Effects of Processing on Mechanical Properties of Polypropylene

Composites

Xin Sui1 2 a Baohui Wang1 2 b Haiming Wu1 Li Wang1 3 Wei Zhao3 Li Li1 2 Hongjun Wu1 2 and Dandan Yuan1 2

1 College of Chemistry and Chemical Engineering Northeast Petroleum University Daqing 163318

China

2 Provincial Key Laboratory of Oil amp Gas Chemical Technology Northeast Petroleum University

Daqing 163318China

3 Daqing Huake Co Ltd Daqing 163316 China

azhisx_81163com

bwangbhnepueducn

Keywords Polypropylene Twin-screw extruder Injection molding machine Elongation at break

Abstract Based on the mechanism of processing and molding of multivariate polypropylene

composite system this paper studies the effect of the screw length-to-diameter ratio and the wedge

angle of the helix angle of the twin-screw extruder on the properties of elongation at break of

polypropylene composite The relationship between injection temperature and injection pressure of

injection molding machine is also analyzed Experiments show that when length-to-diameter ratio is

30 and wedge angle is 16plusmn5o the elongation at break of test sample reaches its maximum value and

tends to be stable When melting pressure is 40 MPa and the injection temperature at 190 degC- 220 degC

injection molding machine can improve the process flowing property of composite materials

Introduction

Polypropylene composites belong to blend-type composite system the content and distribution of the dispersed phase and the interfacial interaction between the dispersed and matrix have different degree of affects on the mechanical and fracture properties of the composites [1 2]

Darnell and Mol [3] put forward a solid conveying theory that is based on solid friction mechanism in 1952 Chung put forward a solid conveying theory that is based on viscosity attached in 1970 This experimental research was based on the published theoretical results The extruding process of twin-screw extruder which was used to make polypropylene composites consists of solid conveying melting and fused mass conveying [4-5] The molding mechanism of multivariate polypropylene composite system has been investigated The effect of the screw length-to-diameter ratio and the wedge angle of the helix angle of the twin-screw extruder on the composite properties have been studied Also the injection molding process conditions of the injection molding machine have been researched

Experimentals

Material Polypropylene powder was self-produced Polyolefin Elastomer (POE) was produced by Beijing Pulihongbin Chemical Materials Co Beijing China Linear Low-Density Polyethylene (LDPE) was obtained from Daqing petrochemical Co Daqing China Accessory ingredient was a commercial product of Nanjing Milan Chemical Co Ltd Najing China

Experimental apparatus Twin-screw extruder was purchased from Nanjing Keya Co Ltd Najing China Injection moulding machine was a commercial product of Dalian Huada mechanical Co Ltd Dalian China Impact tester was purchased from CEAST Co Italy Universal material machine was purchased from INSTRON Co USA

Specimen preparation Polypropylene powder and other additives were added into a high speed mixer to mix uniformity with preset ratio The obtained powder was extruded into granulation by the twin-screw extruder Then the resulted particles were dried and injected into a spline using the injection molding machine

Advanced Materials Research Vols 750-752 (2013) pp 156-159Online available since 2013Aug30 at wwwscientificnetcopy (2013) Trans Tech Publications Switzerlanddoi104028wwwscientificnetAMR750-752156

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Performance test Tensile strength and tensile elongation at break were tested according to the

GBT 1040 Cantilever beam impact was measured according to the GBT 1843 Bending strength

was determined according to the GBT 9341[6-8]

Results and discussion

Effects of screw length-to-diameter ratio on the properties of composites In the extruding

process of twin-screw extruder which was used to make polypropylene composites many screws

with different length-to-diameter ratio can be used This ratio affects the mechanical properties such

as the tensile elongation at break So it is useful to find the optimum ratio to get the high-quantity

composite

Figure 1 is the effect of length-to-diameter ratio of the screw on the properties of composites ie

the tensile elongation at break of the specimen The ratio varies from 10 to 34 It shows that the tensile

elongation at break of specimen is too low when the screw length-to-diameter ratio is very low With

increasing the ratio the tensile elongation at break increases and the growing gradient decreases

