Block copolymers as dispersants and migration inhibitors: incorporation of fluorescent dyes in polyethylene

The problem of dye migration in PE which is of importance for coating and packaging applications was examined with fluorescent colorant C.I. Solvent Yellow 43 as a model of fluorescent dye poorly soluble in PE. These types of dyes are soluble in the PE melt, they show however a strong tendency to crystallize on cooling and to migrate on the surface giving rise to the typical blooming effect. It could be demonstrated by different migration tests that on addition of P(EB)-b-PEO or SEBS block copolymers, having one sequence selectively miscible with PE, the other with the dye, prevent to a very large extent the dye migration and thus its surface crystallization (blooming). This improvement is attributed to the formation, in the PE amorphous phase, of PEO and PS microdomains respectively that are able to solubilize selectively the dye. By fluorescence spectroscopy it could be demonstrated that the dye is selectively solubilized in the PEO microdomains of the P(EB)-b-PEO block copolymer, as well for micelles formed in heptane, as for the blends with PE.