Natural Fiber Reinforced

7/24/2019 Natural Fiber Reinforced

1/7JOM November 200680

Low-Cost Composites in Vehicle ManufactureOverview

In the past decade, natural-fiber

composites with thermoplastic and

thermoset matrices have been embraced

by European car manufacturers and

suppliers for door panels, seat backs,

headliners, package trays, dashboards,

and interior parts. Natural fibers such

as kenaf, hemp, flax, jute, and sisal offer

such benefits as reductions in weight,cost, and CO2, less reliance on foreign

oil sources, and recyclability. However,

several major technical considerations

must be addressed before the engineer-

ing, scientific, and commercial com-

munities gain the confidence to enable

wide-scale acceptance, particularly in

exterior parts where a Class A surface

finish is required. Challenges include

the homogenization of the fibers proper-

ties and a full understanding of the degree

of polymerization and crystallization,

adhesion between the fiber and matrix,

moisture repellence, and flame-retardant

properties, to name but a few.

INTRODUCTION

The utilization of lightweight, low-

cost natural fibers offers the potential to

replace a large segment of the glass and

mineral fillers in numerous automotive

interior and exterior parts. In the past

decade, natural-fiber composites with

thermoplastic and thermoset matrices

have been embraced by European car

manufacturers and suppliers for door

panels, seat backs, headliners, package

trays, dashboards, and interior parts.

Natural fibers such as kenaf, hemp, flax,

jute, and sisal are providing automobile

part reinforcement due to such drivers

as reductions in weight, cost, and CO2,

less reliance on foreign oil sources,

recyclability, and the added benefit that

these fiber sources are green or eco-

friendly. While the United States has not

issued regulations concerning automo-

Natural-Fiber-Reinforced PolymerComposites in AutomotiveApplications

James Holbery and Dan Houston

tive end-of-life requirements, European

Union (E.U.) and Asian countries have

released stringent guidelines. European

Union legislation implemented in 2006

has expedited recent natural-fiber-rein-

forced plastic automotive insertion; by

2006, 80% of a vehicle must be reused

or recycled and by 2015 it must be 85%.1

Japan requires 88% of a vehicle to berecovered (which includes incineration

of some components) by 2005, rising to

95% by 2015. As a result, today most

automakers are evaluating the environ-

mental impact of a vehicles entire

lifecycle, from raw materials to manu-

facturing to disposal.

At this time, glass-fiber-reinforced

plastics have proven to meet the structural

and durability demands of automobile

interior and exterior parts. Good mechan-

ical properties and a well-developed,

installed manufacturing base have aided

in the insertion of fiberglass-reinforced

plastics within the automotive industry.

However, glass-reinforced plastics

exhibit shortcomings such as their rela-

tively high fiber density (approximately

40% higher than natural fibers), difficulty

to machine, and poor recycling proper-

ties, not to mention the potential health

hazards posed by glass-fiber particulate.

An ecological evaluation, or eco-balance,

of natural-fiber mat as compared toglass-fiber mat offers another perspec-

tive. The energy consumption to produce

a flax-fiber mat (9.55 MJ/kg), including

cultivation, harvesting, and fiber separa-

tion, amounts to approximately 17% of

the energy to produce a glass-fiber mat

(54.7 MJ/kg).2

Though natural-fiber-reinforced plas-

tic parts offer many benefits as compared

to fiberglass, several major technical

considerations must be addressed before

the engineering, scientific, and com-

mercial communities gain the confidence

to enable wide-scale acceptance, par-

ticularly in exterior parts where a Class

a

b

Figure 1. (a) A natural fibermat processed into (b) a doorinner panel. Material specifics:1,600 g/m2, 50% Kenaf/50%polypropylene. Photo courtesyof Best Fibers.


2/72006 November JOM 81

Table I. Properties of Typical Thermoplastic Polymers Used in Natural FiberComposite Fabrication*

Property PP LDPE HDPE PS Nylon 6 Nylon 6,6

Density (g/cm3) 0.8990.920 0.9100.925 0.940.96 1.041.06 1.121.14 1.13-1.15

Water Absorption 0.010.02 300

Izod Impact 21.4267 >854 26.71,068 1.1 42.7160 16654

Strength (J/m)

* Selected data obtained from Reference 11; LDPE = low-density polyethylene; HDPE = high-density polyethylene; PP = polypropylene;

PS = polystyrene.

