Pe

SEU

a

ARR1A

KMPDSAR

1

odibhepdnpmps

trtmp

(

0h

J. of Supercritical Fluids 75 (2013) 138– 143

Contents lists available at SciVerse ScienceDirect

The Journal of Supercritical Fluids

jou rn al h om epa ge: www.elsev ier .com/ locate /supf lu

ET and aluminum recycling from multilayer food packaging using supercriticalthanol

.L. Fávaro, A.R. Freitas, T.A. Ganzerli, A.G.B. Pereira, A.L. Cardozo, O. Baron, E.C. Muniz,

.M. Girotto, E. Radovanovic ∗

niversidade Estadual de Maringá, Departamento de Química, Grupo de Materiais Poliméricos e Compósitos, Av. Colombo 5790, 87020-900, Maringá, Paraná, Brazil

r t i c l e i n f o

rticle history:eceived 8 August 2012eceived in revised form8 December 2012ccepted 19 December 2012

a b s t r a c t

Different properties, such as barriers to gas, light, flavor and water vapor, as well as flexibility, are nec-essary for the production of food packages. These properties may be obtained by combining differentpolymers. In spite of the advantages achieved with the use of multilayer films, the recycling process ofsuch material is a challenging task. This study presents an alternative for recycling of a quite common foodpackaging kind, which contains polyethylene (PE), aluminum and poly(ethylene terephthalate) (PET) asa multilayer film. The multilayer packages were delaminated with acetone. PET was depolymerized by

eywords:ultilayer packaging

oly(ethylene terephthalate)iethyl terephthalateupercritical ethanolluminum

ethanol in supercritical conditions. The diethyl terephthalate (DET) was obtained as the main product,presenting high purity and yield of 80%. Also, metallic aluminum was obtained by the PET-depolymerizingprocess. The optimal reaction time was 120 min. The products were characterized by FTIR, 1H NMR and13C NMR spectroscopies, DSC and TGA.

© 2013 Elsevier B.V. All rights reserved.

ecycling

. Introduction

Several properties, including barrier to water vapor, gas, flavorr light, as well as flexibility or rigidity, are necessary for the pro-uction of food packaging. These features are hardly ever found

n one specific starting material. If on one hand a polymer coulde advantageous for having mechanical resistance, on the otherand it could be extremely inconvenient in relation to other prop-rties, such as transparency and permeability [1,2]. Thus, the foodackaging industry needs to develop multilayer films, containingifferent polymers. Multilayer films may be manufactured by lami-ation or co-extrusion. These physical processes combine differentolymers, originating a film with especial chemical, physical andechanical properties [3,4]. Another material that is used in these

ackages is the aluminum, preventing the food from the effect ofunlight and ultraviolet radiations [5].

In spite of the advantages achieved by using multilayer films,he recycling of such kind of material is very difficult. The sepa-ation and classification process of these films are hard task due

o the polymers similarity. Multilayer films are composed of poly-

ers incompatible for extrusion recycling [6–8]. Film containingoly(ethylene terephthalate) (PET) is an interesting example. For

∗ Corresponding author. Tel.: +55 44 30113653; fax: +55 44 3261 4125.E-mail addresses: eradovanovic@uem.br, eradovan@bol.com.br

E. Radovanovic).

896-8446/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.supflu.2012.12.015

the extrusion of PET, it is necessary to achieve higher tempera-tures than those used for the extrusion of other polymers, such aspolyethylene (PE) and polypropylene (PP).

A single medium-sized food packaging factory, for instance,produces about 8 ton monthly of parings of multilayer films con-taining PET. These films are gathered in the factory or turnedinto waste. Thus, the future of multilayer packages has become agreat environmental concern. The separation of polymers beforerecycling would be an interesting method to overcome the limita-tions presented by extrusion-recycling of multilayer films.

