Release Rates of Condensables and Total Volatiles from Rapid Devolatilization of Polyethylene and Polystyrene*†a,b

Abstract

Abstract Batch samples (∼ 10mg) of 63-90μm polyethylene (PE) or polystyrene (PS) powders were rapidly pyrolyzed by healing at 1000°C/s, under helium (nominal pressure I atm), from room temperature to prescribed final (peak) temperatures between 400 and 800°C, whereupon natural cooling of the substrate by radiation and free convection, or forced cooling by inundation with cold nitrogen, was immediately instigated. Yields of total volatiles (total weight loss) and of “condensables” (tars + higher molecular weight volatilizable material) were each measured gravimelrically for systematic variations in peak temperature. Effects of initial particle size (63-90/vm powders and ∼-240jim thick sheets for PE; 63-90. 180-250, and 500-710 ;μm powders for PS), of PS molecular weight (2100 and 850,000 d), and of PE healing rate (100, 10,000°C/s with forced cooling) were also measured. At 1000°C/s. volatilization of 63-90/μm PE or PS particles approached 100% in about 0.7-0.8 s. Weight loss and condensables yields declined with increasing particle size. Weight loss increased and condensables yield declined with the stated increase in PS molecular weight. For 63-90 μm particles and a 1000°C/s heating rate, yields of condensables and total volatiles from either polymer were well correlated from 400-800°C by a multiple independent parallel reaction kinetics model. However, for higher healing rates and larger particle sizes (or beds with > 1 layer of 63-90μm or larger size particles), heat and mass transfer effects on the devolatilization chemistry will, in general, need to be modeled. For PS, effects of initial molecular weight must also be accounted for.