The vegetable fiber commonly known as "kapok" has, during the past few years, come into very general use in the navy as a stuffing fiber. There are now found, as standard equipment, kapok hammock mattresses, bunk mattresses, pillows, cushions, and life preservers, besides various experimental articles such as waistcoats and headgear for aviators. The quantities utilized each year are increasing rapidly and the present indications are that within a few years it will, in our service, entirely displace all other stuffing materials.
The name " kapok " has unfortunately been applied to many fibers closely related in appearance and in botanical origin. Some of the impostors are very inferior in the qualities for which the true kapok is valuable and have to be guarded against in purchasing. The true kapok is the fiber of a tree of the Eriodenron family, whose name, according to the best authorities, is Ceiba pentandra. This tree is indigenous to Central America and perhaps the West Indies; indeed, the word ceiba is Haitien in origin. But the cultivation of the tree has reached its greatest extent in Java, into which it was doubtless imported several hundred years ago.
Java is at present the world's principal source of supply, and is practically the only place where any very great quantity is marketed. There the raising, preparation and export of kapok is one of the principal industries of the island, Soerabaya being the port from which the greatest exportation emanates.
Those interested in the kapok industry in Java make strenuous efforts to have the use of the name restricted to the product of the tree Ceiba pentandra, particularly, perhaps, because India exports considerable quantities of a similar fiber of lower grade and price, the product of the Simul tree.
The true kapok grows upon a large tree in pods something like the horse-chestnut. The pods are in clusters, and when they are ripe the pods split, the outer envelope shrivels somewhat and reveals the fiber and seeds within. The seeds and fiber grow attached to a central core inside the pod, but the fiber is not attached to the seeds as in the case of cotton. If left on the tree, the pods ultimately open so that they allow the fiber to be blown out by the wind, carrying the seeds with it, so distributing the seeds.
When the kapok is gathered for market, however, the pods are taken from the tree before they arrive at this stage of maturity. They are opened by hand, the fiber and seeds separated by beating, sometimes with wands or branches in the hands of low-priced laborers, and sometimes by machine-driven paddles in a large drum or cylinder. When the hand process is used it is carried on inside of an enclosure of netting which prevents the downy fiber from being blown away. During the process the seeds, particles of dirt, fragments of husk and core and pieces of twigs drop to the bottom of the mass, leaving the fiber clean and clear on top.
The fiber is then allowed to dry thoroughly in the sun, after which it is baled much as our cotton is baled in this country, but with cruder methods and materials. Frequently kapok, sent out by Chinese growers, appears here enveloped in matting and bound by bamboo hoops, or grommets made of grasses; the European vendors generally use burlap and steel hoops, or ties.
The seeds furnish, when crushed, a considerable quantity of edible oil, somewhat on the order of our cotton-seed oil, and are of considerable value as food. So far as the writer knows the seed products are not exported. It is said that the fiber itself is used in some parts of Europe in the manufacture of felt, and also that in Germany it has been successfully used in textiles, where, however, its short staple and brittleness make its use difficult.
The most valuable characteristic of this fiber, from the maritime standpoint, is its buoyancy. One pound of kapok will, roughly, support 20 to 30 pounds in fresh water, and will not entirely lose its buoyancy when wet for several weeks. Various theories have been advanced to account for this, but the most plausible seems to be that based upon the surface-tension theory, that is that the fibers are wet very slowly in water so that they displace a volume considerably greater than their own actual cubic contents. It is noted by experiment that when packed firmly, but not tightly, into an envelope, as for example, ticking sewn together in the form of a pillow, the weight supported in water is practically as great as if the envelope were rigid, empty and water-tight. In other words, kapok, when held in mass with moderate firmness, excludes water from the entire volume, moreover it was found that doubling the quantity of kapok in the test cushion did not increase its buoyancy. It is noticeable, too. when kapok is put under gradually increasing hydraulic pressure, that a point is reached at which the object sinks to the bottom. When pressure is released the object rises, but if the pressure is further increased a condition will be attained in which the object sinks and remains on the bottom. This can be explained by the surface-tension theory. When the pressure is applied, if it is not too great, the water presses upon the mass of fiber from all sides and compresses the whole mass to such an extent that it no longer displaces the requisite amount of water to enable it to buoy up itself and its envelope. When the pressure is released the whole mass of fiber expands and its buoyancy increases. When the pressure is considerably increased, however, the surface tension of the mass, and possibly of the individual fibers, is broken down, the water wets each fiber, and its buoyancy is reduced greatly and remains at this low point until the fiber is thoroughly dried out, even if it is then restored.
