Cellulose derivative excellent in liquid absorbing property, process for preparing same and structure containing same

Disclosed is carboxymethyl cellulose or its salt derived from cellulose having a crystal form of cellulose II, wherein the total saturation degree <<F>> represented by the following formula: EQU <<F>>=<<f.sub.2 >>+<<f.sub.3 >>+<<f.sub.6 >> wherein <<f.sub.2 >>, <<f.sub.3 >> and <<f.sub.6 >> represent the probabilities of substitution of substituent groups for OH groups located at the C.sub.2, C.sub.3 and C.sub.6 positions, respectively, of the glucose ring constituting the cellulose, is in the range of from 0.10 to 0.64. This carboxymethyl cellulose or its salt is excellent in liquid absorbing property and is prepared by treating cellulose having a crystal form of cellulose II with an alkali and then reacting the treated cellulose with monochloroacetic acid or sodium monochloroacetate. This carboxymethyl cellulose or its salt can be used in the form of a structure such as a sheet, a woven fabric or a nonwoven fabric.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
The present invention relates to novel carboxy-methyl cellulose 
(carboxymethyl cellulose will be hereinafter referred to as "CMC" for 
brevity), and a process for the preparation thereof. Furthermore, the 
present invention relates to a CMC structure excellent in processability 
and handling property, which is prepared from this novel CMC. 
(2) Description of the Prior Art 
Ordinary available CMC is prepared from natural cellulose (cellulose having 
a crystal form of cellulose I) such as linter or pulp as the starting 
material. Up until now, regenerated cellulose (cellulose having a crystal 
form of cellulose II) has not been used for the starting material of 
ordinary available CMC. There are two reasons for this. First, CMC can be 
easily prepared from natural pulp or linter. (Natural pulp or linter is 
prepared by removing foreign substances from a crude material such as wood 
or cotton linter and is available at reasonable cost.) It is therefore 
unreasonable economically to use, as the starting material, cellulose II 
obtained by further processing such natural cellulose. Second, there can 
be mentioned the state of the cellulose industry which has been 
established based on empirical facts and therefore there is a low level of 
understanding of the nature of cellulose chemistry or science. For 
example, the technique of mercerization (alkali cellulose formation) was 
already known in the 1870's. While it has been applied to modification of 
cotton fabrics for imparting silk-like luster to them, however, it has not 
been applied to modification of regenerated cellulose fibers. Yet 
regenerated cellulose fibers were already developed and marketed about 30 
years after the establishment of the mercerization technique. The reason 
for this is that regenerated cellulose fibers are already similar to 
natural silk fibers, it was so true that application of mercerization was 
not considered necessary. In cellulose industry, it was only about 10 
years ago that the fact the structure of alkali cellulose from cellulose I 
is different from the structure of alkali cellulose from cellulose II was 
accepted. Therefore, the cellulose industry does not have the scientific 
expertise for discriminating the differences in properties among cellulose 
derivatives obtained by the heterogeneous reaction from cellulose I and 
cellulose II, through alkali celluloses. 
Most of ordinary available CMC has a total degree of substitution 
(hereinafter referred to as "&lt;&lt;F&gt;&gt;" for brevity) of the water-soluble 
region. Only CMC used as an ion exchange resin has a &lt;&lt;F&gt;&gt;of the 
water-insoluble region. A bench-scale method in which cellulose in the 
form of a fabric is converted to CMC to improve dyeability has been 
reported, but this research is directed to cotton alone. No literature 
proposes application of this method to regenerated cellulose. 
The processes for preparing CMC from natural cellulose can be roughly 
divided into a water medium method and a solvent medium method. These 
methods are characterized in that in order to increase the permeability of 
reactants, natural cellulose is converted to alkali cellulose and then the 
alkali cellulose is reacted with monochloroacetic acid or sodium 
monochloroacetate. Furthermore, in order to control occurrence of a side 
reaction by monochloroacetic acid or sodium monochloroacetate, such means 
as mechanical pulverization, compression, shearing or stirring is 
customarily adopted so as to sufficiently mix starting cellulose with a 
reactant solution. Accordingly, CMC is obtained ordinarily in the form of 
a powder or ultra-fine fiber. Since CMC is ordinarily used in fields where 
the emulsion stabilizing effect or thickening effect is utilized, CMC is 
used ordinarily in the powdery form. It is pointed out that the 
probability of substitution at the C.sub.2 position in the glucose ring of 
commercial CMC is very large see, for example, Alain Parfondry et al, 
Carbohydrate Research, 57 (1977), 39-40 . 
Since three substitutable OH groups (at C.sub.2, C.sub.3 and C.sub.6 
positions) are present in the glucose ring of cellulose, it is obvious 
that properties of cellulose vary depending upon the probability of 
substitution [&lt;&lt;f.sub.k &gt;&gt;(k=2, 3, 6)] at the respective positions. This 
&lt;&lt;f.sub.k &gt;&gt; naturally differs according to the method for the preparation 
of a cellulose derivative and the kind of the starting cellulose used. 
