From waste to wearable

UC Riverside chemical engineering researchers have completed construction of a multi-kilogram-scale biomass processing facility that transforms forestry and agricultural biomass waste into pulp that can be made into many fiber and textile consumer products.

Arun Raju, left, CE-CERT's associate director of operations and associate research engineer; Don Collins, CE-CERT director and professor of chemical environmental engineering; Charles Cai, associate research professor; and Chad Larson, a junior specialist at a ribbon cutting for a for UCR's pilot-scale, two-story biomass processing unit. (UCR/Stan Lim)

The two-story pilot system demonstrates a breakthrough pulping technology that can enable growers, forest managers, and others to profit from the waste they produce, which is now costly and problematic to dispose of.

"It's cleaner, milder, and uses less energy than traditional kraft pulping," said Charles Cai, an associate research professor who invented the process and led the build-out of the pilot system at UCR. "It doesn't compete with lumber because it can transform substandard wood waste into an on-spec high-value pulp product."

The sustainable pulp produced by the UCR system has qualified as textile-grade dissolving pulp, which is the most valuable kind of pulp. It's used to make cellulose-based fabrics like rayon and lyocell. Sustainable fashion brands, such as Patagonia and Lululemon, use lyocell to make performance sportswear and breathable undergarments.

Housed at UCR's Center for Environmental Research and Technology (CE-CERT), the pilot system uses a patented method called CELF, short for co-solvent enhanced lignocellulosic fractionation, which is both energy-efficient and non-polluting.

"With CELF, the process is so mild that it doesn't break down the material in a destructive way, so harsh conditions are avoided, and the byproducts are usable, not hazardous," Cai said.

The CELF system has several advantages over traditional kraft pulp mills, which operate under severe temperatures, pressures, and caustic conditions.

While conventional mills pulp whole logs from clear-cut forests, the CELF system uses 50 percent less energy to process low-grade biomass such as widely available forest thinning debris, orchard trimmings, and corn stalks-materials that are often burned or left to decay. These waste streams also cause harmful air pollution when they are disposed of by burning.

The CELF method further avoids producing "black liquor," the toxic, caustic waste byproduct of kraft pulping that is particularly harmful to air and aquatic ecosystems. Instead, it yields non-toxic dissolving pulp, along with purified lignin, fermentable sugar syrups, and gypsum.

Lignin-based insulating foam samples of different hardnesses made using the CELF process. (Photo/UCR)

Lignin and gypsum are used to make certain construction building material products.

"Lignin is a natural polymer found in the cell walls of plants that is cleanly extracted by our pilot system to make bio-polyurethane foam panels for home insulation, among other biopolymer products," Cai said.

The gypsum produced is the same material used to make drywall. So, beyond the textile industry, the CELF process may attract interest from construction material manufacturers.

The CELF pilot started recently by processing shredded wood debris or "slash" from California forest clearings overseen by state officials to reduce wildfire risks.

The facility's first client is The Hurd Co., based in Santa Monica, which is exploring CELF's ability to convert almond orchard waste into a high-grade dissolving pulp to be extruded into lyocell to make activewear.

The Hurd Co. also made equipment donations that allowed Cai and his team to complete construction of the pilot system despite the by the Trump administration's suspension of over $1 million in federal grant funds originally designated to this project.

With its pilot facility, UCR is seeking business services agreements with other interested companies to develop biomass-based fibers and to license the CELF technology.

Because CELF can run on a smaller scale than traditional mills, it opens the door for distributed pulp production-potentially at the site of the waste itself, such as farms or forest thinning operations. Growers or forest agencies could install units much smaller than today's pulp factories and process their own biomass waste streams.

Cai emphasized that the project isn't about creating a new material, but about improving how existing materials are made.

"We're not introducing a new textile fiber. We're using a cleaner and cheaper process to make the same dissolving pulp-but from what used to be waste," he said.

"In most cases, we're also solving a waste problem," Cai said. "We're turning what would be a landfill or burn pile liability into something valuable-and doing it in a way that avoids the environmental costs of black liquor processing or deforestation."

Header photo: Charles Cai, the associate research professor who invented CELF process. (UCR/Stan Lim)

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