JPH0582841B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for producing cellulose acetate, and more specifically, the present invention relates to a method for producing cellulose acetate, which is characterized by using a cellulose raw material that has been subjected to a swelling treatment to have an acetic acid retention of 40% or more. The present invention relates to a manufacturing method.

(Prior Art) Cellulose acetate is one of the organic acid esters of cellulose, and its uses are wide-ranging, including clothing fibers, tobacco filter chips, plastics, films, paints, and fillers for optical resolution. It is produced in the largest quantity among cellulose derivatives and is industrially important.

To produce cellulose acetate, first, cellulose raw materials such as wood pulp and cotton linters are pretreated with an appropriate amount of acetic acid, and then poured into a pre-cooled acetic acid mixture to convert into acetic acid ester. cellulose)
to generate. In this case, for example, an acetylation mixture using acetic acid as a solvent, acetic anhydride as an esterification agent, and sulfuric acid as a catalyst is used, but the amount of acetic anhydride is determined based on the total amount of cellulose reacting with this and water present in the system. It is normal to use a considerable excess of the stoichiometric amount. In order to hydrolyze excess acetic anhydride remaining in the system after the acetylation reaction and neutralize a portion of the esterification catalyst, carbonates, acetates, etc. of calcium, magnesium, iron, aluminum, or zinc are added. Add an aqueous neutralizing agent solution consisting of a hydroxide or oxide.

Next, the obtained primary cellulose acetate is saponified and aged by keeping a small amount of acetylation reaction catalyst, such as sulfuric acid, at 50 to 90°C to reach the set values of acetylation degree and polymerization degree. It is converted into secondary cellulose acetate. Once secondary cellulose acetate having the set degree of acetylation and degree of polymerization is obtained, the catalyst remaining in the system is completely neutralized using the above-mentioned neutralizing agent again. , Sometimes without neutralization, the saponification-ripening reaction completed solution is poured into water or dilute acetic acid (or water or dilute acetic acid is poured into the saponification-ripening reaction-finished solution) to separate the secondary cellulose acetate, and the secondary cellulose acetate is washed. The product is obtained by stabilization treatment.

(Problems to be Solved by the Invention) The hue of fibers, films, and plastics obtained by molding cellulose acetate produced by the above method as a raw material is generally slightly yellowish, and this phenomenon This is particularly noticeable in the case of acetate produced using wood pulp as a raw material, and even if it satisfies other required properties, it has poor appearance, resulting in a significant decrease in commercial value. Therefore, in order to industrially obtain fibers, films, and plastics, it is necessary to reduce this yellowness.
In order to improve whiteness, secondary measures are generally taken, such as treating with white pigments, fluorescent whitening agents, bleaching agents, and antioxidants, or adding them during molding. Needless to say, such secondary measures are not essential solutions, and their effectiveness is also limited.

In general, it is becoming difficult to obtain high-quality cellulose raw materials that are cost-effective due to global resource constraints and pollution problems at pulp manufacturing factories. There is a trend of conversion from high-grade wood pulp to low-grade wood pulp. However, when cellulose acetate is produced using low-grade wood pulp as a raw material, the yellowness of the product increases significantly, significantly reducing its commercial value.

There are many documents that touch on what causes the yellow color of cellulose acetate and processed products obtained from it, and various claims have been made by researchers. Among them, it is generally pointed out that non-cellulose components, mainly xylan, are the main cause. , 46, 581 (1963)].

The present inventors focused on the pre-treatment process of cellulose raw materials, and as a result of conducting intensive studies to produce cellulose acetate with excellent hue, the inventors found that the more the cellulose raw materials were treated to increase the degree of swelling, the more likely they were to have acetylation reactivity. The hemicellulose content, especially the xylan content, in the raw material is reduced, and the obtained 2
It was found that the hue of cellulose acetate was improved. Based on this knowledge, further studies were conducted, and it was found that the above-mentioned hue improvement effect as well as other excellent effects could be obtained, and the present invention was arrived at.

(Means for Solving the Problems) That is, the present invention provides a method for producing secondary cellulose acetate in which a cellulose raw material is acetate-esterified and then aged and saponified. The present invention provides a method for producing cellulose acetate having an excellent hue.

The cellulose raw material in the present invention means dissolving pulp, and low-grade cellulose raw materials for viscose and cellulose ether, which have particularly low α-cellulose content, can also be used for cellulose acetate.

