Autoadhesion of EPDM

The adhesive strength of post-crossHnked samples was evaluated by a 180° peel test which measured the force of separation at a constant peel rate (5 mmmin ) at room temperature. The results reported in Fig. 24.3 show the effect of contact time (ranging from 1 h up to one month) in the second step of joint formation at room temperature. Up to approximately 300 h of contact, no effect of time is seen. For longer times, the peel strength increases slightly. Although the scatter is important, this weak trend can be related to crosslinks formed by irradiation in the molecular interphase. This is confirmed by the fact that no separation is observed for these joints immersed in a good solvent such as cyclohexane, whereas spontaneous delamination is observed for shorter contact times. 

Therefore, the presence of crosslinks in the interdiffused depth is clear after long contact times but no crosslinks, or only a few, are formed at shorter times. Because the density of crosslinks inside the elastomer sheets is the same in all cases (the same dose is received), only the effect of diffusion depth on this number of crosslinks in the interfacial domain can explain the observed behavior. Moreover, Eq. (2) tells us that the thickness of the interdigitated zone in- 

These results confirm that the number of interfacial crosslinks depends on the interdiffusion depth and that a critical depth has to be reached to obtain efficient crosslinks for high interfacial strength. 

Preliminary experiments were done on adhesion of the two elastomers considered in Section 24.2.1, polyisoprene and styrene-butadiene copolymer [9]. One sheet was fully crosslinked before contact Then the joints were made with the second uncrosslinked sheet 

Joint Crosslinking conditions Peel rate [mm mln ] Peel strength [k] m- ] 

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