Recent Developments of Kenaf Fiber Reinforced Thermoset Composites: A Review
BySubramaniasarma Sreenivasan,
PhD. Student, University Putra Malaysia
2
Outline• Introduction• Kenaf Fibers• Fiber Interphase And Modifications• Kenaf Thermoset Composites• Processing Methods• Applications• Conclusion
Introductions• The use of Natural Fibers (NF) have been discovered
for a long time.• Daily usage items such as rope, baskets, twine and
cloth. • With the advent of polymers these fibers can be used
as reinforcement material to give better quality.• Modern fibers are mostly synthetic fibers• Commonly Glass fibers have been used as
reinforcement material, but glass fibers have some shortcomings.
KenafKenaf Plants Kenaf Bast Fibers and Cores
Properties NF Glass fibersDensity Low Twice that of NFCost Low Low, but higher than NFRenewability Yes NoRecyclability Yes NoEnergy consumption Low HighDistribution Wide WideCO2 neutral Yes NoAbrasion to machines No YesInhalation Health risk No YesDisposal Biodegradable Not Biodegradable
Kenaf Fibers• Kenaf (Hibiscus cannabinus, L.) is amongst the most widely
used NF. • There are two types of kenaf fibers, i.e. coarse bast fibers and
fine core fibers.• Can be grown in a wide range of temperatures.• 15 MJ of energy consumed to produce a kg of kenaf fibers and
it takes 55 MJ to produce the same amount of glass fibers. • Malaysian produced kenaf fibers cost USD 525 / ton in 2010 In
the same year E-glass fibers which are the most commonly used and cheapest glass fibers cost almost USD 1630/ ton.
Kenaf stalk
FiberApparent Density g/cm3
Tear Index
mN/m2g
Tensile Index N.m/g
Burst Index
KPa.m2/g
Ring Crush Test
KN/m
Core 0.716 5.87 83.09 6.09 2.87
Bast 0.502 20.68 40.83 2.16 1.43
Comparison With Other FibersFibers Density (g
cm3) Diameter
(lm) Tensile strength
(MPa) Young’s modulus
(GPa) Elongation at
break (%)Flax 1.5 40–600 345–1500 27.6 2.7–3.2Hemp 1.47 25–500 690 70 1.6Jute 1.3–1.49 25–200 393–800 13–26.5 1.16–1.5Kenaf 1.2-1.45 20-200 930 53 1.6Ramie 1.55 400–938 61.4–128 1.2–3.8Nettle 650 38 1.7Sisal 1.45 50–200 468–700 9.4–22 3–7PALF 20–80 413–1627 34.5–82.5 1.6Oil palm EFB 0.7–1.55 150–500 248 3.2 25Oil palm mesocarp 80 0.5 17
Cotton 1.5–1.6 12–38 287–800 5.5–12.6 7–8Coir 1.15–1.46 100–460 131–220 4–6 15–40E-glass 2.55 <17 3400 73 2.5Kevlar 1.44 3000 60 2.5–3.7Carbon 1.78 5–7 3400–4800 240–425 1.4–1.8
Fiber Interphase And Modifications• Can be used with thermoset and
thermoplastic composites.• Kenaf fiber is hydrophilic.• Problems with wetting and surface adhesion. • Weak composite properties.• 2 Main treatments– Chemical treatments – Physical treatments
Chemical Treatments• 3 common types of treatment– Mercerization - • Cleans the fiber, reduces stiffness and gives a rough surface
– Silane – (• Changes the polarity of the surface by acting as a
bonding/coupling agent.– Acetylation -• Stabilizes the cell walls against moisture, improving
dimensional stability and environmental degradation.
Physical Treatments• 2 common types – Plasma• Use of partially ionized quasi-neutral gas to chemically
and topographically change the surface.– UV and Corona• Increase the surface energy using corona and UV light
to promote surface adhesion.
Kenaf Thermoset Composites• Thermoplastic – can be heated and melted and
reformed again without any loss of properties. • Thermosetting materials - or ‘thermosets’, are
formed by an in situ chemical reaction. – Formed by a mixture of resin and catalyst.– A non-reversible chemical reaction occurs to form
a hard, infusible product.– Most common resins used with natural fibers are
polyester (UP), vinyl-ester (VE), and epoxy.
Kenaf Thermoset CompositesComposites Tensile strength,
MPa Tensile
modulus, GPaElongation at
break, %Flexural
strength, MPaFlexural
modulus, GPaKenaf reinforced UP 20 - 90 4 - 7 0 - 2 40 - 123 4 - 14Kenaf reinforced VE 40 -50 4 - 5 0 - 3 60 - 80 3 - 5Kenaf reinforced Epoxy 50 - 65 3 - 5 1 - 3 70 - 100 3 - 5
• Optimum fiber content 20%.• Reduced fiber diameters, increased fiber length and
higher cellulose content means better mechanical properties.
• Modified resins, better mechanical properties.
Processing Methods – Hand Lay Up
Fiber• Manual method• Fibers are laid up by hand
Resin• Resin and catalyst is mixed and poured• Low fiber loading (up to 30 %)
Curing• Cured at room temperature. • Poor wetting and strength
Processing Methods – Compression Molding
Fibers• Fibers are laid into the mould cavity or a premix is used.• High Fiber loading (up to 60%)
Mould• Mould with Core and Cavity.• Preheated to 120 -160 °C
Curing• Mould is closed with pressure and allowed to cure• Prevents void and cavities in the final part.
Processing Methods - RTM
Fibers• Fibers are pre-laid into the mould• Pre-dried to prevent air pockets or bubbles
Mould
• Moulds are closed and preheated after fibers are placed.• Resin is then injected into the preheated mould or via
vacuum.
Curing• Mould is then allowed to cure under pressure. • High fiber loading (up to 50%)
Processing Methods - Pultrusion
Fibers• Fibers are pre-twined to form long continuous strands.• Pre-treated fibers to improve adhesion
Resin
• Resin is premixed and fibers are pulled through a resin dipping.
• High fiber loading (up to 70%)
Curing
• The wet fiber are passed through a cross-sectional pre heated die and cured
• Limited to certain cross-sections
Applications• Mostly used in automotive
and construction.• For automotive, external parts
such as bumpers and internal parts such as door panels.
• Insulation panels and roofs for construction
• Upcoming research in aeronautics and aerospace.
• Applications such as sandwiched panels for low load bearing parts.
Vehicle Part Material Used
Interior
Glove Box
Wood/cotton fibers & molded, flax/sisal
Door Panels Flax/sisal with thermoset resinSeat Coverings Leather/wool backing
Seat Surface Coconut fibers/natural rubberTrunk Panel Cotton fibersTrunk Floor Cotton fibers with PP/PET Insulation Cotton fibersExterior Floor Panels Flax mat with polypropyleneBumpers Kenaf reinforced bumpers
Applications
Conclusions• The possibility to replace almost any traditional
composites. • Surface properties must be modified to increase and
promote better adhesion. • Kenaf’s increasing popularity has been identified as
low cost, light weight and low energy consumption. • No injection molding of kenaf reinforced thermosets
especially pre-preg such as bulk molding compounds.
Thank You
Questions and Answers Session