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STUDY OF THE MIGRATION PROCESS OF PVC PLASTICIZERS

BY FTIR A.Marcilla, J.C.Garcia-Quesada*, S. Garcia

Departamento de Ingeniería Química, Universidad de Alicante,

03690 S. Vicente del Raspeig-Alicante, Spain, *e-mail: [email protected]

REFERENCES

1. W. Titow; PVC Technology, 4th Edition, Elsevier Applied Science, New York, 1986.

2. L. Castle, A. J. Mercer, J.R. Startin and J. Gilbert; Food Addit. Contam., 1998, Vol. 5,

3. B. Aurela, H. Kulmala and L. Söderhjelm; Food Addit. Contam., 1999, Vol 16, Nº 12,

4. S. Garcia; Migración de plastificantes de PVC , Tesis doctoral. Universidad de Alicant

ACKNOWLEDGEMENTThe authors wish to thank the financial support provided by the Spanish “Comisión de Investigación C

de la Secretaría de Estado de Educación, Universidades, Investigación y Desarrollo and the Europea

CTQ2004-02187) and by the Generalitat Valenciana (GVEMP06/021, ACOM06/162).

ABSTRACT

VC is one of the most common polymers employed for a wide range of applications, mainly due to its

elative low cost and high versatility. Pure PVC is a rigid polymer at room temperature with a low thermal

tability. Nevertheless, its properties can be easily modified by the presence of the proper additives. Among

ll the additives, it is worth mentioning PVC plasticizers that have been employed to improve flexibility and

oftness. One of the basic requirements of the PVC plasticizers is their permanence in the polymer. Once

hey have been blended and processed, the plasticizer should remain in the item obtained. Nevertheless,

VC plasticizers can be released from flexible PVC by different ways (1): Volatilization, extraction,

migration or exudation under pressure. In most of the flexible PVC applications, PVC is susceptible to be

ept in contact with other polymeric materials. In this case, the migrability of plasticizers is a relevant factor

o be born in mind (2-3).

n the present work, a method based on the utilization of infrared spectroscopy has been suggested to s tudy

he ability of different types of PVC plasticizers (phthalates, citrates and adipates) to migrate towards a

esting polymer (polystyrene has been employed to illustrate the procedure). As migration process occurs,

lasticizer concentration in PVC specimens decrease, obtaining plasticizer profiles with migration time.

Results obtained have allowed a quantitative comparison of the migrability of plasticizers tested, as well as

he calculation of their diffusion coefficients in both PVC and testing polymer, by considering a very simple

model based on finite differences method analysis.

CONCLUSIONS

In the present work a procedure to monitor plasticizers migration from a PVC film to oth

contact has been presented. The applicability of the procedure has been shown w

plasticizers of different types: phthalates, adipates and citrates.

A diffusion model has been developed and combined with the mass balances, solving the

finite differences method to the experimental results obtained. Average diffusion c

plasticizer in the polymer studied have been obtained. The simultaneous correlation of da

the same plasticizers family, by considering the Rouse model, has yielded correlations w

coefficient and hence a good fit. The results obtained have shown marked differences b

studied. Adipates and citrates tend to migrate much more than phthalates. When th plasticizers is studied, a marked dependence of diffusion coefficients with the molec

plasticizer has been observed, in such way that the highest molecular weight plasticize

slower than those of lower molecular weight.

MATERIALS AND EQUIPMENTS

The PVC resin ETINOX 450 from Aiscondel and the calcium-zinc stabilizer Newstab 18

CHEMICALS have been employed. Different PVC plasticizers, with different chemical s

been used: Di-isoheptyl phthalate (DHP), di-(2-ethylhexyl) phthalate (DOP), di-isononyl

di-hexyl adipate (DHA), di-(2-ethylhexyl) adipate (DOA), di-isononyl adipate (DNA), ac

(CA2), acetyl tributyl citrate (CA4), acetyl trihexyl citrate (CA6) . PVC pastes were prepa

PVC resin, the plasticizers and the stabilizer in the following proportions: 100 phr (par

resin) of PVC, 70 phr of plasticizer and 2 phr of the thermal stabilizer.

8020% weight

THFPlastisol

8020% weight

THFPlastisolDissolution

270100C (phr)

1.240.758.1%

weight

StabilizerPlasticizerPVCResin

270100C (phr)

1.240.758.1%

weight

StabilizerPlasticizerPVCResin

Composition Solvent evaporation

0.0

0.5

1.0

1.5

2.0

500100015002000Nº onda(cm

-1)

A b s o r b a n c i a

60 min

45 min

20 min

10 min

THF

C-H (Plastificante)

C-H (PVC)

(Plasticizer)

A b s o r b a n c e

Wavenumber (cm-1)

SAMPLES PREPARATION

PVC pastes were prepared and dissolved in THF. The ATR glass was dipped in the polymeric solution

btaining a uniform layer covering the glass. In order to remove the solvent, the system PVC film-ATR lass was heated by means an infrared lamp, until characteristic absorption bands of THF had disappeared.

