What's the Difference: Thermoset vs. Thermoplastic Carbon ...1 ®™Trademark of The Dow hemical...
Transcript of What's the Difference: Thermoset vs. Thermoplastic Carbon ...1 ®™Trademark of The Dow hemical...
1 ®™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow
1 ®™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow
What's the Difference: Thermoset vs. Thermoplastic Carbon Fiber Composites?
September 2013
Presented by Allan James
With thanks to Pete Cate, Dave Bank, Rainer Koeniger, Mike Malanga, Jay Tudor, Jin Wang
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Dow Automotive Systems
• A leading global provider of advanced material solutions, making vehicles lighter, safer, stronger, quieter and more comfortable
Elastic Adhesives Auburn Hills, MI, USA
Foams & Elastomers Correggio, Italy
Automotive Composites EUR Horgen, Switzerland
Automotive Composites NA Midland, MI, USA
Carbon Fibre (DowAksa)
Yalova, Turkey
Structural Adhesives Horgen, Switzerland
The Dow Chemical Company • More than 5,000 products manufactured at
188 sites in 36 countries
• Selling to customers in 160 countries
• 6500 R&D staff globally
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Thermoplastics & Thermosets
• Thermoplastics and thermosets are structurally different
Amorphous Thermoplastics
Molecular chains held together by weak van der Waals forces or by
hydrogen bonds which reduce strength and stiffness with temperature, and
cause the material to creep under load
Thermosets
Cross-linked molecular structure held together with strong covalent bonds,
creating rigid, thermally-stable, creep-resistant materials which maintain
strength and stiffness very well
Cross link
Semi-crystalline Thermoplastics
Crystalline molecular groups connected by amorphous chains (which undergo
changes at Tg), along with van der Waals forces or hydrogen bonds
Crystal lamella
Amorphous chains
Weak Van der Waal forces
Strong covalent bonds Polyamide Epoxy ABS
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Thermosetting Polymers • Fiber sizing reacts directly with the epoxy network,
creating strong covalent bonds at the interface
• The cross linked network is rigid, and relatively unaffected by changes in temperature resulting in a more consistent structural performance
Semi-Crystalline Polymers • Fiber sizing reacts with amorphous region of the
polymer to create the interface
• Amorphous regions are highly affected by changes in temperature, reducing interfacial strength and lateral stiffness between fibres
Fibre Polymer Interface Detail
Amorphous region
Covalent bonds
Carbon Fibre Carbon Fibre
• The interaction between the polymer and the fibre determines the stability of the composite construction
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The Importance of Low Matrix Material Viscosity
100 micron
• Excellent wet-out of the carbon fibre tows within the fibre weave is key to a strong, durable composite
FIBRE TOW WEAVE FIBRE TOW FIBRE SURFACE
0.5 micron
MATRIX MATERIAL PROCESSING VISCOSITY COMPARISON
RTM Epoxy: ~10 mPa.sec
Polyamide 6 melt: 100,000-200,000 mPa.sec η
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Matrix Material Function in the Composite
• Structural composites must undergo a variety of short- and long-term load cases, generating interfacial forces which are managed by the polymer matrix material
Compressive Forces Shear Forces Tensile Forces
Matrix material must laterally support fibres
and help to prevent fibre buckling
Matrix material must limit inter-laminar shear to preserve
composite stiffness
Matrix material must laterally connect fibres to prevent composite
delamination
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STR
ENG
TH R
ELEV
AN
CE
IN C
RA
SH
STIFFNESS RELEVANCE
Stiffness/Strength Relevance of Automotive Components
CRASH MANAGEMENT SYSTEM
LONGITUDINAL FRONT
