Quantitative adhesion tests

In this test, small spots of the adhesive are placed onto a substrate. Surface preparation, application procedures, and curing conditions are to be as similar as possible to those used in the quantitative test and/or the actual adhesively bonded Joint. The adhesive spots are allowed to cure according to the manufacturers specifications. To test adhesion, this ASTM standard practice recommends the use of a thin stainless steel spatula or similar probe as a prying lever to assess the relative difficulty of removing the adhesive from the substrate. If the results are acceptable, standard quantitative adhesive test procedures can be used to obtain quantitative measurement of the adhesive s performance. 

FIGURE 8.19 Quantitative adhesion test configurations. (a)-(c) From Handbook of Thick Film... 

Some of the quantitative adhesion test configurations are illustrated in Fig. 8.19. These include shear, tensile, and various wire peel tests. The shear test (Fig. 8.19a) involves pulling a wire in a direction that is parallel to the substrate. The primary drawback of this test is... 

D Kondos, M Mayo. Quantitative adhesion testing of reactor and compounded TPOs n. Proceedings of the Fourth International Coatings for Plastics Symposium, Troy, MI, 2001. 

Adhesion tests can be broken into two categories qualitative and quantitative. They vary from a simple Scotch tape test to a complicated flyer tape test, which requires precision-machined specimens and a very expensive testing facility. Quantitative (such as peeling) tests have been developed for coatings on plastics (12), but not to the same extent for metal-to-metal systems. The quantitative testing systems in limited use, mainly in the electronics industry, are not commonly present in production plants but have been used to aid in process development. For quality control purposes, qualitative tests for metal-to-metal adhesion (13) are usually adequate. The adhesion of some plated metal parts is improved with baking for 1 to 4 h at relatively low (120 to 320°C) temperatures. 

A simple, but not very quantitative, hardness test has been used for hundreds of years— the fingernail indentation test. The indentation that a fingernail makes in the edge of an adhesive bond or in the body of a sealant can often be used as an approximate indication of hardness of the material. 

Even with good initial adhesion there was a loss of adhesion for concrete specimens exposed to regular or continuous wetting. Adhesion testing on the deformed surface of a rebar is difficult to perform quantitatively and there is some disagreement over whether the loss of adhesion when wet is permanent, fully or partially recovered if the bar dries out. Even if it is temporary, the bar is more susceptible to corrosion and under-film attack at defects while wet and once corrosion has started it will not recover adhesion. 

As noted in the preceding section, IGC is an excellent tool for measurements of surface properties and of acid base interaction potentials of macromolecular solids (2,10,16). In this section the importance of acid-base interactions relative to the adhesion of PUs is considered in greater detail. IGC has been applied to a series of PU adhesives and to selected polymer substrates, allowing quantitative measurements to be made of the acid/base (electron donor-acceptor) interaction parameters applicable to the surfaces of these materials. Acid base pair-interaction parameters for substrate/PU combinations have been calculated. The bond characteristics of polymer/PU combinations have been measured, in part by conventional lap-shear procedures and in part, by the more recent constrained blister detachment method [11, 12]. Possible relationships between bond properties and acid base interactions have been considered, and a comparison of the two adhesion tests has been made. 

As already noted, the adhesion test data suggests the existence of significant contributions to bond strengths from non-dispersion forces acting at the adhesive/ substrate interface. Indeed, quantitative correlations have been confirmed between I p and either of the two sets of adhesion performance results. A demonstration is given in Figure 7.9, using the more complete blister test data. The correlation coefficient for this linear plot is 0.982. 

As noted earlier and readily seen by the complexity of variables, adhesion testing is a very inexact science. Many tests have been devised in order to characterize the adhesion property. These include both qualitative and quantitative test methods. Examples of qualitative tests are the Scotch tape test and razor blade tests which certify that the adhesion exceeds some... 

There is no single test that will give a quantitative assessment of adhesion, and those which have been proposed all cause destruction of the test piece. It has already been stated that this property is dependent upon mechanical and chemical bonds between the enamel and the metal. One must, however, also consider the stresses set up at the interface and within the glass itself during cooling after fusion or after a delayed length of time. 

Measurement of tensile or shear stress is the most commonly used in vitro method to determine bioadhesion. All in vitro measurements provide a rank order of bioadhesive strength for a series of candidate polymers. Measurement of tensile strength involves quantitating the force required to break the adhesive bond between the test polymer... 

The results of semi-quantitative charge spreading tests suggests that the lateral conductance of polyimide-field oxide interfaces can be sufficiently low to permit reliable device operation. This topic must be addressed in the context of the overall processing of the interface, including any adhesion promoters used. 

Quantitative confirmation of this outcome was obtained by shear tests, for which specimens were prepared both with and without the primer, a steel strip being bonded over the grit by an epoxide adhesive and the test carried out after curing of the second adhesive. Adhesion strengths recorded for the grit and adhesive were as shown in Table VII. 

The success of the tap test depends on the skill and experience of the operator, the background noise level, and the type of structure. Some improvement in the tap test can be achieved by using a solenoid-operated hammer and a microphone pickup. The resulting electric signals can be analyzed on the basis of amplitude and frequency. However, the tap test, in its most successful mode, measures only the qualitative characteristics of the joint. It tells whether adhesive is in the joint or not, providing an acoustical path from substrate to substrate or it tells if the adhesive is undercured or filled with air, thereby causing a mechanically damped path for the acoustical signal. The tap test provides no quantitative information and no information about the presence and/or nature of a weak boundary layer. 

To determine quantitatively the rate of deslzlng of various sizing agents, the test procedure used on a laboratory scale was to pour enough starch solution on to evaporation dishes so that 0,2 to 1.0 g of dried size remained after evaporation of the water. Less than 0.2 g did not provide sufficient accuracy) more than 0.7 g resulted in a thick deposit that caused portions of film to break and flake off in pieces. With enzyme-degraded starch, which had less adhesive characteristics, a fine mesh metal screen was placed on the evaporation dish to serve as a binding agent. 

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