Chemistry and Technology of Polyols for Polyurethanes - PDF
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POLYESTER POLYOLS FOR POLYURETHANES FROM RECYCLED PET *Peter Rossi, ** Edward Kosior, * Pio Iovenitti, *Syed Massod, *Igor Sbarski * IRIS, Swinburne University, Melbourne, Australia 3122, ** Visy Plastics Pty.Ltd, Reservoir, Melbourne, Australia 3073 Abstract devoted to the description of the kinetics of glycolysis reaction . Plastic packaging forms a significant portion of Most of the past research is concerned with the process household waste, and PET soft drink bottles represent a of utilisation of products obtained by using glycolysis. The major percentage of the waste. Consequently, PET bottle PET glycolysates find application in the manufacture of grade material makes up a significant portion of the unsaturated polyesters , polymer concrete resins for feedstock in the recycling plant at Visy plastics. The end unsaturated polyesters , polyurethane foams , and uses are theoretically many, however, there are few polyisocyanurate foams  . applications for less purified grades of recycled PET. This paper presents the preliminary results of an industry based The glycolysis process is conducted over a wide range collaborative research project which aims to investigate the of temperatures (180°C-250°C), during a time period of breaking down of recycled PET into its chemical building 0.5-8 hours and usually a catalyst is used, normally zinc blocks using glycolysis. The main objective is to produce a acetate, at a level of 0.5% by weight of recycled PET used. polyester polyol for the polyurethane industry from Depending on the glycol choice, the glycolysis can be recycled PET and to compare the properties with that of a conducted either at atmospheric pressure or performed virgin resin. under pressure. Introduction At least two significant advantages may be expected by Visy Plastics is a recycling company principally use of PET degradation products for synthesis of respective dealing with post consumer bottle recycling. Recycled PET unsaturated polyester. The first one is a possibility to constitutes 60% of recycled plastic material at Visy Plastics convert the PET waste into valuable product. The other is and is currently shipped in flake form, and for the less that terephthalic acid based unsaturated polyesters can be purified grades of recycled PET, the end use is unclear. obtained without processing difficulties encountered when This paper discusses the use of chemical recycling by using virgin terephthalic acid is used. glycolysis, which often investigates the depolymerisation of recycled PET into monomers and higher oligomers. The intermediates thus obtained can then be used as building In terms of synthesis of a polyester polyol to produce blocks to synthesise other polymers with higher economical polyurethane foam, normally adipic acid is reacted with value, such as polyurethane foams and unsaturated glycolysed PET oligomers at fixed hydroxyl to carboxyl polyesters. ratios of about 1.2-1.5 at 170°C for the first three hours and then to 200°C for ten hours to obtain different molecular weights of polyol. The reaction is performed under Most of the literature published regarding utilisation of nitrogen blanket until target acid value of about one is PET waste to yield a viable product is about unsaturated achieved. Water is removed from the reaction and some polyesters. On the other hand, little of literature concerning times vacuum is used to remove traces of water . polyurethane synthesis from PET waste has appeared. The literature that has been cited deals with mainly rigid foams and polyurethane elastomers, made by using ethylene Polyester based foams are stiffer and stronger than glycol. This paper investigates the likelihood of matching those made from polyethers, with better resistance to branched polyurethane polyol from recycled PET, which is oxidation and high temperatures. Polyester polyols also currently being made from virgin raw materials. differ from polyether polyols in having virtually no unreactive end groups, a factor which contributes significantly to the higher strength of polyester based foams Much attention has been devoted to glycolysis by compared with those from polyethers . ethylene glycol. In this system the effect of the reaction parameters, temperature (190°C-240°C), pressure (0.1- 0.6MPa) and PET to ethylene glycol ratio on reaction rate,  has been investigated. Very few papers have been Materials and Methods Results and discussion Materials Glycolysis of PET waste The materials used were; The glycolysis stage shows the reduction of recycled Recycled PET in form of flakes, grade name: P3 PET to lower molecular weight fragments. The major (General purpose) supplied by Visy plastics, fractions of the glycolysed product by Triethylene glycol (TEG) could be represented by the following species: Triethylene glycol from I.C.I. chemical company,and TEG-TPA-TEG, EG-TPA-TEG, EG-TPA-EG, free TEG Pentarythritol from Hoechst chemical company. and a small amount of free EG. Note: (TPA) stands for terephthalic acid and (EG) ethylene glycol. Glycolysis of PET waste The gel permeation chromatography results indicate PET bottle grade flake was depolymerised by using