Numerous processes for PET depolymerization have beenperformed with different depolymerizing conditions. The mostused processes are glycolysis, hydrolysis and alcoholysis. Theglycolysis process using ethylene glycol depolymerizes PET tobis-(hydroxyethyl) terephthalate (BHET) [9–11]; the hydrolysisprocesses under acidic or basic conditions produce terephthalateacid (TPA) [12–17], and the alcoholysis processes using supercrit-ical methanol and supercritical ethanol in PET depolymerizationhave as products dimethyl terephthalate (DMT) and diethyl tereph-thalate (DET), respectively [17–20]. All of these processes presentboth advantages and drawbacks. Supercritical fluids are verystriking means for running chemical reactions, mainly becauserelatively minor changes in either temperature or pressure into

the system can modify appreciably and continuously the solventand the transport properties of a single solution [21,22]. Anotherpoint, influencing on the reaction, is the variation of the supercrit-ical fluid density because it can change the chemical potential of

critical Fluids 75 (2013) 138– 143 139

s[lduir

fapca

2

sToiod

oah((atvfp

2

t

2

(t

2

v6a

2

iFau

2

M1

u

3000 250 0 200 0 150 0 100 0

Inte

nsity (

a.u

.)

Wavenumber(cm-1 )

2919 cm-1

2850 cm-1

1465 cm-1

1370 cm-1

720 cm-1

1100 cm-1

1240 cm-1

1710 cm-1

A

B

C

S.L. Fávaro et al. / J. of Super

olutes, and also the reaction rate and the equilibrium constant23]. Although methanolysis has been extensively studied in theast years [17–20,24,25], the use of ethanolysis in supercritical con-ition as a PET depolymerization method has few studies [22]. These of this method may be particularly interesting, once ethanol

s an abundant material, mainly in Brazil; besides, it stems from aenewable source and its cost is relatively low.

This study represents an alternative method for recycling of arequently used food packaging kind, which contains PE, Aluminumnd PET, by separation and recycling of PET in multilayer films. Theroduct of depolymerization of PET, by supercritical ethanol, washaracterized by means of FTIR, 1H NMR, 13C NMR spectroscopiesnd thermo-analysis (DSC and TGA).

. Experimental

The parings of multilayer film from the packaging industry wereupplied by Ingaplas Ind. e Com. de Plásticos (Maringá, PR – Brazil).he films were cut to 200 × 300 mm. After, they were washed andven-dried at 60 ◦C for 4 h. The films delamination was performedn acetone (nuclear) at 50 ◦C under stirring for 4 h. The quantityf each material (PE, Al and PET) contained in the packaging wasetermined by gravimetry.

For the depolymerization of PET, 1 gram of sample and 60 mlf anhydrous ethanol (Dinamica) were loaded into the reactort room temperature. Then, the vessel and its contents wereeated (ca. 8 ◦C/min) up to the reaction temperature of 255 ◦CTc ethanol = 241 ◦C). The reaction was carried out at 11.65 MPaPc ethanol = 6.14 MPa). This pressure was attained by the initialmount of the solution in the vessel. After the required reactionime (30, 60 and 120 min), the heating collar was removed, and theessel was quenched to room temperature with large amounts ofresh water. After each run, the reaction product was obtained fromrecipitation in water.

.1. Characterization

The following techniques were used in the analyses of films andhe products of PET depolymerization:

.1.1. Thermogravimetric analysis (TGA)TGA was performed using TGA-50 Thermogravimetry Analyzer

Shimadzu). 6 mg of sample in aluminum pan was heated from 25o 550 ◦C at 10 ◦C/min under flowing N2(g) at 10 mL min−1.

.1.2. Differential Scanning Calorimetry (DSC)DSC was obtained using a DSC-50 calorimeter (Shimadzu) pre-

iously calibrated with indium standard. Sample masses of about mg in an aluminum-closed pan were heated from 25 ◦C to 500 ◦Ct 10 ◦C/min under flowing N2(g) at 20 mL min−1.

.1.3. Infrared spectroscopy (FTIR and FTIR-HATR)The films IR spectra were recorded in FTIR-Pike Miracle ATR, Dig-

lab Scimitar Series using Horizontal Attenuated Totally Reflectanceourier Transformed Infrared spectroscopy technique, FTIR-HATR,nd the spectra of reaction product were recorded in KBr pelletssing a FTIR-BOMEM-100 Spectrometer.

