New attitude in polymers - Self-healing

Abstract

Elastomeric polymers are nowadays used in a broad variety of highly demanding applications. Due to alternating loads, microsized cracks may occur in the material, even before its loading- and lifetime-limit. The consequences can be drastic - failure of components often leads to the loss of production, delays, raising costs or facilities and - in rarely cases - personal injuries. Our endeavour is the equipment of such technically relevant elastomers with a self-healing agent. If microcracks occur in the material, this system should be able to prevent further growing and seal parts of the crack or even the complete crack to restore the mechanical properties. The idea to equip an elastomeric matrix with a self-healing agent is bioinspired: In case of breaks, a variety of plants segregate latex particles and proteins that crosslink in an addition reaction and close the fissure. The matrix elastomers investigated within the presented project are EPDM (ethylene propylene diene-terpolymer type M), NBR (nitrile butadiene rubber) and SEBS (styrene ethylene butadiene styrene), a thermoplastic elastomer. After a centrical splitting of died-cut elastomer strips, SEBS exhibits minor autonomous, intrinsic self-healing effects which are probably caused by molecular inter-diffusion processes as postulated by Wool and O'Connor. EPDM and NBR show no such intrinsic self-healing which can be ascribed to their rather stiff und cross-linked structure. Injured specimens from EPDM and NBR do not exhibit subsequent vulcanisation that might initiate intrinsic selfrepairing. It was also found that blending the elastomeric matrix with middle or high molecular polymers till a limit of 30% leads to distinctive self-healing results for EPDM and SEBS. Another presented strategy is the partial microencapsulation of two-component adhesives. In case of a crack, the encapsulated component is released and initiates a polymeric reaction with the second component which is directly embedded into the elastomeric matrix. © 2010 WIT Press.