The differentiation of biodegradable and non-biodegradable polyethylene terephthalate (PET) samples by FTIR spectroscopy: A potential support for the structural differentiation of PET in environmental analysis

FTIR spectroscopy is usually applied for the analysis of plastics in environmental analysis as a support to the study of their effects on the aquatic living organisms. Here we present a further development of FTIR spectroscopy focused to the discrimination between biodegradable and non-biodegradable polyethylene terephthalate (PET). The FTIR spectra of conventional PET samples of different commercial and domestic uses, joint to certified biodegradable PET samples were included in a digital matrix and then submitted to principal component analysis (PCA). PCA, which explained the 89.1% of the total variance (first factor 84.1% and second factor 5.0% respectively), allowed a preliminary differentiation among non-biodegradable PET and certified biodegradable PET. This differentiation of PET was tested by means of two discriminant analysis methods, the Hotelling's T-2 test and the Mahalanobis distance, which confirmed the PCA results. A re-examination of the FTIR spectra, showed that the two absorption band ratios 898-973 cm(-1) and 1340-1370 cm(-1) are fundamental to discriminate biodegradable and non-biodegradable samples because these band ratios describe the crystalline and the amorphous characteristics of PET. The deconvolution of the -C=O group in the range between 1650 and 1800 cm(-1) and the application of two-dimensional correlation analysis (2DCOS) gave other support for PET discrimination because they showed other structural differences between biodegradable PET and non-biodegradable PET, related to the interactions among its the bands at 1740, 1250, 1120 and 1090 cm(-1). According to these results, it is our opinion that the discrimination between biodegradable and non-biodegradable PET evidenced by FTIR spectroscopy could be further investigated and extended to the analysis of PET present in the marine environment.