.1.4. 1H NMR and 13C NMR spectroscopies

The 1H NMR and 13C NMR spectra were recorded in a Varian

ercury Plus BB 300 MHz spectrometer operating at 75.34 MHz for3C with contact time of 1 ms and recycle time of 1.36 s. The solventsed was acetone-d6.

Fig. 1. FTIR–ATR spectra of delaminated polymers: A) PE, B) PET-side 1 (PET withoutAl) and C) PET met-side 2 (PET covered with Al).

2.1.5. Scanning electron microscopy (SEM)SEM image was obtained using a Shimadzu Superscan SS-550

scanning electron microscope. The samples were gold coated bysputtering technique and observed under different magnifications.Chemical analysis was performed using energy dispersive X-rayspectroscopy (EDX).

2.1.6. X-ray diffractometry (XRD)The diffraction patterns were obtained in an XRD-6000 X-ray

Diffractometer (Shimadzu) with 2� varying between 10◦ and 90◦

at 2◦ min−1.

3. Results and discussion

The multilayer packaging is composed of a layer of PET met-alized with aluminum (12 �m) and a layer (41 �m) of a blend(70/30) of linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE). The packaging was obtained bylamination using an adhesive with two-component solvent-basedpolyurethane adhesive. The composition of packaging was deter-mined after delamination: 48.5 ± 1.0 wt-% of PET, 49.5 ± 1.0 wt-% ofPE and 2.0 ± 0.1 wt-% of Al were found.

Fig. 1 shows the FTIR–ATR spectra of separated films. Thecharacteristic absorption peaks of polyethylene (Fig. 1A) at 2919,2850, 1465, and 720 cm−1 are attributed to methylene asymmet-ric stretching vibration, methylene symmetric stretching vibration,methylene asymmetric bending vibration, and methylene swingin plan vibration, respectively [26]. It is possible to verify at∼1700 cm−1 and at ∼1100 cm−1 the characteristic bands of C Oand C O groups, respectively [27,28]. Such groups could be gen-erated at the PE surface by oxidation due to the environmentalexposition. FTIR spectra of both surfaces of PET film were recorded.Fig. 1B presents the PET (side 1 – PET not metalized) spectrumwith the main absorption bands observed in the FTIR–ATR modewhich are: the aliphatic C H asymmetric stretching vibration at2960 cm−1; the C O stretching vibration at 1710 cm−1; one ofseveral aromatic skeletal stretching vibrations at 1410 cm−1; theC(O) O stretching vibration of ester group at 1240 cm−1; bands inthe skeletal ring at 1113 and 1021 cm−1 indicative of an aromatic

substitution pattern; the O CH2 stretching vibration of ethyl-ene glycol segment at 970 cm−1; and probably the out-of-planedeformation of two carbonyl substituent on the aromatic ring at729 cm−1. The FTIR spectrum of metalized surface of PET (side

140 S.L. Fávaro et al. / J. of Supercritical Fluids 75 (2013) 138– 143

0 100 200 300 400 500

Temperature (ºC)

Film

PET

PE

118 ºC109 ºC

253 ºC

EXO

2ab

dsdpcddlTabmmttDdbpt

50 100 150

(A)

(B)

Temperature (ºC)

(C)

EXO

Fig. 2. DSC curves of film, PE (delaminated) and PET (delaminated).

– PET metalized) presents only noise in the characteristic PETbsorbing region indicating that its surface is completely coveredy aluminum.

Thermal analysis was employed in order to verify whether theelamination process influences the stability of polymers. Fig. 2hows the DSC curves of film and of PE and PET polymers afterelamination. As it could be observed in the DSC curve of film, theeak at ca. 120 ◦C is related to the melting of polyethylene, whichould be confirmed by the DSC PE curve. This peak has a broad shapeue to the presence of different kinds of polyethylene: linear low-ensity polyethylene – LLDPE (melting temperature of 109 ◦C) and

ow-density polyethylene – LDPE (melting temperature of 118 ◦C).herefore, the studied package is composed of PET, aluminum and

mixture of LLDPE and LDPE. Such mixture (LLDPE/LDPE) is usedecause pure LLDPE presents high shear resistance, which makes itore difficult to be processed than pure LDPE [29]. However, filmsade of LLDPE present better mechanical and optical properties

han LDPE. The second peak at 253 ◦C, in the DSC curve relativeo the film, is attributed to melting of PET, also observed in theSC PET curve. For temperatures higher than 400 ◦C the polymersegradation is observed; such temperature range was not changed

y the delamination process, as can be seen in the DSC curves ofure components. The thermogravimetric analyses (Fig. 3) confirmhe delamination process did not change the thermal properties of

400 600 800

0

20

40

60

80

100

We

igh

t lo

ss (

%)

Temperature (ºC)

PE

PET

Film

Fig. 3. TGA analysis of film, PE (delaminated) and PET (delaminated).

