Abstract :
[en] Polylactide (PLA), i.e., a bio-renewable aliphatic polyester, is more and more used in durable and technical applications for which high fire resistance properties are generally required. Fireproofing of bio-based polymers with additives also issued from the biomass is currently an active research subject.
In the case of polyesters in general and PLA in particular, it is well established that the use of flame retardant additives, such as phosphorus compounds, that can generate a charred layer at the polymer surface during combustion is the most effective way to protect the material against fire.
The present research aims at assessing the potential flame retardant effect of three bio-based compounds, i.e., lignin, tannic acid and sodium phytate. Several PLA-based compositions, containing 30 wt% of these compounds, added either separately or in combination, have been prepared in an internal mixing Brabender chamber at 160°C. The fire behavior was studied by cone calorimetry by measuring the heat release rate (HRR) of samples according to the ISO 5660 standard. A 100x100x4 mm3 plate was exposed to a 35 kW/m2 radiant heat flux using a forced ignition.
In order to further investigate the flame retardant action of these additives and to highlight any synergistic or antagonist effects when combined to each other, complementary thermogravimetric analysis and controlled furnace calcination were performed.
Cone calorimetry test showed that each additive displays some fire retardant effect. Lignin and sodium phytate are the most effective ones when used alone in PLA. However, as far as PLA compositions containing binary additive combinations are concerned, cone calorimetry tests showed that the co-addition of tannic acid and sodium phytate leads to a more pronounced reduction of the HRR peak values with respect to neat PLA, i.e.,reduction by more than 50% of the peak of HRR. Further investigations are underway in order to understand the mechanisms of action of these additives and their synergistic combinations.
