The present work deals with the characterization of multi‐walled carbon nanotubes (MWCNTs) filled and unfilled short carbon fiber reinforced epoxy resin composites. Short carbon fibers (10 mm) were selected at various processing stages such as (i) white color polyacrylonitrile fibers (PAN); (ii) pre‐carbonized carbon fibers (Precarb‐CF); (iii) oxidized carbon fibers (OCF); (iv) fully carbonized carbon fibers (CF‐low); and (v) sized carbon fibers (CF Sized). The investigated composites were characterized by three points bending test, hardness test, dynamic mechanical thermal analysis (DMTA), electrical conductivity test, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The results show that the mechanical and electrical properties of the investigated materials markedly depend on the type of short carbon fibers and on the presence of MWCNTs. POLYM. COMPOS., 39:E817–E825, 2018. © 2016 Society of Plastics Engineers

Barium Titanate (BaTiO3) is one of the most promising lead-free ferroelectric materials for the development of piezoelectric nanocomposites for nanogenerators and sensors. The miniaturization of electronic devices is pushing researchers to produce nanometric-sized particles to be embedded into flexible polymeric matrices. Here, we present the sol-gel preparation of crystalline BaTiO3 nanoparticles (NPs) obtained by reacting barium acetate (Ba(CH3COO)2) and titanium (IV) isopropoxide (Ti(OiPr)4). The reaction was performed both at ambient conditions and by a hydrothermal process carried on at 200 °C for times ranging from 2 to 8 h. Doped BaTiO3 nanoparticles were also produced by addition of Na, Ca, and Bi cations. The powders were annealed at 900 °C in order to improve NPs crystallinity and promote the cubic-to-tetragonal (c⟶t) phase transformation. The microstructural features of nanoparticles were investigated in dependence of both the hydrothermal reaction time and the presence of dopants. It is found that short hydrothermal treatment (2 h) can produce BaTiO3 spherical and more homogeneous nanoparticles with respect to longer hydrothermal treatments (4 h, 6 h, 8 h). These particles (2 h) are characterized by decreased dimension (approx. 120 nm), narrower size distribution and higher tetragonality (1.007) in comparison with particles prepared at ambient pressure (1.003). In addition, the short hydrothermal treatment (2 h) produces particles with tetragonality comparable to the one obtained after the longest process (8 h). Finally, dopants were found to affect to different extents both the c⟶t phase transformation and the crystallite sizes.

Barium titanate (BT) recently gained new interest in the preparation of dielectric and piezoelectric lead-free materials for applications in sensors, electronics, energy harvesting and storage fields. Barium titanate nanocomposites can achieve attractive performance, provided that the compatibility between ceramic particles and polymeric matrices is enhanced to the benefit of the physical properties of the final composite. Tuning the particle–matrix interface through particle functionalization represents a viable solution. In this work, surface functionalization of BT nanoparticles (NPs), obtained by hydrothermal synthesis, with 3-glycidyloxypropyltrimethoxysilane, 2-[(acetoxy(polyethyleneoxy)propyl]triethoxysilane and triethoxysilylpropoxy(polyethyleneoxy)dodecanoate, was performed after optimizing the hydroxylation process of the NPs to improve their surface reactivity and increase the yield of grafting. Solid-state nuclear magnetic resonance and thermogravimetric analysis were used to quantify the molecules grafted onto the ceramic nanoparticles. Both bare and functionalized particles were employed in the realization of epoxy- and polydimethylsiloxane (PDMS)-based nanocomposites. Functionalization was proven to be beneficial for particle dispersibility and effective for particle alignment in the PDMS matrix. Moreover, the dielectric constant measurements revealed the potential of PDMS-based nanocomposites for applications in the field of dielectric elastomers.

Poly(vinylidene fluoride)/thermoplastic polyurethane (PVDF/TPU) composites filled with carbon‐black polypyrrole were prepared via melt compounding followed by compression molding and fused filament fabrication. CB‐PPy was added to the blends from 0 up to 15% to possible act as nucleating filler for PVDF β phase in order to increase its piezoelectric response. The influence of blending PVDF and TPU and of the addition of CB‐PPy on the overall crystallinity, content of β phase, and piezoelectric response of composites were investigated by differential scanning calorimetry (DSC), Fourier‐transformed infrared spectroscopy (FTIR), X‐ray diffraction (XRD) and determination of the piezoelectric coefficient (d33). It was found that the addition of TPU to PVDF induced an increase of the crystallinity degree and content of β phase in PVDF. Moreover, although the degree of crystallinity of the composites decreased with the addition of CB‐PPy, the percentage of β phase in PVDF was increased. This effect is more significant in samples with filler concentration higher than 6 wt%. As expected, the d33 of the composites increased as the content of the β phase increased. Furthermore, 3D printed samples displayed lower content of β phase and reduced piezoelectric responses when compared to compression molded samples with same composition.