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Evaluation of rheological and mechanical behavior of blends based on polypropylene and metallocene elastomers
Polymer Testing 21 (2002) 647–652 www.elsevier.com/locate/polytest
Material Behaviour
Evaluation of rheological and mechanical behavior of blends based on polypropylene and metallocene elastomers Ana Lu´cia N. Da Silva a, Marisa C.G. Rocha a, Fernanda M.B. Coutinho Rosa´rio E.S. Bretas d, Marcelo Farah d a b
b, c,*
,
Instituto Polite´cnico, Campus Regional da UERJ, Nova Friburgo, Rio de Janeiro, RJ, Brazil Instituto de Macromole´culas Professora Eloisa Mano-IMA/UFRJ, Rio de Janeiro, RJ, Brazil c Departamento de Processos Industriais, IQ/UERJ, Rio de Janeiro, RJ, Brazil d Departamento de Engenharia de Materiais, UFSCar, Saˆo Carlos, SP, Brazil Received 15 October 2001; accepted 19 November 2001
Abstract Rheological and mechanical studies were performed on polymer blends of different grades of ethylene–octene copolymers (EOCs) and polypropylene (PP). The oscillatory flow properties of EOC, PP and EOCs/PP blends were analyzed using a Rheometrics Dynamic Stress Rheometer, SR 200. The results showed that the systems with elastomers of different grades presented diversified rheological and mechanical behavior. This behavior is probably related to the differences in molecular weight and the long chain branch content present in the copolymers. 2002 Elsevier Science Ltd. All rights reserved. Keywords: Polypropylene blends; Metallocene elastomers; Rheological behaviour; Mechanical properties
1. Introduction In the last decade a lot of interest has focused on the polymerization of a wide variety of olefin monomers by metallocene catalysts. Polymers and copolymers of ethylene, propylene, styrene, higher α-olefins and cyclic olefins have been the main focus of recent studies. Many companies are challenging for commercialization of these new metallocene polymers. Most progress has been achieved in the field of ethylene/α-olefin and ethylene/cyclo olefin copolymers. Those emerging catalyst systems, obtained by the single site constrained geometry technology has allowed for the production of polyolefins with novel molecular architecture. This new technology has produced a variety of polyolefins, including polyolefin elastomers (ethylene/1-octene copoly-
* Corresponding author. Tel.: +55-21-562-7210; fax: +5521-270-1317. E-mail address: [email protected] (F.M.B. Coutinho).
mers—EOCs). These polymers, containing more than 20 wt.% octene, have distinctive properties when compared with elastomeric materials currently available. Due to the long chain branching, EOCs are aimed at competing with thermoplastic olefin impact modifiers, such as EPDM, in the automotive industry [1–9]. Thus, the aim of this work was to evaluate the effect of addition of different grades of metallocene elastomers on the mechanical and rheological properties of PP.
2. Experimental 2.1. Material and blend preparation Commercially available grades of polymers: polypropylene (PP) and ethylene/octene copolymers (EOCs) were used, their specifications are listed in Table 1. DRI is defined as the deviation extent that the rheology of Dow’s Insite Technology Polyolefins (ITP) present relative to the rheology of the conventional linear
0142-9418/02/$ - see front matter 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 1 4 2 - 9 4 1 8 ( 0 1 ) 0 0 1 3 7 - 4
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A.L.N. Da Silva et al. / Polymer Testing 21 (2002) 647–652
Table 1 Characteristics of the polymer samples Material
PP
Manufacturer % 1-octenea DRIa Density at 23 °C (g/cm3)b Mw/Mnb Mnb Melt indexc (g/10 min)
Polibrasil Resinas (Brazil) Dow Chemical (USA) – 24 – 2.0 0.917 0.884 9.2 2.1 46,500 156,000 4.3±0.2 2.5±0.4
a b c
EOC-8100
EOC-8150
EOC-8200
Dow Chemical (USA) Dow Chemical (USA) 25 24 2.0 0.5 0.864 0.871 2.1 2.1 170,000 94,000 1.0±0.2 7.0±0.3
Values supplied by Dow Chemical. measured in IMA laboratory by ASTM D792. measured in IPRJ laboratory by ASTM D1238.
