THERMOSETS & THERMOPLASTICS IN STRUCTURAL COMPOSITES

Transcription

1 THERMOSETS & THERMOPLASTICS IN STRUCTURAL COMPOSITES 25 th April 2013 Presented by Peter Cate With thanks to Dave Bank, Rainer Koeniger, Mike Malanga, Jay Tudor, Jin Wang 1

2 Dow Automo7ve Systems A leading global provider of advanced material solupons, making vehicles lighter, safer, stronger, quieter and more comfortable Automotive Composites NA Midland, MI, USA Elastic Adhesives Auburn Hills, MI, USA Structural Adhesives Horgen, Switzerland Automotive Composites EUR Horgen, Switzerland Foams & Elastomers Correggio, Italy 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 Carbon Fibre (DowAksa) Yalova, Turkey 2

3 Thermoplas7cs & Thermosets ThermoplasPcs and thermosets are structurally different Amorphous chains Cross link ABS Weak Van der Waal forces Polyamide Crystal lamella Epoxy Strong covalent bonds Amorphous ThermoplasPcs Molecular chains held together by weak van der Waals forces or by hydrogen bonds which reduce strength and spffness with temperature, and cause the material to creep under load Semi- crystalline ThermoplasPcs Crystalline molecular groups connected by amorphous chains (which undergo changes at Tg), along with van der Waals forces or hydrogen bonds Thermosets Cross- linked molecular structure held together with strong covalent bonds, creapng rigid, thermally- stable, creep- resistant materials which maintain strength and spffness very well 3

4 Fibre Polymer Interface Detail The interacpon between the polymer and the fibre determines the stability of the composite construcpon 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 spffness between fibres ThermoseYng Polymers Fiber sizing reacts directly with the epoxy network, creapng strong covalent bonds at the interface The cross linked network is rigid, and relapvely unaffected by changes in temperature resulpng in a more consistent structural performance Amorphous region Covalent bonds Carbon Fibre Carbon Fibre 4

5 The Importance of Low Matrix Material Viscosity 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 100 micron 0.5 micron MATRIX MATERIAL PROCESSING VISCOSITY COMPARISON η RTM Epoxy: ~10 mpa.sec Polyamide 6 melt: 100, ,000 mpa.sec 5

6 Matrix Material Func7on in the Composite Structural composites must undergo a variety of short- and long- term load cases, generapng 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 spffness Matrix material must laterally connect fibres to prevent composite delaminapon 6

7 Structural Composite Applica7ons Different vehicle applicapons require different material properpes Low Strength Relevance High Materials must maintain stiffness and strength over thermal / moisture / aging cycle Low SPffness Relevance High Original Source: SPffness Relevance and Strength Relevance in Crash of Car Body Components, European Aluminum AssociaPon, May 2010 Source: Geo Metro car CAE crash model developed by the US Govt Stiffness Dominated Strength Dominated Stiffness & Strength 7

8 Thermal Stability of Different Polymer Types Thermal performance requirements of the applicapon will influence response to load cases, and thus drive polymer choice Epoxy dry Semi-crystalline thermoplastic PA6 dry Amorphous Thermoplastic Modulus (GPa) Tg Epoxy can be tuned via formulapon Tg PA6 (dry) - 40 C C PA6 Data source example: Moisture absorppon in polyamide- 6 by Vlasfeld, Groenewold, Bersee & Picken 8

9 Thermal Stability of Different Polymer Types Thermal performance requirements of the applicapon will influence response to load cases, and thus drive polymer choice - 40 C 80 C Epoxy dry Epoxy wet Semi-crystalline thermoplastic PA6 dry ~75% loss Modulus (GPa) ~5% loss - 40 C C PA6 Data source example: Moisture absorppon in polyamide- 6 by Vlasfeld, Groenewold, Bersee & Picken 9

10 Demo Part Simula7on Temperature Effect Comparison of short Carbon Fibre Epoxy and Polyamide 6 composites in a roof bow, showing overdesign required to achieve same spffness at 80 C Exterior Roof Panel Roof Bows 6 d.o.f. constrained StaPc loads Thickness Increase Thickness Increase Required to accommodate Modulus Loss at 80 C 60% 40% 20% 0% Front Roof Bow CF Epoxy CF PA6 Nylon 10

11 Moisture Stability of Composites Typical structural automopve applicapon condipons also involve moisture exposure to varying degrees Water Absorp7on (%) 4.0% 3.0% 2.0% 1.0% 0.0% - 1.0% Short CF Epoxy Short CF PA6 90 C Water Immersion Moisture absorppon varies with fiber content Water Soak Time (hrs) Same carbon fibre content Significant moisture absorppon is an indicapon of property change in the matrix polymer and ulpmately in the final composite, across the required temperature range PA6 Data sources : Vlasfeld, Bersee & Picken; BASF; Dupont 11

