Effect of bifunctional organosilane on the joint strength of some natural rubber compounds to nylon 6,6

Joint strength of a sulphur-cured natural rubber compound, containing 60 parts per hundred rubber (p.h.r.) by weight precipitated amorphous white silica to nylon 6,6 was measured by means of peel tests. The compound also contained 3 and 7 p.h.r. bis[3-triethoxysilylpropyl-)tetrasulphane (TESPT), a bifunctional organosilane, to prevent the silica from interfering with the reaction mechanism of sulphur cure in the rubber. The rubber was joined to nylon using an organic solvent-based proprietary bonding system. Peel tests were performed at an angle of 90° in air, either at a constant rate or under constant load. At a constant rate, peeling energies up to 17 kJ/m2 were measured. Under constant load, joint failure occurred in a time-dependent manner, and was cohesive in the rubber and in the primer, as well as at the primer/nylon interface. The locus of failure was somewhere between 250 and 700 μm from the covercoat. Notably, the joint strength was not affected by the addition of up to 7 p.h.r. TESPT to the rubber.