New routes to flame retard polyamide 6,6 for electrical applications

Abstract

Polyamide 6,6 is used in many industrial fields such as housing materials, transport or electrical engineering applications. Due to its chemical composition, this polymer is easily flammable. As far as the main applications concern electrical and electronic equipments, its flame-retardant properties become an important requirement. The most discriminating tests are the limiting oxygen index, UL94 and glow wire flammability index. The aim is to obtain high limiting oxygen index values, V0 rating at UL94 test for 1.6- or 0.8-mm-thick samples and a validation at 960°C of the glow wire flammability index. The usual way to fire retard polyamide 6,6 consists of incorporating an important loading of fire-retardant additives, which often reduce the intrinsic properties of the polymer. It is also difficult to combine a thin polymer thickness (e.g. 0.8 mm) and a high amount of additives because of processing issues. In this article, we first carried out a rapid screening to determine the best fire retardant for polyamide 6,6 and its optimized amount to achieve the previously defined fire retardant properties. It was shown that an amount of 23% of aluminium diethylphosphinate Exolit OP1230 allows reaching the requirements. Then, carrying out two different surface treatments (coating of polysiloxanes by plasma-enhanced chemical vapour deposition and use of an intumescent waterborne varnish), we have tried to reach the same results. It was shown that the use of surface treatment alone does not allow reaching the objectives. As a consequence, the combination of the bulk approach at low loadings with the surface treatment was investigated. This new route allows the combination of the condensed phase mechanism of the intumescent barrier with the gas phase mechanism of the OP1230 and leads to very good results: the use of 5% of the flame-retardant additives combined with a 100-µm-thick waterborne intumescent varnish leads to better results than a 23% of additive loading.

Intumescence: Tradition versus novelty. A comprehensive review

“…On the other hand, the coating turned out to be effective after 200h of exposure. The same approach was also exploited in the case of PA66 and PA66 reinforced by glass fibers (GF-PA66) by the same authors in a detailed study [355], combining the use of phosphorus-based flame retardants in bulk with the surface protection by an intumescent coating.…”

“…Triazine derivative containing chemical groups of hydroxyethylamino, triazine rings and ethylenediamine [220] Triazine-containing macromolecules [222] 3,9-Bis-(1-oxo-2,6,7-trioxa- Poly(p-ethylene terephthalamide) [227] Ionic liquid containing phosphorus ([PCMIM]Cl) [228] Poly(hexamethylene terephthalamide) [230] Triazine-based macromolecule [231] M a n u s c r i p t M a n u s c r i p t [17,252] OP950 + sepiolite PET plastics and fibres [253] OP950 + OMPOSS or DPPOSS or FRPOSS PET plastics [254] OP950 + OMPOSS PET fibres [255] Aluminium phosphinate + OMPOSS or DPPOSS PET fibres [256] HEDP/AMS PET fibres [257 ] poly(2-hydroxy propylene spirocyclic pentaerythritol bisphosphonate) PET fibres [258,259] HNCP PET plastics [260] DPSPB + PDMN + OMMT PET plastics [261] EG + MMT PET plastics and fibres [129] M a n u s c r i p t A c c e p t e d M a n u s c r i p t A c c e p t e d M a n u s c r i p t A c c e p t e d M a n u s c r i p t A c c e p t e d M a n u s c r i p t A c c e p t e d M a n u s c r i p t Table 21 Combustion data by Jimenez et al [355] Sample LOI [%]…”

Materials engineering for surface-confined flame retardancy

“…A similar transparent varnish usually applied on wood was also used on glass fibre-reinforced polyamide 6,6 (PA6,6 GF) [8]. A 100 mm thick coating, applied on flame activated surface, was shown to provide LOI values above 50 and V0 rating at both 0.8 and 0.4 mm thickness of the substrate, while GWFI on 1 mm thick substrate was passed at 750 8C.…”

Flame Retardants: Overview

“…Today, this is done somewhat in the form of intumescent paints on steel, but this approach will go further with the use of coatings on complex shapes such as textiles, foams, and likely wood and other complex surface materials. The use of layer-by-layer coatings (73)(74)(75)(76)(77)(78)(79)(80)(81), as well as silicon oxide barriers (82)(83)(84)(85)(86)(87)(88), and metallized surfaces (89) has shown promise to impart flame retardancy to objects, and it seems likely that some flame retardants may also be incorporated into these coatings to provide superior protection. While these newer flame-retardant coatings may not appear to be a discrete chemical technology, they all utilize chemistry to impart durable barriers onto flammable goods to provide flame retardancy.…”