General Processing Guidelines for MagShield® S NB10 in Polypropylene
To achieve a UL94 V(0) rating at 1/8" (3.2 mm) in polypropylene, a loading of 60% MagShield S NB10 magnesium hydroxide by weight of the total compound is usually required. MagShield S NB10 is coated with 1.0% magnesium stearate, using a proprietary process, to improve dispersion and to reduce mixing requirements.
Compounding trials in polypropylene (PP) homopolymer with a melt flow index of 22 at 230°C were conducted using a 40 mm Leistritz twin screw extruder. To obtain the whitest extrudate strands with the least porosity, the following guidelines are recommended:
- Processing temperature between 200°C and 225°C.
- Operating the extruder at low shear rate. The Leistritz extruder, which has a maximum rpm of 400, was operated at 150 rpm. The extruder element setup is available on request.
- Proper venting, preferably vacuum venting of at least 900 millibars near the die, is needed.
- 37.5% PP (22MFI)
- 60% MagShield S NB10
- 1.5% Calcium Stearate
- 1.0% *PolyAd Preblend MM1252-25
UL94 Data at 1/8" (3.2 mm):
- UL94 Rating at 1/8" (3.2 mm): V(0)
- Total Afterflame Time (5 samples): 20 seconds
- Total Afterflame + Afterglow (5 samples): 20 seconds, no afterglow
- Afterflame on any sample to holding clamp: No
- Ignited Cotton: No
Stabilization and processing aids
Addition of stabilizers such as PolyAd Preblend MM1252-25 from Ciba Specialty Chemicals Corporation is helpful in providing good color in the extrudate. Other multi-component stabilizer packages may be used. TiO2 may be added for additional whiteness/brightness.
Additional stearate processing aid can be added up to 1.0% to reduce extruder torque. In these trials, 1.0% calcium stearate was used. Stuktol Company of America’s additive TR 071 has also been proven to be effective with MagShield.
See MagShield data sheets for complete descriptions of products. Other formulations for other polymers and FR standards are available from Martin Marietta Magnesia Specialties’ Technical Service. Please call 800-648-7400 (inside the U.S.) or +1-410-780-5500. Or, email us with your questions.
*PolyAd Preblend MM1252-25, available from Ciba Specialty Chemicals, is:
TM 25% Irganox 1010
TM 20% Irgafox 168
TM 25% Irganox MD 1024
TM 30% Irganox PS-802
Irganox & Irgafox are Trademarks of CIBA Specialty Chemicals