A large collection of plastic bottles.

What is Plastic?

In this blog, we will dive deeply into what plastic is, cover all the fundamentals of plastic, and will provide a solid background for building a basic understanding for the topics covered in the future about plastic recycling.

Types of Plastic

Plastic is a term that is used to describe a wide umbrella of subtypes which fall under the general definition of “plastic”. Within the entire plastic recycling, and remanufacturing process, it is important to note these different types of plastic which are categorized by their chemical compositions. These categorizations are numeric in nature and are classified with a resin, or polymer, identification coding system, numbering 1-7 (with the additions of ABS and PA). These categories are below and will be elaborated on further. It is important to note, that not all plastic materials contain resin codes.

  1. Polyethylene Terephthalate (PET or PETE)
  2. High Density Polyethylene (HDPE)
  3. Polyvinyl Chloride (PVC)
  4. Low-Density Polyethylene (LDPE)
  5. Polypropylene (PP)
  6. Polystyrene (PS)
  7. Other 

Polyethylene Terephthalate (PET, or PETE)

PET is a form of polyester, relative to clothing and fabric, which is heavily used in the manufacturing of plastic bottles or food containers. PET also has heavy implementation with personal care products, medical applications, and various other consumer items. Other uses are: thermoformed sheet, strapping, soft drink bottles, tote bags, furniture, carpet, and paneling. PET is utilized for many consumer products because it is deemed as a highly safe material, especially for packaging; it is recommended for many traits: lightweight, strength, shatterproof, non-reactive, and economical. PET is highly recognized by health officials globally.

PET is a polymer formed from the combination of ethylene glycol and terephthalic acid. Making PET, pellets of PET resin are heated to a molten liquid, which can be easily extruded or molded into almost any shape. Interestingly, PET is the chemical name for polyester, and is generally referred as such when used in creating fabrics; only when utilized for manufacturing containers and packaging, is the resin referred to as PET. This particular type of plastic can be distinguished from the numeral 1 surrounded by chasing arrows.

Pet is a popular choice over glass for many reasons when it comes to consumer-packaged goods, including but not limited to: hygienic, strong, resistant to attack by micro-organisms, does not react with foods or beverages, and will not biologically degrade (also biologically inert if ingested). PET containers that are used in reheating food and beverages contain an additive that crystalizes and strengthens the PET so that it can be resistant against higher temperatures.

In terms of recyclability, PET is the most common form of plastic that is reused in the United States of America, upwards of 1.5 billion pounds of the material is recycled each year (FAQs - Frequently Asked Questions). More items that PET can be used in manufacturing are: PET bottles and containers, carpet and clothing, industrial strapping, rope, upholstery fabrics, boat sails, automotive parts, fiberfill for winter jackets and sleeping bags, construction materials, and a wealth of other varieties of items.

Environmentally, PET is highly sustainable manufacturing material. Feedstocks for the polymer are derived from oil and natural gas, however, 40% of the energy put into its manufacturing can be reused if recycled properly (FAQs - Frequently Asked Questions).

High Density Polyethylene (HDPE)

High Density Polyethylene, or HDPE, is one of the most popular forms of plastic to date. HDPE is made from a process of threading ethylene molecules (ethylene and petroleum) together which are derived from natural gas resources. HDPE is favored for its lightweight, yet strong, and malleable characteristics and is found commonly used in the production of car fuel tanks, piping, and milk jugs. In the manufacturing process, the plastic can be easily molded and welded together providing further flexibility of the material (High Density Polyethylene - What is High Density Polyethylene?). Like PET, HDPE has many similar, and a wide range of uses in the consumer-packaged goods market, inclusive of manufacturing. Many uses include: personal care products, food and beverage containers, bread bags, grocery (handy) bags, cereal box liners, plastic lumber, outdoor patio furniture, playground equipment, automobile parts, trash cans, compost bins, bottle caps, office products, detergent bottles, and recycling bins (P. (2017, December 27). High Density Polyethylene (HDPE)).

Amongst its many uses, HDPE is also highly recyclable material. HDPE product is marked with a number 2 resin identification code, where applicable. This material creates no harmful emissions during production, or use on the consumer end, and will omit no harmful chemicals into the ground. HDPE is stronger material than standard PET. In India, the polymer is actually used to prevent groundwater pollution within the country’s communities (P. (2017, December 27). High Density Polyethylene (HDPE)).

