Role of strain induced crystallization and oxidative crosslinking in fracture properties of rubbers

Type Article
Date 2014-05
Language English
Author(s) Le Gac Pierre-YvesORCID1, Broudin Morgane1, Roux Gérard2, Verdu Jacques3, Davies PeterORCID1, Fayolle Bruno3
Affiliation(s) 1 : IFREMER, Ctr Bretagne, Marine Struct Lab, F-29280 Plouzane, France.
2 : TUS, Thales Underwater Syst, F-06903 Sophia Antipolis, France.
3 : Arts & Metiers ParisTech, PIMM, F-75013 Paris, France.
Source Polymer (0032-3861) (Elsevier Sci Ltd), 2014-05 , Vol. 55 , N. 10 , P. 2535-2542
DOI 10.1016/j.polymer.2014.03.023
WOS© Times Cited 10
Keyword(s) Fracture, Rubber, Oxidation
Abstract Tensile properties and crack propagation properties, especially critical strain energy release rate in mode I, GIC, have been used to investigate fracture properties of elastomers and their relationships with microstructure. These investigations were mainly based on a series of comparisons: first, the behaviour of polychloroprene rubber (CR), undergoing stress hardening due to strain induced crystallization (SIC) and oxidative crosslinking (OCL) was compared with that of chlorinated polyethylene (CPE), which undergoes SIC but not OCL, and with a polyurethane based on hydroxyl terminated polybutadiene (PU) which undergoes OCL but not SIC. Comparisons were also made on CR between fracture behaviour at ambient temperature, where SIC occurs and at 100°C where there is no SIC. Finally, oxidative crosslinking was used to vary in a continuous way the crosslink density in CR and PU, in order to evaluate the role of crosslinking in fracture behaviour.

The results reveal the strong contribution of SIC to fracture strength. Crosslinking, even at low conversion, inhibits SIC which explains the sharp decrease of CR toughness in the early period of exposure to oxidation. When SIC has disappeared, it is possible to appreciate the effect of crosslinking on fracture behaviour. This effect, as evaluated from the density of deformation energy at rupture in tension or from GIC value, is almost negligible while the sample modulus increases regularly as a consequence of crosslinking. It appears that the toughness remains almost constant because it is under the influence of two contradictory phenomena: the negative effect of a reduction of ultimate elongation and the positive effect of a modulus increase. Such behaviour can be explained in terms of heterogeneous distribution of the lengths of elastically active chains. After long exposure, the sample behaviour becomes brittle, very high modulus values indicate that the samples approach, presumably in a heterogeneous way, the glassy state.
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