Preparation And Properties Of Conductive/Anti-static Polymer Nanocomposites

In this thesis, the Low melting point metal (LMPM) and Carbonnanotubes (CNT) as conductive fillers had been used to prepareconductive/anti-static polymer composites and fibers. Four physical/Chemicalmethods were designed to control the morphology of composites. Therelationship between morphology and properties in the composite was studiedin detail.The main results of the thesis were as follows:(1) A new method and theory for preparing conductive/anti-staticpolymer fiber had been proposed. LMPM, due to its high electricalconductivity and easy processability, was employed as the conductive filler toprepare an anti-static polypropylene (PP)/in-situ Ultra-fine metal fibers(UFMF) and/or PP/CNT/UFMF composite fiber via melt blending and thensolid phase drawing processes. In appropriate temperature range, LMPMpowders were in-situ converted into UFMF without aggregation or oxidationin anti-static polymer fibers. The axes of UFMF and polymer fiber were inparallel and the interval of UFMFs decreased obviously, which promoted thepercolated network. In addition, the PP/UFMF fibers showed an increase inconductivity after solid phase drawing, in contrast to PP/CNTs fiber. Thepolymer fiber containing UFMF obtained the better mechanical propertiesthan the fiber without UFMF. Surprisingly, the diameter of UFMF decreasedwith incorporation of nano-filler, such as CNT and Montmorillonoid (MMT).The conductivity and mechanical properties of PP/nano-filler/UFMF composite fiber containing smaller and more uniform UFMF were better thanthat of the PP/UFMF composite fiber.(2) Theory for nanoparticles-hindering coalescence of LMPM drops wasproposed. A conductive polymer/Ultra-fine full-vulcanized powdered rubber(UFPR)/CNT/in-situ ultra-fine metal particles (UFMP) composite withultra-low percolation threshold was prepared via melt blending. Incorporationof UFPR and CNT hindered the coalescing of metal particles and caused ashift to the breakup direction in the breakup/coalescence equilibrium of metalparticles. The prime metal particles with a diameter of about26.4μm werein-situ converted into the UFMPs with a diameter of about932nm. Theconductive network of carbon nanotubes had been perfected and thepercolated threshold decreased due to in-situ formation of UFMPs anddecrease of contact resistance between CNTs and UFMPs. The percolatedthreshold of this composite was only0.25vol%CNT and the volumeresistance of this composite with only1vol%carbon nanotubes and1.96vol%ultra-fine metal particles can reached to89cm. Moreover, the conductivecomposites with UFMP kept more stable electrical response under stretchablestrain than the conductive composite without UFMP.(3) Three types of conductive thermoplastic vulcanizates (TPVs) wereprepared by blending PP, CNT, and UFPR. The CNT locations were differentin these three types of TPVs, i.e., CNT were localized in polymer matrix, inUFPR dispersed-phase, or mainly in the interface. It had been found that TPVwith CNT localized mainly in the interface had the lowest conductivepercolation threshold among these three types of TPVs. Moreover, theconductive TPV possessed good mechanical properties. An ideal morphologyfor the conductive TPV had been found, i.e., most of CNT were localized inthe interface to form a conductive shell covered the rubber particle and a fewof CNTs were dispersed in polymer matrix as bridges to connect theconductive rubber particles to form conductive pathway.(4) The poly (vinyl alcohol)(PVA)-based composite embedded withmodified CNT were prepared. To enhanced the interfacial interaction between CNT and PVA, acid-treated CNTs were grafted with PVA chains,compatibilizing CNTs and the matrix. The better dispersion of CNTs in PVAmatrix was obtained by the introduction of Diphenylmethane4,4’-diisocyanate (MDI) reaction bridges and then PVA molecules onto thesurface of CNTs. Moreover, strong interaction between CNTs and PVA matrixwas evidenced through the measurement results of the melting behavior,polarized Raman measurement, and non-isothermal crystallization behavior ofthe composites. Owing to the reinforcement of CNTs, the tensile strength andmodulus of PVA composite containing0.9wt%CNT were increased by160.7and109.2%, respectively, compared to neat PVA.