Plastics are high‑molecular‑weight resins obtained through polymerization, starting from petroleum or natural gas that is refined and cracked into various petrochemical feedstocks. They belong to the class of polymeric materials. In the early days, coal‑tar products and calcium carbide were the primary raw materials; today, petroleum‑ and natural‑gas‑derived feedstocks such as ethylene, propylene, benzene, formaldehyde, and urea are predominantly used.
Its main constituent is resin. The term “resin” originally referred to lipid substances secreted by plants and animals, such as rosin and shellac; today, it denotes a high‑molecular‑weight polymer that has not yet been blended with various additives. Resins account for approximately 40% to 100% of the total weight of plastics, and the properties of the resin often determine the characteristics of the plastic.
To enhance the performance of plastics, various auxiliary materials—such as fillers, plasticizers, lubricants, stabilizers, and colorants—are added to the polymer, enabling the material to achieve desirable properties. Fillers, also known as reinforcing agents, can improve a plastic’s strength and heat resistance while reducing costs. Plasticizers increase the plastic’s malleability and flexibility, decrease its brittleness, and make it easier to process and mold. Common plastic‑forming processes include molding, extrusion, injection molding, blow molding, spraying, calendering, and roll‑forming. Through these processes, we obtain everyday plastic products such as salt bags, mineral water bottles, plastic panels, and more.
The development of the petrochemical industry has spurred a dramatic advancement in synthetic resins. Coupled with the wide variety of plastic processing and molding techniques, it is now possible to produce products with complex geometries at low cost. The judicious use of various plastic processing additives and the development of plastic alloys have enabled plastics to overcome their inherent limitations, transforming them into innovative materials with numerous superior properties. Plastics have already replaced many traditional materials—such as wood, paper, cotton, and steel—emerging as a rapidly growing class of advanced materials. It is no exaggeration to say that our daily lives are inseparable from plastics.