Dielectric Characterization of Core-Shell Structured Poly(vinylidene fluoride)-grafted-BaTiO3 Nanocomposites.

Dielectric properties of poly(vinylidene fluoride)-grafted-BaTiO3 (PVDF-g-BT) core-shell structured nanocomposites obtained from Reversible Addition Fragmentation chain Transfer (RAFT) polymerization of VDF were investigated by Broadband Dielectric Spectroscopy (BDS). The dielectric constant increased along with the BT content, about +50% by addition of 15 vol% of BT, which was around 40% more than expected from predictions using the usual dielectric modeling methods for composite materials, to be ascribed to the effect of the interfacial core-shell structure. The known dielectric relaxations for PVDF were observed for the neat polymer as well as for its nanocomposites, not affected by the presence of nanoparticles. A relaxation process at higher temperatures was found, due to interfacial polarization at the amorphous-crystalline interface, due to the high crystallinity of materials produced by RAFT. Isochronal BDS spectra were exploited to detect the primary relaxation of the amorphous fraction. Thermal analysis demonstrated a very broad endotherm at temperatures much lower than the usual melting peaks, possibly due to the ungrafted fraction of the polymer that is more easily removable by repeated washing of the pristine material with acetone.

Synthesis and Characterization of Core-Double-Shell-Structured PVDF-grafted-BaTiO3/P(VDF-co-HFP) Nanocomposite Films.

Core-double-shell-structured nanocomposite films consisting of polyvinylidene fluoride-grafted-barium titanate (PVDF-g-BT) incorporated into a P(VDF-co-hexafluoropropylene (HFP)) copolymer matrix were produced via a solution mixing method for energy storage applications. The resulting films were thoroughly investigated via spectroscopic, thermal, and morphological analyses. Thermogravimetric data provided an enhancement of the thermal stability, while differential scanning calorimetry indicated an increase in the crystallinity of the films after the addition of PVDF-g-BT. Moreover, broadband dielectric spectroscopy revealed three dielectric processes, namely, glass-rubber relaxation (αa), relaxation associated with the polymer crystalline phase (αc), and slower relaxation in the nanocomposites resulting from the accumulation of charge on the interface between the PVDF-g-BT filler and the P(VDF-co-HFP) matrix. The dependence of the dielectric constant from the composition was analyzed, and we found that the highest permittivity enhancement was obtained by the highest concentration filler added to the largest concentration of P(VDF-co-HFP). Mechanical analysis revealed an improvement in Young's modulus for all nanocomposites versus pristine P(VDF-co-HFP), confirming the uniformity of the distribution of the PVDF-g-BT nanocomposite with a strong interaction with the copolymer matrix, as also evidenced via scanning electron microscopy. The suggested system is promising for use in high-energy-density storage devices as supercapacitors.

Synthesis of Novel Non-Isocyanate Polyurethane/Functionalized Boron Nitride Composites.

Poly(hydroxyurethanes) (PHUs) have been suggested as isocyanate-free, low-toxicity alternatives to polyurethanes (PUs). However, PHUs present low mechanical properties due to the presence of side reactions that limit the production of high-molar mass polymers. Here, we present the synthesis under mild conditions and atmospheric pressure of bi-cyclic carbonate monomer for the production of PHU nanocomposites with good physical properties. The kinetics of the bi-cyclic carbonate synthesis and its complete conversion to urethane were followed by FTIR. The addition of functionalized boron nitrate (f-BN) with sucrose crystals improved the thermal degradation temperature as well as the glass transition by approximately 20 °C and 10 °C, respectively. The storage modulus of PHU films gradually increases with the concentration of f-BN in the composite.

Use of Novel Non-Toxic Bismuth Catalyst for the Preparation of Flexible Polyurethane Foam.

Foam products are one of the largest markets for polyurethane (PU) and are heavily used in many sectors. However, current PU formulations use highly toxic and environmentally unfriendly production processes. Meanwhile, the increasing environmental concerns and regulations are intensifying the research into green and non-toxic products. In this study, we synthesized flexible polyurethane foam (PUF) using different weight percentages (0.025%, 0.05% and 0.1%) of a non-toxic bismuth catalyst. The bismuth-catalyzed foams presented a well evolved cellular structure with an open cell morphology. The properties of the bismuth-catalyzed flexible PUF, such as the mechanical, morphological, kinetic and thermal behaviors, were optimized and compared with a conventional tin-catalyzed PUF. The bismuth-catalyst revealed a higher isocyanate conversion efficiency than the stannous octoate catalyst. When comparing samples with similar densities, the bismuth-catalyzed foams present better mechanical behavior than the tin-catalyzed sample with similar thermal stability. The high solubility of bismuth triflate in water, together with its high Lewis acidity, have been shown to benefit the production of PU foams.

