The present work was undertaken to examine the evolution of interfacial properties of Kevlar/epoxy laminated composites hybridized by naturally woven Coco Nucifera sheath (CNS). Hand lay-up method followed by hot pressing was performed to fabricate our laminated composites. Broadband Dielectric Spectroscopy (BDS) was adopted to investigate the effect of varying CNS fractions (0%, 25%, 50%, 75% and 100%) on the molecular dynamics and the interfacial adhesion between Kevlar/epoxy and CNS/epoxy. The surface and cross-section morphology of the samples were studied in order to analyze the weaving structures of Kevlar and CNS and the interfaces between epoxy matrix and reinforcements. Differential Scanning Calorimetry (DSC) and Fourier Transform Infrared Spectroscopy (FTIR) were carried out to control the characteristic temperatures and the interactions between the two kinds of fibers (Kevlar and CNS) and the epoxy resin. The BDS results revealed different relaxations: the conduction phenomenon, the primary [Formula: see text] -process and the interfacial polarization, called also MWS polarization, whose dielectric strength [Formula: see text] was calculated using the WinFit software. Hence, Kevlar fibers can be successfully replaced by 25% of CNS natural fibers for advanced structural applications where interfacial adhesion is prime requirement.

The food industry's ever-increasing need to substitute synthetic packaging materials has led to the development of eco-friendly alternatives with improved physical and mechanical properties. The main objective of this work relates to the effect of adding different weight fractions (1, 3 and 5 wt%) of cellulose nanocrystals (CNC) and cellulose nanofibrils (CNF) on the morphological, thermal, structural, biodegradable and mechanical properties of PVA/Chitosan (CS) bio-nanocomposites. The DSC and FTIR results reveal that PVA and Chitosan are compatible due to the strong interactions via hydrogen bonding, which are also proved by the tensile test. The water solubility test indicates the biodegradability of nanocomposites. Furthermore, CNF have significantly enhanced the mechanical properties of PVA/CS. Hence, PVA/CS/CNF nanocomposites can be efficiently utilized for bio-based packaging materials, where good mechanical properties are prime requirements.

Nanocomposites based on waterborne polymer dispersion and biobased nanoparticles have gained significant interest because they offer a wide range of dimensionality and shape, and they are abundantly available from renewable biobased sources. Although polymer-filler interaction is key to the resulting performance of the nanocomposites, these interfacial properties are challenging to measure and analyze. In the present work, dielectric spectroscopy was used to investigate the interfacial characteristics of nanocomposites based on Poly(Butyl-methacrylate) (PBMA) and starch nanocrystals (SNCs) prepared by in-situ emulsion polymerization, where SNCs was the sole stabilizer. Unmodified and vinyltriethoxysilane-functionalized SNCs (VTES-SNCs) were used as both reinforcements and colloidal stabilizers to control the degree of binding of SNCs on PBMA. Two main relaxation processes were detected and identified as Maxwell-Wagner-Sillars (MWS) polarization and dipolar relaxation. The origin of these relaxations and their evolution based on the SNCs content and functionalization were discussed in terms of the SNCs-polymer matrix interaction mechanism. Most notably, an apparent effect of SNCs loading on the electrical conductivity of nanocomposites was revealed, pointing to evidence of percolation of the SNCs despite their non-conductive character.

Due to its intrinsic electrical conductivity, polyaniline (PANI) is one of the most promising conducting polymers for high-performance applications in a wide range of technological fields. However, its poor dispersibility in water and organic solvents markedly imparts its processability and electrical conductivity. Herein, we report a green and one-step approach to preparing stable colloidal dispersions of highly dispersible hybrid nano particles by polymerizing PANI onto chitin nanocrystals (ChNCs) as biotemplates, via initiation through the surface amino groups of ChNCs. Evidence of the grafting of PANI onto ChNCs was supported by transmission electron microscopy (TEM), as well as Raman and Fourier transform infrared (FTIR) spectroscopies. Nanocomposite films were prepared by mixing the PANI-g-ChNCs with a waterborne poly(vinyl acetate) latex dispersion followed by casting and film formation at room temperature. The mechanical properties were tested as a function of the PANI-g-ChNC content. In addition, it was shown that at a proper content of PANI in ChNCs, and over a critical loading in the PANI-g-ChNCs, a conductive film was obtained, without sacrificing the reinforcing effect of the rodlike nanofiller. As a potential application, conductive waterborne adhesives for wood were prepared and the performance of the adhesives was tested. This research provides a facile route to fabricating a new class of hybrid nanofiller from a biobased origin, stable in water and easy to mix with waterborne dispersions, combining the merits of the ChNC nanofiller with the conductivity of PANI.

