With growing technology, new materials are always being developed.

With these new products comes more waste. Plastics are a relatively new product and topic in the consumer waste disposal debate. There are three options: recycle it, incinerate it or discard it in a landfill. Although plastics are a newer discovery, they have become a part of everyday consumer life. In the United States alone, over 75 billion pounds of plastic are produced every year ². Much of this post-consumer waste finds its way to a landfill, where the decomposition process can take anywhere from 10-30 years ². Add non-plastic waste and it is apparent that the landfills are fast filling up and nothing in them biodegrades within a relative amount of time. Therefore, this option is not considered viable. As a result, recycling and incineration of the plastic waste, produced throughout the world, have become the two main choices for disposal.

The words "polymer" and "plastic" are often thought to be interchangeable. This is not actually the case. "Polymer" originates from the classical Greek words "poly", which means "many", and "meres", which means "parts". From this definition, it can be seen that a polymer is a molecule that consists of many repeating identical base units. Many types of molecules, biological and inorganic, are polymeric. The term "plastic" is used to describe commercial materials made from synthetic polymers, excluding elastomers and fibers ³. It should be noted that while plastics are polymers, not all polymers are plastics.

Two of the basic types of polymers are thermoplastics and thermosets. Thermoplastic polymers are linearly structured with slight branching from the base units. Thermoplastics can be heated and formed, again and again. This is due to the fact that the molecules flow under pressure when heated above their melting point. Thermosets, on the other hand, are formed with irreversible cross-linkages of covalent bonds during polymerization, or post-polymerization treatments. Thermosets cannot be heat softened, or be subject to creep or solvent attack, therefore making it impossible to be thermally processed ³. The different types of polymers that are used in consumer products and the waste by sector are shown below ⁴. As can be seen, thermoplastics are the most widely used per sector.

Within the thermoplastic and thermoset categories there are seven different types of plastic resins that are used to package and produce consumer products. These resins are recognized by a numerical coding system created by the Society of the Plastics Industry in the late 1980’s ⁴. The polymers that will be discussed are Polyethylene Terephthalate (PETE), High-Density Polyethylene (HDPE), Vinyl/Polyvinyl Chloride (V), Low-Density Polyethylene (LDPE), Polypropylene (PP), Polystyrene (PS) and the last category consists of all others.

PETE is the most the commonly used plastic. Its mer, along the base unit of the other categories, can be found in the appendix. PETE is used in soft drink bottles, water containers, vegetable oil bottles, dish detergent bottles, peanut butter jars, and most other clear plastic waterproof packaging.

HDPE, also very common, is used to make film containers, vitamin bottles, milk jugs and butter tubs. Most store bags are formed from this plastic. Since it has a crystalline structure, "clear" products made from HDPE are transparent but hazy.

V is used in the manufacture of food wraps, vegetable oil bottles, blister packages and clear health and beauty bottles.

LDPE is used to make caps, plugs, netting, shrink wrap, garment bags and many other plastic bags. This plastic is similar in structure to HDPE but is less dense and more flexible.

Some plastics made with PP are refrigerated containers, butter tubs, yogurt containers, some bags, bottle tops, carpets and some food wraps.

PS plastics include throwaway utensils, meatpacking, protective packing, and some thick rigid colored plastic products. Plastics that have a wax coating over other coverings are also included in this category.

The plastics included in this category are either layered, mixed plastics or thermosets.

The coding system described above is for the most common polymers used for consumer products. These numbers also indicate the ease or difficulty for each plastic to be recycled, one being the easiest and seven having no recycling potential. Since scientists have not yet discovered a means to efficiently recycle many of the higher numbers, other options must be considered. It is also known that not all plastics are recycled, even though they are disposed of and collected. Time and money play a part in this scenario. This is where much of the debate between recycling and incineration stems from.

Prior to 1989, plastics’ recycling was essentially limited to the soft drink bottles collected in a small number of states. Today, plastic recycling has grown into a national network with curbside and drop-off collection programs, recyclers and product manufacturers hungry for a greater supply of post-consumer resins. The chart below shows the growth in the processing of Post-consumer plastic bottles.

Depolymerization technologies include: hydrolysis, methanolysis, and glyocolysis. These technologies convert condensation polymers, such as PETE and polyurethane, into basic chemicals. This method requires clean, single-resin plastics. Depolymerization involves applying adequate amounts of heat and pressure to pre-cleaned waste, which is interacting with a catalytic agent. This is followed by a purification process that produces monomer units. Hydrolysis and glycolysis produce impure monomer yield, while methanolysis results in a pure monomer.

