Chung-Hae PARK, Eric LAFRANCHE, Mylène DELEGLISE-LAGARDERE, Patricia KRAWCZAK Mines Douai, TPCIM. Institut Mines-Télécom

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1 Fabrication par Procédé d Imprégnation Directe de Composites Structuraux à Renort Textile en Fibres Végétales et à Matrices Thermodurcissable ou Thermoplastique Chung-Hae PARK, Eric LAFRANCHE, Mylène DELEGLISE-LAGARDERE, Patricia KRAWCZAK Mines Douai, TPCIM Institut Mines-Télécom

2 Importance o perormance Evolution o Industrial Applications Perormance Cost Environnement Biomedical Aerospace ~20C Military Commercial aircrat Mass transport Today Automotive Importance o cost Construction Tomorrow Environment 2

3 Biosourced Composites, Natural Fibers Flax (lin) and Hemp (chanvre) are comparable with glass iber in terms o speciic stiness. 3 Laurent BIZET, FPCM10

4 State-o-the-Art : Green Washing! Semi-structural (non-structural) parts High perormance structural parts PP or PLA (with low Pmelt) LFRT SFRT Textile Enhance mechanical properties: textile reinorcement (high iber length and content) Avoid thermal degradation (even or engineering polymer with high Tmelt) Decrease the manuacturing cost: direct impregnation without semi-products Clusters: Projets Structurants de Pôles de Compétitivité (PSPC) Mines Douai / TPCIM Project SINFONI Project FIABILIN Hemp Chanvre Flax Lin Positioning o each iber (lax and hemp) as the third technical iber or industrial applications (ater glass and carbon ibers) 4

5 Flax Textile Reinorced Thermoset Composites Resin Transer Molding process Preorming Resin Injection Heating Mold Filling & Curing Releasing Resin low: Darcy s law Q A u D K Fiber reinorcement P Resin Q: low rate A: cross section u D : volume-averaged velocity P: resin pressure µ: resin viscosity K: permeability o iber reinorcement Continuous textile reinorcement at high V : enhance the mechanical properties Low processing temperature: avoid the thermal degradation o lax iber Long process cycle time (due to long resin curing time) 5

6 Dierent Scales in Natural Fibers Porous elementary iber Flax iber in contact with the liquid resin Liquid absorption Fiber swell Liquid penetration into the iber Increase o iber diameter Dry iber Wet iber 6

7 Wetting: Improvement? Characterization! Poor wetting Capillary radius changes due to iber swell & liquid absorption into iber Fibers LRccos mc AP L t 2 Epoxy Capillary H max Good wetting Gravity h max Epoxy 2R c Liquid h max 2L cos R g c L 7 Surace tension: mn/m Contact angle: ~36 (with oil) << 90

8 Permeability o Natural Fiber Textile Unsaturated permeability: time-dependent iber swell, non-uniorm permeability Saturated permeability (K sat ) Two test liquids with dierent iber swell ratios Steady low at maximum iber swell (uniorm in the preorm) sw,oil < sw,water K oil > K water Experiment, Water Experiment, Oil K dp u Darcy dx Q K P1 P 2 A L Permeability [ log10(m 2 )] Model, Water: k=(v ) Model, Oil: k=(v ) K sat QL AP 1 P 2-13 Model, Water: k=0.60 Model, Oil: k= Fiber Volume Fraction 8

9 Permeability [log10(m 2 )] K(V,e = sw2 V ) Dry iber Permeability o Natural Fiber Textile D,o h Wet iber K 1 1 A D,o sw h(1- sw ) Model it, Eq.9 n1 V, e V n, e Permeability [log10(m 2 )] K(V,dry, sw ) K sw 1 A 1 t 2 sw 2 sw V V n n1 n= A= Model it, Eq.9-13 Experiment, Water Experiment, Oil Eective Fiber Volume Fraction -13 Experiment, Water Experiment, Oil Fiber Volume Fraction 9

10 Resin Flow Modeling Liquid absorption Mass conservation Q in Q absorp Q out Q in Q absorp Q u s( ) out Flax iber Fiber swell Permeability Dry iber D (small) h (big) Wet iber D (big) h (small) K u P 10