Fig. 4. DSC curves of ethanolysis products after (a) 30 min, (b) 60 min, (c) 120 minof reaction.

materials. The temperature in which the weight loss rate is greatestfor the film and both polymers (after delamination) is ca. 400 ◦C.

The DSC technique was employed, in analysis of ethanolysisproducts of PET, in order to evaluate the best reaction time, sinceit is possible to observe from melting temperatures the obtainingof monomers or oligomers of different molecular weight. Fig. 4presents the DSC curves for obtained products after depolymer-ization of PET by ethanolysis reaction. Curve A is referent to theproduct obtained after 30 min of reaction, in which the signal thatappears over 150 ◦C indicates the presence of oligomers of differentmolecular weights. The melting temperature is function of lamellarthickness, which presents the trend to be larger with increasing themolecular weight as well as the existence of oligomers with differ-ent sizes. In curve B it is possible to observe signals in the range of100 and 180 ◦C suggesting the presence of oligomers of low molec-ular weights arising from the incomplete depolymerization processof PET for 60 min of reaction. However, the products obtained in thelimit of PET depolymerization by supercritical ethanol are diethyltereftalate (DET) and ethylene glycol, as presented in Fig. 5. Curve Cproves the obtaining of pure DET for 120 min of reaction. The peakat 43 ◦C was associated to the melting of DET, which presented highpurity based on its single sharp peak. The yield of DET for 120 minof reaction was 80%. Therefore, the following data are referent tothe product obtained from 120 min of ethanolysis of PET.

The diethyl terephthalate, like all esters, has two strong char-acteristic bands in IR spectroscopy, one due to the C O stretchingvibration and the other one due to the C O stretching vibration.

Fig. 6 shows the FTIR spectrum of DET. The band that appears at1727 cm−1 was related to the C O stretching vibration. The C O Cpresented two bands at 1130 cm−1 and at 1270 cm−1 attributedto symmetrical and asymmetrical C O C stretching, respectively.

O O

O O CH2CH 2CH2CH 2

Supercritical ethanol

O O

O O CH2CH 3H3CCH2

+ HOCH2CH 2OH

Fig. 5. Scheme of depolymerization reaction of PET by ethanolysis.

S.L. Fávaro et al. / J. of Supercritical Fluids 75 (2013) 138– 143 141

4000 3500 3000 2500 2000 1500 1000 500

-1

Inte

nsity (

A.U

.)

Tstb

NisnfcNaoFcsne6ctabu

200 18 0 16 0 14 0 12 0 10 0 80 60 40 20 0

O

OO

O H2CCH2CH3 CH3

H H

HH

1 1

1 1

223 34 45 5

ppm

123 4 5

Wavenumber (cm )

Fig. 6. FTIR spectrum of product from ethanolysis of PET.

he other characteristic bands of DET are: the aromatic C Htretching vibration at ∼2990 cm−1; the ring C C stretching vibra-ion at ∼1500 cm−1; the CH out-of-plan vibration at 730 cm−1; theand at 3420 cm−1 attributed to overtones of carbonyl group [27].

