Speciality Chemicals Magazine SEP / OCT 2026 | Page 73

FLAME RETARDANTS by suitable combinations of ATH and mineral synergists.

Formulations based on Apyral 40T1 or Apyral 40CD, in conjunction with Actilox PA-B2, Actilox PA-14 or Apyral 120E, achieved FR properties very close to the ATO / ZB reference system: 29 % oxygen( O 2

) versus 30 % O2( Figure 1). All compounds fulfilled UL94 V0 classification at 1.6 mm.

In addition to flame retardancy, particular attention was paid to the thermal stability of the PVC compounds. We used the dehydrochlorination( DHC) test according to ISO 182-3, a conductometric method where a PVC sample is heated at a constant temperature under a stream of nitrogen.

Hydrogen chloride( HCl) gas is released by the degrading material and carried by nitrogen into a vessel of deionised water. The dissolved HCl increases the electrical conductivity of the water. The stability time is defined as the time required to reach a conductivity value of 50 µ S / cm. A longer stability time indicates better thermal stability of the PVC compound.

The ATO containing reference shows a very high DHC stability of 289 minutes. The complete substitution of 5 phr ATO by ATH fillers applied at 25-40 phr loading does not necessarily lead to a marked deterioration in heat stability of the PVC compound. DHC stability times of 174-235 minutes were measured for the ATHbased formulations.

Comparing Compounds 3 and 4 demonstrates the performance benefit of Apyral 40T1 versus Apyral 40CD regarding processing stability of the PVC( 235 min versus 174 min DHC stability). The combinations of Apyral 40T1 with Actilox PA-14 and Apyral 120E performed particularly well, achieving DHC values of > 220 minutes, comparable to the combination of Apyral 40T1 and ZnB.

Results: Physical properties

As expected for systems with high mineral filler content, the increased total filler concentration resulted in a moderate reduction in mechanical properties. Tensile strength decreased from 18.6 MPa for the ATO / ZnB reference to approximately 14.5 – 14.8 MPa for the ATO-free variants, which is still well above typical minimum requirements found in W & C standards. At the same time, elongation at break remained at a high level for flexible PVC applications, ranging from 315 % to 323 %.

The results demonstrate that, despite the complete elimination of ATO and ZnB, these highly mineral filled formulations show excellent FR properties and retain thermal processing stability and mechanical performance. Apyral 40T1 in combination with mineral synergist Actilox PA-14 in particular is a suitable substitute for W & C compounds.

CaCO 3 loading effects

To improve the mechanical properties further, the calcium carbonate content was subsequently reduced substantially. Instead of 50 phr CaCO3, the optimised formulation contained only 15 phr, while the Apyral 40T1 content remained unchanged and Actilox PA-B2 was added as a synergist.

This adjustment led to a marked improvement in the material properties. Tensile strength increased to 18.4 MPa, same as the level of the ATOcontaining reference. Elongation at break increased from approximately 315 % to 347 %, very close to the reference( 362 %).

In parallel, the reduction of CaCO 3 deteriorated DHC stability only very slightly from 197 min to 182 min. Although the LOI value decreased to 27 %, the FR performance evaluated by cone calorimetry is outstanding( see below). The results illustrate that targeted adjustment of the filler package can achieve a balanced compromise between flame retardancy, thermal stability and mechanical performance.

Substituting ZnB

As already demonstrated in the compound series containing high filler load( Figure 1), ZnB can be replaced by alternative mineral synergists. ZnB is known for its smoke reduction efficiency in plasticised PVC. To investigate the substitution potential of ZnB in PVC compounds of lower filler level, cone calorimetry according to ISO 5660 was used. This method can simultaneously determine heat release and smoke release properties.

Apyral 40T1 at 50 phr was compared with 35 phr APYRAL 40T1 combined with 15 phr CaCO3 and 5 phr of synergist( ZnB, Actilox PA-B2 and Actilox PA-14 respectively). Figure 3 displays total smoke release( TSR) and

All formulations contain 100 phr PVC 5 phr Ca / Zn-stabiliser 50 phr DINP

Reference Compound 2 Compound 6

Figure 2- Effect of

CaCO 3 reduction( Compound 6)

Note: AP = Apyral, ACT = Actilox

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