THERMAL DECOMPOSITION OF PRE-CURED PVC-VA PLASTISOLS

AND FOAMS. INFLUENCE OF THE PLASTICIZER CONCENTRATION

A. Zoller and A. MarcillaDepartment of Chemical Engineering, University of Alicante

P.O.Box 99. E-03080 Alicante, Spain

*Corresponding author: e-mail:agnes.zoller@ua.es, tel.:+349653400-2386

[1.] Zoller, A. and Marcilla A., Soft PVC foams. Study of the gelation, fusion and foaming processes. Part III.: Mixed Phthalate ester plasticizers,Journal of Applied Polymer Science, Accepted for publication 2011.

[2.] Beltrán, M. and A. Marcilla, Polymer Degradation and Stability, 1997. 55(1): p. 73-87.[3.] Marcilla, A., S. García, and J.C. García-Quesada, Journal of Analytical and Applied Pyrolysis, 2004. 71(2): p. 457-463. [4.] A. Jiménez, L. Torreand J. M. Kenny, Polymer Degradation and Stability, 2001. 73: p. 447-453.[5.] Rodolfo, A. and L.H. Innocentini Mei, Journal of Applied Polymer Science, 2010. 118(5): p. 2613-2623.[6.] G. Sivalingam, R. Karthikand G. Madras, Industrial & Engineering Chemistry Research, 2003. 42: p.3647-3653.[7.] Wu, C.-H., et al., The Canadian Journal of Chemical Engineering, 1994. 72(4): p. 644-650.

CONCLUSIONS:

The influence of the concentration of the plasticizer on the thermal decomposition of pre-cured

plastisols and flexible foams of PVC-VA prepared with mixtures of two commercial plasticizers has been studied1. A series of PVC-VA plastisols were prepared by mixing 100 phr of the ETINOX 400 a poly vinyl chloride-vinyl acetate copolymer, 100 phr of a mixture of DEP (diethyl phthalate) and DIDP

(di-isodecyl phthalate) of DEP concentration of 0, 25, 50 75 and 100%, respectively. The plastisols were cured in an open mould at 180ºC during 10 min. Plastisols containing chemical blowing agent

produce foams during this curing process. Pre-cured samples and foams have been studied by TGA2. The first peak observed in the DTG curves corresponds to the evolution of the DEP, whereas the second peak corresponds to the overlapping of the evolution of the DIDP and the first step of

decomposition of the resin. Strong interactions between the different components of the formulations are evident, and the presence of ZnO catalyzes the resin decomposition. It has been also observed that these plastisols suffer plasticizer loss by evaporation during curing. Depending on the plasticizer

mixture, each plastisol looses different amount of plasticizer. Finally, it can be deduced that TGA measurements are relevant to follow the thermal transitions of such pastes and allow a better

interpretation of the results obtained, as well as the curing and foaming behavior and foam quality.

Plasticizers Abbreviation Commercial Name

Density (g/cm3)

Molecular Weight (g/mol)

Diethyl Phthalate

DEP Palatinol A 1.118 222

Diisodecyl Phthalate

DIDP Palatinol DIDP 0.966 447

AdditivesAdditives Commercial NameCommercial Name DescriptionDescription

Stabilizer Reagens CL 4 Ca / Zn stabilizer

Co-stabilizer Lankroflex 2307 Epoxidized Soybean Oil (ESBO)

Catalyst ZnO Zinc-oxide

Foaming Agent Unicell D 200 A Azodicarbonamide (ADC)

Resin Commercial Name Description K value

E 400 Etinox 400 vinyl chloride-vinyl acetate copolymer

with a 4.8 % of vinyl acetate, generally

used to prepare plastisols of medium

viscosity.

70

MEASUREMENT CONDITIONS:

• Approximately 6 mg of sample

• TGA in a nitrogen atmosphere (50 mL/min)

• heating rates of 5 K/min from room temperature to 873 K

• Termobalance METTLER TOLEDO, model TGA/SDTA851e/SF/1100

• continuous on-line records of weight loss and temperature

• TGA and DTG curves

RESULTS1:

MATERIALS:

Formulation Resin

Etinox 400

(Phr)

Plasticizer I.

DEP

(Phr)

Plasticizer

II. DIDP

(Phr)

Stabilizer

CL4

(Phr)

Co-stab.

ESBO

(Phr)

Catalyst

ZnO

(Phr)

CBA

ADC

(Phr)

100 DEP 100 100 0 2 6 2 2

75 DEP 100 75 25 2 6 2 2

50 DEP 100 50 50 2 6 2 2

25 DEP 100 25 75 2 6 2 2

0 DEP 100 0 100 2 6 2 2

METHOD OF SAMPLE PREPARATION:

Five PVC plastisols were prepared by mixing

• 100 phr (parts per hundred resin) of the ETINOX 400 PVC resin

• 2 phr of Reagens CL4 commercial Zn/Ca-stearate stabilizer

• 6 phr of Lankroflex 2307 epoxidized soybean oil co-stabilizer

• 100 phr of a mixture of DEP and DIDP of DEP concentration of 0, 25, 50

75 and 100%, respectively.

