Control of microbial contamination of waterborne adhesives and selection of preservative and mildew agent

【Abstract 】 According to the production process of water-based adhesive, product performance characteristics, the study of microbial pollution to the glue, analysis of microbial types, the establishment of suitable for the product of anti-mildew system, how to correctly use anti-mildew agent, in order to solve the problem of colloidal mildew

【Key words 】Water-based adhesive, polyvinyl alcohol starch, microbial anticorrosion and anti-mold compatibility

Water-based (emulsion) adhesives include polyvinyl alcohol water-based adhesives, vinylacetate water-based adhesives, acrylic water-based adhesives, polyurethane water-based adhesives, epoxy water-based adhesives, phenolic water-based adhesives, silicone water-based adhesives, rubber water-based adhesives.Due to its small odor, non-flammable, non-explosive, non-toxic and pollution-free, wide bonding range and other characteristics, it is widely used in construction, packaging, automobile, footwear, daily use, packaging and printing and dyeing industries.In recent years, with the development of building materials decoration and other industries, the national requirements for environmental protection is increasing, the amount of water-based adhesive is becoming larger and larger, due to the water-based (emulsion) adhesive contains a large number of organic matter, polymer materials and water and other microbial substances, the microorganisms in the environment once entering, will rapidly reproduce at the appropriate temperature, Resulting in mildew, viscosity decline, discoloration, odor, gas production, PH value change and so on leading to the loss of use value of commodities.The application of bactericidal preservative is an important means to prevent the deterioration of adhesives, it can kill, inhibit and hinder the growth and reproduction of microorganisms, emulsion is damaged by microorganisms.According to the production and technological characteristics of adhesives, we have studied the link of microbial pollution, the methods and means of controlling microbial pollution, according to the bactericidal mechanism of microorganisms, for the adhesive products produced with nutrients raw materials, choose the appropriate antiseptic and mildew agent, applied in industrial production, and obtained good results.

1. Analysis of microbial content

1.1 According to ISO9252-1989 (E) synthetic latex microbial analysis method, bacteria classification culture with common nutrient AGAR (30±2) ℃ culture for 24-48 hours; Mold (yeast) was cultured at PDA (25±2) ℃ for 3-5 days.

1.2 ISO4833-2003 total colony detection method sample Xg/ml+9XmL diluent (phosphate buffer) → appropriate tenfold dilution sample → choose 2-3 consecutive suitable dilution, Take 1mL each and add them into the sterilization plate (do two parallel for each dilution) →→ add appropriate amount (12-15mL) plate counting AGAR (PCA) (30±2) ℃, 72±3h→→ colony counting.

1.3 GB4789.2-2010 "Food safety national standard food microbiology test total colony determination", the tested sample made into several different 10 times increasing diluent, and then from each diluent were taken out of 1mL in the sterilization dish and nutrient AGAR medium mix, at a certain temperature, after a certain time (generally 48 hours), Record the number of colonies formed in each plate, and calculate the total number of bacterial colonies per gram (or per ml) of the original sample according to the dilution ratio.

2. Microbial population identification

2.1 Mold according to GB4789 16-94 (Identification of common mold), "Common and Commonly Used Fungi" and "Aspergillus and its Related Sexual types" Volume 5 of the Annals of Chinese Fungi.

3. Determination of anti-corrosion and mildew resistance of adhesives

3.1 To simulate the environment of microbial growth and reproduction in nature, design according to the characteristics of microbial reproduction, and investigate the antikilling effect of anti-corrosion and anti-mold agent on water-based adhesive.

3.2 Experimental strains

3.2.1 Standard bacteria

Escherichia coli ATCC25922, Staphylococcus aureus ATCC6538, Pseudomonas aeruginosa ATCC9027, Aerobacter GIM1.108, alkaline bacillus faecalis GIM1.60 and Subaureococcus aureus GIM1.59

3.2.2 Standard mold

Test procedure of Aspergillus Niger, Aspergillus flavus, Aspergillus variegata, Trichoderma green, Pedunculus bredontii, Pachyderma globules, Penicillium orange, Penicillium tetanum, Penicillium Penicillium and Candida albicans The adhesive with good packaging and no microbial contamination was divided into 5 samples of 100g, and then inoculated with 1ml mixed bacterial solution (108- 109cfu/ml) or 1ml mixed mold spore solution (10⁷- 10⁸cfu/ml), stir well, then store the sample at room temperature (25±2℃), and determine the content of live bacteria and live mold in the sample on day 7, day 14, day 21 and day 28, respectively (perform according to Method 1.2).

4. Results and Discussion

4.1 Destruction of water based (emulsion) adhesives by microorganisms

Water based (emulsion) adhesive is usually acrylic ester, butadiene, vinyl acetate and styrene monomer polymerization of water-based emulsion, and then add color paste, dispersant, defoaming agent and thickening agent.These substances are the nutrients of microbial growth and reproduction, as long as the ambient temperature is appropriate, bacteria, mold (yeast) once into the person will multiply and destroy the performance of the product.According to the research on the spoilage adhesives, the destruction effect of microorganisms on water-based (emulsion) adhesives is mainly shown in the following table.

