{"id":107643,"date":"2025-03-14T13:04:07","date_gmt":"2025-03-14T18:04:07","guid":{"rendered":"https:\/\/engineering.wisc.edu\/?post_type=news&p=107643"},"modified":"2025-03-14T13:04:15","modified_gmt":"2025-03-14T18:04:15","slug":"mellow-the-yellow-new-techniques-clarify-recycled-plastic-increasing-their-value","status":"publish","type":"news","link":"https:\/\/engineering.wisc.edu\/news\/mellow-the-yellow-new-techniques-clarify-recycled-plastic-increasing-their-value\/","title":{"rendered":"Mellow the yellow: New techniques clarify recycled plastic, increasing their value"},"content":{"rendered":"\n

A team of University of Wisconsin-Madison engineers has developed a new solvent-based technique for removing stubborn pigments from recycled multilayer plastic packaging. The advance makes recycled plastic more commercially appealing\u2014increasing its market value and moving the industry closer to \u201cclosing the loop\u201d for recycled plastic.<\/p>\n\n\n\n

The research, published in the March 14, 2025, issue of Science Advances<\/em><\/a>, was led by postdoctoral fellow Tianwei Yan and PhD student Charles Granger, who work in the lab of George Huber<\/a>, a professor of chemical and biological engineering at UW-Madison.<\/p>\n\n\n\n

Plastic pollution is a major environmental and sustainability issue, with millions of tons of plastic produced from petroleum products entering landfills, waterways and oceans each year. Despite decades of research, plastic recycling is still very limited; only about 9% of plastic is recycled globally, with much of it downcycled into less valuable products.<\/p>\n\n\n\n

New technologies, however, may help close the loop on recycling, producing high-quality recycled plastic just as good as fresh, \u201cvirgin\u201d plastic. Since 2020, researchers at UW-Madison have made great strides in chemical recycling through a pioneering process called solvent-targeted recovery and precipitation (STRAPTM).<\/p>\n\n\n\n

STRAP is particularly good at recycling colored multilayer, flexible plastics, which include food packaging like bags, pouches, wrappers and films. These types of plastic often incorporate multiple specialized layers that prevent moisture, seal out oxygen and improve strength. STRAP uses a series of solvent washes to dissolve each layer of plastic, which is then recovered and processed into near-virgin plastic. These films also contain a variety of color bodies that are put in by brand owners to market their products.<\/p>\n\n\n\n

In recent years, Huber\u2019s team has refined STRAP. However, the researchers found that the final plastic films they produced often had a yellowish hue to them. That tinge makes the recycled end product much less appealing to manufacturers, reducing the value of the plastic by more than half.<\/p>\n\n\n\n

\u201cTo consumers, yellow might be a sign of age or degradation,\u201d says Granger. \u201cIn these recycled plastics, that\u2019s not the case. It\u2019s just from pigments. But either way, it looks gross.\u201d<\/p>\n\n\n\n

That\u2019s why Granger and Yan set out to discover why recycled plastic film produced via STRAP looked yellow, and what they could do about it. They first tested dozens of pigments, adding them individually to polyethylene, the plastic most used in flexible packaging, running them through the STRAP process to see if they caused the yellowing. Soon, they narrowed the culprit down to Yellow 12, a common organic pigment used to print packaging.<\/p>\n\n\n\n

Most other pigments break down during STRAP processing and are removed by solvents or filtering. But elements of Yellow 12 survive the process, remaining in the solvents used to dissolve the plastic. In the final processing step, in which the recycled plastic is dried, the researchers found that evaporating solvents left behind the pigment in the plastic, causing a yellow sheen in the final product.<\/p>\n\n\n\n

\"George
George Huber<\/figcaption><\/figure>\n\n\n\n

Armed with that knowledge, the team was able to come up with a method to get rid of the color. \u201cThe yellow pigment has a higher solubility in STRAP solvents than other types of plastic pigments due to its chemical structure,\u201d says Huber. \u201cSo the first thing was to pick a solvent that has a lower solubility of that pigment. Then there are a couple of extra steps that really make that plastic come out crystal clear.\u201d<\/p>\n\n\n\n

Working with Chemical and Biological Engineering Associate Professor Reid van Lehn<\/a> and his students, who have developed a sophisticated database of solvent-polymer solubility called SolventNet, the team found a solvent that minimized the solubility of the yellow pigment. Then, Yan and Granger added activated charcoal to the process to bind the color bodies and remove even more of the yellow before using a press to squeeze as much solvent as possible out of the recycled plastic. All of this resulted in clear plastic with no yellow detectable to the naked eye.<\/p>\n\n\n\n