• 2 phr of zinc oxide kicker/catalyst

Five foams were prepared mixing the same formulation with affitional 2 phr

of azodicarbonide as chemical blowing agent

After mixing, the pastes were subjected to a degassing process for 15 min.

with a maximum vacuum of 1 mbar for air removal.

These plastisols were cured in an open mould at 180ºC during 10 min.

DTG of the 5 foams obtained:

•1st: DEP evolution3

•2nd: DIDP evolution+1st decomposition

step of the resin and HCl + HAc loss from the VAc4

•3rd:ZnO/ZnCl2 catalyzed resin

decomposition5,6

•4th:final carbonization of the residue

formed in the resin decomposition process7

The thermal stability of the studied formulations is strongly influenced by the concentration of the plasticizer and

the presence of ZnO. TGA measurements are very convenient and relevant in order to follow the thermal

transitions of such plastisols, as they present a dynamic and complex behavior and allow a quantification of the amount of plasticizer remaining in a given formulation. Plasticized PVC-VA resin decomposes at lower

temperatures, than the pure PVC-VA resin. Quantification of the peak corresponding to the DEP evolution

reveales that DEP evaporates during the processing.Thus, the final foamed product is less plasticized, than programmed. Increasing DEP concentration in the formulation leads earlier decomposition of the resin,

consequently showing the destabilization effect of the compatible plasticizer. Moreover modifies the overlapping of the peaks.The final carbonization of the residue in the last step shows that the foams leave less amount of PVC residue, than that corresponding the resin in the formulation, thus showing another effect of the plasticizer in

the decomposition of the resin. TGA measurements allowed a better interpretation of the results obtained, since

the nominal and actual plasticizer concentration in a cured plastisol may be different depending on the volatility of the plasticizer and its concentration, and the process conditions.

0

20

40

60

80

100

200 250 300 350 400 450 500

Molecular Weight (g/mol)

Ph

r o

f re

ma

inin

g p

las

tic

ize

r

DTG of the pure DEP and DIDP plasticizers and the pure resin E400:

Phr of the remaining plasticizer concentration

vs. molecular weight in pre-cured samples:

�If considering that DIDP Plasticizer does not evaporate

�DEP Plasticizer lost 25 % of the

initial concentration

�Intermediate mixtures looseplasticizer accordingly

-0,0012

-0,001

-0,0008

-0,0006

-0,0004

-0,0002

0

50 100 150 200 250 300 350 400 450 500 550

Temperature (ºC)

Der

ived

Wei

gh

t L

oss

(d

m/d

t) (

1/s

)

The 4 weight loss steps:

1st

2nd

3rd

4th

Etinox 400 resin

100 DEP pre-cured sample has lost

less DEP during the TGA measurement: The formulation has

lost more plasticizer by evaporation

during the curing than the same

formulation containing ADC.

100 DEP foam has lost more DEP (first

weight loss step larger peak corresponding to the DEP evolution) during the TGA

measurement, than the pre-cured sample

without containing ADC: During the foaming process the plastisols containing ADC suffer

less plasticizer evaporation.

Comparison of DTG-s of the 100 DEP foam and 100 DEP pre-cured plastisol:

ABSTRACT:

-0,0012

-0,001

-0,0008

-0,0006

-0,0004

-0,0002

0

50 100 150 200 250 300 350 400 450 500 550

Temperature (ºC)

Deri

ved

Weig

ht

Lo

ss (

dm

/dt)

(1/s

)

100 DIDP foam

25 DEP 75 DIDP foam

50 DEP 50 DIDP foam

75 DEP 25 DIDP foam

100 DEP foam

DTG of the pre-cured plastisols:

-0,0020

-0,0015

-0,0010

-0,0005

0,0000

100 150 200 250 300

Temperature (ºC)

De

rive

d W

eig

ht L

os

s (d

m/d

t) (

1/s

)

100 DEP

75 DEP

50 DEP

25 DEP

0 DEP

-0,003

-0,0025

-0,002

-0,0015

-0,001

-0,0005

0

0 100 200 300 400 500 600

Temperature (ºC)

Deri

ved

We

igh

t L

os

s (

dm

/dt)

(1/s

)

DEP Plasticizer

DIDP Plasticizer

E 400

DIDP: 231°C

Etinox 400: 280°C

DEP: 194°C -0,0020

-0,0015

-0,0010

-0,0005

0,0000

-50 50 150 250 350 450 550

Temperature (ºC)

Deri

ve

d W

eig

ht

Lo

ss

(d

m/d

t) (

1/s

)

100 DEP Foam

100 DEP

REFERENCES:

6th International Symposium on Feedstock Recycling of Polymeric Materials (ISFR2011)

Toledo, Spain, 5 – 7 October 2011