Synthesis of polyester-ether polyols derived from waste polyethylene terephthalate

Synthesis of polyester-ether polyols derived from waste polyethylene terephthalate

苏玲

山东工程技师学院 邮编：252000

LingSu

Department of Materials Engineering and Tourism, Shandong Institute of Engineering Technicians, Liaocheng 252000, China

e-mail: 123872418@qq.com

AbstractThe polyols of polyesters and polyethers derived from petrochemicals are the essential components currently for polyurethane production. In this work, the polyester-ether polyols (PEE polyols) the polyols with high functionality, low acid number and low cost were synthesized using recycled polyethylene terephthalate (PET) as raw material. A single step process was used, in which alcoholysis of PET by diethylene glycol (DEG) and pentaerythritol (PER) into oligomeric polyols was combined with esterification of the oligomers into end product PEE polyols.

Keywords Waste poly(ethylene terephthalate) · Polyols · Polyester-ether

Introduction

Polyethylene terephthalate (PET) is a thermoplastic semi-crystalline polyester with excellent mechanical properties and chemical stability, and no any toxic or side effects on the human organism [1]. It has been widely used in the manufacture of various kinds of products such as films, fibers, containers and especially of food packaging as water and softdrink bottles. The global demand of PET has grown rapidly at the rate of 8.3 % per annum, and the consumption around the world is expected to rise to 58 million ton in 2012 [2]. The extensive applications of the polymeric material lead to a large amount of waste PET generated [3–5]. Although PET does not create a direct hazard to the environment, but its poor biodegradability and photodegradability, make it become one of waste disposal management difficulties [6]. Effective recycling of waste PET can be done by physical methods or chemical depolymerization [7]. Extrusion is most commonly employed as a physical method, and have been industrialized. However, the mechanical properties of the products are poor than original, especially in elongation break. The chemical depolymerization of waste PET is more attractive and has been widely studied, which included hydrolysis by water, alcoholysis by alcohols, acidolysis by acids, glycolysis by glycols, and aminolysis by amines [2, 8–11]. Waste PET is degraded into pure monomers in these processeswhich can be used to produce new products with high quality. The glycolysis reaction into the monomer bis(2-hydroxyethyl) terephthalate (BHET) and oligo-diols of various structures is researched most frequently and deeply among them [12–15]. The obtained products has been widely used in the synthesis of a number of unsaturated polyester resins used in the production of polyurethanes and various copolymers [1, 16, 17].

Experimental

Materials

Waste PET bottles were obtained from local market, cleaned after the caps and the labels had been removed, dried, and cut into approximate 5 mm × 5 mm size pieces. DEG (purity 99.5 %) and MA (purity 99.5 %) were purchased from the local market and used without further purification. PER and zinc acetate were of analytical reagent from Tianjin Chemical Reagent Factory (P. R. China).

Synthesis of PEE polyols

Alcoholysis

The reactions were carried out in a 500 mL, three-necked flask equipped with a mechanical stirrer, a thermometer and a reflux condenser. The flask was immersed in an oil bath. PER and DEG according to a designed ratio of PER/DEG from 0.1 to 0.4 wt % were first pumped into the flask. When the mixture was heated to a designed temperature at 180to 230 oC, PET and ZnAc2 catalyst were also added at PET/DEG of 95 wt % and ZnAc2/ DEG of 0.1 to 0.9 wt %, respectively. The reaction lasted for 30 to 120 min until all the solids disappeared.

Esterification

After the alcoholysis of waste PET period, the reflux device was modified into atmospheric distillation to remove water generated in the process. Calculated MA at MA/DEG of 25 to 28 wt % was slowly charged to the reactor, and the temperature was maintained for 300 to 450 min until the acid number no longer decrease. During the process, samples were taken out periodically for detecting acid number, viscosity and hydroxyl value.

Measurements

The acid number was determined by titration of potassium hydroxide according to ASTM D4662. was based on the reaction of the terminal hydroxyl groups with acetic anhydride. The acidic carboxyl groups resulting from this reaction are neutralized with the equimolecular quantity of potassium hydroxide.The steps of hydroxyl value determination were as follows [19]: 3.000~5.000 g sample was added to 25.0 mL acetylating solution, containing 5.0 % (v/v) acetic anhydride in pyridine. The mixture was heated with stirring at (115 ± 5) oC for 1 h. Afterwards 10.0 mL of water was added, and the heating was continued for 10 min at 100

oC. The mixture was then cooled at room temperature and normal butanol of 15.0 mL were added. The resulting solution was titrated against 1.0 mol/L KOH standard solution using phenolphthalein as indicator.

  The viscosity of the polyols was measured using a rotational viscometer (NDJ-1) at 15 oC. FTIR spectroscopy were recorded on Perkin Elmer Spectrum One spectrometer in the range of 4000–400 cm-1. 1H NMR experiments were carried out on a mercury plus 400 spectrometer operating at resonance frequencies of 400 MHz.

Conclusions

The above results suggested that it is completely feasible to prepare the PEE polyols with high functionality, low acid number and low cost using recycled PET, different alcohols and anhydrids as raw materials.A single step process was used, in which alcoholysis was combined with esterification. This study provides important guidance for the design and synthesis novel environmentally friendly polyols.

References

1. Xi GX, Lu MX, Sun C (2005) Polym Degrad Stab 87:117-120

2. Mansour SH, Ikladious NE (2002) Polym Test 21:497－505

    3. Paszun D, Spychaj T (1997) Industrial & Engineering Chemistry Research 36:1373－1383

    4. Wan BZ, Kao CY, Cheng WH (2001) Industrial & Engineering Chemistry Research 40:509－514

5. Sinha V, Patel MR, Patel JV (2010) J Polym Environ 18:8–25

    6. John S (1998) Wiley series in polymer science, John Wiley&Sons, Chichester, UK, pp 119－182

    7. Genta M, Goto M, Sasaki M (2010) J of supercritical fluids 52:266－275

    8. Kurokawa H, Ohshima M, Sugiyama K, Miura H (2003) Polym Degrad Stab 79:529－533

9. Yamaye M, Nago Y, Sasaki M, Tsuru T, Mukae K, Yoshinaga T, Murayama R, Tahara C (2006) Polym Degrad Stab 91:2014－2021

    10. Kim BK, Hwang GC, Bae SY, Yi SC, Kumazawa H (2001) J Appl Polym Sci 81:2102－2108

11. Abd El-Hameed RS, AL-Shafey HI, Farghaly OA (2012) Research & Reviews in Electro Chemistry 3

    12. Cheng HC, Chen CY, Lo YW, Mao CF, Liao WT (2001) J Appl Polym Sci 80:943－948

13. Baliga S, Wong WT (1989) J Polym Sci Part A Polym Chem 27:2071－2082

14. Halacheva N, Novakov P (1995) Polymer 36:867－874

15. Mori H, Maeda Y, Kubota S, Yamaguchi K, Ito O, Maeda T (2002) Polym J 34:687－691

16. Atta AM, El-Kafrawy AF, Aly MH, Abdel-Azim AAA (2007) Progress in Organic Coatings

   58:13–22

17. Shukla SR, Palekar V, Pingale N (2008) J Appl Polym Sci 110:501－506

18. Szycher M (1999) Handbook of Polyurethanes Chapter 2, pp 1－19, Chapter 3, pp 1－39

19. Karayannidis GP, Achilias DS, Sideridou ID, Bikiaris DN (2005) European Polym J 41:201－210