Expertise
Identification of additives used in the plastics Industry
Polymers are degraded by heat and light initiated oxidation to form radical fragments which then react further with other polymer chains. A manufacturer must counter this process by including UV absorbers and stabilisers in their polymer formulations. This additive package is essential for the successful performance of the polymer. Polymer additives include:
- UV absorbers to prevent photooxidation by absorbing photons which would otherwise create radicals.
- Long term thermal stabilisers including phenolic antioxidants to react with radicals.
- Processing stabilisers to decompose the hydroperoxide groups which are a major source of radicals.
- Plasticisers to modify the mechanical properties of the polymer
- Lubricants to aid processing see PFOS example
- Flame retardants
- Dyes
- Pigments and fillers
A polymer manufacturer requires analytical tools to identify these additives. Liquid chromatography-mass spectrometry (LC-MS) and Gas Chromatography (GC-MS) are the analytical techniques of choice for the analysis of all of the above additives (except pigments and fillers).
Intertek MSG offers a comprehensive analytical approach for the identification of polymer additives:
- The polymer is extracted using an appropriate solvent. The selection of the correct solvent for a particular polymer is essential for the successful extraction of polymer additives. Intertek MSG has huge experience in this area.
- The polymer extract is then analysed by LC-MS and GC-MS using Intertek MSG’s in-house database of 80 polymer additives in addition to the NIST 2008 library of GC-MS spectra (containing more than 191000 spectra).
There is a huge range of polymer additives with different chemical and physical propertites. LC-MS and GC-MS are complementary analytical techniques and their combined use maximises the chance of a successful analysis. LC-MS is better for high molecular weight and more polar additives. GC-MS is better for low molecular weight and less polar additives.
An LC-MS chromatogram of a polypropylene extract is shown below:
It can be seen from this chromatogram that the sample contains the additives, dioctylphthalate, Tinuvin 312, Irganox 1010 and Irgafos 168. Dioctylphthalate is a plasticiser, Tinuvin 312 is a UV absorber, Irganox 1010 is an antioxidant and Irgafos 168 is a processing stabiliser.
Intertek MSG also offers on-line pyrolysis-GC-MS of polymer chips as a quick, low cost procedure to get preliminary data on polymer additives. This technique does not have the comprehensive scope of the solvent extraction-LC-MS/GC-MS procedure which is described above.
Advice is available, so make the call +44 (0) 1642 435788 or email MSGenquiry@intertek.com
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