We live in the Age of Plastics.[i] The quantity of plastic items in your home would likely surprise you. A form of the Greek word, plastikos, plastic means “to mold, form.” Today, the word plastic is commonly used to refer to a singular type of synthetic substance that possesses the qualities, of well, plastic. However, plastic should be thought of as a family of substances, each consisting of a variety of polymers[ii], (Greek for “many parts)[iii].
In general, the majority of mass produced plastics are made from hydrocarbons extracted from the cracking process when refining oil and natural gas. These hydrocarbons, through various chemical processes, become monomers (Greek for “one part”)[iv]which combine to form polymers. These monomers can be linked in different combinations to create diverse plastic resins. Visit this link for a complete list of resins. Resins are typically produced in the shape of pellets. Often these resin producing chemical processes are patented and secretly held by companies.[v] Therefore, we don’t know exactly what types of chemicals have been used in the plastic making.[vi]
Plastic resins can generally be classified into one of two categories: thermosets or thermoplastics. Thermosets are plastics that, once melted, retain their shape and cannot be remelted and reshaped. In other words, they cannot be recycled. They can only be reused as a different shape or as filler. On the other hand, thermoplastics can be reshaped through processes involving reheating and cooling repeatedly. It’s easier to recycle them into something else.
Recycling plastics became more common in the eighties. Since it is impossible to tell what type of plastic you are holding simply by looking at it, pressure was placed on the plastic industry to establish a common classification and identification system. In 1988, the Society of Plastics Industry developed the SPI resin identification coding system to facilitate the plastic recycling process. You will notice a wide variety of different materials listed underneath each plastic resin classification – giving testimony to the volume of different types of plastic polymers
For a printable chart of all 7 identification codes click here. Next month, my last article on plastic will focus on explaining the SPI code in more detail and recycling process itself.
For more detailed information about the plastic making process – visit one of these references: