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Effect of [gamma]-irradiation on glycolysis of PET waste and preparation of ecofriendly coatings using bio-based and recycled materials.

INTRODUCTION

Polyethylene terephthalate (PET) is one of the most versatile plastics being extensively used for the manufacture of various kinds of packaging, especially for soft drink bottles, fibers and films. With a large consumption, the effective use of PET wastes is immensely important for environmental protection [1]. Therefore, chemical, physical, and mechanical recycling of PET has become an important area of research for the academia and industries. Chemical recycling is generally implemented to decompose the PET waste into the original feedstock monomers and is of great interest for preventing hygiene and smell problems [2]. The chemical depolymerization processes include methanolysis, hydrolysis, glycolysis, aminolysis, and amonolysis, wherein glycolysis being the most studied ones since many years [3-5].

Glycolysis of waste PET with ethylene glycol (EG) leads to the production of bis (2-hydroxyethylterephthalate) (BHET) monomer which has been successfully used in the synthesis of a number of polymeric materials [6-8]. Literature indicates that the depolymerization product of PET waste can be made use for synthesis of unsaturated polyesters [9-11, 15], polyurethanes, polyurethane dispersions [16], alkyd resins [6, 7], epoxy, textile dyestuffs, etc. [12, 14, 17].

Current research in the PET recycling is motivated to find newer materials for PET recycling, process optimization to increase the conversion to its monomeric units, reduce the reaction time, process development using ecofriendly alternatives etc. In case of glycolysis process, a longer reaction time (upto 8-10 h) is needed for higher conversion of PET to produce BHET. This is because of the fact that higher molecular weight of PET requires longer reaction time to break into smaller segments subsequently forming BHET. To reduce the reaction period, microwave and autoclave process have been effectively used [14].

Further, Microwave irradiation as a heating technique offers many advantages over the conventional heating such as instantaneous and rapid heating without contact with the material to be heated. The main advantage of microwaves over conventional heating sources is that the irradiation penetrates and simultaneously heats the bulk of the material. Research efforts have thus led to numerous applications in material processing techniques that have resulted in shorter reaction times and greater convenience [15, 21].

Gamma radiation is generally used to improve the mechanical and physical properties of plastic materials [18]. However, excess exposure to these radiation results in deterioration of the overall properties. When absorbed by the material, gamma radiation provides enough energy to the electrons to move to unstable state which are then transferred to other atoms in the polymer chain. This would result in the formation of small to medium size polymeric radicals with lower molecular weights (Fig. 1) subsequently resulting in inferior properties of the material.

In the current study, we report the effect of gamma radiation on properties of PET and its subsequent recycling by glycolysis method using EG. Waste PET samples were irradiated by gamma radiations at different doses and reduction in molecular weight of the polymer was studied using viscometry technique. Higher dosage of gamma irradiation was expected to result in relatively lower molecular mass. The irradiated PET samples were further studied for recycling by glycolysis method using excess EG by conventional as well as under microwave radiation. The objective of the study was to achieve higher conversion of PET to BHET in reduced reaction time by means of reduced molecular mass of PET samples. The study also involved effective use of glycolyzed product of PET waste to prepare ecofriendly binder for surface coating application along with other bio-based monomers like dimer fatty acid, glycerol and sebacic acid.

EXPERIMENTAL

Materials

PET utilized was obtained from waste soft drink bottles and were cut into chips (average size 5 mm x 5 mm). These chips were then washed with soap solution and later with lukewarm water and dried in an air circulating oven at 80[degrees]C for 2 h. Analytical grade EG, acetic anhydride, pyridine, potassium hydroxide, phenol, tetrachloroethane (TCE), sebacic acid, glycerol, p-toluene sulphonic acid (p-TSA), zinc acetate (ZnAc), xylene, and methyl ethyl ketone (MEK) were purchased from SD Fine chemicals India and used without any further purification. Dimer fatty acid was obtained from Setco chemicals, Mumbai. Poly isocyanate cross-linkers were obtained from Asian PPG, Mumbai, India. The percentage isocyanate content of these cross-linkers, hexamethylene di-isocyanate (HDI) trimer (N-3390), HDI biuret (N-75) and 4,4'-methylene diphenyl diisocyanate (MDI) were 19.6, 16.5, and 31.5 having percent nonvolatile matter of 90, 75, and 100 respectively.

Gamma Irradiation of PET

The samples of PET waste were irradiated with gamma radiation at ambient conditions in gamma chamber 5000 (BRIT, Mumbai) using [sup.60]Co as a source of gamma rays. The samples were irradiated with different dosages viz 10, 30, 50, 70, and 100 kGy at a dose rate of 3.24 kGy/h.

Molecular Weight by Viscometry

To study the effect of gamma radiation on properties of PET, molecular weights of raw & irradiated PET waste samples were determined by intrinsic viscosity method using Ubbelohde type of capillary viscometer. PET samples were dissolved in phenol / tetrachloroethane (TCE) solution (60:40 by weight) to prepare 0.5% (w/w) concentrated solution. All the measurements were carried out at 25[degrees]C. Viscometer reading was noted for the blank solution to cover fixed distance under gravity and denoted by [t.sub.0]. Similarly, time required for 0.5% PET solution to pass through same distance was determined and was denoted as t. The procedure was repeated for each sample in triplicate and the average value of all these readings for each sample was used for further calculations. The relative viscosity ([[eta].sub.r]), specific viscosity ([[eta].sub.sp]) and the intrinsic viscosity ([[eta]]) of the solutions were determined by Eqs. 1-3, respectively. The results of the measurement were calculated and listed in Table 1:

[[eta].sub.r] = t/[t.sub.0] (1)

[[eta].sub.sp] = [[eta].sub.r] - 1 = t/[t.sub.o] - 1 (2)

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (3)

where C (g/dL) was the concentration of the polymer solution.-when C = 0, the value of [[eta].sub.sp]/C approximately amounted to [[eta]] which was shown in Eq. 3.

The calculated intrinsic viscosity was used to determine molecular weight of PET by using Mark-Kuhn-Houwink (MKH) equation as given in the following equation:

[[eta]] = [KM.sup.[alpha]] (4)

For PET, the values of MKH parameters, K and [alpha] at 25[degrees]C using phenol/TCE as solvent, are reported to be 3.72 x [10.sup.-4] and 0.73, respectively [20].

Glycolysis of Gamma Irradiated PET by Conventional Method

The glycolysis reaction was carried out using EG at molar ratio of 1:6 (PET:EG). The molecular mass of PET as calculated from its repeating unit is 192 and the same was considered for further calculations. PET flakes, EG, and 0.5% (w/w) zinc acetate catalyst were charged in a three-necked glass reactor equipped with stirrer, thermometer, and reflux condenser. The glycolysis reaction was carried out at 190 [+ or -] 5[degrees]C under reflux in nitrogen atmosphere for reaction times of 2, 4, and 6 h.

After the reaction was complete, the glycolyzed product of PET contained monomeric, oligomeric product, unreacted glycol, and unreacted PET. The cooled mixture was diluted with boiling water under stirring to dissolve BHET, while the oligomeric product was precipitated and separated by filtration. BHET was then separated by recrystallization, filtered, and dried in an air circulating oven at 60[degrees]C for 2 h. Formation of BHET was confirmed by determination of hydroxyl value, melting point, and FTIR analysis. The procedure was repeated for gamma irradiated PET samples for 2, 4, and 6 h of reaction time.

