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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: jc.garcia@ua.es
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)
P l a s t i c i z e r c o n c e n t r a t i o n ( % )
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)
P l a s t i c i z e r c o n c e n t r a t i o n ( % )
DNP
DOP
DHP
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