So long, scent

Features - Equipment Case Studies | Processing

Various technologies can help reprocessors remove the scent memory from recycled plastics.

August 6, 2018

The ReFresher eliminates odors caused by low-volatility, high-molecular-weight substances.
Image: Erema

Recycled plastics have a scent memory. They can retain odors from items they rubbed shoulders with in their first life, whether heavily perfumed detergents, food or gasoline, that can create quality issues for products made with recycled resin, and they can permeate recycling plants.

By employing deodorizing technologies, recyclers can produce higher-value plastics that appeal to markets that might otherwise use recycled resin sparingly, if at all.

American Starlinger, Fountain Inn, South Carolina, and Erema of Austria make equipment that specifically addresses odor, as does Envision Plastics, a recycler based in Reidsville, North Carolina. These efforts are giving fresh life to plastics.

American Starlinger-Sahm: Since the K 2016 trade show, the company has been marketing its odor-reduction technology, which is integrated with its recoSTAR lines for recycling polyolefins. Alan DiUmberto, sales manager for American Starlinger-Sahm’s recycling division, says polyolefins are particularly prone to picking up smells because their molecular chains are less dense than other materials, allowing contaminants to flow more easily and facilitating absorption.

He cites detergent bottles as an example, saying the perfume used in the detergent off-gasses during the injection blow molding process. “So, now, you’ve got an entire plant that’s got this really heavy perfume smell. And if you hit the right combination, then you cause eye irritation and everything else.”

DiUmberto continues, “Instead of being able to put 20, 30, 40 percent of this material back in, you’re limited to maybe only 5 percent.” But, with the Starlinger process, that percentage can be increased, he says.

In the first stage of the process, the material enters the Smart Feeder and is flushed with warm air and homogenized by a rotating disc. The material then enters a Starlinger extruder and passes through a cascade filtration system. It encounters a pair of filters: The first removes larger contaminants, and the second removes smaller particles.

The melt then enters a recoSTAR degassing module, which increases its melt surface and exposes it to high vacuum, extracting persistent odors, according to the company.

After it enters a water-ring pelletizing system, the recyclate travels to the Smell Extraction Unit, a vertical tower that removes chemicals using heat and pressure. The technology is based on a modified PET solid-state polymerization process.

DiUmberto says he knows customers need evidence to justify the addition of expensive equipment, so Starlinger has contracted with Olfasense GmbH, a Kiel, Germany-based company that specializes in measuring odors.

“What we have found is we can remove up to 66, almost 67 percent, odor that is in a product,” he says.

At least one U.S. recycler has adopted the technology: Houston-based Avangard Innovative LP, which installed the Starlinger system in a pelletizing line in December 2017, added a second line in February.

“We’ve had to make some modifications to the unit,” says Jon Stephens, Avangard Innovative chief operating officer. “But the unit is working well now, and we’re pleased with the results.”

Erema: Optimizing the entire recycling chain is essential to effectively removing odors, says Martin Baumann, vice president of sales for Erema North America, Ipswich, Massachusetts.

Erema’s answer to odor control is a combination of its Intarema TVEplus and its ReFresher technologies. Together, these technologies can remove odors from low-molecular-weight and high-molecular-weight polyolefins.

Designed for difficult-to-process materials, such as heavily printed films and moist materials, the Intarema TVEplus pelletizing extruder removes highly volatile substances that cause odors, Erema says.

The extruder provides gentle melting, preventing contaminants from being burnt or reduced in size, so Erema’s Laserfilter can catch them.

The Intarema TVEplus system includes a large-volume preconditioning unit in which material is cut, mixed, heated, dried, precompacted and buffered. “This ensures a long material residence time at high temperature, and high residual moisture in the material vaporizes,” Baumann says.

The system applies reverse degassing, pushing volatiles back into the feed zone and out the cutter compactor; this process prevents them from mixing into the resin under heat. A final, double-venting degassing zone at the extruder removes remaining gas from the melt.

Further downstream, ReFresher thermal technology removes low-volatility, high-molecular-weight odors that remain in the pellets. To save energy, ReFresher captures and reuses heat from the pellets as they leave the extruder.

Baumann says, “The ReFresher is insulated, and we only need to supply a minimum of extra heat to keep the deodorization process going for up to 12 hours.”

Envision Plastics: Tamsin Ettefagh, vice president of sales for Envision Plastics, says recyclers can use additives to encapsulate odors as an alternative to using special equipment. But that solution isn’t sustainable, she adds, as it’s unknown if the odor remains encapsulated each time the resin gets re-extruded. Over time, the costs add up.

Instead, the high-density polyethylene recycler has developed proprietary technology to permanently remove odors in the production of two of its resin lines—Deodorized and EcoPrime. Envision Plastics currently markets its recycled materials for use in air ducts for the automotive industry and in packaging for beauty products, food and beverages.

Ettefagh says the odor-removal technology works for all polyolefins.

Residence time is key, she says. Many inbound materials may need longer residence times for odors to dissipate enough to reach acceptable levels.

Envision has found that deodorizing postconsumer resin makes the resulting recyclate more appealing, giving it a broader array of possible applications. The benefit is evident in a signature product—the OceanBound Plastic resin line. Made entirely from plastic collected near beaches and waterways, it’s available in a deodorized version.

While Envision currently uses the technology for its own resin only, the company is working to license it.

“The Envision devolatization process takes out the variabilities of absorbed chemicals in polyolefins that our feedstocks are exposed to,” Ettefagh says.

The author is a correspondent with Plastics Machinery Magazine and can be contacted at

For more information:
American Starlinger-Sahm Inc., 864-297-1900,
Envision Plastics Industries LLC, 336-342-4749,
Erema North America Inc., 978-356-3771,