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Presented byMoumita Mistri

M.Tech 1st Year student, IIT-KGPMaterials Science Centre

Roll No- 14MS60R03 Course Name: Seminar IICourse code : MS69002

Positive temperature coefficient effect in polymer composites.

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outline

Introduction of PTCR effect.

Applications of PTCR in polymer composites.

Abstract : “ Positive temperature coefficient effect in multiwalled carbon nanotube/high-density polyethylene composites.”

Characterization of CNT/ HDPE composites.

Conclusions .

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Some materials display an abrupt increase in resistivity when the temperature changes only over a few degrees. This phenomenon, known as PTCR effect (positive temperature coefficient in resistivity),

The addition of conducting particles to an insulating polymer is expected to produce a material which displays good conductivity. The conductivity, rather than being a linear function of loading, typically shows the behavior depicted in Fig 1. At the percolation threshold of loading , the filler particles starts toJoin with each other forming a network structure. If it is possible to interrupt that network thermally, there will be a significant increase in the resistivity. This is the basic principle behind the PTCR effect in these materials.

Figure 1 Electrical resistivity versus concentration of conductingparticles in an insulating matrix.

Introduction of PTCR effect

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Particle size,

Aggregate shape,

Dispersion state,

Characteristics of polymers such as

Chemical structure,

Crystallinity,

Processing conditions.

Dependence of PTC behavior of polymer composites

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Flow meters,

Current limiters,

Resettable fuses,

Timing devices in televisions,

Protection circuits,

Temperature sensors,

Self regulating heating elements,

Security systems for electronic circuits,

Applications

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Positive temperature coefficient effect in multiwalled carbon nanotube/high-density polyethylene composites

X. J. He, J. H. Du, Z. Ying, and H. M. Chenga!Shenyang National Laboratory for Materials Science, Institute of Metal Research,Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, People’s Republic of ChinaX. J. HeShenyang Institute of Chemical Technology, 11 Street, Shenyang Economic Development Zone,Shenyang 110142, People’s Republic of China

APPLIED PHYSICS LETTERS 86, 062112 (2005)

Multiwalled carbon nanotube (MWNT) [ produced by CVD ] -filled high-density polyethylene (HDPE)[with a melt index of 0.3 g/10 min ] composites were prepared by a solution-precipitation process, and the temperature dependence of electrical conductivity of the MWNT/HDPE composites was studied. An obvious positive temperature coefficient (PTC) effect was found in the MWNT/HDPE composites with a relatively low MWNT concentration. Compared with that of carbon black (CB)/HDPE composite, the negative temperature coefficient (NTC) effect of the MWNT/HDPE composite at temperature above the melting temperature of HDPE was much less obvious and could be further eliminated after 80 kGy g-ray irradiation.

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Figure 2: (a)TEM image of the as-produced MWNTs and (b) SEM image ofthe 5.4 wt% MWNT/HDPE composite.

Figure 3: Electrical resistivity vs MWNT content for the MWNT/HDPE composites.

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Figure 4: Comparison of resistivity-temperature curve for (a) 5.4 wt% MWNT/HDPE composite and (b)16 wt% CB/HDPE composite; © DSC curve of the 5.4 wt% MWNT/HDPE composite.

Figure 5: Resistivity-temperature curves of the 5.4 wt% MWNT/HDPE composite before and after irradiation.

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The MWNT/HDPE composites prepared by a solution-precipitation process exhibit an obvious PTC effect in the vicinity of Tm of HDPE.

The NTC effect of the composite at temperature above the Tm of HDPE is relatively small and can be eliminated after 80 kGy g-ray irradiation.

The PTC intensity for the MWNT/HDPE composite containing5.4 wt % MWNTs can reach 1.1 * 104

The mechanism of PTC/NTC effect in MWNT/HDPE composites is similar to that of CB-filled polymer composites.

Conclusions

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1. Positive Temperature Coefficient Behavior of Polymer Composites Having a High Melting Temperature.

Jung-il Kim, Phil Hyun Kang, Young Chang NhoRadiation Application Research Division, Korea Atomic Energy Research Institute, P.O. Box 105, Yusong,Daejon 305-600, South Korea

2. PTCR effect in polymer composites. JOURNAL OF MATERIALS SCIENCE LETTERS 22, 2003, 699– 700

3. http://www.electronicshub.org/wp-content/uploads/2013/06/PTC-Vs-NTC.jpg

References

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