Mineral flame-retardant combinations as sustainable substitutes for ATO in flexible PVC
Corina Neumeister and Reiner Sauerwein of Nabaltec share results on new mineral based flame-retardant formulations for use in flexible PVC
All formulations contain 100 phr PVC 5 phr Ca / Zn-stabiliser 50 phr DINP and 50 phr CaCO3
Reference Compound 1 Compound 2
5 phr ATO |
|
40 phr AP 40T1 |
35 phr AP 40T1 |
2 phr ZnB |
2 phr ZnB |
5 phr ACT PA-B2 |
Compound 3 Compound 4 Compound 5
35 phr AP 40CD |
35 phrAP 40T1 |
25 phr AP 40T1 |
5 phr ACT PA-14 |
5 phr ACT PA-14 |
15 phr AP 120E |
Tensile strength [ MPa ] |
18.6 |
14.7 |
14.8 |
Elongation at break [%] |
362 |
316 |
315 |
LOI(% O 2) |
30 |
29 |
29 |
DHC 50 µ S / cm [ min ] |
289 |
223 |
197 |
14.5 |
14.6 |
14.8 |
316 |
318 |
323 |
29 |
29 |
29 |
174 |
235 |
223 |
Figure 1- Highly filled PVC compounds with 50 phr CaCO 3
Note: AP = Apyral, ACT = Actilox
Flame retardancy in plastics is currently undergoing a period of profound technological and regulatory change. Across numerous applications, including wire and cables( W & C), construction products, electrical and electronic components, and automotive parts, demand is increasing for flame retardant( FR) systems that not only deliver high performance but also meet future requirements relating to sustainability, chemical safety and regulatory compliance.
Particular attention is being paid to antimony trioxide( ATO), which has been used for decades as a highly effective synergist in halogencontaining FR systems. Although ATO is extremely effective from a technical perspective, regulatory pressure on antimony-containing additives is steadily increasing. In Europe, it has a harmonised classification as‘ suspected of causing cancer’( Carc. 2, H351), and its potential future uses are being subjected to increasing scrutiny.
Several technical feasable alternatives to ATO are also heavy metal-based compounds and should therefore only be considered as transition solutions. At the same time, processors and OEMs are seeking alternatives that ensure long-term security of supply and regulatory stability.
Against this background, mineral FRs are becoming considerably more important. Aluminium hydroxide( ATH) and boehmite( aluminium monohydrate) act through physical FR mechanisms and are characterised by a favourable toxicological profile and a long history of industrial use.
Their effectiveness is based on endothermic decomposition accompanied by the release of water, which removes heat and dilutes combustible decomposition products. At the same time, a mineral protective layer forms, shielding the material surface from further thermal stress. In addition, mineral FRs typically help to reduce heat release and smoke generation and are regarded as key components of future halogen-free FR concepts.
Materials
A recent study at Nabaltec aimed to investigate such mineral FR concepts using plasticised PVC formulations as an example. It focused on highly filled flexible PVC formulations typically used in cable applications: 100 parts( phr) of PVC resin( K70) stabilised with a calcium / zinc( Ca / Zn) package( 5phr), 50 phr of a Di-iso-nonyl- phthalate( DINP) plastisiser and 50 phr calcium carbonate( CaCO3).
The reference FR system was 5 phr ATO and 2 phr zinc borate( ZnB). The objective was to develop completely ATO- and ZnB- free systems based on ATH in combination with mineral synergists.
Two grades of fine precipitated ATH from Nabaltec were used in this study. Apyral * 40CD is a well-known standard grade for W & C applications with a median particle size( D50) of 1.8 µ m and a specific surface area( BET) of 3.5-4 m 2 / g. Apyral 40T1 is a newly developed surface treated version of Apyral 40CD, optimised for processing into a PVC polymer matrix.
Nabaltec has developed processing additives and FR synergists based on mineral carriers called Actilox * PA-14 and Actilox PA-B2. Both products and Apyral 120E, a fine precipitated ATH with a BET of 11-12 m 2 / g, have been used in conjunction with the aforementioned ATH FR fillers as an offset for ZnB.
Results: Burning behaviour & thermal stability
Limiting Oxygen Index( LOI) according to ISO 4589-2 was used to determine the burning behavior of the PVC compounds. The results show that the reference system can be replaced
72 SPECIALITY CHEMICALS MAGAZINE ESTABLISHED 1981