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The commercial success of electro‐deposition of aqueous coating is mainly concerned with the development of water‐soluble film forming polymers. The field of these water‐soluble polymer systems for surface coating application is growing rapidly and expanding vigorously and they are destined to play a leading role in the near future. This may be mainly attributed to regulations on emissions, environment and ecology. In doing so, the electrodeposition technique offers a remarkable assistance to these systems at comparatively low cost, low energy requirement and high utilization efficiency. Research workers have done work on water‐soluble alkyds, epoxies and acrylics.

For conservation of petochemical solvents and reduction of air pollution, the water soluble polymers will play an important role in surface coating industry. The coatings based on water soluble polymers are thinned with water instead of petroleum solvent. Basically, the water based coatings may be made from oils, alkyds, polyesters, aminoes, phenolics, epoxies and acrylics. In spite of a large number of other synthetic resins being available for use in coating formulations, the alkyd resins surpass all of them in versatility, and low cost; combining a broad spectrum of performance properties with economy. Water soluble alkyd resins are similar to their solvent borne counterparts. The major difference is that their formulation is modified to introduce pendant carboxylic acid groups along the polymer backbone. These pendant acid groups can be neutralised with basic compounds to produce water solubility. Several workers studied preparation and evaluation of film characteristics of water soluble alkyd resins using various types of polybasic acids, polyhydric alcohols and fatty acids. The curing of these resins has been satisfactorily accomplished by stoving in presence of water soluble amino resins.

Water soluble alkyds were prepared from phthalic anhydride, maleic anhydride, trimellitic anhydride and maleopimaric acid separately by monoglyceride process. Pigmented electro coating compositions were prepared from water soluble alkyd resin, red oxide of iron and zinc phosphate. The anodic electrodeposition parameters such as voltage, time, solid content and pH were optimised. The mechanical and chemical properties of different electrocoating compositions were studied. The coating compositions prepared from water soluble alkyd resin based in maleopimaric acid showed good mechanical and chemical properties.

The acute shortage coupled with tremendous increase in cost of various solvents used by paint industry and pollution becoming a serious concern has resulted in intensive study of water‐borne coatings. Water‐borne coatings ideally meet the needs for coating systems which do not cause atmospheric pollutions and at the same time help in conservation of precious and renewable petroleum resources. Many research workers have developed water‐soluble epoxies, alkyds and acrylics to make water‐based surface coatings.

Water soluble epoxy resins were prepared from epoxy resin, linseed fatty acids, maleic anhydride, trimellitic anhydride, maleinised dehydrated castor oil and maleopimaric acid. Pigmented coating compositions for anodic electrodepositions were prepared from water soluble epoxy resins using red oxide of iron and zinc phosphate as pigment. The electrodeposition parameters such as voltage, time, solid content and pH value were optimised. The mechanical and chemical film properties of different electrocoating compositions were studied.

Water soluble epoxy resins were prepared from male‐opimaric acid, linseed fatty acids and epoxy resin. The methylated urea formaldehyde resin and melamine formaldehyde resin were also prepared for curing purposes. The pigmented coating compositions were prepared from water soluble epoxy resins, red oxide and iron and zinc phosphate. These coating compositions showed good water resistance, acid resistance, alkali resistance and lubricating oil resistance.

Acryclic copolymers from methacrylic acid‐ethyl acrylate or butylacrylate were prepared and incorporated into the castor oil alkyd structure. The neutralised product was water soluble. Water soluble hexamethoxy methyl melamine resin was prepared and used as curing agent. Several proportions of water soluble acrylic modified alkyds and hexamethoxy methyl melamine resin were examined at various baking schedules. It was established that 30% of the curing agent gave most satisfactory properties after baking at 150°C for 30 minutes. It was found that ethyl acrylate modified compositions had better scratch hardness and acid resistance than those of the butyl acrylate modified composition. However, the latter had better alkali resistance. These surface coating compositions have been recommended as industrial primers.

The purpose of this paper is to prepare cheap and environmentally friendly water soluble polyester coatings through the glycolysis of poly(ethylene terephthalate) (PET) waste.

A secondary value-added polyester coatings were prepared from PET waste. The first step was the de-polymerisation of PET waste by 2,2-dimethyl-1,3-propanediol with different molar ratios in the presence of different concentrations of zinc acetate as trans-esterification catalyst. The de-polymerised product was characterised by Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance spectroscopy (¹HNMR), differential scanning calorimetry and hydroxyl values. The polyesters were successfully synthesised by esterification of the glycolysed product with adipic acid, isophthalic acid, 2,2-dimethyl-1,3-propanediol and trimellitic anhydride in different ratios. FTIR and ¹HNMR were used qualitatively and quantitatively to elucidate the structure of the prepared polyesters. Hydroxyl value and the physical properties of the prepared polyesters were also investigated. Two different curing agents were used to prepare the coatings based on the prepared polyesters.

Useful coating products were obtained by chemical (glycolysis) of post consumed PET wastes. The 2,2-dimethyl-1,3-propanediol was found to be good glycol in the glycolysis of PET. It was noticed that the rate of glycolysis increases with increasing the amount of catalyst, time of glycolysis and amount of 2,2-dimethyl-1,3-propanediol. N,N-Dimethylethanol amine was a good neutralising agent used for the preparation of water soluble coatings based on glycolysed product of PET.

The use of waste products like PET waste in water soluble coating systems will bring down the costs of the coatings and will also open a new market of recycled plastic materials and, hence, may provide a potential solution to the problems of solid waste management. It is an attractive option for environmentally friendly and efficient disposal of plastic waste.

The paper provides a potential way to use undesirable PET waste as industrial raw material. The coatings prepared are eco-friendly, soluble in water that can replace other expensive polyester coatings that are soluble in organic solvents and not environmentally coatings.

Henning [Metal Finishing, 75, May (1977) p. 64] has compared water‐borne primers and water‐borne total systems for appliances with the corresponding solvent‐based compositions and concludes that high quality finishes are indeed available from water‐based compositions. The author points out that two types of water‐borne coatings are available. The more common emulsion type generally offers good properties and has less than five per cent of organic cosolvent. The water‐soluble or water‐dispersible coatings, on the other hand, generally have properties equal to solvent‐borne coatings but contain up to twenty per cent of organic cosolvent. Generally, the water‐soluble types are more readily applied. On the other hand, they invariably require baking whereas emulsion type coatings can, of course, be formulated for architectural or maintenance applications. Emulsion systems are more sensitive, however, to freezing than are the water‐soluble compositions.

It is well known that water based coatings offer several advantages over solvent based coatings, such as: less air pollution, saving of energy, saving of raw materials and noncombustibility, at least in liquid form and during application.