CHAPTER ONE
INTRODUCTION AND LITERATURE REVIEW
1.1 Introduction
Bisphenol A (BPA) is a synthetic chemical that was originally developed for use as a syntheticoestrogen. It is now one of the highest-volume chemicals produced in the world, with over sixbillion pounds manufactured each year (Welshons et al.,2007). Bisphenol A is used as a monomer in the manufacture of polycarbonate plastics, in the resin lining of food and beverage cans, as a component of dental sealant, in digital media such as CDs and DVDs, and as an additive in other types of plastics (Kang et al.,2006).
The first reported synthesis of Bisphenol A was in 1905 (Zincke.,1905). Bisphenol A was first used in epoxy resin in1939 and in 1966 was incorporated into vinyl ester polymers (Plastics Historical Society., 2007).Large-scale production of BPA began in the late 1950s, when commercial uses for polycarbonate plastics and epoxy resins weredeveloped.
Bisphenol A (BPA) is a high production volume (HPV) chemical (Caunter et al.,2000). Humans appear to be exposed primarily through food packaging uses of products manufactured using Bisphenol A, although those products account for less than 5% of the Bisphenol A used in this country. Releases of BPA to the environment exceed one million pounds per year (Crian et al.,2007).
Bisphenol A (BPA) is an organic compound with the chemical formula (CH3)2C(C6H4OH)2 and IUPAC name:4,4(propane-2,2-diyl)diphenol. It is a colourless solid that is soluble in organic solvents but poorly soluble in water, having two phenolfunctional groups. (Biello., 2008).
BPA may enter the environmentthrough possible physical and chemical breakdownduring disposal and recycling operations within wastewater treatment plants (WWTPs)and also by release from manufacturing industries.Industrial releases of Bisphenol A to the environment are likely to come from wastewaters and washing residue produced during production and processing of products,fugitive dust freed during handling and minor volatilization losses during manufacturing (Mohapatra,2010).
Bisphenol A is a ubiquitous environmental contaminant (Munn et al.,2003). It has been found in the wastewater from factories that produce plastics, beverage or food cans etcand has been identified as the compound responsible for the majority of estrogenic activity of landfill leachate (Welshons et al.,2006).
One of the main sources of Bisphenol A is untreated urban wastewater Treatment Plants (Korner et al., 2000). Most current Wastewater Treatment Plants are not designed to eliminate someemerging contaminants such as Bisphenol A. As a result high portion of emerging contaminantsincluding Bisphenol A enter the aquatic environment via sewage effluents.It can also be found in surface water, sewage effluents, sludge, and treated wastewater discharge. Its presence in sewage effluent means that it is released to rivers and lakes, where it becomes available to aquatic species, including many different species of fish.
In general, studies have shown that BPA can affect growth, reproduction and development in aquatic organisms. Among freshwater organisms, fish appear to be the most sensitive species. Bisphenol A can enter the environment either directly or through degradation of products, such as ocean-borne plastic trash. As an environmental contaminant, Bisphenol A interferes with nitrogen fixation at the roots of leguminous plants associated with the bacterialsymbiont (Sinorhizobium meliloti). The main objective of this present study is to know the various effect of BPA and concentration at which if present in the environment can be harmful and the possible ways of reducing its effects.
1.2 Literature Review
1.2.1 Background of Bisphenol A
Bisphenol A (BPA) is an important industrial chemical that is used primarily to make polycarbonate plastic and epoxy resins, both of which are used in a wide variety of applications. For example, polycarbonate is used in eyeglass lenses, medical equipment, water bottles, digital media (e.g. CDs and DVDs), cell phones, consumer electronics, computers and other business equipment, electrical equipment, household appliances, safety shields, construction glazing, sports safety equipment, and automobiles. Among the many uses for epoxy resins are industrial floorings, adhesives, industrial protective coatings, powder coatings, automotive primers, can coatings and printed circuit boards.(Kang et al.,2006).