homogeneous polyolefins that are reported to have no long chain branching by the following normalized equation [10]: DRI⫽(3.65E6⫻t0/h0⫺1)/10
(1)
where t0 is the characteristic relaxation time and h0 is the zero shear viscosity of the material. The parameters t0 and h0 are determined by a non-linear regression of the experimental data numerically fitted to the generalized Cross equation. For commercial homogeneous polyolefins that have no long chain branching, the h0 vs t0 relationship can be described by the equation: h0⫽3.65E6⫻t0
2.3. Mechanical behavior The tensile tests were conducted at room temperature (25 °C and 55% relative humidity) using samples obtained by compression molding on an Instron Tester (model 4204), according to ASTM D882, at a strain rate of 50 cm/min. Impact strength was measured according to ASTM D256 (V-notched) on an Impact Tester Microtest at room temperature.
3. Results and discussion
(2)
A HAAKE twin screw extruder was used for melt blending the EOCs/PP systems, containing different weight percents of EOC: 0, 5%, 20, 50, 80 and 100%. The screw speed was set at 60 rpm and the temperature profile in the extruder from the feed to the metering zone was set at: 190, 210, 220 and 220 °C. For all compositions prepared, 5 wt.% of calcium carbonate was added. 2.2. Rheological behavior The viscosities of the polymers were measured at low shear rates (w=0.1–100 rad/s) on a cone-plate type rheometer (Rheometrics Dynamic Stress rheometer— SR200) at 220 °C. The oscillatory flow properties, namely the complex viscosiy h* (defined as h∗=h⬘⫺ ih⬙, where h⬘ is the dynamic viscosity or the real part of the viscosity and ih⬙ is the imaginary part of the viscosity), the storage modulus, G⬘ (defined as G⬘=wh⬙, where w is the frequency of the oscillations in rad/s) and the loss modulus, G⬙ (defined as G⬙ = ωη⬘) were measured.
3.1. Rheometrics dynamic stress rheometer results Fig. 1 shows the dependence of the logarithm of the value of the complex viscosity (h*) on the logarithm of investigated frequencies for EOCs, PP and EOCs/PP blends. An expanded scale of the elastic behavior of the systems at lower frequencies is also included. Fig. 1(a) shows that EOC-8150 copolymer tended to show high shear thinning and the EOC-8200 (lower viscosity) tended to present the largest range of Newtonian behavior. Fig. 1 also shows, for the whole range of explored frequency, that EOCs/PP blends exhibited a decrease in viscosity value with increasing frequency, i.e., EOCs/PP blends are pseudoplastic melts. EOC8100/PP system presented a different rheological behavior in relation to the other systems. It was observed that EOC-8100 presented a lower viscosity at lower frequencies and as EOC-8100 content increased, the viscosity of the blends decreased. This behavior may be related to the fact that the addition of 5 (wt.%) of EOC tended to increase the average end-to-end distance between PP coils, and as a consequence interactions between PP molecules may be occurring. As EOC-8100 content increases, the distance between PP coils tended
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649
Fig. 1. Log (h*) vs log (w). (a) EOCs and blends (b) EOC-8100/PP, (c) EOC-8150/PP, (d) EOC-8200/PP
to increase, reducing the occurrence of interactions between PP molecules and thus the viscosity of the blends decreased. At higher frequencies, EOC-8100/PP blend viscosities were between the pure component viscosities, and those values increased as the proportion of EOC-8100 increased. This result may be attributed to the fact that at higher frequencies the effect of the presence of EOC-8100 long chain branches is more significant, and entanglements between branching and the chain segments of EOC-8100 and PP may occur, resulting in an increase in the viscosity values as EOC-8100 