This study focuses on the use of waste hybrid cotton fibers, provided by the textile industry, as reinforcement in unsaturated polyester composites. Hence, to evaluate the performance of white yarns and indigo denim fabrics on the recycled cotton fibers adhesion in unsaturated polyester matrix, dielectric measurements were performed in the temperature range 0–150 ℃ and the frequency range 0.1 Hz–1 MHz on two UP composites (#1 and #2) whose white yarns/indigo denim fabrics relative volume fractions were 1:3 and 1:1, respectively. This dielectric study revealed a better reinforcement/matrix adhesion occurred for the relative volume fraction 1:3. This dielectric analysis was in accordance with thermal and vibration ones based on differential scanning calorimeter (DSC) and FT-IR technique, respectively.

An experimental and theoretical investigation of the scaling laws governing the phenomenon of Maxwell-Wagner-Sillars interfacial polarization in composite materials in dependence on morphology, volume fraction, orientation of fillers, form factor and the presence of interphases is presented in the current study. By considering the complex dielectric function of the matrix and of the fillers, the dielectric spectra are calculated in the frequency range from 10(7) Hz to 10(-2) Hz and compared to dielectric measurements by Broadband Dielectric Spectroscopy, carried out in the frequency range from 10(7) Hz to 0.5Hz and between -90(o)C and 150(o)C. The characteristic frequencies of the global dielectric response are reported to strongly vary with the conductivity value of the conductive phase, while a much weaker dependence is observed upon varying the volume fraction, the form factor and the orientation of fillers. The value of permittivity at low frequency does not change with the conductivity value, whereas a significant variation is observed in dependence on the composite morphology, form factor, orientation of fillers and presence of interfaces with different gradients of properties. Two possible applications of our analysis are reported: (i) measuring the conductivity of materials without employing a direct electrical contact between the electrodes and the sample and (ii) discriminating different phenomena of electrical polarization in complex materials by analyzing the scaling laws. Our study delivers thus a useful and necessary analysis of the dielectric behavior of composite materials, where interfacial polarization effects play a major role.

The dielectric spectroscopy (DS), the differential scanning calorimetry (DSC), the scanning electron microscope (SEM) and the Fourier transform infrared spectroscopy (FTIR) measurements were performed on a poly(lactic acid) matrix reinforced by sisal fibers with different weight fractions (10% and 20%). The obtained dielectric spectra of the neat PLA and the PLA/sisal bio-composites covered a wide frequency range (from 10(-1) to 10(6) Hz) and a temperature domain varying from 20 degrees C to 140 degrees C as it serves to investigate the polymer dynamics and the interfacial properties. The DSC analysis, the SEM micrographs and the FTIR spectra were executed to determine the characteristic temperatures, the degree of crystallinity and the interaction between poly(lactic acid) and sisal fibers. The DS showed different relaxations: the beta relaxation, alpha process and the conduction phenomenon in the PLA matrix. Furthermore, the incorporation of sisal fiber generates additional relaxation processes known as the water polarization and the Maxwell-Wagner-Sillars (MWS) interfacial polarization. The PLA/sisal fiber interface properties were investigated through the calculation of the strength parameters increment epsilon(MWS) as well as the activation energy using the Havriliak-Negami model.

The dielectric properties of bio-hybrid composites based on natural Oil Palm Empty Fruit Bunch (OPEFB), montmorillonite (MMT) and organomodified montmorillonite (OMMT) nanoclay reinforced kenaf (KF)/epoxy are reported in this study. The molecular mobility, interfacial adhesion between KF fibers and epoxy resin matrix, and fragility near the glass transition temperature were evaluated using Broadband dielectric spectroscopy over a wide temperature range from 20 to 180 degrees C and a frequency range from 0.1 Hz to 1 MHz. Obtained results indicated different relaxations: the alpha glass-rubbery transition and the interfacial polarization between KF/epoxy called Maxwell-Wagner-Sillars polarization "MWS(KF/epoxy)" whose amplitude, position and dielectric strength increment epsilon(MWS(kenaf/epoxy)) depends on the type of the added nanofillers. increment epsilon(MWS(kenaf/epoxy)) decrease for all the measured temperatures while the activation energy E-a of the alpha-process and rigidity increase when the nanocharges are introduced. It has been found that the OPEFB, MMT, and OMMT are uniformly distributed in the matrix and act as a link between the KF fibers and the epoxy resin via the formation of new C-O and Si-O-Si bonds.

