US2388487A - Process of making compressed fiber products - Google Patents

Description

Patented Nov. 6, 1945 rnocsss OF MAKING COMPRESSED FIBER PRODUCTS Harry K. Linzell, Long Lake, 111., assignor to United States Gypsum Company, Chicago, 11]., a corporation of Illinois No Drawing. Application January 22, 1940, Serial No. 315,005

8 Claims.

The present invention constitutes an improvement in compressed fiber products and the proces of making the same, and particularly relates to such products as are consolidated or molded under the influence of heat and pressure, the particular novelty of the present invention lying primarily in the use of ferric compounds to improve the properties of the products.

One of the primary objects of the invention is to produce a consolidated product made substantially from cellulosic and/or lignocellulosic fibers, exemplified by wood, straw, grasses, and the like, irrespective of whether these products have been relieved of a portion of their lignin prior to the operations of the process steps hereinafter recited, although better results are generally obtained when a substantial portion of the lignin isretained.

A further object of the invention is to improve the strength, water resistance, and generally desirable characteristics of consolidated, compressed, or molded products, and furthermore to enable the use of somewhat lower temperatures than would ordinarily be required in the hot pressing or hot molding operations which are employed in their fabrication.

As a raw material for the purpose of the present invention, a fibrous lignocellulosic material from vegetable sources, such as wood, straw, grass, bamboo, bagasse, and the like, is preferably employed, first being treated in a suitable. manner by means of a ferric iron compound, whereafter the material containing the ferric iron compound is subjected to the simultaneous application of heat and pressure.

Th remarkable discovery has been made that the effect of heat and pressure upon lignocellulosic material may be modified by the presence of a ferric compound. The effect of such a compound is in general either to enablethe use of lower temperatures to attain the desired amount of consolidation and strength or, at the temperature previously used, to shorten the time during which this temperature is permitted to act upon the material. Furthermore, it has been found that the products resulting from the treatment of lignocellulosic material in the presence of ferric compounds are in general endowed with greater strength than they would have had if the ferric compound had not been employed. In some instances also the degree of water repellence has been increased and the amount of water absorption decreased.

The exact theories underlying the present invention are at present but dimly understood. It

is not known whether, when lignocellulosie fibers are subjected to heat and pressure, the ferric compound exerts a catalytic or quasi catalytic effect upon the lignocellulosic fibers as in possibly accelerating the autogenous production of binders therefrom, whether it combines totally or in part with the lignocellulosic fibers Or the lignin complex therein contained, whether it has an oxidizing or other effect upon certain binders and/or oils which may be used conJointly with the lignocellulosic fibers, or whether the ferric compound itself constitutes, either alone or as a result of its reaction with the lignocellulose, a binder which serves to hold the fibrous particles of the resulting product together. Irrespective of any theory, however, the results obtained are uniformly in the nature of an improvement in th products themselves, as well as an improvement in their mode of fabrication.

The ferric compounds may be employed by themselves-for instance, by being applied in am suitable manner to the lignocellulosic material, be it either in its natural state or comminutedor may be'used conjolntly with binders, fillers, sizing materials, waterproofing materials, or coloring materials, the main point in every case being however the presence of the ferric compound in the material when it is subjected to heat and pressure during fabrication.

The ferric compounds employed may be either water-soluble salts or water-insoluble materials. such as ferric rosin-acid compounds-for ,instance, ferric abietateor compounds of ferric iron with the fatty acids of the glycerides contained in vegetable and animal oils. Ferric sulfate, Feflsot) 3, has been found to be the most eflicacious form of ferric compound for the carrying out of this invention, although the invention is not to be limited solely to the use of ferric sulfate, because it has been found that other ferric compounds may be used. Therefore, when dry or-nearly dry vegetable fibers, such as coinminuted cottonwood, may be sprayed with a dilute solution of a ferric salt. As little as about 1% of the ferric salt based on the weight of the fiber may be used. Ferric sulfate has been found to be particularly suitable. The sprayed fibers may then be dried and placed in a suitable mold and therein subjected to heat and pressure within the range of from 350 F. and up to a temperature short of the development of free carbon. Temperatures within the range of from 425 to 475 F. are particularly suitable for this purpose, as a relatively short pressing time, say 1' to 5 minutes, may be used. The simultaneous presence, during such pressing operation,'of abietic acid or ordinary rosin in an amount less than that of the ferric salt will further improve the products and increase their water resistance. There is probably some combination between the ferric salt and the abietic acid or rosin under these conditions.

