JPS6123921B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing cyanoethylcellulose. More specifically, the present invention relates to a method for producing low-substituted cyanoethylcellulose for the purpose of improving the heat resistance of mixed paper obtained by mixing it with cellulose pulp such as kraft pulp. It is well known that cyanoethylated cellulose improves its heat resistance, and that paper made from cyanoethylated cellulose has good heat resistance. However, it is also known that when cellulose is cyanoethylated, its hydrophilicity decreases and fibrillation by beating is inhibited, so the physical strength of paper made from cyanoethylcellulose is lower than that of paper made from untreated cellulose. . As a method for minimizing such drawbacks, a method has been proposed in which partially cyanoethylated cellulose and untreated cellulose pulp are mixed. For example, Tokkosho
In the method described in No. 41-6606, 50% or more of cyanoethyl cellulose having a nitrogen content of 40% or more,
A method has been proposed in which paper is mixed with less than 50% cellulose pulp such as kraft pulp. However, the patent specification does not include any description regarding the method for producing the low-substituted cyanoethylcellulose. The first characteristic required of cyanoethyl cellulose for paper making is the degree of substitution of cyanoethyl groups (expressed as the number of cyanoethyl group substitutions per anhydroglucose unit of cellulose), which largely controls the physical properties of cyanoethyl cellulose. According to No. 1, cyanoethyl cellulose that meets this purpose has a degree of substitution of about 0.5 to 1.5.
It has a so-called low degree of substitution. This is because fibrillation by beating is inhibited as the degree of substitution increases, and when the degree of substitution of the cyanoethyl group increases to 2 to 3, the product is dissolved in organic solvents (e.g., acrylonitrile, a cyanoethylating agent). This is because the resulting cyanoethylcellulose loses its fiber properties, causing problems in papermaking. As described above, the characteristics that cyanoethyl cellulose with excellent paper-making properties should have include that it is generally a low-substituted cellulose, has a fibrous form, and has excellent resistance to water. Generally, the cyanoethylation reaction between a compound having active hydrogen, especially an organic compound having a hydroxyl group, and acrylonitrile is already well known as a type of Michael reaction, and numerous methods for obtaining cyanoethyl cellulose have been proposed based on this principle. However, the method for producing low-substituted cyanoethylcellulose as in this case involves adjusting the reaction temperature to a low level in the coexistence of a relatively large amount of water when reacting cellulose with acrylonitrile in the presence of an alkali catalyst. Generally, it is caused by For example, in the method described in BP636020, the reaction temperature is
Cyanoethylcellulose with a degree of substitution of 0.55 to 0.8 is obtained by controlling the temperature to 40°C or lower, preferably 5 to 30°C. However, the cyanoethylation reaction is an exothermic reaction, and setting the reaction at such a low temperature is not necessarily an appropriate method for industrial production conditions. A method to improve this drawback is the method described in US Pat. A method has been proposed in which cyanoethylation is carried out at a temperature of 50° C. or lower until an appropriate degree of substitution is reached. Although this method sets the reaction conditions in a relatively high temperature range of 50°C or less, the amount of water in the reaction system is set to be extremely large, more than twice the amount of acrylonitrile, so if the reaction temperature exceeds 50°C, It has the disadvantage that the cyanoethyl group is easily hydrolyzed into an amide group or a carboxyl group, and other side reactions are also likely to be induced. Based on the technical level, the present inventors have intensively studied a method for industrially advantageously producing high-grade, low-substituted cyanoethyl cellulose that does not have the above-mentioned drawbacks and has excellent paper-making suitability. To produce cyanoethylcellulose by reacting the following in the presence of a caustic alkali catalyst, the amount of caustic alkali in the reaction system is 0.01 to 0.1 mol per hydroxyl group of cellulose, and the amount of water is the same.
By adjusting the amount within the range of 0.5 to 3.0 mol, it was found that cyanoethylcellulose having a low degree of substitution having a fiber form can be obtained very easily, and the present invention was completed. That is, by carrying out the present invention, low-substituted cyanoethylcellulose with a degree of substitution of cyanoethyl groups of 1.5 or less and excellent paper-making suitability can be produced under reaction conditions advantageous for industrial production, and under favorable conditions such as hydrolysis of the introduced cyanoethyl groups. It can be easily obtained in the form of high-quality fibers that do not cause any side reactions. To carry out the present invention, cellulosic fibers are first treated with an aqueous caustic solution. At this time, the amount of caustic alkali added is 0.01 to 0.1 mol and 0.5 to 3.0 mol of water per hydroxyl group of cellulose. Adjusting the alkaline aqueous solution
It is essential. At this time, a 5-10% caustic soda aqueous solution is advantageously used as the caustic alkali aqueous solution, and a treatment temperature of about room temperature is sufficient. Furthermore, the present invention can be carried out even more advantageously by using a treatment device that is advantageous for crushing the raw material cellulose, such as a crushing kneader or the like. The cellulosic raw material used in the present invention may be any fibrous cellulose suitable for paper making, such as wood pulp, cotton fiber,
