- Email: [email protected]
The effect of antioxidants on the morphology of gamma irradiated isotactic polypropylene
Radiat. Phys. Chem. Vol. 35, Nos 1-3, pp. 190-193, 1990 Int. J. Radiat. Appl. Instrurn., Part C Printed in Great Britain
0146-5724/90 $3.00+0.00 Pergamon Press plc
THE EFFECT OF ANTIOXIDANTS ON THE MORPHOLOGYOF GAMMA IRRADIATED ISOTACTIC POLYPROPYLENE D. KOSTOSKI, Z. STOJANOVI¢ and Z. KAQAREVI¢-POPOVI¢ "Boris Kidri~" I n s t i t u t e of Nuclear Sciences-Vin~a, P.O.Box 522, 11001 Belgrade, Yugoslavia
ABSTRACT The e f f e c t of two types of antioxidants on the morphology and melting behaviour of gamma i r r a d i a t e d i s O t a c t i c polypropylene has been studied using x-ray d i f f r a c t i o n and d i f f e r e n t i a l scanning calorimetry. The changes in the morphology and decrease of melting temperature and c r y s t a l l i n i t y with absorbed dose are related to the r a d i a t i o n processes in iPP containing a n t i o x i d a n t s . KEYWORDS Gamma i r r a d i a t i o n ; morphology; polypropylene; a n t i o x i d a n t . INTRODUCTION I s o t a c t i c polypropylene (iPP) is a commercially material f o r medical devices such as disposable and Williams, 1983; Kostoski et a l . , 1988) that i r r a d i a t i o n in a i r , even at l ~ s e s (max. 100
important polymer, used e x t e n s i v e l y as a syringes. However, i t is well known (Dann the iPP used is more unstable to gamma ray kGy).
Control of polymer morphology is of primary s i g n i f i c a n c e to d i r e c t r a d i a t i o n effects on polymers and subsequent degradation. Because of that in our previous work (Kostoski et a l . , 1988) we studied the e f f e c t of gamma i r r a d i a t i o n on the morphology of pure iPP. In order to s t a b i l i z e iPP, some kind of antioxidants are added into the homopolymer. The role of antioxidants in the chemical reactions with free radicals and t h e i r e f f e c t on the mechanical properties of i r r a d i a t e d iPP were considered in some previous works (Dann and Williams, 1983; Kagiya et a l . , 1985). However, there are no data about the influence of antioxidants on the m o r ~ g y and melting behaviour of gamma i r r a d i a t e d iPP. The aim of our work was to i n v e s t i g a t e how the presence of phenolic (A5) or the sulphuric type of a n t i o x i d a n t s (A3) a f f e c t the melting behaviour and morphology of u n i r r a d i a t e d and i r r a d i a t e d samples to the absorbed dose up to 100 kGy. EXPERIMENTAL Materials The i s o t a c t i c polypropylene used in our work is1~he flake grade Profax 6501, containing no a d d i t i v e s , with a number average mol. wt=4.5x10 and a p o l y d i s p e r s i t y of 6.5. The types o f antioxidants were used: the phenolic Irganax 1010 Ciba Geigy Co, A5 and the sulphur containing DLTP American Cyanamid Co, A3. The formulations with three d i f f e r e n t contents of antioxidants (0.2, I and 3 wt %) were ~repared using rheometer equippped with Rheomix-600 mixer. The mixing was performed at 190uc with 60 Rpm f o r 8 min. The pure polymer was treated under the same conditions as the formulations. A f t e r the treatment in the mixer, the materials were compression molded i n t o 0.5 mm t h i c k sheets in a laboratory Carver press at a temperature of 190°C and 1.75 Mpa pressure. The molded sheets were e i t h e r air-cooled or r a p i d l y quenched by dipping the press platens into the ice water. 190
7th International Meeting on Radiation Processing
191
The sheets are irradiated in a i r at room temperature in a Co-60 source at 15 kGy/h dose rate. Experimental Methods Wide-angle x-ray scattering (WAXS): Wide-angle x-ray diffractograms were obtained by using a PW 1010 powder diffractometer (CuK-Ni f i l t e r e d radiation). The scan rate used was 0.25~mi~ Melting behaviour: A Perkin-Elme~ Model DSC-2 d i f f e r e n t i a l scanning calorimeter with nitrogen as the purge gas has been used. The samples of 7-8 mg weight cut from the same sheets as in x-ray measurements were analysed by heating from 320 to 470 K at 10 degree/min rate. RESULTS AND DISCUSSION From the diffractograms ( F i g . l ) of the air-cooled samples of iPP with various contents of antioxidants A3 and A5 four peaks can be identified which correspond to the reflections of ~110), (040), (130) and (041). These reflections are assigned to the monoclinic crystal structure. However, in the case of quenched sample the diffractograms have four broad peaks. These broad peaks can be attributed to the low degree of c r y s t a l l i n e form - "smectic" phase whose nature is s t i l l being debated (Hendra et a l . , 1984). From these measurements i t is evident that the influence of the low doses gamma irradiation on the crystal structure of iPP containing various concentration of antioxidants A3 and A5 is p r a c t i c a l l y negligable.
