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Research takes on plastic contamination in cotton

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Plastic contamination in cotton can cost producers as much as 7 cents a pound as it trades below equivalent grades from competing cotton producing countries.
Gin labs in Stoneville, Mississippi, and in Las Cruces, New Mexico, looking at various technologies to help detect and remove plastic from the cotton in the ginning process.

Plastic contamination diminishes the value and damages the reputation of U.S. cotton.  

“Plastic contamination results in a loss in premium,” said John Wanjura, USDA-ARS agricultural engineer at the Lubbock, Texas, USDA ginning lab. 

Wanjura, speaking to the annual Texas Plant Protection Association annual conference via Zoom connection due to Covid-19 precautions, said mills are becoming reluctant to buy U.S. cotton because of an increase in plastic contamination. “We’ve seen an erosion of premiums for U.S. cotton. Mills do not want to handle that contaminated material.” 

He said lost premium costs producers as much as 7 cents a pound as it trades below equivalent grades from competing cotton producing countries.  

“That equates to about a $700 million in lost revenue to the U.S. cotton industry for the 2019/2020 crop, about 20.5 million bales.” 

He said other losses include CCC loan discounts.  

Reputation at stake 

The U.S. reputation for quality is also at stake. 

“Those bales of 71 and 72 calls (plastic contamination codes) just won't be purchased by a merchant. There's not much of a home for them. We can't afford a significant market share loss and a loss of markets overseas to our customers.  

“So, what do we do about it? USDA-ARS has a lot of work going on here at Lubbock and gin labs in Stoneville, Mississippi, and in Las Cruces, New Mexico, looking at various technologies to help detect and remove plastic from the cotton in the ginning process.” 

He said research also continues through the Cotton Structure and Quality Research unit in New Orleans and Texas A&M Department of Biological and Agricultural Engineering.  

He said Cotton Incorporated “is helping to lead a lot of research with funding and technical support.” Industry partners include Lummus and Bratney Companies. 

“We’ve had some success,” Wanjura said. 

He cited monitoring systems that detect plastic at various points in the ginning cycle and systems that detect and remove plastic.  

“We’ve developed a monitoring system to detect and eject plastic in the gin. Another machine, the Golden Lion, currently available from a Chinese company, “is a passive type machine folks at the Las Cruces lab are working on.”  

The Las Cruces lab is also looking at a system that passively removes plastic as it's flowing through the conveyance lines.  

“We’re developing a wrap material performance standard through the American Society of Agricultural and Biological Engineers (ASABE).” He said that standard will apply to the current wrap materials as well as new products coming on the market in the future.  

Wanjura explained that the module feeder inspection system relies on cameras installed to identify buildup on the rollers, so operators can stop and remove the material.  

“The longer that material stays on, the greater the potential for contamination. We’ve made modifications to this system in the last couple of years to make the camera mounts more generalized, depending on pit design.”  

He said an algorithm built into software automatically detects plastic accumulation on the rollers and alerts the ginner to remove that material. 

“Also, we’ve integrated additional camera technology to our RFID scanning system to monitor the unloading and unwrapping of modules to help diagnose potential contamination.  

“Cameras mounted on the truck end of the module feeder record every unloading event to capture any mishaps during the unwrapping process. For every module processed we can see what may have caused a contamination event.” 

Wanjura said work over the past few years includes systems that identify colors during the ginning process to detect contamination. 

“Once the system sees that material, it fires a set of solenoids at the base of the apron and blows air out over about an 8- to 10-inch width to eject the contaminants.” 

He said design challenges include the ability to differentiate colored contaminants from natural cotton colors. “Pink and yellow module wraps overlap the “natural color space” of cotton as equipment tries to detect differences in the cotton versus the plastic.”  

The thickness of the plastic also makes a difference in ease of removal. “It's easier to get rid of bigger or multi-layer plastic,” Wanjura said. “If the plastic comes apart off the module, it's harder to get the single layer of material out than it is the multi-layer material.”  

He said this system is commercialized and installed in several commercial gins, one on the High Plains.  

Consistent results 

“In that location, we see pretty consistent results, almost 90% detection and ejection and efficiency across all of those different colors of module wrap.”   

He said Cotton Incorporated purchased one of the Chinese machines and installed it at the ginning lab in Las Cruces. “[Manufacturers] claim it has over an 80% capability to remove plastic in flowing seed cotton. The results we’ve seen is closer to 60%.” 

He said this machine uses a combination of mechanical and pneumatics to remove plastic. “It blows cotton up into the chamber and the plastic is supposed to stick to the drum, but with this design, the air flow rate was not high enough to get anything to stick to that drum. So, we modified things, increased the air flow and the collection efficiency. After the improvements, we see increased efficiency.” 

Heating it up 

He said a thermal concept for removing plastic also shows promise.  “At about 100 degrees Celsius, or 210 degrees Fahrenheit, plastic will melt and adhere to a metal surface. The idea is to heat up the surface plastic flows over and capture some of the plastic. Once adhered to the metal surface, the plastic is scraped off by a knife on the backside of the drum.”  

Wanjura said addressing the plastic contamination issue must be a collaborative and multi-pronged approach that includes in-field monitoring and tracking, as well as monitoring, detecting and eliminating plastic in the ginning process. 

At $700 million in lost revenue, the stakes are too high to ignore. 

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