Table II. Properties of Typical ThermosetPolymers for Natural Fiber Composites4

Polyester VinylesterProperty Resin Resin Epoxy

Density (g/cc) 1.21.5 1.21.4 1.11.4

Elastic 24.5 3.13.8 36 Modulus (GPa)

Tensile 4090 6983 35100

Strength (MPa)

Compressive 90250 100 100200

Strength (MPa)

Elongation (%) 2 47 16

Cure Shrinkage 48 12

(%)

Water Absorption 0.10.3 0.1 0.10.4 (24 h @ 20C)

Izod Impact, 0.153.2 2.5 0.3 Notched (J/cm)

A surface finish is required. Challenges

include the homogenization of the fibers

properties, and a full understanding of

the degree of polymerization and crystal-

lization, adhesion between the fiber and

matrix, moisture repellence, and flame-

retardant properties, to name but a few.

Technology for implementing natural-

fiber composites into interior trim con-

tinues to be developed by Tier I and TierII automotive suppliers, typically in

partnership with producers of natural-

fiber-based processing capabilities

for mat or other material forms. Com-

pression molding, injection molding,

thermoforming, and structural reaction

injection molding are all processes

utilized to process natural-fiber

composites.

The automotive market sector is not

the only area that has experienced an

increase in natural-fiber usage. Theinsertion of natural fibers in the indus-

trial, building, and commercial market

sectors has experienced a growth rate of

13% compounded over the last 10 years

to an annual use of approximately 275

million kilograms.3However, the use of

natural materials in automotive applica-

tions is not a new idea. In the 1930s and

1940s, Henry Ford strongly advocated

the use of natural materials, including

hemp, producing reinforced soy resin

composites in the manufacture of exterior

body panels. If it had not been for

the long material cure time, and the dif-

ficulty in molding, Fords idea for

alternative materials may have been

implemented.4

Recently, European companies have

taken the lead in natural-fiber composite

development, such as Dieffenbacher

(Germany), BASF (Germany), and

Rieter Automotive (Switzerland). Rieter

Automotive was awarded the top prize

at the 2005 JEC Composite Showcase

for its Acaba (banana) fiber continuous-

fiber processing development, where theprimary energy savings is estimated at

60% or more.5In North America, Delphi

Interior Systems, Visteon Automotive,

Kafus Bio-Composites/Flexform Tech-

nology, and Cargill Ltd., to name but a

few, are actively involved in natural-

fiber-composite development and

manufacture. With rapid advancements

in fully bio-based polymers that may be

processed with natural fibers, it is only

a matter of time before fully bio-based

composites are prevalent within theautomotive industry.

See the sidebar for details on natural-

fiber selection and preparation.

THERMOPLASTIC-

THERMOSET POLYMERS

The manufacture of natural-fiber

composites includes the use of either a

thermoset or thermoplastic polymer

binder system combined with the natural-

fiber preform or mat. In automotive

applications, the most common system

used today is thermoplastic polypropyl-

ene, particularly for nonstructural com-

ponents. Polypropylene is favored due

to its low density, excellent process-

ability, mechanical properties, excellent

electrical properties, and good dimen-

sional stability and impact strength.9

However, several synthetic thermoplas-tics are utilized including polyethylene,

polystyrene, and polyamides (nylon 6

and 6, 6). Common thermoplastic prop-

erties are listed in Table I.

The development of thermoplastic

natural-fiber composites is constrained

by two primary physical limits: the upper

temperature at which the fiber can be

processed and the significant difference

between the surface energy of the wood

and the polymer matrix. Process tem-

perature is a limiting factor in natural-

fiber applications. The generally per-

ceived upper limit before fiber degrada-

tion occurs is on the order of 150C for

long processing durations, although

fibers may withstand short-term expo-

sures to 220C. The result of prolonged

high-temperature exposure may be dis-

coloration, volatile release, poor inter-

facial adhesion, or embrittlement of the

cellulose components. Therefore, it is

important to obtain as rapid a reaction

rate as possible during both surface

treatment and polymer processing to

limit exposure to cell wall components

preventing degradation. The develop-

ment of low-process-temperature surface

treatments with high service capabilities

is viewed as an enabling technology for

the application of natural fibers in com-

posite materials.

