Flame Retardant Synergist Powder: How to Boost LOI Value in Halogen-Free Systems

The flame-retardant synergist powder is a special additive that acts with other active ingredients, making materials resistant to flames. Halogen-free systems are useful for increasing the Limiting Oxygen Index (LOI)—the lowest concentration of oxygen in a mixture of gases that can sustain the flames of the material. Increased LOI values indicate high fire-resistance properties, implying that a material needs to be placed in a very oxygen-filled environment to ignite.

Powders are widely used in plastics, cable production, and coating applications due to their ability to provide environmental protection, which is why manufacturers are abandoning the use of classic halogen antimony compounds due to increasingly strict legislation concerning smoke emissions. This article gives information about various halogen-free synergists and methods of using them efficiently in production processes.

Synergists are powdered additives that amplify the performance of the primary flame retardant, usually through increasing stability of the charring process, decreasing smoke production, or increasing heat absorbency. The addition of synergists enables compounding personnel to reduce the amount of weighty mineral fillers used but increases LOI overall.

By adding a low concentration (about 1-5 percent) of synergist to systems that utilize ATH or APP, you can boost the LOI from a usual 25-28 percent to a great 32-35 percent. This group of substances works wonders with polyolefin plastics (PE & PP) and EVA and epoxy resins for electronic devices.

In addition to conventional chemicals, more sophisticated composite synergists such asSF-600belong to the next step in additive development. Halogen-free and inorganic powder SF-600 can replace conventional retardants (decabromodiphenyl ethane or brominated polystyrenes, etc.) by 20% to 50% without jeopardizing fire resistance. The high decomposition temperature (≥360°C) will guarantee stable operation during manufacturing processes, making it perfect for engineering plastics such as PA, PBT, PET, and polyolefins.

First and foremost, the benefits of using SF-600 are due to its multifunctional character. As already mentioned above, it will increase LOI, serve as a smoke suppressant, and create char formation. Being almost insoluble (≤0.5 g/100 ml) and having a low moisture absorption capacity makes SF-600 unlikely to migrate or precipitate out of materials used in production. It is good news for the manufacturers since it implies reduced material expenses and compliance with RoHS and REACH environmental regulations.

In halogen-free systems, synergists alter the way primary flame retardants react during exposure to intense heat. In the case of a combination of mineral fillers, such as ATH and magnesium hydroxide, synergists decrease the temperature at which sintering occurs, thus allowing more effective liberation of water by the filler and subsequent glazing of the resultant metal oxide particles, forming an impervious barrier to heat and oxygen. The synergists act as fluxing agents when used in combination with APP in intumescent applications, forming a highly carbonized foam layer.

Industrial trials have brought to light the unambiguous advantage of compounding in these blends:

The above-mentioned combinations of formulations would be highly suitable for use in areas where both toughness and fire protection capabilities are expected together:

A Suggested Practical Formulation: Begin by incorporating a synergist in the range of 2%-4% in the lab batches and observe the LOI results along with mechanical testing for elongation at break. Aim for a total of 40%-60% of the flame retardant loading in your formula (primary filler and synergist). The processing temperature should be less than the synergist's water vaporization point during extrusion.

The use of flame-retardant synergist powders provides an effective and convenient means to boost the LOI rating without altering your base compound. Simply by choosing the right type of powder, implementing appropriate surface modifications, and adjusting the dosage rates, you will be able to produce top-notch smokeless products that compete favorably on the international market.

Should you require professional assistance in determining the appropriate flame-retardant synergist powders or any other formulation guidance in general, feel free to contact our technical staffto obtain samples.