Indian Journal of Chemical Technology Vol. 1 0, January 2003, pp. 27-37

Articles

Steady state rheology of PP !PET blends

T Kitano', Ajay Naikb, S A R Hashmib, S R Vashishthab & Navin Chandb* "National Institute of Materials & Chemical Research (AlST), Higashi, Tsukuba, Ibaraki, 305-8565 Japan

bRegional Research Laboratory (CSIR), Habibganj Naka, Hoshangabad Road, Bhopal 462 026, India

Received 5 July 2001 ; revised received 18 March 2002; accepted 10 April 2002

The objective of this study is to report the results of steady state viscoelastic properties in molten state investigated experimentally for PPIPET blends. They were prepared by the elastic extrusion method. The present paper discusses the influence of different types of PP, blending composition and effect of compatibilizer on steady state viscoelastic properties of PPIPET in molten state.

Polymer blends are generally made by extrusion or by two roll mixing method. Apart from these two methods, the blends are also developed by melt blending on an elastic extruder. It is also important to analyze the flow/deformation behaviour of blend systems under a particular extrusion process, and to investigate the flow mechanisms and change of internal structure of these systems 1 .2.

PET (Polyethylene terephthalate) IS a semi crystalline polymer and is used for various applications but it is senSItIve to notch and stress concentration, which restricts its wide applications. The shrinkage of PET makes its moulding very difficult. On the other hand, PP (Polypropylene) can be easily processed on all types of processing machines. The mechanical properties of the PET filled thermoplastic composites have been investigated by many researchers3.4. However, rheological properties of these materials have not been paid sufficient attention. Rheological studies have been reported mainly on the redmud filled and short organic fibre filled systems5- 1 I . Lindsay et. al.3 and Traugott et al.4 investigated the use of compatibilizer for blends of PE and PET. They concluded that adding up to 20% by weight SEBS (Styrene-ethylene-butadiene-styrene) copolymer to a 50/50 (PE/PET) blend in an extruder at 300°C caused some reduction in modulus and yield strength but a dramatic increase in ductility was reported, which increased from 3% elongation to more than 200%. The impact strength was also improved. In this study a new PP/PET blend is prepared by combining

*For correspondence (E-mail: navinchand@rrlbpl.org; Fax: 009 1 -755-587042, 488985)

different types of PP's with PET with and without compatibilizer. Rheological data such as shear rate, shear stress, viscosity and first normal stress difference for these new type of blends have been measured and analysed.

Experimental Procedure Materials

The materials used in this study were several blend systems consIstmg of different types of polyproplylene and a polyethylene terephthalate (PET) melts. Polypropylene (Chisso Polypro Co Ltd, Japan) was used as a matrix material . Table 1 lists the properties of polymer and coupling agents and names of their suppliers used in this study.

Blends preparation PET concentrations used in this study were 5, 1 0,

20, 30 and 50-wt% in the blend. Weighed amounts of PET were fed into the elastic extruder simultaneously with PP. The blend prepared by this apparatus was used as a base material for compression moulding.

Material was kept in a steel mould, pressed in a hot press for 3 minutes under 5 Mpa pressure at 260°C temperature. Then this material along with mould was transferred to water circulating cold press to cool the materials to room temperature under same pressure. Test specimens for steady state rheological properties measurements were cut from the sheets obtained from above press.

Measurements A cone and plate rheometer (RM - 1 4 1 , Nihon

Rheology Kiki Co Ltd, Japan) was used for the measurement of steady state viscoelastic properties of

Articles Indian 1. Chern. Techno! . , January 2003

Table I-Source and specialty of materials used for making PPIPET blends

Sample Name State Source

PP (A 5012) Unmodified, high viscosity Chisso Polypro Co Ltd, Japan

PP (K 7050) Unmodified, low viscosity Chisso Polypro Ltd, Japan

PP (XKP 707W) Modified

PET (MA 2 10 1 ) Virgin

MAH (compatib(lizer) Modified

the samples. The specimens used were made from tQe compression-moulded sheets cut into discs of 27-28 mm diameter. The gap between cone and plate was fixed at 3 mm. Under such gap condition, a test specimen was slightly compressed under molten state. The shear rate varied from 1 0-2 to 10 S-I and the cone angle of 4° was kept constant. The measurements were carried out for all the samples at 265°C. Cone radius was 2 1 .5 mm.

