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Rubber blends butadiene rubber natural rubber styrene-butadiene rubber miscibility

Blending of rubbers is often used to en-hance the properties of rubber prod-ucts. This study deals with blends con-taining rubber only because of the elimination of the potential side effects of the additives. The blends were mixed on a laboratory two-roll mill and in a Brabender internal mixer. Influences of mixing conditions on properties of these blends have been monitored. For the characterization of rubber blends a variety of methods, such as Mooney viscosity measurements, scanning elec-tron microscopy (SEM), or differential scanning calorimetry (DSC) were used.

Eigenschaften von Natur- und Styrol-Butadien-Kautschuken im Verschnitt mit Butadien Kautschuk I Kautschukmischungen Butadien- Kautschuk Naturkautschuk Styrol-Butadien-Kautschuk Mischbarkeit

Das Verschneiden von Kautschuken ist oft für die Verbesserung der Eigenschaf-ten der Gummiprodukten angewandt. Diese Studie beschäftigt sich nur mit den Mischungen der reinen Kautschuke, um den Effekt der Additive zu vermei-den. Die Mischungen wurden auf einem Laborwalzwerk und einem Brabender In-nenmischer hergestellt. Der Einfluß der Mischbedingungen wurde untersucht. Die Charakterisierung der Kautschukver-schnitte (Blends) wurde mit verschiede-nen Methoden ausgeführt.

Figures and Tables:By a kind approval of the authors.

IntroductionSince development of new synthetic po-lymers is very expensive, the standard polymers are often combined in order to obtain new materials with a broader spectrum of properties. Rubbers are mixed for many years, both from proces-sing reasons, and because of require-ments for the properties of the resulting rubber goods. It is very important to choose carefully blended rubbers and additives. Dissimilar immiscible rubbers can result in blends with inferior proper-ties. This property failure has been ascri-bed to three types of incompatibility – thermodynamic, different viscosity and cure rate incompatibility [1].

A number of studies deals with the influence of blend composition on the distribution of fillers or the components of the curing system [2-5] and final pro-perties of vulcanizates [6-9] including their morphology [10]. However, they don´t give any information about influ-ence of mixing conditions or about beha-vior of rubbers.

This work is focused on the blends of natural and styrene-butadiene rubbers with butadiene rubber, which are widely used. The blends contain rubbers only because of elimination of potential side effect of the additives.

Experimental

MaterialsThe used elastomers were natural rubber (NR) LAC 10 (110 1+4 ML) from Liberia, styrene-butadiene rubber (SBR) Kralex 1500 (48 ML (1+4) 100 °C) with 24 wt % styrene content and butadiene rubber (BR) Synteca BR 44 (50 ML (1+4) 100 °C) both from Synthos Kralupy a.s., Czech Republic.

Blend preparationBR, NR, SBR and their blends were pro-cessed on a laboratory two roll mill (roll diameter – 150 mm, length – 400 mm, friction ratio - 11:9, speed regulation – fre-quency inverter Danfoss, manufacturer - Baťa) and on internal mixer (Plasti-Corder lab-station, manufacturer - Brabender). Formulation of blends is in Tables 1 and 2.

The first sets of NR/BR and SBR/BR blends were prepared on a laboratory two roll mill. The mixing time was five minu-tes. The two roll mill was cooled by water. Blends were cut back and forth throug-hout. Speed of the slow roll was 18 rpm for NR/BR blends and 13 rpm for SBR/BR blends. Next five sets of these blends we-re prepared on an internal mixer. The mi-xing conditions in internal mixer (Tab. 3) had been chosen experimentally. The hig-her temperature or higher speed couldn´t

Properties of Natural and Styrene-Butadiene Rubbers with Butadiene Rubber Blends I

AuthorsAlena Kaderabkova, Vratislav Duchacek, Prague, Czech Republic

Corresponding Author:Alena Kaderabkova, researcherUniversity of Chemistry and Technology, Prague, Department of Polymers Technicka 5, CZ-16628 Praha 6 Czech RepublicPhone: +420 220 444 026E-Mail: alena.kaderabkova@vscht.cz

