Recent Developments in High-Performance Thermoplastic

Composites

Allan Murray, Ecoplexus Inc.

Klaus Gleich, Southern Research Institute

ACCE 2003

Overview

• Introduction

• Materials

• Process Technology

• Applications

Specfic Tensile Properties of Polymer Matrix Composites

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 1 2 3 4 5 6

Specific Strength (x106 in.)

Sp

ecif

ic M

od

ulu

s (x

108 in

.)

Metals

Continuous Uni-directional Carbon

Composites

LFT Glass Composites

Continuous Uni-directional Glass Composites

LFT Carbon Composites

Plastics

Glass & CarbonLFT & Continuous

Other FibersVarying Fiber Orientations

Why Use Composite Materials ?

Thermoplastic Composites

BenefitsUnique propertiesVibration dampeningLight weightPotential for low costShelf lifeRecyclable Durability

FatigueCorrosionToughness

LimitationsCost

MaterialsManufacturingTooling

Design know-howManufacturing know-howUse temperature

Thermoplastic Composites

Many Polymer OptionsPolyethylenesPolypropylenesNylonsPolycarbonatesAcrylicsPolyestersPolyimidesPolysulfonesPolyketonesPolyurethanesthe list continues

Many Property Optionsultimate strain > 100%no microcrackingno delaminationdampeningno water uptakelow dielectric propertiesmelt formableweldableelastomeric - plastic - elastic behaviorthe list continues

Cost ChallengeC

os

ts in

$/lb

Automotive Structures$1 - $3/lb

Innovative Materials andProcesses$5 - $20/lb

Typical Aerospace Structure$50 - $100/lb

and more

Materials:Glass Fiber / Polypropylene, SMC/BMC

Processes:Compression Molding, Injection Molding

Materials:Thermoplastic Woven Sheets, Glass,Carbon and Kevlar Fiber, Engineering

PolymersProcesses:

Co-Compression Molding, Co-Injection Molding, Thermoforming

Materials:Carbon Fiber / Epoxy, Carbon

Fiber / BMI, Carbon Fiber /PEEK

Processes:Hand Lay Up

Apply Materials andProcessing Techniques

being Developed forAutomotive Applications to

Aerospace Applications

High-Performance Thermoplastic Composites

• Properties are fiber dominated• Oriented long or continuous fiber reinforcement• High volume fiber fraction (up to 65% by volume) Key benefits:

• Reducing thermal limitations (e.g. creep) caused by the TP matrix system

• Reducing costs and weight and retaining toughness, formability, weldability, short cycle times, recyclability benefits of the thermoplastic matrix

Thermoplastic Materials

Commercial Materials

• GMT (Glass Mat Reinforced Thermoplastics)• Pultruded Products

– LFT (Long Fiber Reinforced Thermoplastics)

– CFT (Continuous Fiber Reinforced Thermopastics)

• Wire coated products• Commingled fibers• Powder coated materials• Film sticking• Slurry processes

Long-FiberThermoplastic Composites

•New Hot-melt Process Produces Fully Wet-out Composite Products

•Wide Range of Polymers and Fibers

•Continuous Tape and Rod Products

•Discontinuous Products with Any Fiber Length

•Glass Products <$1.00/lb

•Carbon Products <$8.00/lb

Pilot Production for Pilot Production for Thermoplastic CompositesThermoplastic Composites

Short Fiber, Long Fiber and Continuous Fiber Composites

Typical short fiber thermoplastic material,granules with fiber length of approx. 2 to 4 mm,resulting fiber length in a part of approx. 0.4 mm

Long fiber thermoplastic material, pellets of ½” and 1 “ fiber length, resulting fiber length in a part of approx. 4-6 mm in injection molding and approx. 20 mm in compression molding

Continuous reinforced thermoplastic material, tape used for woven sheets (thermoforming), filament winding or pultrusion

Typical Pultruded Prepregs

• Fiber:– E-glass, S-glass, Carbon, Aramid, polymer fibers

• Matrix:– PE, PP, PA (6, 6/66, 12, …), PET, PBT, PC, PEI, PPS,

SMA, blends, …

• Fiber content:– 20% - 60% standard, some up to 84%

• Product forms:– Tape, pellets (0.5”, 1”), woven tapes – more complex textile structures in development

