Hybrid kinetic analysis of FR-2 and FR-4 type printed circuit boards: A thermogravimetric analysis

This study investigated the non-isothermal (5, 10, and 20 °C/min) pyrolysis of non-metallic fractions (NMFs) of the FR-2 (phenolic resin reinforced with laminated paper) and FR-4 (epoxy resin reinforced with glass fiber) type waste printed circuit boards (WPCBs), under an inert atmosphere of flowing nitrogen gas. Three iso-conversional kinetic models (Friedman, Flyn-Wall–Ozawa (FWO), and Kissinger–Akahira–Sunose (KAS) approaches) were employed to understand the kinetics of the pyrolysis process. Thermogravimetric-differential thermogravimetric (TG-DTG) analysis revealed that FR-4 NMFs displayed a shift in mass loss above 287 °C at a heating rate of 10 °C/min and reached 95% conversion at 515 °C. In the case of the FR-2 NMFs, two distinct devolatilization zones were observed between 250–330 °C and 330–530 °C. The kinetic investigation revealed mean activation energy values of 264.38 kJ/mol for FR-2 and 221.99 kJ/mol for FR-4. The pyrolysis reaction mechanism for FR-2 NMFs displayed a decreasing trend for conversion (α), which was indicative of the simplified third-order model (F3) until α = 0.5 and shifted to second-order diffusion (D2) in the later part of the conversion. For FR-4 NMFs, the reaction function f(α) is between random nucleation with three nuclei on the individual particle (F3) and random nucleation with one nucleus on the individual particle (F1) over the selected range of conversion. For the FR-2 and FR-4 NMFs, the average ΔH values were 259.30 and 217.00 kJ/mol, and ΔG values were 161.03 and 176.92 kJ/mol, respectively.