Natural antioxidants as melt stabilizers for PE: Comparison of silymarin and quercetin

Kirschweng, Balázs and Vörös, Benedek and Tátraaljai, Dóra and Zsuga, Miklós and Földes, Enikő and Pukánszky, Béla (2017) Natural antioxidants as melt stabilizers for PE: Comparison of silymarin and quercetin. EUROPEAN POLYMER JOURNAL, 90. pp. 456-466. ISSN 0014-3057

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Abstract

The stabilization effect of two flavonoid type natural antioxidants, silymarin (Si) and quercetin (Q), was compared in polyethylene (PE). Additive concentrations changed between 0 and 500 ppm in several steps and 1000 ppm Sandostab PEPQ phosphorus containing secondary stabilizer was also added to each compound. Stabilization efficiency was determined by changes in functional group (vinyl, residual PEPQ) content, melt flow rate (MFR), oxygen induction time (OIT), color and the consumption of the secondary antioxidant during multiple extrusions. The results showed that silymarin is a much less efficient stabilizer in polyethylene than quercetin. The consumption of vinyl groups is faster, melt flow rate and residual stability is smaller in its presence. Silymarin contains less active phenolic hydroxyls than quercetin, but comparison on equal molar basis also shows the inferiority of the compound. The difference can be partially explained by the larger bond dissociation enthalpies of the hydrogens in silymarin, but this antioxidant also accelerates the consumption of the phosphorous secondary stabilizer that must contribute to its smaller efficiency as well. DSC measurements indicate the interaction of the two compounds probably leading to the faster consumption of the phosphorous antioxidant and poor stabilization. Unlike quercetin and dihydromyricetin, the flavonoid type natural antioxidants studied earlier, silymarin is not a good candidate as stabilizer for practical applications.

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