Researchers are using a special form of carbon dioxide to clean the PE containers, allowing some washing and drying stages to be skipped when the material is processed.
The Life Extruclean project is backed by $1.6 million in funding and is coordinated by the Valencia, Spain-based Plastics and Related Materials Research Association (Aimplas). The European Union provided a chunk of the money to support the project.
The group created a white paper on the advancement for Plastics Recycling Update: Technology Edition. It was written by Rosa González, researcher at the Aimplas extrusion department, and Eva Verdejo, head of the Aimplas Sustainability and Industrial Recovery department.
Traditionally, pesticide and solvent container plastics are rinsed at least three times before they’re extruded into pellets, according to the group. This requires significant amounts of water, energy and cleaning agents, and it generates a large volume of wastewater.
The resulting plastics are generally lower quality because of the aggressive washing and drying stages they went through, according to Aimplas.
Life Extruclean is using supercritical carbon dioxide in the extrusion stage to remove contaminants, allowing reclaimers to skip two of the washing and drying steps. It also generates plastics that can be used in higher-value applications, such as new containers for pesticides and solvents.
Supercritical carbon dioxide is created when the gas is brought over its critical temperature (88 degrees Fahrenheit) and pressure (1,071 pounds per square inch). It possesses properties of both a gas and liquid and is becoming an important solvent because of its low toxicity and environmental impact and its high stability. It’s also used in the foaming of polymers.
A gas-injection system introduces supercritical carbon dioxide directly into the extruder, said Barbara Sancho of Aimplas.
“Technology based on supercritical carbon dioxide in extrusion processes is not limited to packages having contained hazardous substances,” Sancho said. “It can be applied to other contaminants present in plastic wastes, where soluble in gas.”