Types of Plastics

Plastic is ubiquitous, used in everything from your cellphone to the kitchen sink. But it’s not all the same – different types of plastics have specific properties that make them better or worse for certain applications, and they can have long-lasting effects on the environment.

Most plastics are synthetic, made from petrochemicals or natural substances such as cellulose or starch. They are chemically treated to form long chains of molecules, called polymers, which are then molded into shapes via techniques such as injection molding, extrusion or blow molding. The specific chemical structure of a plastic determines its specific characteristics. Polymers are often customized to suit their intended uses by attaching various molecular groups, or additives, to the main backbone chain. These side chains, which can also contain oxygen, nitrogen and sulfur, influence the overall performance of a plastic.

Some plastics are classified by the process used to create them, or the physical state and morphology of the polymer. For example, thermoset plastics are set by the chemical bonding that takes place during synthesis. Other plastics are classified by their glass transition temperature (Tg) or tensile strength, and still others are classified by the chemical reactions they undergo during degradation.

When determining the best plastic for a given application, manufacturers take into account not only the material’s properties but its cost, ease of manufacture, safety and recyclability as well. In addition, a plastic’s durability and ability to withstand environmental stresses can have a significant impact on its cost.

Polyethylene (PE)

One of the most common types of plastics, PE is found in beverage containers, food storage bags and trash can liners. It is highly resistant to both heat and cold, making it an excellent choice for packaging items that are likely to be transported and stored outdoors. PE is not prone to leaching chemicals into foods or beverages, and it does not break down easily.

HDPE (High-Density Polyethylene)

Similar to PE, but tougher and more durable, this plastic is a favorite for laundry detergent containers, milk jugs, toilet paper rolls, cleaning products and water bottles. It is able to withstand high temperatures, and can be recycled again and again.

PS (Polystyrene)

Styrofoam is perhaps the most recognizable type of plastic, and it is used to make coffee cups, shipping and product packaging and egg cartons. It is inexpensive, insulates well and holds up to heat well, but it’s also dangerous because it can leak harmful toxins, especially when heated. It’s also not very recyclable.

Other Plastics

This category encompasses a variety of miscellaneous plastics that don’t fit into the other six codes, including polycarbonate and bisphenol A-based (BPA) plastics. These plastics are commonly used in baby-feeding bottles, electronics and automotive parts. Unfortunately, they are also known to leach into the oceans, where they are a significant source of microplastic pollution. To reduce your exposure to these plastics, look for reusable alternatives like glass or stainless steel.