Microcrystalline cellulose is a degradation product of natural cellulose. Microcrystalline cellulose not only retains the green, non-toxic, easy-to-degrade and easy-to-modify nature of natural cellulose. It also has its own unique properties, such as small particle size, high modulus, high crystallinity and low degree of polymerization. It is a bio-based material with superior performance. At present, the raw materials for preparing microcrystalline cellulose are mainly natural plant fibers, of which cotton and wood pulp are mostly used in industry, and herbs or some agricultural and forestry wastes are mostly used in experimental research.
Microcrystalline cellulose is a polymer compound in the form of powder or short rods, with a particle size range of 20 to 80µm. It is odorless, has strong fluidity but does not have Fibrous. Its molecule is mainly composed of crystalline regions, so its crystallinity is relatively high, generally 55% to 80%, and its crystalline type is generally Type I cellulose.
The raw materials for the preparation of microcrystalline cellulose are very abundant. Cotton and wood pulp have high cellulose content and have become the main raw materials for industrial production of microcrystalline cellulose. However, with the increasing demand for wood and cotton in the furniture industry, pulp and paper industry, textile industry and other industries, some other plant fiber raw materials are also used to prepare microcrystalline cellulose, such as grass plants, bamboo plants, Hemp plants and some agricultural and forestry wastes, etc. When preparing bamboo microcrystalline cellulose, its yield, moisture content and crystallinity were 83.37% ± 1.48%, 4.50% ± 0.5% and 78% respectively. All performance indicators are close to commercial grade microcrystalline cellulose. Microcrystalline cellulose prepared from banyan tree bark is rod-shaped, has a length of 90±25µm, an average diameter of 17.1±3.3µm, and a crystallinity index of 75.8%. Its initial thermal degradation temperature reaches 314.6°C and can be used as a biocomposite. Excellent filler. Compared with wood raw materials, these raw materials have the advantages of cheapness, easy availability, low lignin content and short growth cycle, which can reduce the production cost of microcrystalline cellulose to a certain extent.
Research shows that the higher the crystallinity of cellulose, the better its toughness and stretchability. Therefore, microcrystalline cellulose has better mechanical properties and is often used as Material of choice for making composites. Microcrystalline cellulose also has good degradability, and its degradation types are mainly divided into six types, namely acidic degradation, alkaline degradation, oxidative degradation, thermal degradation, microbial degradation and mechanical degradation.
Acidic degradation is the most common degradation method, and it can be used to prepare glucose or nanocellulose after acid degradation. In terms of solubility, microcrystalline cellulose contains many intermolecular and intramolecular hydrogen bonds, making it difficult to dissolve in organic solvents such as water and acetone, but it can be dissolved in dilute alkaline solutions, copper amine solutions and some other solvent systems. , such as ionic liquid system, deep eutectic solvent system and sodium hydroxide/urea system, etc.
After microcrystalline cellulose is dissolved, it is mainly used to prepare regenerated fibers that can replace viscose fibers and new functional cellulose-based materials (nanocellulose, aerogels ).
In terms of chemical modification, since microcrystalline cellulose molecules contain more hydroxyl groups, they can be oxidized, etherified, and esterified under different conditions. modification, acetylation and graft copolymerization. The modified microcrystalline cellulose has good biocompatibility and processability, and can be widely used in functional composite materials and other fields, such as microcrystalline cellulose (C-6 carboxyl group) obtained after oxidative modification Cellulose) can be used to prepare medical hemostatic materials; microcrystalline cellulose modified by etherification can be used to prepare cellulose ether fluorescent materials.
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