1 NR/BR blends formulationBlend NR content [%] BR content [%]N0B100 0 100

N10B90 10 90N20B80 20 80N40B60 40 60N50B50 50 50N60B40 60 40N80B20 80 20N90B10 90 10N100B0 100 0

2 SBR/BR blends formulationBlend SBR content [%] BR content [%]S0B100 0 100

S10B90 10 90S20B80 20 80

S40B60 40 60S50B50 50 50

S60B40 60 40S80B20 80 20S90B10 90 10S100B0 100 0

3 Mixing condidions in an internal mixerStarting temperature [°C]

Speed [min-1] Mixing time [min]

50 30 20

50 20 20

50 40 20

50 30 10

50 30 30

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ROHSTOFFE UND ANWENDUNGEN RAW MATERIALS AND APPLICATIONS

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be used because of rubber degradation. Torque and temperature were measured during mixing. First, NR was masticated alone in the case of NR/BR blends. BR was added after 1 minute.

TestingIn these blends the influence of mixing conditions on Mooney viscosity, morpho-logy and glass transition temperature (Tg) has been monitored. Morphology micro-graphs has been obtained by scanning electron microscope Tescan Vega 3 LMU (manufacturer – Tescan a.s.). The seconda-ry electron detector was used. Molded sheets (thickness – 2 mm) were cooled with liquid nitrogen. Then the frozen sam-ples were broken. SEM was performed on the fracture surface. Mooney viscosity ML (1+4) 100 °C of blends was measured on the variable Mooney viscosimeter V-MV 3000 (manufacturer - Montech Werk-stoffprüfmaschinen GmbH). For determi-nation Tg Differential scanning calorime-ter DSC 2920 modulated DSC (manufac-turer – TA instruments) was used. Para-

Fig. 1: The dependence of temperature on mixing time NR/BR blends at rotors speed of internal Brabender mixer 30 min-1.

1

Fig. 2: Comparison Mooney viscosities of NR/BR blends prepared on a laboratory two roll mill, mixing time 5 min.

2

meters of DSC analysis: sample weight ≈ 5 mg, temperature range - 150 °C - 20 °C, temperature rate 10 K min-1.

Results and discussion

Influence of mixing conditions on Mooney viscosityNR/BR blends with high content of NR prepared on two roll mill has significantly lower Mooney viscosity than blends of

Fig. 3: Comparison Mooney viscosities of NR/BR blends after 20 min mixing on an internal Brabender mixer at rotors speeds 20, 30 a 40 min-1.

3

Fig. 4: Comparison Mooney viscosities SBR/BR blends prepared on laboratory two roll mill, mixing time 5 min.

4

4 Glass transition temperatures

Blend Mixing conditions Tg1 [°C] Tg2 [°C]

N60B40 two roll mill, 5 min -104 -61

N60B40 internal mixer, 20 min-1, 20 min -103 -61

N60B40 internal mixer, 30 min-1, 20 min -104 -62

N60B40 internal mixer, 40 min-1, 20 min -104 -61

N90B10 internal mixer, 30 min-1, 20 min -107 -62

N10B90 internal mixer, 30 min-1, 20 min -104 -62

S50B50 two roll mill, 5 min -107 -53

S50B50 internal mixer, 30 min-1, 20 min -106 -52

the same composition prepared on inter-nal mixer. Figure 2 shows the dependence of Mooney viscosity on the formulation of NR/BR blends prepared on the two roll mill. The higher is NR content in a blend the lower is the Mooney viscosity. This fact can be explained by favorable condi-tions for NR mastication during mixing. Mooney viscosity of NR (blend N100B0) decreased from a value of 110 ML (1+4) 100 °C to value 22 ML (1+4) 100 °C. Moo-

ROHSTOFFE UND ANWENDUNGEN RAW MATERIALS AND APPLICATIONS

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Fig. 5: Comparison Mooney viscosities SBR/BR blends after 20 min mixing on in internal at speed of rotors 20, 30 a 40 min-

1.

Fig. 6: Blend N80B20 (left) and blend N40B60 (right), two roll mill, 5 min.

Fig. 7: Blend N60B40, internal mixer 20 min-1, 20 min (left) and blend N60B40, internal mixer 40 min-1, 20 min (right).

5

6 7

Fig. 8: Blend N60B40, internal mixer 30 min-1, 10 min (left) and blend N60B40, internal mixer 30 min-1, 30 min (right).