With the further increasing of the ratio the tensile elongation at break decreases The tensile

elongation at break of specimen reached maximum and leveled off at the ratio of about 30 The reason

is that the plasticizing ability and mixing properties of specimen have been improved The

experimental materials were in the mixing section of the twin-screw continuous extruder The

extruder would give the resin a strong shear stress in the very short term because the screw

length-to-diameter ratio increased And then the materials were mixed more evenly and gradually

plasticized in the mixing process However the material would cross bonding in extruder if the

length-to-diameter ratio was too high It is difficult for material to extrude and the extruding ability

would be low Therefore it is very important to select an optimum screw length-to-diameter ratio ie

the screw assembly in experiments [9] The vacuum pumping section of the twin-screw extruder

should also be used to remove the volatile components (such as water vapor) and to adjust the resin

pressure So a higher-quantity controlling of mixing properties of the materials can be obtained The

extrusion quality of extruded materials and the properties of the composites can be improved

5 10 15 20 25 30 35

600

700

800

900

1000

tensi

le e

lon

gat

ion a

t b

reak

()

length-to-diameter ratio 5 10 15 20 25 30

600

700

800

900

1000

ten

sile

elo

ngat

ion a

t b

reak

wedging angle

Effects of wedge angle of the helix angle on the properties of composites Figure 2 indicates the

effects of wedge angle of the helix angle on the tensile elongation at break of polypropylene

composites when the degree was in the case of a certain helix angle of the twin screw extruder As

shown in this figure the tensile elongation at break increases with the wedge angle When it ranges

from 16deg to 26deg the tensile elongation at break reaches a high and stable value However with the

further increases of wedge angle the tensile elongation at break decreases The reason may be that

when the wedge angle was between 16deg and 26deg the radial force and lateral force of the extruder were

in the appropriate range At this point the acting forces in material such as shear stress compressive

stress tensile stress and so on would make filler system dispersed optimally in polymer When

Fig2 Effect of the wedging angle on the

tensile elongation at break of composites

Fig1 Effect of the screw length-to-diameter ratio

on the tensile elongation at break of composites

Advanced Materials Research Vols 750-752 157

wedge angle was too high the radial force decreased with increasing the wedge angle The amount of

the material that flows through shear zone reduced and stagnated in the flow path The flowing state

was single and the effect of melting mixing of polymer decreased However if wedge angle was too

low the radial force would increase and the circumferential force decreased relatively As a result the

amount of material that flowed through the shear zone would increase and the material flowed almost

without changing the direction[10] At the same time the shear stress and shearing action of mixture

decreased and the effect of mixing was low Therefore in the case of a certain helix angle it is very

important to select an appropriate wedge angle to enhance the mechanical properties of products

Effects of injection molding of plastic-injection molding machine on the property of

composites Figure 3 demonstrates the relationship between the injection pressure of composites and

injection temperature of the injection molding machine It can be drawn that for the melted polymer in

this experiment when the temperature were 210 degC and 220 degC the injection pressure were 50 MPa

and 40MPa respectively Figure 3 also reveals that the injection pressure decreases obviously at first

and then decreases slightly with the injection temperature increases The reason is the injection

temperature has a great influence on the viscosity and fluidity of the melted polymer When the

injection temperature was low the viscosity and flow resistance of the melt were high Therefore

only a higher injection pressure can make the melt injection molding On the contrary the viscosity

and flow resistance of the melt were low when injection temperature was high The melt can flow

more easily and the specimen can be molded with just a lower injection pressure However the

polymer melt would yellowing or even black spot would appear in it if the injection temperature

increasing continuously at a very high injection temperature Meanwhile the mechanical

characteristics of specimen would decrease and the effect of the temperature on the injection pressure

was low The figure also explains that the required injection pressure increase when average

temperature of injection molding is low In this experiment the temperature of polymer melt was

selected between 200 degC and 220 degC

180 200 220 240 26030

40

50

60

p(M

Pa)

t(

C) Fig3 Effect of the injection temperature on the injection pressure of the composites

Conclusions

(1) The optimum screw length-to-diameter ratio of the used twin-screw extruder was about 30 With

this optimum ratio the flow passage of the screw part had the best pressurized ability and

transportability and the powder can be dispersed and mixed effectively This is mainly because the

shear stress increases with screw length-to-diameter ratio the powder could be sheared much

frequently in the higher-shear-stress zone

(2) For the used injection molding machine the optimum wedge angle of the helix angle was about

