A New Unsaturated Poly(ester-urethane) Based on Terephthalic Acid Derived from Polyethylene Terephthalate (PET) of Waste Bottles

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1 J Polym Environ (2012) 20: DOI /s ORIGINAL PAPER A New Unsaturated Poly(ester-urethane) Based on Terephthalic Acid Derived from Polyethylene Terephthalate (PET) of Waste Bottles A. M. Issam Sufia Hena A. K. Nurul Khizrien Published online: 17 December 2011 Ó Springer Science+Business Media, LLC 2011 Abstract The new unsaturated poly(ester-urethane) was synthesized by the reaction of 4,4 0 -methylenediphenyldiisocyanate with 4,4 0 -di(2,3-butenhydroxyl) terephthalate in the ratio of 1:1. 4,4 0 -di(2,3-butenhydroxyl) terephthalate was first prepared by reacting 2 mol of cis-2-butene-1, 4-diol with 1 mol of terephthalic acid. The terephthalic acid used was derived from the recycling of PET bottles via subjection to saponification process. The synthesized compounds were characterized by CHN analysis, FT-IR, 1 H NMR and UV Vis spectroscopy, with consistency of results showing the presence of the new unsaturated poly(ester-urethane) II. Thermal properties of the new polymer was verified by differential scanning calorimetry and thermogravimetric analysis, whereas the mechanical properties were characterized by tensile, elongation, hardness, adhesion and impact testing. The electrical conductivity and the electrical resistance of the compound were observed with increasing applied voltage. Keywords Recycling Waste polyethylene terephthalate (PET) Terephthalic acid Unsaturated poly(ester-urethane) Thermal properties Introduction Polyethylene terephthalate (PET) is a thermoplastic polyester that is formed by a reaction between terephthalic acid and ethylene glycol [1], which is one of the best known consumers plastic. The demand for PET bottles has been A. M. Issam (&) S. Hena A. K. Nurul Khizrien School of Industrial Technology, University Science Malaysia, Penang, Malaysia issam@usm.my increasing due to its high mechanical strength, low weight, low permeability to gases (important application for soft drink bottles), relatively low manufacturing cost and non-toxicity [2, 3]. Therefore, PET bottles predominantly present as the solid wastes and there are urgent needs to convert PET waste to a new source of raw material of value-added criteria. Most of the past research has found that the end product of PET recycled can be obtained by various reactions such as alcoholysis [4] glycolysis [5, 6] hydrolysis [7, 8] and saponification [9, 10]. The end product such as terephthalic acid (TPA), ethylene glycol (EG) or bis-hydroxyethyl terephthalate (BHET) [11] can be used as a new raw material for preparing other polymers such as unsaturated polyester [12, 13], polyurethane [14], epoxy resin [15], alkyd resin [16] and vinyl ester resin [17]. In recent years there has been increased interest in poly(ester-urethane), which is an important class of polyurethanes. Poly(ester-urethane) is widely used in various applications over the past few decades such as in medical [18 20], matrix composites[21] and biodegradable materials [22] due to its desirable properties. To date, there is no research to synthesis a new unsaturated poly(ester-urethane) from PET waste bottles. Therefore, the new unsaturated diol containing ester group was synthesized and used as a monomer. This monomer was reacted with 4,4 0 -methylenediphenyldiisocyanate (MDI) to produce the new unsaturated poly(ester-urethane). This polymer is expected to have the merits of heat resistant as well as great mechanical properties. Recently, polyesters were shown to have semiconducting properties in an attempt for their use in solar energy storage [23]. In contrast to literature, the reactions recently attempted for derivation of new product from PET revealed electrical insulating properties and are hereby reported.

