Plastics are a complicated group of materials that come in infinite different forms and functions. The most common misconception we come across is that all plastics - regardless of what they are or how big or small they are - are recyclable. This is not true.
You may remember when the number in the triangle DID matter for whether or not something belongs in the recycling. Many people still ask which numbers should go into the recycling cart, and which should not. Following industry standards, our City (along with most states and municipalities) have moved away from the number based system. WHY? The numbers aren't the whole story. In fact, plastics have those symbols to help those within the plastic industry distinguish between types of plastic. They do not indicate that an item is widely recyclable or accepted for recycling in your municipality.  
Plastic resin codes

This misconception has been one of the greatest challenges of the recycling industry because it has been the leading cause of contamination. Different plastics pose different issues when they are brought to the recycling facility. 
Here are some common examples of plastic contamination and how the affect the sorting process:
- Plastic bags full of recyclable (or non-recyclable) items usually removed by laborers in the beginning leg of the process. 
- Plastic bags, wrap, produce bags, (and many more, we call this flexible plastic packaging) can get caught in the rotating machinery, reducing sorting efficiency and/or temporarily shut down the facility. If the plastic wrap gets caught in the machinery and shuts down the facility, workers must climb onto the machinery and cut the plastic out - which is dangerous to worker safety.
- Plastic hoses, hangers, pipes, broom sticks, etc. pose the same problem as plastic bags/wrap. They can wrap around or jam up machinery.
- Small plastic items, like tooth brushes, loose bottle caps, and toys (ex. building blocks, figurines), can either 1) jam up machinery, 2) fall out of the system and become trash or 3) accidentally be baled with a material, and cause contamination further down the recycling line.

The plastics that are accepted in your recycling cart are sorted, baled and shipped to a place where it will be recycled, typically for a net profit. Plastics are sorted at the Billerica recycling facility primarily by optical sorters, which are cameras that measure the density of an object and communicate this information to air jets, which use different pressure streams to send the item to the correct bin (see the image below to see a basic diagram of how an optical sorters work). 

Review of the Impact of Mechanical Harvesting and Optical Berry ...