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Fire retardent product solutions for composite applications

Author: Dean Voice, Technical Service & Business Development Manager, Allnex

Allnex develops and produces fire retardant vinyl esters, unsaturated polyesters and gelcoats utilising Allnex developments in fire retardant resinsvarious halogenated and non-halogenated flame retardant technologies. These products are typically used in underground and above ground mass transit vehicles, power poles, building and infrastructure fabrications.

The flammability properties of these products have been characterised by testing to recognised international industry standards.  

Halogenated products include Hetron FR992, a high performance brominated vinyl ester resin manufactured in Australia under licence to Ashland Inc.  Hetron FR992 laminates can achieve Class 1 Flame spread ratings according to ASTM E84, when the resin is combined with Antimony Trioxide or Antimony Pentoxide synergists. These antimony compounds alone are not fire retardant, however when combined with resins containing chlorine or bromine (halogens), a significant reduction in flammability is achieved in manufactured composite parts. On combustion, these halogens form hydrogen chloride or hydrogen bromide which reacts with the antimony synergist in the vapor phase to form antimony trichloride, antimony oxychloride, antimony tribromide, or antimony oxybromide. These antimony trihalides or antimony oxyhalides inhibit ignition and pyrolysis by acting as “free radical traps”, in the vapor phase. Laminates made from brominated fire retardant vinyl ester resins such as Hetron FR992 and Derakane 510A-40, show excellent chemical resistance towards a wide range of corrosive materials. They are particularly suitable for demanding caustic and sodium hypochlorite chemical service applications.

The requirement for translucency and low colouration in continuous and translucent roof sheeting applications typically limits the available formulation options for cost effective, high performance fire retardent resins. Sheeting laminates fabricated using Ultratec FR Sheeting resin, a halogenated fire retardant vinyl ester and polyester resin blend, can achieve Group 3 fire classifications when tested in accordance with ISO 5660 & AS/NZS 3837, and classified according to New Zealand Building code (NZBC) verification method C/VM2 Appendix A, & National Construction code (NCC) Volume 1 specifications C1.10 & A 2.4 of the Building Code of Australia (BCA).  However, halogenated vinyl ester based resins show relatively poor UV resistance properties in cured laminates on outdoor exposure. Panels produced using this resin require a clear UV stabilised polyester gelcoat on the external surface of the panel to provide good UV protection and resistance to UV discolouration.

Allnex flammability testing

Above: A laboratory test of two panels exposed to fire during comparative testing. The panel on the left was prepared using allnex Fire Retardant Resin and Gelcoat, the panel on the right was made using standard, non-fire retardant polyester resin and gelcoat. The flame is applied to both panels for 10 seconds and then withdrawn. The flame is extinguished almost immediately on the left panel, with minimal smoke emission, while the panel on the right hand side continues to burn following withdrawal of the flame.

For less demanding fire retardant composite applications, more cost effective product solutions include Polyplex 6450, a halogenated resin based on an unsaturated polyester/vinyl ester blend. A flammability rating of UL94HB has been demonstrated for laminates based on this resin, when tested according to UL94. However, significantly lower flammability properties can be achieved via additions of Antimony synergists.

The main disadvantage of halogenated composite products, compared to non-halogenated products, is that they produce more toxic smoke emissions in the event of fire. Increasing industry demands for Fire Retardant composites with low smoke toxicity and density properties are reflected in more demanding classification and testing standards such as NF P92-507:1994, NF F16-101:1988 & EN45545-2, which typically specify limits on smoke emission and smoke toxicity properties for compliance. To meet these more demanding compliance requirements, which are particularly critical for underground mass transport applications, non-halogenated fire retardant composite resin and gelcoat technologies are typically required.

Laminates based on acrylic modified resin blends typically show significantly lower smoke emissions on combustion compared to conventional styrenated fire retardant polyesters or vinyl esters. These resins are intended to be blended with Alumina Trihydrate (ATH) filler, which combines to further reduce flammability of the final composite part. ATH is particularly effective in reducing smoke emissions of most thermoset resins, however the downside is that relatively high loadings (> 40% w/w) are required with most polyesters and vinyl esters to achieve these properties. Consequently, the relatively high filled resin viscosity limits workability and fibre wetout properties during laminate fabrication for some applications. Compared to ATH modified unsaturated polyester or vinyl ester based fire retardant systems, these resins typically achieve much higher fire retardency for equivalent ATH loadings.

For example, a highly fire retardant laminate showing an M1 F0 flammability classification according to French Fire standards NF P92-507:1994, and NF F16-101:1988 is achievable by using our acrylic resin blended with 150 phr (60% w/w) ATH.

Other non-halogenated fire retardant products utilise intumescent formulation technologies to achieve low flammability and reduced smoke toxicity, while maintaining excellent application and handling properties during fabrication and good UV resistance properties in service. An M2 F1 classification has been demonstrated for our Ultratec FR Gelcoat when tested in accordance with French fire standards – NF P92-507:1994 & NF F16-101:1988.  Ultratec FR Gelcoat also achieves a zero flame spread index when tested according to AS1530.3.

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