Adhesive bonding properties, contaminants

Sources of Contaminants or Species Which Could Affect Adhesive Bonding and Bond Properties... 

For many industrial applications of plastics that are dependent on adhesive bonding, cold gas plasma surface treatment has rapidly become the preferred industrial process. Plasma surface treatment, which is conducted in a vacuum environment, affords an opportunity to minimize or eliminate the barriers to adhesion through three distinct effects (1) removal of surface contaminants and weakly bound polymer layers, (2) enhancement of wettability through incorporation of functional or polar groups that facilitate spontaneous spreading of the adhesive or matrix resin, and (3) formation of functional groups on the surface that permit covalent bonding between the substrate and the adhesive or matrix resin. Since plasma treatment is a process of surface modification, the bulk properties of the material are retained. The nature of the process also allows precise control of the process parameters and ensures repeatability of the process in industrial applications. Finally, several studies have demonstrated that these surface modifications can be achieved with minimum impact on the environment. 

FIGURE 19.8. In summary, adhesive joint failure may be caused by a number of factors some not connected with the actual adhesive bond. A common source of problems is the presence of trapped air or other contaminants that serve as loci for failure at the interface (a). Perhaps less common, but of significance, is the presence of contaminants or flaws in the bulk of the adhesive (b) or in the substrate (c) that weaken the physical properties of that phase and lead to joint failure. 

An important difference between metals and plastics is in their surface energy. Polymers have inherently lower surface energy than metals (assuming they are contamination-free) and tend to form intrinsically poor adhesion bonds without some type of treatment. Treatment of plastics only impacts the region near the surface and does not alter the bulk properties of the parts. 

Lamination Inks. This class of ink is a specialized group. In addition to conforming to the constraints described for flexo and gravure inks, these inks must not interfere with the bond formed when two or more films, eg, polypropylene and polyethylene, are joined with the use of an adhesive in order to obtain a stmcture that provides resistance properties not found in a single film. Laminations are commonly used for food applications such as candy and food wrappers. Resins used to make this type of ink caimot, therefore, exhibit any tendency to retain solvent vapor after the print has dried. Residual solvent would contaminate the packaged product making the product unsalable. 

No reaction Contaminant layer determines bond strength Properties of adhesive-contaminant mixture determine bond strength ... 

The use of synthetic materials in biomedical applications has increased dramatically dining the past few decades. Surface properties of polymers are of fundamental importance in many branches of industrial applications (e.g., separation of gasses, liquid mixtures, bonding, coating, adhesion, etc.). Performances of membranes also depend on the properties of their surfaces, since membrane performance is strongly influenced by the surface phenomena. Hence, it is very natural that much attention has been paid to the membrane surface modification. Surface contamination which may lead to deterioration in membrane performance is also known to be governed by the membrane surface properties. Detailed methods for modification of synthetic membranes are discussed by Khulbe et al. [63]... 

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