Structure Control And Characterization Of Polypropylene/ Nickel Coated Glass Fiber Electrically Conductive Composites

Coductive polymer composites(CPCs) were widely applied in antistatic, electromagnetic shielding, electronic packaging, microelectronic devices by virtue of their good process-ability and controllable resistivity. By controlling the structure of conductive network connected by conductive filler in polymer matrix to achieve high performance and multi-function was an important research direction in the preparation of the CPCs. On one hand, on the foundation of pre-prepared polypropylene(PP) / nickel-coated glass fiber(NCGF) conductive composite, the effect of crystalline morphology of PP on conductivity and mechanical properties of PP/NCGF was studied, respectively, through the annealing process and the addition of nucleating agent DBS. On the other hand, anisotropic PP / NCGF composites with aligned NCGF induced by magnetic field during hot compression were prepared. Main work and conclusions were as follows:(1) The PP / NCGF composite was kept 1 h at 150 ℃, then the crystalline of PP was characterized using DSC and XRD, the electrical conductivity and mechanical properties of the composites with annealed was tested. The results showed that the grain size and crystallinity of PP increased after annealing treatment when the NCGF content was low, which destoried the initial conductive network, leading to a decrease in electric conductivity. While the increased crystalline and grain size attained an improved mechanical properties of the PP/NCGF composites, such as tensile strength, Young’s modulus, and a decrease in elongation at break.(2) The effect of the change in crystalline of PP on the properties was investigated by the introduction of nucleating agent DBS into PP/NCGF system. The use of DBS can induce the formation of extra crystalline structure with tiny grain size in PP matrix, and thus promote the perfection of the NCGF conductive network through the “excluded volume effect”. The completed NCGF conductive network can further reduce the percolation threshold of PP/NCGF composites to 0.35 vol%(nickel content). Moreover, the refinement of PP grain weaken the interface between grains and reduced the internal defects. And the incorporation of DBS can reinforce the interfacial interaction between the NCGF and PP matrix, which could serve the PP/NCGF with increased mechanical properties. Meanwhile, the average electromagnetic shielding effectiveness of PP/NCGF/DBS composites increased with the increase of the NCGF content, due to the gradually improved conductive network throughout PP matrix. The loss caused by absorbing electromagnetic wave was the main shielding mechanism.(3) Anisotropic PP / NCGF composites with aligned NCGF induced by magnetic field with a magnetic field intensity of 1 T during hot compression were prepared. The effect of magnetic field duration(DMF) and the NCGF content on the conductivity anisotropy was discussed. With the increase of DMF, the degree of NCGF orientation increased, while the conductivity parallel to the magnetic field direction(σ//) and the conductivity ratio of parallel and perpendicular(σ⊥) to magnetic field direction(RANI) increased first and then decreased. The σ// and RANI reached the maximum with a DMF of 10 min. Moreover, PP molecular chains also aligned along the magnetic field to a certain degree. The σ// and σ⊥ increased with the increase of NCGF content, while the improved conductive network in vertical magnetic field direction with the high NCGF content and the mutual interference between adjacent NCGF inhibiting its orientation in magnetic field, resulted in reduced RANI. Since the orientation of NCGF in a magnetic field, so that the more improved conductive network in parallel to the magnetic field direction was achieved, which resulted in higher electromagnetic shielding effectiveness than that perpendicular(σ⊥) to magnetic field direction.