Abstract
Despite their great antioxidant activities, the use of natural phenols as antioxidant additives for polyolefins is limited owing to their weak thermal stability and hydrophilic character. Herein, we report a sustainable chemo-enzymatic synthesis of renewable lipophilic antioxidants specifically designed to overcome these restrictions using naturally occurring ferulic acid (found in lignocellulose) and vegetal oils (i.e., lauric, palmitic, stearic acids, and glycerol) as starting materials. A predictive Hansen and Hildebrand parameters-based approach was used to tailor the polarity of newly designed structures. A specific affinity of Candida antarctica lipase B (CAL-B) towards glycerol was demonstrated and exploited to efficiently synthesized the target compounds in yields ranging from 81 to 87%. Antiradical activity as well as radical scavenging behavior (H atom-donation, kinetics) of these new fully biobased additives were found superior to that of well-established, commercially available fossil-based antioxidants such as Irganox 1010® and Irganox 1076®. Finally, their greater thermal stabilities (302 < Td5% < 311 °C), established using thermal gravimetric analysis, combined with their high solubilities and antioxidant activities, make these novel sustainable phenolics a very attractive alternative to current fossil-based antioxidant additives in polyolefins.
Highlights
In contact with atmospheric oxygen, polymers undergo oxidative degradation reactions during fabrication processes, storage, and throughout their use [1,2,3,4]
The design of the new bisphenolic antioxidants was based on our earlier studies on the Structure–Activity Relationships (SAR) of ferulic acid-based diphenolic antioxidants [15]
The linker had to be a triol able to carry the two phenolic moieties as well as an alkyl chain allowing the fine tuning of the lipophilic character of the molecule
Summary
In contact with atmospheric oxygen, polymers undergo oxidative degradation reactions during fabrication processes, storage, and throughout their use [1,2,3,4]. We previously reported a library of bisphenolic AO-I derived from HCAs found in lignocellulose (p-coumaric, ferulic, and sinapic acids) and biobased diols (1,3-propanediaol, 1,4-butanediol, and isosorbide) [15] To optimize their antiradical activities, we assessed the structure–activity relationships (aka SAR) of these phenolics [16]. The best candidates, obtained from the reaction between ferulic acid and 1,4-butanediol (BDF), 1,3-propane-diol (PDF), or isosorbide (IDF), exhibited potent antioxidant activities competing with commercially available molecules such as Irganox 1010® Their high thermal stabilities (>200 ◦C) render them compatible with harsh polymer production processes. Once the structural designs were validated, the chemo-enzymatic synthesis of the target structures was optimized through sustainable chemo-enzymatic processes involving a lipase-catalyzed transesterification strategy [23] Their activities and thermal stabilities were benchmarked against that of Irganox 1010® and lipophilic Irganox 1076®, two widely used fossil-based antioxidant additives
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