From the Torque T, normal shear stress crl2 was calculated by using the equation:

. . . ( 1 )

and the viscosity was calculated by using the following equation:

.. . (2)

The first normal stress difference (N I) was calculated by the following relation:

. . . (3) where, cr12, T, R, y , NI and F were normal shear stress, torque, radius of cone, shear rate, first normal stress difference and force respectively.

Results and Discussion

Flow curves, shear stress (-r) versus shear rate (y) for PP (A 501 2)/PET and their blend at various blending ratio are shown in Fig. 1 . The flow curve of PP shows maximum shear stress while PET shows minimum. Flow curves of the blend samples lie in between PP and PET. Blend samples containing low concentration of PET are in the vicinity of PP. Separation between the flow curves for the blend samples increases at higher shear rates.

These variations up to shere rate I s- I are consistent with the following power law:

28

Chisso Polypro Co Ltd, Japan

Untika Co Ltd, Japan

Commercial

-r = Ky n

where, K and n are related to the intercept and slope of the flow curves. Values of the pseudoplasticity index (n) are shown in Table 2 and are 0.85 for PP and 0.9 for PET. Addition of PET initially does not affect the value of n up to 5 wt% PET and then decreases with an increase of PET content up to a value of 0.62 at 50 wt% PET content. The significantly different pseudoplasticity index for blends having different blend composition shows a significant role of PET in the pseudoplasticity of the blend.

Melt viscosity (11) as a function of shear rate is plotted in Fig. 1 on the log-log scale for PP, PET and PP/PET blend. The polymers and blends show insignificant variation in melt viscosity with shear rate at low shear rates and a sharp decrease of melt viscosity with increasing shear rate above 103 S- I .

Figure 2 shows the plot of melt viscosity as a function of blend composition. On initial addition of less viscous component from 5-20 wt% PET to the PP, melt viscosity remains constant. Thereafter, it decreases rapidly on adding 20 to 50 wt% PET.

Figure 3 shows plots of shear stress versus shear rate on double logarithmic scale for low viscosity PP (K 7050), PET and their blends at temperature 265°C. These curves are linear over the entire range of data. These linear curves are consistent with the power low. The values of n indicate that all these polymers and blends are pseudoplastic in nature. Variation of blend composition changes the slope of the flow curve effectively in Table 2 and Fig. 3. This may be due to the fact that viscosity of PP used in this case is different as compared to PP (A 50 12).

Figure 3 also compares the shear viscosities of PP, PET and mechanically blended PP/PET blends at 265°C on double logarithmic scale. The polymer blends have lower viscosities than PP and higher than PET polymer at all studied shear rates. This is similar to the previous blend systems.

Kitano et at. : Steady state rheology of PPIPET blends Articles

Table 2- Compositions of the blends and their n values

Sample PP PP PP PET MAH Density 11 value Name (A 50 1 2) (K 7050) (XKP 707W) (% of PP) (glee)

