Microbial Paints

Paints Raw Materials: Analytical Characterization and Microbial Pigments

Introduction

Paints serve both protective and decorative purposes for various surfaces. The paint's ability to meet desired requirements depends on the properties of raw materials used in paint production, which play an important role in the paint's environmental impact, quality, and safety. Depending on the application surface, water or solvent-based products are used to facilitate application. As the paint dries on the applied surface, the solvent evaporates and resins (solvent or water-based) cure, allowing the paint to establish physical and chemical bonds with the surface. Pigments generally preferred for decorative purposes also have applications as fillers or additives. TiO2, the primary white pigment, possesses excellent opacity. Carbon black is commonly used as the black pigment. Other pigment materials include iron oxide and cadmium sulfide for red color, metallic salts for yellow and orange hues, iron blue for blue color, and chrome yellow for achieving green color—the most preferred compounds. Fillers such as calcium carbonate, aluminum silicate, talc, and kaolin reduce costs while providing paints with flexibility and strength properties. Additives facilitate both paint production and surface application (Figure 1).

Analytical Characterization of Paint Raw Materials

Foam generated during paint production and application is eliminated using antifoaming agents because it complicates dispersion, increases costs, and causes surface defects. The effectiveness of antifoaming agents can be determined in a simple test setup using a graduated cylinder. Functional groups present in the structure of antifoaming agents can be detected using FTIR spectroscopy technique (Figure 2) [1]. When antifoaming agents are deficient or excessive, defects such as fish-eye, pinhole, orange peel, and crater formations are observed. These defects can be more clearly seen under a stereomicroscope. Dispersant additives ensure homogeneous distribution of pigments and fillers within the paint and are used together with wetting agents (surfactants). High wetting rates of pigments and fillers proportionally increase the color strength of pigments. Rheology and viscosity tests help determine the wetting properties of dispersants and fillers. Additionally, using Zeta Potentiometer and Particle Size Analyzer (Mastersizer), the effect of wetting agents on pigment and filler wetting rates can be observed depending on the paint's pH. Using FTIR spectrometry, functional structures formed between pigments and resins, solvents, additives, and fillers can be examined to determine the effect of each substance. Impurities in inorganic pigments and fillers (calcium carbonate, talc, etc.) are identified using XRD and XRF analysis techniques. SEM and EDX analysis are used to determine both surface morphology and elemental content of pigments and materials (Figure 3). The absorption capacity of fillers for solvents and other liquid additives is examined using BET surface area measurement equipment. For detecting organic content in the structure of solvents and resins, GC, GC-MS, HPLC, and LC-MS/MS instruments from the chromatography family are commonly preferred. After paints complete application and drying processes, color and gloss tests are performed. To determine effectiveness against environmental conditions and UV radiation, conditioning and UV resistance tests are carried out. Corrosion and strength tests should also be applied depending on the surface to which the paint is applied. Cracks and yellowing that may form on the paint surface are observed under SEM analysis and stereomicroscope. Special-purpose paints used in different fields are those providing thermal insulation, acoustic absorption, and antibacterial properties. Thermal insulation paints are particularly preferred in extremely hot and cold regions where energy efficiency is important [4]. Acoustic absorbing paints have been developed to address noise pollution, one of today's major problems.

Microbial Pigments

Because some chemical compounds used in synthetic paints are toxic, mutagenic, carcinogenic, and allergenic, interest is increasingly growing in non-toxic, safe, and naturally derived compounds and paints easily obtained from living organisms [5]. Natural pigments are obtained from plant, animal, or microbial sources. Obtaining pigments from animal sources is costly and difficult. While obtaining pigments from plant sources is simple and inexpensive, it has disadvantages such as changes in climate conditions and unavailability for production every season. Bacterial pigments, in contrast to plant pigments, have major advantages: their production is not seasonally affected, they are easily produced under laboratory conditions, high yields can be obtained, and the microorganisms producing them grow rapidly [6]. Additionally, their biodegradability and environmental friendliness are important for a sustainable world. Pigments produced by microorganisms are not necessary for the microorganisms' basic life functions but are secondary metabolites that make microorganisms resistant to various biological agents and stress conditions. Beyond their benefits to microorganisms, many pigments have been shown to possess antimicrobial properties. Consequently, pigments used as paint additives can impart antimicrobial properties to the produced product. The color range of pigments obtained from microorganisms is quite wide, and the positions of some bacterial pigments in the Munsell color system have been determined [7]. Numerous pigment-producing bacteria have been identified to date, and their pigment production processes have been optimized (Table 1). In developed countries, pigments obtained from microorganisms are used in many industries. They are used as colorants in paints, cosmetic products, inks, and papers. In the textile industry, the red prodigiosin pigment obtained from Serratia marcescens is used in dyeing acrylic, polyester, silk, and cotton fabrics [8]. Similarly, the purple violacein pigment produced by Janthinobacterium lividum has been noted to be usable in the production of antimicrobial polyamide fabrics [9]. Additionally, they are used in the food industry both as colorants and to provide antimicrobial properties [7]. In conclusion, due to toxicity problems caused by synthetic pigments, with increased demand for natural pigments, numerous pigment-producing bacteria have been identified, culture conditions and fermentation media have been optimized, and large-scale production of pigments has been achieved.