Polyvinyl Chloride (PVC)

PVC is a thermoplastic which could be re-softened by heating, contrary, plastics which fall under the category of thermosetting are hardened and never become soft again. PVC is supplied in powder form, not pellets like other forms of plastics, making long term storage a favorable attribute of PVC, with traits that allow it to be resistant to oxidation and degradation. During the processing stages, various pigments, and additives, are added to PVC. Another term for PVC is vinyl and is usually utilized in reference to categories like: flooring, decorative sheets, and artificial leather. Vinyl is comprised of 57% chlorine derived from industrial grade salt (increases fire resistance), and 43% carbon (oil and gas). Being less dependent on crude oil and natural gas PVC is regarded as a more sustainable plastic (Agency], V. [. (n.d.). PVC.).

Vinyl is utilized in many different products, and for a wide range of applications ranging from: building/construction, healthcare, electronics, and automotive. PVC is also found in many products: piping, siding, blood bogs, tubing, wire insulation, and windshield system components. Within the building and construction industry 3 quarters of all production of the material goes to this category, and is highly sustainable with low greenhouse gas emissions, energy recourse use; products in this industry that are manufactured with PVC are: cladding, windows, roofing, fencing, decking, wallcoverings, electrical wiring, cable wiring, flooring, and water pipes. Other uses include: packaging (predominantly medicines and shrink-wrap for consumer products), personal care products, various household goods, IV bags, medical tubing, and PVC blood collection bags which were a huge breakthrough for blood banks. Other items include: rain coats, boots, and shower curtains (Polyvinyl Chloride (PVC)).

Vinyl is extremely versatile and customizable being able to have any color property, and a range of physical characteristics.


Low-Density Polyethylene (LDPE)

Low-Density Polyethylene, or LDPE, was first experimented with in the 1930s for the use of high frequency radar cable application. This form of Polyethylene is flexible in its production and is highly favored for its moisture resistance, and low cost to production, although a disadvantage is its low temperature resistance, only capable of handling 200 – 250 Fahrenheit maximum. There are many advantages to using LDPE: low cost to manufacture, impact resistant from -40 to 90 degrees Fahrenheit, moisture resistant, decent chemical resistance, food grade, and processed by thermo plastic methods. LDPE has its disadvantages as well which are: high thermal expansion, poor weathering resistance, subject to stress cracks, hard to bond, flammable, and poor temperature capability (LDPE (Low Density Polyethylene)).

LDPE, although with its limitations, has many applications in consumer products. The variety of availability in manufacturing is wide, encompassing: toys, utensils, films, bottles, pipe and processing equipment, and wire/cable insulations. Other uses of LDPE are: carrier bags, chemical tank linings, heavy duty sacks, and water piping. LDPE has a resin identification code of 4.

Some other telling characteristics of LDPE are that it is nontoxic, lighter than water, has high exposure resistance to a wide variety of lab chemicals, and has a milky white appearance. Due to its polymerization process, LDPE has more side branching than its cousin HDPE, giving its structure a less 3-dimensional appearance, allowing LDPE to be more flexible (Low Density Polyethylene

(LDPE) Labware).

Polypropylene (PP)

Polypropylene is a highly diverse, and widely used polymer within the manufacturing industry, and for good reason. PP is made from a combination of propylene monomers and is a highly functional resin. PP is used for products like: consumer packaged goods, plastic parts for various industries like the automotive industry, special devises (living hinges), and textiles which are widely used globally. Currently, demand for PP is high, annual demand is generally around 45 million metric tons per year on a global scale. By industry, PP has a utilization foothold within: 30% of packaging, 13% of electrical equipment, 10% of household appliances, and 10% of the automotive industry (Staff, C. M. (n.d.)).

As a material, PP has a rather sleek, and slippery, surface which gives it a higher application for specific area like low friction, or contact points for furniture. PP is subject to oxidation at relatively high temperatures. Benefits of PP are: low density, high coefficient of friction, manufacturable into a living hinge, and can be copolymerized. Other uses for PP are found within: dishwasher safe plates, trays, cups, opaque to-go containers, and many toys. Characteristic of PP are that it is chemical resistant, has high elasticity, toughness, fatigue resistant, insulation (high resistance to electricity), and transmissivity. PP does come with its disadvantages which are wide. Some disadvantages of PP are that it is limited to high temperatures, can be degraded by UV rays, low resistance to chlorine (and aromatics), poor bonding properties, flammable, and can be highly susceptible to oxidation (mentioned previously) (Staff, C. M. (n.d.)).