A 1 00 0.906 0.85

B 1 00 1 .34 1 0.90

C 95 05 0.932 0.85

D 90 1 0 0.938 0.83

E 80 20 0.972 0.80

F 70 30 1 .0 to 0.72

G 50 50 1 .099 0.62

H 95 05 0.92 1 0.85

90 1 0 0.926 0.85

J 80 20 0.967 0.82

K 70 30 1 .009 0.85

L 50 50 1 .008 0.78

M 1 00 0.901 0.93

N 90 1 0 0.932 0.93

0 80 20 0.967 0.86

P 70 30 1 .003 0.85

Q 50 50 1 .058 0.83

R 90 1 0 0.979 0.80

S 80 20 0.933 0.89

T 70 30 1 .007 0.80

U 50 50 1 .065 0.70

V 1 00 0.908 0.97

W 95 05 0.927 0.94

X 90 1 0 0.944 0.92

Y 80 20 0.98 1 0.89

Z 70 30 1 .0 1 7 0.87

AA 50 50 1 .080 0.85

1 0000

'" rei 0.. E � 1 000 '" 8 '" :>

1 00 � 1 00/00

� 00/100 co

�+ 0.. E � 95/5

VJ /+' VJ -liC- 90/10 � 1 0 /+' Ui iii +' ____ 80/20 III � (f) ....... 70/30

-+- 50/50

0.01 0.1 10 100

Shear Rate (y). 5"

Fig. I -Shear stress and melt viscosity versus shear rates plots for PP (A 50 I 2)IPET blend at 265°C

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Articles Indian J. Chern. Techno! . , January 2003

30

1 0000 �--------------------------------------------------------------------------------�

CJl <ti 0.. :E: � '(ij 8 II> :>

1 000

1 00

1 0

1 00100

y (5.1) -B- 1 .5

-+- 3 -tr- S. 1 5

-e-- 9. 1 5

...... 1 2 . 1 5

-::

9011 0 ---l

80/20 70/30

Blend C,:>mposition of PP{A 501 :�)/PET blend

-f----------i 50/50 00/100

Fig. 2-Varialion of melt viscosity with blend composition at 265°C for PP (A 501 2)IPET binary blend at various shear rates

1 0000 �----------------------------------------------------------. ----------------------�

CJl <ti 0.. �-: � '(ij 0 u CJl :>

1 000

1 00

1 0

y (S'l) -B- 1 .5

-+- 3 -tr- S. 1 5

-e-- 9. 1 5

l ...... 1 2. 1 5

1 - � 9515 1 00/00

�--------i 90/10 80/20 70/30 50/50 00/100

Blend Composition of PP{A 501 :�)/PET blend

Fig. 3-Shear stress and melt viscosity versus shear rates plots for PP (K 7050)IPET blend at 265°C

Kitano et at.: Steady state rheology of PPIPET blends Articles

10000

-B- 1 00/00 -e-00/100 -+- 90/10 en ni

1000 -.!r-80/20 a.

E ""* 70/30

� --... 50/50 'iii 8 en :>

1 00 <II a. -!::. en en � U5 n; 10 Q) .s::: CJ)

0.1 10 100

Shear Rate (y), S·1

Fig. 4-Shear stress as a function of shear rate for PP (XKP 707W)IPET binary blend at 265°C

On comparing Figs 1 and 3, it was observed that values of shear stress and viscosity of various PPIPET blends and PP are at higher side in Fig. 1 , which is due to the presence of higher viscosity component PP (A SOI 2) in the blend. The slope of the shear stress versus rate curves, however, shows a different behaviour. The low viscosity polypropylene based PP/PET blend show higher sensitivity to the shear rate as compared to higher viscosity PP based blends. Low viscosity PP behaves nearly similar to Newtonian fluid and higher viscosity PP based blends show non­Newtonian behaviour.

Flow curves in terms of shear stress and shear rate are presented in Fig. 4 for modified PP (XKP 707 W)/PET binary blend at various blending ratio. Data on modified PP and PET polymers are also included in this figure to illustrate the behaviour of the blend as well as its two component systems. Flow curves for binary blend at various compositions are quite in the vicinity of curves of matrix PP.

Viscosity data of the modified PP (XKP 707W)/PET binary blend are presented in Fig. S as the variation of melt viscosity with shear rate and blend composition. At any given shear rate melt viscosity is highest at 0 wt% PET content (i.e. unblended PP), and decreases with increase of PET content.

