Thermochromic behavior of pigment red 254 in nylon 6 polymer for high-chromaticity engineering plastics

Advancement in Color-Material-Finishing (CMF) plays a crucial role in enhancing the visual appeal of plastic products, particularly for the high-chroma nylon plastics that are currently in vogue. However, it is inevitable to encounter pigment-dyeing issues in polar engineering plastics during the high-temperature extrusion process, which can lead to intense fluorescence and color fading. This phenomenon, characterized by the dissolution of pigments in a polar environment, can adversely affect the color saturation and weatherability of the pigment, which ultimately cause sharp reduction of aesthetic quality and durability of the plastic. Herein, we develop a modified strategy combined with thermal annealing to realize rapid color recovery in nylon 6, and further reveal the fluorescence and discoloration mechanism of pigment red 254 in nylon 6. Through improving the mobility of nylon chain segments, the rigid heterogeneous nucleation regions centered on the interfacial hydrogen bond between nylon 6 and the pigment molecules loosens with the help of heat treatment, and then the dissolved pigment molecules reaggregate to induce fluorescence quenching. Importantly, as a consequence of the increased lubricity segments, the required thermal annealing temperature and time for color recovery and fluorescence quenching could be significantly shortened from 180 °C for 5 h to 100 °C for 0.5 h. This work provides a feasible approach for the industrial production of high-chroma polar engineering plastics.