Scrap Plastic
Scrap Plastics: "This is a new-to-the-world industry with
huge energy savings.
Recycling plastics uses
only roughly 10 percent
of the energy that it
takes to make a pound
of plastic from virgin
materials" -
Dr. Mike Biddle
President
MBA Polymers
Of the estimated 22.4 million tons of plastics produced in the United
States in 1998, only about 5.4 percent were recovered for recycling.
Plastics used in durable goods (such as cars, electronics, and appliances) account for the largest proportion by weight of plastics in
U.S. municipal solid waste (MSW). However, the mixed waste streams
characteristic of these harder, engineered plastics are difficult to
separate and, thus, complex to recycle. New separation technologies
could increase recycling rates for plastics significantly.
Introduction: The use of plastic in packaging has skyrocketed in that time and recycling has had a hard time keeping up. Society has enjoyed immense benefits from plastic, including greater energy efficiency. But plastics are derived from natural gas and petroleum — finite resources — and our ability to fully integrate plastic into the recycling loop is one of the biggest tests of America's willingness and ability to manage these resources responsibly.
Plastics — synthetic polymers made from oil and natural gas — were introduced less than 100 years ago and quickly became the world's most used raw material.
Plastics are much like natural polymers in amber, turtle shells, animal horns, human fingernails and hair.
Other synthetic polymers include rubber as well as many paints and adhesives.
Polyethylene is one of the simplest polymers — with two atoms of hydrogen attached to each carbon "vertebrae" of the chain.
Polyethylene is one of the simplest polymers — with two atoms of hydrogen attached to each carbon "vertebrae" of the chain.
Polymers are large molecular compounds formed by a change of smaller, identical molecules called monomers. Hydrocarbons derived from petroleum and natural gas are the basic building block of plastics. Carbon atoms provide the backbone of the chain and hydrogen atoms bond to individual carbon atoms along the chain. Polymers are also made in combination with other elements such as oxygen, chlorine, silicon and sulfur to form various resins with unique properties and characteristics.
The Invention of Plastic
Beginning in the 1860s, early man-made polymers were synthesized from cellulose and coal tar, and industrial uses were readily apparent. Various plastic polymers could be used instead of rubber, wood, glass or stone in several manufacturing processes.
Many researchers helped give birth to plastics, but a Belgian-born chemist working in Yonkers, New York, earned naming rights by developing the first all-synthetic plastic.
In 1907, while trying to develop a synthetic varnish, Leo Hendrik Baekeland blended the resin of two chemicals and heated the mix under pressure. The resulting polymer proved useful not only as a varnish, but also for making billiard balls.
And radio cabinets. And buttons. And pipe stems, toilet seats and airplane parts.
A good electrical insulator, this early plastic was also used in the emerging high-tech industries of telephone and camera manufacturing.
Baekeland coined the term "plastics" — from a Greek root meaning "to form" — to describe this new category of man-made materials.
The Plastic Revolution
Extensive use of plastics began during World War I, when the use of petroleum – easier to process into resins than coal – became more widespread.
The sheer material demands of the World Wars, and the economic hardships of the Great Depression in between, led to widespread use of plastics as a cheap substitute for other raw materials in a wide variety of consumer goods.
Though negative associations with plastic as a "cheap substitute" persist, that attribute has placed a wider range of consumer goods within the reach of millions more people. It has helped the plastics industry develop new resins, new uses and spawn entire new industries. Today, plastic is used to make everything from pantyhose to prosthetic limbs, from toys to the window frames on the Space Shuttle.
Plastic's Good Points
The key to plastics' success, their popularity among manufacturers and consumers, is that they can be made to do many things economically.
Plastics can be blended in different formulas and modified with additives to provide a wide range of characteristics to meet various product specifications. There are 40 categories of plastic and several specific grades within these.
Plastics have a wide range of characteristics but most plastics share a few general attributes.
Common attributes of plastics
Chemical Resistance:
Plastics generally hold up well when exposed to corrosive chemicals. It's one reason why so many cleaning products and other corrosive, potentially toxic fluids are stored in plastic.
Thermal Insulation:
Plastics do not transfer heat readily. Thus plastics are used to make siding, pot handles, microwave cookware, foam coffee cups and insulation in refrigerators, freezers and coolers. In textiles, thermal underwear is often made with polypropylene and the fiberfill of insulated winter coats is increasingly made from recycled #1 plastic (PET) bottles.
Electrical insulation:
Plastics do not generally conduct electricity well, the reason so many electric appliances, power cords, outlets and wiring are made of or coated with plastic.
