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Pyrolytic appraisal of a green coloured plastic.

AutorGonzález-Pérez, José Antonio ; Jiménez Morillo, N. T. ; Rosa Arranz, José M. de la ; Almendros Martín, Gonzalo ; González-Vila, Francisco Javier
Fecha de publicación19-may-2014
EditorUniversity of Aston in Birmingham
Citación20th International Symposium on Analytical and Applied Pyrolysis, Birmingham, UK, 19-23 May 2014
ResumenThe chemical structure of a low-density green polyethylene was studied in detail using conventional analytical pyrolysis (Py-GC/MS), bulk C, N, H, O isotopic ratio (TC/EA-IRMS) and compound specific isotope analysis (CSIA) of stable light elements C, N, and H (Py-GC-(FID)-C/TC-IRMS). Py-GC/MS: a series of n-alkane, ¿-alkene and ¿,¿-diene (C8 to C37 chain length) were released. A peak at c. min. 6 was identified as o-Chloroaniline (1-Amino-2-chlorobenzene) corresponding to the plastic¿s green dye. Bulk plastic isotopic values (TC/EA-IRMS) were ¿13C=-30.16±0.60 ¿, ¿2H=-79.23±0.28 ¿ and ¿18O= +15.33±0.59 ¿; ¿15N was not detected due to a relative low signal contribution from the sole N bearing compound o-Chloroaniline. Py-GC-(FID)-C-IRMS confirmed a similar ¿13C (-30.13±0.60 ¿) for the three homologous series (¿,¿-diene -29.48±0.69 ¿; ¿-alkene -29.86±0.36 ¿; n-alkane -30.26±0.54 ¿) but different from that of o-Choloroaniline (-27.13±0.56 ¿). Only for this molecule ¿15N could be measured (+21.87±1.97 ¿). These signatures are in line with tabulated values for synthetic materials but indicate that polyolefin and dye are probably from two distinct origins. Py-GC-(FID)-TC-IRMS in the range where it was possible to unambiguously measure isotope ratio (no co-elution zone between C12 and C19) significantly different compound specific ¿2H values were obtained for the three structures (¿,¿-diene -67.38±2.98 ¿; ¿-alkene -74.74±1.50 ¿; n-alkane -98.87±5.40 ¿). A significant enrichment in the heavy isotope with chain length was observed for n-alkanes, best explained by the quadratic equation ¿2H=0.59Cx2 -16.38Cx+11.01 (r2=0.959). This phenomenon is discussed and explained as a dual effect derived from a) a dilution effect with an increasing chain length and b) double bond resonance from a carbanion (C-) that is produced by scissions in tertiary C and that may behaves as a concentrator of the heavy (2H) isotope. This finding has to be taken into account when measuring compound specific ¿2H in polymeric materials using the hyphenated Py-GC-TC-IRMS technique.
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