For Review Only

STUDY OF THERMAL DEGRADATION OF PVC PLASTICIZED

FORMULATIONS COSTABILIZED WITH d-SORBITOL AND

TRIPHENYL PHOSPHITE

Journal: ANTEC

Manuscript ID: PENG-11-2010-0600.R1

Wiley - Manuscript type: Proceeding

Date Submitted by the

Author:

31-Jan-2011

Complete List of Authors: Haro-Gutierrez, Pilar; Universidad de Guadalajara, Chemistry

Rodríguez-López, Oscar; Universidad de Guadalajara, Chemical
Engineering
Arellano, Jesus; Universidad de Guadalajara, Chemical Engineering
Mendizábal, Eduardo; Universidad de Guadalajara, Chemistry
Jasso, Carlos; Universidad de Guadalajara, Chemical Engineering
Arellano, Martin; Universidad de Guadalajara, Chemical Engineering
González-Ortiz, Luis; Universidad de Guadalajara, Chemistry

Keywords:

Polyvinyl Chloride (PVC) < Polymers, Stabilizers < Other,
Mechanical properties (Film, molded specimens) < Testing and
Characterization

Abstract:

PVC is generally degraded during processing, producing several
undesirable effects. In this work, mixtures of calcium and/or zinc
stearates and epoxidized soybean oil are used as stabilizers. In
addition, to improve overall stability, D-sorbitol or triphenyl
phosphite were added as costabilizers. The formulation composition
was systematically varied considering the following parameters: a)
presence of epoxidized soybean oil, b)CaSt

2

/ZnSt

2

ratio and, c)

presence and type of costabilizer. Thermal stability was followed
during isothermal heating by determining: a) the accumulation rate
of some conjugated polyenes and, b) the changes in the tensile
properties.

ANTEC

For Review Only

STUDY OF THERMAL DEGRADATION OF PVC PLASTICIZED FORMULATIONS

COSTABILIZED WITH D-SORBITOL AND TRIPHENYL PHOSPHITE

Pilar Haro-Gutiérrez, Oscar Rodríguez-López, Jesus Arellano, Eduardo Mendizábal, Carlos F. Jasso,

Martín Arellano and Luis Javier González-Ortiz

Centro Universitario de Ciencias Exactas e Ingenierías, Universidad de Guadalajara, MEXICO

Abstract

PVC is generally degraded during processing,

producing several undesirable effects. In this work,
mixtures of calcium and/or zinc stearates and epoxidized
soybean oil are used as stabilizers. In addition, to improve
overall stability, D-sorbitol or triphenyl phosphite were
added as costabilizers. The formulation composition was
systematically

varied

considering

the

following

parameters: a) presence of epoxidized soybean oil, b)
CaSt

2

/ZnSt

2

ratio and, c) presence and type of costabilizer.

Thermal stability was followed during isothermal heating
by determining: a) the accumulation rate of some
conjugated polyenes and, b) the changes in the tensile
properties.

Introduction

Unless it is stabilized, PVC is degraded during

processing. Such thermal degradation is the result of a
process called ‘‘zipper dehydrochlorination’’, which
generates polyene sequences in polymer chains that may
produce an undesirable color in the material [1]. In
addition, since polyenes are highly reactive, they may
react to form crosslinked polymer chains [1], as well as
low molecular weight molecules [1-2]. As a consequence
of such secondary reactions, the mechanical behavior and
the color of the formulations [1] may be importantly
modified. It is generally accepted that stabilizers may react
with labile chlorine atoms in PVC chains (preventing
further dehydrochlorination) and/or react with the HCl
generated by the degradation process (which accelerates
the degradation process) [1,3]. K, Ca and, Ba carboxylates
are mostly HCl scavengers [1]. However, Zn and Cd
carboxylates are able to scavenge HCl and, also, to react
with labile chlorine atoms [1]. An undesirable effect of the
stabilizing action of zinc stearate (ZnSt

2

) is the production

of

ZnCl

2

,

which

can

promote

the

sudden

dehydrochlorination of PVC chains. [1, 4-5] However, it
has been claimed that such sudden process occurs only
after the ZnCl

2

concentration reaches a certain level [5]; in

such process, ZnCl

2

is consumed [4]. Besides, it has been

experimentally demonstrated that formulations prepared
with mixtures of Zn and Ca carboxylates show a
synergistic stabilizing action [6-9], mainly due to the Ca
carboxylates, which act as ester-exchangers with ZnCl

2

[1,

6-7]. Epoxidized compounds are recognized as HCl
scavengers [1, 8], but can also participate in other

stabilization reactions, where they react simultaneously
with HCl and ZnSt

2

[8]. In the catalytic presence of ZnCl

2

,

epoxidized compounds react with such chloride to
produce a chemical compound that is able to remove
chlorine atoms in PVC chains through an etherification
reaction [1].