Fermentation and Production Processes

Compared to developing global market needs, microbial pigment production volume today remains lower than synthetic paints. By applying various biotechnological tools, there is greater potential to increase total production volume to meet market demands. Commercial pigment production is made possible through the combination of genetic engineering technologies with fermentation technologies. In this context, gene, protein, and metabolic engineering to increase the biosynthetic performance of microorganisms, genome shuffling and scale-up of production, and fermentation strategies play vital roles in the cost-effective and highly stable, maximum, and environmentally friendly production of microbial pigments [7]. Optimization of fermentation conditions and development of cost-effective downstream processes can enable cost-effective production of microbial pigments. Medium optimization includes changes in fermentation conditions such as temperature, pH, incubation time, nutrient sources, aeration, and agitation rate to select conditions that provide optimal yields. Response surface methodology (RSM) has many advantages over classical methods used for medium optimization and requires fewer experiments to obtain an optimal combination of all examined variable factors. Artificial neural networks (ANN) is another technique that can be used to examine the effect of fermentation conditions in addition to optimization for microbial pigment production. Optimization of fermentation conditions thus requires less time and effort, leading to reduced overall costs [10].     References [1] A. Hassan, K. Jumbri, A. Ramli, N. Borhan, Physio-Chemical Analysis of Amide and Amine Poly(dimethylsiloxane)-Modified Defoamer for Efficient Oil-Water Separation, ACS Omega. 6 (2021). https://doi.org/10.1021/acsomega.1c00350. [2] S. Sahebian, S.M. Zebarjad, S.A. Sajjadi, Z. Sherafat, A. Lazzeri, Effect of both uncoated and coated calcium carbonate on fracture toughness of HDPE/CaCO3 nanocomposites, J Appl Polym Sci. 104 (2007). https://doi.org/10.1002/app.25644. [3] P. Wedin, J.A. Lewis, L. Bergström, Soluble organic additive effects on stress development during drying of calcium carbonate suspensions, J Colloid Interface Sci. 290 (2005). https://doi.org/10.1016/j.jcis.2005.04.020. [4] Ş. Balbay, Low-Cost and High-Energy-Savings Thermal Paint Production, Konya Journal of Engineering Sciences. 8 (2020) 693–705. https://doi.org/10.36306/konjes.643725. [5] F.M. Drumond Chequer, G.A.R. de Oliveira, E.R. Anastacio Ferraz, J. Carvalho, M.V. Boldrin Zanoni, D.P. de Oliveir, Textile Dyes: Dyeing Process and Environmental Impact, in: Eco-Friendly Textile Dyeing and Finishing, 2013. https://doi.org/10.5772/53659. [6] M. Aman Mohammadi, H. Ahangari, S. Mousazadeh, S.M. Hosseini, L. Dufossé, Microbial pigments as an alternative to synthetic dyes and food additives: a brief review of recent studies, Bioprocess Biosyst Eng. 45 (2022). https://doi.org/10.1007/s00449-021-02621-8. [7] C.K. Venil, L. Dufossé, P. Renuka Devi, Bacterial Pigments: Sustainable Compounds With Market Potential for Pharma and Food Industry, Front Sustain Food Syst. 4 (2020). https://doi.org/10.3389/fsufs.2020.00100. [8] X. Liu, Y. Wang, S. Sun, C. Zhu, W. Xu, Y. Park, H. Zhou, Mutant breeding of serratia marcescens strain for enhancing prodigiosin production and application to textiles, Prep Biochem Biotechnol. 43 (2013). https://doi.org/10.1080/10826068.2012.721850. [9] M. Kanelli, M. Mandic, M. Kalakona, S. Vasilakos, D. Kekos, J. Nikodinovic-Runic, E. Topakas, Microbial production of violacein and process optimization for dyeing polyamide fabrics with acquired antimicrobial properties, Front Microbiol. 9 (2018). https://doi.org/10.3389/fmicb.2018.01495. [10] B. Rana, M. Bhattacharyya, B. Patni, M. Arya, G.K. Joshi, The Realm of Microbial Pigments in the Food Color Market, Front Sustain Food Syst. 5 (2021). https://doi.org/10.3389/fsufs.2021.603892.   Assoc. Prof. / Şenay Balbay - Bilecik Şeyh Edebali University Central Research Laboratory Application and Research Center (BARUM)   Asst. Prof. / Ardahan Eski - Bilecik Şeyh Edebali University Central Research Laboratory Application and Research Center (BARUM) Assoc. Prof. / Rafig Gurbanov - Bilecik Şeyh Edebali University Central Research Laboratory Application and Research Center (BARUM)