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Radiation stabilization of polypropylene by phenolic stabilizers
Radial.
Phys. Chem. Vol. 42, Nos 1-3, pp. 223-227, 1993
Printed
in Great
0146-5724/93
$6.00
Pergamon
Britain
RADIATION
+ 0.00
Press
Ltd
STABILIZATION OF POLYPROPYLENE BY PHENOLIC STABILIZERS
S. Hassanpour and A. Yousefi* Atomic Gamma Irradiation Center, Organization of Iran, P.O.B. 1136% Tehran, I.R. Iran
Energy
8486
ABSTRACT The radiation stability of polypropylene stabilized with two stabi 1 izers behaviour of phenol i c and synergistic these investigated. The variation .of carbonyl stabi 1 izers have been i ndex and mechanical properties of stabilized and unstabilized been followed for 6 month; after irradiation polypropylene has The extent of chain scission has been followed by KGy iiast?ing the’change in apparent viscosity i&j .
KEYWORDS Polypropylene; behaviour.
Phenol
ic
antioxidant;
Synergism;
Antigonistic
INTRODUCTION Polypropylene ’ one of the most frequently manufacturing d:Iposable articles. medical this polymer is severe1 y deteriorated sterilizing doses (Dunn et al ., 1983). Published results decrease rapidly importantly, the with time following is oxidative in radicals following 1977; Babic et al
used polymers The properties when exposed
for of to
show that physical properties of polypropylene with absorbed increasing dose. More physical properties cant i nue to deteriorate irradiation . This post-irradiation reaction initiated mainly by residual nature and is the sterilization cycle (Williams et al ., ., 1983 ).
It has been reported that the oxidative degradation of polypropylene can be prevented by the addition of radical scavenger. Degradation can further be minimized by introducing suitable additives such as hindered phenols to the polypropylene (Kadir et al .,1983). In addition, combination of low molecular weight phenolic antioxidants with high molecular weight phenolic antioxidants compared with each of these stabilizers when used
*Present Toronto,
Address Toronto,
:
chemical Ontario,
Engineering Canada. 223
Dept.
,
University
of
S. HASSANPOURand A. YOUSEFI
224
Table 1. formulation
Compositioh
PP Pl P2 P3 P4 P5 P6
In
Stabilizer(%)
higher shows present antioxidants
s2 0 0 0.02 0.05
Sl
100 100 100 100 100 100 100
the
phenolic
polypropylene
Polypropylene (%)
Formulation
al one,
of
0 0.05 0.03 0 0.1
0
0.05 0.1
0.05
0
effectiveness (Katbab work, the capabilities have been investigated.
and of
Yousefi, combining
1991). two
Materials Lightly stabilized isotactic of by Hoechst Co. The type butyl-p-cresol (Sl) and Geigy Co.
SamDle
polypropylene powder was supplied stabilizers used 2,6-di-tertwere Irganox 1010 (S2) obtained from Ciba
DreDaration
size mix different extruder was used to Laboratory stabilizer concentrations of with polypropylene. The extruded ground by grinder. To keep the heat history, the pol ypropyl ene the same polypropylene was processed at unstabi 1 i zed also Table 1. shows the composition of the samples under condition. investigation.
IRRADIATION
AND
POST
IRRADIATION
irradiated in were samp 1es dose rate of 12 rays at a was 25 kGy. All irradiated applied and were tested in temperature irradiation up to 6 months.
Carben,*
Itbdex and Mechanical
of carbonyl The bui 1dup made by Eruker Co. Bend load-angle curve obtained
Rheoloaical melt The capi 1 lary
Co-60 gamma air with The radiation dose kGy/hr. samples were kept at room after intervals different
proDerties
group was followed strength of samples from CEAST stiffness
by FTIR model IFS45 were measured by the apparatus.
Sehaviour viscosity rheometer.
of
the
samples
were
measured
with
a
8th International
RESULTS
Rheological
AND
Meeting
on Radiation
225
Processing
DISCUSSION
Behaviour
In figure 1 the variation of melt viscosity with shear rate for the samples irradiated at 25 kGy after 6 months post irradiation aging has been shown. Likewise, the same information is provided for un i r rad i ated samples in Fig. 2. in which the variation of viscosity vs. shear rate is given for pure as we1 1 as stabilized polypropylene samples. Comparison of the Fig. 1 and 2 indicates that there is a general decrease in the apparent viscosity the i r rad i ated samples against the uni rradiated HowevZS ones. the amount of decrease for the stabilized samples is significan;ly lower when compared with the pure polypropylene as indicated in Fig. 1.
APP
;
OPl IF2 / lP3i
FIG.
FTIR
1.
FIG.
2.
