American Journal of Science and Technology
2015; 2(4): 188-194
Published online July 20, 2015 (http://www.aascit.org/journal/ajst)
ISSN: 2375-3846
Keywords Polypropylene,
POE,
SEBS,
Crystallization
Received: June 16, 2015
Revised: June 29, 2015
Accepted: June 30, 2015
The Effect of SEBS and POE on Properties of Polypropylene
Lei Lv1, Xuejia Ding
1, Hanqing Gu
2, Guoying Hu
2
1Beijing biological materials laboratory, Beijing University of Chemical Technology, Beijing, China 2Tianjin Institute of Urology, Tianjin Medical University, Tianjin, China
Email address [email protected] (Xuejia Ding)
Citation Lei Lv, Xuejia Ding, Hanqing Gu, Guoying Hu. The Effect of SEBS and POE on Properties of
Polypropylene. American Journal of Science and Technology. Vol. 2, No. 4, 2015, pp. 188-194.
Abstract In this paper, we focused on the effect of SEBS and POE on the crystallization of
polypropylene, as well as thermal properties. DSC results revealed that the crystallinity of
polypropylene and the rate of crystallization of polypropylene decreased with the presence
of SEBS. While the crystallinity of polypropylene increased with a small amount of POE,
and the crystallinity of polypropylene decreased with a large amount of POE. TGA results
showed that SEBS can decrease the thermal stability of the polypropylene, while the
thermal stability of the polypropylene improved with the presence of POE. In addition,
both POE and SEBS can increase the notched impact strength of polypropylene. SEBS
had better performance than POE in increasing the notched impact strength of
polypropylene.
1. Introduction
Polypropylene (PP) is a kind of cheap materials, which has a good performance
compared with other polymer materials. Polypropylene has an outstanding chemical
property, and it has a good strength and stiffness [1-5]
. So PP is widely used in material
fields, such as the biological medical field, automotive materials field. However, The
application of PP is limited because of its low impact resistance, high rate of molding
shrinkage and high brittleness. Therefore, the modification of PP especially the
toughening modification has become the hotspot in the domestic and overseas[6-10]
. The
impact toughness of PP can be increased by the presence of elastomers such as
ethylene-octene copolymer (POE), styrene-ethylene-butylene-styrene (SEBS) and
ethylene–propylene diene elastomer (EPDM)[11-14]
.
The reason why elastomers can increase the toughness of PP was investigated. In 1956,
Merz found the crack could cause expansion and stress whitening during the stretching[15]
.
He considered that the rubber particles could be stretched when the crack developed, and
the rubber particles could absorb a lot of energy, so the impact strength of materials could
increase. In 1960, Schmitt proposed the theory of crack[16]
. He believed that the rubber
particle could act as the stress concentration points, then it could produce a large number
of small cracks to absorb a lot of energy. At the same time, these large number of small
cracks could weaken the stress when the cracks was developed. Therefore the impact
strength of materials increased. In 1965, Newman found the Shear yielding theory. He
considered that the rubber particles in the matrix resin could produce 3-D static tension,
which could expand the volume and decrease the glass transition temperature[17]
.So the
rubber particles could terminate the crack to improve the impact strength. But the theory
could not explain the stress whitening in the process of the shear yielding stress, for these
reason the theory caused a great controversy, and some people thought 3-D static tension
189 Lei Lv et al.: The Effect of SEBS and POE on Properties of Polypropylene
prefer to induce the craze rather than shear zone. The final
conclusion is still not given because of the complexity of the
toughening phenomenon. Bucknall proposed the craze shear
zone theory in 1972[18]
.He thought the rubber particles played
an important role in toughening PP. At first, the rubber
particles acted as the center of the stress concentration, and
they could induce a large number of the crazes and shear
bands. In addition, the rubber particles could control the
development of the crazes, and prevent the them from
becoming the destructive crack. The stress field of the craze
induced the shear zone, So it could avoid the further
development of the craze. The formation and development of
shear zone needed a large of energy, so impact strength of the
materials increased effectively. Further research showed that
the proportion of crazing and shear zone had an influence on
properties of resin. The toughness of polypropylene increased
with the increasing of the proportion of crazing and shear zone.
The craze shear zone theory not only considered the effect of
the rubber particles, but also studied the influence of
properties of resin. The theory explained the function of the
crazes in detail. On the one hand, the development of the
crazes needed a lot of energy, on the other hand, the craze
could become the cracks. Therefore the theory has been
widely accepted.
Based on the previous research of toughening PP, the
authors of this paper attempted to study the effect of POE and
SEBS on the morphology, mechanical, thermal and crystal
properties of polypropylene.
