| The properties of conductive polymeric composites are related not only to the components and structure but also to the effect of exterior fields on the agglomeration structure of polymer materials during the preparation and applications. In this thesis, the dynamic viscoelastic properties of the filled conductive composites were investigated systematically and correlated with electrical properties of the conductive composites in order to explore the mechanism for the variation and development of the agglomeration structure under the effect of thermal field.1. A study on the dynamic viscoelastic properties of carbon black (CB)-filled high-density polyethylene (HDPE) in the molten state was carried out. When the temperature is above 180℃ in an air atmosphere, the storage modulus (G'), loss modulus (G"), and loss tangent (tanδ) shows particular characteristics. In the low-frequency (ω) region, the modulus increases with increase of the testing time while the tanδ obviously decreases. Also, the higher the temperature, the more notable is the change. We can detect these changes from the deviation of G' (G ") against ω plots from the linearity and the appearance of a characteristic plateau phenomenon. The width and height of the modulus plateau increase with increase of the temperature. When temperature is below 180℃, the testing time and the temperature have no effect on the viscoelastic parameters of HDPE. However, if we use 99% nitrogen gas (N2) as the atmosphere, substituting for air, the viscoelastic parameters reveal an undiscernible change, different from that in an air atmosphere. No changes are found under the protection of the antioxidant (B215). This phenomenon is attributed to the change of structure in HDPE at a temperature higher than 180℃ because of the oxidation-induced crosslinking of HDPE. NI and B215 can prevent HDPE from crosslinking.2. Studies on the correlation between electrical percolation and viscoelastic percolation for the conductive composites were carried out through examining the filler concentration (ψ) dependence of the volume resistivity (p) and dynamic viscoelastic functions. The results reveals that there existed three different ψ-dependent thresholds of viscoelastic percolation, (pG, (pr and . For CB/HDPE composites, when cp is higher than the threshold of modulus percolation pc, G' appears a plateau at low s. The relationship between p and the normalized dynamic storage modulus (G'C/G'P) is studied, in which G'c, G'p are dynamic storage modulus of the composites and the polymer matrix respectively. It is found that when p approaches p a. characteristic change in G'C/G'P appears. Also there exists p -dependent tan and a peak in plot of tan versus a when (p approaches a loss angle percolation (p. It is worth noting that tpc approaches the higher threshold y 2 of the electrical percolation which is generally referred to a change of semiconductor-conductor involving in perfect formation of interconnected structure, and cpr, (p are close to the lower threshold cp\ of the electrical percolation which is responsible for a change of insulator-semiconductor corresponding to the beginning of network structure formation. Substituting parameter K for A, a modified Kerner-Nielson equation is obtained and used to analyze the formation of network structure. It is suggested that the parameter K was associated with CB concentration. The viscoelastic percolation for CB/HDPE, CB/PS, GP/HDPE composites can be verified on the basis of the modified equation, while, no similar percolation is found for CF/HDPE composites because of weak interaction between CF and the matrix.3. The modified Mooney equation was established to estimate the relationship between G' and CB concentration. For GP/HDPE composites, the Mooney equation is modified by replacing filler volume fraction, (p, with effective volume fraction, . For CB/HDPE, CB/PS composites, the Mooney equation is modified on the basis of CB aggregation and effective filler concentration. It is suggested that t... |
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