Adhesives disadvantages

Adhesive Disadvantages. There are some limitations in using adhesives to form assemblies. The major limitation is that the adhesive joint is formed by means of surface attachment and is, therefore, sensitive to the substrate surface condition. Another limitation of adhesive bonding is the lack of a nondestructive quality control procedure. Finally, adhesive joining is still somewhat limited because most designers of assemblies are simply not familiar with the engineering characteristics of adhesives. 

Although insulators other than aluminum oxide have been tried, aluminum is still used almost universally because it is easy to evaporate and forms a limiting oxide layer of high uniformity. To be restricted, therefore, to adsorption of molecules on aluminum oxide might seem like a disadvantage of the technique, but aluminum oxide is very important in many technical fields. Many catalysts are supported on alumina in various forms, as are sensors, and in addition the properties of the oxide film on aluminum metal are of the greatest interest in adhesion and protection. 

Depth-sensing nanoindentation is one of the primary tools for nanomechanical mechanical properties measurements. Major advantages to this technique over AFM include (1) simultaneous measurement of force and displacement (2) perpendicular tip-sample approach and (3) well-modeled mechanics for dynamic measurements. Also, the ability to quantitatively infer contact area during force-displacement measurements provides a very useful approach to explore adhesion mechanics and models. Disadvantages relative to AFM include lower force resolution, as well as far lower spatial resolution, both from the larger tip radii employed and a lack of sample positioning and imaging capabilities provided by piezoelectric scanners. 

Advantages are similar to the epoxy system, in that these can be solventless and do not require thermal energy. Disadvantages unique to this system, however, include the need to inert the cure chamber to avoid air-inhibition of cure as well as some release instability with acrylate adhesives [72]. 

Although the acrylate adhesives are readily available and studies have shown that they can produce reasonable bonding properties, they have the disadvantages of having high shrinkage, high fluid absorption, and low service temperatures. Acrylate adhesive applications would be limited. The development of EB-curable epoxy adhesives would have applications in the aerospace and automotive industry and potential wider uses. The most immediate application for these resin systems is composite repair of commercial and military aircraft. 

Advantages and disadvantages of PMDI compared to other adhesives, especially UF-resins... 

Disadvantages higher price, which fact is partly diminished by the low adhesive consumptions and sometimes shorter press times... 

Compared to other adhesives PMDI shows various advantages, but also some disadvantages (Table 8). 

Plasticizers soften the film and increase the adhesion and the setting speed. The most common are phthalates, adipates and benzoates. The amount added can be in a broad range of 10-50%. They affect the swelling and softening of the PVAc emulsion particles, ensure film formation at room temperature, and the tack of the still wet adhesive. They also provide improved moisture resistance of the bond. Disadvantages are the lower resistance of the bond line against heat, possible migration of the plasticizers and enhanced cold flow. 

Fillers (calcium carbonate, calcium sulfate, aluminum oxide, bentonites, wood flour) increase the solid content of the dispersion. They are added up to 50%, based on PVAc. The purpose of the addition is the reduction of the penetration depth, provision of thixotropic behavior of the adhesive, gap filling properties and the reduction of the costs. Disadvantage can be the increase of the white point and a possible higher tool wear. 

Pt electrodeposits may also be produced from molten salt electrolytes. Such a high-temperature process has the advantage that the deposits are diffusion bonded to the titanium substrate and thus have good adhesion, and, if necessary, thick deposits can be produced. However, they have the disadvantage that because of the complexity of the process there is a limitation on the size and shape of the object to be plated, and the resultant deposits are softer and less wear resistant than those from aqueous solutions... 

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