Depth of cure profiling

Fig. 42. AES depth profiles of copper and sulfur (top) and zinc and oxygen (bottom) for the brass-on-glass adhesion specimens as a function of curing temperature. Reproduced by permission of Gordon and Breach Science Publishers from Ref. [46].

Figure 3.10. Depth profiles of curing conversion of an organic coating containing increasing concentrations of photoinitiator (PI), with fixed concentrations of light stabilizers (UYA and HALS).

In general, upon exposure to UV radiant energy, a photoinitiator can generate free radicals or ions, as pointed out earlier. These are generated at a rapid rate, and their depth profile corresponds to the inverse photon penetration profile. Similar to electron penetration, the final cure profile often deviates from the initial radical or ion distribution, since they can live much longer than the exposure time. The mechanisms of the processes for the generation of reactive species are discussed in detail in Davidson. ... 

The first objective was an in-depth study of the process of cure in the sample between the MDR dies, by considering not only heat transfer through the sample but also the heat generated by the overall cure reaction. Three various EPDM samples were selected with different percentages of peroxide ranging from 2 to 19%, associated with a cure enthalpy between 14 and 51 J/g. Another purpose was to evaluate the state of cure in the sample at various times, and thus profiles of temperature and of state of cure developed through the thickness of the rubber can be obtained at various times, especially associated with typical values of the torque (5, 50 and 95% of maximum torque). Comparison could be made between the values of the state of cure and the value of the torque. 

Increasing amounts of radiation curable materials are being used in coating films for the surface refinement of furniture, wooden floor coverings, paper, etc. Confocal Raman spectroscopy of UV-cured films may be used to examine depth or lateral profiles of the cross-linking process in coatings with a resolution of approximately 1 [549]. The... 

Radiation cross-linking of polyethylene requires considerably less overall energy and less space, and is faster, more efficient, and environmentally more acceptable. Chemically cross-linked PE contains chemicals, which are by-products of the curing system. These often have adverse effects on the dielectric properties and, in some cases, are simply not acceptable. The disadvantage of electron beam cross-linking is a more or less nonuniform dose distribution. This can happen particularly in thicker objects due to intrinsic dose-depth profiles of electron beams. Another problem can be a nonuniformity of rotation of cylindrical objects as they traverse a scanned electron beam. However, the mechanical properties often depend on the mean cross-link density. ... 

The sample is embedded in an uncured polymer resin, cured, then polished to the point of optical smoothness. Specular reflectance issues may complicate the images. The technique can be used for depth profiling and offers an alternative for samples that are difficult to microtome. The technique produces samples that can be imaged with multiple techniques. 

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