PP (A SOI2) was modified by using a compatibilizer, maleic anhydride ( 1 .0 wt% of PP) and was then blended with PET. The compatibilizer used here was fed directly with the polymers in the elastic extruder at 26SoC and 40 rpm. The shear stress-shear rate and melt viscosity-shear rate behaviour of modified and unmodified PP (A SOI2)IPET blends are compared in Figs S, 6, and '7 respectively. Shear stress and viscosity of the compatibilized PPIPET blends increased in comparison with uncompatibilized PPIPET blends with increasing shear rate up to l Os' 1 for all the studied systems. In case of (SOISO)/PP/PET blend, opposite was observed which seems due to the higher concentration of molten PET having nearly one-hundredth part of viscosity of PP (A 5012). Such difference in viscosity makes the system heterogeneous and dominance of viscosity of PET is observed instead of PP. The compatibilizer maleic anhydride is nearly ineffective in such circumstances. Similar plots of PP (K 70S0)/PET systems are shown in Figs 8 and 9.

The first normal stress difference for PP (A SOI2)/PET binary blend system as a functions of shear rate is presented ' in Fig. 10. This figure also compares the effect of compatibilizer on the system. The first normal stress difference N/ increased with increasing shear rates for all the studied system. it

3 1

Articles Indian 1. Chern. Techno!., January 2003

32

II> ro Q. 1 � 'iii 8 II> :>

'" Q. � '" Ul � U5 n; III � en

1 000�------------------------------------------------------------

1 00

1 0

0. 1

• • • • ---- . .. -.-.

1 0

Shear Rate (y), 5.1

PP/PET � 1 00100

___ 00/1 00

........ 95/5

-'- 90/1 0

--)IE- 80120

-0- 70/30

--Er 50/50

Fig. 5-Melt viscosity as a function of shear rate for PP (XKP 707W)/PET binary blend at 265°C

1 00

1 0000,-------------------------------------------------------------�

1 000

1 00

1 0

--&- 95/5

........ 95/5/1

-6- 90/1 0 � 80/20 ..... 70/30 � 50/50

-+- 90/1 011 -iJ- 80/20/1 - 70/30/1 -+- 50150/1

1 +---------------�----------------�--------------�--------------� 0.01 0 . 1 1 0 1 00

Shear Rate (y), 5"

Fig. 6-Shear stress as a function of shear rate for PP (A 50 1 2)/PETIMAH ternary system at 265°C

Kitano et at. : Steady state rheology of PPIPET blends Articles

Vl <Ii Q. E Z-'iii 8 Vl :>

1 0000�--------------------------------------------------------------.

1 000

1 00

1 0

0.01

G 0

-+- 9515

--'- 9515/1

0.1

• �

.....- 9011 0 � 80/20 -+- 70/30 -e- 50/50

-:.t(- 9011 0/1 � 8012011 - 70/3011 ___ 50150/1

1 0

Shear Rate (r). 5.1

Fig. 7-Melt viscosity as a function of shear rate for PP (A 50 1 2)IPETIMAH ternary system at 265°C

1 00

1 0000�-------------------------------------------------------------.

1 000

Cll Q. � Vl Vl

1 00 � (J) lii Q) � (J)

1 0

0 . 1 1

-A- 80120 ........ 90/1 0

-0- 90110/1 -tr- 80120/1

1 0

Shear Rate (y). 5.1

....... 70/30

-e- 7013011

-+- 50/50

-+- 50/50/1

Fig. 8-Shear stress as a function of shear rate for PP (K 7050)IPETIMAH ternary system at 265°C

1 00

33

Articles Indian J. Chem. Techno\.. January 2003

Ul iii Q.