In addition, the filtered product was dried in an air circulating oven at 80[degrees]C for 2 h. This dried product contained hydroxylated oligomer and unreacted PET (low molecular weight) which were then separated by the procedure as described in our earlier study [19] and characterized for determination of saponification number, hydroxyl value as per ASTM methods and for molecular weight by GPC technique. The yield of BHET monomer was calculated using formula as given in the following equation:

Yield of BHET monomer(%) = Weight of BHET monomer produced x 100 / Theoretical yield (5)

Microwave Assisted Glycolysis of Gamma Irradiated PET

The glycolysis reactions were performed in Microwave reactor (MAS-II, Sineo Microwave Chemistry Technology) equipped with a magnetic stirrer and a reflux condenser. The glycolysis reaction was carried out using EG at same molar ratio and 0.5% (w/w) zinc acetate catalyst at 190 [+ or -] 5[degrees]C under nitrogen atmosphere. The reactions were conducted at microwave irradiation power of 300, 500, 700 watts for 20, 30, and 40 minutes. After completion of reaction, the reaction contents were cooled and purified by the same method as discussed in Glycolysis of Gamma Irradiated PET by Conventional Method Section.

Synthesis of Polyester Polyol

Two different Polyester Polyol (PE polyols) were synthesized using various equivalent concentrations of BHET, dimer fatty acid, sebacic acid, and glycerol. Dimer fatty acid and sebacic acid were taken in 70:30 mole ratio while keeping carboxyl to hydroxyl ratio 1:1.4 on equivalent basis. BHET and glycerol were varied from 0.5 to 0.7 moles and 0.6 to 0.47 moles for PE, and PE2 respectively. The required quantities of all the raw materials were charged in the four-necked flask assembled with nitrogen inlet, Dean-Stark and thermometer. The reaction was carried out at 160-180[degrees]C using 0.5% p-TSA catalyst and continued till the acid value reached below 15 mg KOH/g. The PEs were characterized using FT1R, 'H-NMR, and GPC. Figure 2 is a schematic representation of typical reaction scheme of PE polyol synthesis.

Surface Preparation of Mild Steel Panels

The mild steel substrates with dimensions 150 mmx100 mmx0.5 mm were first degreased with cleaner solution for 15 min. These substrates were further washed with tap water and dried. The substrates were then polished with Emery paper 800.

Preparation of PE Polyol Based Coatings

PE polyols were cured with various polyisocyanate curing agents. Xylene-MEK (70:30, v/v) mixture was used as a solvent in appropriate quantity to achieve suitable viscosity for coating application. The coating formulations prepared were applied on the substrates by flow method to obtain uniform layer of the coating material. The coated substrates were given flash off for 15 min and were then kept in an air circulating oven at 120[degrees]C for 20 min to achieve completely cured coating.

Testing

A digital coating thickness gauge instrument, Elcometer 456 was used to measure the dry film thickness (DFT) of each coating as per ASTM D7091-13. A Rhopoint--Novoglass glossometer was used to test the light reflection properties of the specimens according to ASTM D 523-67. Applied coatings were tested for adhesion properties by cross-cut adhesion technique according to ASTM D 3359. Pencil and scratch hardness of the coating was measured on hardness tester according to ASTM D 3363 and IS-104 respectively. Flexibility and load distribution property of the coating were tested by conical mandrel and impact tester as per ASTM D 522 and ASTM D 2794, respectively. Impact resistance was measured on the impact tester with maximum height of 60 cm and load of 1.36 kg.

The chemical resistance of coated substrates was evaluated for acid and alkali according to ASTM D1308-10. The coated substrates were dipped in 10% aqueous solutions of HC1 and NaOH, respectively, for 24 h at room temperature. The water resistance was evaluated by dipping the coated substrates in water for 24 h at ambient conditions according to ASTM D 870. The solvent resistance was measured by rub test against MEK and xylene as per ASTM D 4752-10. The PEs were analyzed for hydroxyl value and saponification number using ASTM D 2849 (acetic anhydride --pyridine) and ASTM D5558-95 respectively.

