US2423469A - Chemically prepared wood pulp product and process for producing the same - Google Patents

Description

Patented July 8, 1947 CHEMICALLY PREPARED WOOD PULP PRODUCT AND PROCESS FOR PRO DUCING THE SALE Paul Henry Schlosser and Kenneth Russell Gray,

Shelton, W'ash., assignors' to Rayonier Incorporated, Shelton Delaware Wash., a corporation of No Drawing. Application May 3, 1944, Serial No. 533,929

9 Claims. 1

This invention relates to the production of cellulosic products, and has for its general object the provision of certain improvements in carrying out one or more of the processing steps in the production of such products. Theinvention is of special advantage in the preparation and processing of viscose derived from chemically prepared wood pulp, and in this connection aims to improve the steps of shredding, filtering and spinning viscose. The invention further contemplates, as a new article of manufacture, a chemically prepared wood pulp product having incorporated therein a mixed ether obtainable by resoda to form the solution commonly known as viscose, which is opacified if desired, filtered, and

acting ethylene oxide with a rosin alcohol. (Such such cellulosic products as rayon and other synthetic fibers, nitrocellulose, cellulose acetate, cellulose ethers, Cellophane and similar cellulosic films or sheets, etc. Wood pulp is commonly prepared and marketed in sheet form, and comminution or shredding is customarily one of the initial steps in its subsequent processing. When wood pulp is used in bulk form, either wet or dry, shredding or comminution is frequently a step involved in'the subsequent processing. Since such subsequent processing usually involves the conversion of the cellulose of the wood pulp to some cellulose derivative and the solution of the derivative in a. suitable solvent, the purpose oi. shredding is to break down the sheet into a fluffy mass or crumb in which the individual fibers will be suitably exposed to the action of the derivative-forming reagent or reagents. Thus, for example, in the production of viscose the wood pulp sheet is customarily steeped in a caustic soda solution to form alkali cellulose, and the alkali cellulose, after pressing and while still in sheet form, is shredded or comminuted to properly prepare the cellulose fibers for the xanthating reaction with carbon bisulflde. The resulting sodium cellulose xanthate is dissolved in dilute caustic spun into filaments.

Normal dissolving wood pulps in present use consist mainly of cellulose, but contain appreciable amounts of non-cellulosic impurities, such as hemi-celluloses, fats, resins, waxes, etc. One of the main objects in the manufacture of a highly refined dissolving pulp is to remove as much as possible of the non-cellulosic impurities, so that a whiter, purer pulp results, which is capable, in the manufacture of rayon, of producing a higher grade yarn.

We find,'however, that not all of the noncellulosic impurities which can be removed are undesirable, and, in fact, certain of such impurities, normally present in small amounts, are highly beneficial in aiding the processing of the pulp into viscose, especially as regards the step of shredding the alkali cellulose. These beneficial impurities which aid the shredding operation are probably of the nature of fiber lubricants which permit the steeped and pressed pulp to be thoroughly shredded into a fiufiy condition more readily and without mechanical damage to the alkali cellulose fibers which would cause them to react incompletely with carbon bisulphide. In a pulp which has not been highly refined, most of these beneficial impurities constitute a portion of the materials removable by organic solvents, as, for example, ether, benzene, alcohol, etc. These beneficial impurities, often loosely termed resins, are mainly of the nature of waxes, fats and resins, the latter often being present in a relatively small amount.

In theory, the problem of making a good pulp could be solved by removing all the undesirable impurities while retaining those impurities which facilitate the shredding operation by lubricating the fibers or otherwise. In practice, such a cleancut separation is difflcult to accomplish directly.

We have discovered that better results are obtainable by removing most or all of the impurities including those which serve beneficially as lubricants to the alkali cellulose fibers during shredding, and then adding to the pulp or to the alkali cellulose prior to the completion of shredding a sufficient amount of an agent capable of acting like, and actually being more eiiective than, the natural beneficial impurities,

White, highly purified or refined wood pulps are very advantageous tor the production of high grade rayon yarns of superior strength and color, and forthis reason, are highly esteemed by the trade. Such highly refined pulps are in general characterized by having an ether extract of about 0.15% or less where such values refer to the amount of natural ether extractable material left in the pulp after the purification processes. While our invention is particularly applicable to such highly refined pulps containing not more than about 0.15% of ether extractable material, it may be applied with certain advantages to the processing of normal dissolving pulps containing substantially more than 0.15% of ether extractable material, although such pulps do not generally yield the highest grade yarns and their processing into shredded alkali cellulose is not accompanied byany particular difficulty.

