Two in One: Recycled Cobalt Aluminate as a Pigment and Synergistic Flame-Retardant Agent for Polylactide.

Cobalt aluminate (CoAlO) pigment, synthesized from recycled aluminum obtained from can seals and transformed into the boehmite phase, was combined with ammonium polyphosphate (APP422) to produce an efficient flame-retardant material for polylactide (PLA) while simultaneously imparting coloration to the polymer matrix. The chemical structure of the pigment was investigated using X-ray photoelectron spectroscopy and X-ray diffraction prior to its integration into PLA in combination with ammonium polyphosphate (APP422). Thermal gravimetric analysis highlights the superior effect of the APP422/CoAlO combination that enables obtaining a greater amount of char, presenting improved thermal stability and an enhanced protective effect, as clearly evidenced by Mass Loss Cone test results. A reduction of 70% in peak heat release was observed when APP422 was combined with CoAlO, in contrast to a reduction of 31% when only APP422 was used at a similar incorporation level. The enhanced flame-retardant properties of the combined APP422 and CoAlO additives can be attributed to a rapid formation of a homogeneous char layer at the surface of the burning material when both additives are used together. This results from the interaction between Co and APP422, which leads to the formation of the thermally stable Co(PO) phase.