Plastics

Very few plastics are used in their commercially pure state. Additives currently used include the following: Finely divided rubbers added to more brittle plastics to add toughness; glass, carbon, boron, or metal fibers added to make composite materials with good stress-strain properties and high strength; carbon black or silica added to improve resistance to tearing and to improve stress-strain properties; plasticizers added to soften a plastic by lowering its glass transition temperature or reducing its degree of crystallinity; silanes or other bonding agents added to improve bonding between the plastic and other solid phases; and fillers such as fire retardants, heat or light stabilizers, lubricants, or colorants.

Filled or reinforced plastics are usually referred to as composites. However, some composites includes neither fillers nor reinforcement. Examples are laminates such as plastic sheets or films adhered to nonplastic products such as aluminum foil, cloth, paper or plywood for use in packaging and manufacturing. Plastics may also be metal plated.

Plastics, both glassy and rubbery, may be crosslinked to improve their elastic behavior and to control swelling. Polymers may also be combined to form blends or alloys.