The present work focuses on the preparation, using a solution process, of flexible conductive nanocomposites based on polyurethane (PU)/polyaniline (PANI) with different mass percentages: 2, 3 and 4%. Because of the low conductivity of the PU + PANI films, these later were doped with inorganic NiCl2. PU + PANI undoped films were synthesized by a “one-shot” process. For doping process, PANI has been doped according to two different methods: The first one consists of the impregnation of the pristine PU + PANI film in a solution of inorganic salt dopant with a solvent (THF) during a soaking time, while the second method uses a “one-shot” process. The structural characterization and conductivity properties of the polymer blends were examined by differential scanning calorimetry, Fourier transform infrared spectroscopy and dielectric measurements spectroscopy. The results show that NiCl2 significatively increases the conductivity compared to pure PU + PANI blends, with better results using the second method of synthesis.

The thermal and dielectric properties of polymer nanocomposites based on polycaprolactone diol-based PU matrix filled with various weight fractions of cellulose nanocrystals (CNCs) (from 0 to 10 wt%) extracted from the rachis of date palm tree were investigated by differential scanning calorimetry (DSC) and broadband dielectric spectroscopy. The emphasis was on clarifying the impact of the addition of CNC nanofillers on the molecular mobility of the PU matrix. Different dielectric relaxations have been found and the corresponding activation energies have been calculated, by means of the Havriliak-Negami model after fitting the dielectric data. The outcomes were explored in terms of molecular dynamics and interfacial processes. With 2.5 wt% of CNC, the strongest adhesion between matrix and reinforcement was acquired. This research was supported by the use of DSC for thermal properties.

The influence of the ZrO2 doping content on the electrical and dielectric properties of soda lime silicate glasses has been investigated through the impedance spectroscopy technique based on dielectric measurements carried out in the frequency range from 0.1 MHz to 1 MHz at temperatures ranging between −20°C and 150°C. The experimental results depict an overall decrease in the electrical parameters [dielectric constant, loss, and alternating-current (AC) conductivity] when ZrO2 was present in the soda lime glass, revealing a blockage of the easy pathways available for charge carrier (Na+) migration, subsequently yielding a reduction in their contribution to the space-charge polarization. This interpretation was also confirmed by the equivalent circuit suggested by ZView software. The resistivity actually increased with increasing ZrO2 content. This result indicates that the internal structure of the soda lime silicate glass becomes more polymerized, electrically rigid, and resistant to the flow of free charge carriers in the presence of ZrO2. Additional measurements using infrared (IR) spectroscopy were used to validate these findings.

Dielectric and thermal characterization of nanohybrid films based on poly(epsilon-caprolactone) biopolymer were investigated. Nano-composites samples with distinct loadings of halloysite nanotubes (HNT) were prepared by in situ Ring Opening Polymerisation of epsilon-caprolactone. The effect of the incorporated HNT on the molecular relaxation process and interfacial polarization of PCL was studied via broadband dielectric spectroscopy (BDS) on a frequency domain starting from 1E-1 to 1E6 Hz and at temperatures ranging from -70 degrees C to 50 degrees C. The BDS measurements revealed four significant dielectric processes alpha-primary relaxation attributed to glass transition, beta-secondary relaxation and two interfacial polarizations due to the semi-crystalline character of PCL and the added HNT fillers. According to our results, the weight ratio of HNT ranging between 3% and 5% is recommended for achieving the highest performing nanocomposite that can be used in several applications.

