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Synergistic Benefits of Metal Hydroxides and Zinc Borate in Flame Retardant Wire and Cable Performance Compounds

Abstract

This paper discusses the use of metal hydroxides such as magnesium hydroxide or alumina trihydrate with zinc borate for formulating high-performance wire and cable compounds, including the polyolefin compounds for data cable jacketing and automotive wire applications. Results of extensive fire performance investigations using UL 94 and cone calorimetry are discussed in order to determine the optimal ratio of borate to metal hydroxide for a given base polymer and compound application. Compound performance tradeoffs associated with using the MDH and borate fire retardant combination are investigated. Enhanced compound performance using the unique MDH particles, such as Vertex™ 100, in combination with Firebrake® ZB-Fine zinc borate is illustrated.

Introduction

Demand growth for halogen-free, low-smoke flame retardant wire and cable products has continued to drive compound design and engineering using certain cost-performance effective flame retardant additives. This has led to continuous research effort to methodically examine some of the commercially available non-halogen fire retardant systems. A new magnesium hydroxide product called Vertex 100 has been developed by J. M. Huber Corporation to offer a set of compound performance benefits such as enhanced fire property at attractive cost. Vertex 100 is characterized by its uniquely engineered particle morphology that forms the key material attributes to enable the significant improvement in compound performance.

Metal hydroxides such as alumina trihydrate (ATH) and magnesium hydroxide (MDH) provide good flame and smoke properties when used at high loading levels (typically 50-60 % by weight for polyolefin-based systems). At these levels, there can be performance tradeoffs such as reduced physical/mechanical properties and processing rheological performance. Zinc borate such as the Firebrake® products is a boron-based flame retardant that can function as an effective charring promoter as well as a smoke suppressant. Adding borates to a metal hydroxide containing compound can result in synergistic performance benefits, notably in the compound fire performance and rheological properties.

The B2O3 released from decomposition of the borate promotes formation of a ceramic layer, along with MDH or ATH. In addition, as with the metal hydroxides, certain zinc borates also give off water when decomposed, diluting the combustible gases and suppressing smoke. Earlier literature reports suggest that the interaction of metal hydroxide with borate can lead to a hard residue with porous structure which functions also as a thermal insulator or barrier protecting the polymer. Such strong chars can prevent the volatile gases from reaching a combustible ambience.

While the metal hydroxide-borate flame retardant system can be used for a broad range of polymers, this study focuses on the synergistic performance of this FR system in an EVA polymer compound system.

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