Moreover, the difference of the starting cellulose results in not only a 
difference of &lt;&lt;f.sub.k &gt;&gt; but also a difference of the internal 
structure. Accordingly, there is a possibility that commercial cellulose 
derivatives called by general names such as CMC, methyl cellulose, ethyl 
cellulose, cellulose acetate, cellulose acetate butyrate, cellulose 
nitrate, hydroxypropyl cellulose, hydroxyethyl cellulose and 
ethylhydroxyethyl cellulose will be converted to derivatives having novel 
structures and properties. 
SUMMARY OF THE INVENTION 
It is the primary object of the present invention to provide CMC or its 
salt having a surprisingly high liquid absorbing property, which is 
derived from cellulose having a crystal form of cellulose II (regenerated 
cellulose). 
More specifically, in accordance with the present invention, there is 
provided CMC or its salt derived from cellulose having a crystal form of 
cellulose II, wherein the total substitution degree &lt;&lt;F&gt;&gt; of the 
carboxylmethyl cellulose or its salt represented by the following formula: 
EQU &lt;&lt;F&gt;&gt;=&lt;&lt;f.sub.2 &gt;&gt;+&lt;&lt;f.sub.3 &gt;&gt;+&lt;&lt;f.sub.6 &gt;&gt; 
wherein &lt;&lt;f.sub.2 &gt;&gt;, &lt;&lt;f.sub.3 &gt;&gt;and &lt;&lt;f.sub.6 &gt;&gt; represent the 
probabilities of substitution of substituent groups for OH groups located 
at the C.sub.2, C.sub.3 and C.sub.6 positions, respectively, of the 
glucose ring constituting the cellulose, 
is in the range of from 0.10 to 0.64. 
This CMC and its salt can be prepared by treating cellulose having a 
crystal form of cellulose II with an alkali and reacting the 
alkali-treated cellulose with monochloroacetic acid or sodium 
monochloroacetate. 
This CMC or its salt can be utilized for a sheet-like, structure, a woven 
fabric structure or a nonwoven fabric structure comprising this CMC or its 
salt as one constituent.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The sodium salt of the CMC of the present invention has a capacity of 
absorbing pure water in an amount at least 20 times its own weight. The 
amount of pure water absorbed can be up to about 100 times its own weight. 
By the term "its own weight" is meant the weight of CMC or its salt which 
has been dried at 60.degree. C. for 8 hours and allowed to stand still for 
24 hours in an atmosphere maintained at a temperature of 18.degree. C. and 
a relative humidity of 60%. 
Even with CMC and its salt derived from cellulose having a crystal form of 
cellulose II, the desired liquid absorbing property cannot be attained if 
the value &lt;&lt;F&gt;&gt; is smaller than 0.10. Furthermore, if the value &lt;&lt;F&gt;&gt; is 
larger than 0.64, the desired liquid absorbing property is not attained 
and the amount of the portion of CMC or its salt which is dissolved out by 
water is increased. Thus, a practical adsorbing material or liquid 
absorbing material cannot be provided. 
Regenerated cellulose is ordinarily cellulose having a crystal form of 
cellulose II, and regenerated cellulose is obtained by converting natural 
cellulose to alkali cellulose and regenerating the cellulose under 
appropriate conditions or by dissolving natural cellulose in a solvent and 
regenerating the cellulose. From the industrial viewpoint, a cellulose 
xanthate solution (viscose) and a cellulose/cuprammonium solution are 
preferred as the cellulose solution to be subjected to regeneration. 
Solutions that can be used in the present invention are not limited to 
these solutions. Cellulose/inorganic acid solutions, cellulose/aqueous 
inorganic salt solutions, and solutions of cellulose in recently found 
cellulose solvents such as dimethylsulfoxide/paraformaldehyde, organic 
solvents/dinitrogen tetraoxide, dimethylformamide/chloral, sulfur 
dioxide/amines, N-methylmorpholine-N-oxide, N-ethylpyridium 
chloride/organic solvents, N,N-dimethylacetamide/lithium chloride, liquid 
ammonia/thiocyanate and dimethylsulfoxide/carbon disulfide/amines can also 
be used. In principle, a solution of a derivative that can easily be 
regenerated to cellulose, for example, cellulose acetate, can also be 
used. An acid or alkali can be used for regeneration of cellulose from a 
cellulose solution such as mentioned above. 
The regenerated cellulose obtained in the abovementioned manner has a very 
high purity, and can be advantageously used for formation of the cellulose 
derivative of the present invention. When &lt;&lt;F&gt;&gt; is smaller than about 
0.65, the CMC tends to retain the X-ray diffractometric crystal form of 
the starting material (see FIG. 2). Accordingly, as described hereinafter, 
the structure, that is, the state of molecular packing, of CMC of the 
present invention (hereinafter referred to as "CMC II") derived from 
regenerated cellulose (i.e., cellulose having a crystal form of cellulose 
II) is different from the structure of CMC (hereinafter referred to as 
"CMC I") derived from natural cellulose (i.e., cellulose having a crystal 
form of cellulose I). This difference results in a great difference of the 
liquid absorbing property. Supposing that the amount of water absorbed 
when CMC is dipped in pure water at 37.degree. C. for 10 minutes is a 
function of &lt;&lt;F &gt;&gt;, the range of &lt;&lt;F&gt;&gt; capable of absorbing water in an 
amount at least 40 times its own weight is from 0.30 to 0.60 in case of 
CMC I and from 0.15 to 0.40 in case of CMC II. Thus, CMC II shows a 
moisture absorbing property at a much smaller value &lt;&lt;F&gt;&gt; than in case of 
CMC I. Accordingly, CMC II is excellent in the property of retaining its 
state and dimension after absorption of moisture (ordinarily, the gel 
state), making CMC II advantageous in practical use. This excellent 
dimensional stability results from the excellent liquid retaining property 
after absorption of a liquid. 
