Adherends chemistry

A denotes adherend chemistry, B adherend structure and topography, C adhesive chemistry, D adhesive structure and topography, E interaction of polymers with metals, and F failure surfaces (locus of failure). 

In seeking to minimize the contact angle or to promote wetting of the adherend by the adhesive, one must consider the effects both of the chemistry of the components and of the morphology of the adherend surface on the observed contact angle. Finally, comment must be made on the dynamics of the wetting process and the factors upon which it depends. 

The effect of the chemical makeup of the adhesive/adherend system on contact angle and wetting is manifest through the influence of such chemistry on the surface free energies of the adhesive-air (or other fluid medium), adherend-air... 

The extent of coating adhesion failure was found to be dependent upon the resistance of the polymer in the coating to hydrolysis by corrosion generated hydroxide. In this study, similar trends have been observed for adhesives. Table I shows the results of salt spray corrosion on a series of bonds between cold rolled steel adherends and adhesives of varying chemistry. The results show that there is a direct correlation between the chemistry of the adhesive polymer and the durability of the series of adhesive bonds studied. The locus of adhesion failure also appears to be related to the type of adhesive chemistry. In this study, adhesives based on polymers having a wide range of hydrolysis resistance were examined. 

In a specific example of adhesive bonds between cold rolled steel and SMC adherends (Table II) an adhesive based on hydrolysis resistant epoxy chemistry (i.e., adhesive E) was compared with an adhesive based on hydrolysis prone urethane chemistry (i.e., adhesive C) in composite to cold rolled steel bonds. After corrosion testing, a significant difference in both retention of initial bond strength and locus of failure was observed. For bonds prepared with adhesive E, little if any reduction of the initial bond strength was observed after corrosion testing. The locus of failure for both the tested and untested bonds was largely in the... 

The Effect of Adhesive Primers. In practice, adhesive bonds involving metal adherends often use primers as pretreatments of the metal surface prior to bonding. Table IV shows the durability of composite-metal bonds prepared with adhesive C over a series of primers (of varying corrosion resistance) in 240 hour salt spray test. The results indicate that the performance of bonds is directly related to the corrosion resistance of the primer used to prepare the adherend surface. In general, the adhesion of the primer to the steel adherend, rather than the adhesive chemistry. 

Metals such as aluminium, steel, and titanium are the primary adherends used for adhesively bonded structure. They are never bonded directly to a polymeric adhesive, however. A protective oxide, either naturally occurring or created on the metal surface either through a chemical etching or anodization technique is provided for corrosion protection. The resultant oxide has a morphology distinct from the bulk and a surface chemistry dependent on the conditions used to form the oxide 39). Studies on various aluminum alloy compositions show that while the oxide composition is invariant with bulk composition, the oxide surface contains chemical species that are characteristic of the base alloy and the anodization bath40 42). 

Overall the surface chemical composition of the reinforcing fibers or the adherends is chemically quite different from the bulk composition of these materials. Specific interactions between epoxies and these surfaces without cognizance of the different surface chemistries can lead to erroneous conclusions about the epoxy-surface bonding or interphase structure. 

Baun, W. L., et al., Chemistry of Metal and Alloy Adherends by Secondary Ion Mass Spectroscopy, Ion Scattering Spectroscopy, and Auger Electron Spectroscopy, ASTM STP 596, American Society of Testing and Materials, Conshohocken, PA, March 1975. 

The chemistry of a structural adhesive is designed to do at least two important things. First, the adhesive must at some time pass through a fluid state in order to wet the adherends. Second, the adhesive in its final state in the bond line must be a solid, high-molecular-weight polymer that is able to carry and transfer mechanical forces. In almost all cases, the polymer matrix of a structural adhesive will be crosslinked. The chemistry must... 

Any bonded construction consists of at least two adherends and one adhesive and contains at least two interphase regions. It is important to remember that the performance of the construction, its durability, its mechanical properties, and its response to tests and challenges, are all properties of the entire assembly. The successful use of adhesives depends on taking account of all parts of the construction and the process. Whereas the adhesive is just one part of the assembly, its chemistry plays an important role in the bonding process. 

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. 

Although the evolution of surface chemistry depicts the hydration of bare surfaces, the same process occurs for buried interfaces within an adhesive bond. This was first demonstrated by using electrochemical impedance spectroscopy (EIS) on an adhesive-covered FPL aluminum adherend immersed in hot water for several months [42], The EIS, which is commonly used to study paint degradation and substrate corrosion [43,44], showed absorption of moisture by the epoxy adhesive and subsequent hydration of the underlying aluminum oxide after 100 days (Fig. 5). At the end of the experiment, aluminum hydroxide had erupted through the adhesive. 

Adherend surface surface chemistry surface topography surface cleanliness... 

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