US3130116A - Process for grinding or pulping wood - Google Patents

Description

A ril 21, 1964 W. GARTNER Filed Aug. 22, 1961 was VACUUM Z 011/5 PROCESS FOR GRINDING OR PULPING WOOD L 0 6 Gil/V05? W000 (ll/P5 INVEN T OR. mil/ELM firm 5K BY M A iiornel s United States Patent Ofilice 3,130,116 Patented Apr. 21, 1964 PROGESS FGR GRINDING GR PULPiNG WOOD Wilhelm Gartner, Neunin'rchen in Odenwald, Germany,

assignor, by mesne assignments, to FMC Corporation,

New York, N.Y;, a corporation of Delaware Filed Aug. 22, 1961, Ser. No. 133,964 Claims priority, application Germany Aug. 24, 196i 1 Claim. (Cl. 162-27) This application relates to the production of mechanical wood pulp and particularly to the production of mechanical wood pulp having greatly improved physical strength and other properties.

Large quantities of. woodnpulp are produced for such uses as newsprint, corrugated papers and the like, by the mechanical grinding of logs. This process involves contacting the log with'a rotating, rough stone wheel, while playing water across the surface of the wheel. This pulping method is opposed to chemical pulping methods, which operate by saturating wood chips with chemicals which facilitate pulping, before the wood fibers are separated into pulp, usually in a digester.

The mechanical grinding method has the advantages that its use provides a high yield of pulp, and that the operating costs are low. However, the pulps produced by this method are weak, and characteristically the fibers produced are short.

Various attempts have been made to improve the properties of these mechanical wood pulps. One attempt has involved impregnating the wood in log form with water, either by prolonged storage or by application of pressure, prior to pulping. While such methods provide somewhat improved pulp properties, they do not provide uni form impregnation of the Wood'with Water, especially in the case of pine wood and the like, and therefore do not provide for uniform pulping and pulp products. Furthermore, the long time immersions involved in these processes are expensive, and this reduces the cost advantage of mechanical wood pulps.

Another method by which it has been attempted to improve mechanical'wood pulp properties has involved cutting the wood into thin log chips or Wood shavings, and impregnating them with aqueous alkali prior to pulping. While the mechanical properties of thepulp are improved by this treatment, the methods no longer have the economy of the mechanical grinding method, in which logs are simply ground on a stone without the expense of cutting the log into chips. Furthermore, this so-called a soda process provides a brown-colored pulp, due primarily to the action of the alkali on the wood fibers, which can be used only for such'papers as packing or corrugated papers.

As indicated above, the described processes for impregnating logs with water suffer the disadvantage that the water is slow to penetrate the wood; furthermore; in the time available incommercial operation, it penetrates only 5 to cm. into the wood. This is a particularly serious problem with resinous woods, such as spruce, and with heartwood;

It isa feature of this invention to provide a method of producing mechanical wood pulps, the fibers of which have excellent strength and'other properties, and are longer.than fibers produced heretofore. by mechanical grinding methods.

It is a further feature of this invention to provide such a method which operates with no serious wastage of the wood.

It has now been found that excellent mechanical wood pulps having a high degree of strength and excellent fiber length may be obtained by grinding logs having diameters of about 6 to 25. cm., if prior to grinding the logs are grooved to a depth of about 50 to 80% of the log diameter, essentially perpendicular to the fiber direction, at intervals of about 2 to cm., and the logs are impregnated'with an aqueous, alkaline, peroxide solution typically containing about 10 to 100 gms. per liter of hydrogen peroxide, 15 to 100 gms. per liter of sodium hydroxide, and if desired, stabilizers such as sodium silicate, phosphates'and the like. A typical stabilizer for the peroxide Will be sodium silicate, which, in a formulation of the above type, will be employed, for example, as a 38 to Baum solution in water in the amount of about 10 to 50 gms. per liter.

In preferred practice of the invention, the impregnation of the groovedlogs will be carried out by subjecting the logs after grooving to the action of an evacuated atmosphere, that-is,about 5 to 50 min. of mercury, for on the order of about /2 to 1 hour, and then immersing the evacuated wood in the aqueous, alkaline peroxide impregnant for about 2 to 6 hours, preferably at a pressure of about 8 to 12 atmospheres gauge pressure; This facilitates penetration of the liquid into the wood, providing more uniform and complete impregnation. It will be apparent that the exact conditions of vacuum, time of evacuation, impregnationpressure and impregnation time will vary With'the type of wood being treated and its dimensions, and may, in some cases, be outside the ranges given.

The process of this invention makes it possible to obtain from otherwise difiiculty pulped woods, for example,

beechwood, mechanical wood 'pulps which have a quality approaching, or even equal to, the excellent qualities ofchemical pulps. The brightness of such mechanical wood pulps can therefore be increased by bleaching with peroxygen chemicals to the point where they are useable as white printing papers. It will be evident this is a marked improvement in the mechanical pulping art.

The single attached drawing illustrates a preferred pulp- 7 ing operation in accordancewith the present invention,

shown in the form of a block-type flow diagram.

The wood treated-by the present process preferably will be a softwood, for example, spruce, pine, poplar, beech and the like, although typical hardwoods may be pulped by the present method with advantage. The grooves provided in the wood are sufficiently wide to permit ready penetration of the liquid 'impregnant, for example, about 1 to 5 mm. wide. Since the-wood removed in grooving is lost, it will be apparent that the grooves should not be excessively wide. However, grooves beyond about 5 mm. in width will be useful where Wood wastage is not a serious problem.

Grooving may be accomplished quite readily by simply sawing the logs to the desired depth, and it has been found that alternate cuts made on opposite sides ofthe log are quite effective, providing for most uniform impregnation. The grooves should be about 2 to 30 cm. apart, as this spacing provides adequate impregnation, without providing an excessive number of grooves, with attendant wastage of wood.