Costabilizers are added to PVC formulations to

improve the efficiency of the stabilizers; some of them are
D-sorbitol [1] and triphenyl phosphite [1]. The stabilizing
mechanism of such costabilizers has been partially
reported [1], being clear that their action is dependant of
the chemical characteristics of system. Although the
degradation-stabilization mechanism of formulations
containing PVC has been extensively studied, there are
few studies that consider the combined effect of three or
more components in industrial grade formulations.
Therefore, in this work, the formulation composition was
systematically

varied

considering

the

following

parameters: a) presence of epoxidized soybean oil, b)
CaSt

2

/ZnSt

2

ratio and, c) presence and type of costabilizer.

The accumulation rate of different conjugated polyenes (6
≤

n ≤ 20) and the changes in tensile properties produced

by isothermal heating after processing were determined.

Experimental

Materials

PVC resin from Policyd S.A. de C.V (Vinycel G-30;

K-Fikenstcher value of 70) was used to prepare the
formulations. Di (2-ethyl hexyl phthalate) (DEHP; purity
of 99.5%) was purchased from Síntesis Orgánicas S.A. de
C.V. ESO was acquired from Resinas y Materiales S.A. de
C.V (Pantopox; oxirane number 6.95% oxygen). CaSt

2

(CaO essay 9.0-10.5%) and ZnSt

2

(ZnO essay 12.5-14%)

were purchased from Alfa Aesar. D-sorbitol from Alfa
Aesar (98 wt %) and triphenyl phosphite from Aldrich (97
wt %) were used as costabilizers. Two different
DEHP/ESO ratios were used: 45/0 or 45/6 (phr/phr). For
each one of the DEHP/ESO ratios, the following
CaSt

2

/ZnSt

2

ratios (phr/phr) were used: 0.0/1.0, 0.2/0.8,

or, 0.4/0.6; in all formulations the total content of stearates
was 1.0 phr. For each ESO concentration, the three
following series were considered: a) without costabilizer,
b) D-sorbitol (0.25 phr) and, c) triphenyl phosphite (0.25
phr).

Page 2 of 7

ANTEC

For Review Only

Sample preparation

The samples to be post-processed were prepared as

follows: (a) dry blending the components, (b) pelletizing
the dry-blend (twin-screw extruder Leistritz 276L/32D)
and, (c) extruding the pellets (to obtain ribbons). The
samples were heated in a forced convection oven
(FRELAB) at 150±5°C (0.5, 1, 1.5, 2 or, 3 h).

Characterization

The changes on the stress-strain behavior of

degraded samples (ASTM D638 type II specimens) were
determined using a Universal Testing Machine from
United (SFM10), characterizing the samples at room
temperature and with a cross-head speed of 50 mm/min.
The concentration of polyenes was determined by UV
spectrophotometry (UV-visible Spectrophotomer Perkin
Elmer Lambda 25).

Results and discussion

The stress-strain curves showed a monotonic stress

increase with deformation; therefore, the Young modulus
(E), ultimate stress (σ) and, deformation at break (ε) were
considered as representative parameters of the mechanical
behavior. For each set formulation-degradation time, 4
equivalent samples were mechanically characterized, and
the correspondent average values and standard deviations
(s

E

, s

σ

or s

ε

) were reported. In order to evaluate the

modifications on the tensile properties that were produced
by the isothermal heating, the following normalized
properties were defined: a) normalized modulus
(E*(t)=E(t)/E(0)),

b)

normalized

ultimate

stress

(σ*(t)=σ(t)/σ(0)) and, c) normalized deformation at break
(ε*(t)=ε(t)/ε(0)). In last relationships, the degradation time
is indicated in parentheses. The use of such normalized
variables allowed separating the plasticizing effect of the
ESO from its stabilizing effect.