As a further alternative, the spraying of the lignocellulosic fibers with the ferric salt may be effected in a rotary drum, and the fibers may be dried within the same drum by passing hot gases therethrough. The dry ferric-salt-treated fibers may be formed into a coherent sheet, for example by sifting them onto -a fiat foraminous forming mold. The thus resulting loosely coherent mat may then be subjected to the heat and pressure and thereby consolidated into a sheet.

The present invention is also applicable to the improvement of the properties of wood. For example, wood may be impregnated with a solution containing a ferric compound and then dried and subjected to heat and pressure. This impregnation may be effected either by immersion or by spraying the ferric salt upon the wood. For example, the surface of a piece of cottonwood, say about 1% inch thick, may be impregnated with a ferric salt solution. When sufficiently impregnated, the treated wood may be dried and then subjected to pressure and heat of, say, from 350 F. up to a temperature approaching that. of carbonization. During such pressing operations it is advisable to operate on bonedry wood or to keep the moisture content of the wood within low limits. With moist wood a screen may be provided on one side of the same to allow the escape of any steam. About 1% by weight of ferric compound is usually sufficient.

As a still further alternative, wood may be impregnated first with a ferric salt, followed by impregnation with a rosin size solution so as to effect the precipitation of the rosin size within .the interstices of the wood. The operation may also be reversed and the wood impregnated first with rosin size and then with the fenic salt. Obviously, the results will be substantially the same, the main point being the formation of the ferric compound in close proximity to or even upon the fibers of the wood.

For the purposes of the present invention, the term "rosin size means the ordinary soluble rosin soap which is usually produced by treating rosin with sodium hydroxide or equivalent material, and such size is commercially obtainable on the market and hence needs no further description. Rosin has been considered as 'consisting particularly of abietic acid, and the terms rosin and abietic acid are used substantially synonymously herein.

The present invention has been found particularly useful in connection with the production of flat sheets or boards by consolidating previously fibrated wood under heat and pressure.

Such boards are commercially classified as "hardboard" or "semi-hardboard," depending upon the density thereof, and are generally about $4; to inch thick.

It has been found that by carrying out the manufacture of such boards in the presence of a ferric compound, the resulting products, for any given set of conditions of pressure and temperature, will be found to be of enhanced strength and to be endowed with many other desirable properties. Furthermore, if in conjunction with the ferric compounds modifying agents are employed, it becomes possible to endow the resulting board with additional desirable properties, such as increased flexibility, better nailing properties, less brittleness, enhanced tenacity, and better water repellence, usually also coupled with decreased water absorption. It appears that when the iron compounds are used alone the results are thus substantially analogous to those already hereinabove described; but when employed in conjunction with modifying agents such as size, resins, waterproofing materials, drying oils, or materials having characteristics similar to drying oils, the ferric compounds operate not only to beneficially affect the lignocellulose but also, in some manner not thoroughly understood, to combine with, react upon, or modify the added materials, whereby, as a result of the conjoint benefits obtained, the products will .be endowed with many valuable properties and will be quite superior to those hitherto manufactured.

It has been discovered that the ferric compounds-for example, the .ferric sulfateappear to have some effect upon the speed of reaction of the formation of autogenously produced binders resulting from the heat and pressure treatmerit of lignocellulose at a given temperature. While it is known that the subjection of ligno- 40 cellulose to temperatures substantially above 350 F. will give rise to the development of such autogenously produced binders, it appears that for any particular temperature the presence of the ferric compounds in some way speeds up the conversion rate with which the constituents of the wood are converted into the autogenously produced binders. This means that a shorter pressing time may be availed of to produce a board of a given specification, thereby obviously speeding up the manufacturing operations, with resulting economic benefits. On the other hand, if this speeding up is not desired, or if the cycle of manufacture is such that a certain time is available, the presence of the ferric compound may be availed of to enable the operation to be carried out at a lower temperature. For example, if in the manufacture of a board without the use of ferric compounds a pressing temperature of 400 F'. is employed, it may be possible, by the use of the ferric compound, at this same temperature to reduce the pressing time as much as 50%; or, by maintaining the pressing time, to reduce the temperature substantially. Both of these effects are obviously valuable.

