Introduction to plastics 

What is plastic?

It is considered as plastic to the group of materials that can be molded when soft and then hardened to retain the desired shape. There are synthetic (artificially created) plastics and natural plastics. We usually associate the word "plastic" with those synthetic materials that were created from natural, non-renewable raw materials such as oil, coal or gas that are heat-treated and converted into polymers (long molecules composed of small, repeating units called monomers) of ethylene and propylene. Eventually, the "pellets" (pellets) that are sent to the mills to be melted and molded into the desired shapes and articles (Figure 1).¹

Figure 1. "Plastic pellets

Types of plastics

There is a Plastic Identification Code which facilitates the classification of plastic into seven categories (Table 1).² The categories are distinguished by a number within a triangle created by three arrows, accompanied by acronyms. These acronyms indicate the chemical formulation of the type of material used to create the plastic article. Many people incorrectly think that the triangle symbol indicates that the item can be recycled, when it actually indicates the type of plastic it was made from.

Table 1. Identification code for each type of plastic, its uses and recyclability.²

Number and acronyms	Type of material	Uses	Recyclability
	Polyethylene Terephthalate	Individual bottles of water, juice and soft drinks, Clothing	High
	High Density Polyethylene	Gallons of water, milk and juice, Containers of cleaners and detergents, Containers of toiletries such as shampoos and conditioners, Pouches	High (Except for the glossary)
	Polyvinyl Chloride	Piping, Building Materials, Trays, Door and Window Frames, Credit Cards	Download
	Low Density Polyethylene	Container closures, Food packaging, IV bags, Bottles and other flexible materials	Median
	Polypropylene	Bottle caps, Diapers, Food storage containers, Coolers, Straws, Plates, Cups, Clothes, Rugs, Carpeting	Median
	Polystyrene	Cups for coffee and other hot beverages, Dishes, Cups	Download
OTHER	Other Plastics (polycarbonate, styrene, nylon, and blends of different types of plastics)	Baby Bottles, Electronic items, Toys, Mattresses	Download

References

1. This Is Plastics: How Are Plastics Made? Accessed February 9, 2023. https://thisisplastics.com/plastics-101/how-are-plastics-made/
2. Bilbao Villena A. Unhooking from plastic. Problems of a ubiquitous material: environmentalists in action. Accessed February 9, 2023. http://www.ecologistasenaccion.org

Author: María E. Ocasio Torres, Ph.D.
Bachelor's Degree in Coastal Marine Biology from the University of Puerto Rico - Humacao
D. in Biology from the University of Puerto Rico - Rio Piedras