In the present invention, the "acetic acid retention amount" is a morphological index representing the degree of swelling of cellulose raw materials, and is the amount of acetic acid contained in the sample after immersing the cellulose sample in acetic acid and removing the liquid by centrifugation under certain conditions. Says the value of amount (%). This is measured by the following method. Weigh out 1 g of a cellulose sample in terms of a dry sample and immerse it in acetic acid (in the case of a cellulose sample that has been subjected to swelling treatment, weigh out 1 g of a sample in terms of a dry sample, and gradually replace the swelling agent with acetic acid. , and finally complete replacement with acetic acid). Next, after centrifugation for 20 minutes at centrifugal effect Z = 1100, the weight of the acetic acid wet sample (Wg) is accurately weighed, and this is poured into 150 ml of distilled water and the sample is tightly stoppered.
After standing for 15 minutes, titrate with N/2NaOH using phenolphthalein as an indicator (titration amount, Aml), and calculate the acetic acid retention amount (%) using the following formula.

Amount of acetic acid retained (%) = 6.005×A/2×W When carrying out the production method of the present invention, first the amount of acetic acid retained is
The cellulose raw material is subjected to swelling treatment using a solvent that provides a degree of swelling of 40% or more. As swelling agents, solvents such as ethanolamine, ethylenediamine, dimethylsulfoxide, formamide and the like are advantageously used. The amount of swelling agent used is 5 to 45 parts by weight per 1 part by weight of the cellulose raw material. Swelling is carried out either by standing still or with good stirring, and the optimum temperature and time for swelling are selected respectively. For example, the temperature is room temperature ~
Appropriate time is 1 hour to 150 hours at 100°C.
After the swelling treatment, the swelling agent is removed from the cellulosic raw material by a suitable method. For example, when using a swelling agent that is compatible with water, remove as much of the solvent as possible by centrifugal dehydration or the like, wash with water, and gently dry, or replace the water with acetic acid. The cellulose raw material treated by this method,
Secondary cellulose acetate is obtained by a known acetic acid esterification method.

(Effects of the Invention) The production method according to the present invention allows cellulose acetate with excellent color to be produced without revising the conventional acetylation process or saponification/ripening process, and for this reason, cellulose raw materials of slightly lower quality can also be used. can.

Furthermore, since the acetylation reactivity of the cellulose raw material is improved by improving the swelling state indicated by the amount of acetic acid retained, the time required for the acetylation process can also be shortened.

(Examples) Examples are shown below to specifically explain the present invention, but the present invention is not limited to the examples shown below. Furthermore, in the examples, parts refer to parts by weight, and % refers to % by weight.

The yellow color of cellulose acetate can be determined by dissolving the sample in a mixed solvent of methylene chloride and methanol (9/1 weight ratio) at a concentration of 12%, and dissolving this solution as follows:
It was measured using a Hunter colorimeter (Hunter Lab model D25D2) according to ASTM-D-1925 (Yellowness Index). The measured value is obtained as a yellowness index, and the larger the value, the more pronounced the yellowness. The average degree of acetylation was measured and calculated according to the method of ASTM-D-871. The intrinsic viscosity of cellulose acetate was calculated by measuring the viscosity of an acetone solution with a concentration of 0.2 g/dl at 25.0±0.1°C.

Example 1 After crushing wood pulp (dissolving pulp, Rheocord XP manufactured by Leonia) with an α-cellulose content of approximately 96%, 100 parts of the same pulp (water content 4%) was poured into 2750 parts of dimethyl sulfoxide and stirred at room temperature. When the mixture was allowed to stand for 6 days and subjected to swelling treatment, the amount of acetic acid retained was 49.7%. The pulp after swelling treatment (acetic acid retention amount 49.7
%) was centrifuged to remove liquid, washed with water, and then gently dried to a moisture content of 4%.

100 parts of pulp treated above (moisture content 4%)
Spray 100 parts of glacial acetic acid evenly over the mixture and let it cool at room temperature.
After stirring and mixing for 120 minutes, the mixture was poured into a pre-cooled mixture of 280 parts of acetic anhydride, 365 parts of acetic acid, and 15.0 parts of sulfuric acid, and mixed with stirring to carry out acetylation at 45°C or lower. Initially, the system had a heterogeneous fibrous shape, but as the reaction progressed, it changed from an opaque waxy shape to a pale yellow transparent starch syrup shape. The completion point of the acetylation reaction was defined as the point at which unacetized fiber pieces were no longer found in the starch syrup-like reaction mixture.
It took 80 minutes.

After the acetylation reaction was completed, 43.6 parts of a 30% aqueous magnesium acetate solution was added to hydrolyze the excess acetic anhydride and neutralize a portion of the sulfuric acid, thereby stopping the acetylation reaction. The amount of catalyst sulfuric acid remaining in the reaction system at this time was calculated to be 6 parts.

