Man-made natural fibers and their composites. Man-made? Natural? Man-made natural fibers!

Transcription

1 Man-made natural fibers and their composites Roberts Joffe 1,2 1 Luleå University of Technology, S Luleå 2 Swerea SICOMP, S Piteå Man-made? Natural? Man-made natural fibers! This presentation is compilation of results of work on development of composites based on regenerated cellulose fibers It is intended to show potential of these fibers as reinforcement for polymer composites for structural applications 1

2 Flax Natural fibers Fiber length, mm Young s modulus, GPa Natural vs glass fibers Specific stiffness Failure strain, % Average strength, MPa Specific strength GF Specific Stiffness Flax Glass 1 Specific Strength Flax Glass mm 2 mm 5 mm 1 mm 2 mm 2

3 Cellulose in natural fibers Structure of natural fibers 3

4 Flax fibers Man made cellulose fibers Manmade natural fiber? Experimental: fibers The type of the fibers is Cordenka 7 Super 3 4

5 Load (N) Stress (MPa) Experimental setup Specimen for bundle tests Single fiber tests are performed according to the ASTM D standard. Tensile tests were performed on Instron 4411 and Instron 3369 machines. Tests were carried out in displacement controlled mode with displacement rate chosen such that strain rate would be equal to 1%/min. Single fiber tests were done with pneumatic grips and 5N load cell. For bundle tests both, pneumatic and mechanical grips were used with 5N load cell. For short term creep tests and loading-unloading experiments Instron 3369 was used. Tensile test of single fibers and bunldes Cordenka bundle tests ("Reference", 1%/min) Bundle-6, 5mm Bundle-11, 1mm Bundle-14, 2mm Compliance is accounted for! E-4 8.E-5 6.E-5 4.E-5 2.E-5.E+ Load-Dicplacement curves, Cordenka 5 mm, "Reference" 25_5 26_5 27_5 28_5 29_ Displacement (mm) 5

6 Stress (MPa) Stress (MPa) Fiber bundle strength (BT) Cordenka bundle tests (no conditioning, 1%/min) 5mm 1mm 2mm Typical load-strain curve from tensile test of loose bundle Batch Number of Strength Strain Stiffness samples [MPa] [%] [GPa] 5B mm "R" B mm "R" B mm "R" Conditioning of fiber bundles (BT) Cordenka bundle tests (1%/min) 1 mm, Dried 5 mm, Dried 5 mm, Ref 1 mm, Ref Batch Number of Strength Strain Stiffness samples [MPa] [%] [GPa] 5B mm "D" B mm "D"

7 Strain, % Strength, MPa Stress (MPa) Conditioning of fiber bundles (BT) 8 6 Cordenka bundle tests (1%/min) Bundle-V (5 mm), Dried Bundle-6 (5 mm) Bundle-A2 (5 mm), Dried/Reconditioned 4 2 Compliance is accounted for! Batch Number of Strength Strain Stiffness samples [MPa] [%] [GPa] 5B mm "R" B mm "D" ± ± ±.5 5B mm "DR" Effect of humidity (BT) Tensile test of 5mm long Cordenka bundles Reference RH=35% RH=65% RH=35%, T=19C, t=3min Conditioned bundles Test Stress, MPa stdev RH=35% RH=65% RH=35%, T=19C, t=3min RH=65%, T=19C, t=3min RH=65%, T=19C, t=3min Four batches were stored at two different levels of relative humidity: 35% and 65% (1 bundles at each RH level) for 7 days. After conditioning in chambers with controlled RH two batches of fibers (one from each RH) were exposed to the T = 19ºC for 3 minutes. Tensile test of 5mm long Cordenka bundles Test Strain, % stdev RH=35% RH=65% RH=35%, T=19C, t=3min RH=65%, T=19C, t=3min Reference RH=35% RH=65% RH=35%, T=19C, t=3min Conditioned bundles RH=65%, T=19C, t=3min 7

8 Stress, MPa, Stress (MPa) Effect of strain effect (BT) Cordenka bundle tests 5mm (no conditioning) %/min 1%/min Batch Number of Strength Strain Stiffness samples [MPa] [%] [GPa] 5B mm "R" B mm "F" Effect of twisting (BT) 8 Cordenka: bundles without twist, 1 mm 6 Typical load-strain curve from tensile test of loose bundle 4 2 Uncoated 3 Uncoated 4 Coated 2 Coated Reference bundles (with twist) Batch Number of Strength Strain Stiffness samples [MPa] [%] [GPa] 5B mm "R" B mm "R" B mm "R"