Because the interfacial adhesion

between the natural fiber and polymer

matrix determines the composite physi-

cal properties, it is usually necessary to

compatibilize or couple the blend.12



NATURAL-FIBER SELECTION AND PREPARATION

Natural fibers can be grouped into bast (jute, hemp, kenaf, flax) produced from fiber-sheaves of dicoltylic plants or vessel sheaves of monocotylic plants, hard fibers fromleaf (sisal, pineapple), fibers derived from seed (cotton), and several others, each havingdistinct mechanical and physical properties (Tables A and B). By far, the most plentifulfiber in the world is wood from trees with an annual world production of 1.75109tonnes

per year from well over 10,000 species. Cotton production, by comparison, is 18.5106

tonnes per year, while kenaf, flax, and hemp are 9.7105, 8.3105, and 2.1105tonnes peryear, respectively Although there are a number of plant fibers in nature, only a few are suited forautomotive application. Cellulose is the main component of natural fibers, althoughthe amount of pure cellulose, hemicellulose, pectin, lignin, and other extractives willvary from fiber to fiber.10 For structural composites produced from natural fiber forvalue-added applications, the most prominent fibers applied are flax, kenaf, and hemp,primarily due to their fiber strength properties. In Table B, the tensile strength and elasticmodulus of the major natural and manmade fibers are listed. Calculating the specificstrength (tensile strength/density) and modulus (modulus of elasticity/density) of naturalfibers and comparing these to E-glass, it is apparent that E-glass is superior to all fibers inspecific strength, although flax fiber is very competitive (1,275 vs. 1,000, respectively).However, the specific modulus of hemp (47) and kenaf (36) favorably compare to that ofE-glass (28). This data indicates that the bast fiber characteristics are comparable or in

some cases, exceed those of glass fibers. Natural fibers can be harvested annually, or in certain cases, such as for kenaf, jute,and hemp, can be planted and harvested two to three times annually. Kenaf, a plant ofAfrican origin cultivated in the United States for a variety of uses including as an oilspill absorbent, can grow to a height of four meters in four to five months and can yieldtwo or three harvests a year in tropical climates.7Jute, which is grown in China, India,and Bangladesh, can be grown in four to six months, although due to synthetic fiberdevelopment has declined in yield in recent years. Agronomically, jute and kenaf haveadvantages in regards to their resistance to climatic extremes, pests, and diseases. Hemp,which grows as a yearly crop in most climates, can be historically traced back more than10,000 years as a source of rope, cloth, and textiles. All of these plants have a high carbondioxide (CO

2) assimilation rate and clean the air by consuming large quantities of CO

2,

which is the main cause of the greenhouse effect. This is true also for sisal, from whichthe same plant can produce fiber for up to 20 years, after which the plant begins to bloom

and then die. Once the bast fiber is harvested, it must go through a process called retting to separatethe fiber from the rest of the plant. Essentially, this is a process to moisten or soak the

Table A. A List of Vegetable and Cellulose Fiber Classifications

Blast Leaf Seed Fruit Stalk Wood Fibers

Flax Sisal Cotton Coconut Bamboo Hardwood

Hemp Manila Kapok Coir Wheat Softwood

Jute Curaua Rice (~10,000+

Kenaf Banana Grass varieties)

Ramie Palm Barley

Banana Corn

Rattan

Compatibilization is any operation per-

formed on the fiber and polymer that

increases the wetting within the blend.

Coupling is a process in which dissimi-

lar polymers or fillers are made into an

alloy by use of external agents called

coupling agents.11This can be achieved

by modifying the polymer matrix,

modifying the fiber, adding surface-

active agents, and by high shear com-pounding. There are many types of

coupling agents including surface-active

agents and reactive chemistries, at times

referred to as functional modifiers. Sur-

face-active agents are materials that

increase interfacial adhesion by acting

as a solid surfactant and that do not form

covalent bonds to the polymer matrix.9

Materials that form covalent bonds to

either the fiber or polymer matrix can be

reacted in-situ during processing. The

result of properly applying a compatibi-lizer or coupling agent to the composite

is an increase in physical properties and

environmental durability.4

The primary thermoset resins used

today in natural-fiber composites for

automotive applications are polyester,

vinylester, and epoxy resins. A com-

parison of typical thermoset properties

is provided in Table II.4In natural fibers,

polar groups emanating from hydroxyl

groups, acetyl, and ether linkages (C-

O-C) are the main structural units and

the primary contributor to mechanical

properties; these also render cellulose

more compatible with polar, acidic, or

basic groups, as opposed to nonpolar

polymers. Polyester resins are widely

used, particularly the unsaturated type

capable of cure from a liquid to a solid

under a variety of conditions. A range of

polyesters is made from different glycols

(polyethylene glycol, ethylene glycol,

etc.), acids (malaeic, anhydride), and

monomers, all having various properties.