Further, if, in order to modify the degree of water resistance of the board, resins or oils are incorporated therewith, either with or without size, it will be found that the water resistance of the products will be greater where the ferric 7 ployed for its manufacture with rosin size, which has ordinarily been precipitated upon the fibers by means of aluminum compounds, such as alum.

aluminum sulfate, and the like.

Therefore, in accordance with the present invention, a ferric iron salt such as ferric sulfate isemployed for the precipitation of the size, resins or oils 'onto the fibers, the main point being to assure the presence of a ferric compound on the fibers. Under some circumstances it may be desirable to use some aluminum sulfate or sulfuric acid conjointly with the ferric salt.

As a more detailed disclosure as to one efi'ective way in which the present invention may be applied to the manufacture of a hardboard, for example, a suitable type of woodsuch as cottonwood pulp wood-4s converted into a pulp by the use of stone grinders or by any other suitable means, as by cooking or .by explosion, and, after the pulp has been screened to remove the large chips, is preferably adjusted to a consistency of about 4%. If it is desired to use size, resins, oils, etc., a suitable quantity thereof may then be added in some convenient form to the fiber suspension. After these materials, when they are used, are blended with the suspension, the mixture may be pumped to whatis known as The ferric-sized stock is transferred to the head box of a board-forming machine where it may be further diluted with some of the white water of the process and the supension then formed into a coherent sheet on a conventional board-forming machine.

At times it may be convenient to treat the loose fibrous material with the ferric iron solution, either hot or cold, and with or without superatmospheric pressures and then to add the rosin size or other materials.

Regardless of the manner in which the said sheet is formed, it is then relieved of its excess moisture in the usual manner, as for example by passing it through a hot air or other type of drier. It is then trimmed to the desired size for the next step in the operation.

Alternatively, the pulp may be made into a mat without the use of the ferric com ounds, and this mat then impregnated or sprayed with a solution of a ferric salt, or a ferric rosin-acid compound may be deposited on the fibers of the mat by alternate impregnation of the latter with solutions of size and of a ferric salt, and the mat then dried to the desired moisture content most suitable for the subsequent pressing operation.

When using oil having drying characteristics, such as soybean oil or linseed oil, it is desirable to oxidize the oil in the sheets prior to pressing. Thereafter, the moisture content of the sheet, whether the same contains oils or other material or not, is preferably adjusted to about 1 or 2%, although it may contain slightly more or less moisture. If the moisture content is materially higher than about 5%, some difiiculty may be encountered in pressing the sheets between the consistency-regulator on a board-forming machine where additional water may be added to bring the pulp to a consistency of, for example, 3 /2%. The amount of size, oil, etc. used may vary from /2% up to about 10% of the weight of the dry fiber, When using oils or other additional materials, these are emulsified with the size in the manner well understood in this industry.

' At this point the ferric iron compound may be added, preferably in the form of a solution of ferric sulfate made by dissolving one part by weight of commercial ferric sulfate in nin parts by weight of water. The addition of the ferric sulfate solution to the pulp causes the precipitation of the rosin size and at the same time throws down any oil or other added resins or binders, as well as the ferric compound formed, onto the suspended fibers.

It basbeen found that in using ferric iron compounds in this manner a hydrogen-ion concentration of about equal to pH 4.8 is desirable. Other concentrations, say within the approxi mate range of from 4 to 6, may be used in practicing the present invention. Therefore, a sufficient amount of ferric sulfate should be added to produce the hydrogen-ion concentration selected. This will depend somewhat upon the ingredients present in the water and the amount of recirculation of white water during the board-forming step, Under certain conditions, as, for example, when using 1% of rosin size and 4% of an oil, the use of 15 pounds of commercial ferric sulfate for about 700 pounds of fiber on the bone-dry basis, which latter is convertible into about 1000 square feet of hardboard of an inch thick, will produce satisfactory results.

imperfo'rate platens to produce a board having two smooth surfaces, unless recourse be taken to the intermittent release of pressure during pressing to allow the vapors forme to escape.

After adjustment of the moisture content, the sheet is pressed under sufllciently high pressure and temperature conditions to effect a consolidation thereof. Although the time, temperature and pressure may be varied, depending upon the type of board to be produced, it has been found that a satisfactory, hard, dense boardwill result when the sheet, for example one containing both size and oils, is pressed for a period of about 3 minutes at a pressure of approximately 1100 pounds per square inch and at a temperature of about 425 1 when no oils are used, either the pressure or the pressing time, or both, are preferably increased somewhat, and the temperature may also be increased. At lower temperatures, the time should be correspondingly increased.

