Mineral fillers are being used in cladding panels, specifically in Alumimium Sandwich Panels to make these more flame-retardant and to make sure the building can meet certain Safety-codes.
ACP is an Aluminium composite Panel also known as ACM Aluminium Composite Material. This is a sandwich panel of two aluminium skins bonded to an extruded core of mineral filled Polyethylene or Polypropylene core.
For the ACP’s that meet fire resistance requirements (Class B1 or A2), the polymer core typically is filled with inorganic flame retardant fillers like ATH (= Aluminium-Tri-Hydroxide) when polymer core processing temperatures are < 200 dC or MDH (= Magnesium-Di-hydroxide) when polymer core(processing temperatures > 200 dC).
For Class B1 typically a mineral FR-loading level of 50 to 60% is sufficient to reach the desired fire performance. In case of using Polyethylene as core material, the use of Portaflame SG63 or Portaflame SG100LV is advised. These ATH-based Portaflame SG grades are suitable for this application because of:
- Good FR performance: consist of 99.5% ATH; endothermic H2O release at 200 dC
- Easy of processing: low moisture; high bulk density; flow- / dosing characteristics; non-abrasive
- Neutral white colour
- Non Toxic
The difference between the Portaflame SG63 and the Portaflame SG100LV here is the lower Oil Absorption value of the Portaflame SG100LV (11 g/100g) compared to the Oil Absorption of the Portaflame SG63 (18 g/100g), mainly due to the particle size distribution (PSD).
The PSD of the Portaflame SG63 is quite narrow with a D-50 of approx. 20 um and a topcut of approx. 60 um, whereas the PSD of the Portaflame SG100LV is more flat, with a D-50 of approx. 33 um and a topcut of 125 um. The lower Oil Absorption value of the ATH-filler will have an effect on the compounding viscosity (lower) and the final MFI (higher) of the PE-composite.
To reach Class A2 is quite a challenge within the industry, especially related to the desired calorific value of the composite material (max. 3 MJ/kg). Considering for example that the calorific value of pure PE is approx. 46 MJ/kg indicates that polymer/binder-level of the composite should be less than 10% !! It is clear that extrudability of such a material will be problematic.
- Choosing a polymer with lower calorific value
- ATH and MDH offer a negative contribution to the calorific value of approx. -1.3 MJ/kg
- Optimisation of the packing properties of the filler will help increasing the loading level
As optimizing the loading level of Sibelco’s ATH-grades, see the graph below:
From our Oil Absorption perspective a product combination of Sibelco’s Portaflame SG200with Portaflame SG30LV used at ratio 80:20 offers the best packing properties and thus the best opportunity for the skilled formulator to reach extreme high loading levels while maintaining a practical degree of processability.