9 Stress (MPa), Stress (MPa), Stress (MPa), Stress (MPa) Stress (MPa) Visco- elastic/plastic behaviour (BT) Number of points Number of points 6 5 Bundle-A Bundle-B Visco- elastic/plastic behaviour (BT) Loading-Unloading: Cordenka 1 mm, no twist, no coating Time (s) 12 1 Loading-Unloading: Cordenka 1 mm, no twist, no coating Cordenka bundle tests ("Reference", 1%/min) Up to.7-1.% strain fiber shows linear-elastic behavior 9

10 Stress (MPa) Stress (MPa), Stress (MPa), Stress (MPa), Visco- elastic/plastic behaviour (BT) Loading-Unloading: Cordenka 1 mm, no twist, no coating Time (s) Cordenka bundle tests ("Reference", 1%/min) Loading-Unloading: Cordenka 1 mm, no twist, no coating Over % strain fiber shows visco- elastic/plastic behavior Visco- elastic/plastic behaviour (BT) Loading-Unloading: Cordenka 1 mm, no twist, no coating Time (s) Loading-Unloading: Cordenka 1 mm, no twist, no coating Time (s) Loading-Unloading with strain recovery (pause between loading steps) shows that there is very significant accumulation of residual strain. 1

11 Normalized stiffness Normalized Stiffness Residual Normalized stiffness Visco- elastic/plastic behaviour (BT) 2. Loading-Unloading: Cordenka 1 mm, no twist, no coating 1. Cordenka 1 mm, no twist, no coating: Stiffness from unloading curve Applied Stress (MPa) Applied Stress (MPa) Apparent stiffness measured from unloading stress-strain curve shows very significant reduction with applied load. Does this mean damage? Visco- elastic/plastic behaviour (BT) Cordenka 1 mm, no twist, no coating: Stiffness from unloading curve Cordenka 1 mm, no twist, no coating: Stiffness from loading curve Applied Stress (MPa) Applied Stress (MPa) Apparent stiffness measured from loading stress-strain curve shows no reduction at all. It means that there is no irreversible damage? 11

12 Creep of RCF Creep of RCF Single fiber creep tests (Region-1) 1 MPa 15 MPa Time (s) Single fiber creep tests (Region-2) 25 MPa 3 MPa Time (s) Single fiber creep tests 1 MPa 15 MPa 25 MPa 3 MPa 45 MPa 5 MPa Time (s) Single fiber creep tests (Region-3) 45 MPa 5 MPa Time (s) 12

13 RCF composites Fiber roving was winded on steel plates, using a filament winding machine (2 layers for UD, 4 for cross-plies) Fiber preforms were impregnated using vacuum infusion Composites with Tribest resin were cured 8h at 8 C Composites with EpoBioX resin were cured 2h at 8 C BioRez laminates cured at 8ºC/16h and 13ºC/15 min Cordenka 7 Super 3 unsized/untwisted bundles untwisted bundles twisted bundles RCF composites Untwisted bundles Twisted bundles 13

14 Stress (MPa) Stress (MPa) RCF composites Tensile properties of UD composites Stiffness of composites: Glass/Tribest UD ~43 GPa Cordenka/Tribest UD ~15 GPa Cordenka/Epobiox UD ~17.4 GPa Cordenka/Tribest Glass/Tribest Cordenka/EpoBioX 14

15 Flax vs RCF composites 35 Stress (MPa) Flax UD Cordenka UD Stress-strain curves of flax and Cordenka fiber composites with Tribest resin (GPa/(g/cm3)) Specific modulus (Gpa/(kg/m3)) Specificstiffness Stiffness of composites, Flax vs RCF vs GF A Lin Flax/ Extrem / Trib. Tribest.5,5 B Lin Flax/ Extrem / Trib. Tribest.2,2 D Lin E Lin I Cord. Unsized J Zero Twist K High Glass/Vinyl Flax/ Flax/ Cord. Cord. GF/VE Extrem / Extrem / Cordenka / Cordenka / Twist 1 ester Bio..2 Bio..22 uns/trib. UT/Trib. TW/Trib. Biorez,2 Biorez,2.2 Tribest Tribest Cordenka / Tribest 15

