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Photoinitiators (PIs) are used to absorb the light energy and generate the free radicals as shown in Figure 3.1, the initiation step. These initiators are added in the range of 1 to 12 % of the total formulation.

The initiation process occurs only during exposure of the material to UV energy. Since the existing free radicals have very short life spans, all of the propagation reactions also stop when the material is no longer under the UV energy source. Consequently, the final product’s properties are achieved immediately after removal from the UV energy source. Exposure to the UV can range from seconds to minutes.