initially the number average molecular weight was high at Triethylene glycol. PET waste flakes, totalling 1194grams, around 700. After five hours the number average molecular equivalent to 6.2 mole repeating unit (molecular weight weight was reduced to 468. If we assume the main fraction 192), were added to 1000grams of Triethylene glycol was TEG-TPA-TEG, the theoretical value average number (molecular weight 150), such that the molar ratio of PET molecular weight is 466, which is a good correlation. The repeating unit to Triethylene glycol was 1:1.1 The mixture longer the reaction leads to further decrease in molecular was charged into a four-necked glass round bottom flask, weight, but after five hours the decrease in molecular which was fitted with a stirrer, reflux condenser, nitrogen weight is quite moderate. inlet and a heating mantle. In terms of 50°C cone and plate viscosity Initially the stirrer was not turned on due to the high measurements, similar trends were observed. After the first ratio of solids to liquids in the flask. The temperature was hour the sample was like a paste and the cone and plate gradually increased to 180°C and the recycled PET flake viscosity could not be measured. After fours of digestion a started melting. It was noticeable by a decrease in size of result of 20poise was obtained. At the five hour stage a PET particles and a cloudiness in the liquid phase was result of 15poise was recorded and the same result of observed. At this stage it was safe to turn the stirrer on and 15poise was recorded at the six hour stage. This suggests begin agitating the mixture. The temperature was slowly the cone and plate viscosity remained stable hence the raised by increments of ten, until a temperature of 230°C depolymerisation was complete somewhere between five was reached. The nitrogen flow was turned on and the and six hours. recycled PET flake dissolved very easily. After about four hours at cook temperature of 230°C, all of the PET Polyester polyol particles were visibly digested. The saturated polyester polyol was made by reacting Samples were taken every hour for gel permeation the glycolysed PET with adipic acid and a small amount of chromatography and 50°C cone and plate viscosity to branching agent (Pentarythritol). The temperature of the monitor the rate of depolymerisation. reaction initially was 150°C and then was raised to 230°C until the end of reaction. Water from the reaction was Preparation of polyester polyol removed continuously until a target acid value of one was achieved. The total time for the reaction was 12 hours. The The glycolysed PET was heated to 150°C and the glycol excess was 35%. The Brookfield viscosity at 25°C stirrer was turned on. Adipic acid and pentaerythritol were was measured and a result of 720poise was obtained. The charged into the round flask at temperature of 160°C and Brookfield viscosity for the polyol made from the virgin mixed for one hour. The glassware was modified to ensure raw materials was 230poise. distillation was possible and a measuring cylinder was used to collect the distillate throughout the course of the reaction. The mixture was gradually heated to 180°C and Conclusion distillate was first noticed. The temperature was increased by increments of ten degrees depending on the vapour The main conclusions from this research are: temperature until 230°C. The temperature was held at • Depolymerisation of recycled PET waste by 230°C and samples were taken every hour for acid value. glycolysis using Triethylene was successfully To increase the rate of the reaction the nitrogen flow, and performed and the digestion was complete stirrer speed was increased, so that more water could be after six hours. removed since the temperature remained constant. The required acid value specification was approximately one. • A procedure was developed to produce a polyester polyol, with hydroxyl excess of 35% and acid value of one. • Further research needs to be conducted, varying the levels of hydroxyl excess and branching agent and to determine the effects these parameters on molecular weight, viscosity and hydroxyl value. References 1. Chen, J, Y, O Y. C; Lin C.C “Depolymerisation of recycled PET under pressure”, Applied Polymer Science 1991, 42, 1501. 2. Baliga, S, Wong, W.T., Depolymerisation of PET recycled from post-consumer soft drink bottles”, Polymer Science, 1989, 27, 2071. 3. Vaidya, U.R., Nadkarni V.M., “Unsaturated polyester resins from PET waste: Synthesis and characterisation”, Ind. Eng. Chem., 1987, 26, 194. 4. Rebeiz, K.S, Flower, D.W, Paul D.R. “Polymer concrete and polymer mortar using resins based on recycled PET”, Applied Polymer Science, 1992, 44, 1649. 5. Speranza, G.P., Grigspy, R.A., “Liquid phase polyols which are alkylene oxide adducts of Terephthalic esters from recycled PET”, US Patent 4485, 196, 1984. 6. Vaidya, U.R., Nadkarni, V. M., “Polyester polyols for polyurethanes from PET waste”, Applied Polymer Science, 1988, 35, 770. 7. Sen Chong, You-Wansze and Chen- Chong lin, “Polyurethanes synthesised from polyester polyol derived from PET waste”, journal of chinese institute of chemical engineering , 26, 289, 1995. 8. Polyurethane Encyclopedia, “Flexible polyurethane foams: chemistry and technology”, 1985, 24, 1096 .