E � ·iii 8 Ul 5

34

1 000.---------------------------------------------------------------�

1 00

1 0

____ 90/ 1 0

--a- 9011 011

-"' 80/20

-6- 80/20/1

-"' 70/30 -'- 50/50

-+- 70/30/1 -l:r- 50/50/1

1 +--------------------.--------------------�------------------_4 0.1 1 0 1 00

Shear Rate (y). 5.1

Fig. 9-Melt viscosity as a function of shear rate for PP (K 7050)/PET/MAH ternary system at 265°C

1 0

PP(A-5012)IPETIMAH -0- 1 00100 -Ir- 95/5 --+- 90/1 0 -- 80/20 -+- 70/30 - 95/5/1

fl - 90/1 0/1 -+- 80/20/1 c e � --+- 7013011 i5 '" '" g (J) 0.1

ti E 0 z 111 u:

0.01

0.001 +---------r---------r-------�-------___f 0.01 0.1 1 0 1 00

Shear Rate (y). 5.1

Fig. 1 00Fi rst normal stress difference-shear rate plots for PP (A 50 l2 )/PETIMAH blend system at 265°C

Kitano et af.: Steady state rheology of PPIPET blends Articles

G) 0 0.1 c PP(K-7050)/PET IMAH e � i5 -+- 90/1 0 fit fit e -&- 80/20 US Iii � 70/30 E 0 � 50/50 z � 0.01 -+- 90/1 0/1 u:

_ 80/20/1 -6- 70/30/1 -+- 50/50/1

0.001 10 100

Shear Rate (y), S-l

Fig. I I-First normal stress difference-shear rate plots for PP (K 7050)IPETIMAH blend system at 265°C

G) u 0.1 <: !! � ;S :g PP(XKP 707W)IPET/MAH

� -e- 1 00100 iii E � 95/5 0 z il 0.01 -6- 9011 0 u::

-&- 80/20 __ 70/30 - 50/50

0.001

1 1 0 1 00

Shear Rate (y), S-l

Fig. 1 2-First normal stress difference-shear rate plots for PP (XKP 707W)IPET blend system at 265°C

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Articles Indian J. Chern. Technol., January 2003

1 0.--------------------------------------------------------------,

� c l!! & 0 '" '" l!! ii) � E 0 z �

i.L 0.1

y (5" ) --a- 1 .5

-+- 3

-.!r- 6. 1 5

-&- 9. 1 5

--lIE- 12. 1 5

0.01 +-------------t-------------+------------+------------t-------------i 1 00/00 95/5 90/1 0 80120 70/30 50150

Blend Composition of PP(A 5012)JPET blend

Fig. 1 3-Variation of first normal stress difference with blend composition at 265°C for PP (A 50 I 2)/PET binary blend at various shear rates

decreased with increasing PET content in PP. In general, compatibil izer increased the N, for all the systems. Simi lar plots for PP (K 70S0)/PET and PP (XKP 707W)/PET systems are shown in Figs S, 1 1 and 1 2 .

Figure 1 3 shows the effect of blending ratio of N, for blends of PP (A SO I 2) and PET at 26SoC with shear rate as parameter. I t is seen that PP/PETISOISO blend shows a minimum value in N,. Value of NJ for pure PP is higher as compared to blend of PP/PET which reduces at PP/PETI (9SIOS) . The value of NJ remains almost constant up to 20% of PET in PP. Thereafter, i t reduces sharply with the increased content of PET in PP, which shows the increased effect of PET in the systems.

Conclusion I ) High viscosity and low viscosity polypropylene

were blended separately with polyester (polyethylene terephthalate) and their flow behaviour at 26SoC were determined. The low viscosity PP based PP/PET blend shows higher sensitivi ty to shear rate as compared to high viscosity PP based blend.

2) Addition of compatabil izer to the blends increase shear v iscosity.

3) First normal stress difference decreases with the increase of PET content and it increases with shear rate.

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Nomenclature

PP (A 5012) - Polypropylene (Unmodified and high viscosity)

PP (K 7050) - Polypropylene (Unmodified and low viscosity)

PP (XKP, 707W) - Polypropylene (Modified)

PET (MA 2 1 0 1 ) - Polyethylene terephthalate (Virgin)

MAH - Maleic anhydrite (Compatibilizer)

cr 1 2 - Normal shear stress (Pa)

or - Shear stress (Pa)

T - Torque (N)

R - Radius of cone (mm)

y - Shear rate (S· I )

11

- First normal stress difference (Pu)

Force (N)

- Viscosity (Pu.s)

- Pseudoplasticity index

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