Surfaces and Adhesion

A more thorough discussion of the relationship between surface properties and adhesion is presented in Chapter 6. Here we present some basic concepts. 

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The seemingly simple question of the relation the characteristics of a mechanically prepared metal surface and adhesion to that surface has sporadically occupied attention for many decades without any very general conclusion being reached [69]. In some recent work, Amada et al. [70,71] grit-blasted a steel substrate, varying the angle between the gun and the specimen surface, and measured the adhesion of a plasma-sprayed alumina coating. They examined profiles of the... 

Naturally occurring fibers such as cotton, cellulose, etc., have short whiskers protruding from the surface, which help to give a physical bond when mixed with rubber. Glass, nylon, polyester, and rayon have smooth surfaces and adhesion of these fibers to the rubber matrix is comparatively poor. In addition, these synthetic fibers have chemically unreactive surfaces, which must be treated to enable a bond to form with the mbber. In general, the fibers are dipped in adhesives in the latex form and this technology is the most common one used for continuous fibers. The adhesion between elastomers and fibers was discussed by Kubo [128]. Hisaki et al. [129] and Kubo [130] proposed a... 

Bendinger, B., Rijnaarts, H. H. M., Altendorf, K. and Zehnder, A. J. B. (1993). Physicochemical cell-surface and adhesive properties of coryneform bacteria related to the presence and chain-length of mycolic acids, Appl. Environ. Microbiol., 59, 3973-3977. 

Adhesion between metallic/organic interfaces is facilitated by a combination of mechanical interlocking, chemical and physical bonding. Physical bonding alone cannot provide for durable, temperature resistant bonds, as van-der-Waals forces present between the metal surface and adhesive molecules are relatively weak. 

For a perfect bonding between lining surface and adhesive, the surface must be absolutely cleaned free of oil, grease and contaminants such as, rust, chemical deposits, etc. In order to eliminate the rust and the scales from old steel vessels meant for relining, sand blasting is carried out twice. This will also provide the required roughness to the surface to be lined. 

Zisman discovered that there is a critical surface tension characteristic of low-energy solids, such as plastics and waxes. Liquids ihat have a lower surface tension than the solid will spread on that solid, while liquids with a higher surface tension will not spread. Examples of critical surface tension values for plastic solids in dynes per cm are "Teflon/ 18 polyethylene, 31 polyethylene terephthalate, 43 and nylon, 42-46. As one indication of the way this information can be used in practical applications, one can consider the bonding of nylon to polyethylene. If nylon were applied as a melt to polyethylene, it would not wet the lower-energy polyethylene surface and adhesion would be poor. However, molten polyethylene would spread readily over solid nylon to provide a strong bond. 

Boundary layer Zone between adherends surface and adhesive layer where adhesion and bonding strengths are effective. 

Figure 6.3 Adhesive forces between adherend surface and adhesive layer.

Primers Substances enhancing adhesion between adherend surfaces and adhesive and delaying ageing processes. In contrast to adhesion promoters, primers are applied to the adherend surfaces. Adhesion promoters are usually admixed to the adhesive (q.v. adhesion promoter). 

Busscher HJ, Kaper HJ, Norde W. 2003. Characterization of poly(ethylene oxide) brushes on glass surfaces and adhesion of Staphylococcus epidermidis. J Biomater Sci Polym Ed 74 313-324. 

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-... 

Polyolefins belong to the most widely used class of polymers in many applications, such as in packaging, building, or transport industries. A combination of polyolefins with other materials can lead to an improvement of various properties. Many polyolefins belong among nonpolar polymers with low polarity and surface energy these polymers excel rather poor adhesion properties with various materials [1], and therefore, these polyolefins require the improvement of their surface and adhesive properties for many applications. In practice, the modification procedure selection for the improvement of the adhesion properties of diflerent polyolefins depends mostly on the required demands for the adhesive joints [2]. 

P. Blais, D.J. Carlsson, G.W. CsuUog, D.M. Wiles, Chromic acid etching of polyolefin surfaces and adhesive bonding. J. Colloid Interface Sci. 47, 36-649 (1974)... 

The surface and adhesive properties of iPP modified by UV radiation in the presence of POCI3 have been studied. Modification of iPP by UV/PCXZI3 results in an increase in surface energy of polymer as well as in an improvement of the mechanical work of adhesion of modified iPP to more polar polymers. 

Mikula, M. Jakubikova, Z. Zahoranov A. (2003). Surface and adhesion changes of atmospheric barrier discharge treated polypropylene in air and nitrogen. J. Adhes. Sci Technol, Vol. 17, p>p. 2097-2110 ISSN 0169 4243. 

The relation between Roughness of surfaces and adhesion is complex practical adhesion sometimes decreases, bnt may increase, as surface roughness gets greater (Adhesion - fundamental and practical). 

On the other hand, perfluorinated polymers likepoly(tetrafluoroethylene), (PTFE), as one of the most important examples, represent a polymer class which is in particular characterized by its special surface and adhesion properties. Perfluorinated segments in polymers often result in strongly nonpolar surfaces with reduced wettability of water or organic molecules, reduced adhesion and yielding, excellent gliding, and antisticking properties, and, in particular, chemical inertness [13,14]. 

Solutions of Polymeric Substances and Resins in Organic Solvents. A distinction is be drawn between adhesives that set by evaporation of the solvent and form an adhesive joint by adhesion of the dissolved polymer to the substrate surfaces, and adhesives for plastics, the solvent of which dissolves and swells the plastics surfaces and joins them by means of migration processes. This allows bonding of plastics that are otherwise difficult to join. The polymer solutes in solution adhesives act primarily as thickeners for establishing certain flow properties and retaining the solvent for the duration of the dissolution process. These solid components also may perform a limited gap-filling function. 

Adhesion failure break between substrate surface and adhesive (poor adhesion)... 

Further, the techniques of Scanning Electron Microscopy (SEM), Specular Reflectance Infrared Spectroscopy (SRIS), and Electron Spectroscopy for Chemical Analysis (ESCA) have proved complementary in this investigation of the relationships between adherend surfaces and adhesive properties. As SRIS results have shown the presence of adhesive on all fracture samples, ESCA and SEM results further clarified the nature of the fracture surface through the presence or absence of a Ti ESCA spectrum and the observation or lack of observation of the substrate structure in the SEM photomicrographs. It is concluded from the results of the three techniques that for the Set I samples, cohesive failure was noted for 219D2 whereas adhesive failure was noted for 220D3. Cohesive failure was noted for samples lm2-517 and lmp2-516 and adhesive failure was noted for 2m2-515 in Set II. 

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