Types of Recyclable Plastics
The types of plastics that are recyclable are an important challenge for the plastic industry. The plastics have a high environmental resistance and can survive in the environment for a long time. The recycling of these post-consumer plastics is considered an important economic tool because energy and material can be re-used.
Polyethylene terephthalate
Recycling symbol of 1 is used to make carbonated drink bottles and fibres. Polyethylene terephthalate (PET) is linear thermoplastic polyester, which has a widespread commercial as a synthetic fiber, film and molding material. There are many ranges of PET that can be used because of its wide range of properties and its ability to control its crystallinity. PET can be recycled by almost all major recycling techniques but some problems may arise because of label adhesives can cause discoloration and lost of clarity. During the recycling process the residual moisture can lead to degradation. (1) Recycled into: Polar fleece, fiber, tote bags, furniture, carpet, paneling, straps, (occasionally) and new containers (2)
High and Low density polyethylene
With a recycling symbol of 2 is used to make bags and blow moulding. Low-density polyethylene with a recycling symbol of 4 is also used for bags and films. Polyethylene (PE) is a thermoplastic polymer and represents the largest constituent of plastic waste. PE exists in two main forms, high-density polyethylene (HDPE) and low-density polyethylene (LDPE). PE has a wide range of uses because of its low cost, high impact resistance, good process ability, excellent chemical resistance and electrical insulation properties. HDPE is mostly recycled by granulation, producing flakes. The contaminants are removed by washing and then the flakes are separated from other plastic components. LDPE is recycled into pellet form with its main recyclable product being stretch film. (3) Recycled HDPE into: Laundry detergent bottles, oil bottles, pens, recycling containers, floor tile, drainage pipe, lumber, benches, doghouses, picnic tables, fencing. Recycled LDPE into: Trash can liners and cans, compost bins, shipping envelopes, paneling, lumber, landscaping ties, floor tile (4)
Polyvinyl chloride
With a recycling symbol of 3 is used for pipes and fittings. Polyvinyl chloride (PVC) is the third-most widely produced plastic. PVC is used in construction because it is more effective than traditional materials such as copper, iron or wood in pipe and profile applications. PVC waste can be managed in three different ways: recycling; disposal with energy recovery (incineration) and as a last resort landfill. (5) Recycled into: Decks, paneling, mud flaps, roadway gutters, flooring, cables, speed bumps, mats (6)
Polystyrene
With a recycling code of 6 is used for foam and protective packaging, containers lids, bottles, trays, tumblers, and disposable cutlery. Polystyrene can be rigid or foamed. General-purpose polystyrene is clear, hard and brittle. It is a very inexpensive resin per unit weight. Polystyrene is one of the most widely used plastics. Polystyrene usually can't be recycled locally and has to be transported to a centralized plant. (7) Recycled into: Insulation, light switch plates, egg cartons, vents, rulers, foam packing, carryout containers (8)
Polypropylene
With a recycling symbol of 5 is used for food packaging. It's found in some yogurt containers, syrup bottles, ketchup bottles, caps, straws and medicine bottles. Polypropylene (PP) has a high melting point and is often chosen for containers that hold hot liquid. (9) Recycled into: Signal lights, battery cables, brooms, brushes, auto battery cases, ice scrapers, landscape borders, bicycle racks, rakes, bins, trays (10)
Polycarbonate, Nylon 6 and Acrylonitrile butadiene-styrene
With a recycling code of 7. Is a wide variety of plastic resins that don't fit into the previous categories are put together into recycling code 7 under miscellaneous (11). Recycled into: Plastic lumber, custom-made products (12)
How Plastic Works
Plastics are made from oil. Oil is a carbon-rich raw material, and plastics are large carbon-containing compounds. They're large molecules called polymers, which are composed of repeating units of shorter carbon-containing compounds called monomers. Chemists combine various types of monomers in many different arrangements to make an almost infinite variety of plastics with different chemical properties. Most plastic is chemically inert and will not react chemically with other substances -- you can store alcohol, soap, water, acid or gasoline in a plastic container without dissolving the container itself. Plastic can be molded into an almost infinite variety of shapes, so you can find it in toys, cups, bottles, utensils, wiring, cars, even in bubble gum. Plastics have revolutionized the world. Because plastic doesn't react chemically with most other substances, it doesn't decay. Therefore, plastic disposal poses a difficult and significant environmental problem. Plastic hangs around in the environment for centuries, so recycling is the best method of disposal. (13)
Steps in Making Plastic
Extrusion
The method of extrusion is one of the main processes in regards to the manufacturing of plastic. Extrusion refers to the process of forming a piece of plastic through the use of certain shaping devices. Heat may be used when forming plastics with this method. One of the most common techniques under this method is called single layer flat sheet extrusion. Manufacturing steps in this process are carried out as follows:
1) Resin is inserted into an extruder and melted.
2) The melted resin is then pumped into a flat sheet die to be sized.
3) Next, the sheet is transferred to cooling rolls.
4) These rolls determine final size, thickness, and width.
5) The flat sheets are wound into continuous rolls.
Molding
A second method used in making plastic involves the molding process. Under this process, a rubber substance is formed within molds by using pressure and heat to cure and form the shapes needed. One of the most common techniques used is injection molding. This method uses a molding machine to perform the production steps. These steps are as follows:
1) The molding machine melts the raw material into a hot liquid state.
2) The hot liquid is transferred to a mold.
3) The cooled mold enables the liquid to solidify.
4) The finished product is extracted from the mold.
