FL-ZB: Zinc Borate (CAS 138265-88-0)

Zinc borate (CAS 138265-88-0) is a multifunctional flame retardant additive used in PVC, polyolefins, rubber, halogen-free cable compounds, and coatings. It functions simultaneously as an FR synergist, smoke suppressant, afterglow suppressant, and char promoter, the only zinc synergist in Flamisol’s portfolio that is compatible with halogen-free FR systems.

FL-ZB Technical Specification

How FL-ZB Works

FL-ZB operates through three simultaneous mechanisms, which is what distinguishes it from FL-ZS and FL-ZHS:

• Glassy char formation: Boric acid released during decomposition forms a viscous glassy layer at the polymer surface, acting as a physical barrier to oxygen and heat transfer.
• Endothermic cooling: Dehydration of the 3.5 water molecules of crystallization at 290–450°C absorbs heat from the combustion zone.
• Afterglow suppression: ZnO formed during decomposition acts as a glowing-combustion inhibitor. FL-ZB is the only zinc synergist that reliably suppresses afterglow, a requirement in several transport and construction fire standards (NFPA 130, EN 45545).

Substrate Compatibility

LSZH Application Guidance

For low smoke zero halogen (LSZH) cable compounds complying with IEC 61034 (smoke density), NFPA 130 (transit), or NEC 2023 (commercial buildings), FL-ZB is the recommended zinc synergist evaluation starting point:

• Evaluate at 5–8 phr as synergist in ATH-based or MDH-based LSZH compounds
• Provides smoke suppression + afterglow control without introducing halogen
• Compatible with MPP, APP, and ZnO co-additives commonly used in LSZH systems