CMC II of the present invention is prepared by using cellulose having a 
crystal form of cellulose II (regenerated cellulose) as the starting 
material and treating it according to a method similar to the known 
carboxymethylation method. Namely, cellulose having a crystal form of 
cellulose II is treated with an alkali and the alkali-treated cellulose is 
reacted with monochloroacetic acid or sodium monochloroacetate. According 
to this method, the starting cellulose having a crystal form of cellulose 
II is converted to alkali cellulose I-II by the alkali treatment, which 
alkali cellulose has a crystal form different from the crystal form of 
alkali cellulose derived from natural cellulose. The form of the starting 
cellulose is not particularly critical. The starting cellulose may be in 
the form of a powder, a fiber, a fabric or a nonwoven fabric. 
The CMC of the present invention can be obtained usually in the form of a 
free acid or a sodium salt, and can be converted to various salts. For 
example, the CMC of the present invention can be converted to salts of 
alkali metals such as potassium and lithium, alkaline earth metals such as 
calcium and magnesium, amphoteric metals such as aluminum, transition 
metals such as titanium, zirconium, chromium and mercury, and lead. 
Ordinarily, a divalent or polyvalent metal reduces the liquid absorbing 
property of the CMC. Therefore, a salt of a divalent or polyvalent metal 
is not preferred when a high liquid absorbing property is desired. 
However, when it is necessary to adjust the liquid absorbing property, the 
species of the metal as well as the substitution degree are important. 
Moreover, each of metals forming salts with CMC can impart peculiar 
characteristics to the CMC in addition to the liquid absorbing property. 
For example, it is expected that the mercury salt will exert a fungicidal 
effect and a lead salt will exert a hemostatic effect. Since the intended 
liquid absorbing property of the present invention is mainly a property of 
absorbing an aqueous solution, the sodium salt is most preferred among 
various metal salts. 
If a specific preparation process is adopted for the production of the CMC 
of the present invention, CMC II especially excellent in the property of 
absorbing a physiological saline solution can be obtained. This CMC II is 
characterized in that the sum of substitution possibilities of 
carboxymethyl groups at the C.sub.2, C.sub.3 and C.sub.6 positions 
&lt;&lt;F&gt;&gt;(=&lt;&lt;f.sub.2 &gt;&gt;+&lt;&lt;f.sub.3 &gt;&gt;+&lt;&lt;f.sub.6 &gt;&gt;) is in the range of from 
0.10 to 0.64 as pointed out hereinbefore, the requirement of &lt;&lt;f.sub.6 &gt;&gt; 
&gt; &lt;&lt;f.sub.2 &gt;&gt; and &lt;&lt;f.sub.6 &gt;&gt; &gt; &lt;&lt;f.sub.3 &gt;&gt; is satisfied, that is, the 
possibility of substitution at the C.sub.6 position is highest, and the 
&lt;&lt;f.sub.6 &gt;&gt;/(&lt;&lt;f.sub.2 &gt;&gt;+&lt;&lt;f.sub.3 &gt;&gt;) ratio is at least 1.5. The value 
of &lt;&lt;F.sub.6 &gt;&gt;/(&lt;&lt;f.sub.2 &gt; &gt;+&lt;&lt;f.sub.3 &gt;&gt;) mentioned here is determined 
according to the following procedures. Namely, sample CMC is dissolved at 
a concentration of about 3% by weight in a 5% by weight solution of NaOH 
in D.sub.2 O. Measurement is carried out on this solution at 60.degree. C. 
by using 100.7 MHz .sup.13 C-NMR (Pulse-Fourier transform type) under 
conditions of 90.degree. pulses, a repetition time of 2 seconds and 5000 
times integration. The value is obtained by performing calculation based 
on the obtained measurement data according to the following equations: 
##EQU1## 
In the above equations, S represents a peak caused to appear because of 
introduction of a substituent at the corresponding position or because of 
introduction of a substituent into any of the C.sub.2, C.sub.3 and C.sub.6 
positions. In the right terms of the equations (1) through (3), all 
symbols express the peak intensity. *CO represents a carbonyl carbon peak 
of the carboxymethyl group. Although two peaks appear in the vicinity of 
C.sub.6s (71 ppm), the peak on the high magnetic field side is designated 
as the peak of C.sub.6s and the peak on the low magnetic field side is 
designated as the peak of the star carbon of the substituent --C*H.sub.2 
COOH. Results of the presumption of the NMR peak positions in the 
respective substitution types are shown in Table 1. 
