PET Oligomer Waste to Modify CAP Characteristics

doi:10.4236/msa.2012.38082

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Materials Sciences and Applications, 2012, 3, 575-579

http://dx.doi.org/10.4236/msa.2012.38082 Published Online August 2012 (http://www.SciRP.org/journal/msa)

575

PET Oligomer Waste to Modify CAP Characteristics

L. C. Mendes*, M. L. Dias, P. S. C. Pereira, L. M. R. Albuquerque

Centro de Tecnologia, Instituto de Macromoléculas Professora Eloisa Mano-IMA, Universidade Federal do Rio de Janeiro-UFRJ,

Rio de Janeiro, Brazil.

Email: *[email protected]

Received May 16th, 2012; revised June 10th, 2012; accepted July 12th, 2012

ABSTRACT

To develop an improved method of reusing poly(ethylene terephthalate) (PET) waste in the production chain, it was

chemically modified with pentaerythritol (PENTE), resulting in PET/PENTE (60/40) oligomer. This was added to

petroleum asphalt cement (CAP) in different proportions—5, 10 and 20 wt%—as a modifier of bitumen characteristics.

The mixture was evaluated by thermogravimetry (TG/DTG), differential scanning calorimetry (DSC), infrared spec-

troscopy (FT-IR), optical microscopy (OM) and the adhesion-peel test. The oligomer enhanced substantially the asphalt

thermal stability-Tonset. OM images showed strong compatibility between components and PET’s amorphization. PET

oligomer increased CAP’s wettability and the mixture presented cohesive fracture through the peel test. The mixture has

excellent potential as paving material.

Keywords: PET Waste; Pentaerythritol; CAP; Recycling

1. Introduction

In recent years, the growing use of polymers in everyday

products has generated an enormous amount of munici-

pal solid waste. This has brought many environmental

problems. In general, these wastes take long time to un-

dergo spontaneous degradation and release toxic gases if

they are burned [1,2]. The majority of discarded polymer

materials are from packaging. Taking into account the

huge potential of plastics and the problems caused by

pollution from waste, there is a growing worldwide trend

to recycle them [3]. When reused, PET packages show

several advantages—lower consumption of water and

energy and environmental and social benefits, among

others [4]. Waste disposal is a main concern of society,

prompting actions by industry and research centers [5-7].

Recently, an article on PET waste oligomerization through

the action of polyfunctional alcohol—pentaerythritol was

published [8].

Polymers have been studied as modifiers of asphalt

mainly to overcome some deficiencies of asphalt cement

and to improve its properties, such as reducing perma-

nent thermal deformation and cracking. As modifier

agents, polymers are compatible and increase asphalt de-

gradation at high temperatures. The asphalt’s characteris-

tics as well as the type and amount of polymer have a

large influence on the appropriate asphaltic mixture [9,

10].

Asphalt cement can be formed naturally, through eva-

poration of surface oil deposits, but the majority comes

from the heavy fraction of petroleum from distillation at

refineries. Petroleum asphalt cement (CAP) consists of

90% - 95% hydrocarbons—saturated and aromatic—and

5% - 10% of structures with hetero atoms (oxygen, sulfur,

nitrogen) and metals, such as vanadium, nickel and iron.

Brazilian CAPs have low sulfur and metals content but

high levels of nitrogen. Asphaltenes and maltenes are the

main asphalt components. They are complex mixtures

consisting of condensed aromatic rings, resins and satu-

rated and aromatic compounds. The ratio between as-

phaltenes and maltenes has a significant effect on asphalt

performance [11-14]. The reuse of plastics as additives

for CAP increases the possibility of using urban plastic

waste in the productive chain [15,16].

This work intended to develop a new material from

plastic arising from municipal solid waste. The discarded

PET was oligomerized by a polyfunctional alcohol. The

PET oligomer was mixed with CAP in different propor-

tions to evaluate its influence on the CAP’s thermal, ad-

hesive and morphological characteristics.