Table 1. Destruction of microorganisms on water-based (emulsion) adhesives

4.2 Effect of microbial content on the quality of water-based (emulsion) adhesives

Due to the differences in the composition and pH of adhesives, the microbial content also varies greatly.Some of the components of the adhesive microbial decomposition is easy to use, generally 1 to 5 days will appear discoloration, odor, its microbial content will also reach 24-72 hours (10⁶-10⁸)cfu/ g.However, the microbial decomposition and utilization of some adhesive components are slow, generally 15-30 days before pH changes and stratification, and the microbial content will gradually increase from 10³cfu/g increases to 10⁶ Above cfu/g.

4.3 Major population of microorganisms that contaminate water-based (emulsion) adhesives 

The main microbial species that cause the deterioration of water-based (emulsion) adhesives are shown in Table 2.

Table 2 Main populations of microorganisms contaminated by water-based (emulsion) adhesives

4.4 Testing of anti-corrosion efficacy in tanks of water-based (emulsion) adhesives - microbial attack challenge test
Water-based adhesives are prone to microbial contamination, and should be produced with high efficiency, broad spectrum, low toxicity, good stability, and good compatibility with the adhesive anti-corrosion and mildew agent.At present, the most commonly used germicidal preservatives at home and abroad are isothiazolinone compound series such as Kathon 886, Acticide MBR, Nicapide BSM and so on. In this experiment, domestic products COMBAT MBS 05 and COMBAT MV, which have good compatibility with domestic adhesives and obvious mildew anti-corrosion effect, meet the requirements of water-based adhesive adding process and are easy to use, were used for comparison experiment.
4.4.1 The microbial attack challenge test results table was made for the water adhesive with different anti-mildew additives and blank samples

[Standard mold] Aspergillus Niger, Aspergillus aflatus, Aspergillus variegata, Trichoderma green, Pedunculus breeders, Pachyderma globules, Penicillium dorsalis, Penicillium tetanum, Penicillium, Candida albicans
4.4.2 The number of live bacteria or mold is more than 10⁵ cfu/g indicates that the sample has been contaminated by microorganisms. The anti-corrosion system cannot effectively suppress bacteria or mold, and the product is prone to quality problems during production, storage and use.
4.4.3 Live bacteria or mold count is less than 10³ cfu/g indicates that the sample can pass the challenging test of microbial attack, indicating that the preservative system has played an effective bactericidal role against bacteria or mold, and the product will be produced, stored and used without quality problems.
4.4.4 In the water-based adhesive, the application of anti-corrosion and mildew agent is an important means to prevent the deterioration of water-based adhesive products, which can kill, inhibit and hinder the growth of microorganisms.

5. Conclusion
5.1 Water based (emulsion) adhesives are easy to be contaminated by microorganisms and have various spoilage, which makes them lose their use value.Generally speaking, the microbial content is less than or equal to 103cfu/g, a mild pollution;Microbial content 10³- 10⁵When cfu/g, it is moderately polluted;Microbial content >10⁵cfu/ g, belongs to serious pollution, at this time the adhesive will produce odor, discoloration and other corruption and deterioration.
5.2 To effectively prevent and control the microbial pollution of the adhesive, we should not only pay attention to the microbial content of the raw material itself, but also pay attention to the cleaning and disinfection measures of the production equipment and production environment.On the one hand, some of the raw materials of the adhesive, such as emulsion, starch, cellulose and production water, are easy to breed all kinds of microorganisms, which is one of the important microbial pollution sources of the finished adhesive;If the raw material microbial content is more than 10⁵cfu/g, it is recommended to replace the material before use.On the other hand, the adhesive production workshop is open, and the production and canning are directly exposed to the air. The pipeline is very long, and often turns and dead corners;Microbial infection in each link of production is an important source of pollution of adhesive products.

5.3 Establish an effective anti-corrosion system: adding a broad-spectrum and highefficiency preservative to the water-based (emulsion) adhesives is a very important means to avoid product spoilage.In practical application, the biological effect of antiseptic is affected by many factors such as the composition and pH of the adhesive.
5.4 Anti-corrosion efficacy test - microbial attack challenge test: At present, the most effective method to test the anti-corrosion and mildew in the adhesive tank at home and abroad is the microbial attack challenge test.This method simulates the growth and reproduction conditions of natural microorganisms, and uses the dynamic change of microbial number within 28 days to preliminatively evaluate the anti-microbial effect of preservatives in adhesives, greatly speeding up the screening process of the anticorrosion system in the tank of adhesives.Generally speaking, the test and evaluation method has great reliability, but due to regional climatic conditions and the actual production, transportation and storage of adhesives and other environmental conditions differences, the actual anti-microbial pollution ability of adhesives is still to be verified in practice.

6. The selection of anti-corrosion and anti-mold agent
6.1 Fungicides are prone to develop resistance after 3-5 years of use, and should be updated to ensure their bactericidal effect.Therefore, we should always cooperate with antiseptic and mildew agent engineer to adjust the germicidal formula to prevent product deterioration caused by the reduction of antiseptic and mildew agent effect caused by microbial resistance.
6.2 Some of the most toxic antiseptic and antifungal agents, such as formaldehyde, sodium pentachlorophenol, arsenic and heavy metal, have good anti-microbial effect and low cost, but they do great harm to human body and the environment.From the point of view of protecting the environment and human health, it is necessary to prohibit or use a small amount of toxic fungicides. Environmental protection products that are harmless to human body and friendly to the environment should be adopted to improve the quality of products.

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