TOWARD AN OPTIMIZED DYNAMIC HEADSPACE METHOD FOR THE STUDY OF VOLATILES IN LOW-DENSITY POLYETHYLENE

A dynamic headspace technique for detecting C-6-C-14 volatile organic compounds (VOCs) in low-density polyethylene (LDPE) is discussed in wh ich VOCs are purged with N-2, trapped at ambient temperatures on Tenax -GC, and identified by gas chromatography/mass spectrometry. The exper imental 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 process es with rate constants of 2.79 x 10(-5) and 1.53 x 10(-3) s(-1) respec tively. Approximately 4.2% of extractable VOCs are present in the vapo r phase at ambient temperature, and 21% of VOCs are liberated instanta neously from Tenax-GC during thermal desorption at 200 degrees 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'' desorpt ion enthalpy of 45.5 kJ mol(-1).