Polystyrene (PS)

Polystyrene, or PS, is utilized highly within manufacturing for its hard, and solid properties, giving it large demand for products that fall under the categories of food packaging, laboratory ware, appliances, electronics, automobile parts, toys, gardening pots, and various types of equipment. PS has another useful trait which is that it can be manufactured into foam like materials (expanded polystyrene/extruded polystyrene) which can be incorporated in insulation, or for cushioning. PS is created by polymerizing styrene. Styrene, interestingly, is found naturally within strawberries, cinnamon, coffee, and beef (What is Polystyrene?).

Detailed uses of PS are various and broad:

  • Appliances - Refrigerators, air conditioners, ovens, microwaves, vacuum cleaners, and blenders.
  • Automotive - used to make many car parts, including knobs, instrument panels, children’s seats, trim, energy absorbing door panels and sound dampening foam.
  • Electronics – televisions, computers, and a wide range of IT equipment.
  • Foodservice – insulation for food products.
  • Insulation - building walls, roofing, refrigerators, freezers, and industrial cold storage facilities.
  • Medical - tissue culture trays, test tubes, petri dishes, diagnostic components, housings for test kits and medical devices.
  • Packaging - CD and DVD cases, foam packaging peanuts for shipping, food packaging, meat/poultry trays and egg carton.


The 7th resin identification code is classified as “other”. This category is reserved for plastics that do not fall under the previous 6 categorized resin codes, and generally depict plastics that are mixed together with one another, layered, or new bioplastics. Polycarbonate (PC) will fall under the category of 7. PC has been in decline for health-related issues with one of its molecules (bisphenol) and will not be elaborated on fully within this text. A great trait of PC is that it is highly shatter proof, and extremely strong. Although PC is in high decline within baby bottles, it still may have application for products like: three and five-gallon large water storage containers, metal food can liners, juice and ketchup containers, oven-baking bags, carbonless paper receipts, eye glass lenses, epoxy resins, dental sealants, compact discs, DVDs, Blu-ray discs, lab equipment, gears, snowboards, car parts, housing for cell phones, computers and power tools.


FAQs - Frequently Asked Questions. (n.d.). Retrieved from http://www.petresin.org/faq.asp 

  1. (2017, December 27). High Density Polyethylene (HDPE): So Popular. Retrieved from https://www.plasticsmakeitpossible.com/about-plastics/types-of-plastics/professor-plastics-high-density-polyethylene-hdpe-so-popular/

Industrial Plastic Recycling. (2018, March 30). Retrieved from http://northstarrecycling.com/industrial-plastic-recycling/

Northern California Compactors. (2017, January 09). Retrieved from http://www.norcalcompactors.net/processes-stages-benefits-plastic-recycling/

Paprec Group Raw material producer of the 21st century. (n.d.). Retrieved from https://www.paprec.com/en/understanding-recycling/recycling-plastic/sorting-plastic-waste 

Resources. (n.d.). Retrieved from https://www.completerecycling.com/resources/plastic-recycling/codes

What is HDPE? (n.d.). Retrieved from http://bearboardlumber.com/bearboard-plastic-advantage/what-is-hdpe.html

High Density Polyethylene - What is High Density Polyethylene ? High Density Polyethylene meaning, High Density Polyethylene definition. (n.d.). Retrieved from https://economictimes.indiatimes.com/definition/high-density-polyethylene

Agency], V. [. (n.d.). PVC. Retrieved from http://www.pvc.org/en/p/what-is-pvc

Polyvinyl Chloride (PVC) | Uses, Benefits, and Safety Facts. (2018, August 21). Retrieved from https://www.chemicalsafetyfacts.org/polyvinyl-chloride-post/

LDPE (Low Density Polyethylene). (n.d.). Retrieved from http://www.upcinc.com/resources/materials/LDPE.html

  1. (n.d.). British Plastics Federation. Retrieved from http://www.bpf.co.uk/plastipedia/polymers/ldpe.aspx

Low Density Polyethylene (LDPE) Labware. (n.d.). Retrieved from https://www.thermofisher.com/us/en/home/life-science/lab-plasticware-supplies/plastic-material-selection/low-density-polyethylene-ldpe-labware.html

Staff, C. M. (n.d.). Creative Mechanisms Blog . Retrieved from https://www.creativemechanisms.com/blog/all-about-polypropylene-pp-plastic

What is Polystyrene? | Uses, Benefits, and Safety Facts. (2018, August 21). Retrieved from https://www.chemicalsafetyfacts.org/polystyrene-post/

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