Kinetic approach on stabilization of LDPE in the presence of carnosic acid and related compounds. I. Thermal investigation

Abstract

ABSTRACT:Carnosic acid and similar compounds exhibit antioxidant behavior in a polyethylene matrix. Thermal resistance of LDPE was investigated at three temperatures (190, 200, and 210°C) by isothermal chemiluminescence. The main kinetic parameters: oxidation induction period (t i ), half oxidation time (t 1/2 ), maximum oxidation time (t max ), and propagation rate of oxidation (v ox max ) were calculated. The inhibition of thermal degradation is proved by the values of these parameters relative to unstabilized polymer: the induction times of stabilized low density polyethylene are of one order of magnitude greater that raw polyethylene, and half oxidation periods are three to five times longer than initial LDPE. Thermal aging of protected low density polyethylene occurs at a much slower rate in comparison with unmodified LDPE. The depletion of stabilizers was also evaluated and the kinetic characteristics (the half-life and the rate constant of consumption for each antioxidant) at three concentrations of all tested additives (0.125, 0.25, 0.50, and 0.75% w/w) were determined. The effectiveness of stabilization was depicted by two values of activation energies calculated from oxidation induction times and maximum oxidation periods. Some considerations on stabilizing mechanism are presented.

Fabrication and Properties of Antioxidant Polyethylene‐based Films Containing Marigold (Tagetes erecta) Extract and Application on Soybean Oil Stability

“…One way to minimize the effect of these extrusion conditions is using stabilizers like antioxidants. Different natural antioxidants, such as α‐tocopherol, carvacrol, carnosic acid, and synthetic, such as Irganox and BHT, have been used as polyolefin's stabilizers. Cerruti et al .…”

“…35 One way to minimize the effect of these extrusion conditions is using stabilizers like antioxidants. Different natural antioxidants, such as a-tocopherol, 3 carvacrol, 4 carnosic acid, 6 and synthetic, such as Irganox and BHT, 36 have been used as polyolefin's stabilizers. Cerruti et al 7 found that tomato extract, which contained more than 80 wt% lycopene, was a good thermal and processing stabilizer for polypropylene films when oxygen partial pressure was relatively low.…”

“…Active food packaging involves the deliberated incorporation of a chemical into the packaging material; when the chemical has antioxidants properties, the active packaging is known as antioxidant active packaging . Also, different natural antioxidants, such as α‐tocopherol, carvacrol and carnosic acid, have been reported as additives for polyolefins. In addition, new films added with natural extracts rich in antioxidants from red grape seeds, white grape seeds, tomato extracts, barley husks, rosemary, oregano, cinnamon oil, clove oil and tea extract have been developed.…”

The potential of flavonoids as natural antioxidants and UV light stabilizers for polypropylene

“…The regulations of the European Union no. 10/2011 defines the use of additives in food packaging, because during the processing or storage of these materials, additives can migrate from the containers and packaging to the food, and for this reason many studies on the use of natural antioxidants to prevent the contact of food with synthetic antioxidants have been carried out in recent years; it is important to remark the excellent results obtained with α‐tocopherol at low concentrations (0.1–2%) for the stabilization of polyolefins1–4; carnosic acid has also been used (0.125, 0.25, 0.50, and 0.75%) to delay the thermal oxidation of PP5; on the other hand, the use of small additions (1 wt %) of essential oils of oregano, savory, and cinnamon to alginate–polycaprolactone copolymer has given interesting stabilizing properties6 as well as the use of essential oils of basil and thyme to provide higher stability to chitosan films has been reported 7. Flavonoids represent a generic group of natural compounds with attracting potential in polymer stabilization owing to the presence of phenolic compounds in their structure.…”

New genre of antioxidants from renewable natural resources: Synthesis and characterisation of rosemary plant-derived antioxidants and their performance in polyolefins

“…In spite of the large volume of literature available on the assessment of the antioxidant activity of rosemary extracts in a variety of unsaturated food lipids and food model compounds [15][16][17] , to our knowledge, there is scant information in the open literature on the stabilising performance of the main rosemary-antioxidants in polyolefins [18][19][20], and the antioxidant role of the ester derivatives of rosmarinic acid in polyolefins under M A N U S C R I P T…”