We have discovered a class of agents, namely, mixed ethers of rosin alcohols, which lubricate or protect the alkali cellulose fibers during shredding, and which are chemically entirely different from the beneficial impurities naturally present in the pulp. These agents are soluble or readily dispersible in water. In general, they are much more efiecti've in promoting shredding than the beneficial impurities naturally present in the pulp. Moreover, these agents exercise a beneficial infiuence upon certain subsequent steps in the preparation and processing of viscose into rayon which the natural beneficial impurities do not exercise. Based on these discoveries, our invention involves improving one or more of the processing steps in the production of cellulosic products from chemically prepared wood pulp by carrying out one or more of the processing steps in the presence of a mixed ether of a rosin alcohol. When applied to the preparation and processing of viscose derived from chemically prepared wood pulp, the invention particularly involves carrying out the shredding oi the alkali cellulose, or at least the final stage of shredding, and the spinning of the viscose in the presence or a mixed ether of a rosin alcohol. Where the invention is practiced solely to improve the spinning of the viscose, it is immaterial from what cellulosic raw material the viscose is derived.

The compounds of the invention are mixed ethers at least dispersible in and. preferably substantially soluble in water which are obtainable by reacting ethylene oxide with a rosin alcohol. As used herein, a rosin alcohol means an alcohol derived by reduction of rosinor abietic acid and consisting of dihydroabietyl, dehydroabietyl, tetrahydroabietyl or abietyl alcohol. More particularly, the compounds are mixed ethers containing a polyethylene oxide radical and a cycloaliphatic hydrocarbon radical derived from abietic acid and selected from the group consisting of the dihydroabietyl, dehydroabietyl, tetrahydroabietyl, and abietyl radicals.

Suitable compounds at least water dispersible will be mixed ethers containing a polyethylene oxide radical with at least three ethenoxy residues and a cycloaliphatic hydrocarbon radical selected from the group consisting of dihydroabietyl, dehydroabietyl, and tetrahydroabietyl and abietyl radicals. In regard to effectiveness there is apparently no practical upper limit for the number of ethenoxy units. The most preferred compounds, however, are mixed ethers containing a polyethylene oxide radical with from 6-20 ethenoxy units and a cycloaliphatic hydrocarbon radical selected Irom the group consisting 4 of the dihydroabietyl, dehydroabietyl, tetrahydroabietyl, and abietyl radicals.

In preparing the mixed ethers of the invention, it is not necessary to use pure rosin alcohols. We have had very good results by condensing ethylene oxide with the mixture of rosin alcohols, commonly sold under the name Hydroabietyl Alcohol, and which consists chiefly of a mixture of dihydroabietyl, dehydroabietyl, tetrahydroabietyl and abietyl alcohols. Examples of specific products are products obtained by condensing approximately 3, 4, 6, 12, 20 and 160 mols of ethylene oxide respectively per average molecular weight of the rosin alcohol mixture known as Hydroabietyl Alcohol. The condensation is brought about by any of the normal methods for reacting ethylene oxide with an alcohol, preferably incorporating an alkali as catalyst with the alcohol. Suitable methods include either adding a small proportion of 48% NaOH or dissolving metallic sodium in the heated rosin alcohol.

While highly refined wood pulps are advantageous for the production of high grade rayon yarns of superior strength and color, the reaction of the shredded alkali cellulose from such pulps with carbon bisulphide is frequently incomplete.

