Surface Modification of Metallic Inserts for Enhancing Adhesion at the Metal–Polymer Interface

A combination of mechanical and chemical treatments was utilized to modify the surface textures of copper and duralumin inserts in order to enhance the adhesion at the metal–polymer interface and provide an adhesive joint with a high loadbearing capacity. Pretreatment of the surfaces with sandblasting was followed by etching with various chemical mixtures. The resulting surface textures were evaluated with a scanning electron microscope (SEM) and an optical confocal microscope. Surface geometry parameters (Sa, Sz, and Sdr) were measured and their relationships to the adhesion joint strength were studied. It was found that the virgin and purely mechanically treated inserts resulted in joints with poor loadbearing capacity, while a hundredfold (duralumin) and ninetyfold (copper) increase in the force to break was observed for some combinations of mechanical and chemical treatments. It was determined that the critical factor is overcoming a certain surface roughness threshold with the mechanical pretreatment to maximize the potential of the mechanical/chemical approach for the particular combination of material and etchant.

Material Factors in Relation to Development Time in Liquid-Penetrant Inspection. Part 1. Material Factors

In technical publications and European Standards the development time (i.e. time of getting out of penetrant from a discontinuity to the material surface) in penetration testing is specified within the range of 10-30 minutes. In practice, however, it is seen , that it is closely connected with the material type and ranges from several minutes to 24 hours. In the literature, only interactions coming from the penetrant are described, whereas those from the material under testing, i.e. the influence of material factors on adhesion between penetrant and material, are not taken into consideration. In this connection, it has been described precisely in the paper the adhesion phenomenon and also it has been indicated the other factors affecting the development time. Recapitulating the adhesion theories presented in the paper, it can be formulated two fundamental circumstances which must occur that adhesion joint may be formed, namely: the approach of the particles of two solids to the distance less than 0,9 nm while the high attractive force occurring between molecules should be connected with possibly low potential energy of the bond formed in this way.

Influence of Vulcanization on Adhesion to Non-Vulcanizing Polymers

According to contemporary ideas the mechanisms of adhesion and co-vulcanization of rubbers have much in common. The phenomenon of co-vulcanization, like that of adhesion of polymers, includes the diffusion of macromolecules and of segments of them, which is particularly intensive in the initial period of vulcanization, when the crosslinks have not yet formed. The difference between covulcanization and adhesion lies solely in the fact that the process of interpenetration of the molecular chains in the former case is sooner or later broken off by the vulcanization process being superimposed upon it, securing the macromolecules or portions of them by strong chemical bonds. This leads to the formation of an adhesion joint considerably superior in strength to a joint in which the molecules diffusing through are attached only by weak intermolecular bonds. It is important to ascertain what is the influence of the vulcanization of elastomers upon their adhesion to polymers not capable of forming chemical bonds with them. This case is of immense practical importance, since unvulcanized rubbers are very often used in combination with vegetable and synthetic fibers which are not capable of vulcanizing. As adhesives we selected elastomers of varying molecular structure, polarity and degree of molecular mobility: butadiene-acrylonitrile rubber (SKN-26), butadiene-styrene rubber (SKS-30A), butadiene-styrene oil-extended rubber (SKS-30ARM-15) and butyl rubber. Using these rubbers we prepared stocks both containing and not containing vulcanizing groups (in the latter case the components of the vulcanizing groups were replaced by an equal quantity of inert filler—whiting). The amount of vulcanizing group was set at the optimum for each rubber. The substrates used were films containing no plasticizers—cellophane (cellulose hydrate) and Perfol' PK-4 (polycaprolactam). The adhesive was applied to the substrate by coating on a calender at the optimum conditions for each elastomer. The specimens produced in this way were plied up and subjected to vulcanization. Vulcanization was carried out in a Berstorff apparatus for continuous vulcanization at 143° C and a specific pressure ≈ 0.85 kg/sq cm. The time of cure was varied between 0 and 88 min.