SBR-EPDM blend

Coated materials are evaluated in S-SBR and in 50 50 blends of S-SBR and EPDM rubbers. In blends, the partitioning of fillers and curatives over the phases depends on differences in surface polarity. In S-SBR, polythiophene-modified silica has a strong positive effect on the mechanical properties because of a synergistic reaction of the sulfur-moieties in the polythiophene coating with the sulfur cure system. In S-SBR/EPDM blends, a coating of polyacetylene is most effective because of the chemical similarity of polyacetylene with EPDM. The effect of... 

Polyacetylene-modified sulfur is evaluated as a curative in a 50 50 blend of S-SBR/EPDM. In pure S-SBR, the mechanical properties decrease with the polyacetylene coating due to a reduced release rate of the sulfur out of its shell. The cure and mechanical properties of the S-SBR/EPDM blend are nearly doubled because of improved compatibility. 

Effect of Plasma-Coated Silica on SBR/EPDM Blend Properties... 

The Payne effects of S-SBR/EPDM blend filled with untreated silica, plasma-modified silicas, and silane-treated silica are shown in Fig. 22. 

Table 8 Compound compositions for silica in the SBR/EPDM blend...

Fig. 22 Payne effect of untreated silica, PA-, PPy-, and PTh-silicas, and silane-treated silica in a S-SBR/EPDM blend. Sample codes are detailed in Table 8...

With the uncoated carbon black, the Payne effect in the SBR/EPDM blend positions itself between those of pure SBR and EPDM. For the plasma-coated carbon black, the blend has a Payne effect value comparable to that of EPDM, at a significantly higher value than the SBR compound (Fig. 29). 

Fig. 30 images of a 50 50 SBR/EPDM blend with (a) 40 phr fullerene carbon black (b) plasma-coated fullerene carbon black (c) unstained section with fullerene carbon black (d) unstained section with plasma-coated fullerene carbon black... 

The stress-strain curves for the SBR/EPDM blends containing uncoated and plasma-coated carbon black are shown in Fig. 31. The blend with plasma-coated carbon black shows a slightly higher stress development in the stress-strain curve, probably due to the better-filled EPDM phase in the blend. 

Fig. 31 Stress-strain curves of the 50 50 SBR/EPDM blend with either uncoated or plasma-coated 40 phr carbon black...

Fig. 33 Cure-rheograms of the SBR/EPDM blends cured with solid line S8 squares PPAS8-1 circles PPAS8-2 triangles PPAS8-3 stars PPAS8-4...

The vulcanization curves of the SBR-EPDM blends with the various types of coated sulfur are presented in Fig. 33. For all samples, a pronounced increase in the final state of cure (maximum torque) is observed. This demonstrates that S-SBR/EPDM blends cured with plasma-acetylene-encapsulated sulfur provide a better covulcanization behavior. 

The tensile properties of the S-SBR/EPDM blends cured with the uncoated and coated sulfur are shown in Fig. 34. It is clear that the compounds with micro-encapsulated sulfur show largely improved tensile strength, elongation at break, and higher moduli. 

Application of a plasma coating onto carbon black is very difficult compared to silica. It was only practically feasible for fullerene soot (left over from the fullerene production), which contains a large amount of reactive groups on its surface. Polyacetylene-plasma-treated fullerene soot provides an improved dispersion in SBR and in a SBR/EPDM blend compared to untreated fullerene black. However, the effect on the stress-strain properties is rather limited and the coating has only a slight effect on the final properties. 

A polyacetylene coating applied on sulfur does not negatively influence its activity and speed as curing agent, but it can increase the scorch time. This effect is probably due to a delayed release of the sulfur out of the polymeric shell. In the SBR/EPDM blend, on the other hand, the plasma-treated sulfur results in higher torque values, an indication that the distribution of the plasma-treated sulfur over the different rubber phases is more homogenous, which is the main effect aimed for in the context of this study. 

Vulcanised SBR/EPDM diblends were quantitatively characterised by solid-state 13C NMR spectroscopy. The SBR/EPDM blend ratio can be determined as well as the czs-1,4, transit and vinyl-1,2 butadienes and styrene ratios in the SBR and the ethylene and propylene contents in the EPDM. No evidence for homo- and co-vulcanisation has been obtained in these systems. No evidences are found for the change in cisitrans ratio in the SBR upon the vulcanisation [52],... 

Elastomers are classically blended to improve the physical and mechanical properties of the final material. For example, Dubey et aiP incorporated suitable amounts of EPDM in the SBR matrix because it was expected to impart significant heat and ozone resistance to the SBR matrix. The irradiation-induced vulcanization of SBR/EPDM blends was proved to combine desired properties and high mechanical strength. For example, the formation of a cross-linked network led to a decrease in elongation at break. Cross-linking restricts the movement of the polymer chain against the applied force. Moreover, to decrease the radiation dose (and hence, the cost of radiation), multifunctional acrylates (MFAs) and allylic reactive molecules were used. 

Dubey, K. A., Bhardwaj, Y. K., Chaudhari, C. V, Bhattacharya, S., Gupta, S. K., Sabharwal, S., Radiation effects on SBR-EPDM blends A correlation with blend morphology. Journal of Polymer Science Part B Polymer Physics 2006, 44, 1676-1689. 

Fig. 12. Tensile strength of normal SBR-EPDM blend based compounds.

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