Twintex - The Commingling Concept

Twintex® Prepreg

Consolidated Composite

Temperature + Pressure

Source: Vetrotex

Twintex – The Commingling Concept

E Glass adapted sizing

Plastic filamentAdditives : - coupling agent- UV stabilizer- natural or black

Source: Vetrotex

Twintex – The Manufacturing Process

GlassTP

Commingling

Roving

Extruder Bushing

Source: Vetrotex

Twintex - Commingled Fiber Products

• Fiber/matrix combinations:– E-glass/PP, E-glass/PET

• Fiber content:– 60 % and 75 % by weight

• Product forms:– Roving, fabric, pellets

Specfic Tensile Properties of Polymer Matrix Composites

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 1 2 3 4 5 6

Metals

Continuous Uni-directional Carbon Composites

LFT Glass Composites

Continuous Uni-directional Glass Composites

LFT Carbon Composites

Plastics

Glass & CarbonLFT & Continuous

Other FibersVarying Fiber Orientations

Twintex

• Limitations:– Matrix material must be usable for a fiber spinning process

limitations in MFI/viscosity, additive type and additive content

TwintexTwintex

Vetrotex TwintexMatrix PP PP PP PP PETReinforcement glass glass glass glass glasswt.% reinforcement 60 60 75 75 65Orientation 1/1 4/1 1/1 UD 1/1Density g/cm3 1.5 1.5 1.75 1.75 1.95Tensile Strength MPa 350 500/180 420 700 440Tensile Modulus GPa 15 24/8 21 38 25Flexural Strength MPa 280 380/160 340 400 600Flexural Modulus GPa 13 18/6.1 17.5 32 22.5Flexural Elongation % 2.5 2.5/3.6 2.5 2 3.25Compression Strength MPa 140 230/100 160 170 410Shear Strength MPa 22.5 24/15 22.5 22.5 43Impact CHARPY un-notched kJ/m2 220 330/90 300 445 300

J/cm3 8 11/3 10 15 10Heat deflection temp. (1.82 MPa) oC 159 159 159 159 257Specific Tensile Modulus (x10^8in) 0.4 0.6 0.5 0.9 0.5Specific Tensile Strength (x10^6in) 0.9 1.3 1.0 1.6 0.9

Source: Saint-Gobain Vetrotex, “Twintex PP and PET Mechanical Properties (non standard)”

Physical Property Data

Powder Impregnated Prepregs – The Hexcel TowFlex-Technology

Source: Hexcel

Fiber Creel Racks

Fluidized Bed Powder Coating

ChamberIR Oven Puller

Take-up System

Charged Resin Powder

To Weaving

To Tapes

To Pellets

Hexcel TowFlex

• Typical fibers:– Carbon, E-glass, S-

glass

• Typical resins:– PP, PA6, PPS, PEI,

PEEK

• Typical product forms:– Flexible Towpreg

– Woven fabric

– Braided Sleeving

– Unidirectional Tape

Specfic Tensile Properties of Polymer Matrix Composites

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 1 2 3 4 5 6

Specific Strength (x106 in.)

Spec

ific

Mod

ulus

(x10

8 in.)

