JPS6122045B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to cellulose graft copolymers in the form of fibers and methods for their production. Cellulose products are the raw material for many absorbent commercial products. Since it is always desirable to improve the absorbency of these products, it has also been desirable to improve the absorbency of natural and regenerated cellulose fibers. Since cellulose is a naturally occurring polymer and is not synthesized, its structure is not easily altered by the copolymerization methods used to make synthetic polymers. The absorbency of cellulose fibers has been improved by changing their chemical structure, and known methods include (1) replacing the hydroxyl groups of cellulose fibers with new chemical groups; (2) crosslinking cellulose chains to create a network; (3) introduce novel groups and crosslink these groups; or (4) graft polymer side chains onto the cellulose backbone. It's a method. These chemical modifications are generally carried out in a liquid (preferably aqueous) slurry, and the resulting modified fibers are then dried to form a pulp board, which is subsequently ground into fluff. These conventional methods mainly produce highly absorbent cellulose fibers, which are generally brittle and therefore difficult to process during mechanical processing, for example when grinding pulp board into pulp fluff. It does not lose its fibrous structure and tends to become very short fibers or powder. Additionally, these conventional products tend to have a high degree of interfiber bonding, which results in the formation of a knot-like mass of solid resin-like material when drying from an aqueous slurry to pulp board. This is a process known as hornification. The nodules are not fibrous, so when pulpboard is ground into fluff, the nodules either break down into a powder or remain intact and are not absorbable in either of these forms. unsuitable for synthetic materials. Thus, although prior art modified cellulose fibers are more absorbent than unmodified cellulose fibers, this absorbency was obtained at the cost of reduced flexibility and loss of other desirable fiber properties. It is. The present invention provides significantly greater absorbency than unmodified cellulose fibers while retaining its fiber properties and avoids the problems found with prior art modified cellulose fibers. Cellulose fibers (natural or regenerated) with a modified chemical structure are obtained. According to the invention, cellulose graft copolymers are obtained which have a main chain of natural or regenerated cellulose in the form of fibers and side chains of polymeric moieties grafted thereto. This cellulose graft copolymer is a highly water-absorbent, soft, nonflammable fibrous material that is commonly used in absorbent clothing, particularly diapers.
Useful in a variety of water or aqueous fluid absorbent products such as menstrual belts, tampons, surgical sponges, etc. The copolymer side chains on the cellulose backbone consist of ionic and nonionic polymer portions. On a weight basis, the side chains of these copolymers can be in an amount of about 25 to about 90%, preferably about 50 to about 85%, of the cellulose graft copolymer. These copolymer side chains are ideally composed of alternating ionic and nonionic polymeric moieties, but may be composed of groups of alternating ionic and nonionic polymeric moieties. I can do it.
A particular side chain can even be composed entirely of one type of moiety or the other, so long as the overall ratio of ionic and nonionic moieties (described below) is maintained. The ionic polymer moiety can be any type of ionic polymer moiety, such as poly(acrylic acid), sodium poly(acrylate), poly(methacrylic acid), potassium poly(methacrylate), poly(vinyl alcohol sulfate), poly( phosphoric acid),
It can also be poly(vinylamine), poly(4-vinylpyridine), hydrolyzed poly(acrylonitrile), and the like. The ionic polymer portion constitutes about 10 to about 80%, preferably about 20 to about 70% by weight of the cellulose graft copolymer. The nonionic polymer moiety can be any nonionic polymer moiety, such as poly(methyl methacrylate), poly(ethyl methacrylate), poly(ethyl acrylate), poly(butyl acrylate), poly(vinyl acetate), It can also be poly(styrene), poly(butadiene), poly(isoprene), and the like. This nonionic polymer portion constitutes about 15 to about 60% by weight of the cellulose graft copolymer. The cellulose fibers used in the preparation of the cellulose graft copolymers of the present invention can be natural cellulose fibers, such as wood pulp, hemp, sugar cane husk, cotton, etc., or regenerated cellulose, such as rayon. Various modified cellulose fibers, such as cellulose ethers and esters, may also be used, provided that such modifications are consistent with the teachings of the present invention. The fibers of the cellulose graft copolymer of the present invention are prepared according to the method of the present invention by combining (a) fibrous cellulose, (b) a copolymerizable monomer that is hydrolyzed to give an ionic moiety after copolymerization, and (c) a copolymerizable monomer that is hydrolyzed to give an ionic moiety after copolymerization. Preferably, it is produced by copolymerizing nonionic, at