2 470 J Polym Environ (2012) 20: Experimental Materials PET bottles of Spritzer (Malaysia) mineral water were shredded into 2.5 cm cm flakes. Chemicals such as sulfuric acid (H 2 SO 4 ) and sodium hydroxide (NaOH) were purchased from Brightchem Co., while solvents such as ethylene glycol, cis-2-butane-1, 4-diol, and 4,4 0 -methylenediphenyldiisocyanate (MDI) were purchased from Aldrich Co. and used without further purification. N,Ndimethylformamide (DMF) was purchased from Fluka Co. and distilled over calcium hydride (CaH 2 ) before used. Instrumentations Perkin Elmer 2000 FT-IR spectrophotometer was used for acquiring the spectra of the polymer and monomer samples in KBr pellets ranged from 4,000 to 400 cm HNMR spectra were recorded on a Bruker 400 MHz NMR spectrometer with dimethyl sulfoxide (DMSO-d6) used as solvent and tetramethylsilane (TMS) as internal standard. CHN microanalyses were performed using Perkin Elmer 2400 Series II Combustion Analyzer. The UV Vis spectra of the samples were recorded with a HITHASHI U 2000 spectrophotometer, while thermogravimetric analysis (TGA) was carried out in nitrogen and oxygen atmosphere with Perkin-Elmer TGA7 series at 20 C min -1 temperature rise for C temperature range, to analyze the thermal stability and degradation of the unsaturated poly(ester-urethane) II. Differential scanning calorimetric (DSC) measurements were carried out with a Perkin Elmer DSC7 series at heating rate of 10 C min -1 in nitrogen to determine the glass transition temperature (T g ) and melting temperature (T m ) of unsaturated poly(ester-urethane) II. The mechanical properties were measured by using a tensile testing machine of Instron Universal Testing Machine Model 1114 according to ASTM D 412 [24]. This test was carried out by using rectangular strips of mm dimensions. The width and thickness of the polymer film was measured and recorded. The polymer film was tested at a cross-head speed of 3 mm/min and gauge length of 60 mm. The test was carried out according to ASTM D 638. Flexural test was performed according to ASTM D 790 by using the same Instron machine. The width and thickness of the polymer film was measured and recorded and the film was tested at a crosshead speed of 3 mm/min. The hardness, adhesion and impact tests of the unsaturated poly(ester-urethane) were applied on substrate with dimensions of 70 mm 9 15 mm 9 10 mm. The hardness test was performed by using the Pendulum Tester (Zwick) Model CS-1370 with Sward-type hardness rocker, according to ASTM D The sample was rigidly mounted on a vertical position and using a pendulum with a force of 10 Joule at the center of the sample. The cross-hatch adhesion test was done according to the cross-hatch adhesion test method ASTM D A lattice pattern of cuts with similar spacing was made on the surface of plates with the cross-hatch cutter and commercial cellophane tape was applied over the lattice. Impact resistance of the coating system is measured by falling weight impact test according to ASTM specification G1466 by SHEEN Tubular Impact Tester. Electrical measurement was carried out by using Keithly 251 tester. Several lighting cycles were performed to measure the electrical resistance of the samples. Samples Preparation Preparation of Terephthalic Acid from PET Bottles The ratio for PET flakes to NaOH pellets to ethylene glycol was 1:2:1.5, respectively. NaOH pellets were first dissolved in ethylene glycol with heating maintained from 60 to 100 C. PET flakes were added into the mixture, while NaOH pellets were partially dissolved. The mixture was well mixed and heated at C in a stainless steel container and the temperature was maintained for around 20 min until the mixture turned milky. The mixture was stirred continuously for 20 min and cooled to room temperature, and then the distilled water was added to dissolve the remaining white precipitates. Further it was stirred and filtered through coffee-filter (mesh width of mm). When the mixture turned clear yellow, a few drops of 5 M H 2 SO 4 were added into this solution until ph 2, the white powder was appeared and filtered by using Buchner funnel (under suction) whereas, the ethylene glycol was obtained as filtrate. The white precipitate (terephthalic acid) was collected and washed several times with water and finally dried in a vacuum oven for 24 h at 60 C. Preparation of 4,4 0 - di(2,3- butenhydroxyl) Terephthalate I 0.05 mol of terephthalic acid was first dissolved in 130 ml of DMF. Then, it was added into the reaction flask together with the solution of 0.1 mol of cis-2-butene-1,4-diol. The mixture was stirred and heated from 150 to 200 C, under nitrogen flow for 3 h and the water was distilled off during the esterification process. As a result, 4,4 0 -(2,3-butene hydroxyl) terephthalate I is formed. Further purification was carried out by using Soxhlet extractor with ethanol as the suitable solvent for a period of 8 h. The purified monomer was washed with cold ethanol several times, then

