Ecological hybrid pigments with improved thermal, light, and chemical stability based on purpurin dye and different minerals for applications in polymer materials

Abstract

A facile and cost-effective route was developed for the production of high-performance hybrid pigments by the stabilization of the natural red dye (purpurin) on mineral supports. For the first time, hydrotalcite (LDH), sepiolite (SEP), and aluminum-magnesium hydroxycarbonate (LH30) with different chemical compositions and structures were used as inorganic supports for purpurin. The physico-chemical properties of the prepared pigments were characterized by time-of-flight secondary ion mass spectrometry (ToF-SIMS), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), color measurements, release kinetic experiments, and thermogravimetric analysis (TGA). Purpurin molecules were confirmed to have been successfully incorporated into the inorganic supports via interactions between the purpurin chromophore and Mg2+, Zn2+ and/or Al3+ ions from the mineral host. The interactions resulted in hybrid pigments with higher thermal stability and lower tendency to migrate, without changing the morphology of the minerals. The hybrid pigments were applied as new colorants for ethylene-norbornene copolymer. The polymer composites were subjected to long-term UV irradiation followed by color and mechanical measurements. The results suggest that purpurin-based hybrid pigments can act as durable and effective colorants. This work provides a novel approach for preparing stable and multifunctional hybrid pigments based on natural dyes and mineral supports.