10
15
20
25
Fig. I. X-ray diffractograms of air-cooled sample containing I wt % A3 or A5 (1), quenched sample containing I wt % A3 ( I I ) and quenched sample containing I wt % A5 ( I I I ) . The fusion endotherms (Fig.2) of the quenched iPP samples which contain different concentrations of antioxidants A3 and A5 have a single broad peaks. However, the endotherms of the quenched samples of iPP which contain antioxidant A3 have bimodal shape while the samples containing antioxidants A5 have a complex shape. The bimodal shape of endotherms has been disscused in our previous work (Kostoski et a l . , 1988). The complex shape of endotherms in the case of quenched iPP containing A5 a n ~ d a n t s can be related to the c r y s t a l l i n e nature of antioxidant A5 (Fig.2). From these measurements i t is observed that the melting temperature and c r y s t a l l i n i t y decrease with increasing absorbed dose (Table I ) . The degree of c r y s t a l l i n i t y of the sample was evaluated from the heat of fusion relative to a value of 209 J/g corresponding to a perfect
192
D. KOSTOSKI et al.
polypropylene crystal (Kagiya et a l . , 1986). These decreases may be caused by radiation-induced scissions that occur ln-~6--~ITe crystalline regions of iPP and which can not be identified by x-ray measurements.
10 mcal S
IV
II
%
~
NTIOXIDANTA ~
L~
IIIi
~
.
~
f
T(K) •
320
.
,
.
I
•
350
.
.
.
I
.
•
.
380
.
i
.
410
.
.
.
I
.
440
.
.
.
470
Fig. 2. Fusion endotherms of quenched samples containing I wt % A5 (1); I wt % A3 ( I I ) and air-cooled samples containing I wt %
A5 ( I I I ) ; I wt % A3 (IV).
Table I. Melting behaviour data of iPP
iPP + I wt % A3 Absorbed dose (kGy)
Melting Crystallinity temperature(K) %
i PP +
I
wt % A5
Melting Crystallinity t e m p e r a t u r(K) e %
air-cooled
0 25 50 100
438.1 436.3 435.7 433.3
53 50 49 48
437.5 437.3 435.1 433.3
52 51 49 48
quenched
0 25 50 100
433.6 432.8 431.0 428.8
40 39 39 37
433.6 432.6 433.1 429.6
40 39 39 39
7th International Meeting on Radiation Processing
193
REFERENCES Dunn, T.S., Williams, E.E., Williams, J.L. (1982). "Investigations of stabilizing additives: Part I. A model sistem for studying radical scavenging activity in solution, "J. Polymer Sci., 20, 1599. Dunn, T.S., Williams, J.L. (1983). "Radiation stability of Polypropylene", J. of Indust. Irradiation Tech., I, 33. Hendra, J.P., Vile, J., Willis, A.H., Zichy, V., Cudby, A.M. (1984). "The effect of cooling rate upon the morphology of quenched melts of isotactic polypropylenes", Polymer, 25, 785. Kagiya, T., Nishimoto, S., Watanabe, Y., Kato, M. (1985). "Importance of the Amorphose Fraction of Polypropylene in the Resistance to Radiation-Induced Oxidative Degradation", Polymer Degrad. and Stability, 12, 261. Kostoski, D., Stojanovi~, Z., Gal, 0., Stannett, V.T. (1988). "The effect of gamma irradiation on the morphology of quenched isotactic polypropylene", Radiat. Phys. Chem., 13, 667.
