The cellulose triacetate according to the formula is a complex organic compound. Previously, it was used for the manufacture of film and film, and now the main field of application is the manufacture of fabrics and films for x-ray studies.
Description
Cellulose triacetate is an ester of cellulose and acetic acid. It is an amorphous substance of white color in the form of flakes or powder.
The chemical formula of cellulose triacetate is [C 6 H 7 O 2 (OCOCH 3 ) 3 ] n , where: n is the degree of polymerization. This value is in the range of 150-700. The average degree of polymerization is 260-300. The molecular weight of the compound is 25-115 thousand g / mol.
The structural formula of cellulose triacetate is shown in the figure below.
This compound is a thermoplastic, that is, it is capable of passing into a highly elastic state when heated, but its thermal resistance is not high. At softening temperature, the color of the material begins to change.
Physiochemical properties
Cellulose triacetate, the formula of which contains 3 acetyl groups of COCH 3 , has the following main characteristics:
soluble in substances such as: glacial acetic acid, chloroform, aniline, pyridine, phenol, formic acid, formamide, liquid sulfur dioxide, methylene chloride (the most common solvent at present);
easily crystallizes when heated to a temperature of 210-225 ° C;
insoluble in water, esters, acetone and ethyl acetate;
low hygroscopicity;
density 1280–1330 kg / m 3 ;
in solutions of acids and alkalis, saponification of the substance occurs, that is, it is unstable;
good light fastness;
high fiber and film-forming properties;
softening temperature - 190-210 ° C, decomposition (degradation) - 230 ° C;
ignition temperature - 295 ° , autoignition - 380-430 ° .
The thermal stability of the substance is increased by the addition of stabilizers (antioxidants, which include amino groups, and other substances).
Synthesis
Cellulose acetate esters were first obtained in 1865 by the German scientist Schutzenberg. Currently, triacetate (or primary cellulose acetate) is synthesized by complete acetylation of cotton or wood pulp using acetic anhydride. This process is irreversible and occurs in the presence of catalysts - sulfuric or perchloric acid. According to the IR spectrum, the use of catalysts with the composition H 2 SO 4 + Mg (ClO 4 ) 2 allows one to obtain compounds with higher quality and technological parameters.
Acetic acid in cellulose triacetate is bound. Its content is in the range of 60-61.5%. Subsequent saponification of this substance is necessary to create a more uniform product. In addition to the anhydride and catalysts, the composition of the acetylating mixture also contains a solvent (homogeneous production method) or a solvent (heterogeneous technology).
Features of the production of cellulose triacetate, distinguishing it from the manufacture of other cellulose ethers, are:
the inability to control the formation of esters;
the need to use a catalyst;
regulation of acetyl groups in the subsequent saponification process.
Varieties
This substance can be obtained in several structural modifications:
When acetylation, that is, the replacement of hydrogen atoms by residues of acetic acid CH3CO (or acetyl group). In this case, the formation of cellulose triacetate I. The process is carried out in a mixture of acetic anhydride and benzene, at a temperature of 55 ° C.
The second modification is synthesized by reprecipitation from a mixture of chloroform and ether. This compound is more stable than the previous type.
Both states of the substance are in equilibrium, which depends on the temperature and type of solvent. The transition from I to II modification is reversible. It can be produced by treatment with various chemicals. At low temperatures, regardless of the feedstock, cellulose acetate I is mainly synthesized, and the second modification is formed at high temperatures for the esterification of cellulose hydrate. The second type of structure can also be obtained by saponification of the first modification with a solution of sodium hydroxide in methyl alcohol.
Fabric manufacturing
As early as 1901, the first patent was issued for the production of artificial fiber from this compound and its industrial development began. The formula of cellulose triacetate, like other acetates of this substance, is characterized by a large difference in molecular weight. In this regard, the initial cellulosic material is heterogeneous, and this affects the spinning properties of the fibers. Low molecular weight fractions also significantly degrade their quality.
The fiber is formed by the evaporation of a liquid in cellulose triacetate solutions in a mixture of acetone with water or in solvents (methylene chloride, ethanol, methanol). Threads are used as cheap raw materials for the production of artificial silk, knitwear and for technical purposes. The use of cellulose triacetate as a basis for fabrics allows to obtain their high consumer characteristics:
sufficient light and heat resistance;
good appearance (resembles natural silk);
resistance to many chemicals and microorganisms;
shape preservation;
hypoallergenicity.
The disadvantages include low hygroscopicity, a decrease in the strength of the fibers when wet, a low resistance to mechanical abrasion, and the accumulation of static electricity.
Cellulose Triacetate: Other Applications
Since 1952, this substance has been the main component in the manufacture of film and film films, magnetic tapes. Currently, it is also used in the production of films for x-ray films. This material is characterized by dimensional stability, low moisture absorption, gas permeability. In some companies, the substance is part of the coatings for sunglasses.
The saponification product of cellulose triacetate is also widely used in industry. It is used in the manufacture of plastics (etrols) and artificial fiber. A distinctive feature of this substance is the possibility of introducing more diverse types of plasticizers in comparison with cellulose triacetate.
In the paint industry, this compound is added to the composition of varnishes for better film formation. According to X-ray diffraction patterns and studying the IR spectrum of the substance, the use of purified syrups of cellulose triacetate can increase the physical and mechanical properties of the films by 20%.