Orthophthalic polyester is the standard

economic resin commonly used, and it

yields highly rigid products with low heat

resistance. Isophthalic polyester is now

more common when moisture resistance

is needed.

Epoxy resins offer high performance

and resistance to environmental degrada-

tion. Typically, the monomer is produced

by reacting epichlorohydrin and bisphe-

nol-A with hardeners such as amines or

anhydrides common in industry. Epoxies

have wide appeal in industry, although

in the automotive industry epoxies have

not gained broad use due to longer cure

schedules and high monomer cost.

Vinylester resins, a relatively new

addition in the family of thermosetting

resins, is usually produced by the reaction

between epoxy resin and an ethyleni-

cally unsaturated carboxylic acid, with

commonly used acids such as acrylic

and methacrylic acid. Vinylester resinscombine excellent chemical resistance,

good thermal and mechanical properties,

and the relative ease of processing and

rapid cure characteristics of polyester

resins. These have have better moisture

resistance than epoxies when cured at

room temperature. Vinylester resins

are similar in their molecular structure

to polyesters, but differ in that the reac-

tive sites are positioned at the ends of

the molecular chains, allowing for the

chain to absorb energy. This results in

a tougher material when compared to

polyesters.

COMPOSITE PROCESSING

The primary drivers for the selection

of the appropriate process technology



Table B. Properties of Selected Natural and Manmade Fibers

Tensile ElasticDensity Elongation Strength Modulus

Fiber (g/cm3

) (%) (MPa) (GPa) ReferenceCotton 1.51.6 7.08.0 400 5.512.6 6,7

Jute 1.3 1.51.8 393773 26.5 6

Flax 1.5 2.73.2 5001,500 27.6 4

Hemp 1.47 24 690 70 4

Kenaf 1.45 1.6 930 53 4

Ramie 3.63.8 400938 61.4128 8

Sisal 1.5 2.02.5 511635 9.422 8

Coir 1.2 30.0 593 4.06.0 9

Softwood Kraft Pulp 1.5 4.4 1,000 40.0 9

E-glass 2.5 0.5 2,0003,500 70.0 9

S-glass 2.5 2.8 4,570 86.0 9

Aramid (Std.) 1.4 3.33.7 3,0003,150 63.067.0 9

Carbon (Std. PAN-based) 1.4 1.41.8 4,000 230240 9

fiber in order to soften and separate the fibers by partial rotting. This process can beaccomplished through several methods where moisture, microorganisms, or chemistrybreak down the bark tissue that binds the fiber and nonfiber portions, making the fiberseasier to separate, during which time the retting process removes the hemicellulose andlignin components. The following retting processes are the most prominent in use today,

and each has certain advantages. Dew retting occurs when the stalks are left in the field so that rain, dew, or irrigationis used to keep the stems moist. This may take up to five weeks and produces a coarsefiber with a light brown color. Water retting occurs when stems are bundled and thensubmerged in water so that bacteria break down the pectin. This takes seven to ten daysand produces a quality fiber. Warm-water retting occurs when bundles are soaked for24 hours, after which the water is replaced. Heat is then applied to warm the batch forthe next two or three days. This results in a uniform, clean fiber. Green retting is an all-mechanical process that separates the components and is used when the fiber is neededfor textiles, paper, or fiberboard products. Chemical retting occurs when chemicals areused to dissolve the pectin, allowing the components to be separated. This shortens thetime to as little as 48 hours when the next process can then be instigated, and produces ahigh-quality product. Although the natural retting process is lengthy, the resulting fibers have many desirablecharacteristics. The chemical retting process is quick but affects several properties,

including a loss in tenacity, color, and luster as compared to the bacterially retted fibers. Natural reinforcing fibers can be modified by a variety of physical and chemical methodsto correct for fiber deficiencies; fibers can be treated to promote bonding and adhesion,dimensional stability, and thermoplasticity. The physical methods for modifying naturalfibers such as calendaring, stretching, thermo-treatment, and weaving or integrationinto yarns do not change the chemical composition of the fiber. Rather, these changethe structural and surface properties of the fiber and thereby influence the mechanicalbonding to polymers. Surface modification of natural fibers can be used to optimizeproperties of the fiber-matrix interface.

