Tannin extract is a kind of chemical product which is made from tannin rich plant materials by water extraction and concentration. Usually brownish yellow to brownish brown, powdery or massive. It is mainly used for tanning and is called vegetable tanning agent in leather industry. In addition, it is also used as mineral processing inhibitor, boiler water treatment agent, drilling mud diluent and metal surface corrosion inhibitor, and condensed tannin extract is also used as wood adhesive.
It can be used as curing accelerator of phenolic resin adhesive to accelerate the curing process. It can also be used as casting and grinding wheel adhesive. It can also be used as metal antirust agent, wood surface finishing agent, boiler descaling / antiscale agent, leather tanning agent, etc.
There are more than 600 kinds of plants in the world that contain more tannin and can be used to produce tannin extract. There are more than 70 plants with high tannin content in China. The time of raw material collection has a great influence on the quality of tannin extract, so timely collection is very important. The moisture content of raw materials for storage shall be less than 20%, and the storage time shall not exceed 1 year. In production, the raw materials were broken first to break up most of the cell walls, which was conducive to the diffusion and dissolution of tannin during extraction. The extract was concentrated and dried by vacuum evaporation to obtain tannin extract. In order to make the product light in color, easy to dissolve and quick to penetrate, in addition to physical purification of raw materials and intermediate products, chemical agents (such as sodium sulfite, etc.) can also be used in the processing process.
Since the 1970s, due to the rapid development of synthetic tanning agents and the decrease of raw material resources, the output of tannin extract in the world has declined. The trend of tannin extract production is to find new high-quality raw materials, establish high-quality and fast-growing raw materials base, reform process and equipment, improve the quality of tannin extract and expand the scope of utilization, and carry out waste residue utilization.