Instrumentation

The FTIR spectra were evaluated on Perkin-Elmer Spectrum 100 Instrument (Perkin-Elmer, USA). Spectra were obtained from KBR pellets at 40 scans and 2 [cm.sup.-1] of resolution in the region of hydroxyl stretching (4000-3000 and 1000-400 [cm.sup.-1]), carbonyl symmetric stretching (1800-1600 [cm.sup.-1]), carbonyl asymmetric and alcohol linkages (1400-1000 [cm.sup.-1]) with the purpose of evaluating the chemical structure of the end-products.

NMR spectra were recorded on Mercury Plus [sup.1]H NMR spectrometer (400 MHz, Varian, USA). The spectra were recorded using dimethyl sulphoxide (DMSO) as a solvent. The chemical shifts in the discussion are reported in parts per million.

The molecular weights of the glycolyzed oligomeric products were measured by Gel Permeation Chromatography (GPC) (Ultrastyrogel column; Waters, USA). HPLC grade tetrahydrofuran (THF) was used as a solvent and monodispersed polystyrene was used as the reference.

Differential scanning calorimetry (DSC) analysis was performed under nitrogen atmosphere with DSC Q-100 equipment (TA Instrument, USA) calibrated with n-octane and indium for determining the glass transition temperature. All the samples were heated from 25[degrees]C to 300[degrees]C at a heating rate of 10[degrees]C/min with nitrogen flow rate 50 mL/min.

Thermogravimetric analysis (TGA) was performed under nitrogen atmosphere on DSC Q-100 instrument for the temperature range of 100-650[degrees]C at heating rate of 10[degrees]C/min with nitrogen flow rate 50 mL/min. For analysis, sample of coating was removed from coated substrates and used for characterization.

RESULTS AND DISCUSSION

Degradation of PET by gamma irradiation has been reported earlier by molecular weight determination [18, 20]. The present study is an attempt to depolymerize PET using gamma radiations and glycolyze it subsequently using excess of EG to achieve higher conversion to BHET. The efficiency of the entire process in terms of achieving the highest possible yield of BHET is evaluated.

Effect of Gamma Irradiation on PET Properties: Reduction in Molecular weight

The intrinsic viscosities calculated and number average molecular weights of irradiated & raw PET waste samples are tabulated in Table 1.

The number average molecular weight of nonirradiated waste PET sample was observed to be 80387.16 g/mol. The exposure to gamma irradiation exhibited significant change in molecular weight. The viscometric analysis thus indicates a proportionate decrease in the molecular weight of PET with respect to the irradiation dose. A dose of 10 kGy exhibited no significant decrease in the molecular weight suggesting a resistance of this molecule towards degradation at lower doses. However doses of 30, 50, 70, and 100 kGy resulted in decrease in the molecular weight by about 15%, 25%, 30%, and 40% respectively suggesting a chain scission of the polymer at these doses resulting in decrease in the molecular weight.

Glycolysis of PET by Conventional Method

The hydroxyl value and melting point for BHET sample were observed as 454 mg KOH/g and 110[degrees]C respectively. The FTIR spectrum of BHET (Fig. 3) shows a transmission band at 3448 [cm.sup.-1] which confirms the presence of O-H stretch. A peak at 2958 [cm.sup.-1] appears because of the stretching vibrations of aliphatic -C[H.sub.2]- group. A transmission band at 1707 [cm.sup.-1] confirms the presence of carbonyl group, whereas peaks at 1509-1404 [cm.sup.-1] correspond to C=C stretch. A peak at 1283 [cm.sup.-1] can be attributed to C-O stretch. The transmission bands at 872 and 726 [cm.sup.-1] show p- substitution on the benzene.

