10 20 30 40 50220
225
230
235
240
245
Gla
ss T
ran
siti
on
Tem
p
No. of Days
Tg of 90°C /90H
Glass Transition Temperatures of Aged Epoxies
Variation of glass transition temperature (Tg).
0 5 10 15 20 25 30 35 40 45 50
3.7
3.8
3.9
4.0
4.1
4.2
4.3
4.43 Point Flexural Test
Ave Flexure S
tress (MP
a)
Ave
You
ng M
odul
us (G
Pa)
Number of Days
100
110
120
130
140
150
160
170
180 60 oC, 90% humidity
90 oC, 90% humidity
Young’s modulus and Flexural stress variation.
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THERMO MECHANICAL PROPERTY VARIATIONS
AVERAGE WEIGHT GAIN %
• No equilibrium of moisture absorption after 90 days – Non-Fickian behavior (I)
• Irreversible process (Chemical reaction).
Moisture has significant effect on the interfacial mechanics and is strongly correlate with the oxidation of CNF surface
Two classes of carbon fiber surface are consideredNo surface modification (Model-I)Modified with –OH (Model-II)
The interactions across the interface are purely non-bonding, i.e., VDW + electrostatic interactions.
Added water plays a role of plasticizer at the CNF/epoxy interface, and it leads to wider attraction region.
After moisture ingression, interfacial force is enhanced with strong fluctuation. Possible reason: enhanced hydrogen bond interaction. Local stress may break some hydrogen bonds (cluster) and leads to the fluctuation.
MOISTURE EFFECT ON INTERFACIAL ADHESION
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SIMPLIFIED MODEL SYSTEM
The barriers are very high. → Hydrolysis (Chemical aging) is very slow in the neat epoxy resin!
(1) Reaction I
(2) Reaction IIHN
OH
+ H2O
OH
+HN
OH
• C-O bond breaking for C from aliphatic and benzene are:– Ea ≥ 265 kJ/mol and ≥ 259 kJ/mol respectively
• C-N bond breaking: Ea ≥ 191 kJ/mol
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• A structure (97% crosslinked) contains ~550 C-N bonds in the main chains(328 from curing reaction and others from initial structure). Meanwhile, it contains only ~ 80 C-O bonds (side chains are neglected).
• Bond scission on C-N bonds is more crucial for mechanical property degradation.
EFFECT OF C-N BOND BREAKING • Structures with different percentages of broken bonds
– 0.0%, 4.0%, 7.0%, 10%, 15%– 3 configurations for each degree of bond scission
Creating broken bonds leads to decreased density
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Assuming that Young’s modulus is linearly correlated with the degree of bond broken, there exists a critical degree at which the epoxy resin breakdown completely.
Percolation Threshold?
cnf/water/epoxy cnf-OH/water/epoxy
H2O
Water at interface
Water embedded into bulk
HYDRATED MODELS
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EXPERIMENTS – REVERSIBILITY
Objective: To study reversibility of epoxies after ageing → Chemical ageing
After drying the wetted epoxies at 90°C for 48h, the following experiments have been conducted
3-Point Bending DMA FTIR
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REVERSIBILITY: TG
No. of days
Tg (°C)
0 238.22
42 234.29
50 235.20
82 234.59
Tg declines weakly with ageing duration – Weak chemical degradation?
0 20 40 60 80
234
235
236
237
238
239
Gla
ss T
ran
siti
on
Tem
p (
oC
)
No. of Ageing Days
60 oC, 90% RH
Decline in Tg of 20°C from as-received (dry) to 49 days (wet) is due to the lowering of intramolecular hydrogen bonding forces and increased moisture concentration which acts as ‘plasticizers’.
Wetted
Re-dried
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REVERSIBILITY: FTIR RESULTS
Bands (cm-1) Assignment
3600-3100 OH stretching
3000-2850 CH stretching of the alkyl
1600-1585 C-C stretching in aromatic ring
1500-1400 C-C stretching in aromatic ring
1335-1250 C-N stretching (aromatic amines)
1250-1020 C-N stretching (aliphatic amines)
1320-1000 C-O stretching (aromatics)
1600 1400 1200 1000 8000.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
Ab
so
rba
nce
Wavenumber (cm-1)
0-day + 2 day of drying 50-day + 2 day of drying 90-day+ 2 day of drying 110-day + 2 day of drying
C-C stretchesin aromatic rings
C-N
*
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4000 3800 3600 3400 3200 3000 2800 26000.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Ab
so
rba
nc
e
Wavenumber (cm-1)
0-day + 2 day of drying 50-day + 2 day of drying 90-day+ 2 day of drying 110-day + 2 day of drying
O-H Stretching
C-H Stretching
N-H
• Weakly increased O-H stretching peak
— There is residual moisture inside the sample even after 2-days of drying.
Irreversible effect due to chemical ageing
UV BARRIER POLYMER-CERAMIC COMPOSITES
Patent no. 2014/123488 A1
Lead-free transparent ceramic; Thickness 0.8 mm
500 1000 1500 2000 2500 3000-5
0
5
10
15
20
25
30
35
40 +00.00 kV/cm +06.25 kV/cm +12.50 kV/cm +18.75 kV/cm +25.00 kV/cm -12.50 kV/cm -18.75 kV/cm
Tra
nsm
ittan
ce (
%)
Wavelength (nm)
UV
- re
gion
IR r
egio
n
Transparency window
Tunable ~55% Transmittance
capability
FEATURES OF THE CERAMIC FILLERS
Potential applications: Complete UV absorption; UV absorption indication through color change; Optical Coating and filter for UV; Tunable electro optic ceramics; etc.. Advantages: Nontoxic, robust and thermally stable, block UV, transparent to NIR, low thermal conductivity, electro optic tunability
POLYMER-CERAMIC COMPOSITE
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E N
eat
5%
10%
20%
Ceramic amount
Film
Film thickness is ~ 160
UV-VIS SPECTROSCOPY ANALYSIS
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WEATHERABILITY TEST CONDITIONS
Specimens kept in UV chamber for a 40 h and tested for their physical (crack) and chemical (degradation) properties.
Q: How long will it take to reproduce 5 years of sunlight artificially?
A: Assuming that sunlight in Singapore is similar to sunlight in South Florida (both are sub-tropical environments) and 1 Y of total UV (295-400nm) in Miami is 280MJ.
The formula is: kJ = irradiance x 3.6 x N hours
So the 1080 hours 1 year. To duplicate 5 years of weathering, the total time would be 5400 h or 225 days. This is a crude assumptions for a guide.
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MECHANICAL PROPERTIES OF THE COMPOSITE FILMS BEFORE AND AFTER UV ILLUMINATION
Sample
Max Tensile strength after UV irradiation
Neat 8% decrease
5% 14% increase
10% 18% increase
20% 11% increase
CONCLUSIONS:
In epoxy based composite immersed in moisture and
temperature, their properties become irreversible,
which is due to chemical ageing
In PE based composites, UV absorbing ceramic fillers
improve the mechanical properties, UV resistance and
suitable for harsh environment applications.
Confidential
Thank you!
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