Metals

Continuous Uni-directional Carbon Composites

LFT Glass Composites

Continuous Uni-directional Glass Composites

LFT Carbon Composites

Plastics

Glass & CarbonLFT & Continuous

Other FibersVarying Fiber Orientations

Carbon Towflex

Glass Towflex

`

TowFlexTowFlexGlass CarbonGlass Carbon

Hexcel Towflex

MaterialTF-CN6-100

TF-CPP-100

TFF-CN6-100

TFT-CN6-100

TFF-CPP-100

TFT-CPP-101

TF-EGN6-100

TFF-EGN6-100

TFT-EGN6-100

TF-CPPS-103

TFF-CPPS-103

TFT-CPPS-103

TF-EGPP-101

TFF-EGPP-100

TFT-EGPP-100

TFF-EGPPS-101

Resin Content (weight %) 38 38 38 38 38 38 34 34 34 43 43 43 30 30 30 35Fiber volume (volume %) 51 45 51 51 45 45 46 46 46 51 51 51 46 46 46 51Composite density (g/cc) 1.45 1.31 1.45 1.45 1.31 1.31 1.77 1.77 1.77 1.59 1.59 1.59 1.64 1.64 1.64 1.96Flexural Strength D790 (MPa) 1517 627 827 1517 524 627 1034 517 1034 1724 869 1724 600 386 600 531Flexural Modulus D790 (Gpa) 107 104 55 107 51 104 34 19 34 114 58 114 32 17 32 27Tensile Strength D3039 (MPa) 1655 821 1655 655 869 352 869 1655 869 1655 290 385Tensile Modulus D3039 (26 Gpa) 116 66 116 59 38 22 38 110 64 110 18 24Compression Strength D695 (MPa) 945 579 441 945 172 579 634 372 634 1055 448 1055 558 248 558 379Compression Modulus D695 (Gpa) 110 110 58 110 49 110 34 26 34 112 63 112 37 21 37 31Specific Tensile Modulus (x10^8in) 3.2 1.8 3.2 1.8 0.9 0.5 0.9 2.8 1.6 2.8 0.4 0.5Specific Tensile Strength (x10^6in) 4.6 2.3 4.6 2.0 2.0 0.8 2.0 4.2 2.2 4.2 0.7 0.8

Physical Property Data

Source: Hexcel Composites (March 2003) www.Hexcel.com

Process Technology

Current Composite Materials and Processes

Process Type of Application

Injection Molding

CompressionMolding

Thermoforming

Hand Lay Up /Vacuum Bag /

Autoclave

Low-StructuralComponents

Semi-StructuralComponents

Structural Components

Composite Performance versus Fiber Length

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0.2

0.4

0.6

0.8

1.0

1.2

0.1 1 10 100Length (mm)

Rela

tive P

rop

ert

y L

evel

Modulus

Strength

Impact

Processibility

Short Fiber ContinuousFillers Long Fiber

Source: OCF

The Long Fiber Advantage

• Stress is transferred to the fibers - the structural members of the composite

• Long fibers create a “skeletal structure” within the molded article that resist distortion and provide unmatched strength, toughness, and overall performance

Source: Ticona

Continuous Fiber Advantage

• In continuous oriented fibers the load is ultimately ‘fully’ transferred to the fiber

• As a result tensile creep is limited in fiber direction

Manufacturing Processes for High-Performance TP-Composites

• Low volume manufacturing processes– Discontinuous processes

• Thermoforming

• Thermoplastic S-RIM, RTM and VARTM

• Thermoplastic filament winding

• Vacuum bag molding

• Net shape preforming (modified P4)

Manufacturing Processes for High-Performance TP-Composites

• High volume manufacturing processes– Discontinuous processes

• Injection molding with – LFT-pellets and concentrates (high performance resin/fiber combinations)– Inline compounding (high performance resin/fiber combinations)– Back molding / local reinforcement

• Compression molding– LFT-pellets and concentrates (high performance resin/fiber combinations)– Inline compounding (high performance resin/fiber combinations)– Back molding / local reinforcement

• Stamp forming– Preheated preforms– Matched metal tools– Potential to manufacture very thin sections (0.5 to 1 mm)– Drapable material required

– Continuous processes• Pultrusion• LFT-extrusion

Materials Used For Liquid Molding Processes

Materials used for liquid molding processes– Cyclics– Reactive nylon– Fulcrum

• Requirement for these materials– Viscosity less than 3000 mPa.s (cP) (better less

than 1000 mPa.s (cP))

Cyclics

• Cyclic form of PBT, PET, PC and others• Only PBT commercial available• Based on a ring shaped cyclical form• One or two part systems• Solid at room temperature – low viscosity resin at

elevated temperature (approx. 150 cP)• Polymerize into the Polymer using a catalyst• Isothermal process• Typical process temperature: 180 – 200 oC

Reactive Nylon

For more information see presentation on

“Reactive Thermoplastic VARTM/RTM/S-RIM”

