Adhesive Properties of Important Materials

The basics and criteria for the selection of adhesives discussed in Chapter 8 refer, to a large extent, to process applications on an industrial scale. Experience shows that when choosing adhesives, users in the nonindustrial sector orientate themselves more on the bondable materials and their adhesive properties. For this reason, the following descriptions of the materials include information on the recommended or even not recommended adhesives with the respective justifications. In addition, it has to be mentioned that a large part of the explanations in Section 8.3 are of universal validity. 

---

In order to understand the widely varying physical properties and adhesion properties of urethanes, it is important to understand the different classes of urethane raw materials and their functions in urethane adhesives. In order to... 

The importance of adhesives lies in the fact that they allow for a combination of the properties of dissimilar materials. For example, a laminate of polyethylene, with its heat sealability and water resistance, is ideally combined with cellophane, a grease resistant material that accepts ink printing, for packaging applications. 

Important factors regarding incoming adherends are the chemical and physical properties of the material. This can be especially important with adhesive bonding because different metal alloys have different surface oxidation, and different elastomers and plastics can have different additives and modifiers. With elastomeric and plastic substrates, lot-to-lot differences should be tested. Often a supplier will change formulations but still be within the requirements of the specification. The difference in formulation may have a profound effect on the quality of the ultimate adhesive bond. 

The backing material and release liner can be fabricated from a variety of materials including polyvinylchloride, polyethylene, polypropylene, ethylene-vinyl acetate and aluminium foil. The most important property of these materials is that they are impervious to both drug and formulation excipients. The most useful backing materials conform with the skin and provide a balanced resistance to transepidermal water loss, which will allow some hydration of the stratum corneum, yet maintain a healthy subpatch environment. The release liners are usually films or coated papers and must separate easily from the adhesive layer without lifting off any of the pressure-sensitive adhesive. Silicone release coatings are used with acrylate and rubber-based adhesive systems, and fluorocarbon coatings with silicone adhesives. 

These results indicate that if the cellular adhesion to a material is to be related to the properties of that material, then it is important to remove the air nuclei from the surface roughness of the material. Otherwise, the air nuclei can dominate the interaction between blood and the material. Further, the immediate question that is raised when these results are considered is how can gas nuclei bring about such a... 

Surface tension is an important determinant of the surface and adhesion properties of polymers. In both solids and liquids, the forces associated with molecules inside the material are balanced because each molecule is surrounded on all sides by like molecules. On the other hand, molecules at the surface are not completely surrounded by the same type of molecules, generating unbalanced forces. There-... 

---