Plastics 101: Basic Chemistry and Identification Codes

We live in a world ubiquitous with plastics. Plastic bottles, containers, tyres, bags, packaging, decorative items and even toys. We are so attuned to the use of plastics in our daily life that it is almost impossible to imagine human evolution without them. Since the discovery of polystyrene in 1839 by Eduard Simon to now; the journey of plastics could hardly be called progressive in the conventional sense. From natural plastic materials (gum, shellac etc) to modified natural material (rubber, collagen, nitrocellulose etc) to completely synthetic plastics of today (Polyvinyl Chloride, epoxy, ploystyrene etc), we have come a long way into the world of plastics. And it is not without reason. Therefore, it is imperative to know about the basic chemistry of various plastics that we use everyday and be able to identify them correctly with their identification codes. We call it the Plastics 101.

Mostly manufactured from petrochemicals -a depleting fossil fuel reserve- the threat of global warming are obvious with increasing plastic use. That being said, their degradability in natural environment poses a bigger challenge. In fact, plastic pollution is undoubtedly the biggest challenge in front of the current generation that deserves immediate action. Then, why aren’t we stopping their use? With properties like easy manufacturing, low cost, plasticity that allows them to be molded into almost any shape, convenience to use etc, one can almost imagine them as a blessing in disguise.

It might not be an exaggerated approximation that we throw away enough plastic each year to encircle earth four times! In India, 42% of plastics are used is in packaging. A CPCB (Central Pollution Control board) survey conducted in 60 major cities found that 15,342.46 tonnes of plastic waste was generated every day, amounting to 56 lakh tonnes a year.

We are slowly but gradually waking up to the dangers posed by plastics. From the massive accumulation of microparticles of plastics floating in the seas killing aquatic life to the deaths of cows due to consumption of waste loaded with plastics, these are just some of the directly observable ill-effects of plastics while the long-term indirect impacts are only now being uncovered. While countries across the globe are progressively banning single-use plastics (about 50% of total plastic use), closer home many states/cities (including Delhi, Himachal Pradesh, Goa, Rajasthan, Trimula, Lucknow, Karwar) have imposed bans on plastic bags of particular thicknesses. The enforcement of these bans are a different question altogether.

But not all plastics are the same. Depending on the constituent polymer type, plastics are classified into seven categories. These codes called SPI resin identification codes were developed by the Society of the Plastics Industry (SPI) in 1988 and used globally. These primarily help in segregating different plastics and aid their recycling. These symbols can be found on plastic packaging uniformly across the world.

Code 1: PET or PETE (Polyethylene terephthalate)

Mostly used in soda, soft drink and water bottles, bottled cooking oil, medicine containers and other consumer product containers. Also component of Polyester fibers (Polar Fleece), thermoformed sheet, cassette tapes, sails for boats, tote bags, furniture, carpet, paneling etc.

These are single-use plastics and must not be reused, refilled, or heated. These can be recycled once into new secondary products, such as textiles, parking lot bumpers,  plastic lumber etc.

Code 2: HDPE (High Density Polyethylene)

This is the thicker than PET, milkier or opaque plastic generally found in milk and water jugs, juice bottles, grocery bags,  base cups, car stops, playground equipment,  detergent, shampoo, and motor oil containers, and toys. Unlike PET plastics, these are safe to refill and reuse. HDPE plastics can also be recycled once into products similar to those for PET plastics.

Code 3: PVC or V (Polyvinyl Chloride)

The most dangerous kind, PVC is found in children’s toys. non-food bottles, cling wraps, shower curtains, pipes, fencing, few other food and detergent containers. It are less likely to be recycled. PVC manufacturing releases dioxin, a potent carcinogen (cancer-causing agent) that can accumulate in animals and humans. It may also have phthalates, chemicals used to soften plastics. Some phthalates are known to be hormone disrupters linked to possible reproductive issues and birth defects. PVC must be avoided as much as possible.

Code 4: LDPE (Low-density polyethylene)

Most commonly used in grocery bags, plastic wraps, shopping bags, dry cleaning bags, and garbage bags. LDPE are also used in dispensing bottles, wash bottles, tubing and molded laboratory equipment. These are thin, soft and flexible plastics. These are safer plastics but not often recycled and thrown carelessly, leading to worst plastic accumulation in the environment due to lighter weight. LDPE can, however, be replaced with reusable bags or bags made of recycled/waste paper. Their usage is preventable and must be replaced with safer alternatives.

Code 5: PP (Polypropylene)

PP is hard but flexible type of plastics found in ice-cream and yogurt containers, drinking straws, syrup bottles, diapers, auto parts, industrial fibers, and dishware. One of the safer plastics but should not be warmed and if not recycled, can create same problems as LDPE.

Code 6: PS (Polystyrene)   

PS is found in rigid plastics like plastic spoons, forks and styrofoam such as those in coffee cups and cafeteria trays. These can also be found in desk accessories, plastic utensils, toys, video cassettes and cases, clamshell containers, packaging peanuts, and insulation board.

These plastics can leach styrene, a carcinogen and neurotoxin fatigue. It can also cause low platelet and hemoglobin values, and chromosomal and lymphatic abnormalities. Study also shows that women exposed to styrene vapors demonstrated menstrual disorders, metabolic disturbances during pregnancy and neurotoxic symptoms.

Code 7: Other (Includes Polycarbonate, Nylon and Acrylic)

Code 7 includes all other plastics not found in the aforementioned six categories. These include other plastics, such as acrylic,nylon,polycarbonate, and polylactic acid (a bioplastic), and multilayer combinations of different plastics.

Polycarbonate plastics found in most baby bottles, 5-gallon water bottles, sports bottles, clear plastic cutlery, and in the lining of food and formula cans contains BPA (Bisphenol-A), an endocrine disrupter. However, code 7 also includes newer compostable bioplastics such as those made from corn, tapioca, rice or potatoes. These category plastics should be avoided unless labeled as the new bio-plastics. Plastics in Other category are imprinted with number 7 or nothing at all and are the most difficult to recycle, so are least likely to be collected or recycled.

To identify the code of plastics that a product is, you can flip the bottle/wrapper/toy or container over and look for the Resin Identification code on the bottom. If the products are not coded, you should feel free to contact the manufacturer for more information or avoid the product. The bottom-line is that we have a right to know fully what we consume and what surrounds us, in order to make an informed decision for us and our future. Next time before making a purchase, do remember to check the plastic code.

Editor