Composite materials (composites) are made when two or more materials with different properties are combined to produce a new material. The physical and chemical properties of each of the constituent materials remain distinct in the new material. These constituent materials work synergistically1 to produce a composite material that has improved properties when compared with the individual constituent materials.
Modern composites
In modern society, composites are commonplace. Fibreglass, developed in the late 1930s, is a well known modern composite. It consists of fine glass fibres woven into a cloth then bonded together with a plastic2 or resin3. The glass makes the material strong, and the plastic makes it more or less flexible. Fibreglass is used for making surfboards, swimming pools and spas, boat hulls and a wide variety of exterior automobile parts.
The different materials that make up a composite function as either the matrix or the reinforcement. The matrix surrounds and binds together a cluster of fibres or fragments of a material with different properties – the reinforcement. At least one of each type of material is needed to make a composite. In fibreglass, the fine glass fibres are the reinforcement and the matrix is the plastic or a resin. Other common composites include plywood (wood veneer sheets and glue), concrete (loose stones and cement) and carbon fibre4 composites (carbon fibre and polymer5 resin).
Increasingly, researchers are exploring biodegradable6 materials to use in making composites. Some are looking into how plant residues (such as kiwifruit or harakeke7) can be used. These new biocomposites have less impact on the environment than materials such as plastic and rubber, as the plant materials are from a sustainable8 resource and the end product is designed to degrade. Research developments like this mean that there may be a future where we don’t have to rely on petroleum-based plastic products.
ZESPRI biospife
The biospife is made from an innovative bioplastic containing biomatter from ZESPRI’s kiwifruit waste stream. The biospife is the result of a collaborative project between ZESPRI and Scion. Read more about the biospife in the Biospife story.
Harakeke surfboard
The harakeke surfboard was made with harakeke fibre replacing traditional glass fibres in fibreglass. The project was undertaken by Biopolymer Network to demonstrate that it is possible to make a water-resistant composite material using biomaterials.
Composites in nature
Composites also exist in nature. Wood is a composite material made of cellulose9 and lignin10. The long fibres of cellulose (the reinforcement) are held together by the matrix (lignin). The binding strength of the lignin is what makes a piece of wood much stronger than cotton, which is also made of cellulose.
A seashell is a composite material made of calcium carbonate crystals (the reinforcement) embedded in a scaffold of protein11 and carbohydrate12 fibres (the matrix).
The reinforcement
The reinforcement is the material that provides strength, rigidity and the ability to carry a load. Glass fibres are the most common reinforcement material. However, many advanced composites use fibres of pure carbon13. Carbon fibres are much stronger than glass fibres, but they are more expensive to produce.
Carbon fibre composites (often simply called ‘carbon fibre’) are light and strong. They are used in a variety of products including aircraft, high-end bike frames, golf clubs and even in bone14 and joint replacements.
The matrix
The matrix is usually a viscous15 material that hardens to give shape to the composite product and to protect the fibres from damage. Modern composites often use plastic to hold the reinforcement together. Plastics can be made malleable16 at high temperatures and moulded into different shapes. The plastic then hardens as it cools.
For some highly specialised purposes, advanced ceramics17, carbon or metals are used as the matrix. Carbon is used for products that are exposed to friction and wear, for example, disc brake pads. The disc brake pads have a framework of carbon fibres (the matrix) in-filled with silica18 (the reinforcement). The resulting material has high wear characteristics as well as being thermally resistant
Why use a composite?
Composite materials are often matched to a particular application. By carefully choosing the reinforcement, the matrix and the process that brings them together, the properties of composites can be tailored to meet specific requirements. Composites have the advantage that they can be moulded into complex shapes. This is a great advantage when producing products such as surfboards, boat hulls or bike frames.
YikeBike
The Carbon YikeBike is an example of a bike whose frame is made from a composite material – carbon fibre. As an urban bike intended for commuter use, the YikeBike needed to be light and strong, to be foldable and portable. The original YikeBike (the Carbon) is extremely light, weighing just 11.5 kg, and it’s also strong, being able to carry up to 100 kg. Find out more about this radical bike redesign.
- synergy: The working together of two things (food components, for example) to produce an effect greater than the sum of their individual effects.
- plastic: A synthetic material made from a wide range of organic polymers (such as polyethylene, PVC and nylon) that can be moulded into shape while soft and then set into a rigid or slightly elastic form.
- resin: A solid or liquid synthetic organic polymer used as the basis of plastics, adhesives, varnishes or other products.
- carbon fibre: A material consisting of thin strong crystalline filaments of carbon often used as a strengthening material in composites.
- polymer: The name given to a family of chemical compounds with a high molecular weight that have a long chain of smaller, identical linked molecules (called monomers). Cellulose is a naturally occurring polymer, although there are many manmade polymers such as nylon. Polymers are especially valued by many industries where they are the essential ingredient of plastics, concrete, glass and rubber. The process by which molecules are linked together to form polymers is called polymerisation.
- biodegradable: The ability of a substance to be broken down physically and/or chemically in the environment into harmless compounds. For example, many chemicals, food scraps, cotton, wool and paper are bio-degradable; plastics and polyester generally are not.
- harakeke: New Zealand flax (Phormium tenax).
- sustainable: A way of using natural products so they are available for future generations.
- cellulose: A stringy and fibrous carbohydrate (a type of polymer made up of glucose molecules) that is the main constituent of the cell walls of plants, especially important in wood, cotton and hemp etc. Used in the manufacture of paper, cotton and other textiles, kapok, cellophane, rayon, explosives and some pharmaceuticals.
- lignin: A molecule produced by plants that provides structure for the cell wall. It supports vascular plant stems and is the substance that binds wood fibres together, making them rigid and strong.
- protein: Any of a large class of complex compounds that are essential for life. Proteins play a central role in biological processes and form the basis of living tissues. They have distinct and varied three-dimensional structures. Enzymes, antibodies and haemoglobin are examples of proteins.
- carbohydrate: Any of a large group of energy-producing compounds, including sugars and starches, that contain carbon, hydrogen and oxygen.
- carbon: A non-metal element (C). It is a key component of living things.
- bone: A specialised form of connective tissue. The presence of the mineral hydroxyapatite helps to give bone its strength and density.
- viscous : Having a thick, sticky consistency between solid and liquid.
- malleable: 1. Capable of being shaped or formed. 2. Easily hammered into shape.
- advanced ceramics: Substances based on metal oxides like alumina (Al2O3), inorganic non-metal oxides like silica (SiO2) and nitrides like silicon nitride (Si3N4). Unlike traditional clay-based ceramics (pottery), advanced ceramics do not necessarily need to be earth-derived.
- silica: Informal name for the chemical silicon dioxide (SiO2). A component of rocks that can make them look white in appearance, for example, pumice has high silica content.
