Abstract
Studies of high temperature oxidation of polyethylene are not much present in the literature though it can really be a problem especially in polymer production and processing. This study aims to detect oxidation flaws in polyethylene and to determine their impact on polymer structure and properties. Besides, we suggest a method via PLS-regression to determine the degree of flaws that can occur during polymer processing due to oxidation. Several kinds of oxidation flaws were reproduced in laboratory at 150°C in an oven operating in air and Raman spectroscopy analysis was performed on each sample. Using statistical tools as chemometrics on these spectra, we have built a Partial Least Square (PLS) model able to predict the oxidation degree of flaws. Interpretation of the model construction and further characterization tests show that oxidation can be followed with the evolution of the crystalline carbon group and of the created carbonyl functions. Finally we suggest possible mechanisms which can explain the high temperature oxidation process in LPDE, and we link them to the modification of the material properties.
Highlights
Low-density polyethylene (LDPE) is the most popular used thermoplastic polymer in the world, with a wide range of applications, in flexible packaging
By combining Raman spectroscopy and chemometrics, this study aims to suggest a method to determine the amount of flaws due to oxidation occurring during polymer processing
The prediction of the oxidation time was based both on the measurement of Raman spectra on the surface of the disk samples oxidized during different times and on the realistic assumption that oxidation along the “polymer cake” thickness can be related to the oxidation time
Summary
Low-density polyethylene (LDPE) is the most popular used thermoplastic polymer in the world, with a wide range of applications, in flexible packaging. LDPE is usually produced by high-pressure radical polymerization. In this process, two kinds of flaws can occur during polymerization and are problematic for LDPE manufactures. The so-called “molten flaws” consist of a mix of two kinds of polymers with different Melt Flow Index (MFI). This is not a real problem if they are present in small quantities because most of the time they will melt and disappear during polymer processing. The “unmolten flaws” such as cross-linking or oxidation affect the polymer structure The presence of these flaws during production will lead to a real weakness for polymer processing. By combining Raman spectroscopy and chemometrics, this study aims to suggest a method to determine the amount of flaws due to oxidation occurring during polymer processing
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