TABLE 1 
______________________________________ 
Calculation of Chemical Shift of CMC 
Chemical Shift (ppm) 
Type of CMC 
C.sub.1 
C.sub.2 C.sub.3 
C.sub.4 
C.sub.5 
C.sub.6 
______________________________________ 
Unsubstituted 
104.7 75.0 76.4 80.0 76.4 61.9 
2-Substituted 
104.3 83.9 75.2 79.6 76.1 61.4 
3-Substituted 
104.3 74.1 84.3 79.2 75.7 61.1 
6-Substituted 
104.4 74.3 75.6 78.9 74.6 70.0 
(72.3) 
2,3-Sub- 103.9 83.0 85.3 78.8 75.5 60.6 
stituted 
2,6-Sub- 104.0 83.1 74.4 78.5 74.3 69.5 
stituted (71.8) 
3,6-Sub- 104.0 73.4 84.7 78.1 73.9 69.2 
stituted (71.5) 
2,3,6-Sub- 103.6 82.3 83.5 77.7 73.6 68.7 
stituted (70.0) 
______________________________________ 
Note 
1 Each value is calculated from the chemical shift of CM--glucose. 
2 CH.sub.2 in the substituent group is expected to appear at about 71.2 
ppm. 
3 COONa in the substituent group is expected to appear at 178.4 and 178.8 
ppm. 
The typical .sup.13 C-NMR spectra (107.5 MHz) of CMC are shown in FIG. 1A 
and FIG. 1B. From these figures, the difference of CMC II [FIG. 1A] of the 
present invention from comparative CMC I [FIG. 1B] is apparent. Numbers 
given in FIG. 1 indicate the positions of carbon atoms forming the glucose 
ring of CMC. The symbol "s" means that the hydroxyl group attached to the 
corresponding C position is carboxymethylated. It is readily confirmed 
that in the CMC of the present invention, the peak of C.sub.6s is large, 
the peak of C.sub.6 (unsubstituted) is low and the &lt;&lt;f.sub.6 &gt;&gt; value is 
large. In comparative CMC, peaks attributed to C.sub.2s and C.sub.3s (at 
about 83 ppm) are clearly observed, showing that &lt;&lt;f.sub.6 &gt;&gt; of CMC of 
the present invention is considerably higher than that of CMC from natural 
cellulose. 
CMC II of the present invention satisfying the above requirements of &lt;&lt;F&gt;&gt; 
and &lt;&lt;fk&gt;&gt; (k=2, 3, 6) is characterized in that the amount absorbed of a 
physiological saline solution (dipping at 37.degree. C. for 10 minutes) is 
20 to 80 times its own weight. In the case of CMC II having an &lt;&lt;F&gt;&gt; value 
of 0.25 to 0.64, the amount absorbed of a physiological saline solution is 
at least 25 times its own weight, and can be up to 80 times its own 
weight. This CMC II is obtained by subjecting regenerated cellulose to an 
alkali treatment without X-ray-diffractometrically complete conversion to 
alkali cellulose and carboxymethylating the resulting alkali-treated 
cellulose. This treatment is to strongly reflect the structure of 
regenerated cellulose on final CMC. By the term "without 
X-ray-diffractometrically complete conversion to alkali cellulose" used 
herein, it is meant that the treated cellulose is a cellulose/alkali 
mixture which has not completely been converted to alkali cellulose from 
the X-ray-diffractometric viewpoint and which does not have a peak at 
2.theta.=30.degree. characteristic to alkali cellulose [see FIGS. 3-I(a) 
and 3-II(a)]. In the case where cellulose II is used as the starting 
substance, a cellulose/alkali mixture having no peak at 
2.theta.=14.degree. is meant. More specifically speaking, a 
cellulose/alkali mixture in which when the relative intensities of peaks 
at 2.theta.=9.degree. and 2.theta.=14.degree., characteristic to alkali 
cellulose, are compared, there is found a relation of 
I.sub.2.theta.(9.degree.) &gt; I.sub.2.theta.(14.degree.) is meant. 
Incidentally, I.sub.2.theta.(9.degree.) and I.sub.2.theta.(14.degree.) 
represent the relative intensities at 2.theta.=9.degree. and 
2.theta.=14.degree., respectively. 
In order to obtain preferred CMC and its salt satisfying the 
above-mentioned requirements of &lt;&lt;F&gt;&gt; and &lt;&lt;f.sub.k &gt;&gt;, it is preferred 
that during the reaction for formation of CMC, the starting cellulose not 
be subjected to an operation such as mechanical pulverization, 
compression, shearing or stirring. Accordingly, in the present invention, 
the starting regenerated cellulose may be subjected to a reaction in the 
form of a sheet, a woven fabric or a nonwoven fabric. Thus, this method is 
advantageous in view of the processability and handling property of the 
final product. 
CMC II obtained according to this method has novel characteristics and is 
different in chemical structure from CMC obtained from natural cellulose 
by the conventional aqueous medium or solvent medium method and also from 
CMC obtained when a method similar to the above-mentioned method of the 
present invention is applied to natural cellulose. In each of these 
comparative products of CMC, the &lt;&lt;f.sub.6 &gt;&gt;/(&lt;&lt;f.sub.2 &gt;&gt;+&lt;&lt;f.sub.3 &gt;&gt;) 
ratio is smaller than 1.1. In this point, they are different from the CMC 
of the present invention. This difference results directly in the 
difference of the liquid absorbing property. More specifically, in case of 
CMC obtained by applying a method similar to the method of the present 
invention to natural cellulose, the &lt;&lt;F&gt;&gt; value is in the range of from 
0.12 to 0.70 and the amount of a physiological saline solution absorbed at 
37.degree. C. does not exceed 35 times its own weight. On the other hand, 
in case of the CMC II of the present invention, if the &lt;&lt; F&gt;&gt; value is in 
the range of from 0.30 to 0.62, the amount of a physiological saline 
solution absorbed is always at least 35 times its own weight. 