for natural-fiber composite manufacture

include the final desired product form,

performance attributes, cost, and ease

of manufacturing. It is imperative to

fully understand the interrelationships

between materials, feed form of the raw

ingredients, process technology, and

the final part design to obtain a quality,

robust, and repeatable manufacturing

process. Several factors must be con-sidered in selecting a process. One must

insure: that the fiber is distributed evenly

within the matrix, that there is adequate

compatibility between the hydrophobic

matrix and hydrophilic fibers, that fiber

attrition is minimized due to processing

to insure reinforcement, that the desired

fiber orientation effects will be imparted,

that thermal stability of the fiber is

maintained throughout the processing

step, and that the moisture inherent

within the fiber is at the desired level,

minimizing problems with swelling or

part distortion.The control of moisture in the fiber and

the effect of moisture after molding are

primary considerations in natural-fiber

composites in automobiles. Three factors

determine the rate at which moisture is

removed from natural fibers: tempera-

ture, relative humidity, and air velocity.

It is quite costly to dry natural cellulose

fiber to less than 1 percent moisture, but

the -OH group in water is more reactive

than the -OH group available in the fiber

components, rendering hydrolysis to be

faster than substitution. The most favor-

able condition for surface reaction isone that requires a trace of moisture and

where the rate of hydrolysis is relatively

slow. The ability to control and minimize

energy input during this process is one

opportunity foreseen with the process-

ing of natural-fiber materials. Similarly,

the ability to eliminate water absorption

during service of natural-fiber-based

composite components is paramount in

industrial applications. For example, it

has been shown in sisal fiber/unsaturated

polyester composites that storage inwater will result in a reduction of up to

50% in flexural modulus.13

Compounding processes that blend

the natural fibers with a thermoplastic

matrix are gaining wide acceptance

due to the high degree of consistency

feasible in the pellet form. The purpose

of a compounding operation is to pro-

duce a pelletized feed stock that can be

processed further, similar to any other

thermoplastic processing technique,

such as injection molding, extrusion, or

thermoforming. There are several types

of compounding processes, including

extrusion, kneading, and high-shear

mixers.

In extrusion, compounded material is

fed into the heated barrel of the extruder

and is heated to promote thermoplastic

flow. Types of extruders include twin-

screw, which can be co-rotating and

counter rotating, and planetary extruders,

including single-screw. All essentially

achieve the same goals: material feed,

heat application, dispersive mixing,

distributive mixing, devolatilization, and

material extrusion through a die.

With kneading, continuous kneading

mixers consist of two long intermeshing

rotors in a heated barrel. Batch-style,

kneading-type compounding equipment

contains two low-speed high-torque

kneading rotors that control mixing time,

temperature, and energy consumption

and is combined with an extruder and

pelletizer to produce pellets.

High-shear mixers use robust mixers



Table IV. Example of Interior and ExteriorAutomotive Parts Produced from Natural

Materials4,14

Vehicle Part Material Used

InteriorGlove Box Wood/cotton fibers

molded, flax/sisal

Door Panels Flax/sisal with

thermoset resin

Seat Coverings Leather/wool backing

Seat Surface/Backrest Coconut fiber/natural

rubber

Trunk Panel Cotton fiber

Trunk Floor Cotton with PP/PET

fibers

Insulation Cotton fiber

Exterior

Floor Panels Flax mat withpolypropylene

Table III. Material Properties ofGlass-Fiber-Reinforced Unsaturated

Polyester and Natural-Fiber-ReinforcedUnsaturated Polyester Composites15

Glass Natural Fiber Fiber

Property (30 wt.%) (35 wt.%)

Flex Strength (MPa) 80 70

Flex Modulus (GPa) 6.0 6.0

Elongation at 2.2 1.9

Break (%)

Impact Strength 38 20 (kJ/mm2)

Density (g/cm3) 1.54 1.42

such as a thermo-kinetic batch-style

machine when fiber length is not a con-

cern.

