Pyrolysis of bulk molding compound: Mechanisms, products characterization, and recovery potential

Thermosetting composite materials pose challenges for recycling due to their complex composition and crosslinked structure. Moreover, energy recovery is hindered by the low calorific value of highly filled and flame-retarded composites. This study focuses on Bulk Molding Compound (BMC), a thermosetting composite based on Unsaturated Polyester Resin, reinforced with glass fibers, and using Aluminum Hydroxide as a flame retardant. Thermal degradation mechanisms of BMC were investigated using Thermogravimetric Analysis coupled with Fourier Transform Infrared Spectroscopy. A lab-scale pyrolysis test was also conducted to explore the recovery and potential applications of pyrolysis products. The pyrolysis process yielded oil (31 % by weight), gas (10 %), and solid residue (59 %). The oil phase contained a notable concentration of styrene (more than 40 %). Analysis of the pyrolysis gas revealed a composition primarily consisting of carbon dioxide, carbon monoxide, hydrogen, and lower hydrocarbons, with a Gross Calorific Value of 7.5 MJ/m3. Additionally, the solid residue obtained from pyrolysis presented opportunities for closed-loop recycling as filler in BMC, and as aggregate in the construction sector. The findings underscore pyrolysis as a promising approach for BMC waste management, offering opportunities for resource recovery.