EPDM A

This variation in friction behavior could be due to the specific apparent crosslink densities or AM values, as shown in Fig. 17. Both PTFE0kGy-EPDM and PTFE20kGy-EPDM have higher AM values and therefore have lower / initial values. Even a slight variation in AM results in different /Wiai values. As soon as AM decreases, as in the case of PTFE500kGy-EPDM, a significant increase in / , i l is... 

Antiozonents protect the rubber surface by the formation of a protection layer, the ozonides on the surface of rubber by reaction of the antiozonents with ozone. Certain polymers also provide good ozone protection. The use of 10-20 parts of EPDM, a low diene rubber, in natural rubber compound significantly increases ozone resistance. 

Some typical elastomers are natural rubber, which is gathered from trees, SBR rubber, which is used a lot in motorcar tires, neoprene, as in wet suits and oil seals, EPDM, a general purpose rubber, butyl, a heat-resistant rubber with the ability to keep the air in car tires, nitrile for oil seals, silicones for heat resistance, fluoro-elastomers for chemical resistance, and last but not least, polyurethanes, which cover a number of the above fields. Table 1.1 shows some of the advantages of castable polyurethanes over conventional rubbers. 

Figure 12.14 129Xe NMR spectra at room temperature of EPDM (a) and of carbon black filled EPDM (85.5 phr). Three different carbon blacks were used (b) carbon black N110, (c) N330 and (d) N550...

In Figure 7 one can see that the temperature of a portion of the EPDM exotherm is increased in the blend compared with the pure EPDM. A possible explanation is that LDPE crystallites are nucleating the crystallization of high-ethylene-EPDM segments. In this case, EPDM crystallites would form layers on LDPE crystallites. 

Figure 19. Scanning electron micrographs from the fracture surface of a PP blend with 20% EPDM. (a, top) Corresponding to Figure 17 (b, bottom) corresponding to Figure 18.

Low-temperature solution processes are state-of-the-art for the production of ethylene/propylene or ethylene/propylene/diene elastomers (EPDR or EPDM). A continuous stirred-tank reactor (CSTR) or a series of two or even more such reactors is used [2]. n-Hexane, n-heptane, or Ce, C7 fractions are the solvents. Catalyst, co-catalyst and other compounds are introduced with the solvent into the reactor. The monomers (ethylene, propylene) are injected as gases other olefins are introduced in liquid form. The polymerization process runs around 50 °C and at pressures up to 2 MPa. Downstream the catalyst/co-catalyst system is deactivated and their residues are dissolved in dilute acid or aqueous NaOH. The copolymer is stabilized with an antioxidant. Steam treatment removes the rest of the solvent and monomers, and agglomerates the product to crumbs. These crumbs are then dried and finished to bales or pellets. 

Best results were achieved with the Zn polysulfonates of EPDM. A typical set of properties is summarized as follows ... 

Figure 15.5 SEM micrographs of NR/EPDM (a and b) 70/30 wt% and (c and d) 60/40 wt% blends. Micrographs (a) and (b) are related to compatibilized blends with 2.5 phr of EPDMSH. (From Reference 56 with permission from John Wiley Sons.)...

Fig. 7 IR spectra of ethylene-propylene-ethylidene norbornene copolymer (EPDM) (A) before and (B) after photocrossunking.

Another interest of irradiation in the field of the conductivity of polymer blends was shown by Faez etal. These authors incorporated EPDM to lANl in order to improve mechanical properties of the material. PANl was doped not with irradiation, but with dodecylbenzene sulfonic acid by reactive processing in an internal blender. To cross-link the EPDM, a phenolic resin and e-beam irradation (75 and 150 kGy) were compared. Contrary to the cross-linking by phenolic resin, the cross-linking by e-beam irradiation did not interfere with the presence of the acid necessary for doping PANl. Consequently, better mechanical properties were obtained. Moreover, irradiation-induced additional conductivity led to a slightly more conductive material. 

EPR is currently replaced by EPDM, a modification with a diene monomer, due to its improved workability. A novel type of elastomer (called a thermoplastic elastomer) exhibits quite revolutionary behavior. Here cross-linking is temporary (at room temperature) while it can flow at higher temperatures, like thermoplastics. The typical one (SBS) is a strictly ordered block copolymer of styrene and butadiene, made by an anionic polymerization. The butadiene chains (at a controlled MW of 70,000) are embedded in a rigid phase of polystyrene spheres (MW of 15,000) thus providing temporary cross-linking at ambient conditions, while being processible at high temperatures like thermoplastics. 

FIGURE 1 CNF distribution in the matrix EPDM. (a) demetallized fiber (b) fiber containing cobalt. 

These dienes, along with ethylene and propylene, are used to make EPDM, a sulfur-vulcanizable elastomer. Generally, EPDM contains 25-60 wt% propylene and 1-5 wt% diene, and is completely amorphous. Metallocene catalysts have inherent advantages in EPDM pol5unerization, the most important of which are the ability to incorporate large amoimts of a-olefin with ease and the avoidance of long ethylene sequences that lead to crystallinity. Catalysts that appear to have found commercial application in EPDM include mono-Cp catalysts such 12 (207) and 14 (208). 

Poly(ethylene-co-propylene-co-ethyl-idene norbornene) (EPDM A)... 

EPDM), a synthetic rubber with a typical Shore A hardness of 50 +5%. Seals for thin-wall piping and ductwork are made of softer EPDM with a Shore A hardness of 40 +5%. This lower-durometer rubber makes it possible to effect a seal at lower torque, thereby avoiding deformation of the piping or ducts. Some seals are made of virgin nitrile rubber for resistance to oils, gasoline, and solvents, as well as synthetic silicon rubber for steam applications. 

Impact-modified copolymer typically is a block copolymer with a rubbery component as one of the components of the matrix. In PP, this rubbery component typically is ethylene propylene diene monomer (EPDM), a synthetic rubber. 

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