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Durability of Polymer Matrix Composites for Infrastructure: The Role of the Interphase

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Title: Durability of Polymer Matrix Composites for Infrastructure: The Role of the Interphase


1
Durability of Polymer Matrix Compositesfor
Infrastructure The Role of the Interphase
K. N. E. Verghese
Advisor Dr. J. J. Lesko
Materials Engineering and Science
Program Virginia Tech
January 19th 1999
2
Outline for Presentation
  • Introduction What is a Sizing?
  • Materials Used
  • Results obtained thus far
  • Mechanical properties of laminates
  • study 1
  • study 2
  • study 3
  • pultruded composites
  • Thermo-mechanical experiments
  • dynamic mechanical analysis of resin and
    composites
  • Environmental Durability
  • hygrothermal aging of resin and composites
  • Acknowledgements

3
What is a Sizing?
A thin film applied to the surface of the carbon
before impregnation with the matrix material.
Phenoxy Particulate Sized
K-90 PVP Sized
4
Why do Sizings Affect Properties?
  • Processability-
  • Sizings protect the brittle carbon fiber
  • Sizings affect the wettability of the carbon
    fiber
  • The Interphase (0-1 ?m) - Causes changes in
    damage initiation and propagation.
  • Interdiffusion results in a concentration profile
    or a mechanical property profile.
  • Changes in stochiometry of the matrix reactants.

5
Why do Sizings Affect Properties?
  • Matrix Plasticization (0-1 ?m) - An Interphase
    with no gradients.
  • Results from a sizing that has diffused to such
    an extent that no gradients exist.
  • Fiber/Matrix Adhesion (0-100 nm) - Causes changes
    in interfacial properties like shear strength.
  • Results from a sizing that is physically or
    chemically bonded to the fiber while interacting
    strongly with the matrix.

6
Influence of the Interface in Fiber Reinforced
Composites
Interfacial Shear Strength (ISS) (ksi/MPa)
Interfacial Failure Mechanism
Fiber Tensile Strength (ksi/MPa)
Transverse Tensile Strength (MPa)
Fiber Tensile Modulus (ksi/GPa)
Material
AU-4
34K/234.4
520/3585
5.4/37.2
Friction
18
AS-4
34K/234.4
520/3585
9.9/68.3
Interfacial
34.2
AS-4C
34K/234.4
520/3585
11.8/81.4
Matrix
41.2
Epon 828/ m-PDA Matrix
525/3.6
13/89.6
-----
-----
-----
Ref M. S. Makhukar and L. T. Drzal, Proc. Fifth
Tech. Conf. of the American Society for
Composites, 1990, 849 - 858.
7
Influence of the Interface in Fiber Reinforced
Composites Continued.
Ref M. S. Makhukar and L. T. Drzal, Proc. Fifth
Tech. Conf. of the American Society for
Composites, 1990, 849 - 858. M. S.
Makhukar and L. T. Drzal, JCM Vol. 25 1991,
pp.932-957 M. S. Makhukar and L. T.
Drzal, JCM Vol. 25 1991, pp.958-991 M. S.
Makhukar and L. T. Drzal, JCM Vol. 26 1992,
pp.936-968
8
Interphase and Interface Formation
  • The sizing life cycle must be tracked to
    fundamentally understand and predict interphase
    and interface formation.

Fiber Preform
9
Structure - Property Effects of Cross-link Density
Tear strength, fatigue life toughness
Static Modulus
Hardness
Tensile Strength
Property
Hysteresis. Permanent Set, friction coefficient
Cross-link density
10
Interphase Micromechanics
Broken Fiber
Tensile Load
11
The Approach
12
Outline for Presentation
  • Introduction What is a Sizing?
  • Materials Used
  • Results obtained thus far
  • Mechanical properties of laminates
  • study 1
  • study 2
  • study 3
  • pultruded composites
  • Thermo-mechanical experiments
  • dynamic mechanical analysis of resin and
    composites
  • Environmental Durability
  • hygrothermal aging of resin and composites
  • Proposed work for the future
  • Acknowledgements

13
Vinyl ester Resins
140-150C
styrene
benzoyl peroxide
The distance between crosslink junctions is one
factor controlling toughness. Higher Mc leads to
tougher materials.
14
Fracture Toughness for Resin
Fracture toughness ---K1c (MPa-m.5)
ASTM D5045-91
Molecular weights are from proton NMR.
Courtesy Ellen Burts and Dr. H. Li
15
Outline for Presentation
  • Introduction What is a Sizing?
  • Materials Used
  • Results obtained thus far
  • Mechanical properties of laminates
  • study 1
  • study 2
  • study 3
  • pultruded composites
  • Thermo-mechanical experiments
  • dynamic mechanical analysis of resin and
    composites
  • Environmental Durability
  • hygrothermal aging of resin and composites
  • Proposed work for the future
  • Acknowledgements

16
Sizing Materials
  • Poly(vinylpyrrolidone)
  • (Brittle Thermoplastic)
  • tensile strength for K90 62 MPa
  • strain to failure 0.9
  • Tg 180C (DSC)
  • Polyhydroxyether
  • (Tough Thermoplastic ?)