2. Experimental

2.1. Materials

Flakes of poly (ethylene terephthalate) (PET) waste with

24% crystallinity degree were supplied by CPR Ltd. (Rio

de Janeiro, Brazil). Commercial pentaerythritol, here

*Corresponding author.

PET Oligomer Waste to Modify CAP Characteristics

576

called PENTE, was provided by S. A. Degussa (São

Paulo, Brazil). Commercial zinc acetate produced by J. T.

Baker was used without further purification. The asphalt

cement was from a refinery.

2.2. Oligomer Preparation

This measurement and others are deliberate, using speci-

fications that anticipate your paper as one part of the en-

tire proceedings, and not as an independent document.

Please do not revise any of the current designations. The

PET/PENT (60/40) blend containing 0.5 wt% zinc ace-

tate catalyst was prepared by melt processing in an Ha-

ake Rheomix 600 internal mixer, at 250˚C, 60 rpm, for

10 minutes. Before processing, PET flakes were previ-

ously dried at 120˚C, for 4 hours [8].

2.3. CAP/Oligomer Mixture

The mixture of CAP with PET/PENTE oligomer in dif-

ferent oligomer proportions (5, 10 and 20 wt%), called

CAP (95/5), CAP (90/10) and CAP (80/20), respectively,

was prepared in a 500 mL glass flask, at 180˚C, with

mechanical stirring (600 rpm) for 2 hours.

2.4. Thermogravimetry and Derivative

Thermogravimetry (TG/DTG)

The TG/DTG curves were obtained by a TA thermoana-

lyzer (Q500) by heating the sample from 30˚C to 700˚C

at a heating rate of 10˚C·min −1 under nitrogen atmos-

phere. The onset temperature (Tonset), maximum degrada-

tion temperature (Tmax) and end temperature (Tend) were

determined.

2.5. Differential Scanning Calorimetry (DSC)

Calorimetric measurements were carried out in a TA

calorimeter (Q1000). The sample was heated from −20˚C

to 100˚C at a heating rate of 10˚C·min −1 under nitrogen

atmosphere (first scan), kept for 2 min to erase the ther-

mal history, and then cooled to −20˚C at the maximum

(second scan). A second heating cycle (third scan) was

performed with the same protocol as the first scan. The

variation in the baseline was evaluated considered the

PET glass transition temperature, Tg, and CAP thermal

transition temperature [17-19].

2.6. Morphological Analysis

The morphology was analyzed under a Zeiss model

THMS 600 microscope from squeezed film between two

glass slides. The assembly was inserted into the micro-

scope in the hot stage and heated from 25˚C to 280˚C,

where it was kept for 2 minutes to eliminate the thermal

history. After that, the cooling was performed until 25˚C.

The morphology of the matrix and dispersed phase was

monitored by taking photographs.

2.7. Peel Test

The adhesive characteristic of the asphaltic mixture was

evaluated based on the ASTM D1876 standard [20]. The

material was poured between aluminum plates with con-

stant thickness and the assembly was taken for peeling in

an Instron machine. The force of peeling was registered

and then test photos were taken to evaluate what kind of

fracturing—adhesive or cohesive had occurred.

3. Results and Discussion

3.1. Thermogravimetry and Derivative

Thermogravimetry (TG/DTG)

Figures 1 and 2 show the degradation and first derivative

curves of the materials, respectively. Table 1 contains

the Tonset, Tmax, and Tend degradation temperatures and

amount of residue. The PET/PENT 60/40 blend pre-

sented three degradation steps. The first one was located

at 100˚C - 175˚C and it was attributed to the absorbed

water. The next one occurred at 250˚C - 325˚C, caused

by the unreacted pentaerythritol. The final step, at 325˚C

- 525˚C, was the result of the degradation process of the

PET/PENTE oligomers.

The CAP’s curve shows a unique degradation step

pattern. Concerning the mixture CAP/oligomer, all of

them presented one stage of degradation. The Tonset and

Tmax were shifted to higher temperatures, indicating a

substantial increase of the CAP’s thermal stability and a

higher degree of compatibility.

