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Intumescents gain interest.

The demand in some market sectors for nonhalogenated flame retardants is focusing new attention on intumescent flame retardants, which foam up at combustion temperatures to form a thick insulating char layer. Until now, these FRs have shown limitations in thermal stability, water sensitivity, plate-out, processing and cost-effectiveness. A number of additive suppliers are working to rectify those problems.

One is Hoechst Celanese Corp.'s Polymer Additives Div., Charlotte, N.C. At the FRCA meeting, the company reported that it is developing ammonium polyphosphate (APP)-based intumescent flame retardants and concentrates for polyolefins, elastomers and thermosets. These avoid excessive water solubility through encapsulation and surface treatment. These products, Hoechst Celanese says, are not yet commercial. To minimize plate-out by these FRs, the company has been careful to select the proper screw configuration for compounding and is using special grades of absorbent and adsorbent fillers that hold the additives in the host matrix. Hoechst also suggests using pigments like Ti|O.sub.2~ that enhance flame retardancy and let the processor reduce FR loading requirements.

Overall cost-effectiveness is achievable, Hoechst Celanese says, through the use of APP-based FRs used with thermally stable polyols and a variety of metal-oxide synergists. A company spokesman says this work should bear fruit later this year with the introduction of an improved line of Exolit IFRs.

Hoechst Celanese's German parent company, Hoechst AG, indicated how this development effort is proceeding with the introduction at the recent K'92 show in Dusseldorf of Hostaflam TP AP 750. This halogen-free, fine, white powder is aimed at PP. It's based on the company's Hostaflam AP 422 APP, but it's max. processing temperature has been markedly increased to 500 F, and its water solubility (and susceptibility to leaching from the polymer) is considerably reduced, the company says. A 25% loading generally provides UL 94V-0 in PP at 1/16 in.

Dead Sea Bromine Group of Israel (represented here by AmeriHaas, Philadelphia) recently reintroduced its FR-910 melamine-based intumescent for PP. The new version is surface treated to raise its processing thermal stability to 445 F.

As reported earlier, a range of Spinflam MF intumescents is newly available from the Functional Chemicals Div. of Himont Inc., Wilmington, Del. According to information obtained at K'92, there are two grades of Spinflam MF 82/PP for PP and copolymers, requiring 24-28% loadings to achieve V-0 at 1/16 in.; three grades of MF 92/PE for PE and copolymers (one for XLPE), requiring 30-40% loadings for V-0 at 1/16 in.; and one grade of MF 80/PU for urethane foams, at 30-35 php. These nitrogen-based products were developed for lower water sensitivity and greater migration resistance than earlier intumescents.

Great Lakes Chemical Corp., West Lafayette, Ind., dedicated late last year a grassroots plant to support its new thrust into nonhalogenated phosphorus-based intumescents aimed at PP, HDPE, LDPE, LLDPE film, and UHMW-PE. Among the first commercial products are NH-1197 (previously called CN-1197) and NH-1511, which has a nitrogen-containing compound blended in for added char formation. Both products melt at 400-420 F. There's also MBR-40, a blend of NH-1197 with a small amount of halogen, also aimed at PP.
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Title Annotation:Flame Retardant News Update; intumescent flame retardants
Publication:Plastics Technology
Article Type:Product Announcement
Date:Mar 1, 1993
Previous Article:Overcoming drawbacks of phosphorus.
Next Article:New halogenated FRs.

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