Mn 19k Tg? 97?C
tensile strength 55 MPa strain to failure
40-100 Tg 97C (DSC)
17
Fully Reversed Fatigue Test Results of Cross-ply
Laminates
50
Run-out
40
Applied Stress (ksi)
30
Phenoxy Sizing
20
PVP-k17 Sizing
fatigue limit for Unsized
10
100
1,000
10,000
100,000
10,000,00
10,000,000
Number of Cycles
18
Outline for Presentation
  • Introduction What is a Sizing?
  • Materials Used
  • Results obtained thus far
  • Mechanical properties of laminates
  • study 1
  • study 2
  • study 3
  • pultruded composites
  • Thermo-mechanical experiments
  • dynamic mechanical analysis of resin and
    composites
  • Environmental Durability
  • hygrothermal aging of resin and composites
  • Proposed work for the future
  • Acknowledgements

19
Poly(hydroxyether) Sizing Materials
Unmodified Poly(hydroxyether)
OH
HO
C
O
CH
O
C
OH
x
Modified Poly(hydroxyether)
OH
HO
C
O
CH
O
C
OH
COOH
x
Poly(hydroxyether ethanolamine)
OH
OH
HO
C
O
CH
N
CH
O
C
OH
OH
x
20
Preparation of sizing/matrix bilayers
Fiber in Matrix
Fiber
Cross section cut and microtomed (room temp. or
cryo)
21
Tapping mode (phase) images of bilayer
cross-sections
a) Carboxy modified poly(hydroxyether) sizing and
Vinyl ester
b) Poly(hydroxyether ethanolamine) sizing and
Vinyl ester
22
Nano-indentation
Courtesy Dr. M. A. F. Robertson
23
Indentation profile across a carboxy functional
poly(hydroxyether)/vinyl ester cross section
140
Plastic Deformation
Elastic Deformation
130
Carboxy functional
Polyhydroxyether
120
110
Vinyl Ester
Depth (nm)
100
Vinyl Ester
10
0
-30
-20
-10
0
10
20
30
m
m)
Distance Relative to Interface (
24
Indentation profile across a poly(hydroxyether
ethanolamine)/vinyl ester cross section
140
Plastic Deformation
Elastic Deformation
130
Polyhydroxyether ethanolamine
120
110
Vinyl Ester
Depth (nm)
100
10
Vinyl Ester
Polyhydroxyether ethanolamine
0
-30
-20
-10
0
10
20
30
Distance Relative to Interface (
m
m)
25
Interfacial Shear StrengthsMicrodebond Test
Materials Fiber AS-4 Matrix 700 g/mol vinyl
ester with 30 wt. styrene cured with 1.1 wt.
Benzoyl peroxide, 130C/20 min.,N2
IFSS (MPa)
Sizing
None
288
Poly(hydroxyether)
43.68.7
Carboxylic acid modified poly(hydroxyether) MPE
52.64.7
Poly(hydroxyether ethanolamine) PHEA
22
Poly(vinylpyrrolidone) PVP
33.86.5
Phosphine oxide modified polyester urethane
56.77.5
Courtesy I. C. Kim and Dr. T. H. Yoon, Korea
26
R-1 Fatigue Response at 10Hz on Notched Specimens
Poly(hydroxyether ethanolamine) Sized Composite
Compression Strength -48.6 ksi Modified
poly(hydroxyether) Sized Composite Compression
Strength -54.3 ksi
50
Modified Poly(hydroxyether) Sizing
40
Poly(hydroxyether ethanolamine Sizing
Run Out for modified poly(hydroxyether)
30
Applied Stress (ksi)
Run Out for poly(hydroxyether ethanolamine)
Run Out for Unsized
20
10
100
1000
10000
100000
1000000
10000000
Number of Cycles
27
Dynamic Modulus Curves for Modified
Polyhydroxyether Sized Composites
28
Residual Strength Test Levels for MPE Sized
Composites
29
Residual Strength Curves on MPE Sized Composites
1.2
_at_ 37 ksi or 0.67
1
_at_ 34 ksi or 0.6
_at_ 31 ksi or 0.56
0.8
Normalized Stress
0.6
3 specimens for
2 specimens for
2 specimens for
0.4
each level
each level
each level
0.2
0
100
1000
10000
100000
1000000
Number of Cycles
30
The MRLife Philosphy
31
Preliminary Fatigue Performance Predictions
(MRLife)
50
Run Out
40
Applied Stress (ksi)
30
20
h Coefficient related to the bonding condition
of the fiber in Xu and Reifsniders
micro-mechanical compression model. 1lt hlt2
for the debonded and well bonded conditions
respectively
10
100
1000
10000
100000
1000000
10000000
Cycles to Failure (Log N)
32
Outline for Presentation
  • Introduction What is a Sizing?
  • Materials Used
  • Results obtained thus far
  • Mechanical properties of laminates
  • study 1
  • study 2
  • study 3
  • pultruded composites
  • Thermo-mechanical experiments
  • dynamic mechanical analysis of resin and
    composites
  • Environmental Durability
  • hygrothermal aging of resin and composites
  • Proposed work for the future
  • Acknowledgements