8

ney viscosity of the NR/BR blends prepa-red on internal mixer has slightly descen-ding trend (Fig. 3). The mastication of NR is inhibited by an oxygen lack and absence of plasticizers. The mixing temperature was ranged between 90 and 100 °C during mixing (Fig. 1). Mastication is not effective at these temperatures. SBR and BR are produced in processable state. Decrease of their Mooney viscosity is not so signifi-cant. Mooney viscosity of SBR/BR blends prepared on the two roll mill increases with decreasing content of SBR (Fig. 4). Mooney viscosity of blends containing from 0 to 60 % SBR is essentially indepen-dent on mixing conditions (Fig. 5).

Influence of mixing conditions on blends morphologyThe secondary electron detector was used for acquirement of micrographs showing blends morphology. Already du-ring NR/BR blends mixing, it was evident that the resulting material will be hetero-geneous. Rubbers tried to separate when they get in touch with each other. SEM micrographs confirmed heterogeneity. It is impossible to say, which phase is NR

and which is BR. Blends with higher con-tent of NR seem to be more heterogene-ous (Fig. 6). Micrographs of blends mixed under various conditions exhibit no noti-ceable differences (Fig. 7, 8). It follows that adjustment of conditions failed to achieve greater homogeneity.

The behavior of SBR/BR blends was totally different. Rubbers were readily mixed. From micrographs, it seems that these blends are homogenous (Fig. 9 – 11). But it is more likely, that SBR/BR blends are heterogeneous with very

small domains. SEM is not able to distin-guish them.

Influence of mixing conditions on glass transition temperatureFor each blend were gained two values of Tg (Tab. 3) corresponding with values of Tg themselves rubbers (TgNR = -61 °C, TgBR = -104 °C and TgSBR = -52 °C). Only the size of the peaks of the derivative curve was changed depending on the contents of rubbers in blends. It follows that neither of SBR and BR were mixed on molecular

Fig. 9: Blend S80B20 (left) and S40B60 (right), two roll mill, 5 min.

9

ROHSTOFFE UND ANWENDUNGEN RAW MATERIALS AND APPLICATIONS

40 KGK · 03 2018 www.kgk-rubberpoint.de

Fig. 10: Blend S50B50, internal mixer 20 min-1, 20 min (left) and blend S50B50, internal mixer 40 min-1, 20 min (right).

Fig. 11: Blend S50B50, internal mixer 30 min-1, 10 min (left) and blend S50B50, internal mixer 30 min-1, 30 min (right).

10 11

level. DSC analysis proved, that NR/BR and SBR/BR blends are immiscible.

ConclusionThe results from DSC and SEM show that NR, BR and SBR are immiscible. Tg values are independent on the mixing method as well as the composition of blends. It was found that SEM is not too suitable for studying morphology of these blends. The SBR/BR blends seem to be homoge-nous, but DSC proves that it is not true. Only Mooney viscosity measurements proved their dependence on the method

of mixtures preparing. The question re-mains whether the increased homo-geneity could be achieved through vulca-nization.

References[1] Ghosh A. K., Debnath S. Ch., Naskar N., Basu

D. K.: J. Appl. Polym. Sci. 81, (2001) 800.[[2] Callan J. E., Hess W. E., Scott C. E.: Rubber

Chem. Technol. 44, (1971) 814.[3] Hess W. M., Chiroco W. E.: Rubber Chem.

Technol. 50, (1977) 301.[4] Walters H. H., and Keyte D.: Rubber Chem.

Technol. 38, (1965) 61.

[5] Massie M., Hirst R. C., Halasa A. F.: Rubber Chem. Technol. 66, (1993) 276.

[6] Singh R., Sangwan S.: IJLTET. 5, (2015) 289.[7] Zhang H., Datta R. N., Talma A. G., Noorder-

meer J. W. M.: IRC 2008, Malaysia, October 2008.

[8] Mohamed R. M.: Thesis. Ain Shams Universi-ty, Cairo 2011.

[9] Freitas de Castro D., Martins A. F., Suarez J. C. M., Reis Nunes R. C., Visconte L. L. Y.: Kautsch. Gummi Kunstst. 56, (2003) 49.

[10] Rocha T. L. A. C., Rosca C., Ziegler J., Schuster R. H.: Kautsch. Gummi Kunstst. 58, (2005) 22.

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