Mineral-Based Flame Retardants in Practice
Mineral flame retardants containing aluminum hydroxide (ATH) or magnesium hydroxide (MDH) are typically added to a formulation in high proportions. The amount that a particular application can tolerate depends on the processing method, such as during the extrusion of a halogen-free, EVA-based cable jacket. A hydrophobic surface coating of ATH or MDH can affect the viscosity of the filled compound, and this effect varies depending on the industry.
Why ATH or MDH Is Added to Plastics
Mineral-based flame retardants delay the onset and spread of fire
Many plastics are based on a hydrocarbon framework and are therefore highly flammable. ATH and MDH are added to them to delay the onset of a fire and slow its spread. A product treated in this way is less likely to contribute to the spread of a fire, and the amount of heat released and the density of the smoke can be reduced. This allows escape and rescue routes to remain usable for longer.
The effect stems from the water bound within the crystal structure of both hydroxides, which accounts for about one-third of their mass. ATH releases this water above approximately 200 °C, while MDH does so above approximately 300 °C. Because the decomposition is endothermic, it draws heat away from the fire, and the plastic decomposes thermally more slowly. The water vapor dilutes the combustible gases and displaces oxygen from the fire zone. The resulting residue consists of metal oxides, which act as a protective layer to block heat input and oxygen access.
The mineral flame retardants from Alpha CALCIT Füllstoff GmbH & Co. KG are all halogen-free. Neither ATH nor MDH produce toxic or corrosive gases when exposed to fire. For the finished product, all formulation components determine whether it is considered halogen-free overall.
In addition, ATH and MDH are environmentally neutral. Even the residue of metal oxides that remains in the product after a fire is harmless.
The effect stems from the water bound within the crystal structure of both hydroxides, which accounts for about one-third of their mass. ATH releases this water above approximately 200 °C, while MDH does so above approximately 300 °C. Because the decomposition is endothermic, it draws heat away from the fire, and the plastic decomposes thermally more slowly. The water vapor dilutes the combustible gases and displaces oxygen from the fire zone. The resulting residue consists of metal oxides, which act as a protective layer to block heat input and oxygen access.
The mineral flame retardants from Alpha CALCIT Füllstoff GmbH & Co. KG are all halogen-free. Neither ATH nor MDH produce toxic or corrosive gases when exposed to fire. For the finished product, all formulation components determine whether it is considered halogen-free overall.
In addition, ATH and MDH are environmentally neutral. Even the residue of metal oxides that remains in the product after a fire is harmless.
Applications
ATH and MDH are used in a wide range of applications, from cables to electronic enclosures
Typical Applications Organized by Application Area
| Field of Application | Typical applications |
|---|---|
| Cables and Wires | Power and Installation Cables, Data Cables, Automotive Wires |
| Building Products | Profiles, building panels, cable ducts |
| Engineering Compounds | Electronics Enclosures, Automotive Applications, Elastomer Products |
During the extrusion of a halogen-free, EVA-based cable jacket, factors such as the degree of filling and the surface coating of the mineral influence how the filled melt can be processed. Several fine ALFRIMAL® grades and ALFRIMAL® MG are intended for use in cable filler and jacket compounds; the corresponding grades are listed in the product lines section.
In construction products such as profiles, building panels, and cable ducts, as well as in technical products such as electronic enclosures and elastomeric articles, ATH and MDH perform the same fire-retardant function. How a coating affects processability in these applications depends, among other factors, on the manufacturing process and the specific application.
In construction products such as profiles, building panels, and cable ducts, as well as in technical products such as electronic enclosures and elastomeric articles, ATH and MDH perform the same fire-retardant function. How a coating affects processability in these applications depends, among other factors, on the manufacturing process and the specific application.
Surface Modification
A hydrophobic coating can alter the flow behavior of highly filled compounds
Surface Modification of ATH and MDH and Its Effect on Processing
ATH and MDH serve as both fillers and flame retardants: They can add volume to the formulation, influence stiffness and surface properties, and also provide fire protection. Since their effectiveness depends on the amount used, high filler levels are the norm. As the filler content increases, viscosity and density rise; the toughness of the compound during processing also increases. Finer grades increase the specific surface area and accentuate the rise in viscosity, while coarser fractions pack more densely and facilitate processing, though they reduce surface quality. Surface-modified, finer grades can improve wetting by the polymer and allow for higher loading levels while maintaining the same processability. Alpha CALCIT Füllstoff GmbH & Co. KG will be happy to advise you on testing these materials in your formulations. Together with you, we will determine whether a coated or uncoated type is suitable for your application and which particle size is appropriate.
Untreated ATH and MDH have a hydrophilic surface that generally wets nonpolar plastics less effectively. A hydrophobic coating can improve wetting and dispersibility in the plastic, allowing for a higher loading in the formulation. The extent to which this affects viscosity depends, among other factors, on the specific application.
Untreated ATH and MDH have a hydrophilic surface that generally wets nonpolar plastics less effectively. A hydrophobic coating can improve wetting and dispersibility in the plastic, allowing for a higher loading in the formulation. The extent to which this affects viscosity depends, among other factors, on the specific application.
| Rheological parameter | Untreated ATH or MDH | Water-repellent ATH or MDH |
|---|---|---|
| Interaction Between Particles | strong attraction between the particles via hydrogen bonds | steric hindrance, low agglomeration |
| Viscosity at High Fill Levels | very high, structurally viscous to pasty | moderate and controllable, approximately Newtonian to slightly structurally viscous flow |
| Yield strength | pronounced; high shear forces are required for it to flow | minimal to none |
| Maximum fill level | low; the critical pigment volume concentration is reached quickly | higher |
The table shows trends. How pronounced these trends are depends, among other things, on your application and formulation.
