JPS5946249B2 - Method for producing insoluble etherified cellulose graft copolymer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process for making highly absorbent materials made by chemically modifying naturally occurring cellulose ether structures.

This modified cellulose ether has a sufficient proportion of ether substituents to be water soluble, but is further modified to make it a highly absorbent cellulose ether.
Cellulose fibers and regenerated cellulose are the raw materials for commercial absorbent products such as menstrual belts, tongues, diapers, and surgical clothing.

Although primarily unmodified cellulose has been found useful in such products, improved materials have been sought in an effort to improve product quality and economics. For example, cellulose ethers, such as carboxymethylcellulose ethers, such as carboxymethylcellulose, exhibit increased absorbency and retention for body fluids;
These desirable properties depend on the degree of ether substitution (D, S,
) was found to increase with Therefore, of course, such materials in insoluble form are useful in products for the absorption of bodily fluids, and such teachings were introduced in October 1961.
It is disclosed in U.S. Pat. Additionally, U.S. Pat.
A particular form of insoluble carboxymethylcellulose is disclosed that is rendered insoluble by wet cross-linking the cellulose by the method described in US Pat.
US Pat. No. 3,678,061 discloses yet another form of carboxymethyl cellulose that is highly substituted and made insoluble by acid and heat treatment. U.S. Pat. No. 3,256,372 discloses grafting hydrophilic polymers onto the backbone of cellulose and our
US Pat. Still other methods of chemical modification of cellulose have been disclosed. Each of these patents and patent applications teaches modified cellulose having absorbency and retention capabilities for body fluids that are greatly improved over the properties of unmodified cellulose. Despite these improvements in the prior art, the search for better absorbent materials continues. Now, according to the present invention, the absorbency and retention properties of modified cellulose of the prior art are far exceeded and hence absorbent bodies of products that absorb and retain body fluids such as menstrual belts, tongues, diapers and surgical garments. It has been found that certain modified celluloses can be obtained which are advantageously used as absorption media in the art.

According to the present invention, ethers which are water soluble when ungrafted and have been made insoluble by having a side chain of a polymeric moiety grafted onto the cellulose backbone in an amount sufficient to render the ether insoluble. An insoluble etherified cellulose graft copolymer is provided. This particular etherified cellulose is a carboxyalkylcellulose and a sufficient amount of etherified groups are present per anhydroglycol unit in the cellulose chain to make such ether water soluble in the absence of graft polymer groups. shall be.

A degree of ether substitution (D.S.) of at least 0.35 ether groups per anhydroglucose unit is generally sufficient.
Such ether salts are generally alkali metal and ammonium salts, such as Li. Na. ．． K or NH3
It should consist of salt. Cellulose ethers are made insoluble by grafting side chains of homopolymer or copolymer moieties onto their cellulose backbone, which side chains can be hydrophilic, hydrophobic, or both hydrophilic and hydrophobic. and should be present in sufficient amount to render the ether insoluble in water.

The amount of side chains that must be grafted onto the main chain depends on the type of ether and the D of ungrafted cellulose ether. S. will change accordingly. For example, D. S. O. In the case of carboxymethylcellulose of No. 4, the side chains represent approximately at least 10% by weight of the grafted cellulose ether.
should be configured. D. S. l. 2, the side chains are at least about 25% by weight of the grafted cellulose ether.
should be configured. Side chains could constitute as much as 90%. Compatible polymers and hydrophobic polymers or copolymers that are both hydrophilic and hydrophobic can be grafted onto the cellulose backbone; Particular benefits can be obtained using coalescence, with which the resulting grafted cellulose ethers exhibit greater absorption and retention, which surprisingly allows such Effects can be obtained.

According to the present invention, a product is obtained by carrying out two reactions on cellulose: etherification and polymer grafting.

The starting material for these reactions can be natural cellulose, such as wood pulse, hemp, sugar cane husk, cotton, etc., or regenerated cellulose such as rayon. Preferably, the etherified cellulose is carboxyalkylcellulose.