This impairment in the xanthating activity of the shredded alkali cellulose is due to some damage to the fibers during the shredding operation or to incomplete comminution or to formation of compressed fiber bundles. In the case of the conventional shredder having revolving blades coacting with a stationary saddle bar, the tendency for such damage is especially great if the clearance between the revolving blades and the saddle bar is a little less than the correct value. In an extreme case, with a very highly refined pulp, shredding, even under optimum conditions, may produce a shredded pulp which xanthates less completely than if the alkali cellulose were not shredded at all. In other cases, it is possible to obtain reasonably satisfactory shredding of the alkali cellulose from highly refined pulps by adjusting the shredder clearance and by experimenting to find the optimum shredding time for the particularpulp and particular shredder. In this manner it is possible in some cases to obtain 1 almost as complete a degree of xanthation of the shredded alkali cellulose from a highly refined pulp as would be obtained with the shredded alkali cellulose from a less pure pulp. But the necessity of constant supervision and adjustment to assure optimum shredding conditions makes the shredding of highly refined pulps too sensitive for satisfactory commercial practice. This sensitivity to damage during shredding of the alkali cellulose from highly refined pulps is overcome, in our invention, by carrying out the shredding operation in the presence of a mixed ether of a rosin alcohol which may be added to the pulp prior to shredding or to the alkali cellulose prior to the completion of shredding. While the invention thus improves the shredding operation, the most note-worthy evidence of this improvement is in the subsequent filtration of the viscose. The improvement in shredding produces a shredded alkali cellulose which reacts substantially completely with carbon bisulphide, and the resultin viscose is comparatively free of unreacted fibers and filtration proceeds more rapidly and economically.

In the spinning of viscose into acid spin baths containing certain metallic salts and especially a zinc salt, incrustations tend to form within the orifices of the spinneret, either partially or completely blocking the orifices. The partial blocking of the orifices causes objectionable irregularities in the thickness of the filaments and frequently causes breaking of the filaments which necessitates interruption of the spinning operation to change spinnerets. The formation of such incrustations is suppressed or minimized in the present invention by carrying out the spinning operation in the presence of a mixed ether of a rosin alcohol. The mixed ether may be added to the viscose or to the constituents entering into the production of the viscose, or may be added to the acid spin bath. While this aspect of our invention relates particularly to improving spinduction of this product, as .a

' When the agent is so incorporated in the wood 1 pulp, by the manufacturer thereof, the pulp ning. conditions in the viscose process where I viscose is normally extruded through spinnerets or other orifices into acid setting baths, it is to be understood that the invention is not limited to the viscose process. but is applicable to any process where cellulosic solutions are extruded through spinnerets or other orifices into aqueous setting baths where incrustations tend to form within the extrusion orifices. In such cases, the 1 invention is only subject to the limitations that the material be added in such a way as to be present in either the spinning solution or spin bath at the time of spinning.

When a mixed ether of the invention has been employed to improve shredding, in accordance with the invention, the mixed ether will be present in the resulting viscose. Although, as hereinafter more particularly explained, th amount oi mixed ether required for securing the contemplated improvement in suppressing or minimizing the formation of incrustations during spinning is slightly greater than the amount required for securing the contemplated improvement in shredding and filtration, there is no objection to carrying out the shredding step in the presence of such amount of said mixed ether as is required in the spinning of the viscose. Indeed, the full advantages of our invention are best realized when a mixed ether of the invention is added to the alkali cellulose prior to the completion of shredding and in amount adequate for securing the contemplated improvement in spinning the viscose.

The most practical and economical manner of securing the desired presence of a mixed'ether of a rosin alcohol during ,the shredding of the alkali cellulose and during the spinning of the viscose is to incorporate such a mixed ether in the wood pulp. This may be advantageously effected by adding the mixed ether to the pulp on the sheet-forming machine subsequent to sheet formation but prior to complete drying, by spraying the pulp sheet with an aqueous solution of the mixed ether or bymeans of a rotating roll partly immersed in such a. solution. If desired,

the mixed ether of a rosin alcohol may be incorporated in the pulp prior to sheet formation, as, for example, by adding the agent to a suspension of pulp in water in a stock chest. In the latter case, the white water should preferably be recirculated in order to prevent considerable loss of the agent when eliminatin water in sheet formation. In any case, there is produced a chemically prepared wood pulp product having incorporated therein a mixed ether containing a polyethylene oxide radical with at comes to the rayon manufacturer in a form' calculated to secure the full advantages of the invention in the preparation and processing of the viscose into high grade rayon yams.