FIREWALL
IP CROSSMEMBER
STRUT TOWER FRONT
FLOOR
TUNNEL
FLOOR CROSSMEMBER
REARWALL
LONGITUDINAL REAR
REAR CROSSMEMBER
STRUT TOWER REAR
ROOFRAIL
A-PILLAR
B-PILLAR
C-PILLAR
SIDEWALL
SILL
ROOF
ROOF CROSSMEMBER
LONGITUDINAL UPPER
COWL
DOORPANELS
DOOR CRASH SYSTEM
DOOR FRAME
DOOR HINGE REINFORCEMENT
Structural Composite Applications
• Different vehicle applications require different material properties
Source: Geo Metro car CAE crash model developed by
the US Govt
Stiffness Dominated
Strength Dominated
Stiffness & Strength
Original Source: “Stiffness Relevance and Strength Relevance in Crash of Car Body Components,” European Aluminum Association, May 2010
Low Stiffness Relevance High
Low
Stre
ngt
h R
elev
ance
Hig
h
Materials must maintain
stiffness and strength
over thermal / moisture /
aging cycle
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Thermal Stability of Different Polymer Types
• Thermal performance requirements of the application will influence response to load cases, and thus drive polymer choice
Mo
du
lus
(GPa
)
-40C 0 50 100 200 300C
Epoxy dry
Semi-crystalline thermoplastic PA6 dry
Amorphous Thermoplastic Tg
PA
6
(dry
)
Tg Epoxy can be tuned
via formulation
PA6 Data source example: “Moisture absorption in polyamide-6…” by Vlasfeld, Groenewold, Bersee & Picken
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Thermal Stability of Different Polymer Types
• Thermal performance requirements of the application will influence response to load cases, and thus drive polymer choice
Mo
du
lus
(GPa
)
-40C 0 50 100 200 300C
Epoxy dry
Epoxy wet
Semi-crystalline thermoplastic PA6 dry 80C -40C
PA6 Data source example: “Moisture absorption in polyamide-6…” by Vlasfeld, Groenewold, Bersee & Picken
~75
% lo
ss
~5%
loss
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Demo Part Simulation – Temperature Effect
• Comparison of short Carbon Fibre Epoxy and Polyamide 6 composites in a roof bow, showing overdesign required to achieve same stiffness at 80C
Exterior Roof Panel
Roof Bows
Static loads
6 d.o.f. constrained
0%
20%
40%
60%
Front Roof Bow Thic
kne
ss In
cre
ase
Thickness Increase Required to accommodate
Modulus Loss at 80C
CF Epoxy
CF PA6 Nylon
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Moisture Stability of Composites
• Typical structural automotive application conditions also involve moisture exposure to varying degrees
Significant moisture absorption is an indication of
property change in the matrix polymer and ultimately in the final composite, across the required temperature range
PA6 Data sources : Vlasfeld, Bersee & Picken; BASF; Dupont
0.0%
1.0%
2.0%
3.0%
4.0%
0 10 20 30 40 50 60
Wat
er
Ab
sorp
tio
n (
%)
Water Soak Time (hrs)
90C Water Immersion
Short CF Epoxy
Short CF PA6 Moisture absorption
varies with fiber content
Same carbon fibre content
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Polymer Property Change after Moisture Exposure
• To predict composite performance, it is critical to understand the increase or decrease of all relevant matrix polymer properties as a result of exposure to application conditions
-40%
-30%
-20%
-10%
0%
10%
20%
30%
40%
50%
60%
Modulus Strength Elongation
Pe
rce
nta
ge C
han
ge
Short Carbon Fibre Composite Measured Properties after 22hrs Water Immersion at 90C
CF PA6
CF Epoxy
Changes in stiffness and strength are typically addressed by proportional
overdesign of the composite
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Demo Part Simulation – Moisture Conditioning Effect
• Short Carbon Fibre Epoxy and Polyamide 6 roof bow application, with overdesign to achieve same stiffness at 25C after humidity exposure*
Exterior Roof Panel
Roof Bows
Static loads
6 d.o.f. constrained
* 22hrs water immersion at 90C, then tested at 25C
0%
10%
20%
30%
Front Roof Bow Middle Roof Bow Rear Roof Bow Thic
kne
ss In
cre
ase