1.2.2 Synthesis of Bisphenol A
Bisphenol A was first synthesized by the RussianChemist A.P. Dianin in 1891(Dianin 1891).This compound is synthesized by the condensation of acetone with two equivalents of phenol. The reaction is catalyzed by a strong acid, such as hydrochloric acid (HCl) or sulfonated polystyrene resin.
(CH3)2CO + 2 C6H5OH → (CH3)2C(C6H4OH)2 + H2O
Equation of Bisphenol A Reaction
Fig1.1: Shows the Structure of Bisphenol A
The first reported synthesis of Bisphenol A was from Thomas Zincke of the University of Marburg, Germany. Zincke acknowledged that the synthesis of BPA, from phenol and acetone, was based on chemical reactions previously reported by others as well as unpublished work (from thesis dissertations) conducted at the University of Marburg. His paper reporting the synthesis of Bisphenol A and a number of related compounds was published in 1905(Zincke., 1905). Zincke reported key physical properties of Bisphenol A (e.g., molecular composition, melting point, solubility in common solvents) but did not propose any application or use for BPA or the other materials he synthesized.
1.2.3 Physicochemical Characteristics of Bisphenol A
Molecular formula- C15H16O2
Molar mass- 228.29 g mol–1
Density – 1.20 g cm–3
Water solubility- 25oC mg/mL
Melting point- 153 °C
Boiling point- 220 °C (493 K) / 4 mmHg °C
Vapor pressure- 87 Pa (190°C)
Appearance – White crystalline solid
(Source: – Lang et al., 2008)
1.2.4 Sources and Usesof Bisphenol A
Bisphenol A is used primarily to make plastics, and products using bisphenol A-based plastics have been in commerce use since 1957 (Allan et al., 2010). At least 8 billion pounds of Bisphenol A are used by manufacturer. It is a key monomer in production of epoxy resin and in the most common form of polycarbonateplastic . The overall reaction to give polycarbonate can be written:
Fig 1.2 Shows the Overall Reaction of Polycarbonate
Polycarbonate plastic, which is clear and nearly shatter-proof, is used to make a variety of common products including baby and water bottles, sports equipment, medical and dental devices, dental fillings and sealants, CDs and DVDs, household electronics, and eyeglass lenses (Fiege et al., 2010).
Bisphenol A is also used in the synthesis of polysulfones and polyetherketones, as an antioxidant in some plasticizers, and as a polymerization inhibitor in PVC. Epoxy resins containing bisphenol A are used as coatings on the inside of almost all food and beverage cans, however, due to Bisphenol A health concerns, in Japan epoxy coating was mostly replaced by PET film. (Byrne et al., 2008). Bisphenol A is also a precursor to the flame retardanttetrabromobisphenol A, and was formerly used as a fungicide. Bisphenol A is a preferred colour developer in carbonless copy paper and thermal paper, with the most common public exposure coming from somethermal point of sale receipt paper. BPA based products are also used in foundry castings and for lining water pipes.
The major world producers of Bisphenol A as of mid-2010 includedBayer(23% share in the Americas, Europe and Asia), Mitsui and Nan Ya Plastics (9% and 8% shares, respectively, in Asia) and SABIC, Dow and Hexion (16.2%, 7.3% and 5.6% shares, respectively, in the Americas and Europe).Two grades of Bisphenol A are sold in the marketplace. PC grade contains a maximum of 0.2% 2,4- isopropylidenediphenol, whereas epoxy grade may contain up to 5-7% of the 2,4-isomer(Byrne et al., 2008).
1.2.4.1. PolycarbonateResins
In commercial practice, the epoxy grade is reported to be the same purity as the PC grade. Producers in Japan and Western Europe and some producers in the United States of America (USA) use PCgrade Bisphenol A to manufacture epoxy resins.The largest market for Bisphenol A is PC resins, accounting forabout 75% of the demand in 2009 in both the USA and Western Europe (CEH, 2008).
