US2537101A - Process for manufacture of wallboard from lignocellulosic material - Google Patents

Description

Patented Jan. 9, 1951 raocrzss FOR MANUFACTURE, or WALL- BOARD FROM LIGNOCELLULOSIC MATE- RIAL Warren R. Smith, Crown Point, N. Y., and Donald F. Othmer, Coudersport, Pa.: said Smith assignor to Donald F. Othmer, William R. White, Jr., and Louis Ricciordi No Drawing. Application June 8, 1948, Serial No. 675,444

3 Claims. 1

Qur invention relates to a process for producing a hard, dense, strong water-resistant wall board and other products from lignocelluloslc materials by the application of controlled heat and pressure for a relatively short length of time to a mixture of such lignocellulosic materials and added materials.

Various types of wall boards have been made by the application of heat and pressure to lignoce lulosic materials obtained in a more or less fibrous form by other preliminary operations. These processes have had to use raw wood, rather than short fibre waste material, such as sawdust. These wall boards are inherently expensive because of the value of the wood and of the cost of the mechanical and chemical operations for reducing to a fibrous state.

In these processes the fibres prepared by mechanical and chemical treating operations have been made in a slurry with water and run through a screen to form a wet lap which is then submitted to the subsequent pressing operations. These processes require a screen box, wherein the water drains out the screen forming the bottom, to leave a sheet of the wet lap the size of the box, or, alternatively, a paper-making machine, such as a fourdrinier, wherein the sheet is formed continuousiy on a moving screen belt.

Where it has been suggested to use chemical substances as additions to the slurry or the otherwise prepared flbrous material, it has been found necessary to subject such chemical substances to a special treatment to bring out or increase its bonding properties, as for instance, by using the distillate of certain acid substances.

The mixture formed between such chemical substances and the ligneous material, where used in a dry form, was not considered fit to be introduced into the press to form the des red final product without a number of intermediate steps in succession, such as storing for a certain length of time, preforming into mats, drying the mats, piling the thus formed material, etc.

In particular, where in such multistep process lignin has been reacted with phenols or, replacing the phenols, with cresols, the ensuing lignin plastics have always proved of very poor quality and have in no wise been suited as wall boards and similar structures in which a high rupture modulus is imperative.

It is, therefore, an object of this invention to make a wall board or similar hard, dense, strong and water-resisting product from waste wood substances which have had no chemical or me- Another object of the invention is the making of such an article by handling only dry or relatively dry material. in a. pulverulent, granular or fibrous form directly and without the making of such material into a slurry or suspension for handling in a wet state.

A further object is to allow the use of sawdust, shavings, and other mill waste directly as it comes from the saw, or other wood forming machine, in a simple, readily operated process, with a minimum of steps and equipment so that such manufacturing operations may be conducted by relatively small plants in isolated places and with a minimum of technical skill.

A particular object in this invention is to use not only the lignocellulosic material as it comes from the factory, but also to use the chemical materials in their crude form without special preliminary treatment.

We have now found that when cresylic acid is added to the fibrous materials as it comes as waste from other operations, for instance, to sawdust by a relatively simple mixing operation, the material can then at once and without intermediate treatment be pressed at a suitable pressure and temperature to give a hard wa l board of properties comparable to those obtained by more complicated methods of manufacture.

This surprising effect may be due to the fact that the cresylic acid activates or catalyzes the bonding action of lignin in the lignocellulosic materials so that it serves as a bonding agent in the finished board to make a hard, dense, strong material. The cresylic acid may be sprayed onto the sawdust after or without adding additional lignin to it.

Another activating agent is phenol which preferably is used in the form of carbolated petrolatum which contains a substantial portion of phenol. Also xylenol has been found useful as an activating agent in our process.

It is also possible to add certain other materials besides our activating agents to the board in order to increase the strength or water resistance or the fire resistance of the boards. In particular, the addition of mineral oils such as petrolatum and other similar semi-solid or solid hydrocarbons gives a product which is more water resistant.

We have also found it advantageous to add additional lignin in some cases, such additional lignin coming from one of the various sources of lignin available, 1. e., from the waste liquors discharged in the various processes for making wood chanical treatment prior to the present operation. 56 pulp for use in making paper, etc., and from the 3 residual solids left after hydrolysis of the cellulose in wood for the making of fermentablesugars for alcohol production, etc.

The lignocellulosic material used in our process may be wood from deciduous or coniferous trees or from other plants than trees. The sizes of the small wood particles may vary considerably so that the waste from different wood converting processes may be used including shavings from planers, different sizes of sawdust from ripsaw and re-sawing operations, cross sawing, etc... etc. In general, it is desirable to use particles having a maximum thickness of not over about 9;" and in many cases a finer material is preferable.

