Solvent-borne Bonding Systems

Bonding agents can be clear solutions but they are frequently suspensions of solids in polymeric solutions. In order to use the products full homogenisation is required. 

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Figures 3.15, 3.16 and 3.17 show two NR compounds, an SBR and an NBR bonded with solvent-borne Chemosils 211/220, a hybrid solvent-borne primer Chemosil 211 with waterborne top coat Chemosil XW7484 and a waterborne system of Chemosil XW1180 primer and XW7484 top coat. Boiling water tests (95 - 98 °C for 2 hours) show 100% rubber retention in all cases (see Figure 3.19).

One-component water-borne polyurethane systems can be derived from polyurethane dispersions or blocked polyisocyanates (refer to Section 3.2.1). Blocked isocyanates are added to the co-reactant resins providing one-component systems with excellent shelf life. This type of adhesives is principally used for non-porous materials and the bonding of unlike metals such as aluminium to steel, and stainless steel to mild steel. They are also usefiil in bonding some of the high pressure laminates such as those based on phenoUcs and melamine [39]. Systems based on water-borne blocked polyisocyanate crosslinkers and suitable waterborne polymers approach the performance levels previously obtained only by solvent-borne systems [16]. 

Currently, waterborne adhesives are being introduced into the shoe industry. Their performance is quite similar to that of the solvent-borne adhesives, so it can be estimated that for several years they will be used in shoe industry. However, the future seems to be directed through the use of moisture-curing holt-melt urethane and thermoplastic urethane adhesives as they are 100% solid reactive systems and evaporation of solvents is not necessary. Although hot-melt urethanes could replace solvent-borne adhesives, this could take longer to occur because of the vastly different equipment requirements and the change in bonding concept by the shoe manufacturers. 

In contrast to the subsystem representation, the adiabatic basis depends on the environmental coordinates. As such, one obtains a physically intuitive description in terms of classical trajectories along Born-Oppenheimer surfaces. A variety of systems have been studied using QCL dynamics in this basis. These include the reaction rate and the kinetic isotope effect of proton transfer in a polar condensed phase solvent and a cluster [29-33], vibrational energy relaxation of a hydrogen bonded complex in a polar liquid [34], photodissociation of F2 [35], dynamical analysis of vibrational frequency shifts in a Xe fluid [36], and the spin-boson model [37,38], which is of particular importance as exact quantum results are available for comparison. 

All three leading soft ionization techniques, FAB, ESI, and MALDI, are used for generating gas-phase ions of CyD inclusion complexes. However, there is still an open question about how accurately mass spectra reflect the solution-phase chemistry. There is no general answer to this question and each system has to be treated separately. A few helpful hints, however, have to be borne in mind. Polar interactions, such as hydrogen bonds and electrostatic attraction, are usually stronger in the gas phase than in solution, especially in polar solvents. Therefore, it is possible to observe some cluster ions in the gas phase which cannot be detected in solution. On the other hand, nonpolar interactions are usually weakened in the gas phase. Thus, some complexes that do exist in solution, as confirmed by spectral methods such as NMR spectroscopy (presented in Chapter 9), cannot be transferred to the gas phase without decomposition. Applying these rules to complexes of CyDs, the conclusion can be drawn that only complexes with relatively polar compounds can be observed in the gas phase [58, 60]. 

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