Figure 1a: Pyrogram of Polystyrene.

column setups were used for the purposes of this preliminary work, with both using Rxi-5ms (Restek, USA) non-polar primary columns (5% diphenyl / 95% dimethyl polysiloxane), and Rxi-17SilMS (Restek, USA) mid-polar secondary columns (50% phenyl / 50% dimethyl polysiloxane). Combinations used were 30m x 0.25mm x 0.25 µm or 60m x 0.25mm x 0.25 µm in the 1st dimensions and 0.8m x 0.25mm x 0.25 µm or 1.9m x 0.10mm x 0.10 µm in the 2nd dimensions, respectively. With the shorter length column set, GC oven temperature rate parameters were 50-300°C at 10°C/min (hold time 6min) with a 2nd oven offset of 15°C, and for the longer length column set, they were 40-250°C at 2°C/min (hold time 10min) with a 2nd oven offset of 5°C. GCxGC modulation frequencies of 1.5sec and 4.0sec were used respectively. In all cases helium carrier gas at 1.2mL/min in constant flow mode was used with split ratios of between 100 and 200. Representative 1D-GC data were acquired using the installed GCxGC column configurations by simply turning off the modulator. The TOFMS acquisition parameters were set to 12 spectra/sec for 1D

Figure 1b: Pyrogram (AIC and XIC overlaid) of Nylon 6.

analyses or 200 spectra/sec for 2D analyses, collecting full scan mass spectra between m/z 45 and 1000.

The transfer line and ion source temperatures were set to 280°C and 250°C respectively.

Results and Discussion

Reference materials were first analysed in 1D in order to create a library of polymer pyrolysis break-down products. The GC-MS data were processed with ChromaTOF® brand software (LECO) that includes deconvolution as part of the automated peak finding feature. Peak areas were calculated with the integration of a single m/z per analyte. Identifications were determined by spectral matching to the NIST library database [3] and additional retention index matching. The acquired pyrograms differ significantly in their complexity and the chemical nature of the polymer degradation products. Four polymers (PS, N6, PC, PMMA) generate simply a large peak of the monomer. An example of styrene and its associated dimer and trimer

from polystyrene are shown (Figure 1a). With N66, PET, and PVC, the main breakdown products of the pyrolysis process are small molecules instead of the monomers. For N66 the dominant pyrolyzate is cylopentanone as a degradation product of adipic acid (Figure 1b). In the case of PVC, benzene and hydrochloric acid (not detected with the MS method used) are the degradation products with the highest signal intensities.

Benzoic acid, benzene, and biphenyl are the three main pyrolysis products of PET. The pyrogram of PE shows a series of triplets in the range of C-8-C30 (Figure 1c). The scission process of the PE pyrolysis is well understood and described in the literature [4,5]. During pyrolysis the carbon backbone is broken, producing smaller hydrocarbons with terminal free radicals, which are stabilised either by hydrogen abstraction or beta scission. This process produces hydrocarbon molecules, which are saturated (n-alkanes), have one double bond (α-alkenes), or have a double bond at each end (α, ω -alkadienes). PP shows the most complex pyrogram of all investigated

Figure 1c: Pyrogram of Polyethylene with repeating units of triplets for each carbon number.

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