Today, natural fiber reinforced biocomposites are mainly applied in the automotive industry. From 1996 to 2000 year, the use of natural fibers in the European automo­tive sector has increased from 5000 to 28,000 tons, respectively. It is evident that flax, hemp and kenaf fibers are among the most applied types of natural fibers. According to automotive industry reports, about 5 to 10 kg of natural fibers are incorporated into every European car5. This figure includes flax fibers, hemp, jute, sisal and kenaf, which all are used in composite production41. The use of flax was reported by the suppliers to be circa 1.6 k ton in 1999, and is expected to rise to 15 to 20 k ton in the near future. The German and Austrian car industry alone employed

8.5 to 9 k ton of flax fibers in 200142. The introduction of every new car model in­creases the demand, depending on the model, by 0.5 to 3 k ton per year.

The automotive industry gives a long list of presumed benefits of natural fiber composites, which includes the general reasons for the application of natural fibers as discussed briefly in the previous sections:

• Low density, which may lead to a weight reduction of 10 to 30%.

• Acceptable mechanical properties, good acoustic properties.

• Favorable processing properties, for instance low wear on tools.

• Options for new production technologies and materials.

• Favorable accident performance, high stability, less splintering.

• Favorable ecobalance for part production.

• Favorable ecobalance during vehicle operation due to weight savings.

• Occupational health benefits compared to glass fibers during production.

• No off-gassing of toxic compounds (in contrast to phenol resin bonded wood and recycled cotton fiber parts).

• Relatively easy recycling (it is not clear whether they mean thermal recycling here).

• Price advantages both for the fibers and the applied technologies.

Obviously the production and application of natural fiber reinforced parts also

brings along some difficulties:

• For the production of nonwovens: presence of shives, dust, very short fibers.

• Uneven length distribution and uneven decortications of the fibers (especially for nonwovens).

• Irreproducible fiber quality combined with availability.

• Variations in nonwoven quality and uniformity due to fiber quality variation.

• Moisture sensitivity, both during processing and during application.

• Limited heat resistance of the fibers.

• Specific smell of the parts.

• Limited fire retardancy.

• Variations in quality and uniformity of produced parts.

• Possible molding and rotting.

TABLE 10.10 Application of Natural Fibers in Automotive Parts

Manufacturer Model Application (dependent on model)

Audi A3, A4, A4 Avant, A6, A8, Roadster, Coupe

Seat back, side and back door panel, boot lining, hat rack, spare tire lining

BMW 3, 5 and 7 Series and others

Door panels, headliner panel, boot lining, seat back

Daimler/ A-Series, C-Series, E-Series, S-Series

Chrysler Door panels, windshields/dashboard, business table, pillar cover panel

Fiat Punto, Brava, Marea, Alfa Romeo 146, 156

Ford Mondeo CD 162, Focus

Door panels, B-pillar, boot liner

Opel Astra, Vectra, Zafira

Headliner panel, door panels, pillar cover panel, instrument panel

Peugeot New model 406

Renault Clio

Rover 2000 and others

Insulation, rear storage shelf/panel

Saab Door panels

SEAT Door panels, seat back

Volkswagen Golf A4, Passat Variant, Bora

Door panel, seat back, boot lid finish panel, boot liner

Volvo C70, V70

The higher volume fraction of lower density natural fibers in natural fiber com­posites also reduces the weight of the final component. Joshi et al. have reported that natural fiber composite components based on hemp fibers applied in Audi-A3 car resulted in 20-30% reduction in weight43. In fact, natural fiber composites are be­coming popular in automotive applications because of this weight reduction. Lower weight components improve fuel efficiency and in turn significantly lower emis­sions during the use phase of the component life cycle. It was estimated that the coefficient for reduction in fuel consumption on gasoline powered vehicles ranges from 0.34 to 0.48 L/(100 kg x 100 km) in the New European Driving Cycle, while the saving on diesel vehicles ranges from 0.29 to 0.33 L/(100 kg x 100 km). In other words, over the lifetime travel of 175,000 km an automobile, a kilogram of weight reduction can result in fuel savings of 5.95-8.4 L of gasoline or 5.1-5.8 L of diesel, and corresponding avoided emissions from production and burning of these fuels.

Mueller and Krobjilowski have studied application of nonwoven composite fabrics in automotive interior components. They have compared carded and nee­dle-punched nonwoven fabrics of 750 g/m2 produced from 50/50 flax/PP, hemp/PP and kenaf/PP5. They concluded that fine fibers improve the mechanical properties on natural composites. For that purpose cotton fiber composites were prepared as acoustic materials and compared with synthetic based composites. The type of res­ins slightly influence on the acoustic properties, while composite thickness depends from the type of synthetic composite should be replaced.

Besides the automobile industry, a growing number of the nonautomotive ap­plications and products are being presented for natural fiber biocomposites. Some of these applications are in the field of energy and impact absorption, such as floor cov­erings that use excellent acoustic properties of the natural fibers, bicycle helmets, security helmets for the construction area, and monitor housings for the computers5.

The construction sector and infrastructure are the second large sector with huge potential for increased applications. This application field is particularly interesting for rural and agri-cultural societies as well as for the countries where natural fiber production is very high.

Other uses of natural fiber based composites are for various furniture elements such as, deck surface boards, and picnic tables42.

10.4 CONCLUSIONS

It is very clear and evident that natural fiber reinforced biocomposites offer a huge potential for future applications not just in the automotive industry, but also in other sectors such as construction, infrastructure and furniture production. The main chal­lenges related to the lower moisture absorption, higher fire resistance, better me­chanical properties, durability, variability, and manufacturing/processing of natural fiber reinforced biocomposites are being addressed by many recent research efforts. Moisture absorption can be reduced through surface modifications of fibers and/or by special coatings. Fire resistance can be improved by the use of in tumescent coat­ings, which eventually may also be made from renewable resources. Mechanical properties and durability are the main areas of research into natural fiber reinforced biocomposites, and many proposed solutions have been found to improve the fiber/ matrix interface. Fiber variability is itself largely uncontrollable, but the develop­ment of quality assurance protocols and diversification of fiber growing sources can address the issue before the fibers reach composite manufacturers. Natural fi­ber reinforced biocomposites have been successfully adapted to nearly every major manufacturing process currently used with synthetic composites, usually with few or no modifications to the processes themselves.

New types of all-cellulose composites were successfully prepared by a surface selective or partial dissolution method of cotton woven textile fabrics. Two different media were used for the fiber surface treatment: i) alkaline scouring with bleaching and ii) enzymatic scouring with acid and alkali pectinases combined with bleaching.

Therefore, future research in the field of natural fiber reinforced biocomposites for infrastructure applications would be most beneficial if directed at one of the highlighted challenging areas, particularly focused on continuing to improve me­chanical properties, moisture resistance, and durability.

KEYWORDS

Biocomposites

Cellulose

Mechanical Properties Natural Fibers PLA

Polymer Matrix Renewable Resources