The Composition-structure-performance Relationship Of Sn/Cu/PA6 Composites

Conductive polymer composites(CPCs)are prepared by incorporating conductive fillers into insulated polymer matrices.These composites are light,cheap,easy to process,and their conductivity can be adjusted in a large range.Therefore,the CPCs are widely used in many fields,such as antistatic materials,electromagnetic interference shielding,sensors,and conductors.Using the low-melting-point metal(LMPM)and the high-melting-point metal(HMPM)as conductive fillers to fill the polymer matrix can counter the separation of the liquid LMPM in processing,and it also solve the problem that the composites filled with high content of the HMPM are difficult to blend fillers with polymer.Furthermore,when the content of the LMPM is high enough,the interaction of LMPM and HMPM causes the formation of the physical continuous metal networks in matrix.At the same time,the composites have excellent conductivity,toughness and fluidity.However,there are few studies on the LMPM/HMPM/polymer ternary composites.Based on current studies,it is difficult to obtain the general rules of such ternary composites and figure out the influence of metal and polymer on these composites.Moreover,the unique properties of the LMPM/HMPM/polymer ternary composites also need to be further studied.Therefore,there are still many problems to be solved for the LMPM/HMPM/polymer ternary composites.In this dissertation,the low-melting-point metal Sn and the high-melting-point metal Cu were used to prepare the Sn/Cu/Polyamide-66(PA6)ternary composites,and the relationship among the composition,structure and properties of the composites was studied.Besides,we also compared the Sn/Cu/PA6 ternary composites with traditional Cu/PA6 binary composites to reveal the differences between them.By investigating the effects of the volume ratio of Sn-to-Cu(Vsn/Vcu)on the composites structures and properties,we found that when the total metal content is high enough,the metal phase of Sn/Cu/PA6 ternary composites aggregates with the increase of Vsn/Vcu,and the morphology of metal phase gradually changes from "sea-island structures" into physical continuous networks.The conductivity and toughness of composites are also enhanced with the perfection of physical continuous networks.When VSn/VCu>2,the conductivity,toughness and fluidity of the Sn/Cu/PA6 ternary composites are even better than those of the composites filled with the same content of Cu powder.In other words,using the LMPM and the HMPM as conductive fillers to fill polymer can obtain the composites with better comprehensive properties than the composites filled with only HMPM.The studies also found that the influence of total metal content(?)on the structure and properties of the Sn/Cu/PA6 ternary composites is different from that of the Cu/PA6 binary composites.In the Cu/PA6 binary composites,the morphology of metal phase do not change with the increase of ?,and the conductivity of composites increases,while the toughness and fluidity of composites gradually decreased.However,for the Sn/Cu/PA6 ternary composites,when VSn/VCu is high,the increasing ? induces the morphology of metal phase transforms from isolated "islands" to physical continuous networks.Although the toughness of ternary composites with VSn/NCu<2 decreases as ? increases,the toughness of ternary composites with VSn/VCu>2 changes differently.When ?>25 vol%,the toughness of ternary composites with VSn/VCu>2 increases with the increase of ?,as a result of gradual perfection of physical continuous metal networks.The comparison of the composites conductivity also showed that the conductivity percolation threshold of the Sn/Cu/PA6 ternary composites(?c)is obviously lower than that of the Cu/PA6 binary composites.As ? increases,the fluidity of the Sn/Cu/PA6 ternary composites with VSn/VCu>1.5 is different from the Cu/PA6 binary composites.In addition,the resistivity-temperature behavior of ternary composites with both relatively high VSn/VCu and ? is distinct from that of binary composites under certain conditions.It was found that the resistivity of the Cu/PA6 binary composites increases with the increase of temperature.And the resistivity of binary composites increases rapidly at the melting point of PA6,which is called the typical positive temperature coefficient(PTC)effect.However,when the temperature increases from room temperature to the melting point of Sn,the resistivity of the Sn/Cu/PA6 ternary composites with VSn/VCu=2.5 is hardly affected by temperature,which is related to the formation of physical continuous networks in the ternary composites.Moreover,this dissertation also compared the results of the Sn/Cu/PA6 ternary composites with those of the eutectic Sn-Cu alloy/Cu/Polyamide-66 ternary composites.The results demonstrated that,the interfacial debonding does not occur between the metal and polymer when the polymer matrix solidifies later than the LMPM,and composites have a good toughness.The comparison results also showed that for the composites with a lower-viscosity polymer matrix,the metal phase are more easily to aggregate during processing,the ?c of the composites is higher,and the separation of the liquid LMPM can be observed in the composites with a lower VSn/NCu.