Injection molding is a versatile process

and is the most widely used processing

technique for making composite prod-

ucts, particularly where intricate shapes

are needed in cyclic, high-volume pro-duction. The benefits include excellent

dimensional tolerance and short cycle

times coupled with few post-processing

operations. According to BMW, it is

possible to manufacture bio-based com-

posites that are as much as 40 percent

lighter than equivalent injection-molded

plastic parts.14 One of the challenges

posed by injection molding natural-fiber

composites is to produce pellets of a

consistent quality. This has been explored

by both North American and European

injection molding equipment suppliers

through a process called direct long-fiber

thermoplastic (D-LFT) molding. In this

continuous process, first developed for

glass fibers, the fibers are spooled and

fed into a heating zone, where the ther-

moplastic is integrated with the fiber

bundles. These bundles are then cut at a

desired length and fed continuously into

an injection molding hopper, and parts

are molded continuously. It is reasonable

to assume that the recent developments

in producing continuous natural-fiber

roving5could be integrated on a large

scale into the D-LFT process. Several

companies are working this development

area.

Thermoforming is mainly used to

produce natural-fiber-mat thermoplastic

composites. The process takes pre-cut

layers of fiber (or preformed mats that

could comprise random fibers or roving)

and polymer sheet that are inserted in a

heated mold, and consolidates the mate-

rial as heat is transferred through conduc-

tion to melt the thermoplastic. The

thermoplastic flows to penetrate the fiber

component, with pressure applied duringthe heating and cooling phases. After

reaching the melt temperature in a hot

press, the molten hybrid material is

consolidated into a composite in a cold

press, with very rapid processing times

possible via combined heating-cooling

presses in parallel (Figure 1).

Compression molding using thermo-

set polymer matrices is another major

platform used to manufacture large parts

for the automotive industry, producing

light, strong, and thin panels and struc-

tures. The primary advantage of this

process is low fiber attrition and process

speed. A comparison of compression-

molded unsaturated polyester compos-

ites reinforced with glass fiber and with

natural fibers (flax) is provided in Table

III. This indicates that the properties are

comparable with properties with similar

fiber loadings. Another method of com-

pression molding is the sheet molding

compound (SMC) process which has

been used for glass composites for years.

Many variations of compression molding

have been developed that are suitablefor automotive application, and recent

developments to combine extrusion and

compression of thermoplastic compos-

ites, initially with glass fibers, are begin-

ning to enter into the automotive indus-

try. This process extrudes large thermo-

plastic fiber bundles, or pre-heated plugs,

into a compression mold in-situ, and then

the compression molds the part. How-

ever, high capitalization costs will pre-

clude this process from large-scale

insertion into the Tier 1 supply chain inthe near future.

The foaming technique produces

foamed products that can be used in

upholsteries and in insulation applica-

tions. After blending the fiber, thermo-

plastic, and blowing agents, the material

is fed into a single screw extruder using

a special force-fed hopper. The extrudate

that leaves the extruder is passed through

a static diffusion-enhancing mixer to

insure the polymer matrix and blowing

agent have been completely integrated.

The temperature of this process insures

the blowing agent has been decomposed,

and then it is passed through a heat

exchanger; the extrudate then passes

Figure 2. Flax, hemp, sisal, wool, and other natural fibers are used to make 50 Mercedes-Benz E-Class components.16



though a nozzle die to the final prod-

uct.

Finally, thermoset polymer composite

manufacture via resin transfer and

vacuum-assisted resin transfer molding

has gained interest from the automotive

industry. The primary benefits of this

processing platform include compound-

ing at low shear and temperatures with

minimal degradation of the cellulose

fiber. Higher fiber loadings to 70% are

possible, as well as good devolatilization.

However, these processes are meeting

resistance due to the high capital expen-

diture requirements.

AUTOMOTIVE

APPLICATIONS

Interest in bio-based materials, and

specifically, natural-fiber-reinforced

composites, coincides not only with

legislation that has been enacted in large

markets such as the European Union but

with the priority of many major automak-

ers interest in global sustainability. The

definition of sustainability relates to

corporate responsibility, extending from

an automakers responsibility to its work-

ers and customers and beyond. For

instance, DaimlerChryslers sustain-

ability efforts have undertaken unprec-

edented technology development and

technology transfer initiatives involving

the use of bio-based materials in the

Philippines, South America, and South

Africa. DaimlerChrysler has gone one

step further, identifying bio-based mate-

rials as one of the two key parts of its

plan to create a global sustainability

network. The second key part is the use

of renewable energies to replace conven-

tional fuels, which are pursuing a bio-

based automotive supply chain that

includes a network, from the farmer to

the automotive distributor.16 Global

automotive suppliers such as Honda

embarked on using natural-fiber materi-

als, such as wood-fiber parts in the floor

area of the Pilot sport utility vehicle

(SUV), a decision that was driven by

engineering considerations as well as

corporate philosophy. Overall, the vari-

ety of bio-based automotive parts cur-

rently in production is astonishing;

DaimlerChrysler is the biggest proponent

with up to 50 components in its European

vehicles being produced from bio-based

materials (Figure 2).