16 Specific strength (MPa/(g/cm 3 )) Specific strength (Mpa/(kg/m3)) Strength of composites, Flax vs RCF vs GF A Lin B Lin D Lin E Lin I Unsized J Zero K High Glass/Vinyl Flax/ Flax/ Flax/ Flax/ Cord. Cord. Cord. GF/VE Extrem / Extrem / Extrem / Extrem / Cordenka / Twist Twist 1 ester Trib. Tribest.5,5 Trib. Tribest.2,2 Bio. Biorez.2,2 Bio. Biorez.22 uns/trib. Tribest UT/Trib. Cordenka / TW/Trib. Cordenka /,2.2 Tribest Tribest Creep of composites Creep test: Tribest resin and composites Glass/Tribest 9 MPa Tribest 6 MPa Cordenka/Tribest 9 MPa Time (s) 16

17 Specific impact strength (kj/m 2 /(g/cm 2 )) Impact strength of composites Cordenka/Tribest Flax/Biorez GF/Polyester Unnotched Charpy test of UD-composites Hybrid composites Tensile strength (MPa) Tensile modulus (GPa) Flax UD 3 22 Cordenka UD Flax crossply Cordenka crossply Hybrid UD

18 Different RCF Typical stress strain curves of CA (Cordenka EHM), CB (Cordenka 184), CC (Enka Viscose), CD (Cordenka 7), CE (Alternative cellulose) and CF (Lyocell) regenerated cellulose fibers and Steam Exploded Flax and Field Retted Hemp fibers. Source: Eichhorn S.J. Deformation Mechanisms in Cellulose Fibres, Paper and Wood J Mater Sci 36 (21) More info Pupure L., Doroudgarian N., Joffe R., Moisture uptake and resulting mechanical response of bio-based composites: Part 1 Constituents, Polymer Composites, On-line first (213). Doroudgarian N., Pupure L., Joffe R., Moisture uptake and resulting mechanical response of bio-based composites: Part 2 Composites, Polymer Composites, Submitted/revised (214). Doroudgarian N., Mechanical and Environmental Durability of High Performance Bio-based Composites, Licentiate thesis, LTU, March 214. Hajlane A., Kaddami H., Joffe R., Wallström L., Design and characterization of cellulose fibers with hierarchical structure for polymer reinforcement. Cellulose (213) 2:

19 SUMMARY (1/2) Regenerated cellulose fibers behave very differently to the other common fibers. Cordenka fibers show decent mechanical properties, although lower than glass fibers or high performance natural fibers. But there are other RCF fibers with better performance. At high humidity levels fibers will take up a lot of moisture which will affect their mechanical performance but this effect seem to be reversible (re-conditioned fibers perform the same as reference fibers). These fibers are highly non-linear at high stresses and significant residual strains are accumulated during the loading. However, there are no indications of damage. Moreover, the creep of composites is not excessive if stress level is within region where fibers show linear elastic behavior. SUMMARY (2/2) The mechanical properties (as well as geometry) of these fibers is very stable which makes it easier to design composite based on this fibers in comparison with natural fibers. RCF are continuous and it is much easier, compare to natural fibers, to assemble them in fabrics with good control over fiber content and orientation. The specific mechanical properties of RCF composites are comparable (or better) with flax and even glass fiber composites. RCF composites show very good impact strength. Combining RCF with other natural fibers into hybrid composites to obtain materials with high strength, stiffness and toughness seem to be very promising. In general RCF fibers have good potential to be used in bio-based composites but there are still some issues that must be resolved (e.g. effect of moisture). 19

20 Acknowledgements I would like to acknowledge colleagues and students who contributed to this work: Birgitha Nyström and Runar Långström (Swerea SICOMP), Liva Pupure, Newsha Doroudgarian and Abdelghani Hajlane (LTU), Baptiste PIERRAT (LTU/EEIGM), Khalid FERJI (LTU/AMASE), Zied Khalil (LTU/Erasmus). Financial support from: Interreg IVA Nord project ANACOMPO (EU and Länsstyrelsen Norrbotten); Erasmus Mundus DocMASE (EU); FP6 project BIOCOMP (EU contract grant number IP ); VR-MENA. 2