Real uniform dispersion of barium titanate, BaTiO 3 , submicrometric particles within Poly(vinylidene fluoride), PVDF, was achieved to understand induced structure, morphology, and crystallization process of the polymer. Composites with uniform dispersions of BaTiO 3 particles within PVDF were accomplished for the first time, blending the polymer with particles by high energy ball milling, HEBM. Different compositions in PVDF/BaTiO 3 composite were considered (0, 1, 5, and 10 weight percent of particles). Morphology and structure were studied by scanning electron microscopy, SEM, and X-ray diffraction, XRD, respectively. From dynamic experiments by differential scanning calorimetry, DSC, thermal transitions were determined and melting and crystallization processes were studied. To understand the main mechanism by which specific morphologies can be obtained a deep kinetic analysis of the PVDF crystallization process was carried out. Cooling rate and BaTiO 3 content did not provide important variations in the PVDF crystalline structure and morphology; however, the presence of BaTiO 3 particles seemed to favor an athermal nucleation, leading to higher fraction of crystals in shorter times.
Ternary thermoplastic systems based on poly(vinylidene fluoride), PVDF, filled with barium titanate, BaTiO3, submicrometric particles and carbon nanotubes, CNT, were prepared. Their structure and morphology were studied as a function of composition and finally correlated with thermal and mechanical properties. High energy ball milling, HEBM, under cryogenic conditions and subsequent hot pressing were used to obtain films with quite uniform dispersion of the nanofillers. The presence of BaTiO3 particles and CNT did not modify the thermodegradation mechanism of the PVDF. However, enough amount of BaTiO3 seemed to inhibit the volatility of the products of pyrolysis, hindering the decomposition of PVDF. The presence of CNT favored the PVDF thermodegradation probably due to improved heat transmission by an increase in the thermal conductivity. Variations in PVDF thermal transitions were more dependent of processing conditions. Improvements in the mechanical properties of PVDF were ascribed to a reinforcing effect of the fillers. This effect only happened below the fraction of percolation of CNT, pointing out that CNT reinforce through an optimum load transfer from the PVDF matrix to the nanofillers. POLYM. COMPOS., 38:227–235, 2017. © 2015 Society of Plastics Engineers
Nanocomposites based on poly(vinylidene fluoride) (PVDF) filled with barium titanate, BaTiO 3 , (BT) particles, and multiwalled carbon nanotubes (MWCNTs) were prepared by high-energy ball milling (HEBM) and subsequent hot pressing. This method of materials preparation allowed obtaining uniform dispersions of the nanofillers. The influence of the particles on the polymer structure and morphology was studied. To understand the origin of changes in the PVDF properties, thermal and electrical behaviors of the PVDF/BT/MWCNT nanocomposites were studied as a function of composition. The addition of BT, MWCNT, or its mixture had not any influence on the PVDF polymorphism. However, calorimetric results pointed out that the presence of the nanofillers exerted nucleation mainly ascribed to the surface to volume ratio of the nanoparticles. The capacitance of the composites increased as the nanofiller content increased, being the effect mainly dependent on the surface to volume ratio of the nanoparticles. The dielectric behavior of the materials as a function of frequency was modeled by a Debye equivalent circuit only below the percolation threshold respect to the amount of MWCNT. The piezoelectric behavior of the ternary nanocomposites was highly affected by the incorporation of the nanofillers only when high dielectric losses occurred above the percolation threshold.
Summary: In this work infrared spectroscopy in the near infrared (NIR) range is used to study the dynamics of polymethylmethacrylate (PMMA) as a pure polymer and when it is modified with silica nanoparticles. Different ways of analyzing FT-NIR spectra were explored taking the temperature as the variable of the systems: i) bands shifts in terms of the first moment of the wavenumber; ii) bands shifts in terms of an absorbance ratio method and iii) absorbance variations in terms of the integrated absorbance. The spectroscopic analysis allowed to study thermal transitions in PMMA and PMMA based nanocomposites. In particular the method based on the use of an absorbance ratio is the most sensible to analyze the thermal transitions. All bands considered could be used to detect thermal transitions reflecting how the vibrations of the groups CH 2 ; CH 3 and C¼O are affected by changes in the free volume of the PMMA. It seems that the PMMA dynamics is more driven by the lateral groups than the backbone of the polymer. The presence of silica nanoparticles, at least when 1% by weight is used, restrains the PMMA motion increasing the relaxation temperatures that can be associated with the glass transitions.
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