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

Abstract

Several ester derivatives of rosmarinic acid (rosmarinates) were synthesised, characterised (1D and 2D NMR, UV and FTIR spectroscopy) and tested for their potential use as antioxidants derived from a renewable natural resource. The intrinsic free radical scavenging activity of the rosmarinates was assessed, initially using a modified DPPH (2, 2-diphenyl-1-picrylhydrazyl radical) method, and found to be higher than that of commercial synthetic hindered phenol antioxidants Irganox 1076 and Irganox 1010. The thermal stabilising performance of the rosmarinates in polyethylene (PE) and polypropylene (PP) was subsequently examined and compared to that of samples prepared similarly but in the presence of Irganox 1076 (in PE) and Irganox 1010 (in PP) which are typically used for polyolefin stabilisation in industrial practice. The melt stability and the long-term thermo-oxidative stability (LTTS) of processed polymers containing the antioxidants were assessed by measuring the melt flow index (MFI), melt viscosity, oxidation induction time (OIT) and long-term (accelerated) thermal ageing performance. The results show that both the melt and the thermo-oxidative stabilisation afforded by the rosmarinates, and in particular the stearyl derivative, in both PE and PP, are superior to those of Irganox 1076 and Irganox 1010, hence their potential as effective sustainable bio-based antioxidants for polymers.The rosmarinic acid used for the synthesis of the rosmarinates esters in this study was obtained from commercial rosemary extracts (AquaROX80). Furthermore, a large number of different strains of UK-grown rosemary plants (Rosmarinum officinalis) were also extracted and analysed in order to examine their antioxidant content. It was found that the carnosic and the rosmarinic acids, and to a much lesser extent the carnosol, constituted the main antioxidant components of the UK-plants, with the two acids being present at a ratio of 3:

Natural antioxidants as stabilizers for polymers

“…Esterification is another way to increase the stability and solubility of phenolic acids. Methyl-, butyl-, octyl-and stearyl esters of rosmarinic acid showed improved thermal stability compared to the nascent phenolic acid, while octyl-and stearyl esters efficiently stabilized low density polyethylene (LDPE), linear low density polyethylene (LLDPE) and PP [132]. The studied derivatives outperformed Irganox 1010 and 1076 at 1000 ppm antioxidant content, but the effect of additive concentration and solubility have not been investigated and reported yet.…”

“…Their largest advantage is the reactivity of the carboxyl group, which can be used in acylation reactions leading to esters with increased number of phenolic hydroxyl groups and increased antioxidant activity, solubility and thermal stability [132]. The enzymatic synthesis of epigallocatechin-3-gallate is shown in Scheme 7 as an example.…”

Triple‐faced polypropylene: Fire retardant, thermally stable, and antioxidative

“…The use of a multifunctional additive rather than mixture of additives with different functionalities leads to facilitation of processing and facile dispersion of additives into the molten polymer . Therefore, there has been a great deal of research to find appropriate ways for tailoring properties of different additives into a unique versatile additive as the next generation of high‐performance multifunctional derivatives—what brings about new challenges in spite of being interesting .…”

“…In a recent work, a flame retardant was developed and applied in poly(lactic acid) (PLA) showing an acceptable efficiency . This flame retardant was the hybrid product of the reaction between three different molecules: β‐cyclodextrin, nanohydroxyapatite, and an antioxidant (commercially available SABO®), and named BSDH in brief . In view of successfulness of the BSDH as a flame retardant for PLA, we were anxious to uncover its potential toward PP as a flame retardant and at the same time as an antioxidation agent.…”

Biowastes from wine as natural additive of polyolefins: Thermo‐ and photo‐oxidation efficiency

“…Vitamin E, known as α‐tocopherol a phenolic compound, was widely studied as an antioxidant in polyolefins, and shown to have a strong stabilizing effect even at low concentrations. The use of curcumin as processing stabilizer into polypropylene has been explored, such as rosemary as antioxidant under melt processing and thermo‐oxidative conditions . Other promising vegetable sources have been studied in polypropylene, such as lignin; green tea, to improve thermal stability; coffee to maintain mechanical properties; ginger roots; and guava leaves …”