EoW March 2009

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EuroWire – March 2009 96
technical article
Table 2 shows the test results on insulation
formulation.
5 Results
SMHs contribute to the combustion
retardancy of the polymeric matrix,
producing a refractory oxide residue
on the surface of the material and
releasing aqueous vapour and carbon
dioxide during the decomposition.
This endothermic process occurs in the
gas phase.
The levels of flame retardance and smoke
generation are strongly influenced by the
choice of components of the compound
and their quantity, particularly plasticisers
and Sb2O3.
The smoke produced by plastic samples
during combustion can be measured
in an NBS chamber according to ASTM
E662. Tests have shown an immediate and
significant increase in smoke generation
even with relatively small quantities of
Sb2O3. Therefore the use of SMHs and the
elimination of Sb2O3 could significantly
reduce the smoke density of PVC
compounds.
Tests of smoke density according to ASTM
E662 are still in progress.
SMHs act as stabilisers stopping the
process scavenging the HCl generated
by the degradation. In this way they stop
the chain propagation reaction and the
initiation step.
However, by scavenging HCL, this type
of stabiliser avoids the autocatalytic
degradation and consequently, overall
degradation is much slower. This stabiliser
provides very good long thermal stability.
The volume resistivity values are very
interesting, and frequency measures are in
progress to evaluate a possible variation of
dielectric properties.
B & B Compounds Srl
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I – 81025 Marcianise (CE) Italy
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6 Conclusion
Findings indicate that Na+MMT does
not enhance the properties of a PVC
compound, as happens with other polymer
matrix such as Nylon, PA 6, PS and PP.
SMHs should be a beneficial alternative
to hazardous additives, such as lead
stabilisers and Sb2O3. The capability to act
as both stabiliser and flame retardant is
especially valuable in cable applications.
Insulated wire is a product with a long
service life. The development of a range
of PVC eco-compounds for insulated wire
sheathing applications is a priority, and to
eliminate hazardous substances should be
a target, contributing to sustainability.
The use of no hazardous additives
allows products to obtain LCA (Life Cycle
Assessment) with low impact in terms
of the environment and human health,
both during their manufacture and their
service life.
This paper was presented at Wire Bologna
‘07, Bologna, Italy in November 2007
and is reproduced with the permission
of the organisers, International Wire
& Machinery Association (IWMA), The
Wire Association International Inc (WAI),
Associazione Costruttori Italiani Macchine
Per Filo (ACIMF) and Comité Européen de
la Tréfilerie (CET). n
Property Unit
Type of filler
Ca/Zn SMHs
Tensile strength
After 168h @ 100° MPa 18
16
19
16.5
Elongation at break
after 168 h @ 100° % 230 240
Heat stability Minutes 120 180
LOI %O2 28* 30
HCl emission mg/g 190 140
Volume resistivity Ω.cm C° 20 1 X 1015 2 X 1015
Table 2 ▲ ▲ *with Sb2O3