EPDM-based blends

NR/EPDM-based sidewalls of radial tires are also prepared to get more durability and appearance. These blends with an EPDM content varying from 30 to 70 phr are used for making cables and conductors. 

Thermoplastic polyolefin (TPO) blends of metallocene-based polyolefin elastomers (POE) with polypropylenes have gained commercial significance because of the improved melt flow and toughness compared to the conventional TPOs based oti EPR or EPDM blends made with high melt-flow PP (Toensmeier 1994). in comparative tests with 70/30 PP/elastomer blends, the blends with POE maintained ductile behavior at —29 °C even with high melt flow index PP (MFl = 35), while the corresponding EPR-based blends were brittle with PP of MFl = 20. In addition, they showed improved knit-line strengths. 

Typically, a 50/50 blend of nitrile rubber and polypropylene is melt mixed with 5 % maleated PP and 1 % ATBN respectively and then cured with SnCl2 (0.5 %). The resistance to hot oil swell (72 h, 100 °C) of NBR/PP blend was found to be significantly better than that of EPDM/PP blend. Typical properties of the commercial dynamically cured NBR/PP TPV (Geolast ) are compared with other PP-based TPVs in Table 19.16. Commercial applications for this TPV were targeted for automotive seals and gaskets in the oil, fuel, and brake systems. However, this blend has not been as commercially successful as the Santoprene -type PP/EPDM-based TPV. 

Reports in the literature on the transport of penetrant molecules through NR based blends and IPN s are few when compared to the existing literature on most common/commercial polymers/blends. The sorption and diffusion of aromatic penetrants into different NR blends such as NR/BIIR, NR/CIIR, NR/neoprene, NR/EPDM, NR/polybutadiene, and NR/SBR were studied by Siddaramaiah et al. The diffusion coefficient (D) of the penetrants was found to range from 6.8 to 84.3 x 10 cm /s at a temperature range of 25-60 °C. Results indicated that the transport data were affected by the nature of the interacting solvent molecule rather their sizes, and also by the structural variations of the elastomers blended with NR. The activation parameters for the diffusion of the penetrants ranged from 4.16 to 30.48 kJ/mol. 

Butadiene reacts with cyclopentadiene to produce ENB as the third monomer for EPDM elastomer manufacture. Also, some of this EPDM is blended with polypropylene in dynamic vulcanization to make the most commonly used thermoplastic vul-canizate (TPV), which is based on PP and EPDM. 

The number of reports on the obtaining of polyesters (mainly PBT-based) and on rubber blends for dynamic vulcanization is growing. The authors point to the multiphase structure (in which the partially vulcanized rubber is the soft phase) and to the properties of the TPEs or the high impact thermoplastics. PEE/nitryl rubber blends [113-115], PBT or PET/acrylic rubber blends [116,117], PBT/rubbery polymer blends [118,119], PBT/ethylene-propylene rubber blends, unsaturated PEE/EPDM rubber blends [73,120,121], and PBT/rubber blends [122,123] are reported. 

The role of accelerators in the curing and mechanical properties of EPDM/SBR blends is investigated. In this study, blend properties were optimised by selecting accelerators with a shorter scorch time and a faster cure rate in the EPDM phase than in the SBR phase. The accelerators investigated included a sulphenamide-based accelerator and a system composed of a combination of a thiuram and thiazole-based accelerator. By use of techniques described in this work, sulphur vulcanisates with compound properties comparable to those cured with a cure system composed of peroxide and sulphur coagent were obtained. The effects of the accelerators in final compound properties are discussed, with reference to mechanical properties, ozone resistance, heat ageing, and compression set. 13 refs. 

A manufacturer considering using a thermoplastic elastomer would probably first consider one of the thermoplastic polyolefin rubbers or TPOs, since these tend to have the lowest raw polymer price. These are mainly based on blends of polypropylene and an ethylene-propylene rubber (either EPM or EPDM) although some of the polypropylene may be replaeed by polyethylene. A wide range of blends are possible which may also contain some filler, oil and flame retardant in addition to the polymers. The blends are usually subject to dynamic vulcanisation as described in Section 11.9.1. 

Coran and Patel [33] selected a series of TPEs based on different rubbers and thermoplastics. Three types of rubbers EPDM, ethylene vinyl acetate (EVA), and nitrile (NBR) were selected and the plastics include PP, PS, styrene acrylonitrile (SAN), and PA. It was shown that the ultimate mechanical properties such as stress at break, elongation, and the elastic recovery of these dynamically cured blends increased with the similarity of the rubber and plastic in respect to the critical surface tension for wetting and with the crystallinity of the plastic phase. Critical chain length of the rubber molecule, crystallinity of the hard phase (plastic), and the surface energy are a few of the parameters used in the analysis. Better results are obtained with a crystalline plastic material when the entanglement molecular length of the... 

---