0146-5724/90 $3.00+0.00 Pergamon Press plc
THE EFFECT OF ANTIOXIDANTS ON THE MORPHOLOGYOF GAMMA IRRADIATED ISOTACTIC POLYPROPYLENE D. KOSTOSKI, Z. STOJANOVI¢ and Z. KAQAREVI¢-POPOVI¢ "Boris Kidri~" I n s t i t u t e of Nuclear Sciences-Vin~a, P.O.Box 522, 11001 Belgrade, Yugoslavia
ABSTRACT The e f f e c t of two types of antioxidants on the morphology and melting behaviour of gamma i r r a d i a t e d i s O t a c t i c polypropylene has been studied using x-ray d i f f r a c t i o n and d i f f e r e n t i a l scanning calorimetry. The changes in the morphology and decrease of melting temperature and c r y s t a l l i n i t y with absorbed dose are related to the r a d i a t i o n processes in iPP containing a n t i o x i d a n t s . KEYWORDS Gamma i r r a d i a t i o n ; morphology; polypropylene; a n t i o x i d a n t . INTRODUCTION I s o t a c t i c polypropylene (iPP) is a commercially material f o r medical devices such as disposable and Williams, 1983; Kostoski et a l . , 1988) that i r r a d i a t i o n in a i r , even at l ~ s e s (max. 100
important polymer, used e x t e n s i v e l y as a syringes. However, i t is well known (Dann the iPP used is more unstable to gamma ray kGy).
Control of polymer morphology is of primary s i g n i f i c a n c e to d i r e c t r a d i a t i o n effects on polymers and subsequent degradation. Because of that in our previous work (Kostoski et a l . , 1988) we studied the e f f e c t of gamma i r r a d i a t i o n on the morphology of pure iPP. In order to s t a b i l i z e iPP, some kind of antioxidants are added into the homopolymer. The role of antioxidants in the chemical reactions with free radicals and t h e i r e f f e c t on the mechanical properties of i r r a d i a t e d iPP were considered in some previous works (Dann and Williams, 1983; Kagiya et a l . , 1985). However, there are no data about the influence of antioxidants on the m o r ~ g y and melting behaviour of gamma i r r a d i a t e d iPP. The aim of our work was to i n v e s t i g a t e how the presence of phenolic (A5) or the sulphuric type of a n t i o x i d a n t s (A3) a f f e c t the melting behaviour and morphology of u n i r r a d i a t e d and i r r a d i a t e d samples to the absorbed dose up to 100 kGy. EXPERIMENTAL Materials The i s o t a c t i c polypropylene used in our work is1~he flake grade Profax 6501, containing no a d d i t i v e s , with a number average mol. wt=4.5x10 and a p o l y d i s p e r s i t y of 6.5. The types o f antioxidants were used: the phenolic Irganax 1010 Ciba Geigy Co, A5 and the sulphur containing DLTP American Cyanamid Co, A3. The formulations with three d i f f e r e n t contents of antioxidants (0.2, I and 3 wt %) were ~repared using rheometer equippped with Rheomix-600 mixer. The mixing was performed at 190uc with 60 Rpm f o r 8 min. The pure polymer was treated under the same conditions as the formulations. A f t e r the treatment in the mixer, the materials were compression molded i n t o 0.5 mm t h i c k sheets in a laboratory Carver press at a temperature of 190°C and 1.75 Mpa pressure. The molded sheets were e i t h e r air-cooled or r a p i d l y quenched by dipping the press platens into the ice water. 190
7th International Meeting on Radiation Processing
191
The sheets are irradiated in a i r at room temperature in a Co-60 source at 15 kGy/h dose rate. Experimental Methods Wide-angle x-ray scattering (WAXS): Wide-angle x-ray diffractograms were obtained by using a PW 1010 powder diffractometer (CuK-Ni f i l t e r e d radiation). The scan rate used was 0.25~mi~ Melting behaviour: A Perkin-Elme~ Model DSC-2 d i f f e r e n t i a l scanning calorimeter with nitrogen as the purge gas has been used. The samples of 7-8 mg weight cut from the same sheets as in x-ray measurements were analysed by heating from 320 to 470 K at 10 degree/min rate. RESULTS AND DISCUSSION From the diffractograms ( F i g . l ) of the air-cooled samples of iPP with various contents of antioxidants A3 and A5 four peaks can be identified which correspond to the reflections of ~110), (040), (130) and (041). These reflections are assigned to the monoclinic crystal structure. However, in the case of quenched sample the diffractograms have four broad peaks. These broad peaks can be attributed to the low degree of c r y s t a l l i n e form - "smectic" phase whose nature is s t i l l being debated (Hendra et a l . , 1984). From these measurements i t is evident that the influence of the low doses gamma irradiation on the crystal structure of iPP containing various concentration of antioxidants A3 and A5 is p r a c t i c a l l y negligable.
