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Morphology and Rheological Properties of PP/SEBS/PS-HI Blends
T. Holjevac Grgurić1, V. Rek2, Ž. Jelčić3, M. Mišak-Mlinac
1
Faculty of Chemical Engineering and Technology, University of Zagreb, Croatia
2
Pliva, Zagreb, Croatia
3
Dioki d.d., Research Laboratory, Zagreb, Croatia
1. Introduction
The final properties of polymer blends are related to the
quality of their morphology, which depends on
processing conditions, composition of the blends,
rheological properties of phases and compatibility of
polymer components. The incompatibility between
polymeric components is responsible for the very poor
mechanical properties of most polymer blends [1,2].
Low adhesion between the phases results with poor
stress transfer across the interface. The interfacial
properties for such incompatible polymer blends can be
improved with the addition of compatibilizers [3,4].
In this work, we report a study of the compatibilizing
effect of styrene/ethylene-butylene/styrene block
copolymer, SEBS, on mechanical and rheological
properties as well as
morphology of immiscible
polypropylene/high impact polystyrene, PP/PS-HI,
blends.
3. Results and Discussion
Torque, TQ, versus content of PS-HI in PP/PS-HI
blends obtained during preparation of the blends in
extruder are reported in Figure 1. The results show
higher value of torque, for the same PS-HI content, in
compatibilized blends. Figure 1. presents lower values
of TQ for blends compatibilized with 7 % of SEBS
block copolymer.
2. Materials and Methods
The investigations were done with high impact
polystyrene,
PS-HI
417,
DIOKI,
Croatia,
polypropylene, PP, Moplen HP 500N, BASF, and their
blends.
Styrene/ethylene-butylene/styrene
block
copolymer, SEBS, Kraton 1650, Kraton Polymers,
Germany, was used as compatibilizer.
PP/PS-HI blends were prepared in two weight ratios,
PP/PS-HI 90/10 and PP/PS-HI 50/50, and in presence of
5 % and 7 % SEBS blok copolymer. The blends were
prepared by using a Haake Record 90 twin extruder,
with the following zone temperatures 150/200/200/210
°C and the frequency of rotation 60 min-1. The
specimens were obtained by injection molding at 230
°C. Torque, TQ, and output were recorded during the
processing in extruder. Mechanical properties were
done at Instron Model 1185, at room temperature and
rate 50 mm/min. Impact strenght was determined
according to ISO 180. Dynamic Mechanical Analysis,
DMA 983, TA Instruments was used to obtain primary
viscoelastic functions, under following conditions; fixed
frequencies 1 Hz, temperature range from -100°C to
150°C, and heating rate 5 °C/min. Scanning electron
microscope, SEM, JOEL J.S.M. – 5800 was used to
investigate the morphology of the samples after the
specimens were cut under liquid nitrogen atmosphere.
Figures 2a) - 2c) show the mechanical properties of pure
polypropylene, PP, high impact polystyrene, PS-HI, and
their uncompatibilized and compatibilized blends. PP
presents higher stress at break, as well as yield stress
than PS-HI (Figure 2b). In relation to impact properties
in Figure 2a) we can observe high value of impact
strenght of PS-HI, what is result of its specific salamitype morphology. The effect of adding SEBS block
copolymer as compatibilizer, results in variations of
impact strenght, stress and elongation at break of binary
PP/PS-HI blends (Figure 2a-2c). It can be seen that the
uncompatibilized PP/PS-HI 90/10 blend presents higher
stress at break as regards to compatibilized blend. SEBS
block copolymer has a tendency to increase elongation
at break, as well as impact strenght of the investigated
blend. This is due to better compatibilization of the
disperze phase PS-HI in the matrix of PP.
Figure 1. Torque value of PP/PS-HI blends
2
impact strenght (kJ/m )
10
0 % SEBS
5 % SEBS
7 % SEBS
8
6
4
2
0
100/0
90/10
50/50
blend composition (PP/PS-HI)
2a)
Proceeding of the 8th Polymers for Advanced Technologies International Symposium
Budapest, Hungary, 13-16 September 2005
0/100
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0 % SEBS
5 % SEBS
7 % SEBS
stress at break (MPa)
25
20
15
10
5
Higher content of compatibilizer in PP/PS-HI 90/10
blend, decrease Tg of soft, ethylene/butylene phase, EB,
to lower values. Storage modul, E`, decrease with
increasing of SEBS block copolymer. SEBS block
copolymer effects at the same way on glass transition
temperatures of hard phases in blend PP/PS-HI 50/50,
but with increasing content of SEBS, T g of soft, EB
phase increases, as well as Tg of soft, polybutadiene,
PB, phase.