12 Polymer Property Change a\er Moisture Exposure To predict composite performance, it is cripcal to understand the increase or decrease of all relevant matrix polymer properpes as a result of exposure to applicapon condipons Short Carbon Fibre Composite Measured Proper7es a\er 22hrs Water Immersion at 90C Percentage Change 60% 50% 40% 30% 20% 10% 0% - 10% - 20% CF PA6 CF Epoxy Changes in spffness and strength are typically addressed by proporponal overdesign of the composite - 30% - 40% Modulus Strength Elonga7on 12

13 Demo Part Simula7on Moisture Condi7oning Effect Short Carbon Fibre Epoxy and Polyamide 6 roof bow applicapon, with overdesign to achieve same spffness at 25 C aper humidity exposure* Exterior Roof Panel Roof Bows 6 d.o.f. constrained StaPc loads Thickness Increase 30% 20% 10% 0% Thickness Increase Required at Room Temperature to accommodate Modulus Loss a\er 22hrs 90 C Moisture Exposure Front Roof Bow Middle Roof Bow Rear Roof Bow CF Epoxy PA6 Nylon * 22hrs water immersion at 90 C, then tested at 25 C 13

14 Moisture & Temperature Combina7on Typical automopve applicapon condipons involve combined exposure to both temperature and moisture Epoxy dry Epoxy wet Semi-crystalline thermoplastic PA6 dry Semi-crystalline thermoplastic PA6 wet Modulus (GPa) Tg PA6 (3% moisture) Tg PA6 (dry) - 40 C C PA6 Data source example: Moisture absorppon in polyamide- 6 by Vlasfeld, Groenewold, Bersee & Picken 14

15 Moisture & Temperature Combina7on Typical automopve applicapon condipons involve combined exposure to both temperature and moisture - 40 C 80 C Epoxy dry Epoxy wet Semi-crystalline thermoplastic PA6 dry Semi-crystalline thermoplastic PA6 wet ~80% loss Modulus (GPa) ~18% loss - 40 C C PA6 Data source example: Moisture absorppon in polyamide- 6 by Vlasfeld, Groenewold, Bersee & Picken 15

16 Moisture & Temperature Combina7on Typical automopve applicapon condipons involve combined exposure to both temperature and moisture - 40 C 80 C Epoxy dry Epoxy wet Semi-crystalline thermoplastic PA6 dry Semi-crystalline thermoplastic PA6 wet ~80% loss Modulus (GPa) Note: as carbon fibre reinforcement is added, the spffness loss is reduced, down to <25% in high wt% conpnuous carbon fibre PA6 composites ~18% loss and <5% in high wt% conpnuous carbon fibre Epoxy composites - 40 C C PA6 Data source example: Moisture absorppon in polyamide- 6 by Vlasfeld, Groenewold, Bersee & Picken 16

17 Component Cost & Mass Comparison Cost and Mass analysis including overdesign to accommodate composite spffness decline at 80 C aper 22hrs moisture exposure Cost Model Output for a Benchmark Carbon Fibre Composite Component $ Composite Material Cost* Composite Material Mass Cost increases more for PA6 than Epoxy as overdesign adds more carbon fibre Original part mass before overdesign 0 wt% 40wt% Chopped 60wt% Woven Carbon Fibre Content and Format CF Epoxy Composite Material 0 wt% 40wt% Chopped 60wt% Woven Carbon Fibre Content and Format CF PA6 Composite Material * Materials only. Processing cost analysis shows further disadvantage for PA6 due to high processing temperatures versus ultra- fast epoxy systems 17

18 So Why Thermoplas7cs? TradiPonally ThermoplasPcs have been perceived to offer advantages of: Lower cost polymers Faster processing Recyclability Advanced Thermoset epoxy chemistry and processing techniques are now: Cost compeppve in the final composite (by oppmising carbon fibre uplizapon) Fast enough to compete favourably with mid to high wt% carbon- fibre thermoplaspcs Efficiently recyclable enabling recovery of high- value usable carbon fiber 18

19 Conclusion: ThermoSets The Benchmark Aper oppmising cycle Pme to match volume targets, the key to compeppve structural composites is to reduce the uplizapon of carbon fibre, as it is the most costly component PRICE PROCESSING Ensure low (~10mPa.sec) viscosity for excellent fiber wet out and maximum interfacial strength; accelerate demold Pmes to <2mins and avoid high temperature processing PERFORMANCE Ensure consistent mechanical performance (spffness and strength) over temperature and humidity range, and sufficient chemical resistance for the applicapon 19

20 THANK YOU FOR YOUR ATTENTION! Peter Cate Strategic MarkePng Manager Composite Structures