Page 513 - Carrahers_Polymer_Chemistry,_Eighth_Edition

476 Carraher’s Polymer Chemistry

TABLE 13.6
Particle Size and Distribution Determination Techniques
Capillary hydrodynamic chromatography Field fl ow fractionation
Fraunhofer diffraction Light obscuration
Light-scattering photometry Microscopy
Phase Doppler anemometry Sedimentation
Ultrasonic spectroscopy

13.14 MEASUREMENT OF ADHESION
Adhesion is the binding of two surfaces where they are held together by primary and/or secondary
bonding forces. A discussion of the types of adhesives is given in Section 18.10. A discussion of sur-
face analysis is given in Sections 13.2 and 13.3. Here we will look at the mechanical measurement
of adhesion. As with all of polymer testing, the conditions of testing are important and experiments

and experimental conditions should be chosen to reflect the particular conditions and operating
conditions under which the material may be subjected to. During the fracture of adhered surfaces,
the bonded surfaces and adhesive are both deformed.
Failure can be affected through a variety of mechanisms. The major mechanisms are through
peeling, shearing, and detachment.
In peel separation, the adhesive simply “peels” away from the surface. Lap shear occurs when the
adhered material is subjected to a force that is applied parallel to the bonding plane. Here the bond
becomes deformed and stretched after initial rupture of some portion of the bond. It is a “sliding”
type of failure. In tensile detachment, bond disruption occurs as force is applied at right angles to
the bonding surface. Tensile detachment is a “ripping” type of bond disruption.
Scratch Testing—Often some type of “scratch” testing can be used to measure adhesion of

thin films. Fingernail and pencil tip results are often used as a first measure of adhesion. Thus,

a person presses their fingernail against the adhered surface watching to see if the adhesive is
removed from the surface. Even in more complex scratch tests, such tests create both elastic
and plastic deformations around the probe tip. The critical load for adhesion failure depends
on the interfacial adhesion and on the mechanical properties of the adhesive. Today, there exist
techniques that give better measures of adhesion. In the microimpact test, the test probe contin-
uously impacts the adhesive along the wear track. This allows the effects of impacts adjacent to

prior impacts to be studied, allowing the influence of large area damage near the impact to be
studied.
Peel Testing—Peel angle is important with 180º and 90º peel angles being the most common. In
general, a small amount of the adhesive is “peeled” away and the force necessary to continue the
peel measured.
Tensile Detachment Testing—A simple description of tensile tests involves attaching two thick
microscope slides to one another so the slides are at right angles to one another. After the bond is
allowed to set up a desired amount, the ends of the top microscope are attached to the measuring
device and the ends of the second, bottom, slide are attached to a load-bearing segment of the appa-

ratus. Eventually, deformation and finally bond breakage occurs as the load is increased.
Lap Shear Testing—Shear can be applied in a number of ways—cyclic, intermittent, static (or con-
stant), or increasing. A simple overlap shear test is described in ASTM-D-1002. This can be illustrated
again using two strong microscope slides. Here, the microscope slides are adhered in parallel to one
another except off-set. After the appropriate setup time, the top and bottom of the slide combination
are attached to the shear tensile measuring device and the experiment carried out (Figure 13.9).

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