Technical Briefs

Flame and Smoke Suppression in Polymers

In both the public and private sectors, there are stringent code requirements which limit the flammability of polymer materials. Ever increasing use of polymers as substitutes for other more common materials such as wood and metals requires polymer substrates to meet mandated limits for flame spread, smoke development and smoke toxicity. Considering that smoke density and toxicity are responsible for more deaths than fire itself, attention needs to be directed specifically to these areas.

Polymeric materials are usually formed into composite substrates as varied as aircraft interiors, fiberglass gratings for industrial facilities, architectural moldings in modern day buildings or computer circuit boards and housings. Polymers also constitute the insulating jacket on wires and cables, the adhesive and fabric of carpets and wall coverings, ceiling panels and furniture. All are required by various codes, regulatory mandates and legislation to have minimal flame spread, smoke development rates and smoke toxicity qualities.

The conventional practices used to achieve the FST standards in polymers were primarily through the use of brominated compounds in combination with antimony trioxide, or high loadings of ATH. Because of the human and environmental toxicity associated with bromine and antimony and the inefficiency of fillers such as ATH which compromise the mechanical properties of all composites, industry and government have demanded new chemistries for flame retardancy.

Rather than suppressing flame and smoke tendencies of combusting polymers through “blanketing” effects in the gaseous phase, there is now another means to achieve flame retardancy with more dramatic efficiency by accelerating char formation accompanied by water formation. It is now possible through the use of materials incorporated into polymer matrices to immediately convert the surface exposed to an ignition source – flame or excessive heat – into an expanding char, i.e. an incombustible layer that does not burn with flame or smoke. The more quickly the char is formed, the more quickly flaming is eliminated and the resultant smoke suppressed to indistinguishable levels. Continued exposure to excessive heat or flame continues to form char at the polymer surface without flame or smoke, which further protects the polymers below the char layer.

This new catalyzed organo-phosphate chemistry by Manufacturing Insight LLC minimizes flame spread and smoke developed. Reported ASTM E-84 results typically are 10/10 or less depending on polymer formulation and smoke toxicity is significantly under the stringent limits defined by IMO MSC.41 (64). Char conversion efficiencies typically increase from the 30% of conventional technologies to more than 70% when using the new chemistries. As the loading levels in most applications are in the range of 10%-20%, mechanical properties are rarely compromised.

The Swedish Chemicals Inspectorate describes in its June 2005 Kemi Report No 1/05 “Survey and Technical Assessment of Alternatives to decabromodiphenyl ether in Plastics” what it believes to be the ideal flame retardant -

“The ideal flame retardant should be compatible i.e. not alter the mechanical properties of the plastic, not change color, have good light stability, resistant towards ageing and hydrolysis, match and begin its thermal behavior before the thermal decomposition of plastics, not cause corrosion, not have harmful physiological effects, not emit or at least emit low levels of toxic gases and be as cheap as possible. It is not always the ultimate truth that the flame retarding system needs to be as cheap as possible. Since we talk about engineering polymers, function is more important than price. This means that certain “popular” relatively cheap and established flame retardants, such as decaBDE, may inhibit the development and use of alternates to come closer to the theoretical properties of the ideal flame retardant.”

The actual properties of Manufacturing Insight’s EFR flame retardants are:

• EFR-2 actually increased the tensile, modulus and impact resistance of a particular customer’s thermoplastic system (based on customer’s qualification testing)
• Does not change color even at high processing temperatures
• Begins char formation before polymer decomposition temperatures are reached
• Contains no metals; is non-corrosive
• Results of toxic gas analysis and Pittsburgh Protocol are negative

Effective in most thermoplastic and thermoset materials, Manufacturing Insight's enhanced flame retardant additives represent the most advanced technology available today.

“We enable industry to process today exceeding the requirements of tomorrow.”

January, 2006