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 dingxj2011@126.com (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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