Chemistry and Technology of Polyols for Polyurethanes - PDF

							            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 [2].
     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 [3], polymer concrete resins for
feedstock in the recycling plant at Visy plastics. The end       unsaturated polyesters [4], polyurethane foams [5], and
uses are theoretically many, however, there are few              polyisocyanurate foams [6] .
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 [7].
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 [8].
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,
[1] 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.


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