Part 2: Gin trash, or as it is called now, cotton gin byproducts, at one time represented a problem to be disposed of, a fire hazard on the gin yard, or an eyesore at the end of ginning season.

As the saying goes, one man’s trash can be another man’s treasure. In recent years, researchers have taken a closer look at gin waste and have found some valuable properties in the burrs, sticks and stems left over after the ginning process.

This series looks at some of the ongoing work that adds value to gin trash.

USDA-ARS scientists have found a treasure in cotton gin trash. Research Engineer Sunghyun Nam, from the Cotton Fiber Bioscience and Utilization Unit in New Orleans, says waste material from cotton ginning has the potential to transform silver ions into silver nanoparticles, creating a hybrid material with numerous applications.

“We see a lot of hidden value in cotton gin trash,” Nam says. “Gin trash disposal options that go into landfills or are composted are costly and sometimes not suitable for all climate conditions.”

Silver nanoparticles, she says, are highly sought after for antibacterial, antifungal, antiviral, electrical, and optical properties. She explains the advantages.

Why is gin trash a good source material for nanoparticle creation? Cotton gin trash is a good source material because components like lignin and hemicellulose can serve as reducing agents for nanoparticle synthesis. These naturally occurring components reduce silver ions into silver atoms. The silver atoms then cluster and grow into nanoparticles on the surface and within gin trash micoparticles. This method eliminates the need for additional chemical agents, such as reducing and stabilizing agents, which are typically required in the chemical synthesis of nanoparticles. So it's not only about repurposing agro-waste but also providing a sustainable and cost-effective nanotechnology solution.

Related:Research adding value to gin cotton byproducts

Cotton gin waste. (Photo by Sunghyun Nam)

Can you explain the process? It is a simple process that does not require any machinery. Gin trash, which is a mixture of burrs, bracts, sticks, and leaf fragments, is first milled into a microparticle powder for material fabrication. Then, the gin trash powder is heated in water containing silver ions. This one-pot treatment effectively activates the gin trash’s ability to produce silver nanoparticles.

How long does the process take? It's very quick. The gin trash can start to produce nanoparticles within several minutes. The easiest way to tell whether nanoparticles are produced is through a color change. Due to the unique optical properties of nanoparticles, the formation of silver nanoparticles in gin trash adds a darker brown color to it. In our tests, we used 30 minutes.

Related:Turning gin trash into compost

How is that powder used? This natural synthesis results in embedding silver nanoparticles inside the gin waste microparticles. Electron microscopic images of the cross-section of the microparticles showed that numerous nanoparticles are uniformly dispersed throughout the entire volume. This organic-inorganic hybrid material can be used to produce new products with antimicrobial properties, such as composites, packaging, particleboard, absorbent materials, or films. Recently, we produced an antimicrobial aerogel (a porous, solid foam) from silver nanoparticle-embedded cotton gin trash nanofibers.

How long have you been working on this? We've been working on this project for about two years now.

Where did the idea come from? The original idea started with raw cotton fibers. Most cotton fibers used in the textile industry are scoured and bleached, processes that consume a lot of energy and chemicals. To promote the use of mechanically cleaned raw cotton fiber, we studied its potential for nanotechnology and found that raw cotton fiber has the ability to produce silver nanoparticles. Some components in raw cotton fiber like pectin and sugars, which are removed by scouring, act as reducing agents for nanoparticle synthesis. We got the idea from the raw cotton fiber and found that cotton gin trash has even more oxidizable components. We were excited about this potential and decided to focus on cotton gin trash.  

Related:Cottonseed back in rations

Scanning electron microscope (SEM) image showing silver nanoparticles produced by cotton gin waste. (Photo by Sunghyun Nam)

How are nanoparticles used? Silver nanoparticles are among the most popular nanoparticles in the nanotechnology industry with an estimated global production of about 500 tons per year. Due to their unique antimicrobial, electrical, and optical properties, silver nanoparticles are widely used in consumer products such as textiles, coatings, paints, pigments, electronics, optics, cosmetics, medical products, and packaging. A simple way to use nanoparticles is to apply them onto materials, but surface-treated nanoparticles can easily detach and leach out during use or washing. Embedding nanoparticles into a material improves their durability. Recently, we developed washable antimicrobial wipes using silver nanoparticle-embedded raw cotton fibers.        

“Our research paves the way for new material applications of cotton gin waste that can protect against microbial contamination,” Nam says.