Lightweight:
Plastic's light weight makes it valuable in applications where strength is needed at a minimal weight. Thus, plastic play structures can be strong enough to support the weight of chidren but be light enough that one person can move them. Nylon pantyhose can be strong and sheer. Kevlar® vests worn by law enforcement officers can allow freedom of movement but still stop the penetration of bullets.
Plasticity:
The word comes from the Greek word for "to form," and the variety of forms plastic can take is another key to its success. Plastics can be stretched into strands and woven into fibers to make textiles or injected into a wide range of simple or complex molds to make car parts, toys, beverage containers and artificial heart valves.
Plastics on an Elemental Level
The basic building blocks of plastics are hydrogen and carbon. The simplest plastics contain only hydrocarbon monomers, but other elements — oxygen, chlorine, fluorine and nitrogen — are introduced to the mix of many plastic polymers.
This contributes to the diversity of potential uses for plastics, but also complicates recycling efforts. For most applications, plastics do not mix well with other plastics. Because of this, recycled plastic must be meticulously sorted by type before it can be reused in new products.
| Elements in common plastics |
| Plastic: |
Contains: |
| Polyvinyl chloride (PVC): |
Chlorine |
| Nylon |
Nitrogen |
| Polyester |
Oxygen |
| Polycarbonates |
Oxygen |
| Teflon® |
Fluorine |
Plastic Elements
In addition to the various elements mixed with hydrocarbons to produce different plastic polymers, various additives are introduced to enhance specific properties or merely to alter appearance.
These additives also complicate recycling efforts. Many black plastic disposable microwave dinner trays, for instance, are made of the same plastic (PET) as plastic soda bottles. But the black plastic cannot be recycled with clear plastic without discoloring it. Because black plastic microwave trays are not available in sufficient quantity to attract manufacturers, many residential recycling programs that otherwise collect PET do not accept these trays.
Common plastic additives
Flame retardants and stabilizers
These additives inhibit the degradation of plastic caused by exposure to oxygen, heat, sunlight and water.
Colorants
Various chemicals are added to plastic consumer goods in response to consumer expectations. Plastic bottles and other packaging are often colorized, sometimes to assist in the marketing cause of brand differentiation, sometimes to help protect the contents from exposure to direct sunlight.
Flow agents
Chemicals are sometimes added to plastics in their fluid state to help them flow properly when they are molded into products.
Release agents
Release agents are sometimes added to help a new plastic product pop out of the mold properly.
Lubricity
Lubricating agents are sometimes added to improve the surface appearance of plastic products or to reduce tack and friction.
Plastic Composites
Consumer goods have long been made with layers of more than one type of plastic. This practice makes such products difficult to recycle, but since durable plastic goods are not a target of most public recycling programs, plastic layering has not been much of an issue.
But the use of laminates in food and beverage packaging is another story. Laminates are meant to make plastic packaging practical where a single layer of plastic won't do. PET plastic is fine for juices, water and soft drinks, for example, but it allows oxygen to seep through. This oxygen shortens the shelf life of products such as tomato juice and beer and compromises the products' flavor.
Bottlers and plastic manufacturers have therefore developed high-barrier bottles — layers of nylon, ethylene vinyl alcohol or liquid crystal polymers sandwiched between layers of PET to better seal out air. Because these various layers cannot be readily separated, such bottles are difficult to recycle with existing recycling programs and technologies.
Sometimes recyclable plastic bottles are wrapped in a colorful layer of PVC, more for marketing purposes than anything. While these bottles are recyclable, the PVC wrap is not, and it should be removed.
Recycling Rates
Thermoplastics, the largest of the two groups of plastics, are inherently recyclable. Once formed into a product, they can be melted down and reformed repeatedly.
In practice, however, only 5.4 percent of plastics discarded annually are actually recycled.
| Plastic in the waste stream |
 |
| Discard weight in millions of tons |
| |
Municipal solid waste |
Plastic waste |
| Total discards |
231.9 |
24.7 |
| Recovered |
69.9 |
1.3 |
Discard weight in millions of tons
SOURCE: U.S. EPA |
Thermosets are the other distinct group of plastics. Unlike thermoplastics, thermosets decompose when reheated and thus are unrecyclable.
Bakelite, the first all-synthetic plastic, was a thermoset. Today, the laminate Formica® and various "super glue" adhesives are among the better known thermosets in use.
SOURCE: VIRGINIA TECH CHEMISTRY LEARNING CENTER
Recycling Vs. Disposal
It takes about as much energy to bury a ton of plastic in a landfill as is stored in 4.67 gallons of gasoline.
Recycling a ton of plastic saves about as much energy as is stored in 197 gallons of gasoline. Recycling HDPE plastic saves slightly more, LDPE slightly less. The energy savings from recycling PET is about the same as the average for plastic.
