Carbon-black-filled rubbers crosslink density

At Pisa University, work has also been carried out on EPDM by Bani and co-workers [103]. Carbon-black-filled EPDM crumb samples were devulcanised by exposing them to microwaves so that their temperature increased to over 300 "C. This process, in a short period of time, produced a rubber that had a relatively low crosslink density and could produce high-quality blends with virgin EPDM due to good interfacial adhesion. Once vulcanised, these blends were found to have superior physical properties to those produced using untreated EPDM crumb. 

The potential use of palm oil fatty acid additive (POFA) as a new rubber ingredient in carbon black-filled NR compounds is examined. It is found that the cure time (t90) and scorch time decrease with increasing POFA concentration. The Mooney viscosity of the rubber compounds also decreases with increasing POFA concentration. The mechanical properties of the carbon black-filled NR compounds are enhanced by the addition of POFA, especially at a concentration of 2 phr. Results of the swelling measurement and scanning electron microscopy indicate that POFA has some effect on crosslink density and also improved filler dispersion. 9 refs. 

Figure 15.33 shows benzene uptake by natural rubber samples. Filled samples absorb less solvent (lower swelling). The carbon black containing sample had a lower benzene uptake than the silica filled sample. The lower swelling of the carbon black containing sample is due to high bound rubber content, the crosslink density of the black filled vulcanizate, and a strong rubber-filler interaction. 

It has been shown that the viscoelastic losses of OH-terminated poly(dimethyl-siloxane), crosslinked with tetra-functional silicates, decreases with increased crosslink density. Furthermore, identical results were obtained when the polymer was crosslinked with y-irradiation, in bulk and in solution this indicates that there is no significant change in the number of interchain entanglements, and these are responsible for the observed losses. Vulcanization studies of poly(di-methylsiloxane)s, y-irradiated up to 500 Mrad, have shown linear correlation of the crosslink density with swelling, indentation and extension behaviour up to 160 Mrad, and exponentially for higher doses. Basic principles for the thermal stabilization of silicone rubbers, filled with carbon blacks and silica, have been discussed and a tentative stabilization mechanism put forward. ... 

The barrier properties of 70/30 acrylonitrile-butadiene mbber/ethylene propylene diene monomer rubber (NBR/EPDM) vulcanizates, when loaded with carbon black fillers [e.g., I SAP (intermediate super-abrasion furnace), HAF (high-abrasion furnace) and SRF (semi-reinforcing furnace)] and using benzene, toluene and xylene as penetrants, have been examined with reference to the type of filler employed [66]. The filled samples were found to exhibit a better resistance to uptake of the three organic solvents when compared to the respective unfilled blends for any given blend ratio. With regards to the three types of carbon black used, solvent uptake was in the order SRF-> HAF-> ISAF-filled samples. The reason for this order was attributed to the better filler reinforcements and enhanced crosslink densities of the matrix as the size of the carbon black particles used was decreased. A similar behavior was also identified for NR/EVA composites [52]. 

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