Cellulose acetate|It is friendly to human and environment, and excellent in durability.
In 1865, cellulose acetate was synthesized for the first time by Schutzenberger, Germany. After that, as a result of a number of studies, cellulose acetate was successfully solubilized in a common solvent such as acetone, which opened the way to industrial production. In Japan, our company began to conduct studies on cellulose acetate in the late Taisho era, and in 1935, succeeded in the industrial production and started selling it on the market. Since then, our company has been innovating technologies and making continuous efforts to deliver the highest quality product.
Cellulose acetate is excellent in chemical resistance, heat resistance, and burning resistance, and in recent years, has attracted attention as a resin that is derived from the natural polymer, cellulose, as a raw material and is friendly to the human body and the environment.

What is cellulose acetate

Fig. 1. General chemical structure of cellulose acetate
Cellulose acetate is a semi-synthetic polymer obtained through the esterification of acetic acid with cellulose that is a natural polymer. Cellulose is a polymer consisting of anhydroglucose units as repeating units, and has three hydroxy groups per unit. Cellulose acetates with different properties are obtained depending on the esterification degree (degree of substitution). The degree of substitution is also expressed as acetyl value (combined acetic acid (%)). Cellulose acetate widely used for industrial applications is broadly classified into two types, i.e., cellulose diacetate and cellulose triacetate with acetyl values of about 55% (degree of substitution: 2.4) and 61% (degree of substitution: 2.9), respectively. Fig. 1 represents the general chemical structure of cellulose acetate.
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Production method for cellulose acetate

Fig. 2. Reaction scheme of cellulose acetate production
Fig. 3. Outline of production process of cellulose acetate
Cellulose acetate is produced through two-step reactions involving the esterification of acetic acid with cellulose and the partial hydrolysis of the resultant ester groups. Fig. 2 and Fig. 3 show the reaction scheme and outline of production process for cellulose acetate, respectively. Highly purified woodpulp or cotton linter is used as the raw material cellulose. Cellulose is activated in a pretreatment step. In the subsequent acetylation step, to the cellulose are added acetic anhydride, acetic acid, and sulfuric acid as a catalyst to carry out the esterification reaction. In the acetylation step, cellulose triacetate in which almost all hydroxy groups have been esterified is generated. In the subsequent ripening step, the addition of water to the cellulose triacetate partially hydrolyzes ester groups to result in cellulose acetate with a desired acetyl value.
Water is added to the solution after the completion of the ripening step to precipitate and separate the cellulose acetate. In the subsequent washing step, the remaining solvent, impurities, and the like are removed. In addition, through a drying step, a cellulose acetate product is obtained. Diluted acetic acid as a byproduct generated in the precipitation and purification steps is concentrated for recycle, or for the raw material for acetic anhydride production.
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Features of cellulose acetate

Cellulose acetate has such features as described below and is widely used in various fields.
  • Stable against sunlight
  • A fabric, a formed article, a coating film, a coating liquid, and the likes made of cellulose acetate has high resistance to sunlight (in particular, ultraviolet rays), does not easily undergo degradation, and hence can be used for a long period of time.
  • Flame resistance and excellent in heat resistance
  • Cellulose acetate is relatively resistant to flame and also has a high melting point so that it is melt and carbonized at 230 to 300℃.
  • Good in chemical resistance
  • Cellulose acetate is the most stable among cellulose derivatives, can be stored for a long period of time, and is durable towards organic and inorganic weak acids, animal and vegetable oils, gasoline, and the like.
  • Excellent in electrical properties
  • Cellulose acetate has low electrical conductivity, has high internal resistance and external resistance, and hence serves as a good insulating material.
  • Friendly to human body and environment
  • Cellulose acetate, which utilizes, as a raw material, cellulose obtained from wood and cotton, has attracted attention as an environmentally friendly resin in recent years.
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Production items of cellulose acetate

Table 1. General physical properties of cellulose acetate
Table 2. Production items of cellulose acetate and their general properties
Fig. 4. Relationship between degree of polymerization and 6% viscosity
Fig. 5. Relationship between acetyl value and degree of substitution
Table 1 shows general physical properties of cellulose acetate.
Cellulose acetate is classified into different production items depending on the 6% viscosity and the acetyl value. The 6% viscosity is used as a measure of the degree of polymerization. Fig. 4 shows the relationship between the degree of polymerization and the 6% viscosity. The acetyl value is a measure of the degree of substitution and represents the weight percent of acetic acid liberated by the saponification of cellulose acetate. Fig. 5 shows a relationship between the acetyl value and the degree of substitution. Table 2 shows the general properties (the acetyl value and 6% viscosity) of the production items. In order to meet customers' needs, our company will consider a specification not shown in the table as well. It should be noted that cellulose acetate of our company is intended for raw materials for general industrial applications and is produced under a quality control as such.
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Solvent for and solubility of cellulose acetate

Table 3. Acetyl value and solubility in various solvents
The solubility of cellulose acetate in a solvent depends on the acetyl value. In general, there is a tendency that, compared to cellulose derivatives such as cellulose nitrate and ethyl cellulose, number of solvent for cellulose acetate is relatively limited and is used under restricted conditions because of the limitation. However, such a property as poor solubility is in tern regarded as excellent features in terms of oil resistance, solvent resistance, and the like. Accordingly, the appropriate selection of a production item and a solvent is a key point in using cellulose acetate. Table 3 shows solubilities of cellulose acetate in typical solvents. The addition of a small amount of an auxiliary solvent such as an alcohol to a main solvent may improve the solubility.
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Solution viscosity of cellulose acetate

Solution viscosity of acetone and dichloromethane systems
The solution viscosity of cellulose acetate depends on a production item (degree of polymerization), the kind of a solvent, and a concentration. Please consider an appropriate formulation in using cellulose acetate. The solution viscosities of cellulose acetate in acetone-based and methylene chloride-based mixed solvents are presented as typical examples.
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Compatibility of cellulose acetate

Table 4. Plasticizers compatible with cellulose acetate
Cellulose acetate itself has no thermoplasticity. The use of an appropriate plasticizer in the thermal molding can lower a softening temperature to a temperature suitable for processing. Further, the addition of a plasticizer can improve the flexibility of a molded article. Table 4 shows a list of typical plasticizers compatible with cellulose acetate.
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Precautions in handling cellulose acetate

Precautions in handling cellulose acetate
There is no report showing that cellulose acetate has toxicity. However, cellulose acetate fine powders may cause dust explosion. See a material safety data sheet (MSDS) of cellulose acetate before handling. Further, some of solvents for dissolving cellulose acetate and additives such as a plasticizer are substances harmful for the human body. Hence, the substances should be handled with care in accordance with the respective material safety data sheets (MSDS).
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