Because the energy used to convert fossil fuels to plastic is lost when plastics are burned for energy, waste-to-energy combustion is a relatively inefficient means of energy recovery. Burning a ton of HDPE or LDPE produces the energy equivalent of about 59 gallons of gasoline. Burning a ton of PET for fuel is even less efficient, generating the energy equivalent of almost 31 gallons of gasoline.
| Energy saved / Energy burned by solid waste management practice |
| Measured in millions of BTUs per ton of plastic |
| Plastic |
Recycling |
Combustion |
Landfilling |
| HDPE |
18.99 |
6.66 |
0.53 |
| LDPE |
24.10 |
6.66 |
0.53 |
| PET |
22.20 |
3.46 |
0.53 |
| For comparison, the BTU value of a gallon of gasoline is calculated at 113,500. |
Recycling Plastic Containers & Packaging
About 79 percent of the plastic recycled in the United States comes from disposable plastic packaging and beverage containers.
Plastic packaging was designed to be disposable, part of the reason it became a focus of waste reduction efforts.
But plastic packaging is also easier to sort through than other plastic products. While there are hundreds of varieties of plastic, just six are used in 60 percent of plastic production, including at least 90 percent of plastic packages and containers.
| U.S. plastic packaging recycling rates: 2000 |
| IN THOUSANDS OF TONS |
|
Disposed |
Recovered |
% recovery |
| Soft drink bottles |
830 |
290 |
34.9% |
| Milk bottles |
690 |
210 |
30.4% |
| Other containers |
2,630 |
260 |
9.9% |
| Bags, sacks & wraps |
4,200 |
90 |
3.2% |
| Totals |
11,190 |
1,030 |
9.2% |
Some industries have set up recycling systems independent of the residential collection system to reduce the environmental impact of certain products.
Makers of polystyrene foam — Styrofoam® or packing peanuts — set up The Peanut Hotline in 1991 to help people looking for ways to recycle loose-fill packaging. As of July 2001, over 250,000 have used the service.
The hotline can help callers find the nearest drop-off site for plastic “peanuts” and similar packaging items. It is maintained by the Plastic Loose Fill Council (PLFC) at (800) 828-2214.
The PLFC says that 30 percent of polystyrene foam is reused. New polystyrene foam now contains at least 25 percent post-consumer recycled content, according to the group.
The organization notes that producing polystyrene foam takes 40 percent less energy, uses 33 percent less water and generates half the air emissions as the production of comparable paper packaging.
Recycling Rates by Product Type
Some plastic products are easier to recycle than others.
The recycling rate for plastic in durable goods — household items with a life expectancy of at least three years — is low, and the recycling rate for nondurable goods such as disposable diapers, trash bags, tableware and shower curtains is negligible.
Greater strides have been made in the recycling of plastic containers and packaging. Recycling rates vary among plastic containers, and leading the pack is the recycling of certain plastic beverage containers.
| 2000 U.S. plastic recycling rates |
| BY PRODUCT TYPE; IN THOUSANDS OF TONS |
|
Plastic disposed |
Recycled plastic |
% recovery |
| Durable goods |
7,540 |
310 |
4.1% |
| Nondurable goods |
4,260 |
0 |
-- |
| Containers & packaging |
11,190 |
1,030 |
9.2% |
| Total plastics in MSW |
24,710 |
1,340 |
5.4% |
Carpet makers have long been allies of recycling. Half of new polyester carpet made in the United States is made from recycled PET bottles.
Carpet discards also contribute significantly to the waste stream. 1.1 percent by weight (more if measured by volume) of all municipal solid waste landfilled each year is carpet.
Efforts to recycle carpet are growing, thanks in part to new chemical recycling processes. Rather than simply melting recycled plastic and forming it into new products, chemical recycling actually breaks plastics down to the molecular level. Contaminants such as backing, dirt and adhesives are removed and the remaining hydrocarbon monomers are repolymerized into new plastic.
About 75 percent of the material — mostly metal — in a car is recycled when the vehicle is junked.
Very little automotive plastic is recycled, though plastic parts, including bumpers, instrument panels, seats and interior trim, make up 10 percent of a car's weight.
The Big Three U.S. automakers — DaimlerChrysler, Ford Motor Co. and General Motors Corp. — have formed "The Vehicle Recycling Partnership" to encourage further development of automotive recycling.
The best hopes currently lie with froth flotation technology which makes it possible to separate small pieces of various plastics and other residue left after a car is shredded and the metals harvested. The residue is placed in hot water and various chemicals are added which will react with certain plastics and make them float. The bouyant pieces are skimmed off and another chemical is added. The technology works now, but is considered too costly and time-consuming for general use.
17.04.2007. 11:01
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