Posted on 22/05/2018 in 32 News
Lignin and tannin as flame retardants

Fouad Laoutid, Materia Nova, Belgium, presented tests of several bio-based FRs in PLA (poly lactic acid). Lignin grafted ammonium phosphate groups enabled to achieve V0 (3mm) but lignin poses challenges because of high variability between different plant origins and different extraction methods. Phosphorus-grafted tannic acid (1.75%P) in PLA (polylactic acid) reduced peak heat release rate by 1/3, but poses issues because it can decompose the polymer.

Phytic acid, a liquid bio-sourced molecule containing phosphorus, could not be used in PLA because of migration issues. A new FR agent, based on a combination of polyethylenameine – tannic acid and phytic acid has been developed and enables overcoming the problems induced by these compounds when used separately. Its incorporation in PLA generated an intumescent, porous char and reduced PHHR by around 50%. Analysis showed that the phosphorus remains in the residue and is not lost in the fire gases.
Valeriia Karaseva, IMT Mines Alès, France, presented tests of using tannins and their borate derivatives in epoxy resin. The latter are produced by the reaction of gallic and ellagic acids with boric acid. The incorporation of these molecules in epoxy resin helps to increase char content and reduce peak of heat release rate by 30%.

Benjamin Chollet, IMT Mines Alès, France, tested different lignins as flame retardants in PLA (polylactic acid). Micro size lignin particles showed better char production (up to 11.5%) and better total heat release THR decrease (up to 19%) than nano scale, and phosphorus functionalised lignin did not show significantly better fire performance.

Stéphane Giraud, ENSAIT-GEMTEX Roubaix, France, presented experiments using zinc phosphinate and alkali draft lignin as additives in polyamide PA11 fibres. Comparatively to neat PA11 fibers, mechanical performance of composite fibers (at 20% loading) was preserved. The fire reaction of textile with the composite fibers is improved with the increase of time to ignition regarding PA11 textile but without any significant decrease of heat release. This demonstrates the complexity of finding effective PIN FR – polymer combinations with bio-sourced materials.