Surface treatment of natural magnesium hydroxide Influence on properties of HFFR cable compounds

Surface treatment of natural magnesium hydroxide Influence on properties of HFFR cable compounds

Surface treatment of natural magnesium hydroxide Influence on properties of HFFR cable compounds

Incorporating high amount of mineral filler into a thermoplastic polymer without compromising fluidity or mechanical properties of the final product is an eternal task of any compound manufacturer. This problem is especially of importance for manufacturers of HFFR cable compounds which are to combine high flame retardancy with smooth surface and nice elasticity. It is necessary to apply inorganic hydroxides (Al or Mg), particles of which are far from spherical shape and do not exactly promote elasticity. Moreover, any mineral filler contains some impurities, which cripple the ageing performance of the compound (the more filler there is – the stronger).

One way to solve described issues is to apply surface treated (or in other words surface coated) filler. Preliminary treating a mineral filler, especially of natural origin, with an organic agent allows to «deactivate» its surface – reduce moisture uptake, suppress interactions between impurities and polymer, improve filler-polymer compatibility and dispersion.

The most widespread and popular surface treatment agents are stearic acid, its derivatives and organo-functional silanes. Stearic acid provides good compatibility along with low cost. On the other hand, silanes provide additional features depending on the functionality, in example ability crosslink along with the polymer. In general, abilities and features of such agents are known, therefore the goal of present work is to investigate potential advantages of different combinations of components.

All agents were tested in a model formulation (Table 1), originally developed for synthetic ATH, replacing half of its quantity with natural magnesium hydroxide «EcoPiren 3,5» with appropriate surface coating.

Formulations      

Ref. Compound    
Ingredient
Trade name phr 
EVA28 MFI=3 
Escorene UL00328 
70
mLLDPE d=0,918 MFI=3,5 
Exceed 3518 
20
LLDPE-g-MAH 
Fusabond E226 
10
Silicon MB 
Silmaprocess AL1142A 
3
Stabilizer
Silmastab AE1527E  0.5
Fine precipitated ATH      Apyral 40CD   160   
Total   263.5

Table. 1 Model formulation of HFFR compound

On the first stage the effect of changing the level of Stearic treatment was evaluated (Table 2). Surface treatment with Stearic acid allows to improve fluidity and elasticity of the compound 10-15%. Increasing level of treatment after 1% does not further improve mechanical properties.

The effect of Stearic acid is definitely notable at 8-10% increased elongation compared to untreated grade, but it still doesn’t allow to reach Reference properties. Therefore, on the next step combinations of agents were evaluated:

  • «Dynasilan VTEO»

  • «Dynasilan 6498»

  • «Dynasilan GLYMO»

  • «Dynasilan AMEO»

  • «Pevalen»

  • «Esterex TM1111»

  • «TPSA»

Surface treatment was performed by preliminary homogenized mixtures of 1:1 ratio. The results are shown in Table 3.

All tested combinations showed higher Tensile Strength in comparison with Stearic acid. The mixture of TPSA and VTEO (FT40 and FT45) showed the best results. Its application increased the elongation at break 15-20% without the elongation at break 15-20% without significant loss of Tensile Strength.

Is it possible to obtain additional benefits using ternary mixtures? This was tested on the next step. Components were also premixed in ratio 1:1:1, immiscible combinations were skipped. The results are shown in Table 4.

No ternary mixture showed better results compared to binary one, though previous step best overall combination Pripol-VTEO-GLYMO performed roughly on the same level.

Thus it is possible to conclude that surface treatment provides a significant bonus to natural magnesium hydroxide performance and a possibility to introduce additional functionality. However, not every issue with natural mineral fillers can be solved by the surface treatment.

Formulations
Ref. Cmpd 
FC 35
FT 35
FT 20  FC 34  FC 38
Base Ecopiren  

EP3,5 

EP3,5 
EP3,5 
EP3,5 
EP3,5 
Coating

None

Stearic acid
Stearic acid
Stearic acid
Stearic acid
Treatment (%wt) 
None 0.5 1.0 1.5 2.0
Properties Apyral  EP3,5   EP3,5   EP3,5   EP3,5   EP3,5 
Density at 23°C  
1.497
1.496
1.489
1.481 1.485  1.500 
MFI – 21,6kg @ 190°C 
13    4    5    6    7    12   
LOI    36    34    34    34    34    34   
Tensile Strength     13    13    12    11    9    8   
Elongation at break     180 135    140    146    139    144   

Table. 2 Stearic acid treatment level effect on compound properties

Formulations
Ref. Cmpd 
FT31
FT32
FT33  FT34    FT28  FT30    FT27  FT29  FT40  FT45 
Treatment of Ecopiren (%wt) 
1.8 1.8 1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.2   
Component 1  
Pevalen
Pevalen
TM111  TM111  GLYMO  AMEO  Pripol  Pripol  TPSA  TPSA 
Component 2 
VTEO
6498
VTEO  6498  VTEO  VTEO  GLYMO  VTEO  VTEO  VTEO 
Properties
Apyral
FT31
FT32
FT33    FT34    FT28  FT30    FT27  FT29  FT40  FT45 
Density at 23°C 
1.497  1.49  1.488  1.491  1.488 1.484  1.48    1.484    1.486    1.482    1.485   
MFI – 21,6kg @ 190°C    13    4.1    6.2    5.2    7.8    6.1    6.3    8.1    7.6    5.6    8.2   
Tensile Strength 
13    12.2    11.5    12.4    11.7    12    11.7    11.8    12.2    11.5    12.5   
Elongation at break 
180    131    138    125    142    132    139    153    147    162    157   

Table. 3 Binary mixtures treatment results

Formulations Ref. Cmpd 
FT23
FT24
FT25    FT26   
Treatment of Ecopiren (%wt) 
1.8 1.8
1.8  1.8 
Component 1 
Pripol
Pripol
Tego 6879  Pripol 
Component 2 
AMEO
VTEO
GLYMO  VTEO 
Component 3 
Tego 6879
GLYMO
Pripol  GLYMO 
Properties Apyral  FT23  FT24    FT25    FT26   
Density at 23°C      1.497
1.487  1.482  1.488  1.483 
MFI – 21,6kg @ 190°C      13 6.9    5.8    6.2    3.4   
Tensile Strength      13    11.3    11.2    10.9    11.2   
Elongation at break      180  145  154  139  147 

Table. 4 Ternary mixtures treatment results

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