The solution employed to impregnate the logs most suitably will be an aqueous, alkaline peroxide solution such as may be prepared from about 15 to gms. per liter of hydrogen peroxide (100% about 15 to 100 gms. per liter'of sodium hydroxide, and a stabilizing amount of a stabilizersuch as sodium silicate, phosphate and the like. If desired, an equivalent solution may be prepared of sodium peroxide in place of the hydrogen peroxide and sodium hydroxide, and if hydrogen peroxide is employed, the sodium hydroxide may be replaced with potassium hydroxide or other alkali.

While the peroxide solution is particularly effective in promoting improved properties in pulp produced from logs, simple impregnation of the grooved log with water has been found to improve pulping and pulp properties significantly, and can be used where desired. Likewise, the water impregnant in this case may be made alkaline as desired, with corresponding physical improvement in the pulp produced.

The following examples are presented only as illustrative of the present invention, and are not to be deemed limiting in any way.

EXAMPLE 1 Spruce logs 1 meter in length, and ranging in diameter from 6 cm. to 25 cm., were decorticated and provided with six 2.5 mm. wide grooves at 15 cm. intervals. The grooves were applied with a saw alternately to opposite sides of the logs, and were cut of the way through the logs.

The grooved logs were then evacuated in a vacuum chamber operating at 20 mm. of mercury for 1 hour, after which they were impregnated at room temperature in a pressure chamber at 10 atmospheres gauge pressure for 2 hours with, an aqueous, alkaline solution composed of of 35% hydrogen peroxide, 2.5% of sodium hydroxide, and 2% of sodium silicate. The uptake of liquid in the wood by this treatment amounted to 80% based on the dry weight of the wood. The wood was then removed from the impregnating chamber and stored for 6 hours at atmospheric pressure, following which the wood was ground in a typical stone mechanical grinder to produce a clean, clear, pulp. The pulp was tested, as shown in Table I which follows Example 2 hereinafter.

EXAMPLE 2 Spruce logs of the same kind and size as used in Example 1, but not provided with the grooves described in Example 1, were decorticated and ground as was the wood in Example 1. The pulp produced by this method was tested in comparison with the pulp from Example 1, with the results reported in Table I which follows.

The following T.A.P.P.I. Standard Tests were employed in obtaining the above values:

2 T 404 Ill-50.

B T 233 sin-53.

It will be seen from the comparative results of Examples 1 and 2 that pulp produced from wood treated by the present process is far superior to pulp produced from untreated wood, both in strength and in fiber characteristics. The improvements are extremely significant, with the pulps produced by the present method being useful in many of the areas in which only chemically produced wood pulps have been useful heretofore.

EXAMPLE 3 Beechwood logs 1 meter in length, and having diameters from about 6 cm. to 25 cm., were decorticated and provided with grooves /2 of the way through the logs; the grooves were 2 mm. wide, and were at 16 cm. intervals. The logs were then treated by impregnation with an aqueous, alkaline peroxide solution by being subjected to an evacuated atmosphere at 20 mm. of mercury for 1 hour, followed by immersion in a Water solution contain ing 5% of 35% hydrogen peroxide, 2% of sodium peroxide and 1% of sodium silicate, in a pressure chamber operated at a. pressure of about 10 atmospheres gauge.

In this case, 94% by weight of the solution was taken up by the wood, and when the wood was ground to produce pulp after 5 hours storage following impregnation, it provided excellent, storing, clean pulp.

EXAMPLE 4 Poplar logs /2 meter in length and having diameters of about 6 cm. to 25 cm. were decorticated and grooved at 15 cm. intervals with saw cuts measuring 2 mm. in width, and extending of the way through the logs. The grooved logs were then evacuated in a vacuum chamber operated at 20 mm. of mercury for 30 minutes, following which they were impregnated with an aqueous, alkaline solution containing 5% of 35% hydrogen peroxide, 2% of sodium hydroxide and 2% of water glass, in a pressure chamber maintained at 9 atmospheres gauge for 2 hours. The liquid uptake in this case amounted to 95%, based on dry wood weight. The logs were ground on a mechanical grinder, and provided excellent, strong, wood pulp.

Pursuant to the requirements of the patent statutes, the principle of this invention has been explained and exemplified in a manner so that it can be readily practiced by those skilled in the art, such exemplification including what is considered to represent the best embodiment of the invention. However, it should be clearly understood that, within the scope of the appended claim, the invention may be practiced by those skilled in the art, and having the benefit of this disclosure, otherwise than as specifically described and exemplified herein.

What is claimed is:

In the production of mechanical wood pulp by grind ing logs having a length of at least /2 meter to produce said pulp, the improvement which comprises, prior to grinding, providing grooves having a width of about 2 to 5 millimeters, 50 to 80% of the way through said logs and at intervals of about 2 to 30 centimeters in a direction essentially perpendicular to the fiber direction of said logs, subjecting the grooved logs to the action of an evacuated atmosphere at about 5 to 15 millimeters of mercury, and impregnating the evacuated logs in an aqueous, alkaline peroxide solution containing about 15 to grams per liter of sodium hydroxide, 15 to 100 grams per liter of hydrogen peroxide, and a stabilizing amount of an active oxygen chemical stabilizer, at a pressure of about 8 to 12 atmospheres for about 2 to 6 hours.

References Cited in the file of this patent UNITED STATES PATENTS 2,360,432 Mackenzie Oct. 17, 1944 2,713,540 Libby -1 July 19, 1955 3,023,140 Textor Feb. 17, 1962 FOREIGN PATENTS 765,341 Great Britain Jan. 9, 1957

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