Natural fibres have been used to reinforce materials for over 3,000 years. More recently they have been employed in combination with plastics. One of the earliest examples (1950) was the East German Trabant car, the body was constructed from polyester reinforced with cotton fibres.

Currently many types of natural fibre are being investigated for use in plastics including: flax, hemp, jute, straw, wood fibre, rice husks, wheat, barley, oats, rye, cane (sugar and bamboo), grass, reeds, kenaf, ramie, oil palm empty fruit bunch sisal, coir, water hyacinth, pennywort, kapok, paper-mulberry, raphia, banana fibre, pineapple leaf fibre and papyrus. Natural fibres have the advantage that they are renewable resources and have marketing appeal. Many, such as pineapple leaf fibre are natural waste products and hence available at minimal cost. However, there can be problems with the technical properties of reinforced materials - moisture absorption is generally high and impact strength is relatively low.

The Asian markets have been using natural fibres for many years. For example, jute is a common reinforcement in India. Natural fibres are increasingly being used in the automotive industry in Europe. In 1999 consumption was 21,300 tons and by 2000 this had risen to 28,300 tons. Packaging is a further application in Europe, particularly in Germany. In North America wood/polymer composites amount to a 300,000 ton/year market for use in building and garden products, particularly decking.

Wood fibres can be subdivided into two types - hardwood and softwood. These have difference properties. Steam explosion is a common pretreatment for wood fibres as it can increase the specific surface and improve properties of composites, however it can also have a negative effect. A compatibiliser such as maleic anhydride can be more beneficial.

This report examines the different fibre types available and the current research. The authors have cited several hundred references to the latest work on properties, processing and applications. The different methods of fibre pretreatment are examined, together with fibre properties, chemistry and applications.

This review is accompanied by summaries of papers from the Polymer Library. These papers are referenced in the report and are also indexed to allow the reader to search for information on specific topics.

Key features

CONTENTS

1. Survey of Natural Fibre Composites
2.1 Description of Fibres
2.1.1 Natural Fibres
2.1.2 Wood Fibres
2.1.3 Man-Made Cellulosic Fibres
2.1.4 Nanofibres
2.2 Structure and Chemical Constituents of Fibres
2.2.1 Cellulose
2.2.2 Lignin
2.2.3 Further Components
2.3 Characteristics
2.3.1 Mechanical
2.3.2 Physical
2.3.3 Chemical

2. Cellulose Based Fibres

3. Methods of Surface Treatment of Natural and Wood Fibres
3.1 Physical Methods
3.1.1 Corona Treatment
3.1.2 Cold Plasma Treatment
3.2 Chemical Methods
3.2.1 Change of Surface Tension
3.2.2 Impregnation of Fibres
3.2.3 Mercerisation
3.2.4 Chemical Coupling

4. Processing of Natural Fibre Reinforced Plastics
4.1 Thermoplastics
4.1.1 Extrusion
4.1.2 Injection Moulding
4.1.3 Compression Moulding
4.1.4 Express Process
4.1.5 Mixing
4.2 Thermosets
4.2.1 Resin Transfer Moulding (RTM)
4.2.2 Sheet Moulding Compound (SMC)

5. Properties of Natural and Wood Fibre Composites
5.1 Mechanical Properties
5.1.1 Tensile Properties
5.1.2 Flexural Properties
5.1.3 Impact Properties
5.2 Physical Properties
5.2.1 Water Absorption
5.2.2 Swelling
5.2.3 Moisture Content
5.3 Biological Properties
5.3.1 Fungi
5.3.2 Bacteria

6. Biologically Degradable Composite Materials
7.1 Automotive Applications
7.2 Building Applications
7.3 Furniture and Panels
7.4 Aerospace Applications
7.5 Others

7. Applications of Natural Fibre Reinforced Polymers

8. Recent Developments in Natural and Wood Fibre Reinforcement of Polymers

9. Conclusion