Since the industrial revolution, humans have used metals. Nature uses polymers. Nearly all biological systems are made of polymers. These polymers not only perform mechanical functions like wood, bone, cartilage and leather, but also regulate chemical reactions (leafs, veins, cells). These natural polymers have been used by humans for thousands of years. They have only recently learned how to make their own polymers. Bakelite, celluloid and formaldehyde were early attempts. They were weak and floppy. It is still a hallmark of simple synthetic polymers that the stiffness of a section is lower than that of metal, wood, or bone. Wood and bone are composites. They are made up stiff fibres or particles embedded in a matrix from simple polymer.
Composites are also easy to make. Industries that make carbon-fibre or high-performance glass (GFRP, CFRP and KFRP), enjoy a higher growth rate (over 10% annually) than any other sector of materials production. These materials are strong, light and stiff. They are expensive but they are being used more in transport, aerospace and sports goods.
Aerospace advanced materials: How to seal and join them.
The new polymers are just as exciting as the composites. New polymers can be made by crystallizing, cross-linking or orienting chains to make them as stiff as aluminum. They will soon find their way into mass production. New processing methods can give polymers resistance to heat and mechanical deformation. This opens up new applications for polymers that have already made inroads into markets once dominated by metals. Designers cannot afford to overlook the many opportunities offered by composites and polymers.
It is wrong to assume that metal components can be simply replaced with components made of newer materials. The new component must be carefully designed as polymers are more flexible, stronger, and tougher than metals. Composites are strong and stiff, it’s true. Composites are strong and stiff, but they can be very anisotropic. Because they are bound with polymers, their properties may change dramatically when there is a slight temperature change. A good knowledge of the properties and origins of polymers is essential for proper design.
For the following benefits, fuel tank sealants, corrosion inhibitor sealants windshield and canopy sealants, high temperature sealants, firewall sealants, electrically conductive sealants, low adhesion sealants for access doors, fast cure sealants for flight line repairs and jointing compounds all use the new technology of aerospace polymer sealants.
For high-performance sealants, polysulphide sealants are made using one of the oldest polymer technologies. They are still widely used, despite their declining popularity.
Polysulfides chemically are liquid polymers that contain sulfur. Other modified polysulfides are called polythioethers. They can be cured with manganese dioxide or lead oxide. You can make polysulfide sealants as a one- or two-component product.
Most commonly, polysulphide sealants can be used to make insulating glass windows. They are excellent at resisting jet fuel and can be used in expansion joint sealants in aircraft construction as well as in other aerospace applications such sealants for aircraft fuel tanks, windshields, and sealants for aircraft fuel tanks. Polysulfides are often used to make electrically conductive sealants.
Polyurethane sealants are made from an organic compound that has excellent corrosion and moisture resistance. Polyurethane sealant can be used in both commercial and industrial applications. Polyurethane can also be used as a coating or as an adhesive for heavy duty applications.