The product purity was determined through 1H NMR and 13CMR, as shown in Figs. 7 and 8, respectively. Three signals were

dentified in 1H NMR and were attributed to the structure, alsohown in Fig. 7. The aromatic ring hydrogen atoms identified asumber 1, presented chemical shift at � 8.1 ppm. The hydrogens

rom ethyl and methyl groups, numbered as 2 and 3, presented thehemical shift at � 4.3 and at � 1.39 ppm, respectively. From 13CMR spectrum six signals can be observed, the signal that occurst � 30 ppm belongs to carbons of acetone (used as solvent). Thether five signals were attributed to the structure also shown inig. 8. The aromatic ring carbons, identified as number 1, presentedhemical shift at � 130 ppm, and those identified as number 2 pre-ented the signal at � 135 ppm. The carbonyl carbon identified asumber 3 showed signal at � 166 ppm. The carbons from ethyl-ne and methyl groups, numbered as 4 and 5 presented signal at �2 and at � 14 ppm, respectively. Since the spectra presented onlyhemical shifts related to DET, it is reasonable to infer that impuri-ies, oligomers and non-reacted PET are not present [22]. The large

mounts of high purity organic products obtained can be explainedy the fact that industrial waste, and not domestic waste, is beingsed in this study.

12 10 8 6 4 2 0

O

OO

O H2CCH2CH3 CH3

H H

HH1 1

1 1

2 23 3

ppm

1 2 3

Fig. 7. 1H NMR spectrum of product from ethanolysis of PET.

Fig. 8. 13C NMR spectrum of product from ethanolysis of PET.

Fig. 9 shows the EDX spectrum from the scanning electronmicroscopy analysis of reminiscent aluminum after depolymeriza-tion of PET by ethanolysis reaction. The peak related to gold is due tothe metallization process before image acquisition. The EDX spec-trum presents two peaks, one at 1.4 keV, attributed to aluminum,and another at 0.5 keV, related to oxygen, indicating that the thinlayers observed in the micrographs (inserted in Fig. 9) are com-posed of aluminum oxide and metallic aluminum. The carbon peakcould be assigned to the polyethylene or residues of PET embed-ded at the aluminum surface during delamination process. Fig. 10shows the XRD pattern of aluminum and the peaks at 2� = 39◦, 43◦,65◦, 78◦ and 83◦ are characteristics of the cubic structure of metal-lic aluminum. The signals at 2� = 32◦, the large signal between 38◦

and 40◦ and the signals at 46◦ and 60◦ refer to the presence of alu-minum oxide [30]. The presence of crystalline polyethylene in thealuminum surface is confirmed by the signals at 2� = 22◦, 24◦, 36◦

and 55◦ [31,32].The ethylene glycol (EG) obtained as a product of reaction was

purified by distillation, considering the large difference of boilingpoint among the components of reaction medium (ethanol: 78 ◦C;water: 100 ◦C; ethylene glycol: 197 ◦C). Fig. 11 shows the 1H NMR

Fig. 9. EDS spectrum of aluminum from ethanolysis of PET. SEM image of aluminumis embedded in the graph.

142 S.L. Fávaro et al. / J. of Supercritica

20 40 60 80

0

200

400

600

800

1000

(222)

(311)

(220)(200)

Inte

nsity (

a.u

.)

2θ

(111)

Al2O3

(C2H4)n-Polyethylene

Fig. 10. XRD diffraction pattern of aluminum obtained from ethanolysis of PET.

8 7 6 5 4 3 2 1 0

s�agpsruc

4

uttOaoTuvpmra

[

[

[

[

[

[

[

[

[

[

[

[

ppm

Fig. 11. 1H NMR spectrum of ethylene glycol.

pectrum of EG after purification. It can be observed the signal at 4.2 ppm, regarding to hydroxyl group and the coupling signalt � 3.6 ppm, attributed to the presence of water in the ethylenelycol sample. Therefore, simple distillation is not enough to com-letely remove the water, considering the high solubility amonguch components. However, the amount of water present in theecovered EG after depolymerization reaction does not prevent itsse for applications that do not require high purity, such as liquidooling systems.

