Franco Speroni

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

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.

Control of Macromolecular Architecture of Polyamides by Poly‐Functional Agents, 1. Theoretic and Experimental Approaches to Star‐Branched Polyamides

In this first paper of the series, a statistical model for star-branched polycondensation of AB type monomers in the presence of a polyfunctional agent RA f was completely developed. The analytical expression obtained for the number-average (DP n ) and weight-average (DP w ) degree of polymerization, and the dispersion index (D) for whole polymer species, linear and star macromolecular chains, were derived as a function of the conversion of the functional group of RA f . An important molecular parameter, mole fraction of star-branched polymer, was introduced. Numerical examples are reported on the relationship between molecular parameters and conversion of the functional group of RA f . It is illustrated that the molecular weight properties of the linear and star-branched polymers in the mixture of the products are very important factors for the application of this kind of polymeric materials. Polymerization of 6-aminocaproic acid was carried out in the presence of terephthalic (T2) and trimesic (T3) acids as tri- and bifunctional agents. The molecular weights calculated are in good agreement with those obtained by size exclusion chromatography (SEC).