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Synergistic effect of ATH and magnesium hydroxide reduce dosage and cost

Synergistic effect of ATH and magnesium hydroxide reduce dosage and cost

29-Jun-09
Techno - commercial information on plastics Industry - News on Plastics Industry - Plastemart.com
 
Synergistic Effect Of Ath And Magnesium Hydroxide Reduce Dosage And Cost

Synergistic effect of ATH and magnesium hydroxide reduce dosage and cost

 

REACH, RoHS, WEEE regulations concerning specific applications such as food contact and voluntary bans by trade associations or companies reduce the suitable fire retardancy formulations. This leads to HFFR solutions based on metal hydroxides, mainly ATH and MDH. The flame retardant effect of Aluminum TriHydrate (ATH) and Magnesium (Di)Hydroxide (MH or MDH) is based on their endothermic decomposition into aluminum oxide or magnesium oxide, forming non-toxic and non-corrosive decomposition products are formed. A wide range of halogen-free, non-toxic, environmentally friendly, flame retardant solutions can be obtained, especially with halogen free polyolefins such as PP. The main advantages include

 
  • Fire behaviour
    • Fire retardancy
    • reduced smoke densit
      Environmentally friendly: Only non-toxic and non-corrosive decomposition products are formed. HFFR polypropylenes are:
    • halogen-free
    • non-toxic
    • non-corrosive
    • non volatile
    • inert
    • recyclable
    • No or little effects on pigmentation
    • Economical
 

A drawback is the density, more than 2, as far as metal hydroxides are used at high levels to obtain fire retardancy, which leads to some issues concerning rheology, process ability and mechanical properties.

 
FR Type
Market shares, %
% AAGR 2005-2010)
ATH
40
5-6
Halogenated
30
3-4
Phosphorus (organic)
15
5-6
Antimony trioxide as a synergist in halogenated systems
10
3-4
Others including MDH, inorganic phosphorus, melamines, boron derivatives, nanomaterials
5
6
Total
100
4-5
Market shares and annual growth rate of FRs
 

 

Technically speaking, it is necessary to converge on a difficult balance of flame retardant properties, low smoke emission with constraints concerning opacity, toxicity and corrosivity of fumes, and fair functional properties.
To address these issues, synergistic additives are used:

 
  • Mineral fillers
 
    • ATH for MDH and vice versa, MDH for ATH
    • Calcium carbonate
    • Kaolin
    • Talc
    • Wollastonite
    • Fumed silica
    • Nanoclays
    • Barium sulphate
    • Zinc borate
    • Calcium borate
    • Ammonium salts
    • Magnesium sulphate heptahydrate
    • Boron derivatives
    • Molybdenum salts
    • Metal oxides: Ni, Co, Fe, Cu, Mn, Zn, Mo
    • Metal nitrates: Cu, Fe
    • Tin derivatives, zinc (hydro)stannate
    • Inorganic complexes or compounds such as, for example Kemgard® products, flame retardants/smoke suppressant additives including zinc molybdate, calcium zinc molybdate, zinc oxide/phosphate, zinc molybdate-magnesium silicate, zinc molybdate/magnesium hydroxide.
 
  • Intumescent additives
    • Polyacrylonitrile fibers
    • Carbon powder
    • Carbon nanotubes
 

High loading levels of inert fillers such as CaCO 3 have a diluting effect for some fire properties. For 100 parts of inert filler, the Rate of Heat Release (RHR), Peak RHR, Smoke Parameter (SP) can be divided by factors as high as 2 up to 4, but other properties can be weakly influenced. MDH and ATH have this diluting effect but, in addition, they act in another similar way, an endothermic decomposition with water release. The following table shows some comparative details.

 

ATH

MDH

Formula

Al(OH) 3

Mg(OH) 2

Water release

35%

31%

?H

-280 cal/g

-328cal/g

Decomposition temperature

230 up to 300°C

330 up to 400°C

Processing temperatures

<200°C

>200°C

Cost

lower

Higher

ATH and MDH property examples
 

ATH and MDH are efficient at loading levels in the order of 150phr (60wt%). Such high loading levels can detrimentally reduce processability, mechanical and other physical properties. Hydroxides are cheaper than most other FRs, However, the end cost is higher. MFRI-versus-Hydroxide-Loading shows the evolution of the MFIs of three grades of polypropylene versus the weight percent of hydroxide is illustrated below:

 

 

The mechanical property decreases, particularly impact strength that can decrease by 40% for a 60% hydroxide loaded PP.
Synergistic additives for hydrated fillers achieve lowering overall filler levels. This does not affect fire performance. Surface treatment of fire retardant additives with organo-silanes, zirconates or titanates can also improve their efficiency. ATH and MDH have mutual synergistic effects allowing to improve fire retardant properties for a same total loading or to lower the total loading for the same fire behaviour. The following exhibit of' LOI-&-SEA-of-ATH/MDH-Mixtures' illustrates high effect of ATH or MDH on the fire resistance (LOI: Limiting Oxygen Index and SEA: Specific Extinction Area) of PP.An optimized formulation, the limiting oxygen index is magnified by a factor slightly superior to 2 versus a neat polypropylene.

 

 
In extrusion trials, the replacement of pure MDH by various MDH/ATH mixtures allows reductions by:
  • 15 up to 20% of the die pressure
  • 15 to 20% of the torque
  •  

     

    ATH/MDH mixtures and use of synergistic mineral FR reduces cost. Prices of additives are, in descending order;

     
    • PP
    • MDH
    • ATH
    • Common white fillers
     

    It is possible to converge on a suitable balance of fire performances, fair physical and mechanical properties with a substantial cost saving in the order of 25-30% as illustrated by the exhibit given below.

     

     

    Some new developments in this sector include:
    The majority of plastic parts are monolithic but composites are developing for the freedom of sophistication. Over moulding and multilayer architectures allow to combine properties of two or more materials leading to new property balances. A.AHMADNIA and ALL (Tailoring the fire retardant performance of polymers using multi-component processing technologies, Antec 2003, p.2755) apply the technology to neat and FR PP. The neat polypropylene is over moulded with various skins of HFFR or a multilayer structure is formed alternating neat and HFFR PP.

    According to the architecture and the considered property, the evolutions can be beneficial or detrimental:

     

    Monolithic structure

    Multilayer structure

    Neat PP

    HFFR PP

    Overmoulding

    Multilayer

    Time to Ignition

    50

    86

    78-80

    87

    Heat Release Rate

    273

    118

    96-111

    105

    Specific Extinction Area

    386

    126

    106-172

    98

    CO yield

    0.017

    0.005

    0.003-0.006

    0

    CO 2 yield

    1.6

    1.5

    1.3-1.5

    1.5

    Fire behaviour versus architecture
     

    (Source:SpecialChem)

     
     
     
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