Uses of natural-fiber reinforcement

have proven viable in a number of auto-

motive parts. Flax, sisal, and hemp are

processed into door cladding, seatback

linings, and floor panels. Coconut fiber

is used to make seat bottoms, back

cushions, and head restraints, while

cotton is used to provide sound proofing,

and wood fiber is used in seatback cush-ions (Table IV). Acaba is used in under-

floor body panels, and other manufactur-

ers are implementing natural ingredients

into their cars as well. For example, the

BMW Group incorporates a considerable

amount of renewable raw materials into

its vehicles, including 10,000 tonnes of

natural fibers in 2004. At General Motors,

a kenaf and flax mixture has gone into

package trays and door panel inserts for

Saturn L300s and European-market Opel

Vectras, while wood fiber is being usedin seatbacks for the CadillacDeVilleand

in the cargo area floor of the GMCEnvoy

and Chevrolet TrailBlazer. Ford mounts

Goodyear tires that are made with corn

on its fuel-sipping Fiestas in Europe.

Goodyear has found that its corn-infused

tires have lower rolling resistance than

traditional tires, so they provide better

fuel economy. The sliding door inserts

for the FordFreestarare made with wood

fiber. Toyota has interest in using kenaf

to makeLexus package shelves, and has

incorporated it into the body structure

of Toyotas i-foot and i-unit concept

vehicle.

Currently, there is a great deal of global

research into the insertion of natural-fiber

composites, and automakers are produc-

ing prototypes that provide a hint into

the future of manufacturing. For exam-

ple, the U.S. Agricultural Research

Service has been developing industrial

Figure 3. On its (a) HarvesterWorks combines,John Deere has replaced steel gull-wing doorswith (b) soy-resin body panels. Photos courtesyof Richard Wool, University of Delaware, withpermission.

a

b

Figure 4. A front-end grillopening reinforcement for theFord Montagetrger.17



and commercial uses for a wide variety

of agricultural products, including waste

items, and groups such as the Soybean

Checkoff and the National Corn Grow-

ers Association that focus on researching

and promoting new markets for mem-

bers crops are supporting research

efforts into new applications for their

feed sources.16

In addition, Tier 1 sup-pliers are actively involved in producing

prototype parts: Visteon has developed

a system for making flax-based instru-

ment panels; Composite Products has

developed a process to produce door

panels from flax; Findlay Industries,

which makes the cargo area floors for

the GM and Honda SUVs and the pack-

age shelves for Saturn and Opel, also

manufactures headliners for Mack

Trucks that are made with a hemp, flax,

kenaf, and sisal mixture; and soy-resin

body panels have been developed that

are currently used on John Deere tractors

(Figure 3).

As mentioned previously, many

experimental parts of complex geom-

etries are currently either in the prototype

or production stages. Figures 4 and 5

illustrate the demanding applications that

can be met with natural-fiber compos-

ites. Figure 4 depicts the front end grill

reinforcement for a FordMontagetrger

produced from a hemp-polypropylene

composite, and Figure 5 depicts the

underbody panel compression molded

from flax-polypropylene for an A-Class

DaimlerChrysler automobile.

CONCLUSIONS

In the last decade, natural-fiber com-

posites have experienced rapid growth

in the European automotive market, and

this trend appears to be global in scale,

provided the cost and performance is

justified against competing technologies.

However, mass reduction, recyclability,

and performance requirements can be

met today by competing systems such

as injection-molded unreinforced ther-

moplastic. Natural-fiber composites will

continue to expand their role in automo-tive applications only if such technical

challenges as moisture stability, fiber-

polymer interface compatibility, and

consistent, repeatable fiber sources are

available to supply automotive manu-

facturers.