Etherification is generally carried out by reacting cellulose with an etherification agent in an alkaline dispersion medium. Sodium carboxymethyl cellulose is R. L. Wh
istler. ．． CarbOhydrate Chemi
stry', VOl. (CellulOse), 322
~327, Academic Press,. Inc. (
(1963), in which cellulose material, particularly cotton linter, is converted to carboxymethyl cellulose by reacting it with chloroacetic acid and aqueous sodium hydroxide in propanol solution. The so-called slurry method for producing sodium carboxymethylcellulose was introduced on October 1, 1967.
No. 7, U.S. Pat. This product is commercially available in powder or fiber form, but D. S. is higher than this, 2.5 to 2.77
It should be noted that the products can be manufactured according to the method described in the Whister reference, supra. The resulting cellulose ether should have sufficient etherification groups to be water soluble in the absence of other treatments.

Generally, for carboxymethyl cellulose, especially their alkali metal salts, a D.I. of at least 0.35. S.
would give this result. By adjusting the etherification reaction time, temperature and ratio of reactants, as is well known in the art, D. S. can be adjusted. According to the invention, the ether has side chains of polymer or copolymer moieties grafted onto its cellulose backbone in an amount sufficient to render the grafted product water-insoluble.

Such side chains may consist of hydrophilic or hydrophobic moieties;
In fact, a given cellulose ether molecule can have various combinations of these types of polymers. Hydrophilic moieties useful for this purpose are polyacrylonitrile and copolymers of acrylonitrile and ethyl acrylate.

The cellulose ethers can be combined in the first case with preformed homopolymers or copolymers or with precursor monomers of these polymers to polymerize the polymers in situ.

In either case, the reaction components are dispersed and the reaction is carried out in a vapor medium or a non-aqueous medium, such as acetone.
Carry out in alcohol (eg methanol, ethanol, isopropanol, etc.), benzene, liquid ammonia, etc. However, preferably the grafting reaction is carried out in an aqueous medium. When grafting is carried out in a liquid medium, it is advisable to add a few drops of emulsifier to the reaction mixture in order to promote dispersion, ie a more homogeneous polymerization of certain monomers.

Examples of such emulsifiers are: Triton ; the average alkyl composition is 90% dodecyl, 9% tetradecyl, and 19% oxytadecyl;
A by Armory & Co. as a solution of % active ingredient, 17% sodium chloride and 50% water.
Cationic quaternary ammonium salts of alkyltrimethylammonium chloride and dialkyldimethylammonium chloride supplied under the trade name rquadl2; such as laurylpyridium chloride. The grafting reaction can be initiated by ionic initiators (eg, alkali hydroxides), cationic initiators (eg, Lewis acids such as boron trifluoride), or radiation (ultraviolet light, gamma rays, electron beams).

However, the grafting can be carried out using free radical initiators such as cerium ion, ferrous ion, cobalt ion, (NH4
) Preferably carried out by a free radical polymerization mechanism using 2S208 cuprous ions or the like. Cerium ion initiators are preferred. Since most free radical reactions are inhibited in the presence of oxygen, brush essentially all the oxygen from the reactor by whisking an inert, non-oxidizing gas, such as nitrogen, helium, or argon, through the system. However, it is desirable to then add a free radical initiator.

The pH range used for the reaction depends on the particular initiator used.

Highly acidic pH (0.8-2
．． Any PH from 3) to highly basic PH (12-14) could be used. For the preferred cerium ion initiator, the PH is less than 7 acidic, preferably from about 0.8 to about 2.3. The grafting reaction can be carried out at temperatures from room temperature (i.e., 20-30°C) to the normal boiling point of the lowest boiling component of the reaction mixture.

If the reaction is carried out at a pressure above atmospheric, the temperature can be above the normal boiling point of the lowest boiling component of the mixture. Also, the reaction mixture can be lowered below room temperature if desired. Satisfactory products can be obtained by grafting originally hydrophilic or hydrophobic polymers or mixed copolymers onto cellulose as described above.

