Development of structured natural dyes for use into plastics

Abstract

This study aimed to identify whether natural dyes encapsulated in a silica matrix via the sol-gel process with the use of alkoxides (as described in INPI patent BR 10 2013 0219835) and subsequently injected into a polyvinyl chloride (PVC) matrix would preserve their original color characteristics after being subjected to Xenon-accelerated weathering (using the ASTM D4452-12 standard). A comparison was conducted of the same natural dyes - carmine, turmeric, indigo and annatto – with and without encapsulation, injected into the same PVC matrix. Color change measurements were made before the weathering test and after 126 h, 252 h, 378 h and 504 h in a Xenon weathering chamber using the ASTM D4459-12 standard. A non-encapsulated Tartrazine dye (INS 102, an azo dye) was used for comparison of the behavior of natural dyes vs. that of synthetic ones. The results pointed to a lack of discoloring protection for the encapsulated natural dyes, which lost saturation more severely than the non-encapsulated ones. It thus follows that some care is required during the encapsulation stages of natural dyes, such as careful dispersion of natural colorants and the inclusion of repeat stages for the encapsulation of the xerogel.