content increases. This behavior was not observed in EOC8150/PP and EOC-8200/PP systems. For EOC-8150/PP blend, in the whole range of explored frequencies, the rheological behavior remained constant, i.e., as EOC8150 content increased, the system viscosities increased. EOC-8150/PP blends presented viscosity values close to EOC-8100/PP blend viscosities at the investigated frequencies. The rheological behavior of EOC-8200/PP blends was different. Up to 100 rad/s frequency, the systems presented an increase in the viscosity as EOC-8200 copolymer content decreased. At higher frequencies, the samples with low EOC-8200 content tended to show high shear thinning and thus the viscosity values became close to the samples with high EOC-8200 content. This behavior may be related to the smaller DRI value (DRI=0.5) in relation to the other grades of elastomers. In other words, the low long chain branch content presents low probability to form entanglements that
reduced the formation of entanglements between PP and elastomer chains, decreasing the material viscosity. The dynamic storage modulus, G⬘, is related to the elastic behavior of the material and may be considered as the storage energy. The dynamic loss modulus, G⬙, represents the dissipated energy. The dependence of G⬘ and G⬙ on the frequency measures the relative motion of all molecules in the bulk and can give important information about the flow behavior of melts [11]. Fig. 2 shows the variation of the elastic modulus (G⬘) with the investigated frequencies of EOCs and EOCs/PP blends. An expanded scale of the elastic behavior of the pure polymers and blends at lower frequencies is also included. Assuming that G⬘ is related to the storage energy, Fig. 2(a) shows that EOC-8150 copolymer (higher molecular weight) presented the highest elasticity, over the frequency range analyzed. Fig. 2 also shows that EOC-8150/PP blend presented higher G⬘ values; however, at high frequencies the system behavior became similar to the behavior of EOC8100/PP blend. The EOC-8200/PP blends presented lower G⬘ values in relation to the other systems. This result is also related to the less pronounced effect of EOC-8200 elastomer long chain branches. EOC-8100/PP blends showed a different behavior at low and high frequencies. As can be observed, the samples with lower EOC-8100 content showed higher elasticity at low frequencies. That behavior may also be
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Fig. 2.
Elastic modulus, G⬘, vs frequency. (a) EOCs and blends (b) EOC-8100/PP, (c) EOC-8150/PP, (d) EOC-8200/PP.
attributed to the formation of PP entanglements. It can also be seen that EOC-8100 presents lower G⬘ values, indicating that the material has lower elasticity at low frequencies. This behavior is probably a result of a conformation change of the molecule due to the occurrence of main-chain entanglements (‘coils’). At higher frequencies, G⬘ values of the blends are between those of the pure polymers. The elasticity of the blends increases as EOC-8100 content increases as a result of the presence of the entanglements between branching and chain segments of EOC-8100 and PP. At high frequencies, EOC-8100 presents higher G⬘ values, indicating that the long chain branches present in EOC-8100 molecules tend to produce entanglements and thus a higher elasticity can be observed. The dependence of the loss modulus, G⬙, on the investigated frequencies of EOC copolymers is shown in Fig. 2. Elastomer EOC-8150 present the highest G⬙ values, over the extensive frequency range analyzed; however, at high frequencies, the G⬙ values of EOC-8150 were similar to those of EOC-8100 copolymer. The elastomer EOC-8200 presented the lower G⬙ values, indicating that this material should be producing blends with lower dissipation of energy.
