Microcrystalline Cellulose is purified partially de-polymerised alpha cellulose. It is comprised of glucose units connected by a 1-4 beta glycosidic bond. These linear cellulose chains are bundled together as microfibril, spiralled together in the walls of a plant cell. Each microfibril exhibits three-dimensional internal bonding resulting in a crystalline structure that is insoluble in water and resistant to reagents. There are, however, relatively weak segments of the microfibril with weaker internal bonding - these are called amorphous regions, or dislocations.
Processing of the cellulose microfibrils begins with shredding the sheets of alpha grade pulp. The shredded pulp is immersed in a hot bath of mineral acid that dissolves the amorphous regions of the microfibrils, whilst leaving the microcrystalline segments intact, so as to break down the long polymer chains. Hydrolysis is carried to the point where a levelling off degree of polymerisation (LODP) is achieved.
Following hydrolysis, chemicals and impurities are removed through a water-washing step, which is followed by spray drying. The slurry is sprayed through hot air jets to evaporate the water. This process produces particles of the desired size and moisture content.
Microcrystalline cellulose has many applications in the pharmaceutical, food, paper and structural composites industries. It is a naturally derived stabiliser, texturising agent, and fat replacer. It is used extensively in reduced-fat sauces, dairy products (including cheese), frozen desserts, whipped toppings, and bakery products.
Microcrystalline Cellulose revolutionised the tableting process because of its unique compressibility and carrying capacity. It compacts well under minimum compression pressures, has high binding capability, and creates tablets that are extremely hard, yet easily disintegrated. This is because the rapid drying produces aggregates of micro-crystals with many dislocations and slip planes that can fracture and realign during tableting. This deformation is primarily plastic, so bonds formed under pressure remain formed after pressure is released, making for a strong, dense tablet, with no capping.
Microcrystalline Cellulose is also highly absorptive due to the capillary action of its surface porosity, making it possible to act as a carrier for liquids and yet retain free flowing and compression properties. Its porosity promotes easy wetting and rapid drying of wet granulation and exhibits good volumetric flow characteristic with low lubricant demand.
Microcrystalline Cellulose is white, odourless, and tasteless. It is insoluble in water, dilute acids and in most organic solvents. It is practically insoluble in sodium hydroxide solution.