The pyrolisis process not only converts plastic waste into basic chemicals, but oils as well. An advantage to pyrolisis is that it can accommodate mixed plastics and resins. Despite its attractiveness, the process is difficult except when recycling polystyrenes (PS) and acrylics.

Dissolution is an up and coming process based on the idea that polymers dissolve in various solvents. By implementing polymer dissolution, the individual components of the mixed or layered plastics can be separated.

One of the more common recycling techniques for PETE, HDPE, and LDPE involves melting the plastic into bales, then breaking these bales apart and grinding them into small flakes. These flakes are then washed and floated to remove heavy contaminants. The cleaned flakes are then dried in a stream of hot air. These flakes can have color pigment added or be run through a pelletizer. The pelletizer forms small beads that can be used in injection molding processes to create new products.

Recycling the most common plastic resins, results in the manufacture of different products. PETE, the easiest plastic to recycle, can re-enter the consumer market as carpets, spun fiber filling, fleece jackets, and ribbons for VCR and audiocassettes. Much of the recycled PETE also returns as new drink bottles. Some uses for recycled HDPE include; non-food containers, piping, and even lumber. LDPE is recovered as trash and grocery bags, tubing, and agricultural film. Although car tires have not been readily mentioned, vulcanized rubber is a polymer. The cross linkages in the tires make it impossible to melt down, but this does not stop tires from being recycled. Tires can be shredded and re-introduced as footwear, or mouse pads.

Although much of the clean thermoplastic manufacturing waste is recycled, remelted, and reformed; primary recycling by these methods is not, at present, an economic option for a majority of the post-consumer plastics or manufacturing wastes that are contaminated. The removal of these contaminants has been difficult and costly. One of the best examples of this is that PVC bottles are hard to differentiate from PET bottles, but one stray PVC bottle in a melt of 10,000 PETE bottles can ruin the entire batch. Many plastics are also treated with additives. PVC contains plasticizers that are difficult to remove. This poses another hurdle for the recycling community. Another problem involving plastics recycling is that the plastic is usually only recycled once. With paper, glass and cans, the recycled product becomes a similar product and can be reused numerous times. Plastic bottles, for example, can be recycled, but can not become food or beverage containers. They are usually re-used once, and turned into carpet or sleeping bag stuffing.

So, even though recycling plastics reduce the need for virgin materials, and also reduce the amount of waste in landfills, a number of plastics still find their way in the dumps. This is because many can not be recycled effectively, or because, after the initial re-use, the product is no longer recyclable and discarded.

As mentioned previously, plastics have become an integral part of the world’s everyday life. Unfortunately, much of the plastics produced are not recyclable, or just do not find their way into a recycling center. Empirical evidence from the Environmental Protection Agency suggests that not more than 50% of the plastics in a town’s solid waste actually gets recycled. In fact, this rate across America is below 20%.⁷ Much of the plastics with additives ,such as plasticizers and resins, can not be efficiently or economically recycled. This leaves one of two options; place the waste in a landfill or incinerate it. If a plastic bottle is discarded into a landfill, the cost and energy required to produce that bottle can never be recovered. This is why many of the incineration plants are constructed with energy recovery in mind. These plants are called waste-to-energy plants. Within this plant, when the plastic bottle is incinerated, a portion of the energy used in production is recovered when the heat from incineration is used to produce steam or electricity. It is important to point out that within a waste-to-energy plant, the separation of plastics and other wastes (the garbage found in your kitchen garbage can, for example) is not required. When garbage and plastics are used in a waste-to-energy plant, there is usually no addition of other fuels to continue the heating process. Plastics, when compared to the other wastes in these plants, release by far, the most energy per unit weight. Plastic accounts for roughly 8% of the solid waste burned, however, it accounts for over 30% of the energy acquired during incineration. ⁷ From the chart below, the gross differences in average heating value per average weight of waste between polymers and all other types of waste can be seen.

In order for polymers to be effectively incinerated, a waste-to-energy facility must be used. A typical waste-to-energy facility uses both chemical and physical methods during incineration to harness the energy and remove pollutants. In most plants, the waste is stored in a large waste pit. The waste is moved (using a crane) into a hopper, which feeds a charging mechanism. The charging mechanism drops the waste at various intervals (depending on the desired combustion rate) onto combustion grates at the bottom of the boiler. In this combustion chamber the solid waste is incinerated at proper temperatures to achieve as much complete combustion as possible. The combustion process generates temperatures between 1,800-2,000 F (980-1,100 C). The gases produced from the combustion process leave the grate section and rise into the furnace. The heat from the furnace is transferred to water within different tanks and pipes, and sent through a steam producing system. This superheated steam produced from the hot gasses is generally used to turn steam-powered turbines, which produce electricity. The solid component of the combustion process has been turned to an ash or dust, and drops, via gravity, into a container.

