Crosslinked polymers failure mechanism

Very recently, attempts have been made to develop PP/EOC TP Vs. In order to make TPVs based on PP/EOC blend systems, phenolic resin is ineffective because the latter needs the presence of a double bond to form a crosslinked network structure. Peroxides can crosslink both saturated and unsaturated polymers without any reversion characteristics. The formation of strong C-C bonds provides substantial heat resistance and good compression set properties without any discoloration. However, the activity of peroxide depends on the type of polymer and the presence of other ingredients in the system. It has been well established that PP exhibits a (3-chain scission reaction (degradation) with the addition of peroxide. Hence, the use of peroxide only is limited to the preparation of PP-based TPVs. Lai et al. [45] and Li et al. [46] studied the fracture and failure mechanism of a PP-metallocene based EOC based TPV prepared by a peroxide crosslinking system. Rajesh et al. 

Black low density polyethylenes have been found to behave differently during thermal oxidation at low temperatures (8.0 to 40°C). The black samples oxidize and crosslink but they do not fall mechanically, as does non-black LDPE. Hawkins(17) has shown the greater thermal stability of black polyethylene as compared to non-black polyethylene In the solid state. Other Investigators (18,19) have demonstrated the activity of carbon black as a free radical trap and others (20) have suggested that polymer radicals form carbon-polymer bonds with the carbon black. The exact reason diy the black samples do not fall mechanically even though they oxidize and crosslink Is not clear and any one, or a combination of all the above factors could be the cause. It appears that the lack of mechanical failure after oxidation Indicates very little or no scission during the oxidative process and finally no further oxidation after the development of the 70% gel found In oxidized samples. 

Nanocomposites with carbon nanotubes have been an area of considerable R D ever since the excellent electrical and mechanical properties of carbon nanotubes were demonstrated. However, attempts to prepare carbon nanotube RPs often result in phase separation of the CNT and polymer phases causing premature material failure. Researchers at Nomadic Inc. and Oklahoma State University developed a layer-by-layer (LBL) assembly process that permits preparing polyelectrolyte/CNT RP with a CNT loading greater than 50 wt%. The excellent mechanical properties of these materials can be improved further by additional chemical action crosslinking of the CNT and polymer phases and by parallel alignment of the CNTs. The LBL method has been used to prepare various types of RPs. 

Let us consider the possible mechanisms of strengthening of epoxy polymers by rubbers. The failure of a polymeric material, as of any solid, proceeds through the development of cracks. In the failure of linear polymers the material structure can change under the influence of mechanical stresses in the tip of the growing crack, which in turn results in orientation and consequently in the strengthening of the polymer in the area of the crack tip. In network polymers (epoxy in particular) the possibility of plastic deformation in the crack tip is lower due to the additional limits on the chain mobility applied by the network chemical crosslinks. This is why one observes a low value of the effective failure surface energy compared with linear polymers. 

The polymers used in EOR may be employed in treatment processes such as mobility control, injection well reprofiling, production well water shut-off, or steam diversion. At temperatures greater than 70-75 C (160-170 F),most water-soluble polymers undergo extensive hydrolysis. As a result, the thickened brine solutions lose viscosity (or in the case of crosslinked gels, they lose gel strength) and are rendered useless . The mechanism of failure is usually precipitation by the reaction of the hydrolyzed polymer with naturally occur ng polyvalent ions. 

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