The preparation and performance of LLDPE/EVA/Mg(OH)2 composites (2)

The preparation and performance of LLDPE/EVA/Mg(OH)2 composites (2)

1.3 Performance test and characterization

Mechanical property ( comply with GB/T 1040.2-2006):

The size of spline length 170mm, width 10mm, thickness 4mm, gauge length 50mm, tensile speed 50mm/min.

Limited Oxygen Index ( comply with GB/T 2406-1993):

the length of spline 80-150mm. Draw a line at 50 mm away from the end of the sample. When the test strip reaches the mark, and the flame extinguishes, record the limiting oxygen index of the sample, or the flame of the sample burns for 3 minutes and extinguished, record the data. Test at least 15 sample until the error of three adjacent groups of data is within 0.5%, and record the data.

Determination of thermal deformation temperature (comply with GB/T 1634.1-2004 ):

Put the test strip flat on the sample rack, set the heating rate at 120 ℃/h, and take the average value of the two samples whose temperature error is within 5 ℃ as the final test result.

Melting crystallization behavior test:

Measuring 3-5 mg of the sample, using nitrogen as the protection gas and control the constant flow velocity, to test three processes. The initial temperature is set to 20 ℃, the termination temperature to 150 ℃, then the temperature to 30℃, and then the temperature to 150 ℃ again.  The heating and cooling rates are both 20 ℃/min.

Volume resistivity:

Smoke density (comply with GB/T 17651.2-1998 ):

A 45 mm cable with an outer diameter of 1 m was prepared and burned in the combustion chamber, 5 min after the flame was extinguished or the test lasted for 40 minutes, When the transmittance no longer decreases, the test ends. Record transmittance.

2 Discussion and results

2.1 Influence of EVA content on LLDPE/EVA composite

According to table 1, along with the increasing of EVA, tensile strength is decreasing. When the EVA content is 50%, tensile strength decreased from 13.8MPa to 11.0 Mpa. It is because the crystallinity of LLDPE is higher than that of EVA(28% VA), and with the adding of EVA, the crystallinity of composite system decreases. And due to the polarity of VA, the high content VA leads to strong polarity, which decreased the tensile strength of non-polarity LLDPE.

The elongation of break increases along with the adding of EVA. It is because VA content can help improve the fluidity of the composite material, and elongation of break increases. From the table 1, we can also see that the LOI also increased, that is because the flame retardant performance of EVA is better than LLDPE, and the volume resistivity has no big change, which means the electricity property of EVA and LLDPE is similar.

During the extruding, we found the material surface extruded with LLDPE is rough, but the material surface extruded with EVA and LLDPE composite us smooth. That means EVA can improve the fluidity and processing technology of the polyolefin. And we can see, as a base resin in this composite, the best proportion of LLDPE and EVA is 70:30 (phr).

EVA Content/%Tensile Strength/MPaElongation at break/%Oxygen Index/%Volume Resistivity/Ω.m

Table 2 Effect of the loading of EVA on properties of LLDPE/ EVA blending system

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