33
Recent Work
50
Run Out
40
Applied Stress (ksi)
30
20
LMWVE stands for low molecular weight vinyl
ester HMWVE stands for high molecular weight
vinyl ester
10
100
1000
10000
100000
1000000
10000000
Number of Cycles (log cycles)
34
Outline for Presentation
  • Introduction What is a Sizing?
  • Materials Used
  • Results obtained thus far
  • Mechanical properties of laminates
  • study 1
  • study 2
  • study 3
  • pultruded composites
  • Thermo-mechanical experiments
  • dynamic mechanical analysis of resin and
    composites
  • Environmental Durability
  • hygrothermal aging of resin and composites
  • Proposed work for the future
  • Acknowledgements

35
Schematic of Pultrusion Line
36
Tensile Strength of Pultruded Composites
37
Longitudinal Flexure Strength Strength
38
Short Beam Shear Strength of Pultruded
39
Tensile Strength Comparison between Model and
Experimental Data
40
Outline for Presentation
  • Introduction What is a Sizing?
  • Materials Used
  • Results obtained thus far
  • Mechanical properties of laminates
  • study 1
  • study 2
  • study 3
  • pultruded composites
  • Thermo-mechanical experiments
  • dynamic mechanical analysis of resin and
    composites
  • Environmental Durability
  • hygrothermal aging of resin and composites
  • Proposed work for the future
  • Acknowledgements

41
Cooperativity Model
  • Intermolecular interactions and constraints
  • Segments move in a cooperative motion
  • Degree of cooperativity - temperature dependence
    of log(aT)

z 6
log(aT)
Glassy State
Tg
Tg/T
Relaxation Phenomena in Polymers Shiro Matsuoka
42
Concept of Cooperativity

20
15
increasing n
10
  • equilibrium
  • bulk polymers

T
5
log a
0
-5
-10
-0.05
0.00
0.05
0.10
0.15
(T-T
)/T
g
g
D. J. Plazek and K. L. Ngai, Macromolecules,
24, 1222 (1991).
43
Vinyl Ester Resins
Vinyl Ester
Styrene
Calculated
Measured
T
T
DSC
g
g
D
C
T
p
Oligomer Weight
Content
M
M
Onset
End
g
c
c
(J/gC)
(g/mol)
()
(g/mol)
(g/mol)
(DSC,C)
(DSC,C)
(C)
700
20
292
300
136
164
152
0.269
700
35
359
569
124
145
136
0.244
1200
20
417
812
115
133
125
0.322
1200
35
513
969
110
126
118
0.298
44
Dynamic Loss Modulus
Vinyl Ester (Mn 1200g/mol, 20 Styrene)
45
Fragility (cooperativity) plot for vinyl ester
resins
20 700g/mol
William-Landel- Ferry equation
35 700g/mol
20 1200g/mol
35 1200g/mol
)
T
log(a
n d(logaT)/d(Tg/T)Tg
fragility (cooperativity)
Tg / T
46
Cooperativity versus molecular weight between
crosslinks
94
1200, 20
92
700, 20
90
88
86
84
n, fragility
82
80
78
1200, 35
76
700, 35
74
72
0.002
0.003
0.004
1/Mc (mol/gram)
47
Fracture toughness versus normalized domain size
48
Master Curve - Matrix
Tg 137C
log E (MPa)
log waT
log w
107C - 164C, 3 C steps, second heat
49
Master Curve - Composite
Tg 123C
log E (MPa)
log waT
log w
93C - 219C, 3 C steps, Phenoxy sizing, second
heat
50
DMA - damping of composites
G PVP Phenoxy
1 Hz, second heat
51
Cooperativity plot for composites
matrix G PVP Phenoxy
increasing n
52
Outline for Presentation
  • Introduction What is a Sizing?
  • Materials Used
  • Results obtained thus far
  • Mechanical properties of laminates
  • study 1
  • study 2
  • study 3
  • pultruded composites
  • Thermo-mechanical experiments
  • dynamic mechanical analysis of resin and
    composites
  • Environmental Durability
  • hygrothermal aging of resin and composites
  • Proposed work for the future
  • Acknowledgements

