Conversion of Waste Expanded Polystyrene into Blue-Emitting Polymer Film for Light-Emitting Diode Applications

The wide range of applications and continuous demand for plastics is causing serious global environmental problems. Massive discharges of expanded polystyrene (EPS) are thought to be primarily responsible for the increased white pollution. Waste EPS has received wide attention in the development of innovative products. White light-emitting diodes pumped by a near-UV chip (n-UV WLEDs) are regarded as a very promising solid-state lighting. The performance of the n-UV WLED is largely determined by the properties of the tricolor luminescence materials. In this work, a blue-emitting polymer film for n-UV WLED applications was developed from waste EPS. First, using waste EPS as a raw material, benzimidazole groups were bonded to PS benzene rings by chemical reactions to obtain modified PS (PS-PBI). Then, a film based on PS-PBI was prepared by a simple solution drop-casting method. The PS-PBI film can emit intense blue light when irradiated with 365 nm light. An n-UV WLED pumped by a 365 nm UV chip was fabricated using PS-PBI film as the blue-emitting layer. The fabricated n-UV WLED shows excellent luminescence properties, such as a bright white light with color coordinates of (0.337, 0.331), a relatively low color temperature (CCT, 5270 K), and an especially high color rendering index (CRI, 93.6). The results prove that the blue-emitting PS-PBI film prepared from waste EPS is a very promising candidate for n-UV WLED applications. The strategy of converting waste EPS into a high-value-added blue-emitting film in this work provides a convenient and feasible approach for upcycling waste EPS, achieving significant environmental and economic benefits.