However, as pointed out here, certain advantages are obtained with ethers grafted with at least partially hydrophilic chains, and a satisfactory way of achieving this is by at least partially hydrolyzed The polymer that can be used is first grafted and the product is then hydrolyzed to produce at least partially hydrophilic grafted chains. Such a hydrolyzable polymer is, for example, polyacrylonitrile, which can be hydrolyzed to a hydrophilic alkali metal poly(acrylate). When polyacrylonitrile and copolymers such as relatively non-hydrolyzable polymeric moieties such as methyl methacrylate, ethyl acrylate, etc. are grafted onto cellulose ethers and then hydrolyzed in a controlled manner, they are partially hydrophilic. A mixed polymer chain is formed which is also partially hydrophobic. Hydrolysis is
This can be done by reacting the grafted ether with an excess of a solution of a strong base, such as sodium hydroxide, potassium hydroxide, lithium hydroxide, etc., preferably under reflux. The concentration of this solution is from about 1 to about 50% by weight. The weight percent of polymer grafted onto cellulose fibers (based on grafted ether) is primarily due to the D. S. Depends on.

In general, D. S. The greater is the weight percent of grafted polymer required to render the otherwise water-soluble cellulose ether insoluble. It has been found that this relationship is essentially independent of the nature of the polymer, ie its hydrophilicity or hydrophobicity. The following table shows the D. S. The above relationship will be clarified when changing .

The grafted cellulose ethers of the present invention are superior in both absorption and retention to the chemically modified forms of cellulose of the prior art and to the aforementioned U.S. Pat.
From the grafted unetherified cellulose described in No.
It was found that the results were significantly better.

Although the product of the invention can be used in powder form, when it is used in the body of a fibrous absorbent material of a product for absorbing bodily fluids, it preferably has an original fibrous structure. Several methods of making such fiber products will be apparent to those skilled in the art from the teachings provided herein. For example, when producing a product of the invention by first producing a water-soluble alkali metal cellulose ether and then grafting it in an aqueous medium, the ungrafted intermediate can be removed by treating it with an aqueous acid solution. can be temporarily insolubilized. Grafting is then carried out in an aqueous medium, preserving the structure of the fibers. After grafting, the product can be treated with an alkali metal hydroxide to restore the ether to its original alkali metal salt form. Alternatively, the reaction sequence could be modified so that the unetherified cellulose is first grafted and then etherified, or the grafting and etherification are carried out essentially simultaneously. In any case, the fibrous structure of cellulose can be maintained. The products of the invention can be used alone or mixed with unmodified cellulose or other absorbent materials in the construction of absorbent napkins, tongues, sponges and the like.

The fibrous products of the invention, alone or in combination with other materials, such as untreated cellulose, can also be made into non-woven fabrics or tissues, such as absorbent napkins, tongues, sponges, etc. Useful in manufacturing. The grafted cellulose ethers of the present invention, their properties and methods of preparation are further illustrated by the following examples.

Example 1 D. S. A series of samples of commercially available sodium carboxymethyl cellulose powders with a .
Hercules,. Inc. ).

20y of each sample was added to 250ml of methanol mononitric acid solution (
1/? 1001 LI of HNO3 in MeOH) at 25 °C
for 20 hours to convert it to the acid form. The acidic material obtained is thoroughly washed with distilled water and then placed in the reactor with 1000 ml of distilled water. Purge nitrogen for 30 minutes to remove oxygen from the system. Then 10 ml of ammonium cerium nitrate solution [0.1 mol Ce() in 1N nitric acid] was added, and after 5 minutes, the predetermined amount of acrylonitrile (5-30T) was added.
The amount of change in I11) is added. The reaction is allowed to proceed for 2 hours at 25° C. under a nitrogen atmosphere. Transfer the resulting grafted cellulose ether to a Buchna funnel and wash thoroughly with water and acetone. Then, the washed ether was dissolved in methanol.
It is converted to the alkali metal salt form by treatment with a solution of % by weight potassium hydroxide at 25° C. for 24 hours. The product is washed with methanol and dried at 105°C. The resulting series of hydrophobic polymer grafted alkali metal cellulose ethers are tested to determine the weight percent of the grafted polymer and the absorption and retention of water and salt solutions.

