The preparation and investigation of polyolefin low temperature positive temperature coefficient composites

Autor: Yu-Jui Wang, 王于瑞
Rok vydání: 2007
Druh dokumentu: 學位論文 ; thesis
Popis: 95
In this study, the low temperature positive temperature coefficient (PTC) composites were produced by blending the carbon black (CB) particles, which concentration is above the critical volume fraction, with Ethylene-vinyl acetate (EVA) as the semi-crystalline polymer matrix in proper processing condition. The effects of the EVA matrix type, the CB type, the relative content between EVA and CB, the blending condition, the processing method of chemical crosslinking, the crosslinking agent content, the condition of plasma treatment, and the secondary matrix content in immiscible-blend composites on the electrical performances of PTC composite were investigated. The change of electrical performances includes the variation of room temperature resistance, PTC and NTC effect. After that various analysis of the morphology, physical properties were carried out on the various EVA/CB composites. In the investigation of chemical crosslinking of EVA/CB composites, the morphology of the crosslinked structure was observed, the PTC intensity increased obviously, and the NTC effect was almost eliminated in the crosslinked composites with high BPO content (0.2phr), whereas the room temperature resistance increased and the switching efficiency /temperature (Tsw) decreased greatly. It was perhaps due to the crosslinking reaction expanded the amorphous region, and made the polymer chains move in earlier temperature region. In addition, EVA pellets were pretreated with different plasma treatment conditions then blended with CB to be expected for enhancing the compatibility and adhesion between polymer chains and CB particles and lowering the room temperature resistance. However, the observed morphology and the electrical performances were slightly similar to the crosslinked EVA/CB composites. In addition, the PTC composite was prepared by melt-mixing of immiscible powder blends of EVA, LLDPE (Linear low-density polyethylene), and CB particles. Three major factors-the weight ratio of EVA and LLDPE, the carbon black content, and the processing method had remarkable effects on electrical performances of the immiscible blends composite. With high EVA/LLDPE weight ratio, the EVA formed as the continuous phase, where CB particles were selectively located, and the LLDPE formed as the dispersed phase, the PTC effect of the uncrosslinked blends composite, mainly caused by the melting of EVA crystallites, was similar but slight decreased to those of CB-filled neat EVA composite and the NTC effect was delayed to higher temperatures and even eliminated. Even the interlocking, co-continuous structure might be formed at the lower EVA/LLDPE weight ratio or in the crosslinked blend composite; both phenomenon of suppressing the PTC effect and delaying the NTC effect became more remarkable. In addition, the room temperature resistance could also be decreased more obviously.
Databáze: Networked Digital Library of Theses & Dissertations
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