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Water Pollutants and Water Pollution
Published in Stanley E. Manahan, Environmental Chemistry, 2022
Another class of emerging pollutants consists of siloxanes (commonly called silicones), including octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, and dodecamethylcyclohexasiloxane. Siloxanes are thermally and chemically very stable, leading to their uses as coolants in transformers, protective encapsulating materials in semiconductors, lubricants, coatings, and sealants. Siloxanes are widely used in personal care products, including deodorants, cosmetics, soaps, hair conditioners and hair dyes, and other products such as water repellent windshield coatings, detergent antifoaming agents, and even food additives. Siloxanes are resistant to biodegradation and as a result are encountered in water that has received wastewater.
Mechanism, Anti-Corrosion Protection and Components of Anti-Corrosion Polymer Coatings
Published in Sanjay Mavinkere Rangappa, Jyotishkumar Parameswaranpillai, Suchart Siengchin, Polymer Coatings, 2020
Akarsh Verma, Naman Jain, Shweta Rastogi, Vaishally Dogra, Sanjay Mavinkere Sanjay, Suchart Siengchin, Rokbi Mansour
Siloxane: Siloxanes are the polymers made up of silicone–oxygen (Si-O) backbone in which each silicone atom has phenyl, methyl or ethyl group and occurs in both linear and cyclic forms, as shown in Figure 4.6. Siloxane coating films have superior colour and gloss retention, ultraviolet resistance and low VOCs emission, but on the other hand it suffers from low mechanical properties due to their brittle nature. As seen from its chemical structure, siloxanes are already in oxide state; therefore, it prevents further oxidation. Polysiloxane may also react with organic compounds or metals to form hybrid coating to overcome the limitation and increase industry application. In 2005, Ahmed et al. [60] fabricated the siliconized epoxy matrix by blending epoxy resin (bisphenol A) with polydimethyl siloxane (hydroxyl-terminated) by employing open-ring polymerization technique. Results show that coating film had good high gloss value and colour retention and also resists to acidic, organic solvent and saline environment. Many researchers also studied inorganic zinc silicate for coating of metallic substrates as anti-corrosion coating. Corrosion resistance is obtained through cathodic protection of zinc silicate, and curing mechanism takes help of atmospheric moisture [61]. Minimum RH of about 50%–60% is required to perform the curing process [62]. Reaction between steel substrate and metallic zinc will occur to some extent.
Water Pollutants and Water Pollution
Published in Stanley Manahan, Environmental Chemistry, 2017
Another class of emerging pollutants consists of siloxanes (commonly called silicones) including octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, and dodecamethylcyclohexasiloxane. Siloxanes are thermally and chemically very stable, leading to their uses as coolants in transformers, protective encapsulating materials in semiconductors, lubricants, coatings, and sealants. Siloxanes are widely used in personal care products including deodorants, cosmetics, soaps, hair conditioners and hair dyes, and other products such as water repellent windshield coatings, detergent antifoaming agents, and even food additives. Siloxanes are resistant to biodegradation and as a result are encountered in water that has received wastewater.
Recent advances in research on cyclic volatile methylsiloxanes in sediment, soil and biosolid: a review
Published in Chemistry and Ecology, 2018
Maocai Shen, Yaxin Zhang, Ye Tian, Guangming Zeng
Siloxanes are composed of alternating silicon–oxygen (Si–O) units and each silicon atom may be linked with methyl, ethyl, phenyl or hydrogen atoms; silicon and oxygen atoms can link into cyclic structure and, based on the International Union of Pure and Applied Chemistry (IUPAC), these compounds were named as cyclic siloxanes. Cyclic volatile methylsiloxanes (cVMS) are generally expressed as Dn (n means the number of silicon atoms) [1,2]. Usually, three low molecular weight cVMS, namely octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexasiloxane (D6), were used in industrial applications and added in personal care products (PCPs) due to their special properties such as hydrophobic nature, low water solubility and surface tension, high volatility, transparency, high thermal stability and lack of smell [3–6]. cVMS were extensively used as alternative solvent in some electronic industry [7]. According to the information from the United States Environmental Protection Agency (USEPA) and the Organization for Economic Cooperation and Development (OECD), D4, D5 and D6 have been scheduled as a high production volume chemical [8,9]. The total use volume was more than 70 t in Sweden in 2002 and 20 t in 2003 for D4, D5 and D6 [10]; the usage of D4 and D5 were about 80 and 50 t in 2003 in Denmark and Norway, respectively [11]. Moreover, the total annual import volumes were more than 100 t for D4, D5 and D6 in 2006 in Canada, respectively [12]. The identities and structures of three cVMS are shown in Table 1.
Enhanced mechanical, thermal and adhesion properties of polysilsesquioxane spheres reinforced epoxy nanocomposite adhesives
Published in The Journal of Adhesion, 2021
Anoop V, Subramani Sankaraiah, S. N. Jaisankar, Sohini Chakraborty, Mary N.L
Reinforcing additives such as graphene oxide, silica, carbon black, fibers and other inorganic metal oxides with sizes ranging from nano to micron have been added to the epoxy resin to enhance the overall application performance.[31–33] Here, nano-sized polysilsesquioxane (PS) sphere was synthesised from two different trifunctional organosilanes to be used as an additive to the epoxy resin. Due to the presence of the siloxane bond in its structure, it shows excellent heat resistance, hardness and electrical properties.[34,35] When compare to other fillers PS particles contain organic constituents on their external surface, which can make them compatible with many polymers and give the dispersion stability in polymer matrix.[36]
Protecting human health and the environment against siloxanes: The role and effectiveness of wastewater treatment technologies
Published in Critical Reviews in Environmental Science and Technology, 2023
Andres E. Ortiz-Ardila, Juan D. Restrepo, Largus T. Angenent, Joseph G. Usack, Rodrigo A. Labatut
Siloxanes are chemical compounds with silyl ether bonds that form monomers, dimers, trimers, oligomers, or polymers (Wang et al., 2019). A typical siloxane molecule consists of two organosilane units linked by two silicon–oxygen (Si–O) bonds (Yentekakis & Goula, 2017) (Figure 1). These molecules are considered recalcitrant due to the high energy required to break their molecular bonds (Figure 1), especially the Si–O bond in cyclic molecules, which is needed to open the siloxane ring and allow further degradation. Moreover, Si–O bonds are shielded by a steric hindrance produced by the cloud of electrons from the methyl groups of the organosilane molecules, providing chemical stability and additional resistance to hydrolysis.