Efforts underway by Tier I and II

automotive suppliers to explore hybrid

glassnatural-fiber systems, as well as

applications that exploit such capabili-

ties as natural-fiber sound dampening

characteristics, could very well have

far-reaching effects. In addition, the cur-

rent development underway of bio-based

resins such as polyhydroxyalkanoate

(PHA) biodegradable polyesters and

bio-based polyols could provide fully

bio-based composite options to future

automotive designers. In short, the devel-

opment of the natural-fiber composite

market would make a positive impact

on farmers and small business owners

on a global scale, reduce U.S. reliance

on foreign oil, improve environmental

quality through the development of a

sustainable resource supply chain, and

achieve a better CO2balance over the

vehicles lifetime with near-zero net

greenhouse gas emissions.

References

1. Directive 2000/53/EC of the European Parliamentand of the Council of 18 September 2000 on End-

of Life Vehicles, Official Journal of the EuropeanCommunities(21 October 2000).2. M. Patel et al., Env. Assessment of Bio-BasedPolymers and Natural Fibers (Netherlands: UtrechtUniversity, 2002).3. Natural Fiber Composite Market Report (LittleFalls, New Jersey: Kline, & Company, 2004).4.Natural Fibers, Biopolymers, and Biocomposites, ed.A.K. Mohanty, M. Misra, and L.T. Drzal (Boca Raton,FL: CRC Press, 2005).5. Banana Fibers Strengthen Exterior Auto Part, Adv.Mat. & Processes, 163 (9) (2005), p. 8.

6. David L. Lewis, Henry Ford and His MagicBeanstalk, The Soy Daily, www.thesoydaily.com/MOShenryford/henryfordDL1.asp (downloaded 8August 2006).7. H. Hutchinson, Research Aims to Make the Land ofthe Automobile Run More Efficiently, Mech. Engr.(July2006), p. 29; www.memagazine.org/july06/features/easygas/easygas.html.8. S.J. Eichhorn et al., Review: Current InternationalResearch into Cellulosic Fibers and Composites, J. ofMat. Sci.,36 (2001), pp. 21072131.9. J. George, M.S. Sreekala, and S. Thomas, AReview on Interface Modification and Characterizationof Natural Fiber Reinforced Plastic Composites, Poly.Eng. and Science, 41 (8) (2001), pp. 14711485.10. A. Bismark et al., Surface Characterization of Flax,Hemp and Cellulose Fibers: Surface Properties and

the Water Uptake Behavior, Polymer Composites, 23(5) (2002), pp. 872895.11. C. Baille, editor, Green Composites(Boca Raton,FL: CRC Press, 2004).12. A.K. Bledzki and J. Gassan, CompositesReinforced with Cellulose Based Fibers, Prog. Poly.Sci.,24 (1999), pp. 221274.13. N.E. Zafeiropoulous et al., Engineering andCharacterization of the Interface in Flax Fibre/Propylene Composite Materials. Part I. Developmentand Investigation of Surface Treatments, Composites:Part A, 33 (2002), pp. 10831093.14. B. Singh, A. Verma, and A. Gupta, Studies onAdsorptive Interaction Between Natural Fiber andCoupling Agents, J. Appl. Polym. Sci., 70 (1998), pp.18471858.

15. T.P. Schloesser, Natural Fiber ReinforcedAutomotive Parts, Natural Fibers, Plastics andComposites, ed. F.T. Wallenberger and N. Weston(Dordrecht, The Netherlands: Kluwer, 2004).16. Sue Elliott-Sink, Special Report: Cars Made ofPlants (12 April 2005), www.edmunds.com/advice/fueleconomy/articles/105341/article.html(downloaded28 August 2006).17. http://mbase.aixhibit.de/nfibrebase/ref_db/main.php?view=detail&position=3, downloaded 10 August200618. http://mbase.aixhibit.de/nfibrebase/ref_db/main.php?view=detail&position=1 , downloaded 10 August2006.

James Holbery is a senior scientist with the Energy

Science and Technology Department at PacificNorthwest National Laboratory in Richland,Washington. Dan Houston is a technical specialistwith the Manufacturing and Processing RIC

Department at Ford Motor Company in Dearborn,Michigan.

For more information, contact James Holbery,Pacific Northwest National Laboratory, EnergyScience and Technology Department, 509 BattelleBlvd., Richland, WA 99352; e-mail [email protected].

Figure 5. The underbody of a Daim-

lerChrysler A-class, compressionmolded flax-propopylene.18

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