US2503443A - Process for impregnating wood with sodium thiosulfate - Google Patents

Description

.l GLCul-wu Slrlan tion of New York rnlocsss FOR fmnnonsrruomon w igh,

sonrotrrnro'surmrn Wv William A. Knapp, New York, N. Y., assignor to Allied Chemical & Dye Corporation, a corpora- I No Drawing. Application November 29, 1946,

Serial No. 713,091

1 Claim. 1

This invention. relates to processes for increasing the flexibility-of wood. I

Various methods are known for rendering wood more flexible and pliable. For example, in the manuifiacture' of basket hoops where flexibility of the woodestrips employed therefor is an important feature, treatment with urea, thiourea and combinationsthereof have been practiced to produce a softening effect on these strips to thus render them sufficiently flexible for subsequent bending operations and prevent excessive breakage. However, these treating agents frequently darkened the wood under treatment, and moreover are relatively high-priced materials.

One object of my invention is to provide lowcost processes for rendering wood flexible without disadvantageous darkening of the wood: Another object is to afford processes for rendering wood strips or sheets flexible for subsequent bending operations without excessive breakage.

Other objects will appear from the following description of my invention.

I have found that when wood is subjected to the action of an agent selected from the group consisting of water soluble thiosulfates, dithio-' nates and polythionates, its flexibility is markedly increased and its color is not deleteriously impaired.

As applied to wood strips such as may be employed in the manufacture of basket hoops, briefly my process is carried out preferably in the following manner.

Wood strips are placed in a rack in layers and each layer or a series of layers is sprinkled with an appropriate amount of one of the above agents such as sodium thiosulfate in crystalline powder form. The rack is then transferred to an autoclave into which steam at superatmospheric pressure is introduced. The steam condensate dissolves the sodium thiosulfate producing a solution which impregnates the wood. After a suitable period of such immersion in an atmosphere of steam, the steam is exhausted from the autoclave, the rack removed, and the wood strips bent into the desired shapes usually before cooling. Only a very small amount of condensate remains in the bottom of the autoclave after the steaming and chemical impregnation period. Thus, practically the entire quantity of softening agent used is absorbed by the wood.

In an alternative method of procedure, wood in any desired form such as strips or sheets may be rendered flexible by immersion in an aqueous solution of one of the above agents, e. g. sodium thiosulfate, for a period of time before being 55 placed in the autoclave to be acted upon by steam. The concentration, temperature, and time of treatment in such a solution may be varied within wide limits as desired. Normally, time of treatment in this solution decreases as the concentration and temperature of the solution increase. However, concentration and temperature should not be made so high as to weaken or discolor the wood being treated. In a modification of the latter procedure, an aqueous solution of the softening agent may be sprayed on the surface of the wood or wood strips and the latter thereafter subjected to steaming in the autoclave.

To obtain good results it is desirable to steam the wood already having the softening agent applied thereto in any one of the above noted ways. Preferably, the treating agent is'sprinkled in powder form on the wood which is then subjected to steaming. The action of the steam brings about a thorough absorption of the softening agent into the wood in a minimum of time. However, some softening and flexibility of the wood is obtained by merely immersing it in an aqueous solution of the softening agent preferably at elevated temperatures and soaking therein for a period of time without subsequent steaming. This feature is also considered a part of my invention.

The agents employed for producing this softening effect include any of the soluble salts of thicsulfuric acid such as sodium thiosulfate, NaaSzOa; potassium thiosulfate, KzSzOa; and ammonium thiosulfate, (NI-1028203; soluble salts of dithionic acid such as sodium dithionate, NazSaOs; potassium dithionate, KzSzOs; and ammonium dithionate, (NHQ2S206; and soluble salts of polythionic acid such as sodium pentathionate, NazSsOs; potassium tetrathionate, K2S4Os; and ammonium trithionate, (NH4)2S306. Although the use of the alkali metal salts such as the sodium salt is preferred, the ammonium salts as well as salts of other metals imparting suflicient solubility in water to the softening agent may be employed with effect. I prefer to employ an alkali metal thiosulfate in my process in the form of one ,of its most readily available salts, sodium thiosulfate, e. g. the hydrated NazSzOaSI-l'zO.

The amount of softening agent used may be varied within rather wide limits. In general, for example, the amount of sodium thiosulfate (Na2S2O3.5I-I2O) to be absorbed or impregnated into the wood may range from 1 to 6 pounds per cubic foot of wood. In terms of for instance wood strips inch x 1% inch x 5 feet long. a to E 3 pounds of sodium thiosulfate per' 100 such strips may be utilized.

The steaming process may be allowed to proceed at varying pressures and for difierent lengths of time provided the combination of temperature thus produced and length of time of treatment are not such as to char the wood by the action of the steam. Thus, in operations such as illustrated in the following example, steam pressures up to 150 lbs. gauge and steaming periods of 10 minutes to 2 hours may be employed. In other operations using wood of greater thickness, steaming time may be proportionally longer.

The following example serves to illustrate the process of my invention.

Wood strips, e. g. from poplar or pine having the dimensions inch x inch x feet long were placed in a cylindrical rack with a grating near the bottom. The'grating served to prevent any of the strips while in the autoclave from 7 being immersed in a small amount of condensate which may collect at the bottom of the autoclave. When the strips were piled to a height of 46 inches, crystalline sodium thiosulfate (N 'a2SzO3.5I-I2O) was sprinkled over the strips in the amount of 1 pound per 100 strips. Another layer of strips of approximately the same height as the first layer was then piled on the first layer and sodium thiosulfate in the amount above noted again sprinkled thereon. This operation was then continued in this fashion with sodium thiosulfate sprinkled between the layers of wood 'strips until the rack was filled. A total of 12 pounds of sodium thiosulfate was used for approximately 1200 strips.

The rack was then placed in a horizontal autoclave-about 5 feet long by 2 feet in diameter, the autoclave closed, and the steam turned on. The batch of wood strips was steamed for 30 minutes at 120 p. s. 1. gauge steam pressure. The pressure was then released, the rack containing the strips removed from the autoclave, and the strips while still warm were bent into hoops for used in the manufacture of-covers for bushel-- size fruit baskets.

wood strips without charring.

In the bending operation an average of '7 strips i broke whereas average breakage of strips which had not been treated or impregnated with one of the above softening agents was 25 to 30 per 100 strips.

While I have described my process principally in connection with increasing the flexibility of wood strips to facilitate subsequent bending into hoops for use in the basket industry, my process is not to be limited to this application, but may be utilized for softening or increasing the flexibility of wood of any substantial or desirable dimensions. The term layers as used in the appended claim is intended to includ relatively thin wood bodies such as strips or sheets.

I claim:

The process of rendering thin strips of wood flexible which comprises applying to the surface of successive layers of said strips piled one on the other, powdered NazSzOzfxHzO in quantity of from 1 to 6 pounds per cubic foot of wood, and immersing said layers in a vaporous atmosphere of steam at superatmospheric pressure of the order of p. s. i. gauge up to p. s. i. gauge for a period of time ranging from 10 minutes up to 2 hours to thereby impart flexibility to said mm A. ENAPP.

REFERENCES CITED 1 The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 84,733 Cowling Dec. 8, 1868 1,398,065 I Carpenter Nov. 22, 1921 1,738,132 Wood Dec. 3, 1929 2,154,433 Boller Apr. 18,- 1939 FOREIGN PATENTS Number Country Date 411,182 Great Britain June '7, 1934