Abstract: The microstructural characterization of 47 samples, respectively of high density polyethylene (HDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), copolymer of ethylene and α-olefins, was performed by pyrolysis hydrogenation gas chromatography/mass spectrometry (Py-H-GC/MS) with 10% Pt on 80-100 mesh Diasolid H as a hydrogenation catalyst. The samples were obtained from 12 domestic plants and 12 plants abroad as well. The sample sizes ranging from 30 to 80 μg were pyrolyzed at 770 ℃ in a flow of hydrogen carrier gas. It was found that short methyl branches as the characteristic isoalkanes of pyrolysis hydrogenation in polyethylene would be related closely to the different classes of polyethylene. The microstructural characterization has been carried out by means of Py-H-GC/MS, according to the relative amount of the four short methyl branches, 5-methyldodecane (5-MC12), 4-methyldodecane (4-MC12), 2-methyldodecane (2-MC12) and 3-methyldodecane (3-MC12) existed in C12-C13 isoalkanes. The Py-H-GC/MS technique will be providing further scientific evidences for the characterization of polyethylene plastics in forensic science.

Key words: microstructural characterization, polyethylene , short methyl branches, pyrolysis hydrogenation gas chromatography/mass spectrometry (Py-H-GC/MS)