DEVELOPMENT OF BIO-BASED FLAME RETARDANT ADDITIVES FOR POLYLACTIDE: POTENTIAL ACTION OF LIGNIN, TANNIC ACID AND SODIUM PHYTATE

1. DEVELOPMENT OF BIO-BASED FLAME RETARDANT ADDITIVES FOR POLYLACTIDE:
POTENTIAL ACTION OF LIGNIN, TANNIC ACID AND SODIUM PHYTATE
Lucie COSTES, Fouad LAOUTID, Sylvain BROHEZ and Philippe DUBOIS
Center of Innovation and Research in Materials & Polymers (CIRMAP), Laboratory of Polymeric and Composite Materials (LPCM),
University of Mons & Materia Nova Research Center, Place du Parc 20, 7000 Mons, Belgium
Laboratory of chemical process engineering, Faculty of engineering of Mons, Rue de l’Epargne 56, 7000 Mons, Belgium
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,
separately or in combination.
PLA composites were prepared by melt blending in a Brabender internal mixer at 160 °C (7 min mixing at 70 rpm). Plates (100x100x4 mm³) for cone calorimeter testing were compression
moulded at 160 °C using an Agila PE20 hydraulic press. Précisez les caractéristiques du PLA utilisé ainsi que les autres additifs
The incorporation of the bio-sourced additives in PLA improves its fire behaviour: reduction of the peak of heat release rate and of the total of heat release during combustion. It also improves
the thermal properties of PLA by decreasing the thermal degradation rate and leading to the formation of a thermally resistant char. The combination of the additives modifies their fire retardant
effect and one of these combinations greatly improves the fire behaviour of PLA. Indeed, the combination of 15% of tannic acid and 15% of sodium phytate leads to an important decrease of
pHRR (-50%) during cone calorimeter test.
By measuring the mass loss after controlled furnace calcination of each additive and each additives combination, and calculating the theoretical mass loss of each additives combination,
antagonist and synergistic effects appear between additives. Combining tannic acid with sodium phytate increases the quantity of thermally resistant char and it morphology. The synergistic
effect between tannic acid and sodium phytate leads to a better fire behaviour in respect to PLA containing 30 wt% of tannic acid or sodium phytate.
Polymer blend processing
Conclusions
Polymer blend properties
Fire testing and thermal analysis
The fire behavior was studied by cone calorimetry by measuring the heat release rate (HRR) of samples according to the ISO 5660 standard. Plates of each formulation were exposed to a 35
kW/m² radiant heat flux using a forced ignition.
Thermogravimetric analysis was used to study the thermal degradation of unfilled PLA and PLA composites: temperature ramp from 100°C to 600°C at a heating rate of 20°C/min using a TGA
device from TA Instruments.
Controlled furnace calcinations of additives, alone and in combinations, were performed to highlight any synergistic or antagonist effects between the additives by measuring the mass loss after
being exposed at high temperature (from 400°C to 600°C) in a muffle furnace.
15% Tannic / 15%
Phytate
15% Lignin / 15% Tannic
10% Lignin / 10% Tannic /
10% Phytate
15% Lignin / 15%
Phytate
PLA
Fire behaviour during cone calorimeter test
No residue
Thermal degradation Residue after furnace calcination
50% tannic/50%
phytic
50% lignin/50%
tannic
Thermally
resistant char
Residue after cone calorimeter test
Samples
Experimental
mass loss
Theoretical
mass loss
Effect
100% phytic 33% - -
100% lignin 38% - -
100% tannic 100% - -
50% lignin / 50% phytate 58% 36%
Synergistic
50% tannic / 50% phytate 64% 67%
Addition
50% lignin / 50% tannic 58% 69%
Antagonist
33% lignin / 33% tannic /
33% phytate
69% 57%
Synergistiv
Thermally resistant char formation