3.2. Mechanical analysis results The effect of the elastomer grade and blend composition on the tensile properties of EOCs/PP systems is shown in Tables 2–4. It can be seen for all systems analyzed that, as EOC content increased, the Young’s modulus decreased as a result of the lowering on the crystallinity of the blends as EOCs were added. The stress at break also decreased as the EOC content increased. It has been reported in the literature [7] that behavior is related to the immiscibility of the components and conseTable 2 Tensile properties of EOC-8100/PP blends Material (wt% of EOC-8100)
Stress at Young’s Toughness break (MPa) modulus (MPa) (MPa)
0 5 20 50 80 100
32±3 55±3 49±5 37±2 12±1 11±1
259±17 111±18 128±20 91±7 20±2 6±1
33±1 149±47 134±43 103±10 44±5 40±6
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651
Table 3 Tensile properties of EOC-8150/PP blends
Table 7 Impact properties of EOC-8200/PPblends
Material (wt% of EOC-8150)
Stress at Young’s Toughness break (MPa) modulus (MPa) (MPa)
Material (wt% of EOC-8150) Impact strength (J/m)
0 5 20 50 80 100
32±3 69±3 48±5 32±5 21±1 10±1
259±17 150±40 120±8 87±4 43±6 6±1
33±1 134±40 118±24 61±10 30±6 18±3
Table 4 Tensile properties of EOC-8200/PP blends Material (wt.% of EOC-8200)
Stress at Young’s Toughness break (MPa) modulus (MPa) (MPa)
0 5 20 50 80 100
32±3 59±6 42±4 32±3 19±1 10±1
259±17 121±23 129±9 20±5 20±2 7±1
33±1 142±35 92±3 42±4 12±5 47±5
Table 5 Impact properties of EOC-8100/PPblends Material (wt% of EOC-8100) Impact strength (J/m) 0 5 20 50
40±2 49±1 81±9 606±28
0 5 20 50
40±2 42±3 68±3 528±40
EOCs/PP blends at room temperature. The results show that EOC-8100/PP and EOC-8150/PP blends have similar impact properties. EOC-8200/PP blends tend to present the lowest impact strength. That behavior should be related to the fact that EOC-8200 elastomer is the copolymer with the lower DRI value in relation to the other elastomers. This means that this material presents a lower deviation in relation to the rheology of the conventional linear homogeneous polyolefins. In other words, for EOC-8200 the elastomeric feature is less pronounced relative to the EOC-8100 and EOC-8150 copolymers.
4. Conclusions Different rheological behavior was observed when different grades of ethylene/octene copolymers were added to PP. The mechanical analysis showed that the systems tend to present similar stiffness. EOC-8200/PP blends tend to present the lowest toughness and impact strength. This behavior is probably related to the long chain branch content present in the elastomers.
Acknowledgements Table 6 Impact properties of EOC-8150/PPblends Material (wt% of EOC-8150) Impact strength (J/m) 0 5 20 50
40±2 44±5 75±6 602±55
quent formation of a bi-phase structure. It is known that the fracture process on the inter-phase is accelerated by the immiscibility of the components. In a general way, the EOC-8100/PP, EOC-8150/PP and EOC-8200/PP systems, produced materials with similar stiffness, whereas EOC-8200/PP samples presented the lowest toughness values in relation to the other systems. Tables 5–7 present the impact strength of the
Financial support from FAPERJ, CNPq, PRONEX, PADCT/FINEP is gratefully acknowledged. We are also grateful to Polibrasil Resinas, Branco Dow, DuPont Dow Elastomers and Quimbarra (Imerys).
References [1] A. Yano, A. Akimoto, in: G. Bendikt, B.L. Goodall (Eds.), Metallocene-catalysed Polymers—Materials, Properties, Processing and Markets, Plastic Design Library, New York, 1998, p. 98. [2] D.R. Parikh, M.S. Edmonson, B.W. Smith, J.M. Winter, M.J. Castille, J.M. Magee et al., in: G. Bendikt, B.L. Goodall (Eds.), Metallocene-catalysed Polymers— Materials, Properties, Processing and Markets, Plastic Design Library, New York, 1998, p. 113. [3] S.H. Chang, J.I. Dong, K. Sung, Journal of Applied Polymer Science 32 (1986) 6282.
