Thermoplastic and Thermosetting Polymers

for Composites

Dr Ian Hamerton

Chemistry

School of Biomedical and Molecular Sciences

University of Surrey

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Outline of Presentation

• Definition of a Composite

• Thermosetting polymers

• Thermoplastic polymers

• Thermoplastic processing

• Use of Composites in Aerospace

• Performance Criteria • Application of LCA to composites • Conclusions• Questions

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Composite

A multi-phase material in which the properties of a continuous phase (matrix) are enhanced by distributed sheet-like, fibrous or particulate

fillers

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Common Thermoset PolymersEpoxy (common, industry standard, versatile)

Vinyl esters (composition, cost properties between epoxies and unsaturated esters)

Unsaturated polyesters (cheapest, good properties at lower temperature, large components/volume production)

Phenolics (lower mechanical properties, retain to high temperature, no toxic flammables)

Polyimides (expensive, but high performance)

Bismaleimides (good hot/wet properties, brittle, cheaper than some polyimides)

Cyanate esters (low loss properties, relatively expensive)

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Selected high performance thermosets

N

O

O

Epoxy

O

O

O

O

O

OH

OH

OH

OH OH

OH

N

O

O

Unsaturated polyestersVinyl polyesters

Phenolics

NCO

Polyimides Bismaleimides Cyanate esters

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Thermosetting PolymersCan offer• Variety of physical forms and viscosities• Wide choice of curing systems• Latitude with processing conditions• Low cure shrinkage • Good chemical resistance• Good mechanical properties• Good fibre/reinforcement adhesion• Thermal stability over wide temperature

range• Good resistance to moisture

But…• Often limited outlife• Usually need to be toughened• Pose significant recycling problems

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Selected high performance thermoplastics

Ar Ar'

O O

** n

Poly(ether ether ketone)s

* O Ar O Ar' *n

Poly(aryl ether)s

* O Ar O Ar'

O

*n

Poly(arylene ether ketone)s

N

O

O

Ar

O

N Ar

H

N

H

Ar N

O

OO

Poly(amide-imide)s

N

O

O

ArN

O

O

Polyimides

* O Ar SO2 Ar' *n

Poly(ether sulphone)s

Ar S ** n

Poly(arylene sulphide)s/ Polyphenylsulphide

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Thermoplastic Polymers

• Will soften above Tg for shaping and harden in this form on cooling

Can offer• Better resistance to moisture and various

industrial solvents than thermosets • Superior flexural and impact properties to

thermosets

But…• Poorer abrasion and dimensional stability to

thermosets• No apparent advantage in static properties or

fatigue• Higher processing temperatures than most

thermosets (generally above 300oC)• Compression strength may be inferior

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Thermoplastic matrices

Tg/oC Tproc/oCPoly(amide-imide)a 275 345-355

Polyarylethersa 220-260 310-345

Polyethersulphonea 220 300-310

Poly(arylene sulfide)a 200-210 345

Polyetheretherketonec 140-145 340-350

Polyphenylenesulfidec 85-95 330

Poly(arylene ketone)c 200-210 370-415

Polyimidea,c 250-280 350-360

Tg = Glass transition temperature a = amorphous

Tproc = Processing temperature c = crystalline

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Thermoplastic processing methods

• Autoclave consolidation• Press forming (rubber assisted

punch or hydro forming)• Double diaphragm forming• Pultrusion• Roll forming• Filament and tape winding

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Aerospace Applications• Combinations of thermoplastics and thermosets

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Aerospace Applications

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Trade offs as compositeProperty T/sets T/plastics

Formulations complex simple

Melt viscosity very low high

Fibre impregnation easy difficult

Prepreg tack good none

Preprepg drape good none to fair

Prepreg stability poor excellent

Processing cycle long short to long

Processing T/P low/moderate high

Fabrication cost high potent. low

Mech. Properties fair to good fair to good

(-54 to 93oC, hot/wet)

Environ. Stability good unknown

Solvent resistance excellent poor to good

Damage tolerance poor/goodfair/excellent

Database very large small

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LCA should address:

• Initial preparation

• Formulation

• Processing

• Lifetime(s)

• Recycling potential

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Conclusions – potential hotspots

• Thermosets– High monomer cost– Long processing cycle– Storage of prepreg (refrigeration)– Repair (poor damage tolerance)– Poor recycling potential

• Thermoplastics– High melt viscosity/impregnation– High polymerization temperatures

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Any Questions?