Antibiotics, antimicrobial agents, mold inhibitors, and fungicides. Antibiotics and fungicides are often referred to as preservatives. Regardless of the professional terminology used, the function of antibacterial agents is to protect polymer materials from microbial erosion. Polymers can affect their appearance after being corroded by microorganisms. Produce moldy odor, become brittle, and cause premature damage.
Most polymer materials are not susceptible to microbial erosion in their pure state without additives. However, when various additives are added, it is possible to promote microbial growth that leads to polymer degradation. Plasticizers, lubricants, and even some heat stabilizers belong to this type of additive. The most common polymer susceptible to microbial erosion is soft polyvinyl chloride, as it typically contains a large amount of such additives.
Improve the ability to resist microbial erosion
In order to improve the antibacterial ability of plastics, there are two main issues that need to be considered. One is the type of additives used in the formula. Reducing the amount of additives known to be susceptible to microbial erosion can give plastics certain antibacterial properties. Plasticizers are used to improve the flexibility of polyvinyl chloride. When selecting plasticizers, considering their antibacterial properties can help reduce the degree of plastic corrosion.
Practice has shown that certain plasticizers, such as phthalates, polyesters, citrate esters, and oxidized hydrocarbons, only slightly increase the corrosion resistance of soft polyvinyl chloride; Adipic acid esters, azelaic acid esters, and pentaerythritol esters have moderate corrosion resistance, as well as sebacates, epoxidized fats (soybean oil and tall oil), and glycerides. The use of non migratory plasticizers, such as tris (toluene) phosphate and polyester, can also help reduce the nutrients that microorganisms on the polymer surface rely on for survival.
The second is to effectively use antibacterial agents. In order for antibacterial agents to effectively exert their effects and prevent microbial growth on the surface of polymers, sufficient quantities of antibacterial agents should be allowed to migrate towards the polymer surface. But the migration speed should not be too fast or seep out of the polymer to avoid reducing the service life of plastic products. A certain amount of preservatives that do not migrate is also important for their effectiveness.
Liquid antibacterial agents suitable for various polymers such as soft polyvinyl chloride, acrylic resins, and siloxane adhesives, which are convenient to use and cost-effective, have been sold. They all have the advantages of good storage stability, good compatibility with pigments, and low shipping costs.
Selection of antibacterial agents
Several different antibacterial agents are used in polymers, among which the most commonly used are 2-octyl-4-isothiazoline-3-one and 10,10 '- oxodiphenyloxazone. Due to strict usage requirements, only a few can be used.
Because antibiotics are considered insecticides, they are all registered with the Environmental Protection Agency under the Federal Insecticides, Fungicides, and Rodenticides Act (FIFRA). All antibacterial agents are currently under the supervision of the Environmental Protection Bureau. Manufacturers of antibacterial agents must provide safety, efficacy, and usage data to the Environmental Protection Agency.
The effectiveness of antibacterial agents must be evaluated in all formulations. There are usually two methods for evaluating the ability to resist microbial erosion: controlled laboratory evaluation and on-site field testing.
Controlled laboratory evaluation is used to quickly determine the ability to resist microbial erosion. Through careful and controlled research, the degree of susceptibility of polymers to erosion can be quickly and easily detected. By appropriate control measures, the migration rate of antibacterial agents, the "natural" corrosion resistance of plastics without preservatives, and the effects produced by different amounts of antibacterial agents can all be detected.Laboratory pre testing
Before actual microbial testing, pre testing can be conducted in an artificial laboratory environment; The artificial environment is established by a carbon arc or weather o meter or Q-plate. This artificial climate is usually suitable for outdoor use. There are two testing methods for polymer materials. One is ASTM G21-85, "Determination of Antibacterial Properties of Synthetic Polymer Materials," which is a standard industrial testing method. It is based on bacteria extracting nutrients from polymeric materials, focusing on the protective properties of preservatives rather than their leaching ability.
The second testing method is ASTM E1428-91, "Evaluation of the performance of antimicrobial agents in solid polymers (or above) to prevent the formation of bacterial stains caused by the network structure of Streptomyces (pink spotted microorganisms)," commonly known as the pink spotted stain test. It targets the problem of diffusion and permanent spots left by byproducts of microbial metabolism in polymer blends. Under the testing conditions, the polymer comes into direct contact with the microorganisms that produce the stain and must prevent the spread of the stain.
For certain special purposes and environments, there are also other testing methods, such as soil burial tests or different microbial composite tests. Previously, some testing methods were based on the leaching ability of fungicides, known as the "inhibition zone", which was considered desirable. But now it is felt that they cannot reflect the vacuum antibacterial ability of polymer blends, especially in outdoor applications. The testing methods briefly introduced above do not require such evaluation.
Outdoor exposure is also used to evaluate the performance of antimicrobial agents in actual environments. Most of these testing sites are located in Florida and Arizona. Due to the high humidity in Florida, it is more conducive to bacterial growth and is therefore more suitable for outdoor exposure testing. The limiting factors for conducting such tests are the long required time (usually several months) and the unpredictability of the environment.