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[4] B. Puka´ nszky, F. Tu¨ do¨ s, A. Kallo´ , G. Bodor, Polymer 30 (1989) 1399. [5] L.A. Utracki, Polymer Alloys and Blends: Thermodynamics and Rheology, Hanser Publishers, New York, 1989. [6] A.K. Gupta, B.K. Ratnam, K.R. Srinivasan, Journal of Applied Polymer Science 45 (1992) 1303. [7] A. Wal, J.J. Mulder, J. Oderkerk, R.J. Gaymans, Polymer 26 (1998) 6781.
[8] P.R. Hornsby, K. Premphet, Journal of Applied Polymer Science 70 (1998) 587. [9] K. Premphet, P. Horanont, Polymer 41 (2000) 9283. [10] S. Lai, T.A. Plumley, T.I. Butter, G.W. Knight, Antec’94 (1994) 1814. [11] A.L.N. Silva, M.C.G. Rocha, F.M.B. Coutinho, R.E.S. Bretas, C. Scuracchio, Journal of Applied Polymer Science 75 (2000) 692.
Material Behaviour
Evaluation of rheological and mechanical behavior of blends based on polypropylene and metallocene elastomers Ana Lu´cia N. Da Silva a, Marisa C.G. Rocha a, Fernanda M.B. Coutinho Rosa´rio E.S. Bretas d, Marcelo Farah d a b
b, c,*
,
Instituto Polite´cnico, Campus Regional da UERJ, Nova Friburgo, Rio de Janeiro, RJ, Brazil Instituto de Macromole´culas Professora Eloisa Mano-IMA/UFRJ, Rio de Janeiro, RJ, Brazil c Departamento de Processos Industriais, IQ/UERJ, Rio de Janeiro, RJ, Brazil d Departamento de Engenharia de Materiais, UFSCar, Saˆo Carlos, SP, Brazil Received 15 October 2001; accepted 19 November 2001
Abstract Rheological and mechanical studies were performed on polymer blends of different grades of ethylene–octene copolymers (EOCs) and polypropylene (PP). The oscillatory flow properties of EOC, PP and EOCs/PP blends were analyzed using a Rheometrics Dynamic Stress Rheometer, SR 200. The results showed that the systems with elastomers of different grades presented diversified rheological and mechanical behavior. This behavior is probably related to the differences in molecular weight and the long chain branch content present in the copolymers. 2002 Elsevier Science Ltd. All rights reserved. Keywords: Polypropylene blends; Metallocene elastomers; Rheological behaviour; Mechanical properties
1. Introduction In the last decade a lot of interest has focused on the polymerization of a wide variety of olefin monomers by metallocene catalysts. Polymers and copolymers of ethylene, propylene, styrene, higher α-olefins and cyclic olefins have been the main focus of recent studies. Many companies are challenging for commercialization of these new metallocene polymers. Most progress has been achieved in the field of ethylene/α-olefin and ethylene/cyclo olefin copolymers. Those emerging catalyst systems, obtained by the single site constrained geometry technology has allowed for the production of polyolefins with novel molecular architecture. This new technology has produced a variety of polyolefins, including polyolefin elastomers (ethylene/1-octene copoly-
* Corresponding author. Tel.: +55-21-562-7210; fax: +5521-270-1317. E-mail address: [email protected] (F.M.B. Coutinho).
mers—EOCs). These polymers, containing more than 20 wt.% octene, have distinctive properties when compared with elastomeric materials currently available. Due to the long chain branching, EOCs are aimed at competing with thermoplastic olefin impact modifiers, such as EPDM, in the automotive industry [1–9]. Thus, the aim of this work was to evaluate the effect of addition of different grades of metallocene elastomers on the mechanical and rheological properties of PP.
