Polymer and Composite

Unfortunately the majority of this plastic ends up in landfills. When plastic is dumped into landfills the decomposition process can take anywhere from 10 to 30 years.

Recycling has therefore become a reasonable solution to the landfill problem.

There are five factors that are necessary in order for the recycling of plastic to be a successful process. First, the supply of used plastic has to be of a large quantity. This large quantity of plastic is collected at certain areas, which is the second step. Once the plastic is collected, the sorting and separating process begins; this is the third step in the process. The sorting and separating process depends upon the type of polymers that make up the plastic. Plastic products are given codes to help the sorting and separating process. The fourth step in plastic recycling is reprocessing. The reprocessing of polymers includes the melting process, the melting process can be accomplished if the polymers have not been widely cross-linked with any synthetics. If the cross-linking of polymers contain too many synthetics, the polymers will be difficult to stretch and less pliable. The final step is the manufacturing of the melted plastic into new products.

The codes on plastic recyclable containers are what help most in the sorting and separating process. The six categories of plastics are separated into two areas: polyethelyne plastics and polymer plastics. The polyethelyne plastics are labeled HDPE, for high density polyethelyne; or LDPE, for low density polyethelyne. The four polymer plastics that are recycled include polyvinyl chloride, labeled V; polystyrene, labeled PS; polypropylene, labeled PP; and polyethylene terephthalate, labeled PETE. These names and labels can seem confusing, but they are a necessity in the recycling process.

There are four types of recycling processes that usually occur: primary, secondary, tertiary, and quaternary. The primary recycling process is recycling materials and products that contain similar features of the original product. This process is only feasible with semi-clean industrial scrap plastics, therefore this process is not widely used. Secondary recycling allows for a higher mixture of combination levels in plastics. When the secondary process of recycling is used it creates products such as fenceposts and any products that can be used in the substitution of wood, concrete, and metal. The low mechanical properties of these types of plastics are the reason why the above products are created. Tertiary recycling is occurring more and more today because of the need to adapt to the high levels of waste contamination. The actual process involves producing basic chemicals and fuels from plastic. The last form of recycling is the quarternary process. This quarternary process uses the energy from plastic by burning. This process is the most common and widely used in recycling. The reason this process is widely used is because of the high heat content of most plastics. Most incinerators used in the process can reach temperatures as high as 900 to 1000 degrees Celsius. For the sake of the environment the new techniques being used with the incinerators have decreased the amount of air pollutants being released.

The use of incineration in the quarternary 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 materials left over form this process are then placed in landfills.

A current promotional program sponsored by the plastics industry emphasizes the positive contributions that plastics make.
And claims listed in those advertisements are accurate.

But as shown in the article on the preceding page, the largest single use for plastics is packaging. Because packaging has a short lifespan, it makes up a large portion of the plastics waste stream. But where does that “waste stream” lead?

In general, the Environmental Protection Agency says that in the early 1990s about 80 percent of all municipal solid waste was sent to landfills, 10 percent was incinerated and 10 percent was recycled. While more and more plastic is being recycled, the EPA estimates that plastics make up about 20 percent of the solid waste that is landfilled.

Most consumers think that the slow degradation of plastics is the primary reason that plastics should be recycled. However, research has shown that other waste, such as paper, wood and food wastes, also degrade very slowly in landfills.

The more serious problem with plastic waste concerns the additives contained in plastics. These additives include colorants, stabilizers and plasticizers that may include toxic components such as lead and cadmium. Studies indicate that plastics contribute 28 percent of all cadmium in municipal solid waste and about 2 percent of all lead. Researchers don’t know whether these and other plastic additives contribute significantly to products leached from municipal landfills.

How toxic are plastics that are burned? Researchers don’t know that, either. Plastics that contain heavy-metal-based additives may also contribute to the metal content of incinerator ash. The EPA is looking for substitutes for lead- and cadmium-based additives.

One additional concern relates to use of petroleum products. All plastics began their lives as petroleum. By increasing plastics recycling, scientists and engineers are able to reduce dependence on petroleum.