The yield of BHET monomer was calculated according to Eq. 5 and the results are depicted in Table 2. In general, it was observed that the yield of monomeric product, BHET increased with increasing reaction time. Further, the exposure to gamma irradiation resulted in more efficient glycolysis yielding higher quantity of BHET than that in case of nonirradiated one. The yield in case of PET sample irradiated with 10 kGy dose was not significantly higher than that obtained in case of nonirradiated PET sample. However PET waste sample irradiated with 30, 50, 70, and 100 kGy dose could significantly increase the yield at all reaction time intervals and thus the reaction time could also be significantly reduced. For instance PET samples irradiated with 50 kGy could reduce the reaction time by 2 h to yield similar quantity of BHET monomer as that obtained using nonirradiated PET waste. However, complete conversion of PET to the monomeric product could not be achieved in 6 h of reaction time. It was also observed that the rate of percentage conversion of PET to BHET decreased with increase of dosage rate.

Oligomeric Product. The dried oligomeric products of irradiated and nonirradiated PET waste samples were evaluated for hydroxyl (HV) and saponification values (SAPV) to study the molecular weight of the oligomers. The HV and SAPV of different oligomer samples after 2, 4, and 6 h of reaction period are as listed in Table 3.

In an ideal situation, it is considered that the PET chains break into low molecular weight ones after the attack of EG molecule on the ester bond subsequently leading to the formation of BHET. This is also accompanied by the fact that molecular weights of these chains reduce with the reaction time. Hence the hydroxyl values of these chains would increase with reaction time while the SAPV would decrease slowly. Similar trend was obtained when all the samples were evaluated in duplicate for HV and SAPV. The HVs of the oligomeric products increased significantly as the reaction time was increased in all cases. In addition, as the dose of high energy radiation was increased, the hydroxyl values increased rapidly because of higher yields of BHET as seen earlier. This is also supported by the SAP Vs obtained which showed a decreasing trend with increasing reaction time in expected order. The trend observed further confirmed the decreasing trend in its molecular weight resulting from the continuous breakdown of polymer structure.

The average molecular mass of the glycolyzed product obtained at various time intervals of reaction was determined by GPC. The number average molecular weight (Mn) and poly dispersity index (PDI) obtained are given in Table 3. It was observed that the molecular weight of the oligomeric product reduced with increase in the reaction time for all the samples irrespective of the irradiation dosages. Similarly for a given reaction time interval, the molecular weight exhibited significant decrease with increasing irradiation dosage. The PDI of the oligomeric mixture also decreased in the same order suggesting continuous reduction in the molecular weight.

Microwave Assisted Glycolysis of Gamma Irradiated PET

The % yield of BHET monomer was calculated based on formula given in Glycolysis of Gamma Irradiated PET by Conventional Method section and the results are depicted in Table 4. It was observed that 70% BHET yield obtained at minimum 20 minutes of reaction time under microwave conditions. Moreover, the exposure of PET to gamma radiations did not show significant effect on yield of BHET irrespective of the reaction time and the yield remained almost in the same range. Microwaves effectively break large polymer chains into smaller ones more rapidly; as discussed earlier in "Effect of Gamma Irradiation on PET Properties: Reduction in Molecular Weight" section where viscometric analysis indicated 40% decrease in the molecular weight of PET waste irradiated with 100 kGy dose as compared to that in case of nonirradiated PET waste. Thus a decrease in molecular weight of PET waste irradiated by even 100 kGy gamma radiations resulted only 2% higher conversion to BHET.

Synthesis of PE Polyol

The acid value, hydroxyl value, and saponification value of the [PE.sub.1] and [PE.sub.2] polyol were observed to be 2.35, 256, 254.84 and 11.64, 185, 234.5 mg KOH/g, respectively.

The FTIR spectrum (Fig. 4) recorded for the PE polyols showed all distinct peaks. Transmission bands at 2924 and 2854 [cm.sup.-1] were because of aromatic and aliphatic -C-H stretching. Transmission band at 1606 cm'1 was attributed to aromatic C=C bond. The presence of aliphatic -C-O linkages in backbone was indicated by 1267 and 1099 [cm.sup.-1]. The C-H bending was confirmed by peak at 1167 [cm.sup.-1]. Band at 1725 [cm.sup.-1] confirmed the presence of -C=O group from carbonyl ester. Pendant hydroxyl groups in the PE polyol were indicated by the broad transmission band at 3446 [cm.sup.-1].