Measurements
The buildup samples has
of been
FIG.
carbonyl followed
3.
near group for 6 months
1716
after
cm -1 in irradiation
FIG.
4.
irradiated at
25
S. HASSANPOUR and A. YOUSEFI
226
kGy. In Figs. 3 and 4 variation of carbonyl group formation in the samp 1 es containing both stabilizers indicates that combination of two phenolic stabilizers does not act in a synergistic fashion and in other words Sl alone is capable of stabilizing polypropylene . It may be concluded that combi nati on of two stabilizers not only does not act in a synergistic fashion but also shows an antigonistic behaviour which results in higher carbonyl index with time.
Mechanical
Properties
The work function of the samples containig various stabilizing compound (see table 1.) irradiated at 25 kGy have been shown in Figs. 5 and 6 as a function of time post irradiation. As seen in these figures the samples containing Sl stabilizer seem to have better work function up to nearly two months post irradiation. These results, in this particular region, are in general agreement with the FTIR carbonyl index measurment. After two months post irradiation the samples containing ~1 and 52 stabi 1 izers together or 52 alone show better stability whose proper assessment may require further research. Bending
'04
1
2
FIG.
6
6
6.
ACKNOWLEDMENT The would like authors the Gamma Irradiation editing of the manuscript.
to thank Center,
Dr. M. Sohrabpour, for supporting of
Director this work
of and
REFERENCES Saf ranj , V. Markovic and D. kotoski i1983j. Babic, D., A. immediate and Radiation degradation of polypropylene, Radiat. Phys. long-time effect on average molecular weigths. Chem. 22 , 3-5, 659. Williams (1983). Radiation stability Dunn, T. S. and J.L. 1 of polypropylene. Ind. Irrad. Tech. 33. (1989). Youshi, K. Makuuchi and I. Ishigaki Kadir, Z. A., F. Durability of radiation sterilized polymers. Polymer, 30,
8th International
Meeting
on Radiation
Processing
August , 1425. Katbab, A. A. and A. Yousefi (1991). degradation of polypropylene comparison of amine as stabilizer. pheno 1 and gamma Chem. 205-301 . 30, Williams, J. L., T. S. Dunn, H. Sugg and Radiation stabi 1 i ty of polypropylene. 445. Chem 9 , A
227
Post
irradiation hindered aromatic Radiat. PhVs. V.
Stannet Radiat.
(1977). Phys.
Phys. Chem. Vol. 42, Nos 1-3, pp. 223-227, 1993
Printed
in Great
0146-5724/93
$6.00
Pergamon
Britain
RADIATION
+ 0.00
Press
Ltd
STABILIZATION OF POLYPROPYLENE BY PHENOLIC STABILIZERS
S. Hassanpour and A. Yousefi* Atomic Gamma Irradiation Center, Organization of Iran, P.O.B. 1136% Tehran, I.R. Iran
Energy
8486
ABSTRACT The radiation stability of polypropylene stabilized with two stabi 1 izers behaviour of phenol i c and synergistic these investigated. The variation .of carbonyl stabi 1 izers have been i ndex and mechanical properties of stabilized and unstabilized been followed for 6 month; after irradiation polypropylene has The extent of chain scission has been followed by KGy iiast?ing the’change in apparent viscosity i&j .
KEYWORDS Polypropylene; behaviour.
Phenol
ic
antioxidant;
Synergism;
Antigonistic
INTRODUCTION Polypropylene ’ one of the most frequently manufacturing d:Iposable articles. medical this polymer is severe1 y deteriorated sterilizing doses (Dunn et al ., 1983). Published results decrease rapidly importantly, the with time following is oxidative in radicals following 1977; Babic et al
used polymers The properties when exposed
for of to
show that physical properties of polypropylene with absorbed increasing dose. More physical properties cant i nue to deteriorate irradiation . This post-irradiation reaction initiated mainly by residual nature and is the sterilization cycle (Williams et al ., ., 1983 ).
It has been reported that the oxidative degradation of polypropylene can be prevented by the addition of radical scavenger. Degradation can further be minimized by introducing suitable additives such as hindered phenols to the polypropylene (Kadir et al .,1983). In addition, combination of low molecular weight phenolic antioxidants with high molecular weight phenolic antioxidants compared with each of these stabilizers when used
*Present Toronto,
Address Toronto,
:
chemical Ontario,
Engineering Canada. 223
Dept.