2. Experimental
2.1. Materials
PP (T30S) was supplied by China Petroleum Chemical Co,
Tianjin branch. The melt flow index (MFI) (at 200°C and 5kg
load) and the density of PP were 4.8 g/10min and 0.91g/cm3,
respectively. Ethylene-octene copolymer (POE, DF840) was
supplied by Mitsui Elastomers Singapore Pte Ltd (Japan). The
melt flow index (MFI) (at 190°C and 21.6kg load) and the
density of POE were 3.6 g/10min and 0.885g/cm3,
respectively. Styrene-ethylene-butylene-styrene (SEBS,
MD6945) were supplied by Kraton Polymer(USA). The melt
flow index (MFI) (at 200°C and 5kg load) of SEBS was
22g/10 min (at 190°C and 5kg load).
2.2. Preparation
Materials must be dried in a vacuum oven for 16h at 80°C.
Then, the mixes were melt-blended according to the
formulations given in Table 2-1 using a co-rotating twin-screw
extruder (ZSK-25WLE) with L/D ratio of 40.The screw speed
of co-rotating twin-screw extruder was 150pm. The
temperature profiles of the barrel were 190°C-200°Cfrom
hopper to the die. After melt-blended, the samples were
pelletized by using pelletizer (SGS50-E).Then the samples
dried in a vacuum oven for 16h at 80°C. And the samples were
injected into standard samples by using injection molding
machine (JPH-10). The barrel temperature of the injection
molding were 180°C-220°C. The injection pressure was
60MPa.The time of cooling was 30s.
Table 2-1. Compositions of the Formulations.
Samples PP/phr SEBS/phr
1 100 0
2 100 5
3 100 10
4 100 15
5 100 20
6 100 5
7 100 10
8 100 15
9 100 20
2.3. Characterization
2.3.1. Mechanical Properties
The samples were prepared according to GB/T 1040.1-2006
and the tensile test was tested according to GB/T
1040.1-2006.The samples were injected into the shape of
dumbbell .The tensile test was tested by testing machine
(UTM). The rate of extension was 50mm/min. The initial
distance of grips was 115mm and the gauge length was
50mm.The tensile strength and elongation at break were
achieved through testing machine (UTM).
The impact strength test was tested by impact testing
machine (XJJD) according to GB/T 1043.1-2008/ISO
179-1-2010. The gap of width was 2mm.The notched impact
strength was achieved through impact testing machine(XJJD).
The notched impact strength was calculated according to
the formula (2-1):
acn=1000×EC/(b×h) (2-1)
acn( kJ/m2) was representing the impact strength
EC (J) was representing the loss impact of energy
h( mm) was representing the remaining gap width
b (mm)was representing the thickness of the spline
The blending test was tested in testing machine(XJJD)
according to GB/T 9341-2008.The bending deflection was
6mm and the speed of blending was 2mm/min.
2.3.2. Crystallization Properties
The crystallization of polypropylene was tested by
DSC-Q20 from TA company (USA) to detect the thermal
transition and monitor the rate of heat flow. The weight of
samples were 5mg.Firstly,The samples were placed in a DSC
pan and rapidly heated at a rate of 20°C/min to 210°C for 5min
to remove all the memory of previous thermal and mechanical
history. Then the samples were cooling at a rate of 5°C/min
from 210°C to 25°C to detect the crystallization temperatures
of PP. At last the samples were melting at a rate of 5°C/min
from 20°C to 210°C to detect the melting properties of PP.
American Journal of Science and Technology 2015; 2(4): 188-194 190
The degree of crystallinity refers to the degree of structural
order in a solid. In a crystal, the atoms or molecules are
arranged in a regular, periodic manner. The degree of
crystallinity has a big influence on hardness, density,
transparency and diffusion.
The degree of crystallinity of polypropylene was calculated
according to the formula (2-2):
XC(%)=∆Hf/∆Hfo×100% (2-2)
XC(%) represented the degree of crystallinity.
∆Hf( J/g) represented melting enthalpy.
∆Hfo(J/g) =209J/g was the heat of fusion of 100%
crystalline polypropylene.
2.3.3. Thermal Properties
Thermal stability was tested by thermal gravimetric
analyzer Q500 from TA company (USA). The temperature
ranged from 50°C to 800°C at a rate of 20°C/min under
nitrogen atmosphere.
2.3.4. Morphological Properties
The morphology of samples were examined by scanning
electron microscopy S-4800 from Hitachi Co. (Japan).All the
samples were fractured in liquid nitrogen and observed after
covered with a thin layer of gold.
3. Results and Discussion
3.1. Mechanical Properties
The effect of POE and SEBS on notched impact strength of
PP/POE and PP/SEBS was shown in Fig. 3-1. From the Fig.