Regarding the mechanical behavior of non-

postprocessed samples, Table 1 shows that such behavior
is practically independent on the formulation composition,
which is a consequence of the low degradation level that
samples underwent during the processing and the low
plasticizing effect of the ESO.

The changes in the modulus values produced by the

degradation process are evidenced in Figure 1. In such
Figure, a catastrophic increment on the modulus can be
observed for the sample stabilized only with ZnSt

2

, which

also showed the highest diminution on the elongation at
break (57% after 3 h of heating). However, its σ value was
maintained almost constant during the degradation
process. Such behavior can be explained as a consequence
of the domain of branching reactions over the chain
scission ones, during the whole degradation process.

Analyzing the effect of the CaSt

2

presence on the E

values, it can be affirmed, for the formulations without
ESO, that its presence is beneficial for the thermal

stability of formulations without costabilizer. However, in
the formulations stabilized with D-sorbitol, its presence
did not produce important changes on the respective
stabilities and, in the formulations containing triphenyl
phosphite, its presence produced a slightly detrimental
effect. Otherwise, in formulations containing ESO, the
presence of such stearate produced a slight improvement
in the thermal stability of formulations containing
triphenyl phosphite, showing a negligible effect on the
other formulations. On the other hand, Figure 1 shows a
beneficial effect on the thermal stability caused by the
addition of ESO. With respect to the costabilizing effect, it
is clear that, in general terms, the addition of D-sorbitol
improved the thermal stability of the modulus. However,
the addition of the other costabilizer produced a negative
effect on such stability.

With regard to the ultimate properties, Table 2 shows

that the post-processing treatment does not produce
important changes on the σ values; in fact, it can be
considered that such changes fall within the expectable
experimental error (~15%). Nevertheless, the heating
produced important decrements on the ε values (between
18 and 57%). The highest ε decrements were observed in
the formulations without costabilizer (especially in the
formulation lacking CaSt

2

). In contrast, the best stabilities

were obtained with formulations stabilized with D-
sorbitol. In addition, in general terms, formulation stability
is not dependent on the CaSt

2

/ZnSt

2

ratio; the only

exception is shown for the formulation stabilized only
with ZnSt

2

, which, as it was explained, showed the highest

degradation level. Finally, the information given in Table
2 clearly indicates that, in the most unstable formulations
(without costabilizer or, containing triphenyl phosphate
series) the ESO presence improved the thermal stability of
the respective formulations. However, such improvement
cannot be observed in formulations containing D-sorbitol.

Figures 2-3 present the initial polyene concentrations

(P

n

°) and the accumulation rates of polyenes (dP

n

/dt) for

both sets of formulations. It can be observed that the
presence of triphenyl phosphite improved the processing
stability for all formulations (lower values of P

n

°). On the

other hand, in general terms, the worst processing stability
was observed in the D-sorbitol series (especially in the
presence of ESO). Analyzing the effect of the CaSt

2

/ZnSt

2

ratio on the processing stability, it can be noticed that the
differences produced by the changes on such composition
parameter were small, falling within the expected
experimental error (~15%), preventing the adequate
establishment of any trend.

Regarding the post-processing stability, the most

unstable formulation was the one stabilized only with
ZnSt

2

, whose values of UV absorbance for degradation

time ≥ 0.5 h were above the validity limit of the Lambert-
Beer law and, therefore, the polyene concentrations cannot
be calculated. For this formulation, the costabilizer

Page 3 of 7

ANTEC

For Review Only

addition notably improved the post-processing stability.
For formulations 45/0, the D-sorbitol was a better
costabilizer (lower values of dP

n

/dt) than triphenyl

phosphite. The increment of CaSt

2

concentration

improved the post-processing stability of formulations
without costabilizer and of those costabilized with
triphenyl phosphite.

In formulations without costabilizer and formulations

containing triphenyl phosphate, the post-processing
stability is improved by the presence of ESO. However,
for formulations costabilized with D-sorbitol, the addition
of ESO did not produce significant changes on the dP

n

/dt

values. Finally, the addition of CaSt

2

to costabilized

formulations produced a negative effect on the post-
processing stability. Otherwise, in formulations without
costabilizer,

since

the

(dP

n

/dt)

Formulation

with

CaSt2

/

(dP

n

/dt)

Formulation without CaSt2

ratios are larger than 1.0, only

for some n values, the global effect of the CaSt

2

presence

on post-processing stability cannot be adequately
established.