In general, we would use the fibers containing the normal amount ofmoisture present in them without drying; and, in fact, we prefer to use a material containing from 5 to 30% water, and up to as much as 50%. Such an amount of water is hardly appreciable mechanically since the material acts as a pulverulent granular material as distirguished from the slurry used in other processes where thematter is in a water suspension containing only one or two percent of fiber.

We would mix the preferred chemical material by spraying if the added chemical is a liquid; or by solid mixers for powder if all the materials are powdered. Any suitable device which gives a substantially uniform mixture of the chemical material with the ceilulosic material may be used.

Having formed the mixture, it is necessary to press under suitable elevated temperature the cellulosic material; and since there will be some moisture to be discharged as well as some gases due to the chemical actions involved, it is necessary to make provision for the discharge of such gases. One suitable manner which has been described in greater detail in one co-pending application, Serial No. 627,092, filed November 6, 1945, and now abandoned, is to place the material between the platens of the press, wherein one platen is either smooth itself or has a smooth plate between it and the cellulosic material; and the other platen has one or more wire screens in contact therewith (or other similar device) so that gases may work their way to the edge of the platen through and around the meshes of the wire screen or similar device and thus escape.

In some cases when relatively thick boards or ob- Jects of other forms having relatively thick sections are to be made, we may use screens or other similar arrangements on both platens so as to allow the discharge of gases from both surfaces.

The sawdust or the ceilulosic material mixed with the activating agent like cresylic acid or phenol acid is pressed for a period of from 7 to 20 minutes, preferably 11 to 13 minutes, with a temperature on the platens in the neighborhood of 178 to 300 0., preferably 245 to 155 C. The pressure may range from approximately 150 lbs. per square inch to any higher value desired but we have found that in the usual case pressures below about 500 lbs. per square inch are entirely adequate although for some purposes we may wish to go as high as 1000 lbs. per square inch. The pressure may be constant but for a number of materials and certain operating conditions it is desirable to gradually build up the pressure during the operation from about 100 to about 500 lbs. per square inch.

There is an inter-relation of the three variables of time, temperature and pressure; and, keeping time constant, a higher temperature on the platens may give the same result at a somewhat lower pressure; or, if the pressure is kept constant, a higher temperature may give this same result in a somewhat lower time. There is required the time to heat the material to a temperature somewhat lower than or approximating that of the platen itself; and the time for this heat transfer will also be reduced by an increase in the pressure due to a compacting of the fibrous material. Beside the time for the heat transfer in heating upthe charge, there is also required some time for the chemical conversion of the lignin and the production of the binding qualities thereby.

Good results have been obtained, for instance, on" the following basis; 600 grams sawdust per square foot with a moisture content of 10-15% were mixed, for instance, by mixing, with 20 grams cresylic acid and 48 grams lignin. This mixture was then subjected to a pressure of 500 lbs. per square inch during a Period of 12 minutes and at an average temperature of 235 C.

In a modification of this same process and using the same materials, the pressure was gradually increased, starting with lbs. and going up to 500 lbs. per square inch.

A variation of the original composition produced likewise highly satisfactory results. In this instance the pressure was kept constant but the cresylic acid content was augmented so that it amounted to 60 grams while the lignin was cut to 20 grams per square foot. The average temperature in this instance was 240 C.

Other examples showing the percentage of activating agent to be added appear from the following table which also indicates the rupture modulus in the last column.

Rupture Lignin (Indulln) 3.37 Lignin 33 Lir nin phenbl 0.20%

In gnlinis the trade-mark for commercially available 8 Whereas we have shown the advantage of the use of certain types of activating agents in the production of a wallboard made directly from sawdust, we have also noted that these same activating agents may be added equally well to similar articles manufactured by other processes and with equal advantage. Thus, for example, in the manufacture of wallboard by exploding wood ghips to give a fibrous mass which then may be formed into a board by suitable and known means, we have found that the addition of our activating agents for the lignin produces a better product than can be produced otherwise and without its use. Similarly, in the production of plastic materials from ligno-celiulose formed by the partial hydrolysis of wood (see for example the paper in I. and E. C., by Raphael Katzen and Donald F. Othmer, vol. 34, page 314, March 1942) the use of our preferred materials for activating the lignin results in substantial advantage if added to the molding powder as usually prepared for use in makingmolded objects.

We have also found that many other shapes and types of. articles besides wall board may be made by our method or reactivating the-lignin or facture because of its tremendous volume of business, our mixtures of materials and our methods of operation as described above and with only minor and self-evident modifications may be employed for making numerous other forms of finished articles. Instead of being formed between flat platens, dies of many patterns may be used with appropriate design and operation to take care of the characteristics of the materials as described above. Panels, doors, counter tops, and many types of architectural shapes as well as a wide variety of molded objects may be fabricated. From this standpoint our invention may be regarded as encompassing a molding powder, as the term is used in the trade. Also, while we refer to wall board as the principal type of manufactured article made hereby, it should be under stood that all of these other items which may be made by modifying the shapes of the dies are likewise included.

