Arylindane diols as safe and sustainable polymer additives

Promovendus/a: Tessy Hendrickx

Promotor(en): Prof. dr. ir. Bert Sels

Plastics play a crucial role in modern life, from packaging and transportation to electronics and healthcare. Yet, their durability often depends on chemical additives such as antioxidants, which prevent plastics from degrading, and plasticizers, which improve flexibility. Today, most of these additives are made from fossil resources. Common examples include synthetic phenolic antioxidants such as butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA), as well as widely used phthalate plasticizers. Although effective, these substances are under growing scrutiny. They can leach from plastics, persist in the environment, and in some cases pose risks to human health. As society moves toward a more sustainable and circular economy, there is a clear need for renewable, safer, and multifunctional alternatives.

In this research, a new class of molecules called arylindane diols was investigated as promising bio-based polymer additives. These compounds can be obtained from lignin, a major component of plant biomass and a side product of industries such as paper pulping and biorefineries. Lignin is especially attractive because it contains aromatic building blocks that can be transformed into valuable chemicals. Among these, arylindane diols stand out for their rigid structure and antioxidant properties, as well as for their potential biological activities. Importantly, many lignin-derived molecules contain o-methoxy groups, which are known to reduce unwanted estrogen-like activity, making them safer candidates for material applications.

A diverse library of arylindane diols was created and systematically tested. This included diisoeugenol (DiE), diisoallylsyringol (DiAS), diferulic acid (DFA), disinapic acid (DSA), and a series of dialkyl ferulates: dimethyl ferulate (DMF), diethyl ferulate (DEF), dibutyl ferulate (DBF), and dioctyl ferulate (DOF). All of them showed strong antioxidant performance, even working better than common commercial additives such as BHT, BHA, and Irganox® 1010, which are currently used in many plastics.

Safety testing provided equally promising results. One key concern with additives is their potential to mimic natural hormones in the body, referred to as estrogenic activity (EA). Substances with high EA can disrupt the endocrine system and interfere with hormone regulation. Among the compounds studied, DiE showed much lower EA than conventional benchmarks, while DiAS, DFA, DSA, DMF, and DEF displayed no detectable estrogen-like effects even at high concentrations. Another important measure is cytotoxicity, which reflects whether a compound harms living cells. Here, effects were generally very low, with DFA and DSA in particular showing negligible toxicity.

The materials performance of these molecules was then tested in two model plastics: polypropylene (PP), a widely used commodity polymer, and polylactic acid (PLA), a biodegradable alternative. In PP, DiE and DiAS improved resistance to oxidative degradation, while in PLA, DOF not only stabilized the material but also acted as a plasticizer, lowering its glass transition temperature (Tg) and increasing flexibility. This rare combination of functions in a single molecule illustrates the unique potential of arylindane diols for advanced material design.

Overall, this research shows that renewable arylindane diols can deliver high performance, low hazard, and multifunctionality. Their development contributes directly to the European Union’s Safe and Sustainable by Design (SSbD) vision, which calls for new chemicals to be developed with safety and sustainability in mind from the very beginning. By connecting renewable lignin feedstocks with the needs of modern materials, arylindane diols emerge as a promising new class of polymer additives for a more sustainable future.