Conclusions

The initial mechanical behavior did not strongly

depend on the formulation composition. The addition of
triphenyl phosphite improved the processing thermal
stability of all tested formulations. Finally, the addition of

D-sorbitol showed to be beneficial for the post-processing
stability of 45/0 formulations.

References

1. R. Bacaloglu, M.H. Fisch, J. Kaufhold, H.J. Sander,

in: “Plastics Additives Handbook”. 5th ed., Zweifel H,
Ed. Hanser, Munich 2001, chap. 3.

2. R.P. Lattimer, W.J. Kroenke, J. Appl. Polym. Sci., 25,

101 (1980).

3. T. Hjertberg, E.M. Sörvik, J. Appl. Polym. Sci., 22,

2415 (1978).

4. E.D. Owen, K.J. Msayib, J. Appl. Polym. Sci. Part A

Polym. Chem.

, 27, 399 (1989).

5. H. Baltacioglu, D. Balköse, J. Appl. Polym. Sci., 74,

2488 (1999).

6. K.B. Abbas, E. Sorvik, J. Vinyl Addit. Technol., 2, 87

(1980).

7. N.L. Thomas, Plast. Rubber Compos. Process Appl.,

19, 263 (1993).

8. R.F. Grossman, J. Vinyl. Addit. Technol., 15, 25

(1993).

9. L.J. González-Ortiz, M. Arellano, C.F. Jasso, E.

Mendizábal, M.J. Sánchez-Peña, Polym. Degrad.
Stab.

, 90, 154 (2005).

Key Words: Poly (vinyl chloride), Stabilizers, Mechanical
Properties.

Table 1. Tensile properties of samples after processing.

CaSt

2

/ZnSt

2

ratio

Without costabilizer

D-Sorbitol

Triphenyl phosphite

E ± s

E

(MPa)

σ

σ

σ

σ ± s

σ

σ

σ

σ

(MPa)

ε

ε

ε

ε ± s

ε

εε

ε

(%)

E ± s

E

(MPa)

σ

σ

σ

σ ± s

σ

σ

σ

σ

(MPa)

ε

ε

ε

ε ± s

ε

εε

ε

(%)

E ± s

E

(MPa)

σ

σ

σ

σ ± s

σ

σ

σ

σ

(MPa)

ε

ε

ε

ε ± s

ε

εε

ε

(%)

DEHP: 45 phr. ESO: 0 phr

0.0/1.0

25±4

19±2

294± 25

40±4

21±1

243±24

35±5

21±1

247±12

0.2/0.8

32±5

20±2

244± 17

41±6

21±1

247±14

38±4

20±1

281±23

0.4/0.6

38±4

20±1

248± 14

36±2

20±1

240±10

31±2

20±2

309±37

DEHP: 45 phr. ESO: 6 phr

0.0/1.0

25±3

19±1

259±12

28±6

20±1

261±22

22±3

18±1

268±16

0.2/0.8

24±2

19±1

257±6

26±5

20±1

274±19

25±2

19±0

253±10

0.4/0.6

26±4

20±1

249±11

28±4

20±1

290±12

26±4

19±1

252±13

Table 2. Rate of change of σ* and ε*of the formulations.

Without costabilizer

D-Sorbitol

Triphenyl phosphite

CaSt

2

/ZnSt

2

ratio

dσ

σ

σ

σ

∗

∗

∗

∗

/dt, h

-1

dε

εε

ε

∗

∗

∗

∗

/dt, h

-1

dσ

σ

σ

σ

∗

∗

∗

∗

/dt, h

-1

dε

εε

ε

∗

∗

∗

∗

/dt, h

-1

dσ

σ

σ

σ

∗

∗

∗

∗

/dt, h

-1

dε

εε

ε

∗

∗

∗

∗

/dt, h

-1

DEHP 45/ ESO 0

0.0/1.0

0.01

-0.19

0.01

-0.08

-0.02

-0.13

0.2/0.8

0.02

-0.09

0.03

-0.06

0.03

-0.10

0.4/0.6

-0.01

-0.10

0.01

-0.08

-0.00

-0.11

DEHP 45/ ESO 6

0.0/1.0

-0.00

-0.06

0.00

-0.08

0.03

-0.07

0.2/0.8

-0.02

-0.06

0.00

-0.06

0.03

-0.05

0.4/0.6

-0.02

-0.06

0.01

-0.08

0.03

-0.06

Page 4 of 7

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For Review Only

0 phr ESO

6 phr ESO

Figure 1. Evolution of the normalized Young modulus with degradation time, corresponding tor formulations prepared with
the indicated CaSt

