The evolution and improvement of plastics that are being achieved day by day are spectacular. Examples of composite plastics are reinforced and laminated plastics.
Reinforced plastics
They are made up of two types of materials: a reinforcing material, which confers tensile strength, and some type of plastic of those studied so far. Both are joined (mixed) to form a whole.
The reinforcement material is usually fiberglass, organic fibers, synthetic fibers, metallic fibers, carbon fibers, etc.
The products obtained have properties superior to those used for their manufacture. Thus, for example, if we reinforce a polyester (whose tensile strength is 7 kg/mm2 ) with fiberglass, whose tensile strength is very low (5 to 6 kg/mm2 ), we obtain a product that can reach 50 kg/mm2 .
New materials are being invented and tested. One of the strongest discovered so far is called Kevlar. It is very difficult to machine and cut, and is mainly used in the manufacture of aircraft, communications satellites, helmets, bulletproof vests, armor and other applications where strength is of paramount importance.
Laminated plastics
Unlike reinforced plastics, in laminated plastics the layers of both materials are overlapped or bonded, but not mixed. The most important are:
- Plastic-glass. It consists of coating the glass with a very thin layer of transparent plastic. This improves resistance to shocks, prevents brittleness, and at the same time serves as a thermal insulator for hot and cold beverages. A recent invention is the Plastishield bottle.
- Plastic-metal. Many metallic products are coated with a thin layer of plastic. Thus, it is worth mentioning tin cans, which have a thin layer of epoxy or phenolic resins, to avoid possible oxidation.
- Plastic-paper or cardboard. It consists of covering the paper or plastic with a thin layer of plastic (generally low density polyethylene) on both sides. Some applications are found in Tetra Pak cartons, book pulp, wrappings, etcetera.
- Plastic-fabrics. They have great application in the field of synthetic leathers (leather goods and upholstery), canvas, etcetera.
- Plastic-plastic. Some containers containing food products, cosmetics, beverages, etc., are usually made by combining several layers of different plastics to obtain an improved product (with high external hardness and high internal toughness).