2. Experimental 2.1. Material and blend preparation Commercially available grades of polymers: polypropylene (PP) and ethylene/octene copolymers (EOCs) were used, their specifications are listed in Table 1. DRI is defined as the deviation extent that the rheology of Dow’s Insite Technology Polyolefins (ITP) present relative to the rheology of the conventional linear
0142-9418/02/$ - see front matter 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 1 4 2 - 9 4 1 8 ( 0 1 ) 0 0 1 3 7 - 4
648
A.L.N. Da Silva et al. / Polymer Testing 21 (2002) 647–652
Table 1 Characteristics of the polymer samples Material
PP
Manufacturer % 1-octenea DRIa Density at 23 °C (g/cm3)b Mw/Mnb Mnb Melt indexc (g/10 min)
Polibrasil Resinas (Brazil) Dow Chemical (USA) – 24 – 2.0 0.917 0.884 9.2 2.1 46,500 156,000 4.3±0.2 2.5±0.4
a b c
EOC-8100
EOC-8150
EOC-8200
Dow Chemical (USA) Dow Chemical (USA) 25 24 2.0 0.5 0.864 0.871 2.1 2.1 170,000 94,000 1.0±0.2 7.0±0.3
Values supplied by Dow Chemical. measured in IMA laboratory by ASTM D792. measured in IPRJ laboratory by ASTM D1238.
homogeneous polyolefins that are reported to have no long chain branching by the following normalized equation [10]: DRI⫽(3.65E6⫻t0/h0⫺1)/10
(1)
where t0 is the characteristic relaxation time and h0 is the zero shear viscosity of the material. The parameters t0 and h0 are determined by a non-linear regression of the experimental data numerically fitted to the generalized Cross equation. For commercial homogeneous polyolefins that have no long chain branching, the h0 vs t0 relationship can be described by the equation: h0⫽3.65E6⫻t0
2.3. Mechanical behavior The tensile tests were conducted at room temperature (25 °C and 55% relative humidity) using samples obtained by compression molding on an Instron Tester (model 4204), according to ASTM D882, at a strain rate of 50 cm/min. Impact strength was measured according to ASTM D256 (V-notched) on an Impact Tester Microtest at room temperature.
3. Results and discussion
(2)
A HAAKE twin screw extruder was used for melt blending the EOCs/PP systems, containing different weight percents of EOC: 0, 5%, 20, 50, 80 and 100%. The screw speed was set at 60 rpm and the temperature profile in the extruder from the feed to the metering zone was set at: 190, 210, 220 and 220 °C. For all compositions prepared, 5 wt.% of calcium carbonate was added. 2.2. Rheological behavior The viscosities of the polymers were measured at low shear rates (w=0.1–100 rad/s) on a cone-plate type rheometer (Rheometrics Dynamic Stress rheometer— SR200) at 220 °C. The oscillatory flow properties, namely the complex viscosiy h* (defined as h∗=h⬘⫺ ih⬙, where h⬘ is the dynamic viscosity or the real part of the viscosity and ih⬙ is the imaginary part of the viscosity), the storage modulus, G⬘ (defined as G⬘=wh⬙, where w is the frequency of the oscillations in rad/s) and the loss modulus, G⬙ (defined as G⬙ = ωη⬘) were measured.
