Polyethylene comonomer characterization by using FTIR and a multivariate classification technique.

Many polyethylene (PE) films used in various packaging applications are based on multi-layer systems and are fabricated by using the coextrusion techniques that can combine different raw materials. The identification of the comonomer type (octene - C8 , hexene - C6 and butene - C4 ) in films, where two or more different linear low density polyethylene (LLDPE) resins are present, is becoming a frequent request. This report presents a novel approach where multivariate classification techniques are used in combination with FTIR for the identification of the comonomer type in coextruded films. A set of different LLDPE coextruded samples have been measured by FTIR, and the resulting spectra processed by Principal Component Analysis (PCA). By projecting the samples to the scores plots a difference is observed as a function of comonomer composition. This approach, compared with others is much faster, as just the time of measuring a film by direct infrared analysis is required.