16plusmn5o In the case of the certain spin speed and pressure difference with increasing of the wedge

angle the shear stress and its width of the distribution increased and the dispersing effect of the

powder can also be improved

158 Advanced Engineering Materials III

(3) For the used injection molding machine the optimum injection pressures was 40 Mpa and

appreciate injection temperature ranged from 190degC to 220degC If the injection pressure and

temperature range were adjusted effectively the viscosity and fluidity of the plastic melt would be

improved obviously This is very useful for the plasticizing and injection of the melt and then the

processing fluidity of material would be improved effectively

Acknowledgements

For the financial support we are grateful to Daqing Huake Co Ltd China

References

[1] MOWRICHARDSON Polymer Engineering Composites[M] 1977

[2] Zhimin Zhang Kaida Zhang Naibin Yang Composite structural mechanics [M] BEIJING

Beihang University Press 1993 7-8In Chinese

[3] H R A J W Extrusion of Plastic Rubber and Metal [M] NEW YORK Reinhold Publishing

Corp 1952

[4] ZTamo Er IKlein Plastics Extrusion Engineering Principle [M] BEIJING Chemical Industry

Press 1984 In Chinese

[5] Li Li The Study of the formation mechanism of polymer blends [D] Beijing University of

Chemical Technology 2007 In Chinese

[6] GBT 1040- 2006 Plastics- Determination of tensile properties [S] In Chinese

[7] GBT 1843- 2008 Plastics- Determination of Izod Impact Strength [S] In Chinese

[8] GBT 9341- 2008 Plastics- Determination of Flexural Properties [S] In Chinese

[9] Riguang Jin Youqing Hua Polymer Physics [M] BEIJIN G Chemical Industry Press 1991 In

Chinese

[10] Jingwu Wang Plastic Modification Technology [M] BEIJING Chemical Industry Press 2004

801-803 In Chinese

Advanced Materials Research Vols 750-752 159

Advanced Engineering Materials III 104028wwwscientificnetAMR750-752 Effects of Processing on Mechanical Properties of Polypropylene Composites 104028wwwscientificnetAMR750-752156

wedge angle was too high the radial force decreased with increasing the wedge angle The amount of

the material that flows through shear zone reduced and stagnated in the flow path The flowing state

was single and the effect of melting mixing of polymer decreased However if wedge angle was too

low the radial force would increase and the circumferential force decreased relatively As a result the

amount of material that flowed through the shear zone would increase and the material flowed almost

without changing the direction[10] At the same time the shear stress and shearing action of mixture

decreased and the effect of mixing was low Therefore in the case of a certain helix angle it is very

important to select an appropriate wedge angle to enhance the mechanical properties of products

Effects of injection molding of plastic-injection molding machine on the property of

composites Figure 3 demonstrates the relationship between the injection pressure of composites and

injection temperature of the injection molding machine It can be drawn that for the melted polymer in

this experiment when the temperature were 210 degC and 220 degC the injection pressure were 50 MPa

and 40MPa respectively Figure 3 also reveals that the injection pressure decreases obviously at first

and then decreases slightly with the injection temperature increases The reason is the injection

temperature has a great influence on the viscosity and fluidity of the melted polymer When the

injection temperature was low the viscosity and flow resistance of the melt were high Therefore

only a higher injection pressure can make the melt injection molding On the contrary the viscosity

and flow resistance of the melt were low when injection temperature was high The melt can flow

more easily and the specimen can be molded with just a lower injection pressure However the

polymer melt would yellowing or even black spot would appear in it if the injection temperature

increasing continuously at a very high injection temperature Meanwhile the mechanical

characteristics of specimen would decrease and the effect of the temperature on the injection pressure

was low The figure also explains that the required injection pressure increase when average

temperature of injection molding is low In this experiment the temperature of polymer melt was

selected between 200 degC and 220 degC

180 200 220 240 26030

40

50

60

p(M

Pa)

t(

C) Fig3 Effect of the injection temperature on the injection pressure of the composites

Conclusions

(1) The optimum screw length-to-diameter ratio of the used twin-screw extruder was about 30 With

this optimum ratio the flow passage of the screw part had the best pressurized ability and

transportability and the powder can be dispersed and mixed effectively This is mainly because the

shear stress increases with screw length-to-diameter ratio the powder could be sheared much

frequently in the higher-shear-stress zone

(2) For the used injection molding machine the optimum wedge angle of the helix angle was about

