The advantages of organic antibacterial agents are: strong initial bactericidal power, instant bactericidal effect, good antibacterial broad spectrum and easy dispersion in powder or liquid. In addition, it has been developed for decades, the technology is mature and the price is relatively cheap. But it also has many fatal weaknesses: such as poor chemical stability and poor heat resistance. Volatile when exposed to heat, light or water, it is difficult to achieve long-term effect; Many polymers are easy to decompose and fail under high temperature, high pressure and high shear processing conditions, and even produce toxic decomposition products. Especially in plastics? It is easy to migrate during use, resulting in short antibacterial life (only 2-3 years) and high cost. Classification of organic antibacterial agents? Organic antibacterial agents can be divided into chemical synthetic antibacterial agents and natural antibacterial agents.
1. chemically synthesized antibacterial agent (see the table below): the main products are alcohols such as isopropanol and ethanol, phenols such as 3- methyl -4- isopropyl phenol and cresol, aldehydes such as formaldehyde, organic acids such as propionic acid and potassium sorbate, and parabens such as 2,4,4- trichloro -2'- hydroxydiphenyl ether (trichlorochloroprene rubber) peroxide. Halogen series, such as N- (fluoro-dichloromethyl sulfur) titanium imide imidazole series, such as 2-(4- thiazolyl) benzimidazole (TBZ) thiazole series, such as 2- n-octyl -4- isothiazoline -3 ketone-nitrile series, such as 2,3,5,6-tetrachloroisothiopentanedinitrile and methylene cyanate pyridine series. Biguanides
Such as 1, 1- hexamethylene bis [5-(4- chlorophenyl) biguanide] digluconate, and others such as cyclic hydrogen compounds, salt acyl aniline compounds, oxydiphenoxy arsenic, etc.
2. Natural antibacterial agents: extracts mainly from natural substances, such as chitosan, are obtained by removing N- acetyl from very hard parts of animal shells, such as natural shells, crab shells, shrimp shells, fish bones and insects. The main products are β- 1, 4- polyglucosamine (deacetylated chitosan polysaccharide), O- hydroxymethyl chitosan (O-CMCh) and other chitosan and Unica? MCAS-25 (microencapsulated hinokitiol), juniper alcohol, etc. Acidic substances, alkaline substances, oil? Fat? Natural antibacterial agents, such as castor oil, Toona sinensis oil, edible oil, etc. Their advantages are that they are not chemicals, they are completely extracted from natural foods or plants, or they can be used directly. In the process of production and use, it generally does not cause pollution to people and animals or the environment, and has good biocompatibility, so it is favored. However, its shortcomings are also obvious: its antibacterial effect is limited, and it cannot be broad-spectrum and long-lasting. After using this kind of antibacterial agent, food and articles will smell or change color, especially the natural antibacterial agent will begin to carbonize and decompose at 150~ 180℃, which greatly limits the application scope. Sterilization mechanism of organic antibacterial agents Because there are many kinds of organic antibacterial agents, the sterilization principle is also different. Natural antibacterial agents: acid and alkali substances destroy the cell wall and cell membrane of microorganisms through them, so that cell proteins are solidified and sterilization is realized; Various alcohols denature cells protein, interfere with cell metabolism and completely sterilize them; Chitosan is a natural antibacterial agent. Its bactericidal principle is that it contains amino acids and belongs to cations, while microbial cell walls are composed of acids and phospholipid anions. The combination of the two hinders the development and reproduction of microorganisms. Some chemically synthesized antibacterial agents hinder the energy metabolism of microbial cells, some hinder the protein synthesis (DNA synthesis) of microbial cells, and some hinder them? The synthesis of microbial cell walls, etc.
Inorganic antibacterial agent:
Inorganic antibacterial agents can be divided into four categories: antibacterial agents containing metal ions; Titanium dioxide photocatalytic (or photocatalyst) antibacterial agent; 3.？ Metal oxide antibacterial agent is an antibacterial agent with far infrared radiation function.
Antimicrobial agents containing metal ions? Inorganic antibacterial agents containing inorganic salts or metal ion complexes have the most varieties, uses and output. It is characterized by high antibacterial and safety, good heat resistance, wide antibacterial range and long validity period. Preparation method: inorganic antibacterial components (metal ions of various inorganic oxides and inorganic metal salts) are fixed on the carrier by physical adsorption or ion exchange.
Antibacterial components: mainly silver, copper, zinc and their compounds; Among them, silver and its compounds are the most widely used.