Next, 12.2 parts of a 30% aqueous magnesium acetate solution was added while the reaction solution was heated to about 60° C. for 30 minutes. The amount of residual sulfuric acid at this time was calculated as 3.5 parts. Thereafter, water was added so that the bath concentration in the system was approximately 85%, and the temperature was further raised and stabilized at 70°C. After that, 2 at 70℃
The time aging reaction continued. Approximately 18.4 parts of 30 after the reaction is completed
% magnesium acetate aqueous solution was added to completely neutralize the sulfuric acid and stop the reaction. A large amount of 10% acetic acid aqueous solution was added to the reaction-completed solution while vigorously stirring it to precipitate and separate secondary cellulose acetate. The precipitated secondary cellulose acetate was collected by filtration and washed with water until virtually no acetic acid was contained.
Thereafter, it was dehydrated and dried to obtain a secondary cellulose acetate product.

The cellulose acetate thus obtained had an average degree of acetylation of 54.7%, an intrinsic viscosity of 1.89, and a yellowness coefficient of 2.9.

Example 2 After crushing wood pulp (dissolving pulp, Rheocord XP manufactured by Leonia) with an α-cellulose content of approximately 96%, 100 parts of the same pulp (water content 4%) was poured into 4400 parts of dimethyl sulfoxide, After stirring for 1 hour at ℃ for swelling treatment, the amount of acetic acid retained was 50.8%.
It was hot. The pulp after swelling treatment (acetic acid retention amount
50.8%) was deliquified by centrifugation, washed with water, and then reduced to a water content of 4%.
Gently dry.

100 parts of pulp treated above (moisture content 4%)
Spray 100 parts of glacial acetic acid evenly over the mixture and let it cool at room temperature.
After stirring and mixing for 120 minutes, acetylation and aging reactions were performed in the same manner as in Example 1 to obtain secondary cellulose acetate. The completion point of the acetylation reaction was approximately 80 minutes after the start of the reaction. The cellulose acetate thus obtained had an average degree of acetylation of 54.8%, an intrinsic viscosity of 1.96, and a yellowness coefficient of 3.2.

Comparative Example 1 After crushing wood pulp with an α-cellulose content of approximately 96% (dissolving pulp, Rheocord
30.2%), uniformly spray 100 parts of glacial acetic acid,
Pretreatment was performed by stirring and mixing at room temperature for 120 minutes.
The acetylation reaction and aging reaction were carried out in the same manner as in Example 1 to obtain secondary cellulose acetate. The completion point of the acetylation reaction was approximately 90 minutes after the start of the reaction, which took a longer time than in Examples 1 and 2. The cellulose acetate thus obtained had an average degree of acetylation of 54.8%, an intrinsic viscosity of 169, and a yellowness coefficient of 6.4.
The intrinsic viscosity was lower than that of 100%, and the yellow color was noticeable.

Example 3 After crushing wood pulp with an α-cellulose content of approximately 94% (dissolving pulp, MAC- manufactured by Waehauser), 100 parts of the same pulp (water content 4%) was poured into 2750 parts of dimethyl sulfoxide and stirred at room temperature. When the mixture was allowed to stand for 6 days and subjected to swelling treatment, the amount of acetic acid retained was 52.6%. The pulp after swelling treatment (acetic acid retention amount 52.6
%) was centrifuged to remove liquid, washed with water, and then gently dried to a moisture content of 4%.

100 parts of pulp treated above (moisture content 4%)
Spray 100 parts of glacial acetic acid evenly over the mixture and let it cool at room temperature.
After stirring and mixing for 120 minutes, acetylation and aging reactions were performed in the same manner as in Example 1 to obtain secondary cellulose acetate. The completion point of the acetylation reaction was approximately 78 minutes after the start of the reaction. The thus obtained cellulose acetate had an average degree of acetylation of 55.4%, an intrinsic viscosity of 1.80, and a yellowness index of 4.0, and the yellowness was improved by 47% compared to Comparative Example 2.

Comparative Example 2 After crushing a wood pulp with an α-cellulose content of approximately 94% (dissolving pulp, MAC- manufactured by Wehauser), 100 parts of the same pulp (water content 4%) (acetic acid retention amount
38.1%), uniformly spray 100 parts of glacial acetic acid,
Pretreatment was performed by stirring and mixing at room temperature for 120 minutes.
The acetylation reaction and aging reaction were carried out in the same manner as in Example 1 to obtain secondary cellulose acetate. The completion point of the acetylation reaction was approximately 93 minutes after the start of the reaction. The cellulose acetate thus obtained had an average degree of acetylation of 55.3%, an intrinsic viscosity of 1.88, and a yellowness coefficient of 7.6.
Yellowness was more noticeable than in Example 3.