3.2. Differential Scanning Calorimetry (DSC)

Figure 3 shows the DSC curves of the PET/PENTE,

CAP and CAP (90/10). The oligomer showed Tg around

61˚C. The CAP presented a thermal transition in the vi-

cinity of 13˚C. All mixtures revealed the same transitions

but that attributed to the Tg of the oligomer shifted to a

lower temperature (43˚C). This corroborated the high

Table 1. TG/DTG of the materials.

Degradation

temperatures (˚C)

Tmax

(˚C)

Residue

(%)

Samples

Tonset T

end

PET/PENTE 60/40125 495 127/285/4769.22

CAP 258 500 441 14.1

CAP (95/5) 238 488 448 0.03

CAP (90/10) 250 490 453 11.9

CAP (80/20) 281 496 448 11.3

PET Oligomer Waste to Modify CAP Characteristics

577

Figure 1. TG curves of the materials.

Figure 2. DTG curves of the materials.

The crystalline phase—disperse droplets is embedded in

the amorphous phase.

degree of compatibility observed in the TG/DTG analy-

sis.

The CAP (95/5) photomicrographs did not reveal any

phase separation. This might have occurred because of

the total dissolution of CAP inside the oligomer matrix.

In the mixtures with oligomer content higher than 5%,

the oligomer induced the fragmentation of the crystalline

domains. There is a sharp phase separation. The matrix is

formed by oligomer and the CAP amorphous phase. The

3.3. Units Morphological Analysis

The photomicrographs of the CAP (Figure 4) and CAP/

Oligomer mixture (Figure 5) show the morphology of

the materials in the solid and molten states. The CAP’s

images are similar and represent a heterogeneous mixture.

PET Oligomer Waste to Modify CAP Characteristics

578

Figure 3. First heating DSC curves of the materials.

(a) (b)

Figure 4. Optical fotographs. CAP: (a) Molten state; (b)

Solid state.

crystalline phase appeared as dispersed small droplets.

3.4. Peel Test

Figure 6 shows the force required immediately before

complete separation of the aluminum plates. For the mix-

tures, even taking into account the experimental errors,

the values of the force were similar, independent on the

oligomer content. The mixtures presented behavior simi-

lar to that of a ductile material.

Figure 7 shows the surface of the aluminum plates

after the peel test. The CAP image revealed voids on the

surface, indicating poor adhesion. For all mixtures, the

oligomer improved adhesion. All surfaces were com-

pletely coated, showing cohesive fracture of the asphaltic

mixture. The results indicated that the presence of the

oligomer increases the resistance to disaggregation and

durability of the asphaltic mixture, making it more suit-

able for paving.

4. Conclusion

In order to produce a new material from plastic waste,

PET was oligomerized by a polyfunctional alcohol and

mixed with CAP. The asphaltic mixture was character-

ized by several techniques. The DSC showed there is

excellent compatibility between the constituents. The

(a) (b)

(e) (f)

Figure 5. Optical fotographs of CAP/oligomer mixture.

CAP (95/5): (a) Molten state; (b) Solid state; CAP (90/10):

state; (f) Solid state.

Figure 6. Pell test of the materials.

presence of the oligomer enhanced the CAP’s thermal

stability. Morphologically, in the mixtures, PET was the

matrix and the CAP crystalline phase appeared as dis-

perse domains. The mixture presented cohesive fracture

and ductile behavior from the peeling evaluation.

5. Acknowledgements

The authors thank Fundação Coordenação do Aperfei-

çoamento de Pessoal de Nível Superior (CAPES) and

PET Oligomer Waste to Modify CAP Characteristics

579

(a) (b)

Figure 7. Surface of the aluminum plates after the peel test:

(a) CAP; (b) CAP (95/5); (c) CAP (90/10); (d) CAP (80/20).

Universidade Federal do Rio de Janeiro (UFRJ) for sup-

porting this investigation.

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