16plusmn5o In the case of the certain spin speed and pressure difference with increasing of the wedge

angle the shear stress and its width of the distribution increased and the dispersing effect of the

powder can also be improved

158 Advanced Engineering Materials III

(3) For the used injection molding machine the optimum injection pressures was 40 Mpa and

appreciate injection temperature ranged from 190degC to 220degC If the injection pressure and

temperature range were adjusted effectively the viscosity and fluidity of the plastic melt would be

improved obviously This is very useful for the plasticizing and injection of the melt and then the

processing fluidity of material would be improved effectively

Acknowledgements

For the financial support we are grateful to Daqing Huake Co Ltd China

References

[1] MOWRICHARDSON Polymer Engineering Composites[M] 1977

[2] Zhimin Zhang Kaida Zhang Naibin Yang Composite structural mechanics [M] BEIJING

Beihang University Press 1993 7-8In Chinese

[3] H R A J W Extrusion of Plastic Rubber and Metal [M] NEW YORK Reinhold Publishing

Corp 1952

[4] ZTamo Er IKlein Plastics Extrusion Engineering Principle [M] BEIJING Chemical Industry

Press 1984 In Chinese

[5] Li Li The Study of the formation mechanism of polymer blends [D] Beijing University of

Chemical Technology 2007 In Chinese

[6] GBT 1040- 2006 Plastics- Determination of tensile properties [S] In Chinese

[7] GBT 1843- 2008 Plastics- Determination of Izod Impact Strength [S] In Chinese

[8] GBT 9341- 2008 Plastics- Determination of Flexural Properties [S] In Chinese

[9] Riguang Jin Youqing Hua Polymer Physics [M] BEIJIN G Chemical Industry Press 1991 In

Chinese

[10] Jingwu Wang Plastic Modification Technology [M] BEIJING Chemical Industry Press 2004

801-803 In Chinese

Advanced Materials Research Vols 750-752 159

Advanced Engineering Materials III 104028wwwscientificnetAMR750-752 Effects of Processing on Mechanical Properties of Polypropylene Composites 104028wwwscientificnetAMR750-752156

(3) For the used injection molding machine the optimum injection pressures was 40 Mpa and

appreciate injection temperature ranged from 190degC to 220degC If the injection pressure and

temperature range were adjusted effectively the viscosity and fluidity of the plastic melt would be

improved obviously This is very useful for the plasticizing and injection of the melt and then the

processing fluidity of material would be improved effectively

Acknowledgements

For the financial support we are grateful to Daqing Huake Co Ltd China

References

[1] MOWRICHARDSON Polymer Engineering Composites[M] 1977

[2] Zhimin Zhang Kaida Zhang Naibin Yang Composite structural mechanics [M] BEIJING

Beihang University Press 1993 7-8In Chinese

[3] H R A J W Extrusion of Plastic Rubber and Metal [M] NEW YORK Reinhold Publishing

Corp 1952

[4] ZTamo Er IKlein Plastics Extrusion Engineering Principle [M] BEIJING Chemical Industry

Press 1984 In Chinese

[5] Li Li The Study of the formation mechanism of polymer blends [D] Beijing University of

Chemical Technology 2007 In Chinese

[6] GBT 1040- 2006 Plastics- Determination of tensile properties [S] In Chinese

[7] GBT 1843- 2008 Plastics- Determination of Izod Impact Strength [S] In Chinese

[8] GBT 9341- 2008 Plastics- Determination of Flexural Properties [S] In Chinese

[9] Riguang Jin Youqing Hua Polymer Physics [M] BEIJIN G Chemical Industry Press 1991 In

Chinese

[10] Jingwu Wang Plastic Modification Technology [M] BEIJING Chemical Industry Press 2004

801-803 In Chinese

Advanced Materials Research Vols 750-752 159

Advanced Engineering Materials III 104028wwwscientificnetAMR750-752 Effects of Processing on Mechanical Properties of Polypropylene Composites 104028wwwscientificnetAMR750-752156

Advanced Engineering Materials III 104028wwwscientificnetAMR750-752 Effects of Processing on Mechanical Properties of Polypropylene Composites 104028wwwscientificnetAMR750-752156