Includes esparto fibers and other similar cellulosic fibers. By the way, generally, the presence of water in the reaction system gives appropriate swelling to the treated material in the caustic alkali treatment step and enables uniform pretreatment, and furthermore, in the cyanoethylation reaction in the next step, the presence of water increases the amount of acrylonitrile used as the cyanoethylation agent. It facilitates diffusion and penetration, but on the other hand, excess water in the reaction system reacts with acrylonitrile to produce ethylene cyanohydrin and oxydipropionitrile, wasting acrylonitrile and further producing cyanoethyl cellulose. It is well known that it also has the negative factor of inducing a hydrolysis reaction. In the present invention, in consideration of this point, the water content of the reaction system is suppressed to the necessary minimum of 0.5 to 3.0 moles per hydroxyl group of cellulose, so the possibility of these undesirable reactions occurring in the next step is extremely low. . Therefore, the resulting product quality is improved, the amount of acrylonitrile consumed by side reactions is small, and it is economically advantageous. Furthermore, the applicable reaction temperature range is wide, and the reaction temperature can be easily controlled. It is easy to understand that this method is advantageous as an industrial manufacturing method. In addition, the amount of alkali as well as the amount of water in the reaction system have a significant effect on the swelling properties of cellulose as well as the reactivity of cyanoethylation in the next step.If the amount is out of the above range, the progress of the reaction will be significantly inhibited or accelerated. It is hard to say that it is industrially advantageous and is therefore undesirable. In short, the first key point of the present invention is to adjust the amounts of water and caustic alkali in the cyanoethylation reaction system to a range of 0.01 to 0.1 mol and 0.5 to 3.0 mol per hydroxyl group of cellulose. As described above, in the present invention, since the amount of water and the amount of caustic alkali in the reaction system are suppressed to the necessary minimum, the cellulosic raw material is uniformly pretreated with an aqueous caustic alkali solution to remove acrylonitrile during the cyanoethylation reaction. It is easily inferred that uniform diffusion and permeation is extremely effective in carrying out the present invention advantageously. The second point of the present invention is to achieve this by using a device that is mainly equipped with a device. Specific examples of such devices include, for example, a crushing kneader. Cyanoethyl cellulose is obtained by adding acrylonitrile to alkali cellulose pretreated according to the above conditions and heating with stirring.
The amount of acrylonitrile added at this time depends on the desired degree of substitution of the cyanoethyl cellulose, but it is usually 3 to 8 times the molar amount, preferably 5 to 8 times the molar amount per hydroxyl group of cellulose, and at the same time There is no problem in diluting with an organic solvent inert to the reaction, such as toluene, benzene, etc., if necessary. Next, regarding the cyanoethylation reaction temperature conditions, as mentioned above, according to the method of the present invention, the water content of the reaction system is significantly lower than that of the conventional method (for example,
(approximately 1/2 to 1/40 compared to the method described in USP 2994634), and the possibility of the aforementioned undesirable side reactions occurring is extremely low compared to conventionally known methods. This makes it possible to take a wider range than the law. Therefore, the reaction can be carried out at any temperature range from the low temperature range adopted in conventionally known methods to the boiling point of the system, but the productivity due to the reaction rate and the ease of controlling the reaction based on the reaction temperature are From 30 to 70℃, preferably 40 to 60℃
It is preferable to set it as °C. The reaction is carried out under such conditions until the desired degree of substitution is reached, and the reaction apparatus may be any apparatus equipped with a stirring apparatus, and is particularly preferably equipped with the above-mentioned concentration apparatus. In order to obtain low-substituted cyanoethyl cellulose having the above-mentioned properties, it usually depends on the reaction conditions, but it is usually
A reaction time of about 120 minutes is sufficient. When the desired degree of substitution is reached, the mixture is cooled and excess caustic acetic acid is neutralized to stop the reaction, and unreacted acrylonitrile is recovered by distillation or the like. The obtained cyanoethyl cellulose is thoroughly washed with water to remove residual acrylonitrile and generated neutralized salts such as sodium acetate. The cyanoethyl cellulose thus obtained is a low-substitution product with a degree of substitution of 1.5 or less and has a fibrous morphology, and is excellent in refractory properties in water and has good paper-making suitability. Next, the present invention will be explained in more detail using examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. Moreover, all the moisture contents described in the examples are expressed on a wet basis. Example 1 Sheet-like wood pulp (NBKP, moisture content 9.6
%) into 2cm squares and put 100g (in terms of dry weight) into a crushing kneader to make a 5% aqueous solution of caustic soda 88.8%.
was added and treated at 25°C for 30 minutes. Next, 785.4 g of acrylonitrile was added and reacted at 45 to 55°C for 30 minutes. The system was then cooled to below 30°C, and then cooled to 10°C.
An acetic acid aqueous solution was added to neutralize excess caustic soda and stop the reaction. Next, unreacted acrylonitrile is recovered by distillation while adding water at appropriate times, the resulting reaction product is suctioned, and the remaining acrylonitrile and sodium acetate are removed by thorough washing with hot water. Cyanoethyl cellulose was obtained. The degree of substitution of the cyanoethyl group in this product was 0.82, and as a result of infrared absorption spectrum analysis, no hydrolyzate by-product was observed.
(See Figure 1b) Furthermore, the refractoriness of this product in water was as good as that of the raw material pulp, and it was excellent in paper-making suitability. Examples 2-3 Cyanoethylcellulose was obtained by cyanoethylating wood pulp in the same manner as in Example 1, except that the reaction conditions were set as shown in Table 1. The obtained cyanoethylcellulose was in a fibrous form with excellent reluctance to dissolve in water, as in Example 1, and as a result of infrared absorption spectrum analysis, no hydrolyzate by-product was observed. Note that the above-mentioned Example 1 is also listed in Table 1 for reference.