,
University
of
S. HASSANPOURand A. YOUSEFI
224
Table 1. formulation
Compositioh
PP Pl P2 P3 P4 P5 P6
In
Stabilizer(%)
higher shows present antioxidants
s2 0 0 0.02 0.05
Sl
100 100 100 100 100 100 100
the
phenolic
polypropylene
Polypropylene (%)
Formulation
al one,
of
0 0.05 0.03 0 0.1
0
0.05 0.1
0.05
0
effectiveness (Katbab work, the capabilities have been investigated.
and of
Yousefi, combining
1991). two
Materials Lightly stabilized isotactic of by Hoechst Co. The type butyl-p-cresol (Sl) and Geigy Co.
SamDle
polypropylene powder was supplied stabilizers used 2,6-di-tertwere Irganox 1010 (S2) obtained from Ciba
DreDaration
size mix different extruder was used to Laboratory stabilizer concentrations of with polypropylene. The extruded ground by grinder. To keep the heat history, the pol ypropyl ene the same polypropylene was processed at unstabi 1 i zed also Table 1. shows the composition of the samples under condition. investigation.
IRRADIATION
AND
POST
IRRADIATION
irradiated in were samp 1es dose rate of 12 rays at a was 25 kGy. All irradiated applied and were tested in temperature irradiation up to 6 months.
Carben,*
Itbdex and Mechanical
of carbonyl The bui 1dup made by Eruker Co. Bend load-angle curve obtained
Rheoloaical melt The capi 1 lary
Co-60 gamma air with The radiation dose kGy/hr. samples were kept at room after intervals different
proDerties
group was followed strength of samples from CEAST stiffness
by FTIR model IFS45 were measured by the apparatus.
Sehaviour viscosity rheometer.
of
the
samples
were
measured
with
a
8th International
RESULTS
Rheological
AND
Meeting
on Radiation
225
Processing
DISCUSSION
Behaviour
In figure 1 the variation of melt viscosity with shear rate for the samples irradiated at 25 kGy after 6 months post irradiation aging has been shown. Likewise, the same information is provided for un i r rad i ated samples in Fig. 2. in which the variation of viscosity vs. shear rate is given for pure as we1 1 as stabilized polypropylene samples. Comparison of the Fig. 1 and 2 indicates that there is a general decrease in the apparent viscosity the i r rad i ated samples against the uni rradiated HowevZS ones. the amount of decrease for the stabilized samples is significan;ly lower when compared with the pure polypropylene as indicated in Fig. 1.
APP
;
OPl IF2 / lP3i
FIG.
FTIR
1.
FIG.
2.
Measurements
The buildup samples has
of been
FIG.
carbonyl followed
3.
near group for 6 months
1716
after
cm -1 in irradiation
FIG.
4.
irradiated at
25
S. HASSANPOUR and A. YOUSEFI
226
kGy. In Figs. 3 and 4 variation of carbonyl group formation in the samp 1 es containing both stabilizers indicates that combination of two phenolic stabilizers does not act in a synergistic fashion and in other words Sl alone is capable of stabilizing polypropylene . It may be concluded that combi nati on of two stabilizers not only does not act in a synergistic fashion but also shows an antigonistic behaviour which results in higher carbonyl index with time.
Mechanical
Properties
The work function of the samples containig various stabilizing compound (see table 1.) irradiated at 25 kGy have been shown in Figs. 5 and 6 as a function of time post irradiation. As seen in these figures the samples containing Sl stabilizer seem to have better work function up to nearly two months post irradiation. These results, in this particular region, are in general agreement with the FTIR carbonyl index measurment. After two months post irradiation the samples containing ~1 and 52 stabi 1 izers together or 52 alone show better stability whose proper assessment may require further research. Bending
'04
1
2
FIG.
6
6
6.
ACKNOWLEDMENT The would like authors the Gamma Irradiation editing of the manuscript.
to thank Center,
Dr. M. Sohrabpour, for supporting of
Director this work
of and
REFERENCES Saf ranj , V. Markovic and D. kotoski i1983j. Babic, D., A. immediate and Radiation degradation of polypropylene, Radiat. Phys. long-time effect on average molecular weigths. Chem. 22 , 3-5, 659. Williams (1983). Radiation stability Dunn, T. S. and J.L. 1 of polypropylene. Ind. Irrad. Tech. 33. (1989). Youshi, K. Makuuchi and I. Ishigaki Kadir, Z. A., F. Durability of radiation sterilized polymers. Polymer, 30,
8th International
Meeting
on Radiation
Processing
August , 1425. Katbab, A. A. and A. Yousefi (1991). degradation of polypropylene comparison of amine as stabilizer. pheno 1 and gamma Chem. 205-301 . 30, Williams, J. L., T. S. Dunn, H. Sugg and Radiation stabi 1 i ty of polypropylene. 445. Chem 9 , A
227
Post
irradiation hindered aromatic Radiat. PhVs. V.
Stannet Radiat.
(1977). Phys.