Fantastic Plastic Make plastic out of a protein found in milk. Learn about the history of plastics, the materials and polymers used in the manufacturing process, and the methods used to shape plastic into objects. Read More Celluloid, the first synthetic plastic, was invented in the 1860s. It was made by mixing cellulose, the material that makes up the cell walls of plants, with camphor, a crystal-like substance found in the wood and leaves of the camphor tree. For many years, celluloid was the only synthetic plastic available. In the late 1800s, casein was discovered. Today, casein is mainly used in the button industry. In the 1900s, scientists discovered that petroleum could be easily processed into raw materials that could be used in the manufacturing of plastics, and petroleum has remained the main product used in plastics production today. The raw materials from petroleum are monomers (small molecules) that are combined, in chemical reactions, with other monomers (natural or synthetic) to create the polymers (large molecules) that are the building blocks of various types of plastics, such as silicones, polyesters, polyurethanes, and acrylics. In a plastics plant, the polymers emerge as plastic pellets or beads, which are then heated and shaped into plastic objects. There are several methods used to shape plastic liquids into plastic objects. One method is extrusion molding. Heated plastic is squeezed through a mold that is open at both ends. The heated plastic goes in one end of the mold, and as it comes out the