If it is desired to produce a more dense board, higher pressure should be employed; and if a less dense product is to be produced, less pressure should be used :orstops provided to prevent too great consolidation of the material. The density may also be increased somewhat by employing higher pressing temperatures or a longer time of pressing.

The presence of a small amount of moisture, say 1 or 2%, in the mat subjected to the high temperature pressing operation is very desirable, as it promotes the closeness of contact between the fibers and probably serves as a plasticizer for the fibers, enabling them to align themselves more accurately. However, the use of the ferric compounds according to the present invention is likewise advantageous in a process in which a bone-dry mat is consolidated under heat and pressure. and also in success wherein a mat containing a relatively large amount of water is consolidated and dried in a press.

The temperature, pressure and time employed in the pressing step may vary between wide limits that are to a degree interdependent and may be varied to yield products of higher or lower density.

Although soybean .oil and linseed oil have been mentioned as optional ingredients of the board, it is of course obvious that other drying materials may be substituted with substantially the same results. Other oils may be perilla oil, tung oil, oiticica oil or any other drying oil or equivalent material. Semidrying oils, such as corn oil or cottonseed oil, may also be used. It i also possible to use paracoumarone-indene resins, stearin pitch or other desired additional ingredients.

In order to demonstrate the marked advan- I tages and novel results obtained by the use of the ferric compounds, particularly ferric sulfate, a number of comparisons were made, working as far as possible under identical conditions, but I substituting for the ferric sulfate an equivalent amount of paper maker's alum (aluminum 'sulfate) and maintaining the same hydrogen-ion concentration, which was approximately equivalent to pH 4.8, it having been found that at that particular hydrogen-ion concentration the optimum benefits were obtained. Boards were prepared with /z% of size-that is, the commonly known rosin soap size, which was precipitated onto the fibers in the one case by aluminum Suifate and in the other by ferric sulfate, in both cases adjusting the mixture to a hydrogen-ion concentration equivalent to pH 4.8 before forma-.

tion of the mat and adjusting the moisture content of the mat to below with pressing conditions of 4 minutes at 425 F. and 1750 pounds per square inch pressure, the board made with aluminum sulfate, and which therefore was free of ferric compounds, had a modulus of rupture of 5600 pounds per square inch, while the one made with the ferric sulfate had a modulus of rupture of 7800 pounds per square inch.

To demonstrate the effect of the iron compounds when both a drying oil and rosin size were present, a comparison was made, producing a board containing 4% of soybean oil and 1% of rosin size, using aluminum sulfate to precipitate the oil and size onto the fibers and working at the aforementioned optimum hydrogen-ion concentration equivalent to a pH of 4.8. The board pressed for 3 minutes at 425 F. and about 1100 pounds per square inch had a modulus of runture of 6130, while when using ferric sulfate instead of aluminum sulfate for the precipitation of the oil and size, the board had a modulus of rupture of 7080.

In another test, employing 3% of linseed oil and 1% of rosin size, and precipitating with aluminum sulfate, the strength of the board pressed at 425 F. for 4 minutes, with an initial pressure of 500 pounds per square inch and a final pressure of 1000 pounds per square inch, was 4980, as compared with 6140 when the ferric sulfate was used. Tests were also made relative to the water absorption of such a board when immersed in water for 24 hours, and it was found that the board made with the aluminum sulfate absorbed 35.5% of water whereas the one made with the ferric sulfate under the same conditions ab-.

sorbed 25.8%.

To demonstrate the possibility of employing comparatively low temperatures, boards were prepared containing 2% linseed oil, 5% soybean oil and 1% rosin size, Pressed'at 38'! 1". for 7 minutes at 1650 pounds per square inch, the board in which aluminum sulfate had been employed as the precipitant had a modulus of rupture of 4900 and a water absorption of 30%, while the one made with ferric sulfate had a modulus of rupture of 6000 and a water absorption of 24%. The lower strength of both of these boards in comparison with those of the other examples hereinabove mentioned is attributable to the lower temperature. Extension of the pressing time or raising of the temperature would have increased the strength of both of these boards, but the relative figures would have been about the same.