The relationship of structure, thermal and water vapor permeability barrier properties of poly(butylene succinate)/organomodified beidellite clay bionanocomposites prepared by in situ polycondensation.

The exploitation of beidellite clay (BDT), used as a nanofiller in the preparation of poly(butylene succinate) (PBS)/organoclay biodegradable nanocomposites, was investigated. A series of bionanocomposites with various loadings of the organoclay (3CTA-BDT) were prepared by in situ polycondensation reaction between succinic anhydride (SuAh) and 1,4-butanediol (1,4-BD) at atmospheric pressure in refluxing decalin with azeotropic removal of water, and the reaction was catalyzed by non-toxic bismuth chloride (BiCl3). X-ray diffraction (XRD) and scanning electron microscopy (SEM) results showed that 3CTA-BDT was likely exfoliated and well dispersed in PBS matrix. Thermal properties (TGA, DSC and thermal conductivity), contact angle measurements and water vapor sorption behavior of the corresponding nanocomposites were also discussed. Compared to pure PBS, a significant reduction of the diffusion coefficient and the water vapor permeability (WVP) by 44 and 37%, respectively, was observed by adding only 5 wt% of 3CTA-BDT. These results could make these bionanocomposites suitable materials for food packaging application.

Sustainable coating material based on chitosan-clay composite and paraffin wax for slow-release DAP fertilizer.

The coating of fertilizers by polymers is one of the most efficient tools for their slow and control release into soil. This strategy avoids excessive use of the fertilizers and increases their availability to the crops needs. In the present paper, hydro-soluble diammonium phosphates (DAP) fertilizer was double coated following the dip-coating process by chitosan-clay composites as inner coating and paraffin wax as an outer coating. The chitosan composite preparation and characterization were deeply investigated. The montmorillonite (MMT) clay incorporation as filler improves the water barrier diffusion, mechanical properties, and thermal stability of the composite. The combination of the swelling behavior of the chitosan-clay composite (inner coating) and the hydrophobic property of paraffin wax (outer coating) was confirmed by the water holding capacity evaluation and the phosphorus release essays in water and soil. Indeed, the phosphorus dissolution from the coated DAP granules was significantly delayed compared to the uncoated DAP. Moreover, the biodegradation study of composite material in soil and the biochemical oxygen demand (BOD) tests revealed that the coating system proposed could be considered as a carbon source for microorganisms after the fertilization process, which confirms its sustainability.

Synthesis of poly(ε-caprolactone)-grafted guar gum by surface-initiated ring-opening polymerization.

This study reports the grafting of poly(ε-caprolactone) (PCL) on guar gum (GG) by in-situ ring-opening polymerization using tetra(phenylethynyl)tin (Sn(C≡CPh)4) as catalyst. The hydroxyl groups of guar gum act as initiators for ε-caprolactone ring-opening polymerization and the resulting poly(ε-caprolactone) binds covalently to the polysaccharide. The highest stability of Sn(C≡CPh)4 allows the reaction in open-air, thereby reducing the cost of the synthesis and provides polymers with high molar mass. Fourier transform infrared (FTIR) and the long-term stability of the suspension PCL-g-GG in dichloromethane confirmed the effectiveness of grafting of PCL into GG. The size exclusion chromatography (SEC) results show that the molar masse of grafted PCL could be modulated by varying the amount of guar gum. From thermogravimetric analysis and differential scanning calorimetry results the thermal stability of PCL-g-GG is greatly improved with different content of guar gum, also the melting temperature and crystallinity increased by increasing the GG content. The scanning electron microscopy (SEM) analyses showed the good adhesion between GG and PCL with 5% of GG contents. It was also revealed by contact angle measurements that the grafting of PCL to GG leads to a decrease of hydrophobicity of PCL. The micro-indentation hardness properties of the prepared PCL-g-GG were significantly improved, as compared to neat PCL.

Electric field alignment of nanofibrillated cellulose (NFC) in silicone oil: impact on electrical properties.

This work aims to study how the magnitude, frequency, and duration of an AC electric field affect the orientation of two kinds of nanofibrillated cellulose (NFC) dispersed in silicone oil that differ by their surface charge density and aspect ratio. In both cases, the electric field alignment occurs in two steps: first, the NFC makes a gyratory motion oriented by the electric field; second, NFC interacts with itself to form chains parallel to the electric field lines. It was also observed that NFC chains become thicker and longer when the duration of application of the electric field is increased. In-situ dielectric properties have shown that the dielectric constant of the medium increases in comparison to the randomly dispersed NFC (when no electric field is applied). The optimal parameters of alignment were found to be 5000 Vpp/mm and 10 kHz for a duration of 20 min for both kinds of NFC. The highest increase in dielectric constant was achieved with NFC oxidized for 5 min (NFC-O-5 min) at the optimum conditions mentioned above.