Lightweight D-LFT Polymer Composites for Semi-Structural Applications

Transcription

1 Advanced Thermoplastic Composites Lightweight D-LFT Polymer Composites for Semi-Structural Applications M.F. Champagne and K. Stoeffler National Research Council, Automotive and Surface Transportation, Canada Ellen C. Lee and Harry Lobo Ford Motor Company, Research and Innovation Center, Dearborn, USA Automotive Lightweighting Efficient Manufacturing Process ACCE Conference Sept 2017 Novi (MI)

2 Rationale Reduction of GHG is a major objective for the industry Vehicle lightweighting = reduced fuel consumption Use of renewable materials from sustainable sources Use materials with reduced energy footprint Would it be possible to substitute glass fibers by cellulosics in molding compounds for semi-structural applications? Cellulosics manufacturing is (a) less energy intensive than GF, (b) sustainable and (c) provides lightweigthing opportunities ( =1.5 vs 2.6 g/cm 3 ) Tap on >30yrs of expertise in extrusion and >10yrs on sustainable materials to move further this project 2

3 Challenges Semi-structural = very stringent set of mechanical/thermal properties Glass Content Tensile Tensile Notched HDT CLTE (wt%) Strength Modulus Izod 1.8MPa (MPa) (GPa) (KJ/m 2 ) ( C) (ppm/ C) Natural fibers properties sufficient? Fiber-matrix adhesion acceptable? Flowability mold filling adequate? Cellulose fibers thermal stability? Natural fibers = crops with expected inherent variability in properties 3

4 Approach Selected Use engineered cellulosic fibers, made from wood waste in a closed loop process Minimize the inherent variability of harvested natural fibers Use a direct compounding technology to control cost D-LFT (a.k.a. ILC) enables to start from neat components and eliminate intermediate costs Formulate compounds to replace glass fibers in «drop-in» solutions Polymer pellets Roving Additives Semi-structural component 4

5 Experimental Platform: Magna-NRC Centre of Excellence Magna-NRC Composites Center of Excellence (MNCCE). Opened in 2010, 7.2 M$ facility, (D-LFT, HP-RTM, Injection, extrusion, compression, etc ). Long fibres Resin and additives D-LFT industrial scale experimental line Extrusion/compression 5 Coperion TSE, 70 mm Up to 600 kg/h Fiber payload 24 actively monitored insertion points Dieffenbacher Press 2500t, 2.8m x 1.8m platens Active levelling system

6 Materials Selected: Overview PP Matricess Reinforcements Coupling Agents/AO 1) Homopolymer Profax PD702 MFI = 35 dg/min 2) Impact Copolymer Ineos 3950 MFI = 34 dg/min 1) Lyocell Cellulosics Biomid 183 tex 2) Rayon Cellulosics Cordenka CR tex 3) Glass Fibers PPG Tufrov tex 1) Coupling Agents/AO AddVance 437i (proprietary mixture of maleated PP with thermal stabilizers and carbon black) Formulations with 30 and 40 wt% natural fibers were extruded, progessively replacing part of the cellulosics by glass fibers 6

7 Engineered Natural Fibers Lyocell Process Pulp is dissolved in NMMO, the solution is spun into in water bath and stretched. Closed loop process, based on reclaimed wood residues. Biomid fibers. N-Methylmorpholine, N-oxide Viscose/Rayon Process Pulp is chemically modified, dissolved at high ph, spun into low ph bath, where it is regenerated back to cellulose and stretched. Closed loop process, sodium sulphate by-product Cordenka fibers 7

8 Engineered Cellulosics vs Glass Fibers: Mechanics Normalized Stress (mn/tex) Glass Fibers Lyocell Rayon Cellulosic fibers show 80% to 90% of glass fibers tenacity, however Energy required to break cellulosic fibers is 2x-4x larger than glass. Aggressive screw design is needed for breaking these tougher cellulosic fibers Strain (%) 8

9 Engineered Cellulosics vs Glass Fibers: Thermal % weight loss Moisture? Residual solvents/chemicals? 80 Cellulosic fibers degradation in oxidative atmosphere is a 2-step process. Weight Loss (%) C/min in air Rayon = 301 C Rayon = 414 C Temperature ( C) Lyocell = 314 C Lyocell = 428 C Noticeable degradation observed in the C range. Might create degradation issues, i.e., local overheating generated by aggressive screw sections. 9

10 Hybrid Composites : Coupling Agent(s) Selection Secondary electron imaging Backscattered electron imaging Bright = Glass fibers Standard maleated PP Excellent coupling with cellulosics Fibers seen on fracture surface are fully covered by matrix material. Good adhesion with glass fibers Most glass fibers seen fracture surface (bright features on BE image) are covered by matrix material. Fibers seen on fracture surface are are fully covered by matrix material. AddComp AddVance 437 improved Excellent coupling with cellulosics and glass All the fibers seen on fracture surfaces are fully covered by matrix material, including the glass fibers (bright features on BE image). 10