Thus, the cellulosic short-fibred material, such as sawdust with activator, may be laid or piled upon the surface of the ply wood assemblage before the assemblage goes to the press. The heat and pressure normally employed for bonding the ply wood units produces an overlay surface thereon. This method has particular utility where perfect top layers in the ply wood assembly are not available, and rough, un-planed lowgrade boards, used in ply wood assembly, may be converted to smooth surfaced member, all im* perfections being covered.

Low grade or rough surfaced planed or unplaned lumber, particularly lumber having imperfections such as cracks, knots, checks, etc., may be provided with improved surface characteristics and up-graded, by similarly coating one or both surfaces of such lumber by means of our process. In such application of our method, a further utility may be realized due to the presence of the activating agent in its tendency to repel insect attack. It will also be understood that such effect can be augmented by the addition of germicidal, fungicidal and insect-repel- I lant materials.

Having thus described our invention, what we claim and desire to secure by Letters Patent is as follows:

1. A process for making wallboard comprising adding an activating agent of the group consisting of phenol, cresol, xylenol, and mixtures thereof, to lignin admixed with natural lignocellulosic material, in the proportion of 2.6% to 10% of activating agent and 3.3% to 10% of lignin, based on the weight of the lignocellulosic material, the amount of water present being no more than that occurring in the lignocellulosic 2 material in its naturally occurring state, followed by the steps of subjecting the mixture of activat ing agent, lignin and lignocellulosic material to heat and pressure between platens, the temperature of said platens being between 178 C. to 300 C, the pressure being at least pounds per square inch.

2. A process for making wallboard comprising adding an activating agent of the group consisting of phenol, cresol, xylenol, and mixtures thereof, to lignin, said lignin consisting of lignin obtained from wood pulp producing processes, admixed with natural lignocellulosic material, in the proportion of 2.6% to 10% of activating agent and 3.3% to 10% of lignin, based on the weight -of the lignocellulosic material, the amount of water present being no more than that occurring in the lignocellulosic material in its naturally occurring state, followed by the steps of subjecting the mixture of activating agent, lignin and lignocellulosic material to heat and pressure between platens, the temperature of said platens being between 178 C. to 300 C., the pressure being at least 150 pounds per square inch.

3. A process for making wallboard comprising adding an activating agent of the group consisting of phenol, cresol, xylenol, and mixtures thereof, to lignin, said lignin consisting of the residual lignin solids obtained after the partial hydrolysis of wood, admixed with natural lignocelulosic material in the proportion of 2.6% to 10% of activating agent and 3.3% to 10% of lignin, based on the weight of the lignocellulosic material, the amount of water present being no more than that occurring in the lignocellulosic material in its naturally occurring state, followed by the steps of subjecting the mixture of activating agent. residual lignin solids and lignocellulosi': material to heat and pressure between platens, the temperature of said platens being between 178 C. to 300 C., the pressure being at least 150 pounds per square inch.

WARREN B. SMITH. DONALD F. OTHMER.

REFERENCES CITED UNITED STATES PATENTS Number Name Date 1,721,315 Novotny July 16, 1929 1,923,756 Sherrand Aug. 22, 1933 2,036,156 Lundback Mar. 31, 1936 2,156,160 Olson Apr. 25, 1939 2,180,547 Peterson Nov..21, 1939 2,247,209 Schorger June 24, 1941 2,283,821 Schorger May 19, 1942 2,319,951 Schorger May 25, 1943 Schorger May 25, 1943

Claims (1)

1. A PROCESS FOR MAKING WALLBROAD COMPRISING ADDING AN ACTIVATING AGENT OF THE GROUP CONSISTING OF PHENOL, CRESOL, XYLENOL, AND MIXTURES THEREOF, TO LIGNIN ADMIXED WITH NATURAL LIGNOCELLULOSIC MATERIAL, IN THE PROPORTION OF 2.6% TO 10% OF ACTIVATING AGENT AND 3.3% TO 10% OF LIGNIN, BASED ON THE WEIGHT OF THE LIGNOCELLULOSIC MATERIAL, THE AMOUNT OF WATER PRESENT BEING NO MORE THAN THAT OCCURRING IN THE LIGNOCELLULOSIC MATERIAL IN ITS NATURALLY OCCURRING STATE, FOLLOWED BY THE STEPS OF SUBJECTING THE MIXTURE OF ACTIVATING AGENT, LIGNIN AND LIGNOCELLULOSIC MATERIAL TO HEAT AND PRESSURE BETWEEN PLATENS, THE TEMPERATURE OF SAID PLATENS BEING BETWEEN 178* C. TO 300* C., THE PRESSURE BEING AT LEAST 150 POUNDS PER SQUARE INCH.