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

## TL;DR

Recycled cobalt aluminate pigment improves polylactide's flame resistance and adds color, using a combination with ammonium polyphosphate.

## Contribution

Introduces a dual-purpose recycled cobalt aluminate additive for flame retardancy and coloration in polylactide.

## Key findings

- Combining CoAl2O4 with APP422 reduces peak heat release by 70% in polylactide.
- The additive forms a stable char layer, enhancing thermal protection during burning.
- X-ray analysis confirms the formation of thermally stable Co3(PO4)2 when CoAl2O4 and APP422 are used together.

## Abstract

Cobalt aluminate (CoAl2O4) 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/CoAl2O4 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 CoAl2O4, 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 CoAl2O4 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 Co3+ and APP422, which leads to the formation of
the thermally stable Co3(PO4)2 phase.