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Resources on Plastics in the Environment (June 2022): Types of Plastics

By Margaret Manion

Types of Plastics

Although hundreds of types of plastics have been developed, only a small number account for most of the plastic now in the world. These include polyethylene terephthalate (PET or PETE), high density polyethylene (HDPE), polyvinyl chloride (PVC or vinyl), low density polyethylene (LDPE), polypropylene (PP), and polystyrene. In Transforming Plastic, Albert Bates explains that plastics can be divided into three categories: thermoplastics, which melt and disfigure after being exposed to high temperatures; elastomers, which are heat resistant but flexible; and thermosets. No longer affected by heat after their initial fabrication, items made from thermosetting polymers cannot be recycled, remolded, or reshaped. Bates informs that the thermoplastics in widest use are PET, PVC, HDPE, LDPE, PP, and polystyrene, while examples of thermosets (or their precursors) also in common use include epoxy, silicone, and phenol (or carbolyc acid). Bates also explains that a few materials (including polyester) can end up either as thermoplastics or thermosets in manufactured goods.

Brydson’s Plastics Materials, as edited by Marianne Gilbert, is the consummate update (8th ed.) of a 1960s classic source of detailed technical information, including chemical composition for all the plastics in common use and many lesser-used ones, encompassing all phases of production, chemical properties, uses, and more. Gilbert is an emeritus professor of polymer technology at Loughborough University, located in the English midlands. By reorganizing and refreshing the classic work, she has ensured its stature as the “plastics bible” for coming years. Readers looking for a beginner’s orientation to plastics might prefer to first consult the webpage published by Carnegie Mellon University as part of its STEM education outreach program, “Macromolecular Products” ( “Macromolecular Products” introduces polymers in terms of their physical structure and properties, including molecular architectures of different types, and helpfully includes a page on the distinction between natural and synthetic polymers. This site offers a user-friendly graphic (“Sample Chemical Structure”) that clearly illustrates how a monomer affords attachment to others of its kind, forming a chain so as to become a polymer.

Aside from classifying plastics by their chemical structure, composition, and physical properties, manufactured plastic items are typically grouped by size (usually after being discarded), although there is some disagreement about the exact size ranges for each category. Large plastic items, typically exceeding 25 millimeters (i.e., plastic water bottles), are known as mega plastics or macro plastics; smaller plastic items are known as microplastics. Recently an even smaller category (nanoplastics, ranging from 1 to 1000 nanometers in size) has been discovered. The latter types are the subject of scholarly attention in Analysis of Nanoplastics and Microplastics in Food, edited by Leo Nollett and Khwaja Siddiqi. Of course, plastics can also be classified by origin: synthetic plastics are those derived from fossil fuels, such as petroleum or natural gas, while bio-based plastics is a term reserved for those plastics derived from renewable biological sources, such as corn and other plants, as detailed in the resources mentioned below.

Works Cited