Rubbers surface pretreatment

The surfaces of many plastics and rubbers have low surface energies (Table 3.1) such that wetting by an adhesive is inhibited unless special surface pretreatment processes have been employed. However, plastics which contain polar groups such as PVC, nylons and acrylics are bondable with a minimum of surface treatment. 

Typical Applications Epoxies, phenolics, meleunines, nylons, PVC, acrylics, polyolefins, polyurethanes, nitrile rubbers and fiberglass-reinforced thermoplastics used to couple inorganic fillers or reinforcing materials with resins surface pretreatment of fillers and reinforcers. 

However, the attainment of good adhesion between smooth surfaces exposes the mechanical interlocking theory as not being of wide applicability. For example, the elegant work of Tabor et al. [1,2] who studied the adhesion between two perfectly smooth mica surfaces and Johnson et aL [3] who examined the adhesion to optically smooth rubber surfaces, clearly demonstrates that adhesion may be attained with smooth surfaces. Also, detailed examination of surfaces roughened by typical industrial pretreatment methods, for example, grit-blasted metallic substrates (Fig. 3.1), usually reveals little... 

Surface-water samples are usually collected manually in precleaned polyethylene bottles (from a rubber or plastic boat) from the sea, lakes, and rivers. Sample collection is performed in the front of the bow of boats, against the wind. In the sea, or in larger inland lakes, sufficient distance (about 500 m) in an appropriate wind direction has to be kept between the boat and the research vessel to avoid contamination. The collection of surface water samples from the vessel itself is impossible, considering the heavy metal contamination plume surrounding each ship. Surface water samples are usually taken at 0.3-1 m depth, in order to be representive and to avoid interference by the air/water interfacial layer in which organics and consequently bound heavy metals accumulate. Usually, sample volumes between 0.5 and 21 are collected. Substantially larger volumes could not be handled in a sufficiently contamination-free manner in subsequent sample pretreatment steps. 

For this reason much attention is being applied to surface science and to the interaction of coating materials with intended substrates. Some plastics— particularly polyethylene, polypropylene—and the silicone rubbers, cannot be covered with high-performance coatings without their surfaces being pretreated. 

Figure 4 Examples of rough pretreated substrate surfaces, (a) Phosphated steel prepared for rubber bonding (cf. Ref 53) (b) PTFE irradiated by argon ions (after Ref. 54).

Some examples in which the mechanical mechanism is important are in the adhesion of polymers (elastomers and rubbers) to textiles. Another example, though somewhat contentious, is the metal plating of a plastic which usually requires a pretreatment to modify the surface topography of the polymer. Usually the increase in adhesion is also attributed to an improved surface force component due to the increased mgosity. 

Bonding Soles to the Lasted Uppers. Polychloroprene and polyurethane solvent adhesives, occasionally also dispersions of the same polymers, are used for this purpose. Various pretreatments are used to improve the bond application of a thin first coat of adhesive, especially for absorbent surfaces priming, in particular the halogenation of vulcanized rubber and thermoplastic rubber soling the use of base-coat primers for nylon and other synthetics, as well as UV-curing primers for EVA and other substrates in athletic footwear. 

Polyurethane adhesives also are suitable for bonding nonpolar elastomers, for example, natural rubber, styrene-butadiene rubber, or ethylene-propylene terpol-ymers, after chemical pretreatment of the surface. 

Adequate pretreatment is indicated by die appearance of hairhne surface cracks on flexing die rubber. Suitable for many syndietic rubbers when given 10-15 min etch at room temperature. Unsuitable for use on butyl, polysulfide, silicone, chloinated polyethylene, Mid poly-urethane rubbers... 

Certain textile fabrics, such as polyester or aramid, possess low surface activity and many times require a special isocyanate or epoxy pretreatment under tension, in much the same manner that the RFL is applied afterwards. So with polyester or aramid cord, two successive dipping operations may be necessary in order to achieve good rubber-to-fabric adhesion. 

As may be seen from Tables 2.3 and 2.5, the surfaces of plastics, rubbers and fibre composites have low surface free energies (typically less than about 50 mJ/m ), in distinction from those of metals, with energies generally greater than about 500 mJ/m. With many plastics, plastic laminates and rubbers it is possible to obtain reasonable or even good adhesive joint strengths with little or no pretreatment. This is shown by the results in Table 4.1. 

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