Flax and Hemp
by George A. Lowry
1938, MECHANICAL ENGINEERING
Hemp Produces Large Crops with Little Attention
Hemp, the strongest of the vegetable fibers, gives the greatest production per acre and requires the least attention. It not only requires no weeding but also kills off all the weeds and leaves the soil in splendid condition for the following crop. This, irrespective of its own monetary value, makes it a desirable crop to grow. In climate and cultivation, its requisites are similar to flax and, like flax, should be harvested before it is too ripe. The best time is when the lower leaves on the stalk wither and the flowers shed their pollen.
Like flax, the fibers run out where leaf stems are on the stalks and are made up of laminated fibers that are held together by pectose gums. When chemically treated like flax, hemp yields a beautiful fiber so closely resembling flax that a high-power microscope is needed to tell the difference and only then, be- cause in hemp, some of the ends are split. ~Wetting a few strands of each fiber and holding them suspended will definitely identify the two because, upon drying, flax will be found to turn to the right or clockwise and hemp to the left or counter- clockwise.
Before the war, Russia produced 400,000 tons of hemp, all of which is still hand-broken and hand-scutched. They now produce half that quantity and use most of it themselves, as also does Italy from whom we formerly had large importations. In this country, hemp, when planted 1 bu per acre, yields about 3 tons of dry straw per acre. From 15 to 20 per cent of this is fiber and 80 to 85 per cent is woody material. The rapidly growing market for cellulose and wood flour for plastics gives good reason to believe that this hitherto wasted material may prove sufficiently profitable to pay for the crop, leaving the cost of the fiber sufficiently low to compete with 500,000 tons of hard fiber now imported annually. Hemp being from two to three times as strong as any of the hard fibers, much less weight is required to give the same yardage. For instance, sisal binder twine of 40 lb tensile strength runs 450 ft to the lb. A better twine made of hemp would run 1280 ft to the lb. Hemp is not subject to as many kinds of deterioration as are the tropical fibers and none of them lasts as long in either fresh or salt water.
While the theory, in the past, has been that straw should be cut when the pollen starts to fly, some of the best fiber handled by Minnesota hemp people was heavy with seed. This point should be proved as soon as possible by planting a few acres and then harvesting the first quarter when the pollen is flying, the second and third a week or ten days apart, and the last when the seed is fully matured. These four lots should be kept separate and scutched and processed separately to detect any difference in the quality and quantity of the fiber and seed.
Several types of machine are available in this country for harvesting hemp. One of these was brought out several years ago by the International Harvester Company. Recently, growers of hemp in the Middle West have rebuilt regular grain binders for this work. This rebuilding is not particularly expensive and the machines are reported to give satisfactory service.
Degumming of hemp is analogous to the treatment given flax. The shards probably offer slightly more resistance to digestion. On the other hand, they break down readily upon the completion of the digestion process. An excellent fiber can, therefore, be obtained from hemp also. Hemp, when treated by a known chemical process, can be spun on cotton, wool, and worsted machinery and has as much absorbency and wearing quality as linen.
SCUTCHING MACHINERY
Several types of machine for scutching the hemp stalks are also on the market. Scutch mills formerly operating in Illinois and Wisconsin used the system that consisted of a set of eight pairs of fluted rollers, through which the dried straw was passed to break up the woody portion. From there, the fiber with adhering shards or hurds, as they are called, was transferred by an operator to an endless-chain conveyor. This carries the hurds past two revolving single drums in tandem or between two opposing pairs of drums in tandem,all having beating blades on their periphery, which beat off most of the hurds as well as the fibers that do not run the full length of the stalks. The proportion of line fiber to tow is 50 per cent each. Tow gr short tangled fiber then goes to a vibrating cleaner that shakes out some of the hurds.
In Minnesota and Illinois, another type has been tried out. This machine consists of a feeding table upon which the stalks are placed horizontally. Conveyor chains carry the stalks along until they are grasped by a clamping chain that grips them and carries them through half of the machine. A pair of inter-meshing lawn-mower type beaters are placed at a 45-deg angle to the feeding chain and break the hemp stalks over the sharp edge of a steel plate, the object being to break the woody portion of the straw and whip the hurds from the fiber.
On the other side and slightly beyond the first set of lawnmower bearers is another set, which is placed 90 deg from the first pair and breaks the other end of the straw over a similar sharp-edged steel plate and whips out the hurds. The first clamping chain transfers the stalks to another to scutch the fiber that was under the clamp at the beginning. Unfortunately, this type of scutcher makes even more tow than the so-called Wisconsin type. This tow is difficult to reclean because the hurds are broken into long slivers that tenaciously adhere to the fiber.
Another type passes the stalks through a series of graduated fluted rollers. This breaks up the woody portion into hurds about 3/S in. long and the fiber then passes on through a series of reciprocating slotted plates working between stationary slotted plates. Adhering hurds are removed from the fiber which continues on a conveyor to the baling press. Because no beating of the fiber against the grain occurs, this type of scutcher makes only line fiber. This is then processed by the same methods as were described for flax.
Paint and lacquer manufacturers are interested in hempseed oil which is a good drying agent. When markets have been developed for the products now being wasted, seed and hurds, hemp will prove, both for the farmer and the public, the most profitable and desirable crop that can be grown and one that can make American mills independent of importations. Recent floods and dust storms have given warnings against the destruction of timber. Possibly, the hitherto waste products of flax and hemp may yet meet a good part of that need, especially in the plastic field which is growing by leaps and bounds.