EuroWire September 2021

Technical Article

Test results derived from the twelve compounds made with 28 per cent VA copolymers are presented in Table 2 . Little difference is observed in volume resistivity and surface resistivity when comparing standard EVA to the new experimental EVA in corresponding formulations. This indicates that the modification to the experimental EVA does not have any significant effects on the surface or volume resistivity of the EVA and therefore should not require significant reformulation for use. Figure 1 shows the shear viscosity of each sample as measured using a capillary rheometer at 190°C with a shear rate of 300 1/s. These results are also listed in Table 2 . In every model formulation, the experimental EVA has a lower viscosity than the standard EVA. This effect is largest in the formulations that do not contain any MA-g PE, and is lowest in the formulations containing 3 per cent MA-g PE. The reduction in viscosity change for samples containing MA-g PE is seen best in the compound containing 3 per cent MA-g PE and no LLDPE. Therefore, we conclude that the effect on compound viscosity is not simply a dilution of the experimental EVA. Instead, we hypothesise that the addition of MA-g PE affects how the new EVA interacts with the formulation components within the compound.

Sample name

MA-g PE (wt %)

EVA type EVA (wt %) LLDPE (wt %)

Cont-1

Cont-28

40

–

–

Exp-1

Exp-28

40

–

–

Cont-2

Cont-28

31

9

–

Exp-2

Exp-28

31

9

–

Cont-3

Cont-28

37

9

1

Exp-3

Exp-28

37

9

1

Cont-4

Cont-28

30

9

2

Exp-4

Exp-28

30

9

2

Cont-5

Cont-28

29

9

3

Exp-5

Exp-28

29

9

3

Cont-6

Cont-28

28

–

3

Exp-6

Exp-28

28

–

3

Table 1 : Description of model compounds used

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One surface-treated magnesium hydroxide sample (MDH) was used as an example mineral flame retardant additive. One linear low density polyethylene sample (LLDPE) with a melt index of 1.0g/10min was used as an example modifier for mechanical properties. One maleic anhydride grafted polyethylene (MA-g PE) with a melt index of 1.5g/10min was used as an example maleic anhydride grafted polyolefin. 3.2 Sample preparation and tensile testing All samples were compounded in a twin screw extruder at 170°C. We produced twelve compounds, each containing 60 per cent of MDH, LLDPE at either 0 or 9 per cent, and MA-g PE at levels of 0, 1, 2 or 3 per cent, with the remainder of the formulation composed of EVA. The formulations and nomenclature are listed in Table 1 . Samples were extruded into 3mm-thick tapes at 180°C. 10cm x 10cm test specimens were cut from each tape sample for testing volume and surface resistivity. Tensile bars were stamped from the tape samples using a press. Tensile testing was conducted by pulling samples at a crosshead speed of 50mm/min. Five tensile bars of each sample were tested; the results reported are average values. Shear viscosity was measured on each sample using a capillary rheometer at 190°C. A shear rate of 300 1/s was used for all shear viscosities shown in this report. 4 Results One of the key challenges in the formulation of highly filled polymer compounds is maintaining flexibility and tensile elongation characteristics when the material contains a high level of filler. For LSZH compounds, filler levels are commonly quite high. Previously we demonstrated that our proprietary modification to a 28 per cent VA copolymer substantially increased per cent elongation and tensile strength of a highly filled compound [5] . Here, we explore how this material performs within a model fully formulated compound.

▲ Figure 1 : Shear viscosity comparison of compounds at 190°C

Volume resistivity (10 13 ohm-m)

Surface resistivity (10 15 ohm)

Shear viscosity (Pa-s)

Tensile elongation (%)

Sample name

Cont-1

4.1

33

1,227.1

180.9

Exp-1

3.9

11

902.5

711.1

Cont-2

2.5

4.7

1,068.7

260.7

Exp-2

5.1

7.1

911.1

506

Cont-3

4

13

1,096.2

236

Exp-3

2.8

33

1,033.4

321.4

Cont-4

2.8

23

1,264.1

141.5

Exp-4

2.2

16

1,094

239.6

Cont-5

2.1

27

1,226.6

152.5

Exp-5

1.4

10

1,116.5

149.2

Cont-6

3.1

5.8

1,096.2

209.4

Exp-6

1.8

4.1

1,033.4

205.8

Table 2 : Test results on 28 per cent VA copolymers

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70

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September 2021