Preparation And Characterization Of PVDF/MWCNTs Nanocomposites

Poly(vinylidenefluoride)(PVDF) is a semi-crystalline polymer,due to itspiezoelectricity, pyroelectricity and complicated crystalline structure PVDF attractedextensive attention. Carbon nanotubes have many unique advantages which meansloading carbon nanotubes into polymers can greatly improve the properties ofpolymer materials.However, according to present study results, it seems thatmorphology and structure of PVDF/CNT nanocomposite is still poorly understood.Therefore in this paper Poly(vinylidene fluoride) (PVDF)/multi-walled carbonnanotube (MWCNTs) nanocomposites were prepared by means of ultrasonicdispersion method. XRD,DSC and FTIR were used to characterize the samples.Effects of different content of MWCNT on the crystalline structure of the compositeswere studied and possible reasons that lead to different crystalline structures of thecomposite were discussed.The results are as following:1.PVDF/MWCNT composites prepared by ultrasonic dispersion method havegood mechanical and electrical properties.2. Proper load of MWCNTs can effectively improve both mechanical andelectrical properties of the composites. Compared with pure PVDF,PVDF/MWCNTcomposites exhibit an improvement of 86% in modulus and that of 12% in strengthhas been achieved at 2.0wt% of MWCNTs.When MWCNTs content is 3.0 wt% theresistance of PVDF/MWCNT composite is 30 ohm·cm,which is 13 orders ofmagnitude lower than that of pure PVDF.3. The result of comparing PVDF/MWCNT composites prepared through twomethods indicates that MWCNTs have a higher uniform dispersion in solution treatedby sonication.Thus performance of the composites was improved, obtaining higher tensile strength and modulus; MWCNTs were covered on the surface of thosecomposite particles, which improve the conductivity of the composites.PVDF/MWCNT composite prepared by mixing MWCNT-DMAc and 0.02 solutionhas a low percolation threshold at 0.07wt%.4.According to the experiment results and First Principle Calculation we knewthatβ-phase in PVDF is induced by loading MWCNTs, and the amount ofβ-phaseincreases with the increasing content of MWCNTs. The formation ofβ-phase isheterogeneous nucleation,some polymer chains obtains energy during the sonicationprocess which became high energy polymer chains(TGTG molecule chain),and thesemolecule chains are able to overcome the energy barrier between TGTG and TTconformation and then are transformed into molecule chains with TT conformation.While TT-type molecule chains absorbed on the CNT surface can act as nucleatingagents ofβ-phase, owing to a strong confining effect of CNTs ,leading to theformation ofβ-phase during the crystallization of PVDF.