3-1 both POE and SEBS could improved the notched impact
strength polypropylene, respectively. The content of POE was
10 phr, the notched impact strength of polypropylene
increased from 2.4 kJ/m2 to 3.5 kJ/m
2. The content of SEBS
was 10 phr, the notched impact strength of polypropylene
increased from 2.4 kJ/m2 to 3.2 kJ/m
2. The notched impact
strength of polypropylene was 4.34kJ/m2 when the content of
POE was 20 phr. The notched impact strength of
polypropylene was 8.19kJ/m2 when the content of SEBS was
20 phr. The notched impact strength of polypropylene
increased by 84% with addition of 20 phr POE. And The
notched impact strength of polypropylene increased by 248%
with addition of 20 phr SEBS. It is well known that SEBS is an
effective toughening agent in blends compared POE. Similar
observation was also reported by Tucker et al.[19]
and
Wilkinson et al[20]
. POE and SEBS had a good compatibility
with PP matrix, so POE and SEBS could act as the center of
the stress concentration to induce a large of the crazes and
shear bands. At the same time the rubber particles could
control the development of the crazes and terminate the
development of crazes becoming the destructive crack. The
stress field of the craze also induced the shear zone ,it could
prevent the further development of the craze. The formation
and development of shear zone needed a large of energy, so
impact strength of the materials increased significantly.
The effect of POE and SEBS on tensile strength of
polypropylene was shown in Fig. 3-2. The tensile strength of
polypropylene decreased significantly in the presence of POE
and SEBS. When the content of POE was 10 phr, the tensile
strength of polypropylene decreased from 36.5 MPa to 23.1
MPa. The tensile strength of polypropylene decreased from
36.5 MPa to 20.2 MPa with the presence of 10 phr SEBS.
From the Fig.3-2.the tensile strength of PP/POE and PP/SEBS
decreased to 21.5 MPa and 20.2 MPa with the presence of 20
phr POE and SEBS, respectively. This could due to the
elastomeric nature of SEBS and POE. The strength of
elastomeric was lower than PP matrix. Similar observations
were reported by Gonza´ lez et al.[21]
and Chiu et al.[22]
Fig. 3-1. The Izod Notched Impact Strength of PP/POE and PP/SEBS.
Fig. 3-2. The tensile strength of of PP/POE and PP/SEBS.
As was shown in Fig. 3-3 the elongation at break of the
polypropylene increased by 380% and 320%, respectively.
The elastomeric nature of SEBS and POE acted as stress
concentrator in the tensile testing, and stress concentrator
could lead to yielding and crazing around the PP matrix. So
the elastomeric can absorb high energy to avoid a highly strain
process.[23]
Fig. 3-4 Showed the blending strength of PP/POE and
PP/SEBS. With the increase of the content of POE and SEBS,
the strength of PP/POE and PP/SEBS decreased. The strength
of PP/POE decreased from 45.9 MPa to 29.4 MPa with the
191 Lei Lv et al.: The Effect of SEBS and POE on Properties of Polypropylene
presence of 20 phr POE. Similarly, The blending strength of
PP/POE decreased from 45.9 MPa to 22.7 MPa with the
presence of 20 phr SEBS.
Fig. 3-3. The elongation at break of PP/POE and PP/SEBS blend.
Fig. 3-4. The blending strength of PP/POE and PP/SEBS
3.2. Crystallization Properties
Fig.3-5 and 3-6 showed the DSC heating and cooling curves
of PP/SEBS .The data obtained from the crystallization and
melting curve of PP/SEBS was shown in Table.3-1.The
temperature of melting peak (Tm), the temperature of
crystallization peak (Tc), the beginning temperature of
crystallization (Tonset) and the degree of crystallinity of
PP/SEBS were summarized From the Table.3-1,it can be seen
that the temperature of crystallization peak (Tc),the beginning
temperature of crystallization (Tonset) and the degree of
crystallinity of PP/SEBS decreased with the presence of SEBS.
When the content of SEBS was 20 phr, the degree of
crystallinity of PP/SEBS decreased from 41.33% to
31.43%.The degree of super-cooling was the difference
between the temperature of melting peak (Tm) and the
beginning temperature of crystallization (Tonset). The rate of
crystallization increased with the decreasing of the degree of
super-cooling. So the rate of crystallization decreased with the
presence of SEBS. It was evident that SEBS can prohibit the
crystal formation in PP matrix, and decrease the rate of
crystallization. A similar result was also reported by Tjong et
al.[24]
Fig. 3-5. Crystallization curves of neat PP and PP/SEBS.
Fig. 3-6. Meltingcurves of neat PP and PP/SEBS.
Table 3-1. Dates of crystallization properties of PP/SEBS.
