EoW March 2010

technical article

enable the production of compounds with this degree of flexibility. Compounds prepared with Levapren ® 700HV did not perform as well at low temperatures as those prepared with Levapren ® 500HV. This is due to the higher Tg of the EVM 70% VA content material, when compared to the EVM 50% VA content grade (–17°C against –28°C), and because the compounding of the Levapren ® 700HV based for- mulation was made using only 15 phr of plasticiser, instead of 20 phr as used in other compounds. Measurements at low tem- peratures for a compound prepared with 20 phr of plasticiser were conducted in previous studies where mechanical properties, such as tensile strength, were rather low.

1991, explaining that LOI for Levapren FRNC cable compounds experiences an increase at constant loading of 190 phr or more on grades with VA content higher than 65% wt. Furthermore internal studies conducted with Geniosil ® XL 33 described an interesting effect on the LOI of compounds prepared with Levapren ® 700 HV and 190 phr ATH (BET=12 m 2 /g). An increase of the silane content up to 3 phr correlated with an increase of the LOI. 3.5 Hot air ageing properties According to the NEK 606 specification, a hot air ageing test must be conducted for 168 hours at 120°C on compounds intended for cable jacketing. To push the limits of developed compounds a more severe test was carried out for 168 hours, 336 hours and 672 hours at 135°C. The values of variation of properties after ageing are reported in Figures 9 and 10 . After 336 hours the first effects of ageing are observed in developed compounds, especially on elongation at break of compounds based on Therban ® LT 2007, Therban ® LT 2007 and Levapren ® 500 HV B ( Figure 9 ). When compared with ageing after 336 hours, retention of properties for developed compounds after 672 hours is good; only minor changes in the variation of properties can be observed, especially for Levapren ® 500HV based compounds ( Figure 10 ). This could be adjusted via an optimisation of heat stabilisation package based on Stabaxol ® P and Rhenofit ® DDA-70.

Figure 6 ▲ ▲ : Elongation at break of cable compounds measured at –40°C and –50°C

Cold Bending –40ºC Cold Bending –50ºC Brittleness Point

A high amount of plasticisers in sole EVM 70% VA content compounds has a negative effect on the overall mechanical properties profile. 3.4 Flame retardant properties The combination of ATH fillers (Apyral ® with BET= 12 and 20 m 2 /g) was present in all compounds and could have contributed the good mechanical

Figure 7 ▲ ▲ : Cold bending measured at –40 °C and –50°C and brittleness point

taken place even when the specific surface filler used is not high enough to ensure a hydrophobation. Effect of plasticiser The combination of 10 phr of Di-n-octyl sebacate (DOS) and (Tris (2-ethylhexyl) trimellitate) TOTM plasticiser provided the cold flexibility necessary for low tempera- tures. TOTM plasticisers are normally used in applications where low volatility is of supreme importance. These applications include wire and cable insulation and automotive interiors. TOTM has unique low migration properties and extraction resistance properties [11] . DOS is an excellent cold-resistant plasticiser with a high impact on glass transition temperature but a higher volatility com- pared to TOTM. Both plasticisers are suitable for EVM copolymers, ethyl cellulose and synthetic rubber and especially suitable for cold-resistant wires and cables or artificial leathers. These low temperature properties are determined by molecular structure. Cold bending at –40°C and –50°C and brittleness point was measured for all developed compounds. Only the com- pound prepared with Levapren ® 700HV did not meet cold bending at –40°C. Only compounds based on Therban ® LT 2007 and on blends of this polymer with Levapren ® 500HV met the bending at –40°C and –50°C, making them suitable for installations operating at such low temperatures ( Figure 7 ). The lowTg of the HNBR grade and the plasticising effect of DOS and TOTM

Figure 8 ▼ ▼ : Limiting oxygen index for developed compounds according to ASTM D 2863

properties as well as good limiting oxygen index (LOI) values. Limiting oxygen index for compounds was conducted according to ASTM D 2863; all compounds displayed values of LOI higher than 34%. A compound based on Levapren 700 HV displayed an exceptionally high LOI value of 46%; this may be explained by the following: High VA content EVM 1. polymers (70%) and their synergy with ATH fillers Lower amount of 2. plasticiser and higher amount of ATH Different particle size ATH fillers combined with zinc borate provide a very compact and stable char in the case of fire. described the synergistic effect of EVM polymers and ATH in Meisenheimer [12]

Figure 9 ▼ ▼ : Hot air ageing test for 336 hours at 135°C

TSVariation (%) EBVariation (%) Hardness Shore A (%)

179

EuroWire – March 2010