The first characteristic feature of the process for preparing CMC II 
according to the present invention is that as pointed out hereinbefore, 
regenerated cellulose is treated with an alkaline solution incapable of 
converting regenerated cellulose X-ray-diffractometrically completely to 
alkali cellulose. As specific examples of the alkaline solution, there can 
be mentioned an aqueous solution containing sodium hydroxide at a 
concentration of, for example, 5 g/dl or less and a water-containing 
organic solvent solution containing sodium hydroxide, the concentration of 
sodium hydroxide being not particularly critical. In the case of the 
latter solution, the concentration of sodium hydroxide is adjusted so that 
no precipitates of sodium hydroxide are formed. As the organic solvent, 
there are preferably used methanol, ethanol, isopropanol, benzene and 
toluene. Conversion of regenerated cellulose to alkali cellulose is 
influenced by the treatment temperature and treatment time. In order to 
prevent X-ray-diffractometrically complete conversion to alkali cellulose, 
the alkali treatment should be conducted at a temperature of 60.degree. C. 
or less within 30 minutes. The amount of sodium hydroxide is preferably 1 
to 4 moles per mole of the glucose residue. The amount of the alkaline 
solution is not particularly critical, but it is ordinarily preferred that 
the alkaline solution be used in an amount of 5 to 20 parts by volume per 
part by weight of regenerated cellulose. 
Monochloroacetic acid or sodium monochloroacetate is added directly or in 
the form of a solution in an appropriate solvent to the regenerated 
cellulose/alkaline solution mixture obtained by the above treatment, 
whereby carboxymethylation is effected. The amount of monochloroacetic 
acid or sodium monochloroacetate may be appropriately determined according 
to the intended &lt;&lt;F&gt;&gt; value of the final CMC. Water, a halogenated 
hydrocarbon or an alcohol is used as the solvent for monochloroacetic acid 
or sodium monochloroacetate. From the viewpoint of the preparation 
facility, it is preferred that the solvent of the alkaline solution used 
for the above-mentioned alkaline treatment be used as the solvent for 
monochloroacetic acid or sodium monochloroacetate. In the process for 
preparing the CMC II according to the present invention, at the step of 
adding the reactant (monochloroacetic acid or sodium monochloroacetate), a 
considerable amount of the free alkali is left in the alkaline solution. 
Accordingly, if the side reaction of the reactant is neglected, it is 
possible to prepare the CMC II of the present invention by mixing and 
reacting regenerated cellulose with a solution formed by adding the 
reactant directly to the above-mentioned alklaine solution. 
Conditions for the reaction of regenerated cellulose treated with the 
alkaline solution with the reactant can be optionally determined. 
Ordinarily, however, this reaction is carried out at a temperature of 
60.degree. C. or less within 90 minutes. In the case where an organic 
solvent is used as the solvent for this reaction, swelling of cellulose is 
limited, though swelling occurs to a considerable extent when an aqueous 
solvent is used. Accordingly, a method may be adopted in which the organic 
solvent (reaction liquid) is forced to be circulated for the reaction 
through a reaction system in which regenerated cellulose is fixed. For 
example, a method can be adopted in which a sheet, fabric or nonwoven 
fabric in the form of a roll is inserted in a cylinder of the inner 
jetting type having jet holes formed on the peripheral wall thereof, the 
cylinder is immersed in a reaction liquid tank to cause the reaction 
liquid to flow from the inside of the cylinder to the outside of the 
cylinder through the jet holes and the reaction liquid in such an 
excessive amount as cannot be contained in regenerated cellulose is 
returned to a reaction liquid feed reservoir, whereby the reaction is 
carried out while circulating the reaction liquid. After completion of the 
reaction, neutralization, washing and drying are carried out according to 
customary procedures. 
The thus-obtained CMC of the present invention can be directly used as an 
adsorbent or a liquid absorber. Of course, the CMC of the present 
invention can be applied to the field where the ion exchange property of 
CMC is utilized. Moreover, the product of the present invention can be 
widely used for medical materials, sanitary materials and industrial 
materials. Furthermore, CMC of the present invention in the form of a 
sheet, a woven fabric or a nonwoven fabric shows excellent processability 
when it is formed into a final product. In the case of conventional 
powdery CMC, in order to obtain, for example, a sanitary article, there 
should be adopted troublesome steps of appropriately arranging powdery CMC 
in a sheet composed of other material and sewing the sheet to a base 
fabric. Moreover, since CMC is in the powdery form, the inherent absorbing 
capacity is not completely exerted. In contrast, if CMC or its salt in the 
form of a sheet, a woven fabric or a nonwoven fabric according to one 
embodiment of the present invention is used for production of a sanitary 
article, the sanitary article can be made only by sewing of this CMC to a 
base fabric, and the absorbing capacity can be fully exerted. This CMC 
structure according to the present invention can be formed into a piled 
material with a sheet, woven fabric or nonwoven fabric composed of other 
material. Needless to say, the CMC of the present invention can be used in 
any form as one constituent of a structure. 
