Clean-Up
In most cases, recycliing requires "clean-up" of the used material. Sometimes only simple washing of the material or with water is needed. Other situations require grinding and extraction. (RDC 4/25/2011)
“Existing recyclers in the United States can blend limited quantities of contaminated synthetic resin materials in recycled products. Large quantities cannot be blended because of the undesirable effects of the contaminants on the recycled synthetic resin material properties. Examples include "plastic lumber" and lower grade plastic products.”
“Aqueous processes can be used to displace the contaminants from the synthetic resin material. However, detergents and/or surfactants are required to assist displacement of the contaminants. A stream of usable contaminant-free synthetic resin material will be generated by this method; however, the displaced contaminants will need additional processing to separate them from the aqueous solutions or dispersions. The aqueous solutions or dispersions themselves will be a secondary waste stream that will require treatment before being recycled or discharged as waste water.”
“Halogenated solvents can be used to dissolve/dilute the contaminants from the synthetic resin material. Again, usable synthetic resin material will be obtained by this process if the solvents do not extract essential components from the synthetic resin material. The halogenated solvent solutions will require distillation to recover the contaminants and recycle the solvents. In general, it is difficult to fully reclaim usable contaminants (such as oil) from the distillate. Furthermore, many halogenated solvents are ozone depleting compounds and potential health hazards to humans, and therefore their use and release into the environment are under regulation and close scrutiny by federal and state governments.”
“Combustible or flammable solvents may be used to dissolve and/or displace the contaminants from the synthetic resin material. Usable synthetic resin material can be generated by this method if the solvents do not extract essential components from the synthetic resin material. The combustible or flammable solvent solutions will require distillation to recover the contaminants and recycle the solvents. Only distillation equipment suitable for combustible or flammable solvents may be used and even then fire safety concerns will be significant. As in the case of the use of halogenated solvents, the contaminant may not be fully recoverable from the distillation.”
Recent US Patents
11/23/2010
7,838,628
System for removing contaminants from plastic resin
Bohnert, Hand and DeLaurentiis of Honeywell, Missouri, have developed a method for cleaning recycled plastics by grinding and extracting with supercritical carbon dioxide. (RDC 4/12/2011)