Natural Phenolic Antioxidants As a Source of Biocompatibilizers for Immiscible Polymer Blends

Antioxidants are widely used in the plastic industry to protect polymers during their processing. In this work, the antioxidant effect of a series of biobased phenolic compounds has been investigated onto a polymer widely used in the industry: poly­(acrylonitrile-butadiene-styrene) (ABS). The antioxidant properties were assessed by measuring the oxidation induction time (OIT). The antioxidant efficiency was directly linked to the number of mesomeric forms of the biophenols. In particular, with 5 wt % of gallic acid, which has 10 mesomeric forms, a very low value of the enthalpy of oxidation (ΔHox) was measured (70 J/g), while ΔHox of ABS is measured to be 270.4 J/g. With phloretic, ferulic, or coumaric acid (4–5 mesomeric forms), an intermediate stage is reached, slightly decreasing ΔHox to 200 J/g. Cinnamic acid, which does not have a phenolic structure, acts as a pro-oxidant of ABS. In addition, the effect of the biophenols to act as compatibilizer of immiscible blends of 30 wt % ABS and 70 wt % polylactide (PLA) was studied. In between 4 and 6 mesomeric forms lead to an efficient compatibilization, according to dynamic mechanical analysis (DMA) and morphological analyses by scanning electron microscopy (SEM). This work shows that a double reaction occurs between the propionic side chain of the biophenolic acids and PLA, on one hand, and between the phenolic part of the biophenols and ABS on the other hand. Interestingly, selected biobased compounds proved to be efficient not only as antioxidants but also as reactive compatibilizing agents in ABS/PLA blends during extrusion processing