The polymer concentration of these samples was determined by nitrogen analysis method.
In this analytical method, the nitrogen content of the graft ether is obtained by the Kirdahl method using an ammonia electrode. This analytical method is described by W. Edited by HOrwitz, 0fficia1Meth
0dsandAnalysis0ftheAss0ci
ati0n0f0fficia1ANalytical
Chemists, WashingtOn. ．． D. C.
, 12th edition, code number 47023 (1975). Absorption of aqueous liquids is determined by the "XOW test" in which approximately 0.57 samples of the test material are accurately weighed and stirred into a beaker containing 100 ml of the aqueous test fluid. After 20 minutes, the mixture is filtered through a nylon trico cloth membrane and allowed to drip for 5 minutes.

Collect the filtrate and measure in a graduated cylinder. [XOW]
That is, the absorption capacity of the material in units of grams of liquid absorbed per y of test material is calculated as follows. The aqueous fluid holding capacity of TextileRes.
J. , 37, 356-366, 1967.

Briefly, this test involves placing the test material into a device that is essentially a Buchner funnel with a porous bottom plate and applying a standard weight to the sample to maintain a standardized confining pressure. The test consists of holding the sample in place using the
The porous plate is placed in contact with a container of liquid, allowing the sample to absorb liquid through the porous plate until it is saturated. By maintaining the sample essentially at the liquid level of the container, the absorbed liquid is kept at essentially zero head with respect to the container. To measure retention capacity, a saturated sample is raised relative to a liquid container, which imparts a hydraulic head to the absorbed liquid, which is arbitrarily chosen as 35.5 cm of fluid. The device includes means for directly measuring the volume of liquid held under this head. Report the retention value as the volume retained per unit weight of sample. The results of these tests using various aqueous salt solutions and water are listed in Table 1.

As a control, a commercially available ether was similarly tested and reported as "unmodified". As a further control, an ether acidified according to the procedure described above and then reconstituted to its original salt form without grafting was tested.
reported in Table 1 as 'treated control'. For comparison purposes,
Wood pulp is also tested and reported as [cellulose fiber]. As is clear from the results in Table 1, the grafting technique of the present invention renders the etherified cellulose insoluble and generally gives the resulting product absorbency (XOW values) at least as good as that of wood pulp.

Retention values increased significantly. Example 2 The procedure of Example 1 is carried out, except that the graft polymer is made hydrophilic by converting the polyacrylonitrile to an alkali metal polyacrylate by a hydrolysis step.

The acidified grafted cellulose ether obtained from grafting step)* of Example 1 was refluxed for 1 hour with a 6% potassium hydroxide (or sodium, if specified) solution in a 90%/20% (by volume) solution, then ethanol/
The acidified grafted cellulose ether is hydrolyzed by washing with an aqueous solution and drying at 105°C. Polymer content, absorption and retention were determined by the method described in Example 1 and the results are reported in the table. It is clear from the tabulated results that, as in the previous run, the soluble cellulose ether was effectively rendered insoluble by the grafting.

Despite this insolubilization, in this grafted hydrophilic polymer portion, the XOW value of the grafted ether far exceeds that of cellulose fibers. As in the previous example, retention values are also greatly improved. Example 3 Example 3 except that in addition to adding acrylonitrile to the grafting reactor, varying amounts of ethyl acrylate were added to graft both poly(ethyl acrylate) and poly(acrylonitrile) polymeric moieties onto the cellulose. Perform step 2.

