Polymer Synthesis CHEM 421 Advantages of Composite

advertisement
Poly(arylene ether)s
Polymer Synthesis
CHEM 421
PEEK
PES
• Characteristics
–Thermal stability
–Hydrolytic stability
–Wide range of properties
Nucleophilic Aromatic
Substitution
Polymer Synthesis
CHEM 421
PES
Nucleophilic Aromatic Substitution: Polymer Synthesis
CHEM 421
Mechanism
Meisenheimer Complex (an intermediate)
F > NO2 > OTs > SOPh > Cl, Br, I
- Reverse order for aliphatic substitution
- NO2 never lost in aliphatic systems
- In aliphatic SN2 displacement
R-I > R-Br > R-Cl > R-F
First step is R.D.S and favored by more electron withdrawing group
Nucleophilic Aromatic
Substitution
• Important features
– Activating group and leaving group combinations
Polymer Synthesis
CHEM 421
Nucleophilic Aromatic
Substitution
Polymer Synthesis
CHEM 421
PES
• Important features - Conversion to phenate
Nucleophilic Aromatic
Substitution
• Important features
– Conversion to phenate
– Dehydrating agent
» Upset stoichiometry
– Solvent
Polymer Synthesis
CHEM 421
Nucleophilic Aromatic
Substitution
• Important features
– Activating group and leaving group combinations
Polymer Synthesis
CHEM 421
Poly(arylene ether)s
PEEK
• $25 lb
• Tg = 144 °C
Tm = 335 °C
Polymer Synthesis
CHEM 421
Poly(arylene ether)s
Polymer Synthesis
CHEM 421
PEK
O
O
C
n
PEKK
Composite Materials
Polymer Synthesis
CHEM 421
• Composites have been used in airplanes
since the 1950s
• Critical applications of composites started
in the early 1980s
• Composite materials have some fundamentally
different characteristics from metals
• A composite is defined as two or more materials
that retain their identities in the combination
while yielding properties superior to either
• Common composite types include fibrous, laminate and particulate
– They can employ glass, aramid or carbon fibers
– Various resins are used as the "matrix" bonding individual materials together
into the desired form.
Advantages of Composite
Construction
Polymer Synthesis
CHEM 421
• Structural Tailorability
– Fibers are able to be oriented in directions that are best for the design.
– Metals have the same properties in all directions.
• Lightweight Strength
– The advantage of being lighter than metals is usually misunderstood
– Composites indeed have lower density than most metals
– But for structural stability and with other design reasons, composite
airplanes usually weigh the same as metal airplanes
– By using a greater amount of lighter material, structural parts like skins
are relatively thicker
– A composite aircraft has the feel of a more sturdy airplane, and also
has better dampening (less vibration transmission)
Advantages of Composite
Construction
Polymer Synthesis
CHEM 421
• Better aerodynamics
– Composite manufacturing more readily allows complex curved surfaces
with fewer joints, seams and rivets
– Easier to get smooth surfaces for laminar flow designs which
contributes to additional speed.
• Stealth Potential
– Ability to minimize radar cross section
– Electronic transparency means antennas can be hidden inside for
streamlining without loss of reception.
• Simple assembly
– Aircraft assembly simplified, since many of the fasteners and small
parts can be replaced with larger, more integrated structures.
General Beliefs…
Polymer Synthesis
CHEM 421
• Composites are thought to be corrosion and
fatigue resistant
– “…Composites are not subject to corrosion from natural or
man made elements…”
– “…Certainly with composites, fatigue is less of an issue
than with metals"
Scott W. Beckwith
Technical director
Society for the Advancement of Material &
Process Engineering
General Knowledge about
Composites
Polymer Synthesis
CHEM 421
• Things that mitigate the ESC problem include:
–Crystallinity
–Filled systems
–Crosslinking
Example from the Scientific
Literature
Polymer Synthesis
CHEM 421
• “Environmental Stress Cracking and Solvent
Effects in High-Performance Polymeric
Composites”
Dillard, Kander, et. al
Composite Materials
ASTM, 1996
• ESC of carbon fiber-reinforced thermoplastic
and thermoset composite systems were
investigated
Three-point Bending Tests
Polymer Synthesis
CHEM 421
Graphite fiber reinforced, thermoplastic toughened cyanate ester thermoset system
Graphite fiber reinforced, semicrystalline thermoplastic composite
Graphite fiber reinforced, amorphous thermoplastic composite
One hour exposure at room temperature,
not under any load…
Fracture Mode – Unexposed
Polymer Synthesis
CHEM 421
Graphite fiber reinforced, thermoplastic toughened cyanate ester thermoset system
• Matrix enveloping
the fibers
• Failure primarily in
the matrix (good
thing)
• Ductile fracture
Fracture Mode – Solvent Exposed
Polymer Synthesis
CHEM 421
Graphite fiber reinforced, thermoplastic toughened cyanate ester thermoset system
• One hour exposure to
solvent
– at room temperature
– not under load…
• Fibers relatively clean
• Brittle, interfacial
failure
• Ductile fracture
Conclusions
Polymer Synthesis
CHEM 421
• “Environmental Stress Cracking and Solvent
Effects in High-Performance Polymeric
Composites”
• 10 – 30% drop in bending strength under
“safe” experimental conditions
• Differences in failure modes upon solvent
exposure
• Propensity for interfacial failure
Research Questions
Polymer Synthesis
CHEM 421
• Are the long-term prospects clear for
structural, load-bearing composites
immersed in jet fuel in the F-22, JSF and
Comanche?
• What are the most appropriate methods for
long-term aging studies of environmental
stress cracking of composites for such
applications?
• Are there effective, easily implementable
methods for mitigating solvent-induced ESC
in composites?
Download
Related flashcards
Materials science

50 Cards

Semiconductors

39 Cards

Materials science

63 Cards

Solids

11 Cards

Create flashcards