Surface Modification Of Carbon Nanoparticles And The Compatibilization Effects On PVDF/PLLA Blends

The incorporation of carbon nanoparticles into immiscible polymer blend is a simple and effective pathway to prepare high performance composite materials.The selective distribution of nanoparticles at the polymer-polymer interface has attracted siginificant attentions because it can not only improve compatibility of polymers but also facilitate the formation of nanoparticle network with very low percolation threshold.The selective immobilization of nanoparticles at the interface is often determined by the affinity of the nanofiller to the polymer component(thermodynamics)and/or the order of mixing(kinetics)of the polymer blend.However,the interfacial nanoparticle usually cannot improve the mechanical properties of the polymer blend due to the lack of chain entanglement between the nanoparticles and the polymer components.In this work,we present a novel thermodynamic compatibility strategy based on reactive carbon nanoparticles.This approach can effectively improve the interfacial adhesion and thus enhance the mechanical properties of the composite materials.The main contents of the paper are as the follows:(1)Synthesis of reactive carbon nanoparticles: Two kinds of carbon nanoparticles with different aspect ratios,zero-dimensional hydroxylated carbon black particles(Hydroxy CB)and one-dimensional hydroxylated carbon nanotubes(Hydroxy CNTs)were used as the starting points to synthesize epoxy carbon black(Epoxy CB)and epoxy carbon nanotubes(Epoxy CNTs)by modification by silane coupling agent.The ring-opening reaction between the terminal carboxyl groups of PMMA-COOH and and epoxy groups was then initiated under the alkaline condition.The reactive carbon nanoparticles(Reactive CB and Reactive CNTs)containing both epoxy group and long side chains of PMMA were characterized by FT-IR,TGA,XPS and so on.Moreover,various types of reactive carbon nanoparticles were synthesized by varing the molecular weights of PMMA-COOH.(2)Compatibilization of the immiscible PVDF/PLLA blends by reactive carbon nanoparticles: Reactive CB and Reactive CNTs were added to PVDF/PLLA(50/50)blends,and the relationship between composite morphology and properties of the blends was investigated.During the melt mixing,a ring-opening reaction between the epoxy groups and the terminal carboxyl group of PLLA occurred,resulting in the exist of PLLA grafted on the surface of nanoparticles.The PLLA chain on this double-grafted carbon nanoparticle was entangled with the PLLA component,and the PMMA chain was compatible with the PVDF component.The resultant double-grafted nanoparticle can be exclusively located in the PVDF-PLLA interface and functioned as compatibilizer.Therefore,the composite blends material showed better mechanical properties due to the improved interface adhesion by reactive nanoparticles.Moreover,the morphology of polymer blends was dependent on the aspect ratio of nanoparticles: it can be shifted from a typical sea-island morphology by Reactive CB to a bi-continuous structure by Reactive CNTs.The stability of carbon nanocomposites in secondary processing was also studied.It was found that the carbon nanoparticles were stably located at the interface,and the morphology of the materials remained stable during long-term processing.(3)Properties of the prepared composite materials: As a class of functional materials,carbon nanoparticles were often used to prepare conductive or thermally conductive materials.The selective location of carbon nanoparticles at the interface could be beneficial to reducing the surface resistance of the blend materials and improving the thermal conductivity of the materials significantly.At the same time,it was shown that the carbon nanoparticles located at the interface were more likely to form a network than the carbon nanoparticles with identical loading.The conductivity and thermal conductivity of the prepared material were improved significantly.