Evaluation of Model Compounds – Polypropylene Film Interactions by Fourier Transformed Infrared Spectroscopy (FTIR) Method
Résumé
The interactions of methyl esters, methyl ketones and aldehyde compounds with polypropylene (PP) film were investigated. PP film, placed on a glass vial, was immersed in aqueous solution containing a model flavour compound. After a determined time at 45°C, the PP film was analysed by Fourier transform infrared spectroscopy (FTIR), allowing us to follow the speed of sorption and to quantify its relative rate. For PP films, we observed that the sorption strongly depended on the structure of sorbed molecules. For each functional group of flavour compounds, the sorption increased as the carbon chain number increased. A linear chain of 12–14 carbons favours the sorption more than a linear chain of eight carbons. Concerning functions, the rate of sorption usually decreases from esters to ketones and to aldehydes. High sorption was observed for flavour compounds with a low difference of solubility parameter (SP) value between the film and flavour [(dpolymer − dflavour)2 value]. Furthermore, by using the proposed thermodynamic affinity concept, represented as the contribution of three interactive molecular forces [dispersion (dd), polar (dp) and hydrogen bonding (dh)] between two SP values of film and flavour, packaging materials with high flavour preservation against sorption can be designed. We have a good correlation between the kinetic sorption by FTIR and the SP concept.