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

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.

Long term stabilization of PE by the controlled release of a natural antioxidant from halloysite nanotubes

“…The goal was to study the dispersion and controlled release effect and not the development of an industrial package. All our studies on natural antioxidants showed that flavonoids usually are much more efficient than traditional phenolic antioxidants currently used in industrial practice [17][18][19][20].…”

“…The antioxidant effect of curcumin [17], quercetin [18] and dihydromyricetin [19] was studied in a Phillips type polyethylene in the presence of a phosphorous secondary stabilizer and the stabilization efficiency of all three exceeded considerably that of the synthetic phenolic antioxidant routinely used in large quantity in industrial practice. The efficiency of another natural antioxidant, silymarin, a flavonolignan compound with the same basic structure as quercetin proved to be much less efficient [20].…”

Puerarin, an efficient natural stabilizer for both polyethylene and polypropylene

“…A series of research results suggested that the effects of natural antioxidants in stabilizing of polyolefin come from the interaction of natural antioxidant and secondary antioxidant. [12,15,16,18] Thus, the interaction between puerarin and PEPQ was discussed in this section. For comparison, PE or PP modified with only PEPQ (PE-P 0 -P and PP-P 0 -P samlpes) and PE or PP modified with only puerarin (PE-P 1200 and PP-P 1200 samlpes) were prepared.…”

“…Quite a few of natural compounds derived from plants have been used as stabilizer for foods [3][4]5,6] and polymer. [7][8][9][10][11][12][13][14][15][16][17][18][19] Lignin that comes from cell walls of woods and grasses is a natural macromolecule polyphenol. PE mixed with a mass of lignin exhibited preferable thermooxidative stability and processing stability.…”

“…β-Carotene as the most important representatives of carotenoids [1] could improve the thermo-oxidative stability and processing stability of PE. [11] The application of quercetin, [12][13][14] rutin, [15] silymarin, [16] and curcumin [17,18] as thermo-oxidative and processing stabilizer for PE even at low concentrations has been proved by many investigators. Phytic acid mixed with PE and PP to improve their thermo-oxidative stability.…”