Recent Developments of Kenaf Fiber Reinforced Thermoset Composites: A Review

BySubramaniasarma Sreenivasan,

PhD. Student, University Putra Malaysia

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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