The present invention will now be described in detail with reference to the 
following examples, which by no means limit the scope of the invention. 
EXAMPLE 1 
This example is given to illustrate that the difference of the structure 
among starting celluloses is likely to be retained after 
carboxymethylation and that the CMC of the present invention is excellent 
in the liquid or moisture absorbing property. 
10 g of a cellulose fiber regenerated from a cuprammonium solution (crystal 
form of cellulose II, X-ray diffraction peaks at 2.theta.=9.5.degree., 
12.0.degree., 20.1.degree. and 21.5.degree., crystallinity of 49.8%, 
degree of polymerization (DP) of 460) was immersed in 50 g of an aqueous 
solution containing sodium hydroxide in an amount of 1.34 moles per mole 
of the glucose residue at 30.degree. C. The cellulose fiber was allowed to 
stand in this state for 20 minutes. Then, 6.4 g of isopropyl alcohol 
containing monochloroacetic acid in an amount of 0.56 mole per mole of the 
glucose residue was added. The temperature was elevated to 60.degree. C., 
and the reaction was conducted for 90 minutes in the stationary state. 
After completion of the reaction, neutralization and washing were effected 
with a liquid mixture of methanol and hydrochloric acid. The &lt;&lt;F&gt;&gt; value 
of the thus obtained filamentary CMC was 0.34, and the &lt;&lt;f.sub.6 
&gt;&gt;/(&lt;&lt;f.sub.2 &gt;&gt;+&lt;&lt;f.sub.3 &gt; &gt;) ratio was 1.8. In the X-ray diffraction 
pattern of this CMC, peaks were observed at 2.theta.=9.5.degree. and 
20.1.degree.. It was confirmed that there was a tendency of retaining the 
crystal form of cellulose II. This CMC was vacuum-dried and allowed to 
stand in an atmosphere maintained at a temperature of 18.degree. C. and a 
relative humidity of 60%. Then, the weight of CMC was measured, and the 
CMC was dipped in pure water maintained at 37.degree. C. for 10 minutes. 
Excessive water was removed by standing for 20 minutes and the weight was 
measured. It was found that CMC absorbed water in an amount 58 times its 
own weight. 
For comparison, natural cellulose (crystal form of cellulose I, X-ray 
diffraction peaks at 2.theta.=9.degree., 14.7.degree., 16.4.degree. and 
22.6.degree., crystallinity of 50.4%, DP of 470) was treated and 
carboxymethylated under the same conditions as described above. The &lt;&lt;F&gt;&gt; 
value was 0.25, and the reaction efficiency of monochloroacetic acid was 
lower than in the above-mentioned example of the present invention. 
Furthermore, carboxymethylation was carried out in the same manner as 
described above except that sodium monochloroacetate was used instead of 
monochloroacetic acid and the amount of sodium monochloroacetate was 
increased to 0.70 mole per mole of the glucose residue. The &lt;&lt;F&gt;&gt; value 
was 0.33 and the &lt;&lt;f.sub.6 &gt;&gt;/ (&lt;&lt;f.sub.2 &gt;&gt;+&lt;&lt;f.sub.3 &gt;&gt;) ratio was 1.1. 
Also this comparative CMC tended to retain the crystal form of cellulose 
I. The amount of water absorbed at 37.degree. C. in this comparative CMC 
was only 45 times its own weight. 
The &lt;&lt;F&gt;&gt; was measured according to the neutralizing titration method. The 
crystallinity was determined according to the method of L. Segal et al 
Text. Res. J., 10, 786 (1959). The X-ray diffraction diagrams of CMC of 
the present invention, comparative CMC and starting celluloses are shown 
in FIG. 2, in which I(a) shows the X-ray diffraction pattern of the 
starting cellulose of a crystal form of cellulose I, II(a) shows the X-ray 
diffraction pattern of the starting cellulose of a crystal form of 
cellulose II, I(b) shows the X-ray diffraction pattern of CMC obtained 
from the former starting cellulose and II(b) shows the X-ray diffraction 
pattern of CMC obtained from the latter starting cellulose. 
EXAMPLE 2 
This example is given to illustrate that CMC of the present invention 
having an &lt;&lt;F&gt;&gt; value of 0.10 to 0.64 is capable of absorbing water in an 
amount at least 20 times its own weight. 
Nine kinds of CMC differing in the &lt;&lt;F&gt;&gt; within the range of from 0.09 to 
0.75 were prepared according to the method described below by using 
regenerated cellulose having a DP of 400 and a crystallization degree of 
46%, which was formed from viscose. Namely, 10 g of regenerated cellulose 
was immersed in 50 g of an aqueous solution of NaOH having a concentration 
of 5% by weight at 25.degree. C. A predetermined amount of sodium 
monochloroacetate dissolved in isopropanol was added to the mixture and 
reaction was carried out at 60.degree. C. for 90 minutes. After 
neutralization and drying, the amount of pure water absorbed at 37.degree. 