Due to the fact that much of the plastic waste when incinerated produce poly-aromatic-hydrocarbons, hydrochloric acid gas and other various possibly harmful by-products, the waste-to-energy plant is equipped with a variety of air-pollution control devices such as carbon filters, lime slurries and electrostatic or mechanical filters. Wet scrubbers incorporate the lime to remove almost 85% of the sulfur dioxide produced during combustion, while the electrostatic or mechanical filters are used to remove the heavy metals. When these pollution controls are in place, a comparatively small amount of emissions are produced. A typical waste-to-energy plant generates less sulfur and nitrogen oxides than most existing coal and oil-fired power plants. These types of plants that are located in the United States produce less than 1% of the carbon dioxide emitted in America.

The processes and safety measures mentioned above, show many reasons why the incineration of plastics and consumer waste in general is a very good option in the recycle, incineration, landfill debate. As mentioned in the recycling section, tires are also a polymer, and although tires can be recycled to produce a limited amount of other useable materials, they have been proven to be useful when incinerated.

The Modesto Energy Tire Disposal Project burns whole tires at 2500 F. This is the temperature required to completely and cleanly incinerate scrap tires. The Modesto facility feeds 19,000 tires a day into two boilers. The heat generated from the tires burning converts water into steam, which drives a turbine generator that produces 300,000 kW hours of electricity a day. This electricity is then sold to Pacific Gas & Electric Co.

However, burning plastics, tires, and other polymers is not emission free, and by-products of a toxic nature are produced. These pollutants can be reduced and should be able to make way for cleaner and easier polymer incineration.

Recycling as compared to incineration is a better a way to recycle because of "resource conservation" and "waste reduction". Through effective resource conservation the impact on the Earth can be minimized if the Earth’s resources are used wisely. To do this, we must more efficiently manage natural resources and lessen the environmental impact of the products we use from raw materials, to production, to distribution and on through ultimate disposal. How do plastics contribute to effective resource conservation? From production through waste management, plastics help conserve resources. Their unique properties and characteristics (light weight, durability, formability) enable manufacturers to minimize the raw materials used, energy consumed and waste generated in the production of goods ranging from automobiles to coffee cups⁷.

Plastics help to reduce waste disposal because they are strong and lightweight. Plastics have an increased life span that makes it easy to recycle. Their physical properties allow them to be used in multiple applications, while their durability and flexibility allow them to be used again and again. An example: laundry products are being packaged in reusable plastic bottles. Reuse of plastic helps offset trash disposal costs and reduces the amount of waste sent to landfills. Because of plastics superior qualities most businesses recycle them. "A 1998 study identified 1,792 businesses that handle and/or reclaim (sort, process, and/or produce) post-consumer plastics." ⁷ Plastics can be recycled back into any application, from food and beverage containers to automobile parts.

Unlike recycling, incineration does not allow the reuse of plastics. Plastics are completely discarded with incineration. However, there are some advantages to incineration of plastics. "The use of incineration in the quaternary process is most beneficial because through the high temperature heating process the incoming waste is reduced by 80% in weight and 90% in volume. The material left over from this process are then placed in landfills." ⁶ Plastics are also safe in waste-to-energy facilities. Experts agree that properly equipped, operated and maintained facilities can meet the latest U.S. standards for air pollution control. Plastics are typically derived from petroleum or natural gas giving them a stored energy value higher than any other material commonly found in the waste stream. Plastics, however, can actually help save energy. Only 4% of the U.S. energy consumption is actually used to produce plastic’s raw materials, including feedstocks. ⁷

The environmental damages caused by recycling are less than the environmental damages caused by landfill and incineration. In addition, some forms of recycling are less environmentally damaging than others.

Managing waste will always entail some tradeoffs. All of the three options, recycling, incineration and landfills have some disadvantages. Landfills which produces no emissions, fails to take advantage of the energy value inherent in plastic. Incineration on the other hand, recovers the energy in plastic materials and reduces the volume disposed solid waste by up to 90% of its initial pre-burn volume. The problem with this method is that is produces an ash residue which must be managed. This is one of the reasons why recycling is favored over incineration. Money is being saved and also reuse of the plastics. Every aspect is benefited from recycle for the environment, businesses and consumers.