In the extrusion of EVA, PE, and PP
In thermoplastics such as EVA, PE, and PP, the coating can reduce melt viscosity. When extruding a halogen-free, EVA-based cable jacket, this can reduce die pressure and help prevent melt fracture, which appears as “shark skin” on the jacket surface. At the same time, higher throughput rates may be achievable at lower processing temperatures.
In Paints and Varnishes
In paints and coatings, the coating can counteract the formation of highly thixotropic structures. Hydrophobic ATH or MDH can be used to formulate high-solid systems that remain suitable for spraying, rolling, and brushing despite their high filler content. Sedimentation stability in the container can also be improved.
In polyurethane foam insulation materials
For polyurethane foams, the filler is suspended in liquid reactive components such as polyols and must be evenly distributed within them. If the viscosity of the suspension remains low, it can be metered in a finely dispersed state through the mixing head. This can contribute to a uniform cell structure and consistent insulation properties in the finished foam.
In paste-like sealants
Paste-like sealants can achieve a controllable base viscosity through the functionalization of the mineral surface. Rheological additives can then be dosed more precisely, allowing the stability in construction or automotive joints to be adjusted independently of the flame retardant.
In structural and hot-melt adhesives
In structural and hot-melt adhesives, the coating can prevent premature blocking during joining. If the viscoelastic flow behavior is maintained, thin, agglomerate-free bond gaps and high adhesive forces can be achieved.
Request a Technical Product Recommendation
Tell us about your application—we’ll identify the appropriate grade and product family from our portfolio and assist you with the initial sampling process.
Selection
The product in the target system will show you which type is right for your application
Summary of Selection Criteria for Coated and Uncoated Types
Whether ATH or MDH is the appropriate base depends, among other factors, on the process window, the achievable fill level, and the product’s optical and mechanical requirements. You can find a comparison of both materials and the criteria for selecting the active ingredient base on the page explaining the difference between ATH and MDH. The flame retardant provides the active principle; the fire behavior is determined by the interaction with the matrix, the fill level, and the product geometry. Therefore, the product is evaluated in the target system. For EVA-based cable sheathing, only testing with your specific formulation will determine whether a coated type facilitates extrusion and passes the required fire safety test.
Product Lines
Coated models are available in both ALFRIMAL® lines
Mapping of Active Ingredient Base and Surface Finish
ALFRIMAL® is our line of products based on aluminum hydroxide. Among other things, the surface treatment varies within this line. Among the coated grades is ALFRIMAL® 549 XS HS, which features a special hydrophobic coating. This bright white, halogen-free ATH can reduce viscosity and is intended for media-resistant solid surface materials.
ALFRIMAL® MG is based on magnesium hydroxide and is available with or without a hydrophobic surface coating. This line is suitable for processing temperatures at which ATH would already be releasing water. Grades and particle sizes are listed on the ALFRIMAL® MG product page for both coated and uncoated versions.
ALFRIMAL® MG is based on magnesium hydroxide and is available with or without a hydrophobic surface coating. This line is suitable for processing temperatures at which ATH would already be releasing water. Grades and particle sizes are listed on the ALFRIMAL® MG product page for both coated and uncoated versions.
Overview of ALFRIMAL® Types
| Type Group | Types | Median particle size d₅₀ | Whiteness Level Ry | Intended Applications |
|---|---|---|---|---|
| ALFRIMAL® Finest | 104, 105, 106 | 4 µm, 3 µm, 2 µm | 97, 97, 98 | Filler and coating compounds for cables, rubber products, elastomer foams, and solid surface, along with other ATH grades |
| ALFRIMAL® 104 HS, 106 HS | 104 HS, 106 HS | 4 µm, 2 µm | white, without a "Ry" designation | Filler and specialty jacket compounds for cables, rubber products, elastomer foams, and thermosets |
| ALFRIMAL® 506 P, 509 P | 506 P, 509 P | 1.4 µm, 1.3 µm | 98, 97 | Filler and coating compounds for cables, rubber products, and elastomer foams |
| ALFRIMAL® 440 S through 449 S | 440 S, 443, 444 S, 446, 447 S, 448, 449, 449 S | 6 to 18 µm | 94 to 97 | Plastics, rubber, resins for foams, insulation, sealants, and coatings; paints and varnishes; floor and road markings; UP resins |
| ALFRIMAL® XS | 547 XS, 549 XS, 549 XS HS | 15 µm, 20 µm, 20 µm | 97, 96, 96 | Solid Surface for wall paneling, shelves, countertops, radiator covers, and window sills |
| ALFRIMAL® MG | MG 2, MG-H 2, MG 4, MG-H 4, MG 8 | 2 µm, 2 µm, 4 µm, 4 µm, 8 µm | 94, 94, 93, 93, 95 | Sheath compounds for cables, elastomers, and TPEs; insulating plastics for white goods; roofing membranes |
d₅₀ and whiteness are average values and are not legally binding; the areas of application are not exhaustive.
You can find additional ATH grades, such as ALFRIMAL® 501 X, 802, and 849 S, on the Aluminum Hydroxide Flame Retardants product page, and the MDH grades on the Magnesium Hydroxide Flame Retardants product page. The table alone does not indicate which type is suitable for your formulation, because every formulation is different.
Technical Consulting
We assist with the testing of ATH and MDH in your formulation
Technical advice and samples for your tests
During the technical consultation, please provide us with a general description of the matrix, processing methods, and target requirements. Together, we will then narrow down the suitable types and provide samples for your own testing. For an EVA-based cable jacket, this information includes, among other things, the filler used to date, the temperatures in the extruder, and the required fire resistance test. In addition to our standard grades, tailor-made solutions may also be considered. Tests using your formulation are conducted in your laboratory, in coordination with our laboratory, where we test the grades ourselves.
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