US1973637A - Process of utilizing fibrous materials - Google Patents

Description

Patented Sept. 11, 1934 UNITED STATES PATENT OFFICE raocsss OF UTILIZING FIBROUS MATERIALS No Drawing.

Application'June 7, 1930,

Serial No. 459,823

9 Claims. (Cl. 92-9) such as sugar cane bagasse, corn stalks, straw,

wood, cotton, and the like, a dense, strong, board-like product in which there may be developed substantially the full strength of the fibrous materials employed.

This product, which will be designated as hard panel board, is made by subdividing the raw material into fiber bundles, which may be accomplished through a light digestion and subsequent refining, which fiber bundles, after sheeting with a water content of approximately 50%, are subjected simultaneously to compression and heat, whereby they are compacted and cemented into a dense, grainless, board-like sheet.

The raw materials, such as wood, bagasse, and

the like, in addition to cellulose, contain a substantial amount of encrusting and binding substances, particularly lignin, and it has been discovered that according to the known processes of the manufacture of hardboard that lignin and other material other than cellulose tend to prevent the development of the full strength of the finished product, and in addition the presence particularly of the lignin causes development in the process of manufacture of certain acids which prevent the development of the full strength of the fibers in the finished product. In the manufacture of hard panel board it is necessary that the fibrous units from which the board is prepared-must be maintained relatively large, that is, a large percentage thereof must comprise fiber bundles rather than individual fibers such as are used in paper-making, since a large percentage of ultimate fibers will form a sheet which is so dense that the moisture cannot be properly removed within a reasonable time in the final operation, that is, the drying of the sheet while subjected to high pressure.

A method has been discovered whereby the disadvantages of the presence of lignin and the other foreign materials, such as pentosans, inorganic matters, and the like, have been overcome, which method comprises essentially the steps whereby the fiber bundles from which the board is made are hydrated without actual removal of lignin and without breaking down the material into ultimate fibers.

The disadvantage of the presence of lignin and other foreign materials is overcome by producing hydrationof the fibers in which, while it has not been determined whether a physical or chemical phenomenon is involved, it is known there is produced a more or less gelatinous condition of the cellulose, and in this particular instance, since the hydration is but relatively slight, the gelatinization is only of the surface of the fiber bundles.

In the preparation of the raw material alkali is employed in an amount insufficient to remove the lignin butin an amount sufiicient to cause softening of the lignin and, at least, incipient hydration of the surface of the fiber bundles of the mass. The raw material is lightly digested with an alkali, such as calcium oxide, sodium hydroxide, and the like, and is then preferably brushed out'in a beater while hot and in the presence of the alkali, or is hot shredded or the like, which operations cause a slight degree of hydration of the fiber bundles-into which the raw material has been formed through the light solution and disintegrated by the'explosive process, but in either base it is advisable that this initial treatment be followed by a relatively light refining operation, preferably whileheated and with alakli present, whereby the material is divided into the required fiber bundles somewhat hydrated through the processes of manufacture to which it has been subjected. The initial alkalinity should be of about pH 8.2 and maintained above about pH 5. but also the wetted fibrous stock must be highly buffered at about pH 8.2 or higher so that the alkalinity will not be changed too greatly in the final step of the process.

The raw material, which has been subjected to the necessary preliminary treatment for subdividing it into the required fiber bundles and to produce an initial hydration thereof, is preferably thoroughly washed and is then ready for sheeting in a machine in its essentials of the type that it is used for the manufacture of paper.

Bagasse, as well as other of the raw materials of the grass family which may be used in ing matters be removed in so far as possible in the preliminary preparation of the raw material.

It has been discovered that if in the process of preparation a highly buffered alkaline solution is used, and in particular if such solution contains salts of calcium and magnesium such as calcium carbonate, calcium chloride, magnesium carbonate, and the like, the alkalinity of the initial treatment may be substantially maintained 'so that the coloring matters, which are dissolved or extracted from the raw material, are either precipitated or are absorbed by and carried out of solution by other substances which are precipitated, due to the maintained alkalinity of the initial treatment.

The prepared material after being sheeted is passed to a press to be subjected to heat for drying while maintained highly compressed, and it has been found that still further advantageous results are obtained by carrying out this final pressing and drying operation under alkaline conditions, particularly if there is a buffer present. In this final pressing and drying operation the fiber in effect is recooked under the conditions of high temperature and high compression and, if thereis an alkaline agent present, it is further hydrated since it is characteristic that such action of hydration shall occur, and it has been determined in the course of experiments that the extent of hydration relatively determines the board strength.