. Conclusions

The depolymerization of PET took place by reaction with ethanolnder supercritical conditions. The obtained products in this reac-ion are diethyl terephthalate and ethylene glycol. The diethylerephthalate is easily obtained through precipitation in water.n the other hand, ethylene glycol could be purified from ethanolnd water by distillation. The obtained diethyl terephthalate wasf high purity as confirmed by DSC, 1H NMR and 13C NMR.herefore, the depolymerization of PET, from multilayer packages,sing ethanol under supercritical conditions has proven to be aery attractive route, considering the viewpoint of obtaining high

urity products and low time-reaction necessary, once the startingaterial is composed of several constituents, and the generated

esidues could be easily recovered. Considering the high value-dded of aluminum and the environmental impact caused by its

[

l Fluids 75 (2013) 138– 143

inappropriate disposal, the recovery of aluminum-embedded PETsurface by the ethanolysis is extremely advantageous. The PEobtained during delamination process could be easily recycled byextrusion. The method can be considered environmentally benign,since the solvents used (acetone and alcohol) were recovered bydistillation.

Acknowledgements

S. L. Fávaro is grateful to CNPq (Brazil) for her doctoral fellow-ship. A. R. Freitas thanks CAPES (Brazil) for the doctoral fellowship.The authors wish to thank the COMCAP–UEM by the SEM analysis.

References

[1] P.H. Munoz, R. Catala, R. Gavara, Effect of sorbed oil on food aroma loss throughpackaging materials, Journal Of Agricultural And Food Chemistry 47 (1999)4370–4374.

[2] F. Forlin, J.A.F. Faria, Considerac ões Sobre a Reciclagem de Embalagens Plásticas,Polímeros 12 (2002) 1–10.

[3] A. Badeka, A.E. Goulas, A. Adamantiadi, M.G. Kontominas, Physicochemicaland mechanical properties of experimental coextruded food-packaging filmscontaining a buried layer of recycled low-density polyethylene, Journal Of Agri-cultural And Food Chemistry 51 (2003) 2426–2431.

[4] S. Chytiri, A.E. Goulas, K.A. Riganakos, A. Badeka, M.G. Kontominas, Volatileand non-volatile radiolysis products in irradiated multilayer coextruded foodpackaging films containing a buried layer of recycled low density polyethylene,Food Additives and Contaminants 22 (2005) 1264–1273.

[5] A.K. Kulkarni, S. Daneshvarhosseini, H. Yoshida, Effective recovery of pure alu-minum from waste composite laminates by sub- and super-critical water,Journal of Supercritical Fluids 55 (2011) 992–997.

[6] V. Siracusaa, P. Rocculib, S. Romanib, M.D. Rosab, Biodegradable polymers forfood packaging: a review, Trends in Food Science & Technology 19 (2008)634–643.

[7] S. Chytiria, A.E. Goulasb, K. Riganakosa, M.G. Kontominasa, Thermal, mechani-cal and permeation properties of gamma-irradiated multilayer food packagingfilms containing a buried layer of recycled low-density polyethylene, RadiationPhysics and Chemistry 75 (2006) 416–423.

[8] B. Singh, N. Sharma, Mechanistic implications of plastic degradation, PolymerDegradation and Stability 93 (2008) 561–584.

[9] J.Y. Chen, Y.C. Ou, C.C. Lin, Depolymerization of poly(ethylene terephthalate)resin under pressure, Journal of Applied Polymer Science 42 (1991) 1501–1507.

10] U.R. Vaidya, V.M. Nadkarni, Polyester polyols from glycolyzed PET waste: Effectof glycol type on kinetics of polyesterification, Journal of Applied Polymer Sci-ence 38 (1989) 1179–1190.

11] M.E. Viana, A. Riul, G.M. Carvalho, A.F. Rubira, E.C. Muniz, Chemical recycling ofPET by catalyzed glycolysis: kinetics of the heterogeneous reaction, ChemicalEngineering Journal 173 (2011) 210–219.

12] S.D. Mancini, M. Zanin, Influência de Meios Reacionais na Hidrólise de PET Pós-Consumo, Polímeros 12 (2002) 34–40.

13] G. Guc lu, T. Yalcınyuva, S. Ozgumus, M. Orba, Simultaneous glycolysis andhydrolysis of polyethylene terephthalate and characterization of products bydifferential scanning calorimetry, Polymer 44 (2003) 7609–7616.

14] G.M. Carvalho, E.C. Muniz, A.F. Rubira, Hydrolysis of post-consumepoly(ethylene terephthalate) with sulfuric acid and product characterizationby WAXD, 13C NMR and DSC, Polymer degradation and Stability 91 (2006)1326–1332.

