EVA/organoclay-based nanocomposites

Compound mixing was performed on different compounding equipment. For EVA organoclay-based nanocomposites, a laboratory twin-roll mill and an internal mixer heated to 145 °C were used. A corotating twin screw extruder from Leistritz, Germany, with a 27-mm screw diameter and an aspect ration of 40 L/D was used to generate polyethylene nanocomposites. The mass temperature was 190 °C at the extruder die. 

Table 7.1 Temperature at the maximum degradation rate of the main decomposition peak (DTG) measured by TGA under airflow at 20 °C/minfor EVA and EVA-based nanocomposites with different organoclay content...

The great improvements in flame retardancy caused by the organoclays also opened the possibility of decreasing the level of ATH within the EVA polymer matrix. The content of ATH needed to maintain 200 kW/m as a peak heat release rate could be decreased from 65 to 45 wt% by the presence of only 5 wt% organoclays within the EVA polymer matrix. Reduction in the total amount of these fillers resulted in improved mechanical and rheological properties of the EVA-based nanocomposite. 

TABLE 7.1 Maximum Temperature at the Main Degradation Peak Measured by TGA Under Airflow at 20°C/min for EVA and EVA-Based Nanocomposites with Different Organoclay Contents"... 

All compounds were melt-blended in a Brabender mixing chamber. It is evident from the results in Table 7.4 that all the filled polymers had improved flame retardant properties. For EVA and EVA-based nanocomposites containing 2.5 phr of filler, the PHRR decreased as follows EVA > organoclays purified MWCNTs. For EVA and EVA-based composites containing 5.0 phr of filler, the PHRR decreased as follows EVA > organoclays > purified MWCNTs = crude MWCNTs. Crude MWCNTs were as effective in the rednction of PHRR as purified MWCNTs Increasing the filler content from 2.5 phr to 5.0 phr caused an additional flame retardant effect that was most significant when purified or crude MWCNTs were used. 

An example of FRNH cables passing UL-1666 is shown in Fignre 7.5. The outer sheath was based on a nanocomposite with an industrial EVA-ATH-organoclay composition. The analogons coaxial cable was tested with an outer sheath based on EVA-ATH. In both compounds the relation of polymer to filler was the same and Table 7.2 presents the results. The improved flame retardant properties were due to the formation of a char layer during... 

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