Fulcrum• ISOPLAST matrix (Dow proprietary engineering

thermoplastic polyurethane)– Thermoplastic viscosity issues addressed by ability to

reverse polymerization in the melt stage, reducing viscosity to ensure good impregnation

– Repolymerizes upon cooling, retaining traditional thermoplastic composite advantages

• High impact resistance• Recyclability• High elongation to failure (~2.5%, versus ~1-1.5% for

thermosets)• Zero-emissions processing

• Fulcrum is the combination of ISOPLAST and pultrusion, with specific hardware design

• Provides 10-fold line speed improvement over typical thermoset pultrusion lines

• Allows thermoforming, welding, and overmolding of finished pieces

Thermoformed Fulcrum Components

Figures from “Fulcrum Thermoplastic Technology; Making High-Performance Composite via Thermoplastic Pultrusion” Dow Plastics, January 2000

Dow FulcrumMatrix Polyurethane Polyurethane Polyurethane PolyurethaneReinforcement glass glass glass glassv.% reinforcement 76.6 (wt.) 45 55 66 (wt.)

Density g/cm3 1.91 1.74Tensile Strength MPa 1000 980Tensile Modulus GPa 45 43Elongation at Break % 2.5 1.5Flexural Strength MPa 1150 1050Flexural Modulus GPa 48 40Longitudinal Flexural Strength MPa 1080 1340Longitudinal Flexural Modulus GPa 35 44Transverse Flexural Strength (MPa) 151 122 151Compressive Strength 790 430 440Compressive Modulus 46 35 35Specific Tensile Modulus (x10^8in) 0.9Specific Tensile Strength (x10^6in) 2.145v.% and 55v.% data from Matweb.com76.6wt.% and 66wt.% data from “FULCRUM: Thermoplastic Composite Technology, Making High-performance Composite via Thermoplastic Pultrusion” Dow Plastics, January 2000

Physical Property Data

Reactive Thermoplastic VARTM/RTM/S-RIM

• Similar the thermoset process

• Reaction of at least two components creates a thermoplastic resin that can be melted, pre-shaped, welded, …

• Low viscosity is required

• Possible materials: Nylon, TPU, C-PBT (Cyclics)

Problems Connected With Thermoplastic RTM

• Reaction can be stopped or made incomplete by– Moisture

– Chemicals in fiber sizing• Most of the thermoplastic compatible sizings are not developed for

such type of processes

• Availability of compatible sizings in form of fabric is very limited

– Oxygen

• Only limited support of material manufacturers• Material costs (in case of c-PBT)

Thermoforming

Heat in Oven Thermoforming Operation

FinishedProduct

Thermoforming

• Weight performance:– Good weight/performance ratio for fabric reinforced sheets due to

continuous fibers– Reduced weight/performance ratio for extruded sheets depending on

the resulting fiber length• Design flexibility:

– Limited, especially for complex geometries– Simulation tools available

• Processability:– Stabilization against oxidation necessary– Fiber disalignments with continuous fibers possible depending on

geometry, material, tooling and process conditions • Recyclability:

– High rate of production scrap (fixation)– No direct recyclability– Use in other processes like plastication of regranulation

TP S-RIM, RTM, VARTM

• Weight/performance:– Excellent

• Design flexibility:– Limited to preforming capability, flow length and flow

behavior of the resin• Processability:

– Reaction can be sensitive to moisture and fiber sizing• Recyclability:

– Production scrap due to preforming step depending on preforming method

– No direct recyclability; can be used in other processes

TP Filament Winding

• Weight/performance:– Excellent

• Design flexibility:– Limited to symmetric parts that can be wound on a mandrel

• Processability:– Higher oxidative stabilization required

• Recyclability:– Low rate of production scrap– No direct recyclability– Scrap can be used in other processes

Vaccum Bag/ Hand Lay-Up

• Weight/performance– Excellent due to continuous fiber reinforcement

• Design flexibility– Limited to drapability and to the posibility of manually lay up

• Processability– Higher void content due to low pressure consolidation– Using autoclave to reduce void content– Often fiber disalignments