The amount of the said mixed ethers used in the practice of the invention is relatively small, ranging from 0.01 to 0.25%, by weight on the bone dry weight of the wood pulp used, when.

the agent is incorporated in or added to the pulp or to the viscose. So far as the objectives of the invention are concerned, there is little, if

any, improvementby increasing the amount of the mixed ethers above 0.25%, and such higher amounts give rise to certain disadvantages. These disadvantages include the causing of excessive softness in the sheet resulting in mechanical difllculties in steeping, excessive ballformation in xanthation, difilculties in the dissolving operation due both to the excessive ball formation in the xanthating step and due to excessive foaming in the viscose solution. Also, there will be considerable dlfllculty in obtaining a completely deaerated viscose which is absolutely necessary for satisfactory spinning. Higher concentrations of the mixed ethers also unduly lower least three ethenoxy residues and a cycloaliphatic the surface tension of the viscose, thus changing the coagulating conditions so that the viscose cannot be satisfactorily spun by standard The amount of the mixed ether of a rosin alcohol required for securing the contemplated improvement in shredding' and filtration is generally slightly less than the amount required for securing the contemplated improvement in suppressing or minimizing the formation of incrus tations during spinning. Thus, the contemplated improvement in shredding and filtration will generally be broughtabout by from 0.02% to 0.05% of the mixed ether, and rarely would more than 0.1% be required. For suppressing or minimizing the formation of incrustations, the mixed ether should be present in the viscose in amount of at least 0.05% and often 0.1% or more. These percentage figures are based on the bone-dry weight of the pulp used. When the mixed ether is incorporated in the spin bath, the amount present inthe spin bath may advantageously be 0.001 to 0.1% by weight on the weight of the bath.

While it is our preferred practice to 111001130? rate the mixed ether in the wood pulp product, which preferably is a highly refined pulp containing not more than about 0.15% of ether extractable material and is commonly marketed in sheet form, the presence of the agent, during the processing steps of shredding, filtering, and

spinning may be secured in any other appropri-' the agent may be sprayed upon or otherwise suita ably added to all or a portion of the alkali cellulose prior to shredding or prior tothe completion of shredding. Finally, in those cases where the invention is not practiced in the. shredding and filtering steps, the mixed ether of I a rosin alcohol may be incorporated in the vlsnew article of manufacture. is one of the aspects of the invention.

cose or the spin bath, and in such cases the suppressing and minimizing of the formation of incrustations will be attained where the viscose is made of other cellulo sic raw materials as well as wood pulp. However, we believe it will generally be found more advantageous to incorporate the mixed ether in the initial wood pulp product, both as a matter of convenience and economy in preparing and processing the viscose, and because a very uniform distribution of the agent throughout the pulp is easily attained.

When the invention is practiced for effecting the hereinbefore-mentioned improvements in shredding and filtering, certain further economies are effected in the subsequent steps of xanthating,- dissolving and filtering. In viscose solutions there is usually a certain amount of undissolved fibers and gel-like material due to the incomplete reaction of the cellulose with the carbon bisulphide during xanthation. Prior to spinning, the viscose solutions are filtered several times to remove these gels and undissolved fibers. In the event that theviscose solutions contain excessive amounts of undissolved and partially dissolved fibers, filtration is an expensive operation. In such cases the filters become rapidly clogged and the filter media must be changed frequently in order that the Viscose will pass through in a reasonable time. Frequent changing of the filter media is expensive not only as regards consumption of filter cloth but also in view of the very considerable amount of labor involved and also since a certain amount of viscose is lost every time the filter is opened up. Furthermore, when the viscose solutions contain very large proportions of gel-like material, filtration is usually not altogether satisfactory in that some of the smaller gel-like particlestend to pass through the pores of the cloth with adverse eflect upon the spinning operation. It has heretofore been the practice in the viscose industry, when processing pulps which tend to yield viscose solutions high in undissolved material and having poor filtration properties, to minimize such difficulties by carrying out the xanthation with amounts of carbon bisulphide considerably in excess of that normally required. Use of excess carbon bisulphide is ex-' the shredding operation that the alkali cellulose subsequently reacts much more completely with carbon bisulphide and yields a viscose solution very free from undissolved and partially dissolved cellulose particles and having good filtration properties. This result can be accomplished not only without the use of excess carbon bisulphide, but in many cases satisfactory viscose solutions can be obtained using amounts of carbon bisulphide very substantially less than the amounts normally required.