least partially non-hydrolyzable monomers. The resulting non-hydrolyzable cellulose graft copolymer is reacted with an excess amount of a strong base solution to hydrolyze the hydrolyzable portion of the grafted polymer portion to an ionic form such as a salt of a strong base; At the same time, a non-ionic, non-hydrolyzable portion of the grafted polymer remains. Although it is within the scope of the present invention to prepare a desired cellulose graft copolymer by grafting a preformed copolymer or a preformed homopolymer onto a fibrous cellulose main chain, as described above, It should be understood that in-situ manufacturing is preferred. Additionally, the mixture of cellulose and the two monomers can be polymerized in a single reaction mixture (which is preferred) or the polymerization can be carried out by adding first one monomer and then the other. It is also within the scope of the invention to carry out the process in stages. The cellulose graft copolymer of the present invention comprises a fibrous cellulose, b a copolymerizable monomer that can be hydrolyzed to form an ionic polymer portion after copolymerization, and c a copolymerizable nonionic monomer. Produced by copolymerizing at least partially non-hydrolyzable monomers. The reaction components can be dispersed and the reaction carried out in a vapor medium or a non-aqueous medium such as acetone, alcohols (eg, methanol, ethanol, isopropanol, etc.), benzene, liquid ammonia, and the like. However, it is preferred that the reaction is carried out in an aqueous medium. In order to promote dispersion in the liquid medium and thus homogeneous polymerization of certain monomers (eg, butadiene), it is desirable to add a few drops of an emulsifier to the reaction mixture. Examples of such emulsifiers are Triton・
Sodium lauryl sulfate; Sodium lauryl trimethylammonium chloride; Armor & Co.
and Company) by Arquad 12
Active Ingredients Supplied as 33% Sodium Chloride
Cationic quaternary alkyltrimethylammonium chlorides and dialkyldimethylammonium chlorides and dialkyldimethylammonium chlorides in the form of solutions of 17% and 50% water with an average composition of 90% dodecyl, 9% tetradecyl and 19% octadecyl Ammonium salts; such as laurylpyridinium chloride. This copolymerization reaction is carried out using ionic initiators such as ceric ions, ferrous ions,
It is carried out by a free radical copolymerization mechanism using free radical initiators such as cobaltic ions, cobaltic ions, cuprous ions, etc., with ceric ion initiators being preferred. Since most free radical reactions are inhibited by the presence of oxygen, the reaction mixture and reaction vessel can be heated by bubbling a non-oxidizing gas, such as nitrogen, helium, argon, etc. into the system before adding the free radical initiator. It is desirable to expel substantially all oxygen from the air. The PH range for this reaction depends on the particular initiator used. High acidic PH depending on specific initiator
(PH0.8-2.3) to highly basic pH (PH12-14) can be used. For preferred cerium ion initiators, the PH is acidic, ie, less than 7, preferably from about 0.8 to about 2.3. The temperature of the copolymerization reaction is room temperature (i.e. 20-30
℃) to the normal boiling point of the lowest boiling component of the mixture. When the reaction is carried out at a pressure above atmospheric pressure, the temperature could be above the boiling point of the lowest boiling component of the mixture. Also, the reaction mixture can be cooled below room temperature if desired. The hydrolyzable polymer portion of the resulting cellulose graft copolymer fiber is reacted by reacting the fiber with an excess of a strong base, such as a solution of sodium hydroxide, potassium hydroxide, lithium hydroxide, and similar bases, under reflux. Let it hydrolyze. The concentration of this solution can be from about 1 to about 50% by weight, and the temperature of hydrolysis can be from room temperature to reflux temperature. A preferred method for producing the cellulose graft copolymer fiber of the present invention is as follows. E.
10 mmol of cerium () ammonium nitrate (ceric) per 100 ml of 1N nitric acid as described in Schwabet al.
An initiator solution of this cerium salt is prepared by dissolving the cerium salt (dmmonivm nitrate). The wood pulp is then dispersed in water and dry nitrogen is bubbled into the dispersion with stirring. A small amount of the initiator solution is then added to the stirred dispersion while bubbling with nitrogen gas, followed by the aforementioned mixture of hydrolyzable and non-hydrolyzable monomers. The total amount of monomer added is usually at least four times the amount of wood pulp present. After the reaction has continued for a period of time (generally 1 to 4 hours), the resulting cellulose graft copolymer is washed, hydrolyzed as described above, washed again, and dried. Preferred ionic polymeric moieties are sodium poly(acrylate) and preferred nonionic polymeric moieties are poly(methyl methacrylate), poly(ethyl acrylate) and poly(butadiene).
