Toward an Optimized Dynamic Headspace Method for the Study of Volatiles in Low-Density Polyethylene

Abstract

A dynamic headspace technique for detecting C6−C14 volatile organic compounds (VOCs) in low-density polyethylene (LDPE) is discussed in which VOCs are purged with N2, trapped at ambient temperatures on Tenax-GC, and identified by gas chromatography/mass spectrometry. The experimental variables are quantitatively modeled to enhance sensitivity of the technique. The rate of extraction of VOCs from LDPE and the rate of isothermal desorption of VOCs from Tenax-GC are first-order processes with rate constants of 2.79 × 10-5 and 1.53 × 10-3 s-1 respectively. Approximately 4.2% of extractable VOCs are present in the vapor phase at ambient temperature, and 21% of VOCs are liberated instantaneously from Tenax-GC during thermal desorption at 200 °C. The chromatographic peak area associated with each VOC, and the total peak area in the chromatographic window, vary with desorption temperature in accordance with the van't Hoff isochore with an “average” desorption enthalpy of 45.5 kJ mol-1. Keywords: Low-density polye...