3 J Polym Environ (2012) 20: filtered and finally dried in a vacuum oven at 60 C for 24 h. The melting point and yield were C and 72%, respectively. Elemental analysis: Found: C, 62.66; H, 5.82, C 16 H 18 O 6 Calc.: C, 62.74; H, Preparation of Unsaturated Poly(ester-urethane) II The general polymerization equation and the structures are given in Scheme mol of 4,4 0 -methylenediphenyldiisocyanate (MDI) in 125 ml of DMF was added to a mixture of diol I (0.05 mol) in 100 ml of DMF at 50 C for 1 h. Subsequently the temperature of the reaction mixture was increased to 100 C and continued to stir under nitrogen gas flow for 24 h. The polymer II thus prepared was precipitated in distilled water, filtered and washed several times with distilled water, then with methanol and dried for 24 h in a vacuum oven at 70 C. The yield was 83%. Elemental analysis: Found: C, 66.17; H, 5.11; N, 4.89, C 31 H 28 N 2 O 8 Calc.: C, 66.90; H, 5.03; N, Results and Discussion Structural Elucidation for Monomer I and Unsaturated Poly(ester-urethane)II FT-IR spectrum of terephthalic acid showed the presence of C = O band at 1,685 cm -1. Whereas, C = C stretching of the aromatic ring was significantly shown at 1,574 and 1,510 cm -1. The asymmetrical stretching of OH group appeared at 3,064 cm -1 while the symmetrical stretching band appeared at 2,551 cm -1. The absorption bands at 1,424 and at 937 cm -1 were attributed to the C O stretching and C O H deformation, respectively. To confirm the structure suggested by FT-IR, the 1 H NMR spectrum of terephthalic acid was performed and Fig. 1 showed a broad peak at 13.3 ppm, corresponding to the proton of hydroxyl group and a strong singlet peak at 8.1 ppm was attributed to the protons of aromatic ring. FT-IR spectrum (Fig. 2) of 4,4 0 -di(2,3-butene hydroxyl) terephtholate I showed OH stretching at 3,364 cm -1 from cis-2-butane-1, 4-diol and a new peak was observed at 1,715 cm -1, which indicate the presence of the C = O bond in ester group. In addition, the absorption bands 1,572, 833 and 725 cm -1 were assigned to the C = C aromatic, para position and H C = C H cis configuration, respectively. Unsaturated poly(ester-urethane) II was the result of the reaction between monomer I with 4,4 0 - methylenediphenyldiisocyanate (MDI) in the ratio of 1:1. The FT-IR spectrum of unsaturated poly(ester-urethane) II showed in Fig. 3. The characteristic absorption bands of the urethane carbonyl C = O and the NH stretching groups appearing at 1,717 cm -1 and at 3,307 cm -1, respectively, confirmed the presence of urethane linkage in the backbone of polymer II. Apart from these absorption bands, the presence of the olefin C = C group at 1,649 cm -1 and stretching of the aromatic ring C = C at Scheme 1 Synthesis of 4,4 0 -di (2,3-butenhydroxy) terephthalate I and unsaturated poly (ester-urethane) II

4 472 J Polym Environ (2012) 20: Fig. 1 1 H NMR spectrum of terephthalic acid in DMSO-d 6 Fig. 2 FT-IR spectrum of 4,4 0 di(2,3-butenhydroxyl) terephtholate I Fig. 3 FT-IR spectrum of unsaturated poly (ester-urethane) II 1,599 and 1,518 cm -1 also confirms the chemical structure of polymer II. The 1 H NMR spectrum of polymer II was shown in Fig. 4. The spectrum showed two characteristic singlet peaks at 9.5 and 3.9 ppm due to the protons in the secondary amine of the urethane linkage ( O OC NH) and the protons of methylene (Ph CH 2 Ph), respectively. A singlet at 5.9 ppm was due to the proton in the alkene ( CH =CH ) group and two duplet at 6.8 and 7.8 ppm were due to the p-position and finally a singlet peak at 8.11 ppm assigned to the terephthalic aromatic protons. The UV Vis spectrum of monomer I in Fig. 5a showed one absorption band, whereas polymer II in Fig. 5b showed three absorption bands. This is due to the fact that the chromophore units in the monomer I undergo extension by conjugation via the urethane linkages, O CO NH. The urethane linkage containing unpaired electrons on oxygen and nitrogen atoms enabled many resonance structures to

5 J Polym Environ (2012) 20: Fig. 4 1 H NMR spectrum of unsaturated poly(esterurethane) II in DMSO-d 6 was examined in various solvents and revealed that the polymer II soluble in high polarity solvents such as dimethyl sulfoxide (DMSO), DMF and 97% sulfuric acid but insoluble in common solvents such as benzene, xylene, hexane, chloroform, and diethyl ether. Properties of Unsaturated Poly(ester-urethane) II Fig. 5 a UV Vis spectrum of 4,4 0 -di(2,3-butene hydroxyl) terephtholate I. b UV Vis spectrum of unsaturated poly (ester-urethane) II exist, thus, resulting in pseudo-conjugation [25]. The results of elemental and spectroscopic analyses confirmed the structure of the polymer II. The solubility of polymer II The melting point (T m ) and glass transition temperature (T g ) of unsaturated poly (ester-urethane) II were analyzed by differential scanning calorimetry (DSC) and the data were presented in Table 1. The unsaturated poly (esterurethane) II was heated at 10 C min -1 in nitrogen. It was apparent from the diagram that the T g was appeared at 147 C while T m was appeared at 268 C. First, the sample was held for 1 min then cooled. When cooling, a single exothermic peak was observed at 200 C, arising from crystallization. The second run was carried out by reheating of the polymer at the same condition. This time the T g was found at 152 C and T m at 273 C. Overall, the resultant glass transition temperature (T g ) was at C. During the transition temperature, the sample changed in its behavior from being glassy to rubbery. The melting point for the new unsaturated poly(ester-urethane) was at C, the high melting point reflects the high stability of the unsaturated poly(ester-urethane) II. Thermal stability and degradation of polymer II was analyzed based on thermogram obtained from the TGA at constant heating rate of 20 C min -1 in the temperature range of C under nitrogen atmosphere.