11 x 10-8 Dependence on Fiber Content and Flow Length V Flow ront position square vs. time 2 P * x V C x * x * Kx, t P V in 1 l R V =0.34 so t t 2 sw t t X x x 2K t P in V =0.56 K=const. K(x,t) K(x,t) & sink Mass sink eect (delaying the low ront progress) increases as iber content and part size increase x 2 (1-V,0 )/P in [m 2 s] Experiment,V,0 = Experiment,V,0 = Experiment,V,0 = x 2 (1-V,0 )/P in [m 2 s] Drooping by sink eect Experiment,V,0 = Experiment,V,0 = Model 1: K constant 0.5 Model 1: K constant 1 Model 2: K(t,x)(V Model 2: K(t,x)(V,t ),t ) Model 3: K=K(t,x)(V Model 3: K=K(t,x)(V,t ); s=s(t,x),t ); s=s(t,x) micro micro Time [s] Time [s] 11

12 Thermoplastic Matrices Decrease the manuacturing cost Short process cycle time (< 2 minutes or automotive applications) Direct impregnation without semi-products (commingled yarn, powder impregnated abric, ilm stacking) Adopt high perormance engineering polymers (e.g. Polyamide) Avoid the thermal degradation o natural ibers: Tdegrad (170 C) < Tmelt Poor impregnation (Void/porosity) Thermal degradation Air voids or porosities due to poor impregnation, poor iber-matrix compatibility, resin shrinkage or moisture dissolution Process window Temperature & Time 12 Minimize the iber exposure to heat Maximize the local pressure

13 Compression Resin Transer Molding Short cycle time Open gap Fiber placing Resin injection Compression RTM Longitudinal low P inj L l u P cap K P tow inj P L l cos D pore cap 1, CRTM Transverse low Maximize resin velocity inside the tow P comp H l u P cap K P tow comp P H l cos D pore cap 1, 13

14 Manuacturing Process Scheme Isothermal mold illing to avoid the temperature drop during the impregnation 1. Preorm preheating 2. Resin injection and preorm placement Press Hot resin Preorm T iber =T high 3. Mold closing and holding Convection oven Mold T mold =T iber =T press =T resin =T high 4. Cooling Press 1 (Hot) Two presses at dierent temperature (hot and cool) to reduce the cooling time Press 2 (Cool) T mold =T iber =T press =T resin =T high T composite =T mold =T high T composite =T press =T low 14

15 Process Conditions 1. Temperature : 195, Preheating : 2 min 3. Impregnation time : 60 s, 90 s 4. Pressure condition : 1.5 bar (40 s, 70 s), 21 bar (20 s) 5. Materials : Flax 2 2 twill textile NATTEX Reactive bio PA 6. Fiber volume raction ~ 42%, Thickness ~ 1.8 mm Fiber preheating : 2 min Resin injection Compression : 60, 90s Impregnation at 1.5 bar (40 s, 70 s) Holding at 21 bar (20 s) 15

16 Impregnation Quality The thermal degradation o lax iber was not observed. Compression : 60 sec Good impregnation Compression : 90 sec Good impregnation Incomplete impregnation Good impregnation 16

17 Mechanical Properties Mechanical properties obtained by tensile tests (V ~ 42%, average value o #1,2 and #2,1) Average tensile modulus : 13.5 ± 1.9 GPa Average tensile strength : 130 ± 22 MPa Condition Cooling Fiber preheating #1,1 Slow In the oven #1,2 #2,1 Fast In the oven #2,2 Fast In the mold Film stacking, PA 11(V :39%): 11.9 GPa ±0.8 #1,1 #1,2 #2,1 #2, Film stacking, PA 11(V :39%): 107±6.5 MPa #1,1 #1,2 #2,1 #2,2 17

18 Conclusions Natural iber textile reinorcements should be employed or high perormance structural applications. The resin low in the natural iber reinorcement induces resin absorption and iber swell : inluence on the process cycle time and the inal part quality. Direct thermoplastic melt impregnation into natural iber reinorcement within a short cycle time is easible without the thermal degradation o ibers. Industrial applications o natural iber textile should be careully selected by considering the manuacturing process, the matrix type and the pros/cons o reinorcement. Aeronautics / Railway / Automotive Process cycle time / Material price (natural iber textile are not cheap!) Multi-unctionality: Aesthetics / Thermal & acoustic isolation / Recyclability 18