Single-part adhesive systems

While the composition and sequence of the amino acids have been known since 1983 (2,3), methods for increased-scale extraction were not developed until 1985. This scaled production has allowed for the development of single-part adhesive systems (Cell-Tak adhesive) for the immobilization of biologically active moieties to inert substrates. It has also permitted research on two-part adhesive formulations for the bonding of tissues. This paper specifically addresses the biocompatibility issue with descriptions of the immobilization of cells to Cell-Tak protein-coated plasticware, methods for wound closure, and preliminary toxicology data. 

Epoxy-based systems are the most widely used structural adhesives. They are encountered everywhere in car manufacture, aircraft, building and construction industries, metal fabrication and the home. They are available as single-part and two-part. 

The second means of transforming a liquid adhesive entirely into a solid without the loss of a solvent or dispersion medium is to produce solidification by a chemical change rather than a physical one. Such reactive adhesives may be single-part materials that generally require heating or exposure to electron beam or UV or visible radiation (see Radiation-cured adhesives) to perform the reaction, and which may be solids (that must be melted before application), liquids or pastes. The alternative two-part systems require the reactants to be stored separately and mixed only shortly before application. The former class is exemplified by the fusible, but ultimately reactive, epoxide film adhesives and the latter by the two-pack Epoxide adhesives and Polyurethane adhesives and by the Toughened acrylic adhesives that cure by a free-radical Chain polymerization mechanism. 

Two-part systems Single-part, cured via catalyst or hardener Moisture-curing adhesives Radiation (hght, ultraviolet, election heam, etc.)-curing adhesives Adhesives catalyzed hy the substrate... 

Modified silanes (MS) are odourless, non-corrosive and do not contain isocyanates, solvents, silicones or PVC. They are normally available as single-component adhesive sealants (although two-part systems are also available) and require atmospheric moisture during the cure cycle. 

In essence, the durability of metal/adhesive joints is governed primarily by the combination of substrate, surface preparation, environmental exposure and choice of adhesive. As stated earlier, the choice of the two-part nitrile rubber modified epoxy system (Hughes Chem - PPG) was a fixed variable, meeting the requirement of initial joint strength and cure cycle and was not, at this time, examined as a reason for joint failure. Durability, as influenced by substrate, surface preparation, and environmental exposure were examined in this study using results obtained from accelerated exposure of single lap shear adhesive joints. 

Part-reacting the isocyanate and mixing in additional polyol in situ has the effect of reducing the viscosity and ease of handling of the adhesive in comparison with first-generation single component systems. Both components are normally liquid at room temperature and therefore these types of products can be processed at lower temperatures. They still contain 20-40% monomer but are of much lower viscosity and thus adhere well to a variety of substrates and have rapid cure rates. 

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