Melt stabilisation of Phillips type polyethylene, Part I: The role of phenolic and phosphorous antioxidants

et al. 2015

Self Cite

The stabilising efficiency of curcumin was studied in polyethylene during processing and under oxygen at high temperature. The effect of the natural antioxidant was investigated at concentrations of 0 to 1000 ppm in combination with a phosphonite secondary antioxidant (Sandostab P-EPQ) of 1000 and 2000 ppm, respectively. The polymer was homogenized with the additives then processed by six consecutive extrusions taking samples after each processing step. The samples were characterized by FT-IR spectroscopy, melt flow index, colour, and OIT measurements. Compared to the effect of pure phosphorous antioxidant, the melt stability of PE is increased already at 5 ppm curcumin content. The melt as well as the high temperature oxidative stability (OIT) of the polymer are controlled by both types of antioxidants. Curcumin hinders the oxidation of polyethylene and the formation of long chain branches during processing, which can be attributed to the fact that curcumin is not only a hydrogen donor but its unsaturated linear moiety can also scavenge alkyl and oxygen centred macroradicals. Curcumin discolours polyethylene already at small concentrations but the colour fades with increasing number of extrusions.Keywords: curcumin, natural antioxidant, polyethylene, stabilisation, phosphonite 3 IntroductionStabilisation of polyolefins with natural antioxidants got into the focus of attention recently because of the unknown effects of the reaction products of synthetic phenolic antioxidants on human health [1]. Health safety has vital importance in many application areas, like food contacting objects (e.g., packaging materials, water pipes), medical applications, toys, etc. The small molecular mass additives used in polyolefins for stabilisation, colouring, or antiblocking are generally polar compounds, therefore their solubility is small and migrate onto the surface of the polymer during application [2]. Their dissolution into contacting substances cannot be avoided but any harmful effect must be prevented.Among the natural antioxidants, first α-tocopherol was studied extensively for the stabilisation of polyolefins [e.g., 3-9]. Intensive research resulted in the application of α-tocopherol for the stabilisation of ultra high molecular mass polyethylene (UHMWPE) used as total joint implant [e.g., 10-15]. Even an ASTM standard specification was implemented for medical grade UHMWPE blended with vitamin E [16]. The study of different natural antioxidants in polymers has been widely extended lately. The goals of the investigations are mainly the improvement of the safety of packaging materials and the development of functional packaging [e.g., 17-25].Curcumin, 1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione, is the principal curcuminoid of Curcuma longa rhizomes (turmeric). The powdered root is used as a spice, food colorant, and food preservative. The effects and reactions of curcumin have been the subject of investigation in the fields of biology, medicine, pharmacology, and in the food industry yielding a la...

show abstract

Section: Resultssupporting

confidence: 68%

“…The concentration of the functional groups (unsaturated and carbonyl) of polyethylene and the residual concentration of the phosphorous antioxidant were determined by FT-IR spectroscopy using a Tensor 27 (Bruker) spectrophotometer [41]. Five parallel measurements were carried out on each sample.…”

Section: Methodsmentioning

confidence: 99%

Efficiency of curcumin, a natural antioxidant, in the processing stabilization of PE: Concentration effects

Kirschweng

et al. 2015

Self Cite

show abstract

“…The concentration of the residual phosphonite and that of the vinyl and carbonyl groups in the processed polyethylene were determined from the absorbance spectra of compression-moulded films [9]. The UV-VIS spectra of 100 µm thick films were recorded in the wavelength range of 200-600 nm using a Unicam UV 500 type spectrophotometer.…”

Section: Methodsmentioning

confidence: 99%

“…The phosphorous antioxidant inhibits degradation reactions by decomposing hydroperoxide groups to alcohols and it reacts also with carbon-centred, peroxy and oxy radicals [1,7,8]. Its efficiency is affected strongly by its chemical composition and thermal stability, as well as the amount of oxygen present [7][8][9][10]. Hindered phenols terminate autoxidation by trapping alkylperoxy, alkoxy and alkyl radicals [11][12][13][14].…”

Section: Introductionmentioning

confidence: 99%

Study of the effect of natural antioxidants in polyethylene: Performance of β-carotene

Major

et al. 2014

Self Cite

The effect of β-carotene on the behaviour of polyethylene stabilized with α-tocopherol and a phosphonite antioxidant was studied under processing and storage conditions. The amount of β-carotene ranged between 0 and 2000 ppm. The polymer was characterised by different methods after processing then during and after storage at ambient temperature in light and dark. β-Carotene hinders the oxidation of polyethylene and does not increase the chain extension reactions during processing, though more vinyl groups and phosphonite molecules react. β-Carotene colours polyethylene strongly already at low concentrations. The reactions of the polymer and β-carotene are affected strongly by the storage conditions. The presence of β-carotene does not influence the stabilizing efficiency of the primary and secondary antioxidants. In dark the molecular structure of the polymer does not change appreciably, while the reactions of β-carotene lead to an increase in the yellowness index. In light the molecular characteristics of polyethylene undergo significant changes indicating long chain branching. The polymer fades rapidly after an induction period. The length of the induction period is not influenced by light. The rate of the degradation reactions of β-carotene during storage is controlled by its concentration and film thickness. Visible autoaccelerated decomposition in light renders β-carotene candidate as an indicator in active packaging materials.

show abstract

“…While one of the main roles of the primary stabilizer is to hinder the oxidation of the secondary stabilizer, the rheological properties of the polyolefin melt depends on the efficiency of the latter [10].…”

mentioning

confidence: 99%

Natural antioxidants as stabilizers for polymers

Kirschweng

et al. 2017

157

126