The PE polyol was also characterized by [sup.1]HNMR as shown in Fig. 5. The signals of chemical shift at [delta] = 4.0 indicate the presence of -C[H.sub.2]- represents the linear aliphatic chain present in structure. The signals of chemical shift at [delta] = 4.3 ppm indicates the presence of ethylene units in the structure. The signals of chemical shift at [delta] = 8.1 ppm marks the presence of aromatic entity in the structure. The signals chemical shifts at [delta] = 4.2 and 3.8 ppm, represents the presence of OOCC[H.sub.2]C[H.sub.2] and OC[H.sub.2]C[H.sub.2] groups of glycolyzed PET, respectively.

The molecular weight distribution of the PE polyol synthesized was determined by GPC. The number average molecular weight (Mn) for PE polyols [PE.sub.1] and [PE.sub.2] were observed to be 17,263 and 10,923 g/mol, respectively. The chromatogram obtained also showed a broad molecular weight distribution for the polyester product.

Coating Properties

The polyurethane coatings were formulated using various kinds of polyisocyanate curing agents. The curing agent N-3390 with a heterocyclic ring, MD1 containing aromatic ring and N-75 with an aliphatic chain were selected to study the effect of their structures on the overall coating properties of cured polyurethane systems. These polyisocyanates with varying content of isocyanate functionalities were also expected to have an impact on final coating properties. The average thickness of the coatings applied was observed to be 55-70 [micro]m.

Mechanical Properties. All the coatings evaluated showed excellent gloss which can be attributed to its polyurethane backbone. The coated substrates were evaluated for mechanical performance as shown in Table 5. Scratch hardness and pencil hardness showed results in assent for both the polyol systems. This is a characteristic of polyurethane linkage that films formed are tough and difficult to notch off. Films with MDI were the hardest amongst the series because of the synergetic effect of higher cross-link density and aromatic nature of polyisocynate cross-linker. For any coated substrate, impact resistance is considered as an ability to uniformly dissipate the energy of the momentarily shock made by an object. The nature of polymer backbone and the free volume available between the chains play a crucial role in this. Impact resistance of all the systems was observed to be satisfactory. All the films could sustain the impact when indenter was released from a height of 60 cm. This could be because of flexible nature of the films formed because of the presence of long aliphatic chains present in dimer fatty acid resulting in free volume available between adjacent chains. Dimer fatty acid and sebacic acid used in preparation of PE polyol were responsible for flexibility of the film. Flexibility test was passed by all the films. Performance of cross cut test in all the films was excellent. This could be because of the presence of polar structure in the cross-linker, which proves useful in wetting of and adhering to the substrate firmly.

Chemical Resistance. Acid and Alkali resistance were investigated and the results are given in Table 5. All the films showed excellent chemical resistance wherein no damages occurred to any of the films kept in acid and alkali solution for more than 72 h. Coated films showed good resistance to xylene rub test which could be because of the presence of long hydrocarbon chains in the polymer backbone offering good stability towards nonpolar solvents. Similarly the rub resistance in case of MEK was also observed to be good reflecting complete curing of resin.

Thermal Properties. Thermal properties of all the coatings were evaluated by DSC and TGA. Glass transition temperature (Tg) for [PE.sub.1] with cross-linkers N 3390, MDI, and N75 were observed to be 47.72[degrees]C, 45.19[degrees]C, and 38.46[degrees]C respectively (Fig. 6). Similarly, Glass transition temperature (Tg) for [PE.sub.2] with cross-linkers N3390, MDI, and N75 were observed to be 52.85[degrees]C, 45.17[degrees]C, and 34.1[degrees]C respectively (Fig. 6). Higher Tg values of polyurethane coatings could be correlated to the type of hardeners used. In case of N-3390 is a HD1 trimer containing heterocyclic isocyanurate ring; whereas MDI is an aromatic diisocyanate which contributed to the higher Tg values of the films cured with it. Substantially lower Tg values of polyurethane films could be because of the lower cross-linked density compared to other films as the cross-linker used in this case was N75 which is an aliphatic polyisocyanate.

