Structure of Adhesives

Secondary Ion Mass Spectrometry used as a solo Instrument or in concert with other methods has proven to be an excellent technique for studying the surface chemistry of adhesive bonding materials. The application of SIMS is shown in re.lation to pretreatments of metals and alloys, chemistry and structure of adhesives, and locus of failure of debonded specimens. 

Perhaps the most apt definition of analysis of adhesives is their qualitative and quantitative characterization. Since the early days of adhesive development, the elementary chemical analysis of adhesives has provided valuable information on the structure and purity of materials. Chemical methods of analysis are simple and cheap but labor intensive. The use of such techniques for analysis has been decreasing over the past 30 years. This is due to the complexity of the polymeric structures of adhesives as well as the development of much powerful and sophisticated instrumentation. More recently, advances in computer technology have been combined with analytical instruments to give speed, resolution, simplicity, and minimal sample requirements that were unimaginable two decades ago. 

The molecular description of the formation of an adhesive layer does not take into account the polymeric structure of adhesives either. It is based on determination of the number of adhesion or molecular bonds, n, per unitary area of a true contact surface and the energy of a single bond between two surfaces. During the formation of such bonds the adhesion strength. A, can be expressed by a specific work spent on the destruction of the adhesive joint ... 

The chemical interaction of organosihcon compounds and copolymers of etltylene with vinyl acetate and copolymers of ethylene with viityl acetate and maleic anhydride was studied by IR spectroscopy absorption and Attenuated Total Reflection (ATR). An emichment of the surface layers of polymers by siloxane phase was found, that may be useful in the design of the chemical structure of adhesive materials for different purposes. 

Prepared generally by ester interchange from polyvinylacelate (ethanoate) using methanol and base also formed by hydrolysis of the acetate by NaOH and water. The properties of the poly(vinyl alcohol) depend upon the structure of the original polyvinyl acetate. Forms copolymers. Used as a size in the textile industry, in aqueous adhesives, in the production of polyvinyl acetates (e.g. butynal) for safety glasses. U.S. production 1980... 

Returning to more surface chemical considerations, most literature discussions that relate adhesion to work of adhesion or to contact angle deal with surface free energy quantities. It has been pointed out that structural distortions are generally present in adsorbed layers and must be present if bulk liquid adsorbate forms a finite contact angle with the substrate (see Ref. 115). Thus both the entropy and the energy of adsorption are important (relative to bulk liquid). The... 

Table 1. Chemical Structures of Constituents of Principal Wood Adhesives...

Cathodic protection of reinforcing steel with impressed current is a relatively new protection method. It was used experimentally at the end of the 1950s [21,22] for renovating steel-reinforced concrete structures damaged by corrosion, but not pursued further because of a lack of suitable anode materials so that driving voltages of 15 to 200 V had to be applied. Also, from previous experience [23-26], loss of adhesion between the steel and concrete due to cathodic alkalinity [see Eqs. (2-17) and (2-19)] was feared, which discouraged further technical development. 

Chothia, C. Jones, E.Y. The molecular structure of cell adhesion molecules. Annu. Rev. Biochem. 66 823-862, 1997. 

Other topics recently studied by XPS include the effects of thermal treatment on the morphology and adhesion of the interface between Au and the polymer trimethylcy-clohexane-polycarbonate [2.72] the composition of the surfaces and interfaces of plasma-modified Cu-PTFE and Au-PTFE, and the surface structure and the improvement of adhesion [2.73] the influence of excimer laser irradiation of the polymer on the adhesion of metallic overlayers [2.74] and the behavior of the Co-rich binder phase of WC-Co hard metal and diamond deposition on it [2.75]. 

Rider and Amott were able to produce notable improvements in bond durability in comparison with simple abrasion pre-treatments. In some cases, the pretreatment improved joint durability to the level observed with the phosphoric acid anodizing process. The development of aluminum platelet structure in the outer film region combined with the hydrolytic stability of adhesive bonds made to the epoxy silane appear to be critical in developing the bond durability observed. XPS was particularly useful in determining the composition of fracture surfaces after failure as a function of boiling-water treatment time. A key feature of the treatment is that the adherend surface prepared in the boiling water be treated by the silane solution directly afterwards. Given the adherend is still wet before immersion in silane solution, the potential for atmospheric contamination is avoided. Rider and Amott have previously shown that such exposure is detrimental to bond durability. 

The primary challenge facing adhesive bonding of metals is to obtain sufficient durability of a bonded structure. Initial bond strength in metal-polymer adhesive joints is almost invariably excellent. Challenging the application of adhesives in polymer-polymer joining, however, is the problem of obtaining a joint that is... 

Polymers containing long alkyl side chains, typically between 16 and 22 carbon atoms in length, have been used extensively as low adhesion backsizes for PSA tape products for many years. The general structure of such polymers is shown schematically in Fig. 8. The alkyl side chains are attached through a bridging group, R, to the polymer backbone, and the backbone may contain comonomers,... 

The structure of the isobutylene-derived polymers is hydrocarbonaceous and is non-polar, so poor adhesion to many surfaces is obtained. The addition of polar resins may improve adhesion. 

This chapter first reviews the general structures and properties of silicone polymers. It goes on to describe the crosslinking chemistry and the properties of the crosslinked networks. The promotion of both adhesive and cohesive strength is then discussed. The build up of adhesion and the loss of adhesive strength are explained in the light of the fundamental theories of adhesion. The final section of the chapter illustrates the use of silicones in various adhesion applications and leads to the design of specific adhesive and sealant products. 

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