FTIR Imaging Coupled With Principal Component Analysis For Study Of Photooxidation Of Polyolefin

FTIR spectroscopic imaging is a visible tool for characterizing the distribution of different chemicals in heterogeneous materials.It is based on the combination of FTIR spectroscopy and bright field microscopy. Since one FTIR image is composed of hundreds or thousands of spectra, it is important to extract information from the original data set. Conventional approaches to explore images sacrifice much of information of the original massive data set. Principal component analysis (PCA) is a widely used chemometric tool and is applied to analyze the FTIR images. By analyzing the principal components (PCs) of the entire images, the spectral variance of the imaging area is described and some latent information is displayed.Polypropylene (PP) and polyethylene (PE) are widely used due to their versatile properties and low cost. They are subjected to oxidative degradation initiated by ultraviolet (UV) radiation when being used outdoor. In this work, the photooxidation of PP and PE are investigated by FTIR imaging coupled with PCA. The oxidized product varies from different photooxidized period of PP. Carboxylic acid is the major oxidized product in the initial period from 0 h to 8 h while ketone becomes the major one when the irradiation time is increased to 12 h. Carboxylic anhydride is identified for the first time in oxidized PP after 16 h irradiation. Carboxylate ester is also observed in the oxidized PP after 32 h irradiation.Possible mechanisms forming these products have been discussed. For PE, ketone is the major oxidized product and a little ester is observed after irradiating 23 hours.Photooxidation is preferred to occur on the surface and decreases from the surface to the interior. The steric inhomogeneity of photooxidation process of polyolefin is visualized using this imaging technique. Comparing with PP, PE is not easy to be photo-oxidized.