Robyn Gai and Frank Chen
KMT industrial HK limited
Abstract: The article introduces the significance of halogen-free flame retardants Mg(OH)2. KMT R&D center has conducted several different tests of the compound by applying different Mg(OH)2 grades in the same EVA-based compound.
Key Words: magnesium hydroxide, Mg(OH)2, HFFR compounds, polymer science
Magnesium hydroxide (Mg(OH)2, also known as MDH, MH) is an excellent flame retardant for plastics, polyethylene, polypropylene, polystyrene, rubber products and ABS resins and etc. Widely used in rubber, chemical, building materials, plastics and electronics, unsaturated polyester and paints. Compared with aluminium hydroxide, it has below advantages：
- When being heated, MDH and ATH both generate water and metal oxide. Water absorbs heat, and metal oxide covers the surface of polymer. But MgO can absorb more acid than Al2O3.
- Magnesium hydroxide (MDH) degrades at 340℃, 140℃ higher than Aluminum Hydroxide (ATH) does, so MDH is better for plastics required high processing temperatures.
3. MDH dissociation energy is 1.37kJ/g; ATH dissociation energy is 1.05KJ/g, and the thermal capacity of MDH is 17% higher than ATH also. So MDH has higher flame retardant efficiency.
4. Magnesium hydroxide with more carbonization can reduce more smoke.
5. MDH particle is softer than ATH, so less abrasion will happen during the compounding process which is good for the compounding machine.
To compare two different grades of MDH, KMT lab has conducted several tests between Magnifin H5 and PM5SM.
2. Test Preparation
2.1. Materials Preparation
Prepare the following materials:
Ethylene-vinyl acetate copolymer (EVA), grade 7470K, vinyl acetate (vA) content is 26%, from Formosa Plastics Group; Magnesium hydroxide (MDH) KMT PM5SM, particle size of 1~2μm, from KMT INDUSTRIAL HK LIMITED; Magnigin H5, the particle size is 1.6~2.0μm, from USA.
2.2. Test Machine
Pare the following machines:
Sample making: Banbury, Plate Curing Press; Mould; SY-6210-A Electronic Pulling Force Machine.
Test: universal testing machine, melt flow tester, oxygen index meter.
2.3. Test Condition
Keep the test lab site temperature at 23 degrees Celsius and the humidity at 40%.
2.4. Samples Preparation
Preheat the Banbury to 100 °C-120 °C, the mixing time is 30 minutes, the mixing temperature is 200 ± 10 °C.
Put the dough into the mould which is preheated well in advance (the thickness of the mould frame is 1 ± 0.1 mm), then use plate Curing Press tabletting (prepress: 10MPA, pressure: 10-15mpa, temperature: 220 °C, preheat for 2 Min), After tabletting cooled to 40-50 °C and got the samples.
3. Test Result
Table 1 Basic technical data of two kinds of MDH
|MDH||Particle size(D50）||Purity||Whiteness||Coated or Not|
In order to test the performance of the modified MDH, the KMT lab team compared Magnifin H5 with the PM5SN. The results are as follows.
3.1. Differences of Elongation at Break
|Sample||Elongation at Break(%)|
Table 2 shows the difference of elongation at break when adding different grades of MDH. The elongation of PM5SM is higher than that of Magnifin H5.
3.2. Differences of Tensile Strength
From table 3, it can be seen that the tensile strength of PM5SM is higher than that of Magnifin H5.
3.3. Differences of MFI
Form table 4, we can tell that the MFI of PM5SN is quite similar with Magnifin H5.
3.4. Differences of LOI
Table 5 shows the differences of LOI. The LOI of PM5SM is 2.5 higher than Magnifin H5, which means the PM5SM is harder to burn than Magnifin H5. This result refers that PM5SM’s flame retardant performance is better.
Table 6 MDH comparison test
|Elongation at break(%)||200±5||195|
|Tensile Strength (MPa)||15.28||13.6|
MDH could be an ideal flame retardants for its excellent flame retardancy and smoke suppression effect. According to the above tests, KMT-PM5SM shows better mechanical properties than Magnifin H5 in terms of elongation at break, tensile strength, MFI and LOI in this EVA-based formula.
KMT INDUSTRIAL HK LIMITED, headquartered in Gansu, China, research and manufacturer magnesium hydroxide, natural brucite powder and aluminum hydroxide.