| Abstract: | A new technique for improving the strength of bonded joints between various materials and different adhesives is described. Increased strength was obtained by mechanical Surface Activation Beneath Reactive Adhesives (SABRA). This technique results in higher bond energies due to the creation of free radicals. The surfaces were activated by abrasion with emery paper in the presence of the adhesive itself (epoxy), or of some suitable primer such as methyl methacrylate, acrylonitrile (AN) or hydrogen sulfide gas. The effects of this technique were demonstrated by four different methods: 1) Improved wetting of standard epoxy or water drops on the treated surface. 2) Achievement of bond energies between primers and polymeric surfaces exceeding the energy of solution in solvents, which were revealed by attenuated total reflectance infrared. 3) The detection of free radicals created by bond scission during abrasion by means of diphenylpicryl hydrazyl, (DPPH), a free radical scavenger, monitored by spec-trocolorimetry, 4) Destructive testing of single lap joint test Pieces, scarfed tube joints and pee) test samples. These experiments will be described in a second paper. The theoretical base of the new approach is supported by a tentative estimate of energies set free by mechanochemical creation of free radicals and the excess heat released during abrasion. |