While making recycled plastic clearer might seem like it\u2019s just fixing a cosmetic problem, Huber says it is a critical step in making plastics recycling economically feasible. \u201cOne of the biggest challenges with plastics recycling is contaminants, and one of the biggest issues is dealing with color,\u201d he says. \u201cClear plastic is worth two to 10 times more than colored plastic. That\u2019s because every company wants to have their special color or logo on their packaging. With clear plastic you can add that color. But color also makes it harder to recycle.\u201d<\/p>\n\n\n\n

Yan and Granger say they would like to use their methodology to remove other contaminants found in recycled plastics, including other problematic pigments, dirt and debris, and chemical contaminants like bromine and PFAS.<\/p>\n\n\n\n

George Huber is the Richard L. Antoine Professor in chemical and biological engineering at UW-Madison. Reid Van Lehn is the Hunt-Hougen Associate Professor in chemical and biological engineering. This work was partially supported by a gift from Ross Annable.<\/em><\/p>\n\n\n\n

Other UW-Madison authors include Kevin L. S\u00e1nchez-Rivera, Panzheng Zhou, and Styliani Avraamidou.<\/em> Other authors include Steven Grey and Kevin Nelson of Amcor in Neenah, Wisconsin, and Fei Long and Ezra Bar-Ziv of Michigan Technological University in Houghton, Michigan.<\/em><\/p>\n\n\n\n

This work was funded by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Bioenergy Technologies Office under Award Number DE-EE0009285 to G.W.H and DE-EE0010294.<\/em><\/p>\n\n\n\n

Top image image: Tianwei Yan (left) and Charles Granger have developed a method for removing yellow pigments from recycled plastic film, like the one Yan holds, greatly increasing their marketability.<\/em><\/p>\n","protected":false},"author":106,"featured_media":107646,"template":"","meta":{"_acf_changed":false,"_tec_requires_first_save":true,"_mbp_gutenberg_autopost":false,"_EventAllDay":false,"_EventTimezone":"","_EventStartDate":"","_EventEndDate":"","_EventStartDateUTC":"","_EventEndDateUTC":"","_EventShowMap":false,"_EventShowMapLink":false,"_EventURL":"","_EventCost":"","_EventCostDescription":"","_EventCurrencySymbol":"","_EventCurrencyCode":"","_EventCurrencyPosition":"","_EventDateTimeSeparator":"","_EventTimeRangeSeparator":"","_EventOrganizerID":[],"_EventVenueID":[],"_OrganizerEmail":"","_OrganizerPhone":"","_OrganizerWebsite":"","_VenueAddress":"","_VenueCity":"","_VenueCountry":"","_VenueProvince":"","_VenueState":"","_VenueZip":"","_VenuePhone":"","_VenueURL":"","_VenueStateProvince":"","_VenueLat":"","_VenueLng":"","_VenueShowMap":false,"_VenueShowMapLink":false,"_tribe_blocks_recurrence_rules":"","_tribe_blocks_recurrence_description":"","_tribe_blocks_recurrence_exclusions":"","footnotes":""},"department":[2386],"focus_area":[2401,2382],"news_category":[38],"news_tag":[],"class_list":["post-107643","news","type-news","status-publish","has-post-thumbnail","hentry","department-chemical-biological-engineering","focus_area-computing-and-data-driven-engineering","focus_area-energy-sustainability-and-environment","news_category-research"],"acf":[],"_links":{"self":[{"href":"https:\/\/engineering.wisc.edu\/wp-json\/wp\/v2\/news\/107643","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/engineering.wisc.edu\/wp-json\/wp\/v2\/news"}],"about":[{"href":"https:\/\/engineering.wisc.edu\/wp-json\/wp\/v2\/types\/news"}],"author":[{"embeddable":true,"href":"https:\/\/engineering.wisc.edu\/wp-json\/wp\/v2\/users\/106"}],"version-history":[{"count":4,"href":"https:\/\/engineering.wisc.edu\/wp-json\/wp\/v2\/news\/107643\/revisions"}],"predecessor-version":[{"id":107654,"href":"https:\/\/engineering.wisc.edu\/wp-json\/wp\/v2\/news\/107643\/revisions\/107654"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/engineering.wisc.edu\/wp-json\/wp\/v2\/media\/107646"}],"wp:attachment":[{"href":"https:\/\/engineering.wisc.edu\/wp-json\/wp\/v2\/media?parent=107643"}],"wp:term":[{"taxonomy":"department","embeddable":true,"href":"https:\/\/engineering.wisc.edu\/wp-json\/wp\/v2\/department?post=107643"},{"taxonomy":"focus_area","embeddable":true,"href":"https:\/\/engineering.wisc.edu\/wp-json\/wp\/v2\/focus_area?post=107643"},{"taxonomy":"news_category","embeddable":true,"href":"https:\/\/engineering.wisc.edu\/wp-json\/wp\/v2\/news_category?post=107643"},{"taxonomy":"news_tag","embeddable":true,"href":"https:\/\/engineering.wisc.edu\/wp-json\/wp\/v2\/news_tag?post=107643"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}