Effects of Cooling Methods on Dielectric Properties of MMT/LDPE

doi:10.15541/jim20150206

Abstract

Abstract:

The melting intercalation method was used to prepare montmorillonite/low density polyethylene (MMT/LDPE) nano-composites. Through natural air cooling, rapid air cooling, water cooling, and oil cooling methods, the effects of different preparation processes on the dielectric properties of the composites were studied. The MMT/LDPE composite materials were characterized by XRD, FTIR, AFM, PLM, DSC, and TSC test. All experimental results show that the surface modified nano-MMT particles have been exfoliated and uniformly disperse in polyethylene. Different cooling processes have influence on the crystallinity of the composites. The oil cooling sample has higher crystallization rate and smaller crystal size. The density and depth of trap in the composites with nano-MMT are increased, which effectively improves dielectric properties of the polymer. Space charge in the composites by oil cooling process is evidently inhibited under 20 kV/mm and 40 kV/mm field strength. The peak value of positive charge is decreased by 63.57% and 51.39% as compared with that of natural air cooling. The oil cooling sample shows the smallest conductivity, and the largest breakdown strength. In the frequency range of 1-10⁵ Hz, the dielectric constant and dielectric loss angle tangent of other threetypes of rapid air cooling, water cooling and oil cooling samples decrease at different degrees in contrast to natural air cooling sample.

Key words: low-density polyethylene, nano-MMT, cooling methods, dielectric propeties

CLC Number:

TB332
TM215

CHENG Yu-Jia, ZHANG Xiao-Hong, ZHOU Xue-Dong, GUO Ning, CHENG Ru-Ru, ZHANG Tian-Xu. Effects of Cooling Methods on Dielectric Properties of MMT/LDPE[J]. Journal of Inorganic Materials, 2015, 30(12): 1295-1302.

Figures/Tables 13

Fig. 1 XRD patterns of MMT and MMT/LDPE specimens

Fig. 2 FTIR patterns of MMT and MMT/LDPE specimens

Fig. 3 AFM images of MMT/LDPE. (a) Height map; (b) Phase diagram

Fig. 4 PLM images of MMT/LDPE. (a) Natural air cooling; (b) Rapid air cooling; (c) Water cooling; (d) Oil cooling

Fig. 5 DSC curves of LDPE and MMT/LDPE samples during heating and cooling

Fig. 6 TSC spectra of samples

Fig. 7 Relationship between conductivity and field strength for four types of samples

Fig. 8 Weibull distribution parameters of four types of samples

Fig. 9 Frequency dependences of dielectric properties of various samples

Fig. 10 Space charge distribution in MMT/LDPE samples under various electrical field. (a) Natural air cooling; (b) Rapid air cooling; (c) Water cooling; (d) Oil cooling

Fig. 11 Changes of space charge distribution in various samples with short-circuited time. (a) Natural air cooling; (b) Rapid air cooling; (c) Water cooling; (d) Oil cooling

Table 1 Average charge density of MMT/LDPE samples under different electric field

Electrical field	10 kV/mm	20 kV/mm	40 kV/mm
Natural air cooling	0.58522	1.74640	2.03929
Rapid air cooling	0.59581	1.79236	2.08940
Water cooling	0.50265	1.74408	1.67510
Oil cooling	0.34720	1.19120	1.57720

Table 2 Charge density distribution of MMT/LDPE system with short-circuit time/ (C•m-3)

Short circuit time	60 s	900 s	1800 s
Natural air cooling	1.95505	1.16921	1.01754
Rapid air cooling	1.99370	1.16921	1.01754
Water cooling	1.60711	0.95444	0.75726
Oil cooling	1.04666	0.65901	0.59119

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