Study on the pyrolysis characteristics and reaction mechanisms of WLED packaging materials

The waste light-emitting diode (WLED) is a new type waste electrical and electronic equipment (WEEE). The volume of waste WLEDs is huge and effective recycling and treatment have attracted widespread attention. However, it’s difficult to handle the WLED packaging materials in the recycling process because of the complex structure. Few studies have been conducted to analyze the efficient recycling of WLED packaging materials. In this study, the pyrolysis characteristics, pyrolysis kinetics and product composition of light-emitting diode (LED) packaging materials methyl phenyl silicon (MPS) were investigated using TG analysis, kinetic analysis, TG-FTIR analysis and Py-GC/MS analysis. Density functional theory (DFT) calculation was further combined to study the pyrolysis process of MPS. The TG analysis showed that the MPS pyrolysis was divided into two stages: 310–561 °C and 499–980 °C. The apparent activation energies of MPS pyrolysis were calculated by Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) methods to be 144.68–149.76 kJ·mol−1 (Stage I) and 95.99–105.47 kJ·mol−1 (Stage II), respectively. The pyrolysis kinetic reaction model of MPS was determined by the Coats-Redfern (CR) method: D1 for Stage I, C2 for Stage II. According to the TG-FTIR and Py-GC/MS analysis results, 8 major gaseous products in the MPS pyrolysis process were identified, including CO2, benzene, HCl, biphenyl, chlorobenzene, styrene, ethylbenzene and chlorodimethylphenylsilane. Finally, the formation mechanism of different pyrolysis products was determined by DFT calculation. The pyrolysis characteristics and pyrolysis mechanism of WLED packaging materials may be helpful for the optimization of WLEDs pyrolysis recycling process and the regulation of pyrolysis products.