53
Moisture Uptake Plots
Specimen Dimensions for Study 4cm x 0.764cm x
0.254 cm
54
Diffusion Theory Ficks Law
Rigorous Solution
Semi-infinite Case
D is evaluated from the initial slope of a graph
of moisture content as a function of t1/2
55
Effects of Exposure Temperature on Diffusion
Coefficient for Derakane 441-400
All aging performed under isothermal conditions
and complete immersion in water.
-14
2.03E-07
-15
-16
5.37E-08
2.5E-08
ln D (cm2/sec)
-17
1.18E-08
-18
-19
-20
0.0026
0.0028
0.003
0.0032
0.0034
1/Temperature (1/K)
56
Saturation Moisture Content Theory
Modified Henrys Law
where xw is the weight fraction of water in the
polymer and VP is the vapor pressure at the
test temperature of the bulk liquid phase and is
computed using the Claussius-Claypron equation
which is as follows
where p, ?Hsub, R, T and T are the vapor
pressure at the triple point, heat of
sublimation, gas constant, temperature and
triple point temperature respectively.
57
Effects of Exposure Temperature on Henrys
Constant for Derakane 441-400
58
Fourier Tranform Infrared (FTIR)Spectra of
Derakane 441-400
59
Reverse Thermal Effect (RTE)
60
Activation Energy for the RTE Process
D 4.76E-10 exp(2.28E04/RT)
Activation Energy 5.7 KCal/mole Theoretical
Hydrogen Bond Energy 5 KCal/mole
0.12
-11
0.1
-12
0.08
Moisture Content ()
-13
0.06
Hydrogen Bonding!
0.04
-14
0.02
-15
0
0.0028
0.003
0.0032
0.0034
0.0036
14
0
2
4
6
8
10
12
1/Temperature (1/K)
Time (hours1/2)
61
Chemical Structure Comparisons
CH3-GMA (Model Resin System)
Reference H. K. Shobha, M. Sankarapandian, A. R.
Shultz, and J. E. McGrath, Macromol. Symp. 111,
73-83 (1996)
62
FTIR of Model Resin System
63
RTE on Model Resin System
64
Moisture Uptake in Unidirectional Composites
1.2
G'
Immersion in water bath at 62C
Low Spread Phenoxy
PVP K90
OCF Glass Fiber
1
0.8
Moisture Content ()
0.6
0.4
0.2
0
0
5
10
15
20
25
30
35
40
45
Time (hours
1/2
)
65
Outline for Presentation
  • Introduction What is a Sizing?
  • Materials Used
  • Results obtained thus far
  • Mechanical properties of laminates
  • study 1
  • study 2
  • study 3
  • pultruded composites
  • Thermo-mechanical experiments
  • dynamic mechanical analysis of resin and
    composites
  • Environmental Durability
  • hygrothermal aging of resin and composites
  • Proposed work for the future
  • Acknowledgements

66
Proposed Work
1) Focus on studying unidirectional composite
response
As Received Material
Saturate composites in water at 62C
Fatigue Tests on composites
Tg and cooperativity measurements
Quasistatic Tension Short Beam Shear Tests
Freeze-Thaw Tests
IITRI compression tests
Quasistatic Tension Short Beam Shear Tests
?45 laminate tensile tests
67
Proposed work continued
2) Blend Properties
Study blends of 1) PVP K90/ vinyl ester 2)
Phenoxy/vinyl ester
Saturate composites in water at 62C
Tg and cooperativity measurements
  • 3) Pultrude composites at Strongwell to study the
  • effect of coating thickness (eg. Phenoxy)
  • effect of sizing molecular weight (eg. PVP K90
    vs. K30)

68
Proposed work continued
3) Fatigue response of hygrothermal aged
cross-ply composites. 4) Incorporate the effect
of the interphase into MRLife. 5) Try and model
the interphase by using blend data in a code
written by Dr. Pagano and Dr. Tandon
69
Acknowledgements
  • Dr. R. Parnas and Dr. D. Hunston at NIST
  • Dr. M. Puckett, The Dow Chemical Company
  • Clint Smith, Strongwell Inc.
  • Dr. Pagano, Wright Patterson Airforce Base
  • Dr. H. Li
  • Lu Shan, 1998 SURP student
  • Chris Robertson, Chemical Engineering Dept.
  • Rob Jensen, Chemistry Dept.
  • Ellen Burts and Maggie Bump, Chemistry Dept.
  • Norman Broyles, Chemical Engineering Dept.
  • Mark Flynn
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