Thermoforming
Plastic may also be made through the process of thermoforming. This steps used to make plastic using this method are:
1) Extrusion of a sheet
2) Placing this sheet into a mold
3) Using a heat source and a vacuum-able force to form the sheet into the respective mold (14)
Impact Plastic has on Sea Creatures
Everyday we use many things that make our life easier. Walking through the supermarket we can also find hundreds if not thousands of items to make our life and daily routine simpler. Individually wrapped food, plastic baggies for storage, unbreakable bottles, and disposable plastic items we use everyday like razors, shampoo bottles, and cups to name a few. To us humans, it is part of our lives to use such items, but to marine life it's a floating minefield. Using plastic isn't a bad thing, but what we do with it when we are done is the most important, a simple decision that can save the sea creatures. When the plastic reaches our waters, whether it be a plastic bag, drifting fishing nets, or just plastic debris poses a huge threat to the sea creatures that depend on the ocean for food. Like stated earlier in the introduction in the Pacific Ocean there is a huge plastic waste dump that is twice the size of the United States. An estimate of 10 percent of the world's plastic waste will find its way into the sea and will end up in the Pacific Ocean. The sea currents will then transport the plastic waste into ocean dead zones, which are large areas of water that move slowly in circular patterns. The currents trap the plastic debris into one large constantly moving mass of plastic. As the currents slowly move in circular patterns the plastic is being broken down into plastic dust those sea animals then mistaken for food. Plastic does not biodegrade; instead, it photo-degrades with sunlight, breaking down into smaller and smaller pieces, but they never really disappear. These plastic pieces are eaten by marine life, wash up on beaches, or break down into microscopic plastic dust. Over 100,000 marine mammals and one million seabirds die each year from ingesting or becoming entangled in plastic. Plastic can also remain on the surface and can remain there for hundreds of years. Plastic is very durable and strong which is what makes it so harmful if and when it reaches our oceans. The Center for Marine Conservation has divided their data into debris that they have found and 58% is of plastic and the twelve most frequently found are:
1. cigarette butts
2. paper pieces
3. plastic pieces
4. styrofoam
5. glass pieces
6. plastic for food bags
7. plastic caps and lids
8. metal beverage cans
9. plastic straws
10. glass beverage bottles
11. plastic beverage bottles
12. styrofoam cups(15)
Three Marine Zones
There are three marine zones in which sea creatures find their food. Scientists divided the bodies of water into three basic areas:
The surface zone
The very surface of the water where it meets the air and things float where you can see them.
The pelagic zone
The open water below the surface where neutrally buoyant fish swim and plankton float.
The benthic zone
What lies beneath the bottom of the water; consist of mud, sand, or rock. (16)
Many different forms of sea creatures will find their food in these three different zones. The surface zone animals such as birds will find most of their food on the surface. They will skim along above the oceans surface and scoop up small floating fish. The pelagic zone which is where many fish get their food source, these fish are pelagic feeders. These fish will swim about eating other fish and plankton. The benthic zone animals such as whales, turtles, and sea otters will swim along the bottom of the ocean floor and skim for food and there are labeled as benthic feeders. The sea creatures that swim in these three different zones of the ocean will come into contact with different forms of plastic. The bird that is skimming the oceans surface will accidentally eat small bits of floating plastic mistaken for food. PET is a high strength transparent plastic that is resistant to heat and will sink in water. HDPE is tough and chemical and moisture resistant and will float in the water. PVC is hardy, chemical resistant and transparent and will sink in water. LDPE is tough and lightweight. It's a barrier to moisture and floats in water. PP is hard, resistant to chemicals, transparent, and will float in water. PS is stiff, transparent, has a smooth surface and will sink in the water. EPS (expanded polystyrene recycling symbol 6) is lightweight, heat resistant and will float in the water. Polycarbonate, Nylon 6 and Acrylonitrile butadiene-styrene recycling symbol 7 or also known as other means the plastic is made up of resin other than the ones listed above. Depending on the characteristics will result in the items floating or sinking in the water. The many sea creatures that live in the ocean will come into contact with the discarded plastic that eventually ends up in their home. The plastic is not natural to their environment and because the sea creatures don't recognize it they will mistaken it for food, get entangled or cut and injured. In the research study titled
Plastic ingestion by planktivorous fishes in the North Pacific Central Gyre
by C.M. Boerger, G.L. Lattin, S.L. Moore, C.J. Moore found that there is a significant amount of marine debris that has accumulated in the North Pacific Central Gyre (NPCG). They documented the effects on larger marine organisms through cases of entanglement and ingestion. The documented the ingestion and quantify the amount of plastic found in the gut of common planktivorous fish in the NPCG. Each plastic was taken from the gut of the fish and was counted, weighed and categorized by type, size, class, and color. The results were approximately 35% of the fish examined has plastic pieces in their guts. A total of 1375 pieces of plastic, ranging from 1 to 83 pieces per fish and averaging 2.1 pieces per fish were collected from the guts. Qualitatively, ingested plastic consisted primarily of fragments:
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- 94% film
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- 3% fishing line
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- 2% rope
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- 1% styrofoam and rubber
The highest percent of color was:
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- 58.2% white
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- 16.7% clear
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- 11.9% blue
The above percentages of color of the most commonly found plastic in the guts of the fish were similar to the color of the area's plankton, which is the primary food source for the fish. Plastics, both large and small pieces, are a complex problem in the marine environment. The types of plastic that the sea creatures eat and encounter will depend upon where they live and eat. As humans we can only see the plastic on the oceans surface, but they are many types on the ocean floor as well. We need to make an effort to not forget that this problem exist because we can's see the pollution. The sea creatures will continue to be affected unless we make careful choices of what we do with our plastic and how we dispose of it. (17)