In the drying operation in the .press the sheeted material is subjected between platens to a pressure which may vary from 200 to 900 pounds per square inch, while simultaneously subjected to a temperature correspondent to that of steam between about 20 to pounds per square inch, the average operating conditions being a press pressure of about 500 pounds per square inch, with a drying steam temperature correspondent to about that of steam at 50 pounds per square inch. When subjected to the heat and pressure just mentioned, and particularly when there is included an alkali and a buffer salt, the fibrous materials are softened, compacted, and pressed into intimate contact and, due to the presence of the alkali, at least the surfaces thereof are hydrated, which hydrated gelatinous or mucilaginous surfaces are pressed into and held tightly in intimate contact, so that as the mass is dried out the fibers are firmly bound to one another in intimate contact to form a hard, dense, board-like final product. i

In the sheeting of the fiber bundles, or subse quently thereto but prior to the pressing operation, the alkali is added and may be, for instance, ammonia added as ammonia hydroxide,

or sodium carbonate, sodium hydroxide, or the like. For example, a 1% addition of ammonia produces quite satisfactory results, and the time of soaking or treatment of the sheet with the ammonia prior to pressing is immaterial, due to the volatile nature thereof, whereby it is rapidly distributed through and penetrates the mass. A 1% sodium hydroxide solution requires about thirty minutes for sufficient penetration through the fiber bundles of the mass to produce the required hydration when subjected to the heat and pressure of the final operation, and a 1% solution of sodium carbonate requires approximately forty-five hours soaking of the fiber to obtain like results.

In the pressing, due to the moisture and '00 the heat applied, there is a tendency for production of acids produced largely from the lignin and pentosans which quickly neutralize the alkali which may have been added, so that the effect of the added alkali may be more or 80 less lost quickly.

In view of this neutralization of the alkali by the acids formed, it is advisable that a buffer salt such as, for instance, calcium chloride, calcium carbonate, and the like, be added with the alkali, whichbuffer salt will absorb the effect of the acids produced and assist in maintaining the alkalinity of the mass during pressing, whereby the board is formed under alkaline conditions favorable to the desired hydration.

In this connection the use of the calcium compounds or of the magnesium compounds is particularly desirable, since they either precipitate in situ the coloring matters which may be dissolved from the fibers under the conditions of pressing, or they form precipitates with other constitutents of the, material, which precipitates absorb the coloring matters, whereby the coloring matters cannot concentrate to form spots in the finished product.

It is obvious that those skilled in the art may vary the steps and combinations of steps con-v stituting this method within'the scope of this invention without departing from the spirit thereof, and therefore it is not desired to be limited to the foregoing disclosure except as may be demanded by the claims.

What is claimed is:-

1. In the manufacture of hard panel board the initial step of preparation comprising disintegration of fibrous vegetative material into fiber bundles in the presence of an alkali highly buffered to maintain substantial neutrality, such fiber bundles subsequently and without complete removal of the highly buffered alkali formed into a dense, hard, board-like material by subjection in initially moist condition to the simultaneous application of heat and pressure.

2. In the manufacture of hard panel board from vegetative fibrous materials the initial preparation of the raw material with an alkali and buffer salt, the material containing alkali and buffer salt and from an initially moist condition containing substantially as much water as fiber, is subsequently subjected simultaneously to high temperature while highly compressed.

3. The process of manufacturing products from raw material of vegetative growth wherein the material is softened and the coloring matter of the raw material is removed by digestion in an alkaline liquor including calcium chloride and whereinv the alkalinity is maintained throughout the digestion.

4. The digestion of fibrous materials, wherein the fibrous material is digested in an alkaline liquor containing calcium chloride, the digestion being initiated at an alkalinity of about pH 8.2 and maintained above a pH of about pH 5.

5. The process of manufacturing products from raw material of vegetative growth wherein the material is softened and the coloring matter of the raw material is removed by digestion in a alkaline liquor highly buffered with containing calcium chloride.

6. In the manufacture of hard panel board 1 the initial step of preparation comprising disintegration of bagasse into fiber bundles in the presence of an alkali. and including a salt of calcium such fiber bundles having an alkali and calcium salt content subsequently from an 150 the steps of digestion of the fibrous material wherein the material is but lightly digested in a highly buffered alkaline liquor, with the subsequent step of, while maintained in alkaline buffered condition, the simultaneous application of relatively high heat and pressure to the initially moist fiber stock resulting from the digestion.

9. The method of manufacturing from fiber a dense, grainless hard panel board wherein the raw fibrous material is lightly digested in an alkaline solution, highly buflered with a calcium bufier salt, whereby the cementitious bonds of the fiber bundles oi. the fibrous material are weakened and the surfaces of the fiber bundles are slightly gelatinized, the digested fiber subsequently, while moist, subjected to a high pressure with simultaneous application of heat, whereby the fiber bundles having their surfaces gelatinized are compacted into a dense relation and dried while the high pressure thereon is maintained.

ELBERT C. LATI-IROP. FERGUS A. IRVINE.