2

/ZnSt

2

ratio and ESO content. Series: (•••)

without costabilizer,

(───)

D-sorbitol

,

(───) triphenyl

phosphite

.

0.0

0.5

1.0

1.5

2.0

0.0

0.5

1.0

1.5

2.0

2.5

3.0

E

*

t, h

0.0

0.5

1.0

1.5

2.0

0.0

0.5

1.0

1.5

2.0

2.5

3.0

E

*

t, h

0.0

1.0

2.0

3.0

4.0

5.0

0.0

0.5

1.0

1.5

2.0

2.5

3.0

E

*

t, h

0.0

0.5

1.0

1.5

2.0

0.0

0.5

1.0

1.5

2.0

2.5

3.0

E

*

t, h

0.0

0.5

1.0

1.5

2.0

0.0

0.5

1.0

1.5

2.0

2.5

3.0

E

*

t, h

0.0

0.5

1.0

1.5

2.0

0.0

0.5

1.0

1.5

2.0

2.5

3.0

E

*

t, h

0.0/1.0

0.0/1.0

0.2/0.8

0.2/0.8

0.4/0.6

0.4/0.6

Page 5 of 7

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For Review Only

Figure 2. Initial polyene concentration (P

n

°) and accumulation rate of polyenes (dP

n

/dt) for formulations DEHP 45/ESO 0,

prepared with the indicated CaSt

2

/ZnSt

2

ratio. Series: (•••)

without costabilizer,

(───)

D-sorbitol

,

(───) triphenyl

phosphite

.

0

10

20

30

6

8

10

12

14

16

18

20

n

P

°

n

,

µµµµ

m

o

l/

L

0

10

20

30

6

8

10

12

14

16

18

20

n

P

°

n

,

µµµµ

m

o

l/

L

0

10

20

30

6

8

10

12

14

16

18

20

n

P

°

n

,

µµµµ

m

o

l/

L

0

10

20

30

6

8

10

12

14

16

18

20

n

d

P

n

/d

t,

µµµµ

m

o

l/

L

h

0

10

20

30

6

8

10

12

14

16

18

20

n

d

P

n

/d

t,

µµµµ

m

o

l/

L

h

0

10

20

30

6

8

10

12

14

16

18

20

n

d

P

n

/d

t,

µµµµ

m

o

l/

L

h

0.0/1.0

0.0/1.0

0.2/0.8

0.2/0.8

0.4/0.6

0.4/0.6

Page 6 of 7

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For Review Only

Figure 3. Initial polyene concentration (P

n

°) and accumulation rate of polyenes (dP

n

/dt) for formulations DEHP 45/ESO 6,

prepared with the indicated CaSt

2

/ZnSt

2

ratio. Series: (•••)

without costabilizer,

(───)

D-sorbitol

,

(───) triphenyl

phosphite

.

0

10

20

30

6

8

10

12

14

16

18

20

n

P

°

n

,

µµµµ

m

o

l/

L

0

2

4

6

8

10

6

8

10

12

14

16

18

20

n

d

P

n

/d

t,

µµµµ

m

o

l/

L

h

0

10

20

30

6

8

10

12

14

16

18

20

n

P

°

n

,

µµµµ

m

o

l/

L

0

2

4

6

8

10

6

8

10

12

14

16

18

20

n

d

P

n

/d

t,

µµµµ

m

o

l/

L

h

0

10

20

30

6

8

10

12

14

16

18

20

n

P

°

n

,

µµµµ

m

o

l/

L

0

2

4

6

8

10

6

8

10

12

14

16

18

20

n

d

P

n

/d

t,

µµµµ

m

o

l/

L

h

0.0/1.0

0.0/0.1

0.2/0.8

0.2/0.8

0.4/0.6

0.4/0.6

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