It will thus be seen that in every instance the ferric compounds asserted a beneficial effect, which was quite different from that obtained with the use of aluminum sulfate. In addition the ferric sulfate acts as a precipitant to precipitate the size, oil or resin upon the fibers.

While ferric compounds are recited as being 7 employed in the present invention, it will be obviferric condition prior to its incorporation with the lignocellulose or its use as a precipitant. In such cases where the iron compound alone is availed of, for example in that modification of the invention where it is sprayed onto the fibers,

even the ferrous compound may be used for that purpose, provided it be permitted to become oxidized, or be deliberately oxidized, to the ferric condition prior to the application of heat and pressure.

Utilizing some of the principles set forth in connection with that phase of the invention involving the manufacture of hardboardin' other words, where rosin-acid or resin-acid compounds are presentand as a further exemplification of some of the aspects of the present invention, the ferric abietate or ferric rosin-acid compounds may be separately prepared, or procured, and dispersed upon cellulose, lignocellulosic material such as fibrated wood, wood fiour, and sawdust, or other fibrous or comminuted material, either organic or inorganic, either by admixing it there? with as a powder or by dissolving the ferric rosinacid compound in a solvent thereof and mixing the solution with the fiber or comminuted material. A solvent suitable for that purpose is chloroform. Of course, the solvent must be driven off before proceeding furtlhar, the main object being the deposition of the ferric rosin-acid compound upon the fibrous or comminuted material, wood fiour, sawdust, etc. In that manner a molding material may be produced which can be handled in much the same manner as the well-known plastic molding compositions such as those of the phenolic resin type. In other words, such a mixture may be pressed at a suitable temperature to form hot-molded products which may be used for industrial purposes.

It has also been found that a small amount ofoil, preferably of the drying type, helps to plaspipes, handles, electrical insulating material, boxes and containers, rulers, etc.

Saving for himself such equivalents and modiflcations as will readily occur to those familiar with the art into which this invention falls, the inventor claims:

1. Process of accelerating the formation of autogenously produced binders resulting from the treatment of lignocellulosic materials under pressure at a temperature above 350 F., but short of the .carbonization of the material, which comprises carrying out the process in the presence of a ferric compound with the lignocellulosic material initially containing not over of moisture.

2. Process of making lignocellulosic hardboard which comprises compressing a mat of lignocellulosic fiber containing initially not substantially more than about 5% of moisture, and a ferric compound at a temperature above 350 F. but below the point of carbonization.

3. Process of accelerating the formation of autogenously produced binders when heating relatively dry lignocellulosic material initially containing not substantially over 5% of moisture under pressure to a temperature between about 350 F. and a temperature approaching that of carbonization, which comprises carrying out said heating under pressure in the presence of a ferric 3 compound.

4. Process of making hardboard which comprises forming a mat of lignocellulosic fibers which are associated with a, ferric compound, adjusting the moisture content of said mat to not over 5% of moisture, and subjecting said mat to a temperature between 350 F. and that short of carbonization, while simultaneously compacting the mat by thereto applied pressure, thereby forming therein autogenously developed binders resulting from the partial decomposition of the lignocellulose, and whereby said formation of binders is accelerated by the presence of said ferric compound.

bonization.

6. Process of making hardboard consisting essentially of lignocellulosic fibers self-bonded by therefrom developed autogenous binders which comprises forming a mat of such fibers, impregnating said mat with a, solution of a ferric salt, adjusting the moisture content of the thus impregnated mat to not exceeding about 5%, and thereafter compressing the mat into a dense mass at a temperature above 350 F. but below the point of carbonization.

7. Process of accelerating the formation of autogenously produced binders resulting from the treatment of lignocellulosic materials under pressure at a temperature above 350 F., but short of the carbonization of the material, which comprises precipitating a water-insoluble ferric compound upon lignocellulosic material, adjusting the moisture content of said material to not exceeding about 5%, and thereafter compressing the material into a dense mass at a temperature above 350 F. but below the point of carbonization.

8. Process of accelerating the formation of autogenously produced binders resulting from'the treatment of lignocellulosic materials under pressure at a temperature above 350 F., but short of the carbonization of the material,- which comprises carrying out the process in the presence of ferric sulfate with the lignocellulosic material initially containing not over 5% of moisture.

HARRY K. LINZELL.