Typical structures of two cellulose ethers are given in Figures 1.1 and 1.2. Each β-D-dehydrated grape of a cellulose molecule
The sugar unit (the repeating unit of cellulose) is substituted with one ether group each at the C(2), C(3) and C(6) positions, i.e. up to three
an ether group. Because of the presence of hydroxyl groups, cellulose macromolecules have intramolecular and intermolecular hydrogen bonds, which are difficult to dissolve in water.
And it is difficult to dissolve in almost all organic solvents. However, after etherification of cellulose, ether groups are introduced into the molecular chain,
In this way, the hydrogen bonds within and between molecules of cellulose are destroyed, and its hydrophilicity is also improved, so that its solubility can be improved.
greatly improved. Among them, Figure 1.1 is the general structure of two anhydroglucose units of cellulose ether molecular chain, R1-R6=H
or organic substituents. 1.2 is a fragment of carboxymethyl hydroxyethyl cellulose molecular chain, the degree of substitution of carboxymethyl is 0.5,4
The substitution degree of hydroxyethyl is 2.0, and the molar substitution degree is 3.0.
For each substituent of cellulose, the total amount of its etherification can be expressed as the degree of substitution (DS). made of fibers
It can be seen from the structure of the prime molecule that the degree of substitution ranges from 0-3. That is, each anhydroglucose unit ring of cellulose
, the average number of hydroxyl groups substituted by etherifying groups of the etherifying agent. Due to the hydroxyalkyl group of cellulose, its substitutional
The etherification should be restarted from the new free hydroxyl group. Therefore, the degree of substitution of this type of cellulose ether can be expressed in moles.
degree of substitution (MS). The so-called molar degree of substitution indicates the amount of etherifying agent added to each anhydroglucose unit of cellulose
The average mass of the reactants.
1 General structure of a glucose unit
2 Fragments of cellulose ether molecular chains
1.2.2 Classification of cellulose ethers
Whether cellulose ethers are single ethers or mixed ethers, their properties are somewhat different. Cellulose macromolecules
If the hydroxyl group of the unit ring is substituted by a hydrophilic group, the product can have a lower degree of substitution under the condition of a lower degree of substitution.
It has a certain water solubility; if it is substituted by a hydrophobic group, the product has a certain degree of substitution only when the degree of substitution is moderate.
Water-soluble, less substituted cellulose etherification products can only swell in water, or dissolve in less concentrated alkali solutions
middle.
According to the types of substituents, cellulose ethers can be divided into three categories: alkyl groups, such as methyl cellulose, ethyl cellulose;
Hydroxyalkyls, such as hydroxyethyl cellulose, hydroxypropyl cellulose; others, such as carboxymethyl cellulose, etc. If the ionization
Classification, cellulose ethers can be divided into: ionic, such as carboxymethyl cellulose; non-ionic, such as hydroxyethyl cellulose; mixed
type, such as hydroxyethyl carboxymethyl cellulose. According to the classification of solubility, cellulose can be divided into: water-soluble, such as carboxymethyl cellulose,
Hydroxyethyl cellulose; water-insoluble, such as methyl cellulose, etc.
1.2.3 Properties and applications of cellulose ethers
Cellulose ether is a kind of product after cellulose etherification modification, and cellulose ether has many very important properties. like
It has good film-forming properties; as a printing paste, it has good water solubility, thickening properties, water retention and stability;
5
Plain ether is odorless, non-toxic, and has good biocompatibility. Among them, carboxymethyl cellulose (CMC) has “industrial monosodium glutamate”
nickname.
1.2.3.1 Film formation
The degree of etherification of cellulose ether has a great influence on its film-forming properties such as film-forming ability and bonding strength. Cellulose ether
Due to its good mechanical strength and good compatibility with various resins, it can be used in plastic films, adhesives and other materials.
material preparation.
1.2.3.2 Solubility
Due to the existence of many hydroxyl groups on the ring of the oxygen-containing glucose unit, cellulose ethers have better water solubility. and
Depending on the cellulose ether substituent and the degree of substitution, there are also different selectivity for organic solvents.
1.2.3.3 Thickening
Cellulose ether is dissolved in aqueous solution in the form of colloid, wherein the degree of polymerization of cellulose ether determines the cellulose
Viscosity of ether solution. Unlike Newtonian fluids, the viscosity of cellulose ether solutions changes with shear force, and
Due to this structure of the macromolecules, the viscosity of the solution will increase rapidly with the increase of the solid content of cellulose ether, however the solution’s viscosity
Viscosity also decreases rapidly with increasing temperature [33].
1.2.3.4 Degradability
The cellulose ether solution dissolved in water for a period of time will grow bacteria, thereby producing enzyme bacteria and destroying the cellulose ether phase.
The adjacent unsubstituted glucose unit bonds, thereby reducing the relative molecular mass of the macromolecule. Therefore, cellulose ethers
The preservation of aqueous solutions requires the addition of a certain amount of preservatives.
In addition, cellulose ethers have many other unique properties such as surface activity, ionic activity, foam stability and additive
gel action. Due to these properties, cellulose ethers are used in textiles, papermaking, synthetic detergents, cosmetics, food, medicine,
It is widely used in many fields.
1.3 Introduction to plant raw materials
From the overview of 1.2 cellulose ether, it can be seen that the raw material for the preparation of cellulose ether is mainly cotton cellulose, and one of the contents of this topic
It is to use cellulose extracted from plant raw materials to replace cotton cellulose to prepare cellulose ether. The following is a brief introduction to the plant
material.
As common resources such as oil, coal and natural gas are dwindling, the development of various products based on them, such as synthetic fibers and fiber films, will also be increasingly restricted. With the continuous development of society and countries around the world (especially
It is a developed country) who pays close attention to the problem of environmental pollution. Natural cellulose has biodegradability and environmental coordination.
It will gradually become the main source of fiber materials.
Post time: Sep-26-2022