It is. In early experiments, the use of acrylic acid as the starting hydrolyzable monomer for the introduction of the preferred ionic polymeric moieties revealed that the cellulose base of both the hydrolyzable and non-hydrolyzable monomers It has been found that instead of graft copolymerization onto the chains, a significant amount of homopolymerization of the hydrolyzable monomer occurs. Therefore, other hydrolysable acrylic monomers were tested and it was found that the use of acrylonitrile as the starting hydrolysable monomer introduced the preferred ionic polymer moiety. The non-hydrolyzable monomer used is, of course, in the form of the desired non-ionic polymer moiety. Examples are methyl methacrylate, ethyl acrylate and butadiene. After the polymerization reaction is complete, the aforementioned poly(acrylonitrile) moieties are hydrolyzed to yield ionic "alkali metal poly(acrylate)" moieties. The cellulose graft copolymer fiber of the present invention is
significantly larger than unmodified wood pulp (about 4 to about 9
double the absorbency, while still retaining its fiber shape. Additionally, the cellulose graft copolymers of the present invention do not embrittle and honify like prior art modified cellulose fibers. A further unexpected and useful quality of the hydrolyzed cellulose graft copolymer fibers of the present invention is that
Although untreated cellulose fibers are highly flammable,
The fibers of the present invention are non-combustible. Absorbent materials made from the fibers of the present invention are therefore suitable for use in areas requiring severe precautions against flames. For example, it can be used advantageously in hospitals, nursing homes, etc. The cellulose graft copolymer fiber of the present invention is
It can be used alone or in combination with unmodified cellulose fibers or other absorbent materials in the manufacture of absorbent diapers, tampons, sponges, etc.
The fibers of the present invention can also be made into nonwoven fabrics, which are useful in making absorbent diapers, tampons, sponges, and the like. The cellulose graft copolymer of the present invention and the method for producing the same are further illustrated by the following examples. EXAMPLE A solution of cerium () ammonium nitrate is prepared by dissolving the cerium salt in 1N nitric acid at a concentration of 10 mmol/100 ml. In a three-necked flask equipped with a stirrer, a gas whisk, and a dropping funnel,
Add 500ml of water and 5g of wood pulp. The wood pulp is dispersed in the water with stirring and dry nitrogen is bubbled into the dispersion for 15 minutes with continued stirring. To this stirred dispersion, add 12.5 ml of cerium()ammonium nitrate initiator solution while bubbling with nitrogen. A mixture of 5.5 g methyl methacrylate and 15.0 g acrylonitrile is added to the stirred mixture and the whole is allowed to react for 1 hour at room temperature. After 1 hour, the resulting unhydrolyzed cellulose graft copolymer is transferred to a Buchner funnel and washed thoroughly with water and acetone. The washed fibers are then refluxed for 30 minutes with an excess of 6% sodium hydroxide solution to hydrolyze the hydrolyzable polymer portions. The resulting hydrolyzed cellulose graft copolymer fibers are washed thoroughly with water, pressed to remove excess water, and dried in an oven at 100° C. to form pulp board. The composition of the resulting product is shown in the table (sample no. 5). Example The drying process of Example is repeated with different amounts of methyl methacrylate and acrylonitrile. The amounts of methyl methacrylate and acrylonitrile used as well as the composition of the product obtained are shown in the table. EXAMPLE The method of the example is repeated using ethyl acrylate instead of methyl methacrylate. The amounts of ethyl acrylate and acrylonitrile used as well as the composition of the product obtained are shown in the table. EXAMPLES The pulp boards of Examples and are cut into pulp fluff and then formed into absorbent pads. For comparison, pads made of unmodified wood pulp were also made, and the fluid retention properties of these pads were
Textile Res. J., 37 , 356-366 (1967).
Testing Apparatus). Briefly, this test involves placing a sample pad into what is essentially a Buchner funnel with a porous bottom plate, and placing a standard weight above the sample to maintain a standard confining pressure to hold the sample at a predetermined position. Consists of holding in position. The porous plate is brought into contact with a container of fluid, and the fluid is absorbed through the porous plate into the sample to saturate it. By holding the sample essentially at the liquid level of the container, the absorbed fluid is placed at essentially zero head with respect to the container. To determine fluid retention, the saturated sample is raised relative to the fluid container, thereby imparting a water head to the absorbed fluid, which is arbitrarily chosen to be 36 inches (91 cm) of fluid. The device is equipped with means for directly measuring the volume of fluid held under this head. The volume retained value is reported as the volume retained per unit weight of fiber absorbed. The values obtained are listed in the table and under the heading "Fluid Retention". The fluid used in these experiments was a 1% by weight aqueous sodium chloride solution, which approximates the absorption properties of menstrual fluid.