YPolymer nanocomposites based on organo-modified Beidellite nanoclays (1-3 wt%) and poly(butylene succinate) (PBS) were elaborated and investigated using Scanning electron microscope (SEM), X-Ray diffraction (XRD), Differential Scanning Calorimetry (DSC) and Broadband Dielectric Spectroscopy (BDS). SEM analysis and XRD diffractograms demonstrated a good dispersion of added nanoclays in the poly(butylene succinate) matrix. A possible correlation between the crystallinity rate provided by the DSC results and the dielectric response of the samples was evaluated in order to establish a morphology-property relation. Additionally, a step-like variation related to an enthalpic relaxation within the rigid amorphous fraction (RAF) indicated a delayed contribution of this region to the overall dynamics of the polymer. The BDS results have shown various relaxation processes for which the activation energies were calculated after fitting the dielectric data by means of the Havriliak-Negami model. No significant effects of the added nanofiller on the glass transition temperature were observed. The extracted parameters confirm that a 2 wt% of Beidellite exhibits a better matrix/filler adhesion and hence improved interfacial properties. Thus, such filler load is recommended for a higher performing nanocomposite with potential applications.

The dielectric properties of fluorinated cyano copolymer poly(acrylonitrile-co-2,2,2-Trifluoroethyl methacrylate) (poly[AN-co-MATRIF]), reinforced with a natural Moroccan beidellite nanoclay organomodified with cetyltrimethylammonium bromide were studied. The effect of varying nanofillers loadings (1 wt%, 2 wt%, 3 wt%, and 5 wt%) on the molecular dynamics was investigated using broadband dielectric spectroscopy from 10(-1)to 10(6)Hz and temperatures ranging between 30 degrees C to 100 degrees C. For the copolymer matrix, the real(epsilon('))and imaginary parts(epsilon(''))of the dielectric permittivity curves revealed three dielectric processes: the secondary beta, the primary alpha and an ionic conduction phenomenon. Furthermore, incorporating of organomodified nanoclay, generated an additional relaxation process known as the Maxwell-Wagner-Sillars (MWS) interfacial polarization. The interface properties were investigated through the calculation of the strength parameters increment epsilon(MWS)using the WinFit impedance analysis software. At the range of 3 wt% of load, the orientation of the dipolar groups is reduced, caused by the high interaction and the strong adhesion involving the poly(AN-co-MATRIF) matrix and beidellite nanoclay. The part of nanoinclusions participating in the particle-polymer interaction is increased, forming a rigid polymer/clay interfaces. The evaluated parameters confirm that a weight ratio of 3% of organomodified nanoclay is recommended to obtain a most performing nanocomposite that can serve in several applications such as fuel cells, lithium ion batteries, and photovoltaics.

The reported simulation results could be considered as one of the firsts modeling of the effect of temperature on the electrical breakdown phenomenon in polyethylene nanoscale. The breakdown begins with an abrupt increase of the external current density without a subsequent saturation. Our results show that the increase of temperature at a constant applied DC voltage leads to a breakdown and to a decrease of the insulator's lifetime. These outcomes are strongly linked to the injection of free charges into the sample and to the temporal evolution of the conduction current.

Throughout this work, an experimental and theoretical analysis of the molecular dynamics, correlated with the alternating current conductivity sigma(ac)(omega, T),of unidirectional piezoelectric composites used as actuators and/or sensors in different systems was carried out. The 3D-representation of the imaginary partM ''(omega, T)of the electric modulus shows, apart from the presence of the classical secondary beta and the primary alpha dipolar relaxation processes, the appearance of a new peak attributed to the Maxwell-Wagner-Sillars (MWS) interfacial polarization whose amplitude depends on the rate of reinforcement. In our case, since we are usually within the range of fragile materials, the stiffness of the 26% fiber content composite is about 4.5 times greater than that of 13.4% (via the fragility parameterD), shows a less pronounced curvature and the nature of the relaxation times is closer to the Arrhenius type. Due to the high dispersion of the conductivity with the frequency of applied electrical field in the range (1-10(4) Hz), Jonscher's "universal power law" has been revised by adding a new term, which takes into account the displacement current density. The ac conductivity adjustment procedure, using the new obtained expression, turns out to be accurate and follows the experimental data reported in the low, high, and even intermediate frequency domains. This theoretical approach allowed us to determine the key parameters ( increment epsilon,tau(max), horizontal ellipsis ) unique to each relaxation process, and to demonstrate the MWS interfacial polarization that is directly linked to the adhesion between the PZT fibers and the epoxy resin matrix.

