Application of polyethylene terephthalate scraps for the manufacturing long oil alkyd resin

Abstract

A new aspect of work that covers Polyethylene terephthalate (PET) waste recycling and application in coating industry is presented through this report. It was shown that chemical recycled PET can be used in the manufacturing long oil alkyd resin. In Sri Lanka alone, about 6.5 million polyethylene terephthalate bottles (water bottles, food and other liquid containers, etc) are used monthly. Then large amount of Polyethylene terephthalate scraps are discharged in to the environment. The development of effective recycling technology was based on chemical de-polymerization of post-consumer PET bottles in order to use manufacturing alkyd resin based paint. The depolymerization of PET can be carried out in many ways such as glycolysis, hydrolysis, aminolysis, methanolysis and simultaneous hydrolysis and glycolysis. The useful material terephthalic salt can be synthesis through the hydrolysis process of PET. That could be used to derive terephthalic acid. This terephtalic acid can be used for alkyd resin process. Alkyd resins were any of a large group of thermoplastic resins that were essentially polyester made by heating polyhydric alcohol with polybasic acids or their anhydride and used chiefly in making protective coatings. Originally, alkyd resins were merely the reaction products of phthalic anhydride and glycerine. But these products were too brittle to make satisfactory coatings. The use of oils or unsaturated fatty acids in combination with the brittle alkyds resulted in the air-drying coatings which revolutionized the chemical coating industry. The properties of Terephthalic acid have far same to the phthalic acid. Phthalic anhydride was used as a main material in esterification reaction of alkyd resin process. Then pththalic anhydride could be replaced by Terephthalic acid. This process has been done in two stages. At the first stage, reaction between PET waste and sodium hydroxide were used to produce terepththalic acid. At the second stage, application of terepththalic acid was done in the manufacturing process of long oil alkyd resin. That could be used in industrially. Terephthalic salt could be produced successfully by hydrolysis process using Ethylglycol and sodium hydroxide at the higher temperature (180°C). The reacting mixture was neutralized using strong Acid to take Terephthalic acid. Then terephthalic acid could be applied in alkyd resin process without filtering. This new application of the recycled PET in synthesis of alkyd resin had provided same properties of normal alkyd resins. This method was cost saving method by reducing Rs. 3.00 per one kilogram of resin. As well as this can be used as environmental friendly method to give a better solution for the environment pollution due to plastic waste.