Contents lists available at ScienceDirect Progress in Organic Coatings journal homepage: www.elsevier.com/locate/porgcoat Functionalized nanosilica as an antimicrobial additive for waterborne paints P. Dileep a , Sinto Jacob b , Sunil K. Narayanankutty a, * a Department of Polymer Science and Rubber Technology, Cochin University of Science and Technology, Kerala, Pin-682022, India b Department of Chemistry, St. Aloysius College, Elthuruth, Thrissur, Kerala, Pin-680611, India ARTICLE INFO Keywords: Waterborne paint Nanosilica Biocide Surface modification ABSTRACT Waterborne paints are sensitive to humidity and susceptible to microbial attack. To prevent aesthetic bio-de- terioration, biocides are used. Some of these biocides leach out from paint film during aging. In this paper, we report the use of functionalized nanosilica as a non-leaching biocide. We used nanosilica (NS), nanosilica modified with p-nitrophenol (PNP-NS) and silica fume (SF) as antimicrobial agents in commercial waterborne paint at 0.5–2.5 % of total solid content in paint. It was observed that 2 % PNP-NS improved the antifungal properties by 100 % and 13 % compared to the control sample and commercial antifungal paint, respectively while the antibacterial property was improved by 50 % and 19 %, respectively. The algal defacement test showed more predominant values for paint with PNP-NS compared to paint with NS, SF, and commercial an- tifungal paint. The X-cut adhesion, hardness, opacity and water resistance of the dry paints were evaluated after application. The viscosity and opacity of paint films were not much affected by the additives NS and PNP-NS upto 2 %. Improved X-cut adhesion, hardness and water resistance were achieved with NS and PNP-NS. This study demonstrates that NS and PNP-NS are good additives to improve the antifungal and antibacterial prop- erties of waterborne commercial paints. 1. Introduction Paint is a dispersed pigmented liquid, mastic or powder coating material, consisting of different organic and inorganic ingredients and forms a solid film when applied to a surface as a thin layer. Deterioration and aesthetic biodegradation of paint film due to de- position of dust, mechanical rupture, enzymatic activity, microbial colonization, weathering process, etc. are major challenges [1,2]. Wa- terborne paints are attacked by microbes as they contain water and organic materials, which could act as the nutrients for the micro- organisms [3,4]. Biocides (antifungal agents) are added to paint to in- hibit the growth of microorganisms on the surface of the paint film [5]. The most commonly used biocides in paint industries are [N-cyclo- propyl-N-(1,1-dimethylethyl)-6-(methylthio)-1,3,5-trizaine-2,4dis- mine], 3-Iodo-2-propynyl N-butylcarbamate, Tetra- chloroisophthalonitrile, Zinc pyrithione etc. They are used either individually or in combinations to make the product more durable [6]. Some of the biocides leach out from paint film when exposed to rainwater causing environmental pollution and health hazards such as allergy, asthma and immunological reactions [7]. The leaching gradu- ally reduces the biocide content of the film leading to the growth of microorganisms on the film [8,9,10]. Carbendazim, OIT, and Diuron combination have been in use for exterior surface protection for many years [11,12] because of the strong fungicidal activity of carbendazim, an active algaecidal function of OIT and active agrochemical herbicide action of Diuron. Recently the use of this combination is restricted due to their toxic and carcinogenic effect on environment and health [13]. To overcome the drawbacks such as leaching, pollution, low dur- ability and high cost the old organochlorides and organometallic compounds based biocides are replaced by solid porous materials. These porous materials can encapsulate and stabilize the molecules of biocides inside their pores and increase the efficiency of biocide [14,15,16]. Incorporation of inert inorganic nanoparticles can improve the wear-resistance and antibacterial properties of organic coatings [17]. Silver and copper have been used as antimicrobial fillers in coatings to prevent fungal and bacterial attacks [18,19]. Zirconia compounds have wide range of applications like dental implants, paints, etc. due to better biocompatibility, antifungal, antibacterial property and low toxicity [20,21,22]. J. Eversdijk et al. [23] have shown that the intercalation of biocides in nano-clay particles results in their controlled release in service. A. Kamtsikakis et al. [24] studied the possibility of en- capsulating antifouling compound Zinc pyrithione in biodegradable https://doi.org/10.1016/j.porgcoat.2020.105574 Received 15 October 2019; Received in revised form 5 January 2020; Accepted 28 January 2020 ⁎ Corresponding author. E-mail address: sncusat@gmail.com (S.K. Narayanankutty). Progress in Organic Coatings 142 (2020) 105574 0300-9440/ © 2020 Elsevier B.V. All rights reserved. T