A variety of plastic additives are used to provide useful properties for polymer materials, but they are also very vulnerable to microbial attack, so antibacterial agents can be added to plastics to enhance their resistance to microorganisms, thereby helping to maintain the properties of plastics and extend the service life of plastic products.

Frist. Reasons for the erosion of plastic products by mouldy microorganisms

Most synthetic polymer materials have strong bacterial resistance and can resist the damage of microorganisms, but there are also some varieties (such as polyurethane, aliphatic polyester, etc.) because of its special structure is easy to be damaged by microorganisms.More important is the plastic processing process to add stabilizer, lubricant, plasticizer and other additives, these additives become a nutrient source of bacteria and mold, especially plasticizer more easily become a source of microbial food.

1. Polyvinylchloride (PVC) : commonly used additives in plastics, such as plasticizers, starch fillers, thickeners, lubricants, etc., are especially vulnerable to microbial growth threats. Microorganisms use plasticizers and other ingredients as their carbon sources, which will cause material discolcolation, odor, viscosity, and eventually brittle. 

2, polyurethane (Polyurethanes, PUR) : foamed polyurethane is especially easy to be attacked by microorganisms.The reason is that the foamed polyurethane has a porous structure, so that it is easy to deposit soil, dust and fungi or bacterial spores, and then promote the growth of microorganisms on the surface of the polyurethane.Polyester polyurethanes are more susceptible to microbial influences than polyether polyurethanes, resulting in poorer product performance.

3. Polyethylene (PE) : Generally, compared with plasticized PVC and polyurethane, polyethylene is less susceptible to microbial invasion.Low molecular weight polyethylene (<10,000) and polymers with relatively small branching degree are at high risk of microbial invasion.

4. Polyesters: Polyesters are generally resistant to microbial degradation and will only be exposed to microbe under special circumstances, e.g. polyesters derived from e-caprolactone are exposed to microbial degradation.

5. Silicones are generally made up of silicone monomers such as silicon monomers, silicone oil filler, pigment, crosslinking agent, coupling agent, catalyst and so on.If you want to do with mildew proof function, you must add silicone mildew proof agent in the raw material

Scond. plastic products are harmed by mildew and microbial erosion

The biological corrosion of plastics caused by mold and rot microorganisms mainly hasthree different modes of production:

1. Microorganisms use the components in plastics as nutrient sources to directly degrade;

2. Indirect degradation or change of the appearance of plastic products caused by microbial metabolites (e.g., acids, enzymes, pigments);

3. Surface effect caused by settling on the surface of plastic products without degradation of microorganisms.

The main effects caused by the activities of microorganisms include:

1. Discoloration: the color of the mycelium of the mildew microorganism itself or the secretion of the secondary metabolites such as pigment, which leads to various stains such as pink, yellow and black on the surface of plastic.

2, The change of electrical conductivity: mildew microorganism in large numbers on the plastic surface, produce some conductive proteins, polysaccharides and other substances, changed the conductive properties of polymer materials, its insulation properties because of microbial invasion and change;

3, The reduction of mechanical properties: mold microorganisms to a variety of plastic additives as food sources, resulting in the constant degradation of plasticizers and other additives, making plastic embrittlement, shrinkage, further lead to the loss of tensile strength and integrity, and finally greatly shorten the service life of plastics;

4, Accumulation of dirt: due to the plastic surface is invaded by microorganisms, increase the surface roughness, make dirt more easy to accumulate on the surface, thus causing a vicious cycle, accelerate the degradation of plastic, deterioration;

5, Solvent and gas permeability: plastic is constantly corroded, will lead to solvent and gas permeability improvement, storage or isolation of liquid, gas effect will be reduced or even failure;

6, Odor: microbial metabolism will lead to the production of amines, ammonia or hydrogen sulfide, and these metabolites will form an unpleasant odor.

Third. Antibacterial agents suitable for plastic products

1, The significance of plastic antibacterial agents 

Plastic antibacterial agent added in plastic, so that plastic products themselves have antibacterial properties, not only can prevent microbial damage to plastic, and then avoid unnecessary chemical and physical changes in plastic products, or cause unnecessary appearance changes in plastic products;But also can in a certain period of time will stick to the plastic on the microorganism to kill or inhibit reproduction, so as to protect the use of plastic products from microbial damage, improve the health and hygiene of products.