These graft copolymers are then hydrolyzed according to the method of Example 2 to produce cellulose ethers grafted with at least partially hydrophilic polymers. The amount of grafted polymer is determined by measuring the weight difference before and after grafting. Additionally, the retention and absorption properties of these graft copolymer ethers were measured and reported in the table. As is clear from the above table, grafting of the copolymer rendered the otherwise soluble cellulose ether insoluble.

As shown by the XOW value, the grafting of the copolymer results in
A product is produced that is more absorbent than wood pulp or grafted with a hydrophobic homopolymer, but somewhat less absorbent than grafted with a hydrophilic homopolymer. Example 4 Meth0ds0fCarb0hydrateCh1m
istry101. , R. L. Edited by Wllstler,
Academic Press,. N. Y. (1963)
, P. A series of fibrous sodium carboxymethylcelluloses are made according to the method described in 322.

In this method, a fully bleached kraft wood pulp of 157 southern pines is slurried in 400 ml of isopropanol. To this slurry, 23% by weight aqueous sodium hydroxide 40me is slowly added with stirring over a period of 30 minutes at room temperature. 187 monochloroacetic acid was slowly added to this mixture over 2" K3O minutes with stirring, and the mixture was allowed to react for 3 hours and 30 minutes while maintaining the temperature at 55°C. The thus treated fibers were then filtered from the reaction mixture. The slurry thus formed is then transferred to a beaker containing a 70%/30% volume methanol/water solution and sufficient acid is added to neutralize the slurry thus formed.The slurry is filtered and the resulting fibers are initially Wash with 70% volume methanol-water and then 95%/5% volume methanol/water. The washed fibers are dried at 70° C. for 2 hours. The product obtained has a degree of fibrous substitution of 0.64. sodium carboxymethylcellulose.As listed in the table,
Various amounts of hydrolyzed acrylonitrile homopolymer and acrylonitrile/ethyl acrylate copolymer are grafted onto the fibrous cellulose ether according to Examples 2 and 3 above. The XOW values for these grafted samples and treated and untreated controls as well as comparative unetherified cellulose fiber samples are also reported in the table. Comparative Examples For comparative purposes, unmodified and several chemically modified materials were evaluated for their fluid retention and XOW values and are listed in the table below.

The material labeled "Cellulose Fiber" is a fully bleached grafted wood pulp of untreated ground southern pine. "
Materials marked "CMC" are D.C. S. is 0.35 or more and is sodium carboxymethyl cellulose manufactured by Hercules. The material labeled "crosslinked CMC" is wet crosslinked sodium carboxymethyl cellulose made according to the method described in the aforementioned US Pat. No. 3,589,364. [Hydrolyzed PAN grafted cellulose] is a completely hydrophilic hydrolyzed*{(
It is a natural unetherified cellulose grafted with poly(acrylonitrile) homopolymer, which constitutes approximately 66% by weight of the grafted fibers. "Hydrolyzed copolymer grafted cellulose" is a partially hydrolyzed acrylonitrile/ethyl acrylate (50/50
unmodified cellulose to which a molar ratio of monomers) copolymer is grafted, which copolymer constitutes approximately 90% by weight of the grafted cellulose, and which is described in U.S. Pat.
This material is described in No. 627. These materials were compared to samples of the etherified grafted cellulose of the present invention for fluid retention and XOW values and are listed in the table below. As Table V shows, in all cases the materials of the present invention outperform various other chemically modified and unmodified comparative cellulose material samples in fluid retention and XOW values.

Claims (1)

[Claims] 1 A method for producing an absorbable insoluble etherified cellulose graft copolymer, the degree of substitution per anhydroglucose unit being 0.
．． Carboxymethyl cellulose having 35 to 1.2 carboxymethyl groups is copolymerized with a side chain of a polymer moiety selected from the group consisting of polyacrylonitrile, a copolymer of acrylonitrile and ethyl acrylate to the cellulose main chain to produce the ether. A process characterized in that cellulose is made insoluble and then converted into a salt form by treatment with a strong base.