0
100/0
90/10
50/50
blend composition (PP/PS-HI)
0/100
Table 1. Glass transition temperatures Tg, storage
modulus, E`, and intensities of loss tangent, tgδ, for
PP/PS-HI blends
b)
0 % SEBS
5 % SEBS
7 % SEBS
45
elongation at break (%)
40
35
30
25
20
15
10
5
0
100/0
90/10
50/50
blend composition (PP/PS-HI)
0/100
c)
Tg PB
°C
E”
Tg EB
°C
E”
Tg PP
°C
E”
Tg PS
°C
E”
E`
GPa
25 °C
Is
EB
tg
Is
EB
tg
Is
PP
tg
Is
PS
tg
PP/PS-HI
90/10
/
/
24,86
117,9
2,500
/
/
0,057
0,129
PP/SEBS/PS-HI
90/5/10
/
- 23,71
31,05
122,4
2,311
/
0,021
0,058
0,132
PP/SEBS/PS-HI
90/7/10
/
- 26,07
31,67
119,4
2,288
/
0,023
0,058
0,133
PP/PS-HI
50/50
-80-90
/
20,20
113,3
1,967
/
/
0,050
0,233
PP/SEBS/PS-HI
50/5/50
- 85-90
- 40,02
26,64
116,1
2,371
0,026
0,020
0,049
0,253
PP/SEBS/PS-HI
50/7/50
- 76,9
- 36,01
30,13
122,3
1,834
0,027
0,024
0,051
0,261
UZORAK
Figure 2. Mechanical properties of PP, PS-HI and
PP/PS-HI blends; a) impact strenght, b) stress at break,
c) elongation at break
By increasing SEBS content from 5 % to 7 % , impact
strenght increase, while elongation at break decrease.
The same behaviour of impact strenght is observed for
blend PP/PS-HI 50/50, but the effect of SEBS block
copolymer is lower than in PP/PS-HI 90/10 blend.
Dynamic mechanical analysis of the investigated blends
show multiphase, heterogeneous character of PP/PS-HI
blends. DMA results for binary PP/PS-HI 90/10 blend
presents two glass transitions, T g, of hard phases; Tg of
polystyrene, PS, phase,
at 117 °C and Tg of
polypropylene, PP, phase, at 24 °C (Figure 3, Table 1).
SEBS block copolymer added as compatibilizer,
increase temperature of glass transitions of hard phases,
Tg of PS phase as well as Tg of PP phase, as regards to
binary blend. For PP/SEBS/PS-HI blends just one Tg of
PS phase was obtained, due to good affinity of PS block
of SEBS and polystyrene, PS, of PS-HI.
SEM analysis of uncompatibilized PP/PS-HI blend
show two-phase morphology with PS-HI particles
disperzed in the PP matrix, as a result of high interfacial
tension. On SEM micrographs we can observe a lot of
holes formed from the stretching in the fracture. The
addition of SEBS block copolymer to binary PP/PS-HI
blend, which is located at the interface between PP and
PS-HI, changes its phase morphology. The size of the
disperzed PS-HI particles is reduced in both
compositions, with 5 % and 7 % of added
compatibilizer, but the effect is more pronounced with
higher content of SEBS block copolymer.
It can be seen a better adherence of the disperzed phase
in the matrix, as well as reducing of holes in presence of
SEBS block copolymer as compatibilizer in PP/PS-HI
blends.
140
PP/PS-HI 90/10
PP/SEBS/PSHI 90/5/10
PP/SEBS/PSHI 90/7/10
120
100
E" / GPa
80
60
40
20
PP/PS-HI 50/50
PP/SEBS/PSHI 50/5/50
PP/SEBS/PS-HI 50/7/50
0
-150
-100
-50
0
50
100
150
200
T / °C
Figure 3. The loss modulus, E",of PP/PS-HI blends
4 a)
Proceeding of the 8th Polymers for Advanced Technologies International Symposium
Budapest, Hungary, 13-16 September 2005
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References (max. 10)
b)
[1] Ismail H.H., Nasir M.: Polymer Testing 21: 163170 (2002)
[2] Papadopoulou C.P., Kalfoglou N.K.: Polymer 41:
2543-2555 (2000)
[3] Bassani A., Pessan L.A.: J. Appl. Polym. Sci. 88:
1081-1094 (2003)
[4] Santana R.M.C., Manrich S.: J. Appl. Polym. Sci.
88: 2861-2867 (2003)
.....
c)
d)
Figure 4. SEM microphotographs of PP/PS-HI blends
a) PP/PS-HI 90/10, b) PP/SEBS/PS-HI 90/5/10,
c) PP/SEBS/PS-HI 90/7/10, d) PP/SEBS/PS-HI 50/5/50
4. Conclusion
The results show that SEBS block copolymer produce
an improvement in toughness of PP/PS-HI blends. The
effect of compatibilizer is the most pronounced in blend
PP/PS-HI 90/10 with 7 % of SEBS.
The results of SEM analysis show that SEBS block
copolymer act as a compatibilizer in immiscible PP/PSHI blends. The stronger interactions of SEBS between
the disperze phase, high impact polystyrene and the
matrix, polypropylene results in reducing the average
particle size of PS-HI, and increasing the interfacial
adhesion between the both phases.
Proceeding of the 8th Polymers for Advanced Technologies International Symposium
Budapest, Hungary, 13-16 September 2005