• Recyclability– High rate of production scrap possible depending on the size of the

material sheets and the part geometry– No direct recyclability– Scrap can be reused in other processes

LFT-Injection Molding

• Weight/Performance– Lower end of thermoplastic composites due to reduced fiber length in

the final part– Improvements possible by using local reinforcements (using pultruded

sections, sheets or tapes of continuous composites localized strengthening and stiffening, reduction of warpage)

• Design Flexibility– High– Flow channels and positions of gates have to be carefully designed

• Processability– Highly stable

• Recyclability– Low production scrap rate– Can be reused in the same process

Compression Molding

• Weight/Performance– Medium– Retaining fiber length gives excellent properties for a random oriented

material, but is lower than using a fabric– Local reinforcement or fabric reinforced GMT improve it (using

pultruded sections, sheets or tapes of continuous composites localized strengthening and stiffening, reduction of warpage)

• Design flexibility– High– Special simulation tools available

• Processability– Very stable process

• Recyclability– Some production scrap due to trim operations– Scrap can be added and reused in the same process (GMT only sheets

can be reused in the same process, but not recommended)

Curv

• Self-reinforced polypropylene• Consists of “hot compacted” polypropylene fiber or tape

– Surface of tape or fiber melts during compaction to form the “matrix” that binds the directional elements together

• Oriented morphology provides over six-fold increase in tensile strength and nearly 5-fold increase in tensile modulus over isotropic polypropylene, with ~2% weight penalty

• Nearly doubles tensile strength of 40% random mat short glass polypropylene, with comparable modulus and 22% weight savings

• Elimination of glass reinforcement has several advantages:– Increased recyclability– Reduced weight– Lower temperatures and pressures for thermoforming– Reduced irritation in the workplace– High strain to failure, with good impact strength

Data from “A New Self-Reinforced Polypropylene Composite” Jones, Renita S. and Derek E. Riley

Curv

Density g/cm3 0.92Tensile Modulus GPa 5Tensile Strength MPa 180

Heat deflection temperature oC 455 KPa 1601820 KPa 102

Notched Izod impact J/m +20oC 4750

-40oC 7500

Thermal expansion /oC x 10-6 41Specific Tensile Modulus (x10^8in) 0.2Specific Tensile Strength (x10^6in) 0.8from BP document “A New Self-Reinforced Polypropylene Composite” Jones, Renita S. and Derek E. Riley, 2002

Physical Property Data

Pultrusion• Weight/performance

– Good to excellent due to continuous reinforcement

• Design flexibility– Low design flexibility– Limited to constant cross sections, but can be shaped (pull/press)

• Processability– Only limited experience available– Depends on stabilization of the material as well as used material form

• Recyclability– Low rate of production scrap expected– No direct recyclability– Can be used in other processes

LFT-Extrusion

• Weight/performance– Medium weight performance– Depends on retaining fiber length

• Design flexibility– Low design flexibility– Limited to constant cross sections– Can be post shaped or pull formed

• Processability– Not a lot of experience– A stable process is expected using the right die design

• Recyclability– Low rate of production scrap– Can be reused in the same process

EconomicsProcess Cycle Time Tooling Costs Scrap Rate Overall Economics

Thermoforming Medium Low High Good for low volume production with no or limited thickness variation

TP S-RIM, RTM, VARTM

Medium to long, up to several minutes

VARTM: low, single sited tool

RTM: low to medium

S-RIM: Medium

Depends on preforming technique; often high for complex shaped parts

Good for low volume production

TP Filament Winding Medium to long, depending on number of tapes and heating system

Low to medium Low Good for symmetrical parts in low to medium volume production

Vacuum Bag/

Hand Lay-up

Long; manual preparation can be hours for a part

Low, single sided tool

Medium to high

Good for prototyping. Not recommended for production scale.

Injection Molding

-LFT

-ILC

Short cycle times; typically 50 – 80 sec.

High; steel tools with ejector pins and slides

Very low Excellent for high volume production

Compression Molding

-GMT

-LFT

-ILC

Short cycle times; typically 35 – 60 sec.