Dielectric and electrical properties of bio-nanocomposites based on poly (?-caprolactone) (PCL) with different amounts of organomodified montmorillonite clay (MMT-ODA) were investigated by broadband dielectric spectroscopy in the frequency range from 1Hz to 1MHz and in the temperature range from -100 to 25°C. These nanocomposites were prepared by in situ Ring Opening polymerization of ?-caprolactone in open air by using titanium alkoxide as a catalyst. Due to the semicrystalline structure of PCL, the high number of modes and its overlap, the relaxation patterns observed on dielectric spectra were complicated. These relaxation data were modeled using the H-N empirical equation with the contribution of conductivity. The local dynamics of PCL were unaffected by the increase of nano-clay amount, in agreement with the DSC values of glass transition temperature. The PCL/MMT-ODA 3 wt% exhibited the lowest value of dielectric strength, indicating the strongest adhesion between PCL matrix and organo-modified clay. As for PCL/MMT-ODA 5 wt%, the presence of agglomerate made the adhesion between PCL and MMT-ODA very weak. The obtained findings were congruent FTIR and XRD results. The electrical conductivity of PCL was analysed according to the Jonscher’s law. The obtained exponent s values referred to three models corresponding to different temperature ranges.

The main focus of this work is the investigation of dielectric properties of nanocomposites based on poly(vinyl alcohol) (PVA) matrix and cellulose nanofibrils (CNFs) reinforcement. Nanocomposites films with different CNFs content were prepared by simple mixing of PVA solution and CNFs suspension in water and water evaporation. Dielectric spectroscopy of the nanocomposite's films over a large temperature domain between similar to 50 degrees C to 170 degrees C and a frequency range of 0.1 Hz to 1 MHz was studied to probe the molecular mobility and interfacial transition of the material. In addition, differential scanning calorimetry (DSC) and spectroscopic analysis by FTIR and Raman were performed to further evidence interaction between CNFs and PVA matrix. Different relaxations were detected, namely 13 and a relaxations, water polarization and interfacial polarization known as Maxwell-Wagner-Sillars polarization (MWS), with magnitude and position being dependent on the CNF content.

An efficient approach to obtain polymeric materials with high permittivity values and low dielectric losses is presented in the current study. For this purpose, dielectric measurements by means of broadband dielectric spectroscopy, numerical simulations, and analytical calculations have been carried out for bilayer structures consisting in an insulating and a conductive polymer layer. Polyethyleneterephtalate and polytetrafluoroethylene have been used as insulating layers while, as conductive materials, blends of polyvinyl acetate with an ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate. The dielectric properties of the samples have been investigated in a broad frequency (from 10(-1) to 10(7) Hz) and temperature range in order to determine, through the analysis of the scaling laws governing the interfacial polarization effects, the characteristic frequency ranges and the amplitude of the enhanced permittivity. An excellent agreement is found between the experimental results, the numerical simulations, and the analytical calculations. Finally, we show that bilayer polymeric materials with permittivity values as high as epsilon=556 and with low dielectric losses (tan()= 0.001) can be readily obtained by the current approach. This could have multiple applications, especially in the field of organic electronics. (c) 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47551.

In this work, the influence of the incorporation of nanoparticles (organo-modified montmorillonite Cloisite 30B) in polyamide 6 (PA6) on rigid amorphous fraction (RAF) formation had been explored employing Differential Scanning Calorimetry (DSC), Flash Differential Scanning Calorimetry (Flash DSC) and Broadband Dielectric Spectroscopy (BDS) techniques. The existence of a RAF in PA6-montmorillonite nanocomposite films is available from specific heat capacity measurement at the glass transition region of the nanocomposites. It was shown that at high C3OB content, this fraction becomes larger. Using Flash DSC, it was possible not only to measure the heat capacity step at the glass transition of the materials, but also to provide quantitative knowledge on the kinetics of crystallization and nucleation of PA6-based nanocomposites. The dielectric relaxation spectroscopy measurement was investigated, in the frequency range 0.1-10(6) Hz and varying temperature from 20 to 200 degrees C, which highlight different relaxation phenomena: the alpha dipolar relaxation, the alpha c relaxation and Max-well-Wagner-Sillars (MWS) interfacial polarizations. As C30B content increases, a MWS relaxation emerges in the nanocomposites, thus revealing the increase of RAF in the nanocomposite with high C30B content.