C. was measured. The obtained results are shown in Table 2. 
For comparison, natural cellulose (polymerization degree of about 350, 
crystallization of 41%) obtained by acid-hydrolyzing Polynier pulp 
customarily used for production of CMC and pulverizing the hydrolyzed 
cellulose by a ball mill was treated in the same manner as described above 
to obtain comparative CMC samples differing in the &lt;&lt;F&gt;&gt;. The amount of 
pure water absorbed at 37.degree. C. was measured. The results are shown 
in Table 2. 
The amount of absorbed pure water was determined according to the method 
described in Example 1, and the &lt;&lt;F&gt;&gt; value was determined according to 
the neutralizing titration method. 
TABLE 2 
__________________________________________________________________________ 
CMC of Amount of 
Com- Amount of 
Present &lt;&lt;f.sub.6 &gt;&gt;/ 
Absorbed 
parative &lt;&lt;f.sub.6 &gt;&gt;/(&lt;&lt;f.sub.2 &gt;&gt; 
Absorbed 
Invention 
&lt;&lt;F&gt;&gt; (&lt;&lt;f.sub.2 &gt;&gt; + &lt;&lt;f.sub.3 &gt;&gt;) 
Water (times) 
CMC &lt;&lt;F&gt;&gt; &lt;&lt;f.sub.3 &gt;&gt; Water 
__________________________________________________________________________ 
(times) 
(a) 0.09 .infin. 17.5 (a) 0.05 10.2 14.2 
(b) 0.10 156 23.0 (b) 0.13 8.3 19.0 
(c) 0.22 156 52.0 (c) 0.20 1.1 27.0 
(d) 0.30 2.2 52.0 (d) 0.27 1.3 42.5 
(e) 0.34 2.8 60.0 (e) 0.35 1.0 44.0 
(f) 0.40 18 37.0 (f) 0.47 0.81 62.0 
(g) 0.52 1.6 24.0 (g) 0.59 0.52 44.0 
(h) 0.64 1.9 21.0 (h) 0.64 0.43 44.0 
(i) 0.75 1.3 15.0 
__________________________________________________________________________ 
From the results shown in Table 2, it is seen that CMC of the present 
invention having a total substitution degree &lt;&lt;F&gt;&gt; of 0.10 to 0.64 has a 
high pure water absorbing property and the absorbing property is highest 
when the &lt;&lt;F&gt;&gt; value is about 0.22 to about 0.34. In case of comparative 
CMC, the highest absorbing property is obtained when the &lt;&lt;F&gt;&gt; value is 
0.35 to 0.59. In short, CMC of the present invention is characterized in 
that the &lt;&lt;F&gt;&gt; value giving a highest absorbing property is smaller than 
in case of comparative CMC. Therefore, the stability of the gel after 
absorption of pure water in case of CMC of the present invention is much 
better than in case of comparative CMC. 
EXAMPLE 3 
This example is given to illustrate that CMC of the present invention 
satisfying the requirement of &lt;&lt;F.sub.6 &gt;&gt;/(&lt;&lt;F.sub.2 &gt;&gt;+&lt;&lt;F.sub.3 
&gt;&gt;).gtoreq.1.5 absorbs a large amount of a physiological saline solution. 
CMC of the present invention was prepared by treating 10 g of regenerated 
cellulose (the same as described in Example 1) prepared from a 
cuprammonium ammonium solution of cellulose with a reaction liquid having 
a composition shown in Table 3. In Table 3, "reaction liquid (a)" is a 
mixed solution of 38.2 ml of isopropanol, 22.4 ml of methanol and 12.8 ml 
of water containing 3.3 g of sodium hydroxide. This mixed solution was 
used for immersion of the cellulose at normal temperature for 20 minutes. 
Then, "reaction liquid (b)" was added to the mixture and 
carboxy-methylation was carried out at 60.degree. C. for 90 minutes. In 
Table 3, "reaction liquid (b)" is a solution of 2.5 g of monochloroacetic 
acid in 6.6 ml of isopropanol. After the carboxymethylation, 
neutralization was carried out according to customary procedures by using 
a liquid mixture of methanol and water containing acetic acid, and formed 
CMC was washed with methanol. 
For comparison, natural cellulose (DP of 400, crystallinity degree of 
50.1%) was converted to CMC according to the same procedures as described 
above. 
With respect to each of the CMC of the present invention and comparative 
CMC, the physiological saline solution absorbing property was evaluated. 
The results are shown in Table 4. 
As described in Example 1, in order to prepare comparative CMC having an 
&lt;&lt;F&gt;&gt; value equivalent to that of the CMC of the present invention, the 
amount of monochloroacetic acid used as the reactant had to be increased. 
