Sandy Miller HaysAgricultural Research Service
February 12, 2013
Chances are, if you think about it, that the answer to that question is “yes.” If you have a newspaper around your house, or a magazine, or cereal boxes, or books, or—even more likely—toilet paper, you’ve got wood pulp on hand.
Alas, when your parents told you as a kid that “money doesn’t grow on trees,” they were speaking the truth. While we talk about “paper money,” it’s not actually paper made of wood pulp. According to the U.S. Department of the Treasury’s Bureau of Engraving and Printing, our paper money is actually a blend of 75 percent cotton and 25 percent linen, which helps give it that distinctive “feel” (and also helps it survive a trip through your washer and dryer when you accidentally leave a few bucks in your pants pocket on laundry day).
So pulp is already an important part of our everyday lives. But some scientists of the Agricultural Research Service (ARS) are aiming to make that part even sweeter.
Okay, maybe I’m stretching a point on the “sweeter pulp,” but the truth is that we Americans love our sweets, and a primary source of sugar is sugar beets. In fact, the United States is among the world’s largest sugar producers, and according to the U.S. Department of Agriculture’s Economic Research Service, since the mid-1990s, about 45 percent of our total domestic sugar production has come from sugarcane, while the lion’s share—that other 55 percent—has come from sugar beets.
In case you’ve never seen a sugar beet, they’re not one of Nature’s more glamorous creations. They look something like a turnip, and can weigh somewhere in the range of two pounds. Once the sugar’s been extracted from them, there’s a significant amount of pulp left over. And since they’re the leading source of all that sugar that we Americans love to eat, that adds up to more than 1 million tons of sugar beet pulp generated annually in the United States. Wouldn’t it be great if we could find some useful purpose for it?
That’s what some scientists of the Agricultural Research Service (ARS) thought, too, so they’ve been looking into whether you can turn all that sugar beet pulp into a biodegradable plastic—or, to be more precise, a “thermoplastic,” which is a plastic that becomes soft when heated. The idea is that we could use sugar-beet-pulp-based thermoplastic to make those white, spongy, disposable food containers like you might see at your favorite fast-food restaurant.
The bioplastic is made from both sugar beet pulp and a biodegradable polymer called polylactic acid, or PLA, using a piece of equipment called a twin screw extruder. PLA is a commercially available polymer that’s made from the sugars in corn, sugarcane, switchgrass, and other plants such as (you guessed it) sugar beets—in other words, renewable feedstocks.
Extrusion is already widely used in large-scale production of food, plastics and composite materials—and best of all, it’s very cost-effective.
The ARS scientists showed that up to 50 percent sugar beet pulp can be incorporated with PLA to produce a thermoplastic composite with mechanical properties similar to those of polystyrene and polypropylene, which are the compounds now used to make those white, squishy food packages. The new thermoplastic is cost-competitive with commonly used petrochemical plastics.
As they say on the info-mercials, “Wait, there’s more!” ARS scientists also have been able to use a process called extrusion compounding to turn sugar beet pulp into a thermoplastic-like material with the assistance of water and/or glycerol. That material can then be processed by extrusion or injection molding.
The resulting thermoplastic is very similar to low-density polyethylene, the type of material used for opaque plastic containers, bags, and film coverings, plus the addition of some PLA can enhance its water resistance. The end product could contain as much as 98 percent sugar beet pulp.
How would we use sugar beet plastic? Think yogurt cups, cottage cheese tubs, or any other kind of thin, opaque plastic container. Also think extra income for sugar beet growers and beet sugar processors, and the environmental benefits of a natural, non-petroleum-based, renewable “plastic” that’s not going to be sitting in a landfill for the next 1,000 years.
That’s sweet news for just about everybody!
The Agricultural Research Service is the chief in-house scientific research agency of the U.S. Department of Agriculture. You can read more about ARS discoveries at http://www.ars.usda.gov/news/.