15] O. Sato, K. Arai, M. Shirai, Hydrolysis of poly(ethylene terephthalate) andpoly(ethylene 2,6-naphthalene dicarboxylate) using water at high tempera-ture: Effect of proton on low ethylene glycol yield, Catalysis Today 111 (2006)297–301.

16] D. Paszun, T. Spychaj, Chemical recycling of poly(ethylene terephthalate),Industrial & Engineering Chemistry Research 36 (1997) 1373–1380.

17] T. Yoshioka, T. Sato, A. Okuwaki, Hydrolysis of waste PET by sulfuric acid at150 ◦C for a chemical recycling, Journal of Applied Polymer Science 52 (1994)1353–1355.

18] M. Genta, M. Goto, M. Sasaki, Heterogeneous continuous kinetics modeling ofPET depolymerization in supercritical methanol, Journal of Supercritical Fluids52 (2010) 266–275.

19] M. Goto, Chemical recycling of plastics using sub- and supercritical fluids, Jour-nal of Supercritical Fluids 47 (2009) 500–507.

20] Y. Yang, Y. Lu, H. Xiang, Y. Xu, Y. Li, Study on methanolytic depolymerization ofPET with supercritical methanol for chemical recycling, Polymer Degradationand Stability 75 (2002) 185–191.

21] H. Machida, M. Takesue, R.L. Smith Jr., Green chemical processes with

supercritical fluids: properties, materials, separations and energy, Journal ofSupercritical fluids 60 (2011) 2–15.

22] R.N.E. Castro, G.J. Vidotti, A.F. Rubira, E.C. Muniz, Depolymerization ofpoly(ethylene terephthalate) wastes using ethanol and ethanol/water in super-critical conditions, Journal of Applied Polymer Science 101 (2006) 2009–2016.

critica

[

[

[

[

[

[

[

[

[

S.L. Fávaro et al. / J. of Super

23] G. Sivalingam, G. Madras, Kinetics of degradation of polycarbonate in super-critical and subcritical benzene, Industrial & Engineering Chemistry Research41 (2002) 5337–5340.

24] T. Sako, I. Okajima, T. Sugeta, K. Otake, S. Yoda, Y. Takebayashi, C. Kamizawa,Recovery of constituent monomers from polyethylene terephthalate withsupercritical methanol, Polymer Journal 32 (2000) 178–181.

25] M. Banchero, A. Ferri, L. Manna, The phase partition of disperse dyes in the dye-ing of polyethylene terephthalate with a supercritical CO2/methanol mixture,Journal of Supercritical fluids 48 (2009) 72–78.

26] S.L. Fávaro, A.F. Rubira, E.C. Muniz, E. Radovanovic, Surface modification of

HDPE, PP, and PET films with KMnO4/HCl solutions, Polymer Degradation andStability 92 (2007) 1219–1226.

27] M. Zenkiewicz, M. Raucheisz, J. Czuprynska, Comparison of some oxidationeffects in polyethylene film irradiated with electron beam or gamma rays,Radiation Physics and Chemistry 68 (2003) 799–809.

[

l Fluids 75 (2013) 138– 143 143

28] L. Kupper, J.V. Gulmine, P.R. Janissek, H.M. Heise, Attenuated total reflectioninfrared spectroscopy for micro-domain analysis of polyethylene samples afteraccelerated ageing within weathering chambers, Vibrational Spectroscopy 34(2004) 63–72.

29] D. Abraham, K.E. George, D.J. Francis, Rheological characterization of blends oflow density with linear low density polyethylene using a torque rheometer,European Polymer Journal 26 (1990) 197–200.

30] M.E. Straumanis, Absorption correction in precision determination of latticeparameters, Journal of Applied Physics 30 (1959) 1965–1969.

31] A.M.E. Baker, A.H. Windle, Evidence for a partially ordered component

in polyethylene from wide-angle X-ray diffraction, Polymer 42 (2001)667–680.

32] M.F. Butler, A.M. Donalda, A.J. Ryanb, Time resolved simultaneous small- andwide-angle X-ray scattering during polyethylene deformation 3. Compressionof polyethylene, Polymer 39 (1998) 781–792.