Strong adhesive systems

It is worthwhile drawing attention to health hazards associated with film infected water systems which also cause corrosion. Two of the most common are Legionnaires disease and so called humidifier fever . Because of strong adhesion of biofilms and diffusion rates through the film treatment based on cleaners and chemical sterilisers such as chlorine often fail similar considerations apply to other systems in industry, e.g. food, paint, oil and gas are examples where biofilm activities have given massive problems. 

Observations of large contact angles in emulsions were first reported by Aronson and Princen [105,106]. The authors have studied oil-in-water droplets stabilized by anionic surfactant in the presence of various salts. Similar systems were studied by Poulin [110]. Anionic surfactants such as sulfate, sulfonate, or carboxylate surfactants [106,110] exhibit a good stability and a strong adhesion in the presence... 

Thermosetting adhesives are, in general, two-component systems, and may be cured either at ambient or at elevated temperatures. After the components have been mixed, the glue has a limited time of application. Phenol formaldehyde, polyester resins and epoxies are being used the latter show a very strong adhesion to practically all materials. 

Note that good wetting is necessary for bond formation. However, it is not the sole criterion for a strong adhesive joint. Several other important parameters, as noted in the sections that follow, strongly affect the adhesive strength of epoxy systems. 

Figure 31.28 Scanned images of Prohesion salt spray-tested A1 panels with chromated plasma coating systems prepared by anode magnetron plasmas Primer G could not be removed from the whole Al panel due to the strong adhesion, and only the portion with pitting corrosion occurred underneath could be stripped off with paint stripper solution.

Since it was observed that fluorine contamination was a possibility and had potentially detrimental effects as described in Chapter 10, the excellent primer adhesion achieved with Tfs/(Ar) and Tcs/(Ar), shown in Table 31.3, has significant importance in the practical application of the plasma technique without any of the potentially deleterious effects of fluorine-based systems. Argon plasma treatments on both flow system TMS (Tfs) and closed system TMS (Tcs) polymers were then investigated as an additional system modification that could provide strong adhesion without the incorporation of fluorine-containing monomers in the quest to produce chromate-free coatings systems. 

In the case of direct application of E-coat to IVD specimens (one of the systems that showed excellent adhesion performance in both the tape test and the accelerated adhesion test), due to the high throw power of the E-coating process, the deep penetration of E-coat into the porous IVD structure creates mechanical interlocking and thus strong adhesion. Because of this development of mechanical interlocking, neither the tape test nor the accelerated adhesion test could distinguish the effect of plasma treatment on adhesion performance. 

The superior corrosion performance and strong adhesion of the plasma coating system can be attributed to the coating properties and, more importantly, to the nature of interfacial chemistry. Two techniques were applied to study the surface and interfacial chemistry of the plasma coating system (1) in situ plasma deposition and XPS analysis and (2) in-depth profiling of sputtered neutral mass spectroscopy (SNMS). 

Another interesting procedure for obtaining a two-layer system involves [97] the formation of a base layer of the polymeric photoinitiator, through a spin coated film onto different substrates, followed by their immersion, under UV irradiation, into multifunctional acrylic formulations dissolved in solvents unable to remove the base layer from the substrate. By this method, a top layer of crosslinked acrylic resin is obtained, having strong adhesion to the substrate. The replacement of the polymeric photoinitiator by a low-molecular-weight analogue... 

This emulsion is not a liquid-liquid system, but is an aqueous dispersion of solid polymer particles. Therefore, if the Tg were above room temperature (at which the emulsion is applied), the polymer segments, lacking segmental mobility, would not diffuse readily from one particle of the emulsion into another after evaporation of the water medium in which the copolymer emulsion is prepared. The result would be a powdery film. Conversely, when the Tg is reduced below room temperature, segmental mobility in the copolymer leads to diffusion and formation of a flexible, strong adhesive film from the latex by coalescence of the emulsified particles during drying at room temperature. 

Coating formulations and properties have been detailed in technical bulletins (31). The epoxy-polyamide system is popular because it provides an unusual degree of inherent corrosion resistance. This will be discussed in detail later. The system is unusually tolerant as compared to related systems, such as amine cured, since the ratio of components is not particularly critical. Tolerance is also demonstrated because it may be applied to wet surfaces and to surfaces with tightly bound rust. Indeed, formulations are available that may be applied under water to structures such as submarines and off-shore oil well riggings. Both the corrosion resistance and the tolerance relative to application on poorly prepared wet surfaces are believed to be functions of the surface activity of the polyamide resin. Related also to the surface activity are the unusually strong adhesive properties that the system demonstrates with a broad range of substrates. 

In the end, the mechanism that causes strong adhesion of the coating particles to the cores is due to mechanical forces acting in the system. It works best, if the coating particles are somewhat harder than the core material. Because the coating particles are often so small, that no dislocations are present in their structure, they behave as very hard entities (see Section 5.4). Therefore, it is for example possible to partially embed submicron-sized Ti particles in the surface of glass. 

These copolymers have a wide range of possible applications. DHA-co-4VP and DHA-co-NVP copolymers are excellent for rubber-steel and rubber-polyester adhesive systems respectively. In addition, quaternized DHA-co-4VP copolymers promote strong adhesion of rubber to polyester tire cord in vulcanized composites. 

Strong adhesive bonds are expected to form between solids with atoms of similar size, similar interatomic distances, and chemical bonding that would maximize W. Strong adhesive bonds would also be formed for systems that exhibit large elastic deformations before bond breaking occurs, because of the large values of for these systems. Polymers and macromolecules with chains that can rearrange in response to mechanical forces are examples of this type of system. Because of the flexibility of the molecular chains, the work of adhesion also increases due to increased area of contact (i at the interface, since the total adhesive force is Iri... 

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