11 Hybrid Composites : Processing Conditions Polymers/Additives Rovings Gases Venting Extrusion/Compression conditions Fibers used «as is» (i.e. no drying) Extrusion T: 210 C Screw speed: RPM (depending on fiber content ) Q = kg/h (depending on GF ratio ) T tool =52-60 C, P=1250 tons Cycle time 90 sec Part kg 11 Flow «Load floor» molded part 90 cm 35 cm

12 Hybrid Composites : Processing Conditions Roving Feeds Roving Mixing/Debundling/Wetting Gases Venting 30 mm «Zahnmisch» element (ZME), 70 mm 1 st train of 3x30mm «Zahnmisch» element (ZME), reverse-flighted, forward -«teethed» Flow 2 nd train of 3x30mm «Zahnmisch» element (ZME), reverseflighted, forward - «teethed» «the purpose of the ZME element is to achieve high distributive mixing» K.Young, A. Lim and P. G. Andersen Proceedings of the Polyolefins International Conference

13 Hybrid Composites : Tensile Properties Total fibers in hybrids = 40 wt% 70 Total fibers in hybrids = 40 wt% Young Modulus (GPa) 5 4 Total fibers in hybrids = 30 wt% Stress at max (MPa) Total fibers in hybrids = 30 wt% Average of 5 specimens, cut in MD Average of 5 specimens, cut in MD Glass Fibers Content Portion (wt%) Glass Fibers Content Portion (wt%) 13

14 Hybrid Composites : Impact and Heat Resistance Copolymer, 30 wt% Total fibers Notched Izod (kj/m 2 ) Copolymer, 30 wt% Total fibers Total fibers in hybrids = 30 wt% Total fibers in hybrids = 40 wt% Heat Distortion Temperature ( C) Total fibers in hybrids = 30 wt% Total fibers in hybrids = 40 wt% 0 Average of 10 specimens, cut in MD Average of 3 specimens, cut in MD Glass Fibers Content Portion (wt%) Glass Fibers Content Portion (wt%) 14

15 D-LFT on Cellulosic Rovings: Specific Challenges Use of cellulosic rovings as substitute for GF is possible, however Difficult to open and cut the rovings into manageable fiber lengths in the standard D-LFT process 15

16 Lab-Scale D-LFT Line: Scaling Down the Production Line Log die, 50-mm wide, scaled-down version of our production line Fiber payload Leistritz 34mm, kg/h, tear down and re-assembly in < 24hrs Versatile setup that allow the development of low TRL concepts at much lower costs 16 Shear-edge plaque tool. Fitted to a 30t press Scaled-down setup was successfully validated using PP/GF compounds. 9 screw designs and multiple processing conditions were then efficiently tested.

17 Lab-Scale D-LFT: Cellulose Dispersion/Distribution Polymers Additives Rovings Flow Solid bed of pellets Melting/Mixing Molten polymer Mixing Atmospheric Vent Very aggressive melting/mixing zone 13 x 7.5mm thick kneading 90 3 x 15mm thick kneading 60 Extrusion/Compression conditions Fibers used «as is» (i.e. no drying) T Extruder = 215 C Q = 7-15 kg/h N = rpm T tool = 60 C P = 27 tons Cycle time sec Part 70g Materials Homo PP (MFI 35 g/10min) Cordenka CR tex AddVance 437 improved 12 cm «Mini-DLFT» test plaque 16.5 cm 17

18 Insertion in Solid Polymer Bed: Cellulosics Fiber Length Materials PS, injection-grade (MFI=14 dg/min) 30 wt% Rayon Cellulosic Fibers Extrusion/Compression conditions Fibers used «as is» (i.e. no drying) T Extruder = 215 C Q = 15 kg/h N = 180 rpm T tool = 60 C P = 27 tons Cycle time 60 sec Part 70g Fiber Extraction Molded plaque immersed in THF 1 week, no agitation Room temperature 18

19 Demonstrator Molding: Lower Front-End Tool at MNCCE 160 cm Complex part, with many fine details (ribs, pins, hooks..) Requires 3 molten material charges, generating 2 weld lines Shot size kg Prototype aluminum tool ca

20 Front-End Carrier Prototype Tool: Description Punch Movable sections in the punch, to assist part ejection Core Deep section Narrow section Large/flat section 20

21 Front-End Carrier Prototype : Molding Part successfully molded up to 30wt% cellulose fibers. Charges exhibit some «puffing». Degradation starts to be noticeable at higher fiber content. 21

22 Summary and Outlook Complex demonstrators were successfully molded from the best formulations reinforced with engineered cellulose fibers from sustainable sources. Reduction in stiffness and strength is observed. Thermal and impact resistance are significantly lower than the targeted specifications. Hybrids with glass fibers allow to improve properties, however, the expected weight reduction is then less attractive. 22

23 Potential Future Work Develop formulations based on 100% sustainable materials An expanding range of polyamides synthesized from diols and diamines are commercially available Tackle the challenges related to the addition of cellulose fibers to nylons Develop overmolding D-LFT compression processes Addition of local reinforcements to improve overall performance, while maintaining reduced weight. Woven aramid substrate PA6/GF base plate Lightweight protection panels 23

24 Questions? Michel F. Champagne (450)