【table】

Table: Examples The materials of Examples and are cut into pulp fluff and combined with an equal amount of unmodified wood pulp fluff. The fluff mixture was compressed to a density of 0.4g/
cc, form into a cylindrical tampon with a diameter of approximately 0.57 inches (1.45 cm) and an axial length of approximately 1.68 inches (4.27 cm). One end of the tampon was immersed in a 1% by weight aqueous sodium chloride solution for 20 minutes while the tampon was encased in a hydraulically expanded polyethylene sleeve and maintained under 24 inches (61.0 cm) of compressive water pressure on both sides. The capacity of the tampon to the aqueous sodium chloride solution, which simulates the conditions of use, is thus determined. Allow the excess fluid to drip from the tampon, release the pressure, determine the weight of water absorbed by the tampon, and record the capacity of the tampon as unit volumes of fluid absorbed per unit weight of tampon.

【table】

【table】

[Table] As can be seen from the table, the grafted cellulose sample (1) containing only the nonionic polymer moiety methyl methacrylate (MMA in the table and EA in the table) has a moderate only show different absorption capacities. In this regard, although the grafted moieties of MMA and EA are generally non-ionic and therefore hydrophobic, when they are hydrolyzed, the surface properties of these grafted fibers, especially those of EA-grafted fibers, are affected and this It is recognized that this describes the changes in surface properties associated with wood pulp. At the other extreme, samples grafted with only ionic polymer (Na-Acry in table and table)
gelled, ie, a gel formed on the outside of the absorbent sample tested, thereby preventing further absorption of fluid into the central portion of the sample. In sharp contrast to these extremes, samples having a combination of ionic and non-ionic polymeric moieties grafted onto the cellulose backbone in accordance with the present invention show a significant increase in the fluid retention of uncompacted absorbent pads. It can be seen that there is a significant increase in the absorbent properties, both with respect to the absorbent capacity, of compressed fibrous objects such as tampons. moreover. It is clear that in the preferred range of compositions of ionic and non-ionic polymeric portions, absorption is maximized. EXAMPLE The product of the example, and
After mechanical processing in a hammer mill to form a pulp fluff, they are tested for their ability to maintain their fiber properties. A 5 g sample of fluff was placed in the bottom of a 1000 ml pipette tube, and air was pumped out to 3.5 g.
A controlled constant flow rate of cubic feet per minute (99.1 per minute) is introduced through a pet cock at the bottom to cause the sample to dance, thereby causing the individual fibers of the sample to flow through the top of the tube. The knot content of the fluff obtained is determined according to the constant air blowing method, which consists of escaping through an opening while leaving heavy knots or lumps at the bottom. The nodules are then removed and weighed, and the nodules content (as % by weight of the sample) is determined and recorded in the table and in the table. In addition, samples of the fiber fluff are examined microscopically to determine the arithmetic mean of the fiber lengths. Place the fibers in a microscope slide and cover with a glass plate. Take a photograph of this slide at 53x magnification and measure the length of each fiber. The arithmetic mean of these fiber lengths is calculated and the results are reported in Table and.