TABLE 3 
__________________________________________________________________________ 
Conditions for Preparation of CMC II of Present Invention 
Reaction 
Reaction Reaction 
Reaction 
Liquid (a) 
Liquid (b) Liquid (a) 
Liquid (b) 
CMC of Present 
(g/10 g of 
(g/10 g of Comparative 
(g/10 g of 
(g/10 g of 
Invention 
cellulose) 
cellulose) 
&lt;&lt;F&gt;&gt;*.sup.1 
CMC cellulose) 
cellulose) 
&lt;&lt;F&gt;&gt;*.sup.1 
__________________________________________________________________________ 
(1) .sup. .sup. 0.09*.sup.3 
(1) 64 7.1 0.20 
(2) 64 5.7 0.20 (2) 64 8.6 0.35 
(3) 64 8.6 0.39 (3) 192 25.5 0.59 
(4) 192 19.8 0.52 
(5) 192 25.5 0.64 
__________________________________________________________________________ 
Note 
.sup.1 determined according to the neutralizing titration method 
.sup.2 the amount of NaOH corresponded to 1.34 moles per mole of the 
glucose residue 
.sup.3 the amount of monochloroacetic acid corresponding to 0.143 mole pe 
mole of the glucose residue 
TABLE 4 
__________________________________________________________________________ 
Distribution of Substitution Degree and Physiological 
Saline Solution Absorbing Property 
Physiological Saline 
Solution Absorbing 
CMC &lt;&lt;F&gt;&gt;*.sup.1 
&lt;&lt;F&gt;&gt;*.sup.2 
&lt;&lt;f.sub.6 &gt;&gt;/(&lt;&lt;f.sub.2 &gt;&gt;/&lt;&lt;f.sub.3 &gt;&gt;) 
Property (times) 
__________________________________________________________________________ 
Present Invention 
(1) 0.09 0.03 .infin. 17.5 
(2) 0.20 0.14 4.95 26.0 
(3) 0.39 0.26 265 40.0 
(4) 0.52 0.54 8.20 58.0 
(5) 0.64 0.64 5.86 30.0 
Comparison 
(1) 0.20 0.23 0.50 22.0 
(2) 0.35 0.40 1.10 19.0 
(3) 0.59 0.59 0.52 29.0 
__________________________________________________________________________ 
Note 
*.sup.1 determined according to the neutralizing titration method 
*.sup.2 determined by NMR 
The &lt;&lt;F&gt;&gt; values determined by the two methods are different in the lower 
substituted products. It is believed that this difference is due to the 
Overhauser effect. 
As is seen from the results shown in Table 4, the &lt;&lt;f.sub.6 &gt;&gt; value of the 
CMC of the present invention is large, and this large &lt;&lt;f.sub.6 &gt;&gt; value 
makes a great contribution to enhancement of the capacity of absorbing a 
physiological saline solution. 
From X-ray diffractometry, it was confirmed that in the course of 
preparation of the CMC of the present invention, no/complete alkali 
cellulose is formed. The results are shown in FIG. 3. In FIG. 3, I(a), 
II(a), I(b), and II(b) show X-ray diffractometric diagrams of the 
following celluloses. 
I(a): Cell I+alkaline solvent, Cell I 
II(a): Cell II+alkaline solvent, Cell II 
I(b): Cell+18% NaOH, Na-Cell I-I 
II(b): Cell II+18% NaOH, Na-Cell I-II 
It is seen that CMC or its salt of the present invention is formed by 
carboxymethylation of cellulose treated with an alkaline solution in which 
X-ray diffraction peaks of the starting cellulose II at 
2.theta.=10.degree., 20.degree. and 21.degree. are retained. 
Characteristic peaks of ordinary alkali cellulose at 2.theta.=14.degree. 
and 30.degree. do not appear in this alkali-treated cellulose. This holds 
good when natural cellulose is treated by a method similar to the method 
of the present invention. 
EXAMPLE 4 
This example is given to illustrate that a CMC structure having a good 
processability and a good handling property can be obtained from 
regenerated cellulose in the form of a nonwoven fabric according to the 
present invention. 
A nonwoven fabric of regenerated cuprammonium rayon filaments 
(Bemlease.RTM. supplied by Asahi Kasei Kogyo K.K.) was cut into square 
pieces having a size of 10 cm x 10 cm. The cut pieces were piled so that 
the total amount became 10 g. A nonwoven CMC fabric having an &lt;&lt;F&gt;&gt; value 
of 0.37 and an &lt;&lt;f.sub.6 &gt;&gt;/(&lt;&lt;f.sub.2 &gt;&gt;+&lt;&lt;f.sub.3 &gt;&gt;) ratio of 1.89 was 
prepared from this piled fabric according to the method described in 
Example 3. This carboxymethylated nonwoven fabric could absorb a 
physiological saline solution in an amount 40 times its own weight. 
Furthermore, the nonwoven fabric could absorb artificial urine 
(urea/NaCl/MgSO.sub.4 /CaCl.sub.2 /H.sub.2 O weight ratio 
=1.94/0.8/0.11/0.26/97.09) in an amount 45 times its own weight and 
artificial blood (NaCl/Na.sub.2 CO.sub.3 /glycerol/Na -CMC/water weight 
ratio =1.0/0.4/10.0/0.46/88.14) in an amout 35.0 times its own weight. 
This CMC nonwoven fabric could easily be cut and sewn to other material 
and could easily be formed into a body fluid absorber. 
EXAMPLE 5 
To 10 g of CMC (e) of the present invention obtained in Example 2 was 
supplied water to highly swell the cellulose, and 30 g of Manila hemp was 
added to the swollen cellulose. Water was further added and the dispersion 
was sufficiently mixed and then cast on a paper-making net to remove water 
while methanol was added, whereby a filter product was obtained. This 
product was excellent in the wet strength over a filter product obtained 
by using CMC of the present invention alone, and the product had a very 
good shape-retaining property. The product could be used as a body fluid 
absorbing material, an ion exchange material and a water-removing material 
.