A new class of textiles combines high flame retardancy with improved physical properties

"Flame retardant phosphorus compounds are usually added to the polymers as additives," explains Dr. Mourgas. "However, large quantities of phosphorus compounds are required to achieve a good fire protection effect. And this usually occurs at the expense of the physical and physiological properties of the textiles". Dr. Mourgas lets plastic granulate trickle through his hands. It consists of a polyamide that has been chemically modified in the DITF laboratories. In contrast to the usual method of adding phosphorus compounds to the polymer as an additive, these could be incorporated directly into the polymer chains in low concentrations. This occurs during polycondensation, i.e. the synthesis of the plastic in reactor vessels. This chemical process is usually designed to produce molecules with as long a chain as possible, i.e. polymers with a high molecular weight. This is a precondition for the subsequent ability to spin the polymer granulate into textile fibers. 

New process for lower phosphorus content levels

But that is also where the difficulty lies: When added in large quantities as an additive, these phosphorus compounds prevent the formation of long molecular chains and thus act as chain breakers. The resulting plastic cannot be processed into fibers at all or only with great difficulty, and the additive leaks from the fibers over time as a result of ageing and washing processes.

The process developed at the DITF is more elegant: Only small amounts of phosphorus compounds are required to achieve comparably good flame retardancy. The compounds are chemically coupled to the molecular chains and thus bonded to the polymer much more firmly than would be possible with additive admixtures. "We call these polyamides intrinsically flame retardant," explains Dr. Mourgas. "This means that the flame retardant is built directly into the polyamide. This allows us to achieve a permanent, long-lasting flame retardant effect". 

By reducing the required flame retardants, the achievable molecular weight can be controlled much better during synthesis. The viscosities of the plastic melt can be precisely adjusted to guarantee the optimum ability to spin the polymer into fibers.