3.1. Rheometrics dynamic stress rheometer results Fig. 1 shows the dependence of the logarithm of the value of the complex viscosity (h*) on the logarithm of investigated frequencies for EOCs, PP and EOCs/PP blends. An expanded scale of the elastic behavior of the systems at lower frequencies is also included. Fig. 1(a) shows that EOC-8150 copolymer tended to show high shear thinning and the EOC-8200 (lower viscosity) tended to present the largest range of Newtonian behavior. Fig. 1 also shows, for the whole range of explored frequency, that EOCs/PP blends exhibited a decrease in viscosity value with increasing frequency, i.e., EOCs/PP blends are pseudoplastic melts. EOC8100/PP system presented a different rheological behavior in relation to the other systems. It was observed that EOC-8100 presented a lower viscosity at lower frequencies and as EOC-8100 content increased, the viscosity of the blends decreased. This behavior may be related to the fact that the addition of 5 (wt.%) of EOC tended to increase the average end-to-end distance between PP coils, and as a consequence interactions between PP molecules may be occurring. As EOC-8100 content increases, the distance between PP coils tended
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649
Fig. 1. Log (h*) vs log (w). (a) EOCs and blends (b) EOC-8100/PP, (c) EOC-8150/PP, (d) EOC-8200/PP
to increase, reducing the occurrence of interactions between PP molecules and thus the viscosity of the blends decreased. At higher frequencies, EOC-8100/PP blend viscosities were between the pure component viscosities, and those values increased as the proportion of EOC-8100 increased. This result may be attributed to the fact that at higher frequencies the effect of the presence of EOC-8100 long chain branches is more significant, and entanglements between branching and the chain segments of EOC-8100 and PP may occur, resulting in an increase in the viscosity values as EOC-8100 content increases. This behavior was not observed in EOC8150/PP and EOC-8200/PP systems. For EOC-8150/PP blend, in the whole range of explored frequencies, the rheological behavior remained constant, i.e., as EOC8150 content increased, the system viscosities increased. EOC-8150/PP blends presented viscosity values close to EOC-8100/PP blend viscosities at the investigated frequencies. The rheological behavior of EOC-8200/PP blends was different. Up to 100 rad/s frequency, the systems presented an increase in the viscosity as EOC-8200 copolymer content decreased. At higher frequencies, the samples with low EOC-8200 content tended to show high shear thinning and thus the viscosity values became close to the samples with high EOC-8200 content. This behavior may be related to the smaller DRI value (DRI=0.5) in relation to the other grades of elastomers. In other words, the low long chain branch content presents low probability to form entanglements that
reduced the formation of entanglements between PP and elastomer chains, decreasing the material viscosity. The dynamic storage modulus, G⬘, is related to the elastic behavior of the material and may be considered as the storage energy. The dynamic loss modulus, G⬙, represents the dissipated energy. The dependence of G⬘ and G⬙ on the frequency measures the relative motion of all molecules in the bulk and can give important information about the flow behavior of melts [11]. Fig. 2 shows the variation of the elastic modulus (G⬘) with the investigated frequencies of EOCs and EOCs/PP blends. An expanded scale of the elastic behavior of the pure polymers and blends at lower frequencies is also included. Assuming that G⬘ is related to the storage energy, Fig. 2(a) shows that EOC-8150 copolymer (higher molecular weight) presented the highest elasticity, over the frequency range analyzed. Fig. 2 also shows that EOC-8150/PP blend presented higher G⬘ values; however, at high frequencies the system behavior became similar to the behavior of EOC8100/PP blend. The EOC-8200/PP blends presented lower G⬘ values in relation to the other systems. This result is also related to the less pronounced effect of EOC-8200 elastomer long chain branches. EOC-8100/PP blends showed a different behavior at low and high frequencies. As can be observed, the samples with lower EOC-8100 content showed higher elasticity at low frequencies. That behavior may also be
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Fig. 2.
Elastic modulus, G⬘, vs frequency. (a) EOCs and blends (b) EOC-8100/PP, (c) EOC-8150/PP, (d) EOC-8200/PP.
attributed to the formation of PP entanglements. It can also be seen that EOC-8100 presents lower G⬘ values, indicating that the material has lower elasticity at low frequencies. This behavior is probably a result of a conformation change of the molecule due to the occurrence of main-chain entanglements (‘coils’). At higher frequencies, G⬘ values of the blends are between those of the pure polymers. The elasticity of the blends increases as EOC-8100 content increases as a result of the presence of the entanglements between branching and chain segments of EOC-8100 and PP. At high frequencies, EOC-8100 presents higher G⬘ values, indicating that the long chain branches present in EOC-8100 molecules tend to produce entanglements and thus a higher elasticity can be observed. The dependence of the loss modulus, G⬙, on the investigated frequencies of EOC copolymers is shown in Fig. 2. Elastomer EOC-8150 present the highest G⬙ values, over the extensive frequency range analyzed; however, at high frequencies, the G⬙ values of EOC-8150 were similar to those of EOC-8100 copolymer. The elastomer EOC-8200 presented the lower G⬙ values, indicating that this material should be producing blends with lower dissipation of energy.