6 474 J Polym Environ (2012) 20: Table 1 Thermal properties of unsaturated poly(ester-urethane) II Material Differential scanning calorimetery (DSC) Thermogravametric analysis (TGA) Glass transition temperature (Tg) Melting point (Tm) Degradation Polymer II First run Second run First run Second run First Second Third Residue at 800 C 147 C 152 C 268 C 273 C 321 C 425 C 472 C 23% Fig. 6 TGA thermograph of unsaturated poly (ester-urethane) II Enhancement of thermal stability of the polymer II observed in the present study can be attributed to the incorporation of the aromatic and unsaturated ester groups. The temperature required for 10% degradation (T 10 ) and the amount of char at 800 C were summarized in Table 1 and the decomposition behavior in nitrogen atmosphere shown in Fig. 6. From the data of Table 1 and Fig. 6, itis evident that the decomposition of polymer II was occurred in three steps. The curve indicated that the first degradation of the polymer occurred at 321 C, with a second degradation at 425 C and a third degradation occurring at 472 C. The trends indicated here suggest that the first degradation was plausibly due to the cleavage of urethane linkages whereas, the second degradation was likely to arise from the cleavage of ester groups and finally the third degradation occurred was due to the aromatic rings. As a result, 23% of the residue was left at 800 C was due to the presence of the aromatic and ester groups. The results of tensile strength (Standard Deviation, SD: 0.27), elongation strain at rupture (% elongation) (SD: 0.38) and impact analyses (SD: 0.33) of unsaturated poly (ester-urethane) II films before and after aging for one week at 90 C were summarized in Table 2. The results Fig. 7 Current Voltage graphs of unsaturated poly (ester-urethane) II showed enhancement in the mechanical properties with exposure time. The secondary amines NH and carboxyl groups COO in the main chain of polymer II leads to the hydrogen bonding, which provides the distinctive thermal and mechanical properties of the material and accounts for its usefulness in a wide range of applications [26, 27]. Therefore, the pressure resistance of polymer II increased, followed by an increment in elasticity. The hardness test (SD: 0.33) of the unsaturated poly(ester-urethane) II showed the flexibility of the film as well as a good impact resistance. The adhesion test was carried out by cross-hatch and the polymer II exhibits an excellent adhesion property, which was no film detachment observed in the adhesion test. Sample of polymer II was characterized by the current voltage measurement and it was pressed at a pressure of 2 metric tons per cm 2 in order to produce discs weighing about 0.3 g each and the discs were connected directly to pin probe with a gap of 3 mm. Current voltage measurement was taken, as showed in Fig. 7. Besides, the polymer II response to the light was tested with a fluorescent lamp directed to the samples for 5 min with intensity of 10,000 Table 2 Mechanical properties of unsaturated poly(ester-urethane) II Material Tensile strength (MPa) % Elongation Hardness Adhesion Falling weight impact tester (cm) Before aging After aging Before aging After aging Before aging After aging Polymer II B a a 5B (0% of coating are detached)

7 J Polym Environ (2012) 20: Fig. 8 Incremental resistance increase after each lightning cycle lumens/m 2. The lighting process was repeated for several times to study the sample light response with time. The original test condition without lighting showed 144 MX of resistance. Meanwhile, when the sample was lit once, resistance to light increased to 180 MX. The light resistance gradually increased with the increase in the number of lighting on the sample. When the sample was lighted four times, the resistance was as high as 413 MX and the results illustrated in Fig. 8, revealed that the light resistance increased after each lighting cycle. Therefore, the new unsaturated poly(ester-urethane) II behaved as an electrical insulator with values in hundreds of mega-ohm. Conclusion Saponification of PET could offer high yield and high purity of the