The thermal degradation of coatings was evaluated by thermal gravimetric analysis (TGA). The results obtained were plotted as weight percent degraded against the temperature as shown in Fig. 7. Polyurethane coatings with aliphatic polyisocynate cross-linker N-75 showed lower thermal stability as compared to the polyurethane coatings cured with MDI and N-3390 because of the aromatic and heterocyclic isocyanurate moiety present in the cross-linked backbone which results in enhanced stability. Polyurethane coating with N-75 cross-linker decomposed in two distinct stages wherein the aliphatic moiety present in polymer backbone decomposed in the first stage and the aromatic and heterocyclic structures present in polymer backbone decomposed in the second stage at higher temperatures. Overall all the coatings showed good thermal stability irrespective of types of hardeners used.

CONCLUSION

The effect of gamma radiation on properties of PET was investigated and subsequent recycling of PET by glycolysis method was studied. Gamma radiation decreased the molecular weight of PET in dose dependent manner as confirmed by the viscometric analysis. Radiation processing of PET improved the efficiency of glycolysis of PET using excess of EG. Preprocessing of PET waste using gamma radiation yielded higher amount of BHET as compared to that in case of nonirradiated PET samples by conventional method. Moreover, under microwave conditions, the exposure of gamma irradiation on PET did not show significant effect on yield of BHET irrespective of the reaction conditions.

A new approach for the synthesis of polyesters for coating applications, that combines the chemical recycling of PET with the use of materials derived from renewable resources (succinic acid, dimer fatty acid, glycerol) was developed. Formation of polyester resin implied that glycolysed product of PET was a successful replacement for one of the glycols from standard formulation for the resin. All the systems of polyurethane coatings exhibited overall good performance properties. BHET, glycolyzed product of PET waste, was proved to be one of the potential raw materials for polyester synthesis to generate value added product for coating application.

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Vandana Jamdar, (1) Mukesh Kathalewar, (1) R.N. Jagtap, Kumar Abhinav Dubey, (2) Anagha Sabnis (1)

(1) Department of Polymer & Surface Engineering, Institute of Chemical Technology, Nathalal Parekh Marg, Matunga (E), Mumbai 400019, India

(2) Radiation Technology Development Division, Bhabha Atomic Research Centre, Department of Atomic Energy, Government of India, Mumbai 400085, India

Correspondence to: Dr. A.S. Sabnis; e-mail: as.sabnis@ictmumbai.edu.in Contract grant sponsor: Board of Research in Nuclear Sciences (BRNS), India.

DOI 10.1002/pen.24158

Published online in Wiley Online Library (wileyonlinelibrary.com).

TABLE 1. Intrinsic viscosity [[eta]] & number average molecular
weight [Mn] of PET waste samples.

Dose    [t.sub.0]             [[eta].sub.r] =   [[eta].sub.sp] =
(kGy)     (sec)     t (sec)     t/[t.sub.0]     [[eta].sub.r]-1

0          415        709         1.7084             0.7084
10         415        703         1.6939             0.6939
30         415        675         1.6265             0.6265
50         415        652         1.5710             0.5710
70         415        641         1.5445             0.5445
100        415        618         1.4891             0.4891

Dose       [[eta]] =
(kGy)   [[eta].sub.sp]/C   Mn (at 25[degrees]C)

0            1.4168              80387.16
10           1.3879              78148.35
30           1.2530              67931.57
50           1.1421              59836.88
70           1.0891              56040.24
100          0.9783              48398.55

TABLE 2. Percent yield of BHET at different interval of time by
conventional method.

