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Essential Resources : Composition

 linup of plastic composition types

Knowing what plastic your container is made of.

Not all but most plastic containers we use on a daily basis for food, storage and packaging have a number.  This number refers to the resin identification codes - surrounded by chasing arrows and molded, formed or imprinted on the container.  Typically you will find the code on the bottom.  Some containers like jars will have this code along the threaded top edge.  The word "resin" typically means "plastic type"


High density polyethylene (HDPE) High density polyethylene (HDPE)

 Description:  Polyethylenes are the most widely used family of plastics in the world. The versatile polyethylene polymer has the simplest basic chemical structure of any plastic polymer (repeating units of CH2: one carbon and two hydrogen molecules) making it very easy to process and thus extremely popular for numerous low value applications - especially packaging. HDPE has long virtually unbranched polymer chains which align and pack easily making it dense and very crystalline (structurally ordered) and thus a stronger, thicker form of of polyethylene. Properties:  stiffness, strength, toughness, resistance to moisture, permeability to gas, ease of processing. 

 Typical Use:  Plastic bags (grocery), opaque milk, water, and juice containers, bleach, detergent and shampoo bottles, garbage bags, dishes, yogurt and margarine tubs, cereal box liners, some medicine bottles. Also used in Tyvek insulation, PEX piping, plastic/wood composites.



Low density polyethylene (LDPE) Low density polyethylene (LDPE)

Description:  Polyethylenes are the most widely used family of plastics in the world. The versatile polyethylene polymer has the simplest basic chemical structure of any plastic polymer (repeating units of CH2: one carbon and two hydrogen molecules) making it very easy to process and thus extremely popular for numerous low value applications - especially packaging. LDPE polymers have significant chain branching including long side chains making it less dense and less crystalline (structurally ordered) and thus a generally thinner more flexible form of of polyethylene. Properties:  strength, toughness, flexibility, resistance to moisture, ease of sealing, ease of processing. 

Typical Use:  Mostly for film applications like bags (grocery, dry cleaning, bread, frozen food bags, newspapers, garbage), plastic wraps; coatings for paper milk cartons and hot & cold beverage cups; some squeezable bottles (honey, mustard), food storage containers, container lids. Also used for wire and cable covering.



 Polyethylene terephthalate (PET or PETE or polyester) Polyethylene terephthalate (PET or PETE or polyester)

Description:  PET is the most well known member of the polyester family of plastic polymers. It initially gained widespread use as a wrinkle-free fiber (commonly called "polyester"), and the majority of its production still goes toward textile manufacturing. It has become extremely popular for food and drink packaging purposes because of its strong ability to create a liquid and gas barrier - so oxygen cannot get in to spoil food, and the carbon dioxide that makes drinks fizzy cannot get out. Properties:  clarity, lightness, strength, toughness, barrier to liquid and gas.

Typical Use:  Bottles (water, soft drink, juice, beer, wine, mouthwash, salad dressing), peanut butter/jam jars, oven-ready and microwaveable meal trays, detergent and cleaner containers. Also used in liquid crystal displays, film for capacitors, insulation for wire and insulating tapes, and as a common finish for wood products such as guitars, pianos and vehicle/yacht interiors.



Polypropylene (PP) Polypropylene (PP)

 Description:  Polypropylene is used for similar applications as polyethylenes, but is generally stiffer and more heat resistant - so is often used for containers filled with hot food. It too has a simple chemical structure (many methyl groups of CH3 - one carbon and three hydrogen molecules) making it very versatile. It's crystallinity (structural order affecting hardness & density) is quite high, somewhere between LDPE and HDPE. Properties:  strength, toughness, resistance to heat, chemicals, grease & oil, barrier to moisture.

 Typical Use:  Food containers (ketchup, yogurt, cottage cheese, margarine, syrup, take-out), medicine containers, straws, bottle caps, Britta filters, Rubbermaid and other opaque plastic containers, including baby bottles. Other uses include disposable diaper and sanitary pad liners, thermal vests, appliance parts and numerous car parts (bumpers, carpets, fixtures). 



Polystyrene (PS) Polystyrene (PS)

Description:  Polystyrene is commonly associated with the trade name Styrofoam food containers and packing peanuts made of expanded PS (EPS), which is essentially foamed PS that has been puffed up with air. PS synthesis requires benzene, a known carcinogen, to form the monomer styrene, which is reasonably anticipated to be a human carcinogen. Apart from low cost, low strength foam, PS can be made as a clear, glassy, hard polymer used for things like cutlery and cd cases; also higher impact versions exist for harder applications. Properties: versatility, clarity, easily formed. 

Typical Use:  EPS: Styrofoam food containers, egg cartons, disposable cups and bowls, take-out food containers, deli food plates, packaging, packing peanuts, bike helmets. Harder clear/opaque PS: disposable cutlery & razors, compact disc & dvd cases. High impact PS: hangers, smoke detector housing, licence plate frames, medicine bottles, test tubes, petri dishes, model assembly kits




Key references for the above text:

  • Anthony L. Andrady, ed. Plastics and the Environment. Hoboken, NJ: John Wiley & Sons, 2003.
  • Susan Freinkel. Plastic: A Toxic Love Story. New York: Houghton Mifflin Harcourt, 2011.
  • Rick Smith & Bruce Lourie. Slow Death by Rubber Duck: How the Toxic Chemistry of Everyday Life Affects Our Health. Toronto: Alfred A. Knopf, 2009.
  • E.S. Stevens. Green Plastics: An Introduction to the New Science of Biodegradeable Plastics. Princeton & Oxford: Princeton University Press, 2002.
  • Beth Terry. Plastic Free: How I Kicked the Plastic Habit and How You Can Too. New York: Skyhorse Publishing, 2012.
  • R. C. Thompson, C. J. Moore, F. S. vom Saal and S. H. Swan, eds. "Theme Issue: Plastics, The Environment and Human Health." Philosophical Transactions of the Royal Society B. Vol. 364, No. 1526, 27 July 2009.
  • Michael Tolinski. Plastics and Sustainability: Towards a Peaceful Coexistence between Bio-based and Fossil Fuel-based Plastics. Salem, MA: Scrivener Publishing, 2012.



IMPORTANT NOTES: While we strive to provide as accurate and balanced information as possible on our website, Essentials by Catalina cannot guarantee its accuracy or completness because there is always more research to do, and more up-to-date research studies emerging -- and this is especially the case regarding research on the health and environmental effects of plastics.None of the information presented on this website is intended to be professional advice or to constitute a professional service to the individual reader. All matters regarding health require medical supervision, and the information presented on this website is not intended as a substitute for consulting with your physician.

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