【table】

【table】

[Table] As can be seen from the table, as long as the amount of nonionic polymer moiety is maintained within the aforementioned range, the grafted cellulose copolymer can be improved in terms of fiber length and nodule content after mechanical treatment. It can be seen that it exhibits the same physical properties as wood pulp. However, as the amount of non-ionic polymer moieties in the fibers containing ionic polymer moieties decreases and beyond a certain limit, the nodule content increases significantly and thus the fluff part of the milled pulp. makes it unsuitable for use in clothing. With respect to fiber length, when the nonionic polymer portion is reduced below the aforementioned range, the average fiber length is reduced to the point where the material can practically be considered a powder. In this regard, the material cannot be used as a component of fibrous wood pulp. Example (comparative example) A dispersion of 5 g of wood pulp in 500 ml of water was
Prepared in a three-necked flask equipped with a stirrer, gas whisk and stoppered funnel. Whisk dry nitrogen into the dispersion for 5 minutes. Then add 12.5 ml of an initiator solution of cerium () ammonium nitrate and add a few drops of Triton
−100 Add emulsifier. A mixture of 23 g acrylonitrile and 2 g liquefied butadiene is added to the stirred nitrogen flushed dispersion.
The system is then sealed against the atmosphere and the whole is allowed to react for 4 hours at room temperature. At the end of this time,
The resulting cellulose graft copolymer fibers are transferred to a Buchner-Routh and thoroughly washed with water and acetone. The water-washed fibers are refluxed for 30 minutes with an excess of 1.5N sodium hydroxide solution, washed with water, and dried in a hot air oven at 60°C. The resulting fibrous hydrolyzed cellulose graft copolymer contains 74% ionic polymer fraction and 7.4% nonionic polymer fraction, based on total copolymer weight, in the uncompacted state. The maximum capacity is 13c.c./g and the retention is 8.4
cc/g. A tampon with a density of 0.4 g/cc blended with untreated wood pulp at a ratio of 50% by weight has a capacity of 5.2 cc/g. The fluid used in all these tests is a 1% sodium chloride solution. Although no measurements were taken, this product is considered to have a high occurrence of lumps. EXAMPLE 5 g of cotton (Johnson & Johnson Red Gross brand) in 500 ml of water in a three-necked flask equipped with a stirrer, a gas whisk and a stoppered funnel.
Brand)] and at the same time bubble nitrogen into the dispersion for 30 minutes. To this stirred, nitrogen-flushed dispersion are added 12.5 ml of a solution of this cerium salt at a concentration of 1 mole of cerium()ammonium nitrate per 1 part of 1N nitric acid. After stirring for an additional minute and bubbling with nitrogen, 12.5
A mixture of ml acrylonitrile and 12.5 ml ethyl acrylate is added to the stirred dispersion and the whole is allowed to react for 1 hour at room temperature. The resulting fibers are washed and hydrolyzed as in Example 1. The resulting hydrolyzed cellulose graft copolymer fibers are pressed to remove excess water and oven dried at 100°C to form sheets. This cellulose copolymer contains 51% ionic polymer portion and 36% nonionic polymer portion, based on total weight. When this sheet is ground into fluff, it exhibits excellent fiber properties and absorbency. Examples Samples 2 to 8 whose compositions are in the table and Samples 2 to 2 in the table