The major world producers of PC resins in 2008 were as follows (% of world capacity): Bayer (30%), SABIC (27%), Teijin (11%), Dow Chemical (9%) and Mitsubishi Companies (which includes Mitsubishi Chemical, Mitsubishi Gas Chemical and Mitsubishi Engineering Plastics; 8%). The consumption by end use for 2009 in the USA was as follows (% share): optical media (19%), building and construction (18%), transportation (16%), appliances and computers/business equipment (15%), medical (10%) and “other”, including packaging(22%). Large returnable, refillable water bottles (primarily 19- litre, but also 11- and 23-litre) currently account for the majority of PC used in packaging applications, consuming 10% of PC per year. Additional products included in this categoryare food service items such as sports bottles, baby bottles, pitchers, tumblers, home food containers and flatware.
1.2.4.2 Epoxy Resins
The second largest end use for Bisphenol A is epoxy resins, accounting for about 22% of demand in 2009 in both the USA and Western Europe. Epoxy resins contain one or more epoxide (or oxirane) groups that are further cured by reaction with a curing agent or hardener, typically an amine (CEH, 2007).
Epoxy resins based on Bisphenol A and epichlorohydrin, also known as conventional or Bisphenol A diglycidyl ether (referred to as BADGE or DGEBPA) epoxy resins, account for 90–95% of production in the USA. Although conventional epoxies comprise the majority of epoxy resin consumption, four other types of basic epoxies are of commercial importance: brominated resins, novolac resins, cycloaliphatic resins and phenoxy resins. By varying the ratio of epichlorohydrin to Bisphenl A, as well as the operating conditions, conventional epoxy resins of low, medium and high molecular weight can be produced, with molecular weights ranging from as low as 350 (liquid epoxies) to as high as 8000 (solid epoxies). Liquid resins consist of 80–90% BADGE, with the remaining 10–20% composed of higher molecular weight oligomers. The common process for the manufacture of (conventional) solid epoxy resin is the socalled advancement or fusionprocess. In the presence of a catalyst, liquid epoxy is reacted with Bisphenol A and is “advanced” to a higher molecular weight resin.
The consumption of epoxy coatings by end use for 2007 in the USA was as follows (% share): protective (or surface) coatings (48%), bonding and adhesives (14%), flooring, paving and construction (8%), composites (9%), electrical and electronic laminates (6%), embedding and tooling (4%), vinyl ester resins (4%) and other (16%).
1.2.4.3 Surface Coating
Surface coatings accounted for about 50% of all epoxy resin consumption in 2009 in the USA. The consumption of epoxy surface coatings by end use in 2006 in the USA was as follows (% share): powder (25%), containers and closures (14%), industrial maintenance and marine finishes (29%), automotive primers (13%), machinery and equipment (4%) andfurniture and appliances (17%).
Solid badge low molecular weight resins are the most common type of epoxy resin used in surface coatings. The general types of epoxy surface coatings include solvent-borne, waterborne, powder coatings, radiation-curable and epoxy esters. Solvent-borne coatings are typically used for food can interiors, whereas waterborne coatings are used in beverage can interiors (CEH, 2007). Solvent-borne coatings, either one-component systems that are heat cured or two-component systems that cure at ambient temperature, account for about 40% of epoxy coating demand in the USA. Solvent concentration is typically more than 40% by volume. One-component systems consist of a combination of epoxy resin and co-reactant that can crosslink at elevated (baking) temperatures. These systems are used for food container interiors and coil and wire coatings. Two-component systems are composed of a curing agent and an epoxy resin that are mixed prior to use. Two-component systems are used in maintenance and marine coatings, tank and pipe coatings, and aircraft primers. Waterborne coatings, which account for 25–30% of epoxy coating demand in the USA, are mostly used in beer and beverage can interior coatings and automotive electrodeposition primers. Waterborne epoxy systems contain 15–20 solids (volume per volume), a water content of 75–85% and an organic content of 1–5%.Usually, basic resin producers sell liquid epoxy resin to large coatings producers such asPPG, Valspar, BASF and ICI, which advance the resin to make it suitable for coatings.