We claim:

1. The method of improving the processing of refined chemical pulp containing not more than 0.15% ether-extractable matter into viscose comprising adding to one of the viscose forming materials a mixed ether having attached to the ether oxygen a polyethylene oxide radical with at least three ethenoxy residues and a cycloaliphatic radical selected from the group consisting of the di- 8 hydroabietyl, dehydroabietyl, tetrahydroabietyl and abietyl radicals, said ether being added in an amount of from 0.01% to 0.25% by weight based on the weight of the bone dry pulp.

2. Th method of improving the processing of refined chemical pulp containing not more than 0.15% ether-extractable matter into viscose comprising adding to one of the viscose forming materials a mixed ether having attached to the ether oxygen a polyethylene oxide radical with from 6 to 20 ethenoxy units and a cycloaliphatic radical selected from the group consisting of the dihydroabietyl, dehydroabietyl, tetrahydroabietyl and abietyl radicals, said ether being added in an amount of from 0.01% to 0.25% by weight based on the weight of the bone dry pulp.

3. In the processing of wood pulp into rayon by the viscose process, the improvement which comprises adding to one of the viscose forming materials at a stage prior to completion of shredding from 0.01% to 0.25% by weight based on the bone dry weight of the pulp of a mixed ether having attached to the ether oxygen a polyethylene oxide radical with at least three ethenoxy residues and a c'ycloaliphatic radical selected from the group consisting of the dihydroabietyl, dehydroabietyl, tetrahydroabietyl and abietyl radicals. r

4. In th processing of wood pulp into rayon by the viscose process, the improvement which comprises carrying out at least one of the steps consisting of shredding, filtering and spinning in the presence of from 0.01 to 0.25% by weight based on the bone dry weight of the pulp of an added mixed ether having attached to the ether oxygen a polyethylene oxide radical with at least three ethenoxy residues and a cycloaliphatic radical selected from the group consisting of the dihydroabietyl, dehydroabietyl, tetrahydroabietyl and abietyl radicals.

5. In the processing of wood pulp into rayon by the viscose process, the improvement which comprises carrying out at least one of the steps consisting of shredding, filtering and spinning in the presence of from 0.01% to 0.25% by weight based on the bone dry weight of the pulp of an added mixed ether having attached to the ether oxygen a polyethylene oxide radical with from 6 to 20 ethenoxy units and a cycloaliphatic radicalv selected from the group consisting of the dihydroabietyl, deh'ydroabietyl, tetrahydroabietyl and abietyl radicals.

6. The method of treating refined chemical pulp containing not more than 0.15% ether extractable matter which comprises adding to the refined chemical pulp from 0.01% to 0.25% by weight based on the bone dry weight of the pulp of ainixed ether having attached to the ether oxygen a polyethylene oxide radical with at least three ethenoxy residues and a cycloaliphatic radical selected from the group consisting of the dihydroabietyl, dehydroabietyl, tetrahydroabietyl and abietyl radicals.

'7. The method of treating refined chemical pulp containing not more than 0.15% ether extractable matter which comprises adding to the refined chemical pulp from 0.01% to 0.25% by weight based on the bone dry weight of the pulp of a mixed ether having attached to the ether oxygen a polyethylene oxid radical with from 6 to 20 ethenoxy units and a cycloaliphatic radical selected from the group consisting of the dihydroabietyl, dehydroabietyl, tetrahydroabietyl and abietyl radicals.

8. As a new article of manufacture, a refined 9 chemical pulp product containing not more than 0.15% of natural ether-extractable matter and having incorporated therein from 0.01% to 0.25% by weight based on the bone dry weight of the pulp of a mixed ether having. attached to the ether oxygen a polyethylene oxide radical with at least three ethenoxy residues and a'cycloali phatic radical selected from the group consisting of the dihydroabietyl, dehydroabietyl, tetrahydroabietyl and abietyl radicals. i

9. As a new articl of manufacture, a refined chemical pulp product containing not more than 0.15% of natural ether-extractable matter and having incorporated therein from 0.01% to 0.25% by weight based on the bone dry Weight of the pulp of a mixed ether having attached to the REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Number 1 Bruson Nov. '7, 1939