10
15
20
25
Fig. I. X-ray diffractograms of air-cooled sample containing I wt % A3 or A5 (1), quenched sample containing I wt % A3 ( I I ) and quenched sample containing I wt % A5 ( I I I ) . The fusion endotherms (Fig.2) of the quenched iPP samples which contain different concentrations of antioxidants A3 and A5 have a single broad peaks. However, the endotherms of the quenched samples of iPP which contain antioxidant A3 have bimodal shape while the samples containing antioxidants A5 have a complex shape. The bimodal shape of endotherms has been disscused in our previous work (Kostoski et a l . , 1988). The complex shape of endotherms in the case of quenched iPP containing A5 a n ~ d a n t s can be related to the c r y s t a l l i n e nature of antioxidant A5 (Fig.2). From these measurements i t is observed that the melting temperature and c r y s t a l l i n i t y decrease with increasing absorbed dose (Table I ) . The degree of c r y s t a l l i n i t y of the sample was evaluated from the heat of fusion relative to a value of 209 J/g corresponding to a perfect
192
D. KOSTOSKI et al.
polypropylene crystal (Kagiya et a l . , 1986). These decreases may be caused by radiation-induced scissions that occur ln-~6--~ITe crystalline regions of iPP and which can not be identified by x-ray measurements.
10 mcal S
IV
II
%
~
NTIOXIDANTA ~
L~
IIIi
~
.
~
f
T(K) •
320
.
,
.
I
•
350
.
.
.
I
.
•
.
380
.
i
.
410
.
.
.
I
.
440
.
.
.
470
Fig. 2. Fusion endotherms of quenched samples containing I wt % A5 (1); I wt % A3 ( I I ) and air-cooled samples containing I wt %
A5 ( I I I ) ; I wt % A3 (IV).
Table I. Melting behaviour data of iPP
iPP + I wt % A3 Absorbed dose (kGy)
Melting Crystallinity temperature(K) %
i PP +
I
wt % A5
Melting Crystallinity t e m p e r a t u r(K) e %
air-cooled
0 25 50 100
438.1 436.3 435.7 433.3
53 50 49 48
437.5 437.3 435.1 433.3
52 51 49 48
quenched
0 25 50 100
433.6 432.8 431.0 428.8
40 39 39 37
433.6 432.6 433.1 429.6
40 39 39 39
7th International Meeting on Radiation Processing
193
REFERENCES Dunn, T.S., Williams, E.E., Williams, J.L. (1982). "Investigations of stabilizing additives: Part I. A model sistem for studying radical scavenging activity in solution, "J. Polymer Sci., 20, 1599. Dunn, T.S., Williams, J.L. (1983). "Radiation stability of Polypropylene", J. of Indust. Irradiation Tech., I, 33. Hendra, J.P., Vile, J., Willis, A.H., Zichy, V., Cudby, A.M. (1984). "The effect of cooling rate upon the morphology of quenched melts of isotactic polypropylenes", Polymer, 25, 785. Kagiya, T., Nishimoto, S., Watanabe, Y., Kato, M. (1985). "Importance of the Amorphose Fraction of Polypropylene in the Resistance to Radiation-Induced Oxidative Degradation", Polymer Degrad. and Stability, 12, 261. Kostoski, D., Stojanovi~, Z., Gal, 0., Stannett, V.T. (1988). "The effect of gamma irradiation on the morphology of quenched isotactic polypropylene", Radiat. Phys. Chem., 13, 667.