Samples are prepared consisting of 2 g pads of compressed and uncompressed grafted cellulose copolymer fibers corresponding to No. 7. In addition, the samples 2 to 8 of the table and samples 2 to 7 of the table, made according to the methods of Examples and corresponding in all respects to the samples listed above, but not hydrolyzed, are Further pads are made using fibers having the composition described under the heading Unhydrolyzed Products. Similarly, hydrolyzed and unhydrolyzed samples of the cellulose acrylonitrile butadiene graft copolymer of the Example are prepared. Hydrolyzed and unhydrolyzed pads are flame tested in which each sample is grasped with a pair of scissors and held in the hottest part of the flame from a Bunsen burner for 10 seconds.
Then take out the sample. Samples that retain a flame or red glow after removal are characterized as combustible, and the remaining samples are characterized as non-flammable. The results of these tests show that in each case the unhydrolyzed sample is highly flammable, whereas the hydrolyzed sample is non-flammable. Examples Cellulose graft copolymer fibers were made according to the method of the examples. However, in this case, the EA/AN ratio of the unhydrolyzed product is 52.0/30.0, and sample 3 in the table
and 4. When this fiber was tested as described in Example 4, its fluid retention rate was 12
It was cc/g. This value is between samples 3 and 4 in the table. The fluid retention rate was also measured using the method described in Example 4, but with a water head of 1.5 inches (3.8 cm) instead of 36 inches (91 cm), and the result was 17 c.c./g. Example XI (Comparative) Cellulose graft copolymer fibers were made using the method of the example, but using azobisisobutyronitrile instead of cerium ammonium nitrate as the free radical initiator. This fiber was prepared using the method described in Example 4 with a water head of 36 inches (91 cm) and a water head of 1.5 inches (3.8 cm).
When the fluid retention rate was measured at 1c.c./g
and 7c.c./g. Example XII (Comparative) Cellulose graft copolymer fibers were made using the method of the example, but using ammonium persulfate instead of cerium ammonium nitrate as the free radical initiator. Example XI (comparative example)
When tested by the method described in 1., the 36-inch water head fluid retention rate was 1 c.c./g, and the 1.5-inch water head fluid retention rate was 6.7 cc/g. Example XII (Comparative Example) Fluid retention of wood pulp Example XI (Comparative Example)
When tested using the method, 1 c.c./c. at 36 inches of water head.
g, 7 c.c./g at 1.5 inches of water head. A comparison of the fluid retention rates of the products of Examples, Example XI (Comparative Example), and Example XII (Comparative Example) and the wood pulps listed in the table is as follows.

[Table] The reason why the fluid retention rate (cc/g) of fibers copolymerized with AIBN or ammonium persulfate is almost the same as that of wood pulp is because these catalysts do not cause graft polymerization and are homogeneous. This is thought to be due to the formation of polymers.

Claims (1)

[Claims] 1. A monomer that can be relatively easily hydrolyzed to form an ionic polymer portion after graft copolymerization to natural cellulose fibers or regenerated cellulose fibers;
The monomers forming the nonionic polymer moiety, which are relatively non-hydrolyzable after graft copolymerization, are ceric ions, ferrous ions, cobalt ions, cuprous ions, or Graft polymerization is carried out using a metal ion free radical initiator selected from the group consisting of a mixture such that the total grafted portion constitutes 25 to 90% by weight of the total cellulose graft copolymer produced; The resulting cellulose graft copolymer is hydrolyzed to obtain an ionic polymer portion of 10 to 80% by weight based on the total cellulose graft copolymer and 15 to 60% by weight based on the total cellulose graft copolymer. 1. A process for producing highly absorbent fibrous materials, which consists in obtaining a graft copolymer having a nonionic polymeric part.