High; steel tools with ejector pins and slides

Low – medium depends on cut outs. Scrap can be reused

Excellent for high volume production of large components

Pultrusion Continuous process; not enough experience on throughput

Medium Low Limited experience available

Extrusion Continuous process; throughput mainly limited by cooling capacity of calibration die

Medium to high Low Expected to be cost

effective for profiles

Applications

Applications For High-Performance Thermoplastic Composites

• Aerospace and defense:– Radomes, wing and fuselage sextions, anti-ballistics

• Infrastructure and Construction– Window profiles, rebar, beams, structures, composite bolts

• Consumer / recreational– Orthotics, safety shoes, sporting goods, helmets, personal injury

protextion, speaker cones, enclosures, bed suspension slats

• Auto and truck– Bumper beams, skid plates, load floor, seat structures

• Transportation– Railcar structure, body structure and closures

• Energy production and storage– Oil and gas structura tube, wind turbines

BMW M3 Bumper Beam

Source: Jacob Kunststofftechnik GmbH & Co. KGwww.jacob-kunststofftechnik.de

- Beam and crush columns manufactured using Hexcel TowFlex PA6- Parts welded by high frequency vibrational welding- 2 versions: Standard M3 based on glass fiber reinforcement (approx. 40 cars / day) M3 CSL (limited to 1600 total) using Carbon fiber reinforcement

Helmets

Military helmet for Norwegian ArmyMade by Cato Composites50,000/yearTEPEX antiballistic 302Aramid/PA6 continuous reinforcement

Source: Bond-Laminates GmbHwww.bond-laminates.com

Source: Bond-Laminates GmbHwww.bond-laminates.com

White water helmet Made by PrijonTEPEX dynalite 701Glas, Carbon, Aramid/PA6.6Continuous reinforcement

Aircraft Applications

Fixed wing leading edge for AirbusFokker Special Products/AirbusTEPEX semipreg 107Non fully consolidated, flexible layers of continuous fiber reinforced thermoplasticsGlass/PPS

Wing access panel for AirbusFokker Special Products/AirbusTEPEX semipreg 207Non fully consolidated, flexible layers of continuous fiber reinforced thermoplasticsCarbon/PPS

Mine Sweeper Armouring

•Made from TEPEX antiballistic 302•Aramid/PA6•Continuous reinforced•Made by Kvaerner

Source: Bond-Laminates GmbHwww.bond-laminates.com

Safety Shoes

• Composite Toecap– History:

• Composite Toecaps were manufactured in the past using GMT with 50% fiber glass content

• Changing the regulations, this was not sufficient to meet the 200 J requirement

– Newer development:• 65 g / piece (metal 105 g /piece)

• 200 J resistance

• Made from Twintex and LFT, 60% fiber glass, PP

• Manufactured by Security Composites Ltd. (UK)

Others• GF/PP composite tank Produced by Covess (Belgium) using

Twintex and GMT, welded out of 3 pieces and designed to withstand pressure to 100 bar

• Evaluation of thermoplastic composite rebars made with the Fulcrum process

• Thermoplastic composite bolts made by Clickbond Inc. using a thermoforming approach

• Loudspeaker cones, electronic housings and lightweight carbon fiber reinforced structural applications for the automotive industry made by Centrotec AG

• Prototype of a continuous fiber reinforced PP boat (JEC 2000 Innovation Award) made from Twintex using vaccum bag molding. Developed by Halmatic, Ltd.

• Golf club shafts made from PPS/carbon prepreg tape with 66 – 68% fiber content. Multi-step operation including a table rolling, a compression and an oven consolidating step. Manufactured by Phoenixx TPC.

The Future of Thermoplastic Composites

• Will go to more structural applications using different technical thermoplastics in combination with glass, carbon and synthetic fibers.

• Will replace metal applications and reduce weight.

• Improved processing methods will be developed and applied.

Conclusions

• High-performance thermoplastic composites with fiber-dominated properties are a way to – lower cost – higher performance – short cycle times– Recyclability

• Pre-impregnation can improve wet out and performance over commingled prepregs

• Materials and manufacturing methods are available

Acknowledgements

• Aaron Brice and Erik Nolte, Stewart Automotive Research, LLC