This fiber is especially desirable for stuffing both afloat and ashore on account of its resiliency, its freedom from organic dirt and vermin and the ease with which it can be renovated and washed. Its resiliency makes it, in mattresses, extremely comfortable to sleep upon. The other two qualities above mentioned make it perhaps the most sanitary stuffing material known. Care has to be exercised in tufting the mattresses, however, to keep the stuffing from "crawling."
When kapok is loose it is highly inflammable and the dust from it during its repicking and "fluffing-up" process, is said to be explosive. One manufacturer in Philadelphia who has been working it for many years told the writer of a fatal explosion in his plant due to the arcing of an electric switch in a room filled with such dust. But when packed firmly, as in a mattress, it is probably no more inflammable than hair.
Its extreme lightness makes the kapok in a mattress cost less than hair for the same mattress. It is not quite so cheap, computed on a like basis as cotton, but is much superior in every other way.
In the purchase of kapok under the Navy Department difficulty was at first encountered by the lack of specifications upon which to purchase. The material is usually graded according to the district in which it was raised, as Japara, Madoura, Semarang, Porrong, Soerabaya, etc., and the standard was "prime Japara." Importers have informed the writer that they can specify, in their purchases in Java, "fair average crop of the season," which is vague to say the least. Specifications, however, are gradually being developed, which allow real competitive bidding and assure a grade suitable for naval requirements. In this, buoyancy is the determining factor, and no kapok which does not show a buoyancy of 25 pounds when one pound is packed in a pillow ticking 13" x 13" X 4", after 24 hours in water, and retain a considerable portion of this buoyancy after being barely afloat for two weeks, should ever be accepted as naval stuffing fiber. The microscope is useful also to detect adulteration; kapok shows a straight, untwisted, cylindrical, unicellular structure, with thin walls, tapering from a large end to a point, whereas cotton shows a flat, twisted, ribbon-like fiber, with much thicker walls.
The color, luster, resiliency and cleanliness of the fiber all have to be considered. The first two are particularly hard to describe in specifications and can be judged only by an expert. But, in general, it is not safe to accept a dead, lusterless kapok, as it invariably lacks resiliency, powders, breaks and balls up easily, and is deficient in buoyancy initially and protractedly.
Dutch writers state that the importers of Amsterdam, which is the principal market for kapok, will not accept fiber which has been compressed to a density greater than about 9.35 pounds per cubic foot, but heretofore American importers have made no such restriction. The more densely the material is compressed the less the freight, so the tendency on the part of the importers is to compress it as much as possible. The Dutch buyers evidently consider that excessive compression is detrimental, but, owing to the difficulty in obtaining in America any kapok so loosely shipped, experiments looking toward the determination of the effects of great compression have not yet been carried out, although efforts are being made to do so.
Like most tropical trees, the Randoe, the name by which the tree that bears kapok fiber is called in Java, has frequently upon its branches at the same time fruit in various stages of maturity, from the blossom to the ripened pods. Over-ripe, green and wind-fallen pods are said by Dutch writers to produce an inferior grade of kapok. Probably the curing, the density of packing and the method of refluffing and stuffing into envelopes all have an effect upon the buoyancy and the durability; therefore, all of these points need to be considered in purchase and manufacture.
In the use of kapok-stuffed articles, in service, precautions need to be taken to prevent them from being wet for any great length of time, as kapok rots under such conditions, and to prevent exposure to fire. Reports from the service generally indicate that kapok has found favor, and there seems to be little doubt but that its use will increase.
New sources of supply are being investigated by the Navy Department, as well as other varieties, but results of experiments along these lines are not yet available. For the present it is safest to confine purchases to Java kapok.