Adhesives Aged surfaces

Gerace, M. J., and Gerace, J. M., Surface Activated Rubber Particles Improve Structural Adhesives, Adhesives Age, December 1995, pp. 26—31. 

Minford, J. D., Effect of Surface Preparation on Adhesive Bonding of Aluminum, Adhesives Age, July 1974. 

DeLollis, N. J., and Montoya, O., Surface Treatment for Difficult to Bond Plastics, Adhesives Age, January 1963. 

Pressure-sensitive or permanent-tack adhesives are, as their name implies, adhesives that remain sticky even when dried or cured. This means that they are capable of bonding to surfaces simply by the application of light pressure. This makes them arguably the most convenient products available today from the end user s viewpoint and undoubtedly, accounts for the success they enjoy. Although figures are hard to come by, a survey by Business Trend Analysts quoted in the June 1990 issue of Adhesives Age shows that pressure-sensitive adhesives grew from 38% of total adhesive sales in the United States in 1980 to 44.6% in 1988, at an annual rate of 12%, to reach a sales value of 4.9 billion in 1989. 

Marceau, J.A. et al. A wedge test for evaluating adhesive-bonded surface durability. Adhesives Age, October 1977, pp. 28-34. 

A review of the XPS results in Tables 2 and 3 suggests that for the lOV chromic acid anodized Ti 6-4 adherend, the high Ti surface concentration on the L13-10-50 adhesive failure surface (APS) thermally aged for 10,000 hr is associated with the lowest strength, it is proposed that long-term thermal aging of bonded lap shear samples weakens the surface oxide. The high Ti concentration observed on the L13-10-50 adhesive failure surface (APS) results from the fracture of the surface oxide layer. 

The fact that the adhesive failure surface (APS) of Sample No. PPQ-10-36 which had been aged similarly to Sample No. L13-10-50 does not give a significant Ti peak suggests a difference in the interaction of L13 and PPQ with the surface oxide layer. We have shown (7) such a difference in the heats of immersion of L13 and PPQ primer solutions with anatase titanium dioxide. 

J.D. Minford, "Effect of Surface Preparations on Stressed Aluminum Joints in Corrosive Saltwater Exposure," Adhesives Age, 2, No. 10, 36 (1980). 

Figure W.2 An illustration of good and poor wetting by an adhesives spreading over a surface. (Ref Schneberger, G.L., Chemical Aspects of Adhesives Bonding, Adhesives Age, March 1970)...

This washed surface was then allowed to age in air and we have measured again adhesion forces after 2 months (Fig. 6). The behaviour of this aged surface becomes again hydrophilic and is very similar to the one observed for the PP6s surface. It means that an outermost layer of Tinuvin 770 has reappeared on the surface. The additives contained in the bulk of the material have migrated toward the surface. The adhesion map obtained in water with a -CH3 tip (cf Fig. 8) shows a homogeneous distribution of low adhesion forces, i.e. of Tinuvin 770. 

W. D. Bascom and R. L. Patrick, "The Surface Chemistry of Bonding Metals with Polymer Adhesives", Adhesives Age, 17,... 

The objective of surface treating is to obtain a joint where the weakest link is the adhesive layer and not the interface. Thus, destructively tested joints should be examined for mode of failure. If failure is cohesive (within the adhesive layer or adherend), the surface treatment is the optimum for that particular combination of adherend, adhesive, and testing condition. However, it must be realized that specimens could exhibit cohesive failure initially and interfacial failure after aging. Both adhesive and surface preparations need to be tested with respect to the intended service enviroiunent. 

Devine, A. T., and M. J. Bodnar, Effects of Various Surface Treatments on Adhesive Bonding of Polyethylene, Adhesives Age, May 1969. 

SBR adhesives are used in applications where low stress but high flexibility and resistance to shock are needed. If ageing is critical, SBR adhesives should not be used. SBR adhesives have relatively low surface energy and therefore can be used as general-purpose adhesive to join several substrates. 

Thermal aging is another simple pretreatment process that can effectively improve adhesion properties of polymers. Polyethylene becomes wettable and bondable by exposing to a blast of hot ( 500°C) air [47]. Melt-extruded polyethylene gets oxidized and as a result, carbonyl, carboxyl, and hydroperoxide groups are introduced onto the surface [48]. 

The effect of thermal aging on polyethylene and isotactic polypropylene have been studied by Konar et al. [49]. They used contact angle, contact angle hysteresis, and XPS to characterize the modified surfaces of the polymers. Hysteresis increased with aging temperature. In the case of polyethylene, thermal aging led to a significant increase in adhesion strength of polyethylene with aluminium, but the increase in the case of polypropylene was much less marked. 

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