3.2. Mechanical analysis results The effect of the elastomer grade and blend composition on the tensile properties of EOCs/PP systems is shown in Tables 2–4. It can be seen for all systems analyzed that, as EOC content increased, the Young’s modulus decreased as a result of the lowering on the crystallinity of the blends as EOCs were added. The stress at break also decreased as the EOC content increased. It has been reported in the literature [7] that behavior is related to the immiscibility of the components and conseTable 2 Tensile properties of EOC-8100/PP blends Material (wt% of EOC-8100)
Stress at Young’s Toughness break (MPa) modulus (MPa) (MPa)
0 5 20 50 80 100
32±3 55±3 49±5 37±2 12±1 11±1
259±17 111±18 128±20 91±7 20±2 6±1
33±1 149±47 134±43 103±10 44±5 40±6
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651
Table 3 Tensile properties of EOC-8150/PP blends
Table 7 Impact properties of EOC-8200/PPblends
Material (wt% of EOC-8150)
Stress at Young’s Toughness break (MPa) modulus (MPa) (MPa)
Material (wt% of EOC-8150) Impact strength (J/m)
0 5 20 50 80 100
32±3 69±3 48±5 32±5 21±1 10±1
259±17 150±40 120±8 87±4 43±6 6±1
33±1 134±40 118±24 61±10 30±6 18±3
Table 4 Tensile properties of EOC-8200/PP blends Material (wt.% of EOC-8200)
Stress at Young’s Toughness break (MPa) modulus (MPa) (MPa)
0 5 20 50 80 100
32±3 59±6 42±4 32±3 19±1 10±1
259±17 121±23 129±9 20±5 20±2 7±1
33±1 142±35 92±3 42±4 12±5 47±5
Table 5 Impact properties of EOC-8100/PPblends Material (wt% of EOC-8100) Impact strength (J/m) 0 5 20 50
40±2 49±1 81±9 606±28
0 5 20 50
40±2 42±3 68±3 528±40
EOCs/PP blends at room temperature. The results show that EOC-8100/PP and EOC-8150/PP blends have similar impact properties. EOC-8200/PP blends tend to present the lowest impact strength. That behavior should be related to the fact that EOC-8200 elastomer is the copolymer with the lower DRI value in relation to the other elastomers. This means that this material presents a lower deviation in relation to the rheology of the conventional linear homogeneous polyolefins. In other words, for EOC-8200 the elastomeric feature is less pronounced relative to the EOC-8100 and EOC-8150 copolymers.
4. Conclusions Different rheological behavior was observed when different grades of ethylene/octene copolymers were added to PP. The mechanical analysis showed that the systems tend to present similar stiffness. EOC-8200/PP blends tend to present the lowest toughness and impact strength. This behavior is probably related to the long chain branch content present in the elastomers.
Acknowledgements Table 6 Impact properties of EOC-8150/PPblends Material (wt% of EOC-8150) Impact strength (J/m) 0 5 20 50
40±2 44±5 75±6 602±55
quent formation of a bi-phase structure. It is known that the fracture process on the inter-phase is accelerated by the immiscibility of the components. In a general way, the EOC-8100/PP, EOC-8150/PP and EOC-8200/PP systems, produced materials with similar stiffness, whereas EOC-8200/PP samples presented the lowest toughness values in relation to the other systems. Tables 5–7 present the impact strength of the
Financial support from FAPERJ, CNPq, PRONEX, PADCT/FINEP is gratefully acknowledged. We are also grateful to Polibrasil Resinas, Branco Dow, DuPont Dow Elastomers and Quimbarra (Imerys).
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