Just the flax, ma’am

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Last week I wrote about converting agricultural residue such as wheat straw into bio-fuels. But there are other uses for some crop residue.

Take flax straw, for example.

For most flax growers that phrase immediately provokes the Henny Youngmanish riposte, “Please!”

That’s because flax straw has traditionally been seen as a problem to be managed rather than of any value in its own right. Flax stems contain tough fibers which decay very slowly. That makes them hard to incorporate into the soil after harvest and means they’re still around to cause problems seeding equipment in the spring.

Prairie flax farmers have traditionally burned flax straw, although more recently straw choppers have provided an alternative: they chop the straw fine as it comes off the combine and spread it evenly over the field.

But the fact is, the very fibers that make flax straw a problem also make it potentially valuable.

People have used flax fibers for thousands of years to make linen cloth: that’s what Egyptian mummies are often wrapped in. The plant came to Canada in 1617 and, as settlers moved west, was often one of the first crops planted. It’s an excellent crop for the prairies because it matures rapidly even in a cool, short growing season.

Pretty much all the flax grown in Canada today, however, is oilseed flax, grown for its seeds, rather than fiber flax. Oilseed flax varieties tend to be shorter and have more branches (and hence more flowers and more seeds) than the fiber varieties that are still grown in Europe.

Nevertheless, oilseed flax straw does contain fibers: they’re just shorter. And since, in 2001, Canada produced an estimated 720,000 tonnes of flax straw, there’s lots of it about.

Which is why a lot of people are looking at ways to make profitable use of it.

The fibers in a flax stem are embedded in the bast tissue which lies just under the waxy skin. Glue-like pectins bind the fibers to the stem’s woody core.

To free the fibers you have to dissolve the pectins, a process called retting. The simplest method, dew retting, involves spreading the straw evenly over the ground. Soil microorganisms do the rest, over a period of anywhere from three to seven weeks, depending on the weather.

Researchers would like to replace this rather haphazard method by further developing enzyme retting, which would use selected pectin-degrading enzymes to ret the straw under controlled conditions. This produces cleaner and more consistent fiber, but right now it’s experimental and expensive.

The retted straw is next threaded through fluted rollers that break the stems but only kink the fibers. A scotching turbine then scrapes the broken stem parts from the fibers.

The resulting ribbon-shaped fiber bundles are still relatively coarse and thick, which is fine for some uses. For others, however, these bundles must be further broken down to the much thinner–and rounder–“ultimate fibers.”

Since flax ultimate fibers are roughly the diameter and length of cotton fibers, this process is called “cottonization.” It’s traditionally been done by running the fiber bundles through extremely fine-toothed combs. This only works with well-retted fibers and it produces a lot of dust and waste fibers, which has made cottonized flax too expensive to compete directly with cotton in the textile industry, even though flax fibers are 50 percent more absorbent than cotton, making flax clothing extremely comfortable in hot weather.

Alternative methods of cottonizing flax are now being researched. If the cost comes down, the interest in using flax in textiles will shoot up–which might make it worthwhile for farmers to consider growing taller varieties of oilseed flax for fiber, or focusing on fiber flax varieties instead.

But there are also many uses for the fibers found in the oilseed varieties already grown on the prairies. They’re already being used in specialty papers and to replace fiberglass in automotive parts like dashboard. They might also be used to “sweeten” recycled paper pulp (adding strength to the finished product), blended into insulation batts with properties similar to that of the familiar fiberglass batts used today, and more.

Fiber, it seems, could be healthy not just for individuals, but also for provincial economies.

Permanent link to this article: https://edwardwillett.com/2008/03/just-the-flax-maam/

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