Release Behavior of Liquid Crystal Monomers from Waste Smartphone Screens: Occurrence, Distribution, and Mechanistic Modeling

Abstract

Liquid crystal display (LCD) screens can release many organic pollutants into the indoor environment, including liquid crystal monomers (LCMs), which have been proposed as a novel class of emerging pollutants. Knowing the release pathways and mechanisms of LCMs from various components of LCD screens is important to accurately assess the LCM release and reveal their environmental transport behavior and fate in the ambient environment. A total of 47, 43, and 33 out of 64 target LCMs were detected in three disassembled parts of waste smartphone screens, including the LCM layer (LL), light guide plate (LGP), and screen protector (SP), respectively. Correlation analysis confirmed LL was the source of LCMs detected in LGP and SP. The emission factors of LCMs from waste screen, SP, and LGP parts were estimated as 2.38 × 10–3, 1.36 × 10–3, and 1.02 × 10–3, respectively. A mechanism model was developed to describe the release behaviors of LCMs from waste screens, where three characteristics parameters of released LCMs, including average mass proportion (AP), predicted subcooled vapor pressures (P L), and octanol–air partitioning coefficients (K oa), involving coexistence of absorption and adsorption mechanisms, could control the diffusion-partitioning. The released LCMs in LGP could reach diffusion-partition equilibrium more quickly than those in SP, indicating that LCM release could be mainly governed through SP diffusions.

Concentrations, Profiles, and Potential Sources of Liquid Crystal Monomers in Residential Indoor Dust from the United States

“…It is likely that emission rates of LCMs from LCDs can vary depending on the electronic products. Screen size, type of LCM and their diffusion kinetics, and the type of screen protector can play a major role in the emission of these chemicals from LCDs . The concentrations of ∑LCMs in indoor dust from households with vinyl and wooden flooring were significantly lower than those of carpeted ones (Table S8; p < 0.05, Mann–Whitney U test).…”

“…Other studies have reported that M-PCH–CCHB, E-MPEB, and CN-PPTP can arise from smartphone screens, reflecting variation in the composition of LCMs among different manufacturers, models, and production time. , Among F-LCMs, FPP-BCHC, (trans,trans)-3,4,5-trifluorophenyl 4′-ethyl-[1,1′-bi­(cyclohexane)]-4-carboxylate (TTFC-EBC), 3,4,5-trifluorophenyl 4′-propyl-[1,1′-bi­(cyclohexane)]-4-carboxylate (TrFPrBC), FPeBC, TFPrBCB, 1-butoxy-2,3-difluoro-4-(trans-4-propylcyclohexyl)­benzene (BDFPrCB), and trans-4-(4-fluorophenyl)-4′-propyl-1,1′-bi­(cyclohexane) (FPPrBC) were found in dust but not in electronic displays analyzed in our study. Studies have reported that TFPrBCB and FPPrBC originate from television displays and BDFPrCB from smartphones . LCMs are used as a mixture of several analogues in digital displays.…”

“…Liquid crystal monomers (LCMs) are synthetic chemicals, generally characterized by a biphenyl or cyclohexane skeleton with a possible halogen substitution and are increasingly used in liquid crystal displays (LCDs) of electronic/electric devices . LCMs can be categorized based on structure and function as biphenyl analogues (BAs), cyanobiphenyl analogues (CBAs), and fluorinated biphenyl analogues (FBAs), based on functional groups such as olefinic, ester-based, biphenyl, and acetylenic compounds, or based on their fluorine content as nonfluorinated (NF-LCMs) and fluorinated LCMs (F-LCMs) . Fluorine enhances stability, reduces viscosity, and improves electro-optical properties of LCMs .…”

“…Fluorine enhances stability, reduces viscosity, and improves electro-optical properties of LCMs . F-LCMs are more prevalent than NF-LCMs in the LCD panels of televisions (TVs), smartphones, and computers. , Applications of LCMs have evolved rapidly due to their significance in altering digital display technology in electronic devices. − The global production of organic light emitting diode (OLED) and LCD is forecasted to reach 450 million m 2 in 2025 . Disposal of electric and electronic waste, including screens and monitors, can be a major source of environmental release of LCMs.…”

“…1 LCMs can be categorized based on structure and function as biphenyl analogues (BAs), cyanobiphenyl analogues (CBAs), and fluorinated biphenyl analogues (FBAs), 2 based on functional groups such as olefinic, ester-based, biphenyl, and acetylenic compounds, 3 or based on their fluorine content as nonfluorinated (NF-LCMs) and fluorinated LCMs (F-LCMs). 4 Fluorine enhances stability, reduces viscosity, and improves electro-optical properties of LCMs. 5 F-LCMs are more prevalent than NF-LCMs in the LCD panels of televisions (TVs), smartphones, and computers.…”