[Table] Comparative Examples 1-2 Cyanoethyl cellulose was obtained by cyanoethylating the same wood pulp in the same manner as in Examples 1-3, except that the reaction conditions were set as shown in Table 2. Comparative example 1 as cyanoethylation reaction temperature range
In Comparative Example 2, the temperature was set at 40 to 50°C, and in Comparative Example 2, the temperature was set at 45 to 55°C, but in both cases, the heat generated during the reaction was extremely runaway. Although it was cooled in a water bath, it was extremely difficult to lower and maintain the temperature within a predetermined temperature range. The obtained cyanoethyl cellulose is fibrous, but according to infrared absorption spectrum analysis, it has a concentration of 1670
A new absorption based on carbonyl groups was observed near cm ^-1 , indicating that some of the cyanoethyl groups were hydrolyzed (see Figure 1c). When this material is immersed in water, it swells significantly and its resistance to disintegration in water is also shown in Example 1.
The results were inferior to those obtained in steps 3 to 3.

【table】

[Table] As is clear from the above examples and comparative examples,
In conventionally known methods that are outside the scope of the present invention, the heat generated during the reaction is extremely high and it is extremely difficult to control the temperature within a predetermined range, and the resulting product is also partially susceptible to hydrolysis and is difficult to dissolve in water. However, by carrying out the present invention, it is possible to easily obtain a low-substituted cyanoethyl cellulose that does not have these drawbacks and has excellent paper-making suitability. Furthermore, control of the reaction temperature is extremely easy compared to conventionally known methods, and it goes without saying that the method of the present invention is advantageous for industrial production.

[Brief explanation of the drawing]

Figure 1 and Figure 2 show the infrared absorption spectra of raw material NBKP and cyanoethyl cellulose. a is the infrared absorption spectrum of NBKP used as a raw material, b is the cyanoethyl cellulose obtained in Example 1, and c is the infrared absorption spectrum of the cyanoethyl cellulose obtained in Comparative Example 1.

Claims (1)

[Claims] 1. When producing cyanoethylcellulose by reacting cellulose and acrylonitrile in the presence of a caustic alkali catalyst, the amount of caustic alkali in the reaction system is 0.01 to 0.01 per hydroxyl group of cellulose.
The degree of substitution of the cyanoethyl group is 1.5, characterized by adjusting the amount of water to 0.1 mol and the same amount of water in the range of 0.5 to 3.0 mol.
The following method for producing low-substituted cyanoethylcellulose. 2. Claim 1 is characterized in that the caustic alkali is caustic soda, the cyanoethylation reaction temperature is 30 to 70°C, and the reaction treatment device is mainly equipped with a sizing device having a cellulose crushing function. A method for producing low-substituted cyanoethyl cellulose according to claim 1.