For many years, TCMTB has been the most widely used and most reliable in leather mildew prevention, and has been listed as a standard leather additive by the United States and New Zealand. It has also been used in American military leather.

TCMTB and OITZ are products recommended by the International Joint Environmental Committee for the use of clean processes in leather production because of their low toxicity, wide applicability, low harm to the environment and human body, and easy biodegradation.

TCP contains PCP, which affects its use. Some German companies strictly limit the TCP content in leather to less than 1ppm. In addition, other phenolic compounds are threatened again. For example, 0PP is relatively safe for humans and the environment, but it has been listed as a carcinogen in California, USA. According to environmental requirements, PCP, TCP, p-nitrophenol, -teaphenol, p-chlorodiphenol, etc. are strictly restricted.

Benzothiazole fungicides mainly includes mercaptobenzothiazole (MBT) and 2-(thiocyanatomethylthio)benzothiazole (TCMTB).

MBT can be obtained by heating dithiobenzoic acid, 2,2′-dithiodibenzothiazole and triphenylphosphine in benzene. MBT has a broad-spectrum bactericidal effect, but its toxicity is relatively high. First, mercaptobenzothiazole is made into sodium salt and reacted with bromochloromethane in acetone solution to obtain 2-(chloromethylthio)benzothiazole, and then 2-(chloromethylthio)benzothiazole is reacted with ammonium thiocyanate in acetone to obtain 2-thiocyanatomethylthiobenzothiazole. The commodity 2-thiocyanatomethylthiobenzothiazole (TCMTB) is generally a 30% emulsion.

In agriculture, it can be diluted 1000~1500 times to prevent and control anthrax, bacterial angular spot, damping-off, vine blight, powdery mildew, etc. of fruits and vegetables. In the leather industry, it can be used as both a bactericide and a mildew inhibitor.

Bactericidal and mildew-proof tests show that TCMTB can not only effectively inhibit common harmful bacteria on raw hides, but also inhibit molds such as Aspergillus niger, Penicillium wilt, Aspergillus flavus, Penicillium apicalum, and Trichoderma on leather.

In addition to being used for raw hide preservation and water immersion preservation, it can also be used for mildew prevention of wet blue leather and dry leather, and can also be used for mildew prevention of protein finishing agents and protein coatings.

During use, if TCMTB encounters sulfide or sulfite, it will decompose into MBT with poor bactericidal effect and high toxicity. It will be inactivated under alkaline conditions: after being absorbed by oil, its effective concentration around bacteria will be reduced. Therefore, when using it, it is necessary to avoid these problems as much as possible to obtain a good bactericidal effect.

Isothiazolinone compounds are a new type of high-efficiency broad-spectrum bactericides with bactericidal, algaecidal, and antiseptic functions. They have good killing effects on Escherichia coli, Bacillus subtilis, Aspergillus niger and other microorganisms, and have been widely used in various fields of industry. Its bactericidal mechanism is that the bactericide molecules can penetrate the cell wall of microorganisms and enter the cell interior, and combine with the alkaline bases on the nucleic acid (RNA and DNA) in the cell, thereby inhibiting the regeneration and reproduction of microorganisms.

The isothiazolinone bactericide was first patented by the American Rohm & Haas Company (ROHM&HAAS), and the product code is Kathon series. In the late 1980s, my country also began the research and development of this series of bactericides, and the development focus was on the application in cosmetics and detergents, and later it was used for sterilization and algae removal in industrial circulating cooling water.

Now isothiazolinone bactericides have been widely used in various fields of industrial production. At present, there are two main isothiazolinone bactericide products on the market. One is methylisothiazolinone and its vapor, mixed at a ratio of 1:3~3.5, and the content of active ingredients in the product is not less than 1.5%; the other is n-octylisothiazolinone, with an effective content of 45%. The synthesis routes of these two compounds are basically the same. They can both be obtained from methyl acrylate as raw material through three steps of sulfidation, amidation and cyclization. The difference is that during the amidation process, if methylamine is added for reaction, methylisothiazolinone is generated, and if n-octylamine is added for reaction, n-octylisothiazolinone is generated.

Although methylisothiazolinone and n-octylisothiazolinone are both good fungicides, they have their own advantages and disadvantages when used. Methylisothiazolinone has good water solubility and can be made into a solution for use. While n-octylisothiazolinone has better bactericidal properties than methylisothiazolinone, it has poor water solubility and cannot be directly dissolved in water. When used in leather, n-octylisothiazolinone can be made into an emulsion of a certain concentration with an appropriate emulsifier and added to the leather.

Phenol bactericides and mildew inhibitors include trifluorophenol (TCP), pentafluorophenol (PCP), o-phenylphenol (OPP), para-chloro-m-methylphenol (CMC), etc. PCP is the earliest phenolic bactericide and mildew preventer. It has a broad spectrum and high efficiency of bactericidal properties and can effectively kill a variety of bacteria. It is relatively stable to temperature and pH value. However, at high concentrations, PCP can react with proteins in leather to make the grain surface coarser and harder.

PCP is carcinogenic, and burning substances containing PCP will release highly toxic chlorinated benzoquinoline and furan, so its use was first strictly restricted by the German government. The maximum amount allowed in leather is 5 mg/kg of absolutely dry sample. TCP, as a substitute for PCP, is also highly toxic. OPP, as a bactericide and mildew preventer, is relatively safe for the human body and the environment, but some people also believe that it is a carcinogen, and its use has also been restricted in some local regulations in the United States.

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