Study On Structure And Properties Of Carbon Filled PVDF/PMMA Polymer Composites

In this dissertation, using typical PVDF/PMMA miscible polymerblend as a matrix, several kinds of carbon materials such as carbon black(CB), vapor grown carbon fiber (VGCF) and expanded graphite (EG) asfillers, conductive composites are produced. The effects of carbon fillertypes and contents on micro-structure, electrical conductivity, rheologicalbehavior, dynamic mechanical properties, crystallization behaviors andmiscibility of the composites are investigated.The results show that the percolation thresholds of CB, VGCF andEG filled PVDF/PMMA polymer blends are 1.25, 4 and 12phr fillercontent, respectively. It is found that either CB or VGCF is preferentiallylocated in the PVDF amorphous phase, resulting in a double percolationphenomenon for CB/PVDF/PMMA and VGCF/PVDF/PMMAcomposites.Dynamic mechanical analysis (DMA) of CB,VGCF and EG filledPVDF/PMMA composites shows that the addition of carbon fillers inducethe increase of storage modulus, the decrease of loss factor and the shift of glass transition temperatures to higher temperatures compared withunfilled PVDF/PMMA blends. Meanwhile, the storage modulus of carbonfilled composites increases with increasing filler concentration when thetemperatures are below the glass transition temperature, but does notincrease linearly.The kinetics of isothermal and non-isothermal crystallization ofcarbon filled and unfilled PVDF/PMMA blends are studies by means ofdifferential scanning calorimetry. The results show that, for isothermalcrystallization, the crystallization half time of PVDF increases withincreasing crystallization temperature, the values of Avrami exponent areevaluated around 2.5, indicating the heterogeneous nucleation followedby three-dimensional crystal growth. For non-isothermal crystallization,compared with unfilled PVDF/PMMA blend, crystallization peaktemperature increases, crystallization half time and crystallinity decreasefor CB and VGCF filled composites. The Ozawa equation and the methoddeveloped by Mo are successful in describing the non-isothermalcrystallization process. Moreover, the activation energy values calculatedby Arrhenius method and Kissinger method suggest that CB and VGCFfilled PVDF/PMMA blends have lower crystallization ability than thoseof unfilled blends duo to the retard effect of carbon filler surface on themobility of PVDF polymer chains.The miscibility of unfilled and CB,VGCF filled PVDF/PMMA, blends is investigated by DMA and crystallization kinetics methods. Forunfilled PVDF/PMMA blend, there is only one glass transitiontemperature and the surface free energy values of PVDF crystals increasewith increasing PMMA content, indicating that the system is miscible.However, for CB and VGCF filled PVDF/PMMA blends, there are twoglass transition temperatures and the surface free energy values of PVDFcrystals are almost constant and independent of PMMA content,indicating that the loading of CB and VGCF can induce micro-phaseseparation of PVDF/PMMA blends.