Preparation And Properties Of Polymeric Composites Filled With Sn-Pb Alloy

Due to the relatively low melting point, Sn-Pb (Tm=183癈) alloy filled in the polymer matrix will melt during the processing and application, and the state transition between rigid particles and deformable droplets can thus be achieved. Therefore, the Sn-Pb alloy loaded polymer composites have many special properties for their low melting point, which are not held by usual materials. In this master dissertation, the researches have been focused on the electrical properties and dynamic rheological behaviors of Sn-Pb alloy loaded polymer composites.In the first chapter, we summarize the research background of the polymer composites' electrical properties and rheological behaviors and describe our main research point.The influences of preparation conditions on the electrical properties of polymer composites have been studied. It is found that processing temperature and processing method are the determining factors of the electrical conductivity of Sn-Pb alloy loaded polymer composites. In order to achieve excellent electrical conductivity, the composites should be processed at temperature below the melting point(Tm) of the alloy by ball milling method. This is because that the original structure and segregated dispersion of fillers are kept under these processing conditions, and the conductive networks are thus easily formed. The resistivity-temperature characteristics of Sn-Pb alloy loaded polymer composites vary with the selection of polymer matrices. When the amorphous polymer, such as polystyrene (PS), is used, the composites exhibit distinctive positive temperature coefficient (PTC) effects near the Tm of the alloy fillers instead of the Tm of polymer matrix. When the semi-crystalline polymer, such as high-density polyethylene (HOPE), is used as matrix, double PTC effects appear. The first PTC transition emerges at the Tm of the polymer matrix as usual, while the second one appears at the Tm of the Sn-Pb alloy. The improvement of reproducibility for the resistivity-temperature characteristic of Sn-Pb alloy loaded polymer composites has been performed by the surface treatment of alloy fillers with titante. In addition, we have also studied the effect of various solvents on the resistivity of the Sn-Pb alloy loaded polymer composites. The results reflect that at aillcritical time the composites' resistivity ratio improves rapidly and in the end reach a maximum value.After the study of electrical properties for Sn-Pb alloy loaded polymer composites, attention has been paid to their dynamic Theological behaviors. The dynamic rheological measurement shows a new peak of loss tangent at the Tm of the alloy. When the powder HOPE is used as matrix in the composites, which can exhibit d-PTC phenomena, there are many similar laws between the composites' electrical properties and dynamic rheological behaviors. At the temperature below the Tm of the alloy, the rigid alloy particles form networks in the polymer matrix, the "second plateau" of G'~w curves is found in the low frequency range. However, even at very low filler contents, the deformation and relaxation of deformable droplets lead to the emergence of the second plateau. When the grain HDPE is used as matrix in the composites, there exits a minimum value in the low frequency range of G'~ " curves, which is dependent on the alloy volume content and the measurement temperature. Increasing the measurement temperature, prolonging the heat preservation time before the measurement, enhancing the alloy content can do the same affect on the special relaxation of the composites. The surface treatment of the alloy fillers decreases the loss tangent due to the improvement of interfacial adhesion.