If you are not already familiar with the symbols that resemble a recycling triangle found under most plastic containers, most people would have at least seen or notices it. The purpose of the symbols which have number from 01 to 07 in it, are exactly what you would think - which is to provide an efficient way to separate and recycle plastics.
The symbol, known as 'SPI resin identification coding system' is developed by 'The Society of the Plastics Industry, Inc (SPI)' in 1988. SPI is a trade association that represents the plastic industry in the United States. Plastics are manufactured using different polymer types, these different polymer types contains different properties that supports different usage with different strength, clarity, versatility and chemical components. This introduced a challenge for recycler as unintentional combination of different polymer would ruin a plastic mixing, causing it unusable and sometimes with health and safety issues too.
The Resin Identification Code was introduced to address this exact challenge. Although not required by all federal legislation, manufacturers throughout the world adopted the code.
A common misconception with the Resin Identification Code is with the number in used. Some people thinks that the higher the number, the tougher the material and in turn, safer for food storage. The reality however, shows that the numbers have zero correlation with these properties It is merely a randomly assigned number to represent the polymer types it contains. The seven codes found are as follows:
01 Polyethylene terephthalate (PET, PETE) - Clear and tough, commonly used as soft drink plastic bottles, plastic jars, mineral plastic bottles and salad dressing. When recycling, it is sorted based on colour and added into mixer. It is also often reused as is for school projects or disinfection of ultraviolet radiation.
02 High-density polyethylene (HDPE) - Strong and moisture resistant, commonly used in plastic bottles, Plastic pipes, plastic jars and plastic jerry cans. HDPE reduces the health and environment problem caused by PVC and more durable as compared to glass, metal and cardboard. Another interesting use case is the use of recycled material to be processed by recycle bots into filament for 3D printers.
03 Polyvinyl chloride (PVC) - Versatile and tough, commonly used in pipes, fences and electric cable insulation. PVC is one of the materials with high health and safety concern sighted by many organizations. It is not suitable for food use and gradually eliminated from hospital use.
04 Low-density polyethylene (LDPE) - Flexible and easy to seal, commonly used for container and food packaging. LDPE has wide application usage and also resistance to chemical. Also used in playground slides, parts of computer hardware and plastic storage.
05 Polypropylene (PP) - Strong and heat resistance, commonly used in microwavable ware and clothing. PP is susceptible to chain degradation from exposure to heat and UV radiation such as that present in sunlight.
06 Polystyrene (PS) - Versatile and clear, commonly used as food container and food packaging. According to American Chemistry Council and Hong Kong Food and Environmental Hygiene Department, PS is safe for use in foodservice products.
07 Other (often polycarbonate or ABS) - Varied properties depending on chemical compound. Polycarbonates for example are commonly used in electronic components, plastic storage, plastic draws and medical applications.