Thickness Increase Required at Room Temperature to
accommodate Modulus Loss after 22hrs 90C Moisture Exposure
CF Epoxy
PA6 Nylon
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Moisture & Temperature Combination
• Typical automotive application conditions involve combined exposure to both temperature and moisture
PA6 Data source example: “Moisture absorption in polyamide-6…” by Vlasfeld, Groenewold, Bersee & Picken
Mo
du
lus
(GPa
)
-40C 0 50 100 200 300C
Epoxy dry
Epoxy wet
Semi-crystalline thermoplastic PA6 dry
Semi-crystalline thermoplastic PA6 wet
Tg P
A6
(d
ry)
Tg P
A6
(3
% m
ois
ture
)
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• Typical automotive application conditions involve combined exposure to both temperature and moisture
PA6 Data source example: “Moisture absorption in polyamide-6…” by Vlasfeld, Groenewold, Bersee & Picken
Mo
du
lus
(GPa
)
-40C 0 50 100 200 300C
Epoxy dry
Epoxy wet
Semi-crystalline thermoplastic PA6 dry
Semi-crystalline thermoplastic PA6 wet
~80
% lo
ss
80C -40C
Moisture & Temperature Combination
~18
% lo
ss
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• Typical automotive application conditions involve combined exposure to both temperature and moisture
PA6 Data source example: “Moisture absorption in polyamide-6…” by Vlasfeld, Groenewold, Bersee & Picken
Mo
du
lus
(GPa
)
-40C 0 50 100 200 300C
Epoxy dry
Epoxy wet
Semi-crystalline thermoplastic PA6 dry
Semi-crystalline thermoplastic PA6 wet
~80
% lo
ss
80C -40C
Moisture & Temperature Combination
~16
% lo
ss Note: as carbon fibre
reinforcement is added, the stiffness loss is reduced, down to <25% in high wt% continuous carbon fibre PA6 composites…
…and <5% in high wt% continuous carbon fibre Epoxy composites
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Cost Model Output for a Benchmark Carbon Fibre Composite Component
CF Epoxy Composite Material CF PA6 Composite Material
Component Cost & Mass Comparison
• Cost and Mass analysis including overdesign to accommodate composite stiffness decline at 80C after 22hrs moisture exposure
0 wt% 40wt% Chopped 60wt% Woven
Carbon Fibre Content and Format
Composite Material Cost*
* Materials only. Processing cost analysis shows further disadvantage for PA6 due to high processing temperatures versus ultra-fast epoxy systems
Cost increases more for PA6
than Epoxy as overdesign
adds more carbon fibre
$€
0 wt% 40wt% Chopped 60wt% Woven
Carbon Fibre Content and Format
Composite Material Mass
Original part
mass before
overdesign
kg
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So Why Thermoplastics?
• Traditionally Thermoplastics have been perceived to offer advantages of:
– Lower cost polymers
– Faster processing
– Recyclability
• Advanced Thermoset epoxy chemistry and processing techniques are now:
Cost competitive in the final composite (by optimising carbon fibre utilization)
Fast enough to compete favourably with mid to high wt% carbon-fibre thermoplastics
Efficiently recyclable enabling recovery of high-value usable carbon fiber
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Conclusion: ThermoSets The Benchmark
• After optimising cycle time to match volume targets, the key to competitive structural composites is to reduce the utilization of carbon fibre, as it is the most costly component
PERFORMANCE
Ensure consistent mechanical performance (stiffness and strength)
over temperature and humidity range, and sufficient chemical resistance for
the application
PROCESSING
Ensure low (~10mPa.sec) viscosity for excellent fiber wet out and maximum
interfacial strength; accelerate demold times to <2mins and avoid high
temperature processing
PRICE
MINIMISE
CARBON FIBRE
UTILIZATION!
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THANK YOU FOR YOUR ATTENTION!
Allan James
NAFTA Marketing Manager Composites
Email: [email protected]
www.dowautomotive.com