HPMC (hydroxypropyl methylcellulose) and CMC (carboxymethyl cellulose) are both commonly used cellulose derivatives, widely used in food, pharmaceuticals, construction and other fields.

1. Chemical structure and preparation method

HPMC:
Chemical structure: HPMC is a semi-synthetic polymer compound obtained by reacting natural cellulose with propylene oxide and methyl chloride after alkali treatment.

The main structural unit is the glucose ring, which is connected by 1,4-β-glucosidic bonds, and some hydroxyl groups are replaced by methoxy (-OCH?) and hydroxypropyl (-CH?CHOHCH?).
Preparation method: First, cellulose is treated with sodium hydroxide solution to form alkali cellulose, then reacted with methyl chloride and propylene oxide, and finally neutralized, washed and dried to obtain HPMC.

CMC:
Chemical structure: CMC is an anionic cellulose derivative obtained by reacting cellulose with chloroacetic acid under alkaline conditions.
The main structural unit is also a glucose ring, connected by 1,4-β-glucosidic bonds, and some hydroxyl groups are replaced by carboxymethyl (-CH?COOH).
Preparation method: Cellulose reacts with sodium hydroxide to form alkali cellulose, which then reacts with chloroacetic acid, and finally neutralizes, washes and dries to obtain CMC.

2. Physical and chemical properties.

Solubility:
HPMC: Soluble in cold water and some organic solvents, insoluble in hot water. When the solution is cooled, a transparent gel can be formed.
CMC: Soluble in cold water and hot water to form a viscous colloidal solution.

Viscosity and rheology:
HPMC: Has good thickening effect and suspension stability in aqueous solution, and has pseudoplastic (shear thinning) rheological properties.
CMC: Has high viscosity and good rheological properties in aqueous solution, showing thixotropy (thickening when stationary, thinning when stirred) and pseudoplasticity.

3. Application fields

HPMC:
Food industry: as thickener, stabilizer, emulsifier and film former, used in ice cream, dairy products, jelly, etc.
Pharmaceutical industry: used as binder, disintegrant and controlled release agent for tablet preparation.
Building materials: used in cement mortar and gypsum products to improve water retention and workability.
Cosmetics and personal care products: used in lotions, creams, shampoos and shower gels, etc., to provide thickening and stabilizing effects.

CMC:
Food industry: as thickener, stabilizer and emulsifier, used in jam, jelly, ice cream and beverages.
Pharmaceutical industry: used as binder, disintegrant for pharmaceutical tablets and film former for pharmaceutical capsules.
Papermaking industry: used as wet strength agent and surface sizing agent to improve the dry strength and printability of paper.
Textile industry: used as sizing agent and finishing agent to improve the strength and gloss of fabrics.
Daily chemical industry: used as thickener and stabilizer for detergents, toothpaste and skin care products.

4. Environmental protection and safety

Both HPMC and CMC are non-toxic and non-irritating polymer materials that cannot be decomposed by digestive enzymes in the human body and are generally considered safe food additives and pharmaceutical excipients. They are easily degraded in the environment and have little pollution to the environment.

5. Cost and market supply

HPMC is mainly used in fields with high performance requirements due to its complex preparation process, relatively high production cost and high price.

The production process of CMC is relatively simple, the cost is low, the price is relatively economical, and the application range is wide.

Although HPMC and CMC are both cellulose derivatives, they show different characteristics and uses due to their different chemical structures, physicochemical properties and application fields. The choice of which cellulose derivative to use usually depends on specific application requirements and economic considerations.