EoW March 2009

technical article

4 Research and development

As can be seen in XRD and SEM, Na+MMT is exfoliated. XRD pattern of Na+MMT shows a peak of 2θ=7.2 but XRD pattern PVC/Na+MMT compound decreases intensity. Several properties for cable applications were investigated: heat stability – CEI 20-34 • LOI for flame retardance – CEI 20-22/4 • accelerated ageing – CEI 20-34 • HCl emission – CEI EN 50267-1 • volume resistivity – ASTM D 257 • smoke density – ASTM E 662 • temperature Index – ISO 4589-3 • PVC/Na+MMT compound, though exfoliated, shows some decreases in these properties. In Figure 3 the TGA (Thermo Gravimetric Analysis) is reported as weight loss %/ temperature. The first drop is the de-hydrochlorination. The second drop between 425° and 600°C shows a loss of toluene and xylene, formed from the polyolefin reticulated by the temperature. Further heating causes the formation of aromatic polycyclic structures. As show in Figure 3 , at the first drop the loss of volatile substances is CaZn. Table 1 shows that

The feature that makes them interesting, and worthy of increasing scientific and technological excitement, rests in fundamental length scales dominating the morphology and properties of these materials. Between layered silicates the Mont- morillonite (Na+MMT) avoids to obtain intercalated polymer. MMT is environmentally friendly, naturally abundant and economical. It has been applied in numerous industrial fields due to its good performance-cost ratio.

B & B Compounds’ research activity has focused on the preparation and characterisation of: nano-structured material with • Na+MMT Sintetized Mineral Hydrozides (SMHs) • heavy metal free systems stabilisers • Ca-Zn Tests were carried out using two basic formulations of soft PVC used in sheathing and insulation for electrical cables. In the case of incorporation of Na+MMT investigating the dispersion degree means SEM ( Figure 1 ) and XRD ( Figure 2 ).

Tetrahedral sheet

Silicon atom

Oxygen atom

Tetrahedral sheet Octahedral sheet

Aluminium

C-axis

Note the size of the featured clay (Montmorillonite) is 1mm thick and 100 – 500nm wide

MMT ▲ ▲

MMT smectite grouping, consisting of silicate layers of approximately 200nm in length and 1nm thick. The spacing between stacked layers is approximately 1nm. The outstanding feature of MMT is that the silicate layers can be expanded and even de-laminated by organic molecules under proper conditions. Thus, during the processing of polymer/MMT nanocomposites, the nanoscale silicate layers can be dispersed in the polymer matrix and the reinforcement phase forms in-situ on the molecular level, which is very different from conventional filled composites. Moreover, it has been found that the polymer/ MMT nanocomposites can be prepared by conventional processing techniques, such as extrusion and injectionmethods. shows di-octahedral

Figure 1 ▲ ▲ : SEM PVC/Na+MMT

Figure 2 ▲ ▲ : XRD Na+MMT and PVC/Na+MMT

Figure 3 ▲ ▲ : TGA SMHs compounds/CaZn compounds

Table 1 ▼ ▼ *with Sb 2 O 3

Type of filler

Property

Units

Ca/Zn

Na+MMT

SMHs

15 13

10 5

15 14

Tensile strength After 168h @ 100° Elongation at break after 168 h @ 100°

MPa

380 370

140 90

390 400

%

Heat stability

Minutes

60

10

100

LOI

%O

29*

25

29

2

HCl emission

mg/g

190

198

150

0.01 X 10 14

1.2 X 10 14

Volume resistivity

Ω.cm C° 20

0.06 X 10 14

95

EuroWire – March 2009