Adhesion, chemical pretreatment surface

Some of these techniques using electrons and photons as probes of the surface chemistry have been described in this symposium by other authors. In this paper methods of surface analyses using beams of ions will be described. Emphasis is placed on ion scattering spectrometry (ISS) and secondary ion mass spectrometry (SIMS). Examples are shown for adhesive bonding applications including determination of locus of failure, contamination, cleaning and thermal and chemical pretreatments. 

The outdoor durability of epoxy bonded joints is very dependent on the type of epoxy adhesive, specific formulation, nature of the surface preparation, and specific environmental conditions encountered in service. The data shown in Fig. 15.19, for a two-part room temperature cured polyamide epoxy adhesive with a variety of fillers, illustrates the differences in performance that can occur due to formulation changes. Excellent outdoor durability is provided on aluminum adherends when chromic-sulfuric acid etch or other chemical pretreatments are used. 

Conventional coating approaches to TPO, which rely on the use of substrate pretreatments such as flaming, corona discharge, plasma or chemical pre-treatment, have led to a substantial oxidation of the surface, which enhances adhesion. These pretreatments, however, have a limited service life before the surface reverts to its unoxidized, apolar condition. 

The adhesion or welding of wood surfaces to each other on the basis of a chemical pretreatment of the surfaces and probably heat activation. 

Grinding, brushing or sanding (with the exception of the above-mentioned Saco method) do not cause chemical modifications of the material s surface. A clean surface results with a characteristic structure corresponding to the composition of the material, as shown in Figure 7.6. Therefore, physical and chemical pretreatment methods are aimed at the chemical modification of the surfaces. Thus, on the one hand it is possible to further enhance the adhesive forces for extremely high demands on bonded joints, and on the other hand, to make poorly bondable material (e.g., plastics) bondable at all. Since physical methods are mainly used in bonding of plastics, they are described in Section 9.2.4. 

Independent of the chemical structure, industrially available adhesives are characterized by the formation of strong adhesive bonds on the respectively pretreated surfaces of the materials described. This results in the criteria for adhesive selection described in Chapter 8. 

On that basis, the book intends to bridge current issues, aspects and interests from fundamental research to technical apphcations. In seven chapters, the reader will find an arrangement of latest results on fundamental aspects of adhesion, on adhesion in biology, on chemistry for adhesive formulation, on surface chemistry and pretreatment of adherends, on mechanical issues, non-destructive testing and durability of adhesive joints, and on advanced technical applications of adhesive joints. Prominent scientists review the current state of knowledge about the role of chemical bonds in adhesion, about new resins and nanocomposites for adhesives, and about the role of macromolecular architecture for the properties of hot melt and pressure sensitive adhesives. Thus, insight into detailed results and broader overviews as well can be gained from the book. 

Recent advancements have yielded methodologies for chemically pretreating the polyetherimide surface thereby introducing a chemical component to the metal olymer bond b. These schemes were both nonaqueous and aqueous. FmthennoFe, the methods employed an adhesion promoter or else relied on chemical modiHcation of the polymer. ... 

Optimisation of surface pretreatment is the key to maximising joint durability. The adhesive influences the surface oxide layer and the surface oxide layer influences the boundary layer polymer matrix the whole must therefore be viewed as a unique system for every adherend-adhesive combination. The interplay of chemical bonding... 

One of the most important factors in adhesive bonding is the surface condition of the substrate, i.e. the surfaces of the materials to be joined. Since adhesion takes place only at the interface between the component and the adhesive, it is evident that surface preparation or chemical pretreatment has a crucial bearing on the quality of the adhesive bond. 

Substrates with low surface energy usually have few or no polar groups, which provide only little or no interaction with the adhesive. Such substrates need either a physical surface preparation, e.g. a plasma treatment or a chemical pretreatment by use of an organic adhesion promoting layered system. 

It is always difficult to get durable bonds on many surfaces without surface preparation or chemical pretreatments. The use of primers and a complete portfolio of activators and primers for glass, ceramic, plastics, metals, wood, etc. improves the adhesion. 

Suitable methods of surface pretreatment for mass-production applications must be discussed and coordinated with the technical service department of the adhesive manufacturer. Adhesive manufacturers have established treatment methods for the main substrates encountered in industrial production and working instructions for users. They are in a position to offer their customers the best professional advice. This approach offers the right chemical pretreatment, which contributes best to the specific adhesive system. Table 4 lists the typical surface pretreatment options for a range of common substrates. 

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. 

Abstract. This chapter is concerned with an in-depth examination of the adherend surface pretreatments used prior to structural adhesive bonding. It encompasses the various substrates encountered, particularly but not exclusively, in the aerospace industry. It compares and contrasts mechanical, chemical and electrochemical methods used for substrates comprising aluminium alloys, titanium, stainless steel, thermoplastic and thermoset fibre reinforced composites and non-metallic honeycomb. Scanning and transmission electron microscope techniques are used to analyse and characterise many of the pretreated surfaces so produced. 

In the late 1990s, researchers at NASA/LaRC developed a chemical pretreatment for titanium alloys which did not require the use of chromic acid or chromate salts [63]. The resultant surface is reputed to have excellent compatibility with structural adhesives of high thermal-oxidative resistance in other words, suitable for bonding titanium components in supersonic aircraft. 

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