2, The type of plastic antibacterial agent 

At present, there are many kinds of antimicrobials available, basically divided into inorganic antimicrobials, organic antimicrobials and natural antimicrobials. Each kind of antibacterial mechanism, antibacterial effect, toxicity, compatibility with materials,antibacterial material made of antibacterial long-lasting antibacterial and MIC (the minimum concentration of inhibitory microorganisms) and MBC (the minimum concentration of killing microorganisms) are not the same. Each has its own advantages, so the antibacterial performance of different antimicrobials is not the same.

China carried out the research of antibacterial plastics and antibacterial agents for plastics in the 1990s, and made great progress in the late 1990s, especially titanium series and silver series of inorganic antibacterial agents are widely used in household appliances, building materials, textiles, daily necessities and other fields, but at the same time also exposed a series of problems. Although inorganic antimicrobials have the advantages of heat resistance, durability, continuity and safety, there are some disadvantages, such as silver antimicrobials, weak mildew protection, large amount of addition, high cost, easy discoloration and so on.And natural antibacterial agents because of the general sterilization effect, easy to decompose, poor heat resistance, plastic field is basically not used.For this reason, researchers have turned their eyes to the field of organic antimicrobials. Organic small molecule fungicides have the advantages of strong initial bactericidal power, immediate bactericidal effect and broad antibacterial spectrum, and both powder and liquid are relatively easy to disperse to resin, synthetic technology is relatively mature, relatively cheap, the disadvantage in heat resistance and safety is weaker than inorganic antimicrobials.

3, The necessary conditions of antimicrobial agents

First of all, the antibacterial agent used in plastics should have good antibacterial performance, on gram-negative bacteria (E. coli, etc.), Gram-positive bacteria (Staphylococcus aureus, etc.) with antibacterial activity, antibacterial rate of more than 90%;If there is a mildew prevention requirement, the mildew prevention grade of mixed mold should reach grade 0-1.Refer to 《QB/T 2591-2003 Antibacterial plastics antibacterial properties test method and antibacterial effect》, 《ASTM G-21 Standard Practice for Determining Resistance of Synthetic Polymeric Materials to Fungi; Materials to Fungi》;

Secondly, plastic products may often be used outdoors or in the environment with water, so when choosing antibacterial agents for plastics, we should fully consider the possibility of washing and dissolution of the products in the process of use, to ensure that the antibacterial properties of the products in the process of use to maintain adequate aging;

Third, weather resistance, heat resistance and antimicrobial stability in the process of processing and use is also a factor that should be considered when choosing plastic antimicrobial agents;

Fourth, the antibacterial agent and plastic matrix has the appropriate compatibility and migration, to ensure the long-term effectiveness of antibacterial plastic products;

Fifth, antibacterial agents will not have a negative impact on the performance or appearance of plastic products, and antibacterial agents should have storage stability or a certain service life;

Sixth, antibacterial agent is convenient to use, and at the same time to the human body, animals and the environment (including the production process and use environment) has better safety.

4, The development of antibacterial additives 

Focus on the development of organic polymer antibacterial agents, not only in-depth study of the antibacterial mechanism of these antibacterial agents, but also increase and resin polymerization method research, speed up the development of high efficiency broad spectrum, low toxicity, can be recycled cheap polymer antibacterial agents, especially organic polymer antibacterial materials masterbatch should be paid more attention and attention. Attach great importance to safety and environmental protection, as antibacterial materials widely used daily necessities and people's lives are closely related, in addition, a large number of antibacterial plastic products for export, developed countries and regions on the added additives safety and environmental protection requirements are relatively high, especially pay attention to some heavy metal ion components of antibacterial materials used in the field of food and daily use toxicity research, And waste antibacterial materials in some toxic components escape, caused by pollution to the environment.

Four, antibacterial plastic application field

1. The application of antibacterial plastics in tablecloth Tablecloth in wine restaurants, kitchen tables have a large number of applications, and very close contact with people.On the one hand, because the tablecloth has contact with all kinds of people, it will inevitably be contaminated with all kinds of mildew microorganisms;On the other hand, the rice residue on the tablecloth is also conducive to breeding a variety of germs, such as Staphylococcus aureus, Salmonella, Escherichia coli and other microorganisms that cause food poisoning.Human hands, bowls, chopsticks and tablecloth contaminated with mouldy microorganisms after contact, will cause cross infection of diners.Therefore, the use of antibacterial tablecloth can not only ensure its own cleanliness, but also help to prevent infectious diseases.