SEBS/
% Tm/°C Tonset/°C Tc/°C
(Tm–Tonset)/
°C △△△△H/J/g Xc/%
0 164.81 125.77 122.82 39.04 86.4 41.33
5 163.99 123.94 121.84 40.05 82.91 39.67
10 164.27 123.9 121.03 40.37 77.73 37.19
15 164 123.75 120.99 40.25 74.8 35.79
20 164.58 123.5 120.62 41.08 71.96 34.43
Fig.3-7 and Fig.3-8 showed the DSC heating and cooling
thermograms of PP/POE. The data obtained from the
crystallization and melting curve of PP/POE was shown in
Table.3-2.From the Table.3-2,it can be seen that the
temperature of melting peak(Tm) decreased slightly with the
presence of the POE. The degree of crystallinity of
polypropylene increased from 41.33% to 45.54% with
5%POE added. A small content of POE had the effect of
heterogeneous nucleation in PP matrix, it could increase the
American Journal of Science and Technology 2015; 2(4): 188-194 192
degree of crystallinity of PP/POE, as well as the rate of
crystallization. However the crystal formation can be
prohibited with a large content of POE. The degree of
crystallinity of PP/POE decreased 35.77% with the 20 phr
POE added. A similar result was also reported by Li[25]
.
Fig. 3-7. Crystallization curves of neat PP and PP/POE.
Fig. 3-8. Melting curves of neat PP and PP/POE.
Table 3-2. Dates of crystallization properties of PP/POE.
POE/
% Tm/°C Tonset/°C Tc/°C
(Tm–Tonset)
/°C △△△△H/J/g Xc/%
0 164.81 125.77 122.82 39.04 86.4 41.33
5 163.58 126.13 122.81 37.45 95.18 45.54
10 163.98 126.06 122.66 37.92 92.2 44.11
15 163.88 125.23 122.18 38.65 79.02 37.8
20 163.74 124.72 121.66 39.02 74.75 35.77
3.3. Thermal Properties
Fig.3-9 showed the TGA curves of PP/SEBS. The thermal
stability of PP/SEBS was characterized by the temperature of
degradation and summarized in Table.3-3.It could be seen that
the temperature of degradation decreased from 467.77°C to
431.05°C with the presence of 20 phr SEBS. SEBS could
decrease the thermal stability of PP matrix. Similar research
was reported by Deqiang, Zhang[26]
.The polyethylene (PE)
and polybutylene (PB) chain contained in chain had easy
degradation ,they could generate a large number of the activity
of free radical. So the thermal stability of PP matrix decreased
with the addition of SEBS.
Fig. 3-9. TGA curves of PP/SEBS.
Table 3-3. The effect of SEBS with different content on thermal stability of
PP/SEBS blends.
SEBS/% 0 5 10 15 20
Degradation
temperature/°C 450.74 443.8 443.28 443.18 398.98
Table 3-4. The effect of POE with different content on thermal stability of
PP/SEBS blends.
POE/% 0 5 10 15 20
Degradation
temperature/°C 450.74 450.00 452.14 452.07 452.14
Fig. 3-10. TGA curves of PP/POE.
Fig.3-10 showed the TGA curves of PP/POE. And The
temperature of degradation was summarized in Table.3-4.It
can be seen that the temperature of degradation increased from
450.74°C to 452.14°C with the presence of 20 phr POE. It was
193 Lei Lv et al.: The Effect of SEBS and POE on Properties of Polypropylene
evident that the POE could increase the thermal stability of PP
matrix slightly. Similar research was reported by S.J. Wang[27]
.
3.4. Morphological Properties
Fig. 3-11. SEM micrographs of fracture surface of the samples.
Fig.3-11 (a),(b),(c) showed the SEM micrographs of the
fracture surface of the samples. From Fig.3-11 (a) it was could
be seen that the fracture surface of PP matrix was clear ,and
the amount of craze was small. But the fracture surface of
PP/POE and PP/SEBS was rough, and the number of craze
increased with the presence of POE and SEBS. It was evident
that POE and SEBS could act as the center of the stress
concentration to induce a large of the crazes and shear bands,
so the impact strength of the materials increased with the
addition of POE and SEBS.
4. Conclusion
Ethylene-octene copolymer (POE)/polypropylene (PP) and
styrene-ethylene-butylene-styrene polypropylene (SEBS)/
polypropylene (PP) were prepared by melt compounding
using co-rotating twin-screw extrude. Both POE and SEBS
can toughen polypropylene. SEBS had a better effect of
toughening polypropylene. DSC results revealed that both the
rate of crystallization and the degree of crystallinity of
polypropylene decreased with the presence of SEBS. While
the crystallinity of polypropylene increased with a small
amount of POE, and the crystallinity of polypropylene
decreased with a large amount of POE. TGA results showed
that the thermal stability of PP matrix decreased with the
addition of SEBS, while the thermal stability of PP matrix
increased with the presence of POE.SEM results showed the
impact strength of the materials increased with the addition of
POE and SEBS.
Acknowledgments
The authors thank the National Science and Technology
Infrastructure Program (2014BAI11B12) for financial
support.
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