ATR glass

+PVC layer

PS sheet

Thermocouple Electrical Heating

Electrical heater

PS

ATR glass

PVC layer

30-60mm

PS1mm

Thermocouple

)(

)(2

Cl C PVC

OC Plast

A

A R

)(

)(1

H C PVC

H C Plast

A

A R

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

500100015002000

Nº onda(cm-1

)

C-Cl (PVC)

C-H (PVC)

C-H(Plastificante)

C=O(Plastificante)(Plasticizer)

(Plasticizer)

Wavenumber (cm-1)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

500100015002000

Nº onda(cm-1

)

C-Cl (PVC)

C-H (PVC)

C-H(Plastificante)

C=O(Plastificante)(Plasticizer)

(Plasticizer)

Wavenumber (cm-1)

MIGRATION TEST

he ATR glass, with the PVC film, arranged in sandwich disposition with a PS sheet, a thermocouple and a

ectrical heater. The plasticizer present in PVC tends to migrate to PS in more or less extension to anyaterial kept in contact. In this case, it migrates to the PS sheet, being all the process controlled by the

asticizer diffusion in PVC and PS, as well as by the plasticizer transfer from PVS phase to PS phase. The

tter process could be simplified by describing it for example as a function of partition constant). The

ermocouple and the electrical heating permit to perform the experiment at a constant temperature (70ºC in

is case).

Plasticizer concentration in the surface in contact with the ATR glass has been determined by the utilization

of calibration curves obtained by representing the following areas ration versus plasticizer concentration:

Infrared spectra obtained presented, as expected, characteristic bands of the PVC resin and the plasticizer.

The evolution of absorption bands of the plasticizer reveals how plasticizer is migrating from PVC to PS.

Logically concentration profiles were also dependent on film thickness, which was measured by a

ultrasound DEFELSKO 100 device. Due to the fact that film thickness was not identical in all cases, some

deviations between expeected and experimental trends are observed. It makes unavoidable themathematical treating of experimental results.

FINITE DIFFERENCES ANALYSIS

Due to the fact that this is a non-lineal problem, it is

necessary to use a numeric procedure, as for example the

finite differences method. The finite differences method has

been employed to solve the mass balances along both

polymer layers, and the three parameters (both diffusion

coefficients and the partition constant) have been optimised

so that the sum of the squared differences among

experimental and generated concentrations are as low as

possible.

In order to apply the finite differences procedure, all the system has been discretiz

schematically in the Figure. All the system was divided in a number of elements or cell

to ensure that the solution did not depend on such parameter, i.e., the cells number. E

cell is represented by its node, located in its centre. In this case, the PVC layer was d

elements, while the PS sheet in 100. Higher numbers of elements required extremely lo

times, while results obtained were almost identical. More details about the calculations

be found elsewhere (4).

C

PVC

x

1 2 3

SOME RESULTS OF THE MODELLIZATION

Acetyl triethyl citrate

0

20

40

60

80

100

120

0 2 00 0 4 00 0 6 00 0 8 00 0 1 0 00 0 12 00 0time (minutes)

P l a s t i c i z e r c o n c e n t r a t i o n

( % ) Experimental

Calculated

Di-(2-ethylhexyl) phthalate

0

20

40

60

80

100

120

0 2 00 0 4 00 0 6 00 0 8 00 0 1 0 00 0 12 00 0time (minutes)

P l a s t i c i z e r c o n c e

n t r a t i o n

( % ) Experimental

Calculated

Di-isononyl adipate

0

20

40

6080

100

120

0 2 00 0 4 00 0 6 00 0 8 00 0 1 0 00time (minutes)

P l a s t i c i z e r c o n c e n t r a t i o n

( % )

Experimental

Calculated

01.27·10-103.41·10-8CA6

04.28·10-103.89·10-8CA4

03.11·10-106.53·10-8CA2

Citrates

00.70·10-90.50·10-8DNA

01.07·10-90.70·10-8DOA

01.44·10-93.52·10-8DHA

Adipates

01.28·10-114.51·10-8DNP

02.00·10-114.87·10-8DOP

02.68·10-114.93·10-8DHP

Phthalates

Pa

co Difusion

coefficient in

PS(cm 2 /s)

Difusion

coefficient in

PVC(cm2 /s)

Plasticizer Plasticizer

type

01.27·10-103.41·10-8CA6

04.28·10-103.89·10-8CA4

03.11·10-106.53·10-8CA2

Citrates

00.70·10-90.50·10-8DNA

01.07·10-90.70·10-8DOA

01.44·10-93.52·10-8DHA

Adipates

01.28·10-114.51·10-8DNP

02.00·10-114.87·10-8DOP

02.68·10-114.93·10-8DHP

Phthalates

Pa

co Difusion

coefficient in

PS(cm 2 /s)

Difusion

coefficient in

PVC(cm2 /s)

Plasticizer Plasticizer

type

0

20

40

60

80

100

120

0 2 00 0 4 00 0 6 00 0 8 00 0 1 0 00 0 1 20 00time (minutes)

P l a s t i c i z e r c o n c e n t r a t i o n ( % )

DNA

DOA

DHA

0

20

40

60

80

100

120

0 2 00 0 4 00 0 6 00 0 8 00 0 1 0 00 0 1 20 00time (minutes)


CA6

CA4

CA2

0

20

40

60

80

100

120

0 2 00 0 4 00 0 6 00 0 8 00 0 1 0 0 00 1 2 00 0time (minutes)


DNP

DOP

DHP

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