Study On Control Distribution Of Conductive Fillers And Morphological Regulation Of Conductive Polymer Composites

Electrically conductive polymer composites?CPCs?have received much attention owing to their excellent electrical,mechanical and molding processability.The key to preparing CPCs with excellent properties is to achieve high conductivity at low conductive particle content.However,the formation of conductive network in conventional materials of random dispersion often requires a high amount of the conductive filler addition.In addition,due to the random distribution of conductive fillers,the conductive properties of the materials are same in different directions,which greatly limits the use of the conductive polymer composites.Therefore,the effective distribution of conductive filler will determine the final conductivity of the composites.From the point of distribution of conductive filler and regulation morphology,this paper focus on controlling the effective distribution of conductive filler in the polymer matrix,and constructing efficient and anisotropic conductive network.In order to solve the above problems,from the segregation effect and orientation of the magnetic particles,this paper design conductive composites with different morphological structures,which significantly reduce the conductive percolation threshold value,and has anisotropic conductivity.The main contents include the following three aspects:?1?Improvement on the electrical property of conductive polymer composites is dependent on the controllable dispersion of conductive additives in polymer matrices to form a conductive network.Here we show a segregated electrically conductive network is assembled in poly?L-lactide?/poly??-caprolactone?/multi-wall carbon nanotubes?PLLA/PCL/MWCNTs?composites.First,the MWCNTs were dispersed in PCL to obtain the PCL/MWCNTs phase.Second,the PLLA particles were well coated with PCL/MWCNTs phase at 100?.Finally,the coated PLLA particles were compressed above the melting temperature of PLLA to form PCL/MWCNTs segregated structures.The morphological observation showed MWCNTs successful location in continuous PCL phase,resulting in an ultralow percolation threshold of 0.0085 vol%MWCNTs.To our best knowledge,it is the lowest percolation threshold in PLLA-based or PCL-based conductive composites at present.The composites with the segregated structure with only 0.05 wt%of MWCNTs loading achieved high electrical conductivity of 3.84x10-4S/m.Furthermore,the composites with the segregated structure not only showed 10%higher Young's modulus than that of the correspondingly conventional composites,but also maintained high elongation at break and tensile strength.?2?Morphological control has been efficiently used to improve the properties of polymer blends/composites.Here we introduce a non-invasive approach to regulate the morphologies of isotactic polypropylene?iPP?/linear low-density polyethylene?LLDPE?blends via magnetic self-organization.First,ferric oxide?Fe₃O₄?particles are added into LLDPE melts to form an LLDPE+Fe₃O₄ master batch.Second,the master batch is melt-mixed with iPP to form the iPP/?LLDPE+Fe₃O₄?composites with a random distribution of LLDPE+Fe₃O₄ droplets.Finally,the randomly distributed Fe₃O₄ particles self-organize into particle chains in a magnetic field,which induce LLDPE droplets to coalesce with each other to form a strip morphology.The composites with a parallel strip morphology exhibited mechanical enhancement in comparison to the composites with the droplet morphology.For example,the Young's modulus and storage moduli?at-30°C?of the 80/20-10 composites,where the iPP/?LLDPE+Fe₃O₄?ratio is 80/20,and the content of Fe₃O₄ particles in LLDPE is 10 wt%,with a parallel strip morphology along the tensile direction being 12 and 36%higher than that of the samples with the droplet morphology,respectively.Complex viscosity of the samples with the strip morphology is lower than that of the samples with the droplet morphology because of interfacial slip.?3?Anisotropic conductive composites with segregated electrically conductive network was constructed in poly?L-lactide?/poly??-caprolactone?/multi-walled carbon nanotubes/nickel?PLLA/PCL/MWCNT/Ni?composites by the alignment of Ni particles in a low magnetic field.First,the MWCNTs were met-mixed with PLLA to form PLLA/MWCNT composites,and then pulverized into microscale PLLA/MWCNT particles with 425-850?m.Second,the Ni particles were dispersed in PCL to get PCL/Ni composites,and then coated with PLLA/MWCNT particles at 100°C,which is between the melting temperature of PCL and PLLA.Third,the coated PLLA/MWCNT particles were compressed to form the PLLA/PCL/MWCNTs/Ni composites with segregated structure.The remarkable conductive anisotropy of the segregated samples was found after the magnetic alignment in a low magnetic field of⁴7.5 mT at 100°C for 30 min.The electrical conductivity of the segregated samples diametrically increased at the direction parallel to the magnetic field,while decreased at the direction perpendicular to the magnetic field after the magnetic alignment of Ni particles in PCL phase.The electrical conductivity in the parallel direction exhibited almost six orders of magnitude higher than that in perpendicular direction with 4.5 wt%Ni and 0.7 wt%MWCNTs.The conductive anisotropy was also easily regulated by controlling the treating time or changing the direction of the magnetic field.However,the electrical conductivity was maintained at both vertical and parallel directions in the conventional composites after the magnetic treatment because Ni particles preferred to disperse in continuous PLLA phase,where the Ni particles cannot be aligned at 100°C.