2. The application of antibacterial plastics in floor leather and wallpaper Plastic floor leather and wallpaper is the most used material in people's home, in the process of use is easy to deposit dirt, microbes, etc., this is on the one hand because plastic floor leather and wallpaper are easy to produce electrostatic adsorption dust and microorganisms, on the other hand is because plastic floor leather and wallpaper contain rich nutrients, in the right environment will make microorganisms multiply.Dust and microorganisms on floor leather and wallpaper will fly in the room with people's activities in the room or other reasons caused by air circulation, dispersed in the air, affecting people's health.Therefore, it is very important to prevent the harm of microorganisms on plastic floor leather and wallpaper.

3, Antibacterial plastic in other areas Household appliances, kitchen supplies, food packaging, stationery, auto parts, auto interior decoration, wire and cable, leather, paper, textile, building materials, wood and plasticcomposite materials and other fields.

Five, plastic organic antibacterial agent

Combat-tech manufactures antimicrobials classified according to their active components, including 10,10'-oxydiphenoxalphane (OBPA), 4,5-dichloro-noctylisothiazolinone (DCOIT), n-octylisothiazolinone (OIT),1,2-benzisothiazolin-3-one (BIT).All are organic compounds widely used in the soft PVC and polyurethane industries.They belong to the broad spectrum antibacterial agents. They are extremely effective against fungi, bacteria and algae. All have excellent heat resistance and can maintain good performance during the processing of soft PVC, polyolefin and polyurethane.

1. Combat OBPA (10, 10'-oxydiphenoxazine) :

This product is OBPA prepared with 5%DOTP. Physicochemical properties: OBPA belongs to organic arsenic compounds, pure product for gray white powder, has a certain irritating smell.Melting point 180~184℃, thermal decomposition temperature 300~380℃.Insoluble in water, in the general organic solvent solubility is small.

Safety: OBPA is a moderately toxic compound.In rats, the LD50 is 54mg/kg for acute transoral and 250mg/kg for acute transdermal.

Application: OBPA can be mildew, antibacterial, anti-algae at the same time, is one of the most cost-effective antibacterial agents in the industrial field.It can be added to PVC products, plastic products, PVC floor materials, wall paint, paint, Marine antifouling, ink, paper, cable and so on.The amount added to indoor and outdoor plastic products is generally 0.5-1%, and the mildew proof grade can reach 0.

Advantages and disadvantages: easy to apply, cost-effective.But there are some issues with security and it is currently banned in Europe.

2. Combat DCOIT, Combat BIT, or Combat OIT (Isothiazolinones)

Isothiazolinone DCOIT and OIT have broad antibacterial properties and are economical and less toxic alternatives to OBPA. The use of DCOIT and OIT in a variety of polymers, such as PVC flooring, wallpaper, roofing, and exterior decorations, has seen strong growth. This growth is due to the expansion of market demand and the replacement of OBPA by DCOIT and OIT. It is usually 20% DOTP as the carrier of DCOIT or OIT.

Physicochemical properties: DCOIT pure product is white powder, active ingredient >99.0%.Melting point: 42.2~42.8℃.Heat resistance above 250℃.Water solubility is relatively small, soluble in some organic solvents.Safety: DCOIT is a low toxic compound.Rat acute transoral LD50>2000mg/kg, rabbit acute transdermal LD50>2000mg/kg.

Application: DCOIT has special effects on fungi, algae and bacteria, has been widely used in paint, coatings, polyethylene, polyurethane, sewage, paper, wood and other fields, can also be used in adhesives, ink.The amount added in indoor and outdoor plastic products is generally 0.5-1.0%, and the mildew proof grade can reach 0.

Advantages and disadvantages: easy to apply, contain halogen, no heavy metals.

3. Combat BIT (1, 2-benzoisothiazolin-3-one) 

Physicochemical properties: pure white powder, soluble in alcohol, thermal stability is greater than 200℃, has good UV resistance.

Safety: BIT is a low toxic compound.In rats, LD50>2000 mg/kg for acute transoral and acute transdermal.

Application: BIT is used in polyurethane products such as plastic foams, washers, insulating materials, and PVC flooring and fabrics.Does not react with additives, does not affect product performance, thermal stability is greater than 200℃.Good UV resistance,

outdoor use will not fail.The amount added to indoor and outdoor plastic products is generally 0.5-1.0%, and the mildew resistance grade can reach level 0

Advantages and disadvantages: BIT does not contain halogen, heavy metals, chemical stability, and does not react with additives.