Carrier materials: mainly zeolite, silica gel, glass, calcium phosphate, zirconium phosphate, silicate, titanium oxide, whiskers and so on.
Antibacterial mechanism: ① Heavy metal ions react with sulfhydryl group (-SH) of protein, which destroys the activity of cell synthetase of bacteria and makes cells lose the ability of division and reproduction and die. ② Metal anions combine with bacteria, destroying the normal metabolism of bacteria, leading to the death of microorganisms or inhibiting their reproduction. The study of inorganic antibacterial materials (agents) is a new type of antibacterial agent successfully developed in the mid-1980 s. Its popularity was in the late 1980s. Therefore, the development of new inorganic antibacterial agents and the innovation of antibacterial processing technology have been formed. Because of its unique advantages, it has become a hot spot in antibacterial research. It represents the development direction of antibacterial agents, and has great development and application potential and good development prospects. ? TiO _ 2 photocatalytic antibacterial agent TiO _ 2 and other oxide semiconductors can be used to produce hydrogen and oxygen from water, treat water, deodorize, oxidize and remove air pollutants such as nitrogen oxides. It is a multifunctional antibacterial agent. Its characteristic is that it does not produce antibacterial effect without illumination, that is, light is necessary for oxide photocatalyst to produce active oxygen.
Action mechanism: The main bactericidal mechanism is that TiO2 _ 2 generates electron-hole pairs after being irradiated, and reacts with OH- and O2 adsorbed on its surface to generate hydroxyl radical and superoxide anion radical O2-. These two radicals are very active. When encountering bacteria, it directly attacks the cells of bacteria, extracts H atoms of organic matter or attacks its unsaturated bonds, which leads to protein variation and lipid decomposition of bacteria, thus killing bacteria and decomposing them, thus achieving the functions of sterilization, mildew prevention and deodorization.
It is an interesting subject to develop photocatalytic antibacterial agents with antibacterial activity even in the dark by actively utilizing the characteristics that the antibacterial activity of TiO2 _ 2 is different from that of silver antibacterial agents which depend on the dissolution of metal ions. Metal oxide antibacterial agent? Oxides with antibacterial activity include magnesium oxide (MgO), calcium oxide (CaO), zinc oxide (ZnO) and calcium preparations, which exist in sintered powders of ceramics, oysters, fans and natural ores. Its antibacterial mechanism is that bacteria are injured by external forces until they die. Similar to the effects of anti-biomass and anti-microbial agents. ? Antimicrobial agents with far-infrared radiation function These antibacterial agents include magnesium-aluminum-silicon-zirconium-rare earth system (white) and manganese-iron-cobalt-nickel-copper-chromium system (black). It is a light-heat conversion functional material. It absorbs light and heat from environmental species and outputs it in the form of far infrared radiation energy. At room temperature, it can emit far infrared rays with the wavelength of 2 ~ 18 micron, activate air and water, and generate hydroxyl radicals and active oxygen, thus killing bacteria.
Composite antibacterial agent:
Among inorganic antibacterial agents, silver antibacterial agent is resistant to high temperature (above 550oC) and has good antibacterial effect (10- 15 years). Although the antibacterial effect is outstanding, silver has high cost and active chemical properties, and is easily converted into brown silver oxide or reduced to black elemental silver by ultraviolet light catalysis. This not only reduces the antibacterial performance, but also makes white or light-colored products unusable. Therefore, its application in a wider range is limited. Although the zinc-based antibacterial agent has no discoloration problem and is cheap, its antibacterial performance is low and it cannot meet the antibacterial requirements. Internationally, after more than 20 years of research, Japan has made great progress in improving the discoloration of silver antibacterial agents, which has initially solved this problem, but the cost remains high. Organic antibacterial agents are mainly used in Europe and America, while inorganic antibacterial agents have only been used in recent years.
In recent ten years, Chinese researchers have made fruitful explorations in tracking the development direction of international inorganic antibacterial agents. In order to effectively inhibit microorganisms, the inorganic-organic composite antibacterial agent was developed by using more than two kinds of drugs and using ion exchange and multilayer coating technology.
Its characteristics:
A. Overcome the limitation and scope of drug effect, and make the antibacterial spectrum wider; Overcoming the drug resistance of microorganisms; It can prolong the aging of antibacterial agents, that is, extend the addition period. Can produce antibacterial effect at low concentration. Large specific surface area, easy to mix with polymer materials.