derived terephthalic acid, sufficient for the synthesis of unsaturated poly(ester-urethane) II. Besides, thermal properties of unsaturated poly(ester-urethane) II was improved by the incorporation of aromatic and unsaturated ester groups. The resultant material exhibited melting point of approximately 260 C, which is higher than the melting point of conventional polyurethane. Other than thermal resistance, the new unsaturated poly(esterurethane) II exhibited good adhesion, tensile as well as impact properties and exhibited good electrical resistance. Acknowledgments The authors would like to acknowledge University Sains Malaysia for short term grant No. 304/PTEKIND/ The authors would like to thank Dr. Shahrom Mahmud for his assistance in measuring the conductivity. References 1. Scheirs J, Long TE (2003) Modern polyesters: chemistry and technology of polyesters and copolyesters. John Wiley & Sons, Hoboken, p David EN, Medhat SF (2005) New motivation for the depolymerization products derived from poly (Ethylene Terephthalate) (PET) waste: a review. Macromol Mater Eng 290: Sinha V, Patel MR, Patel JV (2010) PET waste management by chemical recycling: a review. J Polym Environ 18: Recovery Process for Ethylene Glycol and Dimethylterephthalate (1991) U.S. Patent 5,051, Vaidya UR, Nadkarni VM (2003) Unsaturated polyester from PET waste: kinetics of polycondensation. J Appl Polym Sci 34: Baliga S, Wong TW (2003) Depolymerisation of poly (ethylene terephthalate) from post-consumer soft-drink bottles. J Polym Sci Part A: Polym Chem 27: Campanelli JR, Kamal MR, Cooper DG (1993) A kinetic study of the hydrolytic degradation of poly (ethylene terephthalate) at high temperature. J Appl Polym Sci 48: Yoshioka T, Sato T, Okuwa A (1994) A Hydrolysis of PET waste by sulfuric acid at 150 C for a chemical recycling. J Appl Polym Sci 52: Oku A, Hu LC, Yamada E (1997) Alkali decomposition of poly (ethylene terephthalate) with sodium hydroxide in non-aqueous ethylene glycol. J Appl Polym Sci 63: Firas A, Dumitru P (2005) Recycling of PET. Eur Polym J 41: Cesare L, Piero M, Corrado B, Giancarlo B (2006) Chemical recovery of useful chemicals from polyester (PET) waste for resource conservation: a survey of state of the art. J Polym Environ 14: Vaidya UR, Nadkarni VM (1987) Unsaturated polyester resins from poly (ethylene terephthalate) waste synthesis and characterization. Ind Eng Chem Res 26: Aslan S, Immirzi B, Laurienzo P (1997) Unsaturated polyester resin from glycolyzed polyethyleneterephthalate: synthesis and comparison of properties and performance with virgin resin. J Mater Sci 32: Vaidya UR, Nadkarni VM (1988) Polyester polyols for polyurethanes from PET waste: kinetics of polycondensation. J Appl Polym Sci 35: Atta AM, El-Kafrawy AF, Aly MH, Abdel-Azim AA (2007) A New epoxy resins based on recycled poly (ethylene terephthalate) as organic coatings. Prog Org Coat 58: Karayannidis GP, Achilias DS, Sideridou ID, Bikiaris DN (2005) Alkyd resins derived from glycolized waste poly (ethylene terephthalate). Eur Polym J 41: Atta AM, Elnagdy SI, Abdel-Raouf ME, Elsaeed SM, Abdel- Azim AA (2005) Compressive properties and curing behaviour of unsaturated polyester resins in the presence of vinyl ester resins derived from recycled poly (ethylene terephthalate). J Polym Res 12: Lamda NMK, Woodhouse KA, Cooper SL (1998) Polyurethanes in biomedical applications. CRC Press, Boca Raton FL 19. Moehle RT, Farnworth CL, Hibdon D, Patterson RC (2006) U.S. Patent Sridharan S (2004) U.S. Patent Lakshmi SN, Cato TL (2007) Biodegradable polymers as biomaterials. Prog Polym Sci 32: Umare SS, Chandure AS (2008) Synthesis, characterization and biodegradation studies of poly(ester urethane)s. Chem Eng J 142(1): Claes GG (2007) Transparent conductors as solar energy materials: a panoramic review. Sol Energ Mat Sol C 91: ASTM D 412: 06ae2 (2006) Standard test methods for vulcanized rubber and thermoplastic elastomers tension 25. Issam AM, Ismail J (2006) New aromatic poly(azomethine urethane)s containing o-tolidine moiety in the polymer backbone. Des Monomers Polym 9(3):

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