51313-02070-Use of FTIR Spectroscopy to Characterize Nitric Acid Oxidation of Polyethylene Grades

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Product Number: 51313-02070-SG

ISBN: 02070 2013 CP

Author: Margit Weltschev

Publication Date: 2013

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Resistance to oxidative degradation by nitric acid is one of the properties selected for the comparison of polyethylene grades in a European standard on suitability proof for alternative plastic resins used for packagings and intermediate bulk containers (IBCs) for the transport of dangerous goods.
Measurements of IR absorption spectra of microtome slices cut from the wall of jerricans which were pre-storage with 55 % and 70 % nitric acid for 21 and 28 days at 40 °C with the FTIR spectrometer showed the changes in the structure of the pol-yethylene grades.
The intensities of IR bands at 1565 cm 1 ( NO2) 1630 cm 1 ( C=C) and 1654 cm 1 ( O NO2) increased with rising treatment time with 55 % nitric acid as a result of the oxidative damage by the nitric acid. Therefore values of absorbance were used to compare the grades due to their resistance to oxidative degradation. The high increase of the absorbance of the ( C=C) band in the region 1630 1690 cm 1 is attributed to paraffinic chain cracks because of the acid impact associated with the appearance of (-C=C) bands. The absorbance of the ( O NO2) band formed as result of the nitration process is low at a temperature of 40 °C whereas the absorbance of the ( C=C) band is higher due to the splitting of the polyethylene paraffinic chains.
The penetration depths of 55 % nitric acid into the polyethylene grades measured with FTIR are basically suitable for the evaluation of the resistance to oxidative deg-radation of polyethylene grades.