The Great Pacific Garbage Patch

Although most of the discarded plastic finds its way into landfills, about 16% is combusted to produce energy [2]. Since plastic is derived from petroleum products, its energy yield is almost as high as fuel oil; plastic yields 19,900 BTU/lb whereas oil yields 20,900 BTU/lb [3]. However, the incineration of plastics produces air pollution by releasing chemicals such as hydrogen chloride, dioxin and fine particulate matter [2]. Another way of dealing with plastics is recycling, but this only accounts for about 7% of the plastics encountered in municipal solid waste centers [1]. Because plastics pose a threat to human and wildlife health when disposed of in landfills or through incineration, engineers are working to increase recycling rates by improving current recycling technologies while also developing biodegradable polymers for future use.

A plastic is made up of individual molecules called monomers, which are linked together to form long chains called polymers. Each polymer has unique chemical properties, physical properties, and functions [4]. Consumer plastics are largely made from six different polymer resins, which are indicated by a number etched onto the surface. The numbers or resin codes are numbered from 1 to 7. Fig. 2 outlines the different polymer resins, their resin codes, main properties, general applications, and potential recycled products. The chemical composition and function of each resin controls where the resin can be recycled and the recycling rate [1]. According to the EPA, plastic with resin code 7 (mixed plastic or other less-commonly used polymers) accounts for 22% of total plastic waste, but is the least recycled with a rate of 6%. This could be attributed to the difficulty of separating mixed plastic during the recycling process. On the other hand, PET, or resin code 1, only accounts for 12% of the total plastic waste, but has a recycling rate of about 20% [1]. Because of its widespread use in drinking bottles, PET is very identifiable and easy to sort.