              % Yield of BHET
                  monomer
                at Time (h)

Dose (kGy)   2 h    4 h    6 h

0            34     50     55.3
10           41.6   51     55.2
30           46.4   54.6   57
50           52     56     59.8
70           53.8   57.2   60
100          55.4   58.3   62.4

TABLE 3. Hydroxyl and saponification values and molecular weight of
oligomeric product.

                 Hydroxyl value           Saponification value
                  (mg of KOH/g)              (mg of KOH/g)

Dose (kGy)     2 h     4 h      6 h      2 h      4 h      6 h

0            165.51   190.21   245.07   530.35   524.89   505.25
10           214.74   239.56   256.77   523.15   517.35   495.85
30           224.15   268.80   290.19   519.79   485.39   465.67
50           250.25   280.29   320.73   494.28   470.55   464.82
70           260.45   285.49   325.57   489.12   464.87   459.13
100          276.89   310.45   335.67   478.44   455.39   451.59

                   Molecular weight (g/mol)

                2 h          4 h          6 h

Dose (kGy)   Mn    PDI    Mn    PDI    Mn    PDI

0            690   1.87   580   1.53   445   1.39
10           540   1.82   490   1.51   440   1.33
30           510   1.59   425   1.32   386   1.29
50           438   1.46   390   1.31   360   1.28
70           430   1.37   402   1.29   354   1.23
100          410   1.30   365   1.24   340   1.23

TABLE 4. Percent yield of BHET at different interval of time& power
by microwave method.

Reaction time   0 kGy   50 kGy   100 kGy

300 watts
  20 min        70.5     71.9     73.1
  30 min        72.8     73.2     73.1
  40 min        73.8     74.8     74.1
500 watts
  20 min        72.1     72.3     75.2
  30 min        74.1     73.1     76.4
  40 min        74.9     74.4     75.5
700 watts
  20 min        72.3     74.1     73.9
  30 min        74.3     73.9     74.6
  40 min        73.9     75.5     74.9

TABLE 5. Mechanical properties and chemical resistance of polyester
polyol.

Mechanical properties of polyester polyol

                                          [Pes.ub.1]

Test method              N-75              N-3390              MDI

Dry film thickness       50-85             55-80              50-80
  ([mu])
Gloss(60[degrees])       85-90             95-102             99-103
Scratch hardness (kg)     1.3               1.6                1.5
Falling dart impact              Intrusion = 1.36 kg-60 cm,
                                 Extrusion = 1.36 kg-60 cm
Pencil hardness           3H                 3H                 6H
Cross cut adhesion        5B                 5B                 5B
Flexibility (mm)           0                 0                  0
Chemical Resistance of
  Polyester Polyol
Acid resistance                            >72 h
Alkali resistance                          >72 h
Solvent resistance                       >200 rubs

                                          [Pes.ub.2]

Test method              N-75              N-3390              MDI

Dry film thickness       50-80             55-85              50-85
  ([mu])
Gloss(60[degrees])       88-90             95-100             98-103
Scratch hardness (kg)     1.3               1.6                1.6
Falling dart impact              Intrusion = 1.36 kg-60 cm,
                                 Extrusion = 1.36 kg-60 cm
Pencil hardness           4H                 5H                 5H
Cross cut adhesion        5B                 5B                 5B
Flexibility (mm)           0                 0                  0
Chemical Resistance of
  Polyester Polyol
Acid resistance                            >72 h
Alkali resistance                          >72 h
Solvent resistance                       >200 rubs
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Title Annotation:Polyethylene terephthalate
Author:Jamdar, Vandana; Kathalewar, Mukesh; Jagtap, R.N.; Dubey, Kumar Abhinav; Sabnis, Anagha
Publication:Polymer Engineering and Science
Article Type:Report
Geographic Code:9INDI
Date:Nov 1, 2015
Words:5524
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