Example 4 After crushing wood pulp with an α-cellulose content of about 94% (dissolving pulp, Aristaple manufactured by Western Pulp), 100 parts of the same pulp (water content 4%) was poured into 2750 parts of dimethyl sulfoxide and kept at room temperature. So 6
When the mixture was allowed to stand for a day and subjected to swelling treatment, the amount of acetic acid retained was 50.9%. The pulp after swelling treatment (acetic acid retention: 50.9%) was centrifuged to remove liquid, washed with water, and then gently dried to a moisture content of 4%.

100 parts of pulp treated above (moisture content 4%)
Spray 100 parts of glacial acetic acid evenly over the mixture and let it cool at room temperature.
After stirring and mixing for 120 minutes, acetylation and aging reactions were performed in the same manner as in Example 1 to obtain secondary cellulose acetate. The completion point of the acetylation reaction was approximately 80 minutes after the start of the reaction. The thus obtained cellulose acetate had an average degree of acetylation of 55.7%, an intrinsic viscosity of 1.81, and a yellowness coefficient of 3.2, and the yellowness was improved by 51% compared to Comparative Example 3.

Comparative Example 3 After crushing wood pulp with an α-cellulose content of approximately 94% (dissolving pulp, Alice Staple manufactured by Western Pulp), 100 parts of the same pulp (water content 4%) (acetic acid retention amount 32.6%) A pretreatment was performed by uniformly spraying 100 parts of glacial acetic acid and stirring and mixing at room temperature for 120 minutes. The acetylation reaction and aging reaction were carried out in the same manner as in Example 1 to obtain secondary cellulose acetate. The completion point of the acetylation reaction was approximately 95 minutes after the start of the reaction. The cellulose acetate thus obtained had an average degree of acetylation of 55.2%, an intrinsic viscosity of 1.81, and a yellowness coefficient of 6.5, and was more yellow than Example 4.

Example 5 After crushing wood pulp with an α-cellulose content of approximately 91% (dissolving pulp, L-5 manufactured by Jujo Paper Industries), 100 parts of the same pulp (water content 4%) was dissolved in dimethyl sulfoxide.
When the mixture was added to 2,750 parts and left at room temperature for 6 days for swelling treatment, the amount of acetic acid retained was 52.3%. The pulp after swelling treatment (acetic acid retention: 52.3%) was centrifuged to remove liquid, washed with water, and then gently dried to a moisture content of 4%.

100 parts of pulp treated above (moisture content 4%)
Spray 100 parts of glacial acetic acid evenly over the mixture and let it cool at room temperature.
After stirring and mixing for 120 minutes, acetylation and aging reactions were performed in the same manner as in Example 1 to obtain secondary cellulose acetate. The completion point of the acetylation reaction was approximately 91 minutes after the start of the reaction. The cellulose acetate thus obtained had an average degree of acetylation of 55.1%, an intrinsic viscosity of 1.60, and a yellowness index of 6.7, and the yellowness was improved by 43% compared to Comparative Example 4.

Comparative Example 4 After crushing wood pulp (dissolving pulp, L-5 manufactured by Jujo Paper) with an α-cellulose content of approximately 91%, A pretreatment was performed by uniformly spraying 100 parts of glacial acetic acid and stirring and mixing at room temperature for 120 minutes. The acetylation reaction and aging reaction were carried out in the same manner as in Example 1 to obtain secondary cellulose acetate. The completion point of the acetylation reaction was approximately 97 minutes after the start of the reaction. The cellulose acetate thus obtained had an average degree of acetylation of 55.3%,
The intrinsic viscosity is 1.59, the yellowness coefficient is 11.7, and Example 5
The yellow color was more pronounced than that of .

Claims (1)

[Scope of Claims] 1. A method for producing secondary cellulose acetate in which a cellulose raw material is acetate-esterified and then aged and saponified, characterized in that a cellulose raw material subjected to a swelling treatment with an acetic acid retention of 40% or more is used. Production method. 2. The method for producing cellulose acetate according to claim 1, characterized in that an organic solvent is used for the swelling treatment to achieve an acetic acid retention of 40% or more. 3. The method for producing cellulose acetate according to claim 2, wherein the organic solvent is dimethyl sulfoxide.