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Natural fibers are extracted from natural resources such as stems of plants. In contrast to synthetic fibers (e.g., carbon fibers), natural fibers are from renewable resources and are eco-friendlier. Plant fibers are important members of natural fibers. Review papers discussing the microstructures, performances and applications of natural plant fiber composites are available in the literature. However, there are relatively fewer review reports focusing on the modeling of the mechanical properties of plant fiber composites. The microstructures and mechanical behavior of plant fiber composites are briefly introduced by highlighting their characteristics that need to be considered prior to modeling. Numerical works that have already been carried out are discussed and summarized. Unlike synthetic fibers, natural plant fiber composites have not received sufficient attention in terms of numerical simulations. Existing technical challenges in this subject are summarized to provide potential opportunities for future research.

Polymer (polar/nonpolar)/metal composites (PMC) were prepared under different process conditions. In polar PMC, dipolar relaxation plays a predominant role below percolation threshold (f_c) and anomalous low frequency dispersion (ALFD) becomes dominant above f_c while ALFD is the only likely possibility for nonpolar PMC above f_c. The magnitude of relaxation exponents "m", "p" and "n", evaluated from the experimental results using Jonscher's universal dielectric response (JUDR) laws, falls within the universal limit ~ [0, 1] with additional feature of strong dependence on volume fraction of conductor (f_con). The decrease in the relaxation exponent "m" with an increase of f_con is directly linked with decrease in the number of dipoles of the polymer in the composite and is accompanied by a distribution of relaxation time due to increased heterogeneity of the system. The magnitude of the relaxation exponent "n" decreases at f_c, due to the prevalence of Maxwell–Wagner–Sillar polarization contributed by uncorrelated electrons.

Breakthroughs can be expected in multi-component ceramics by adjusting the phase assembly and the micro–nanostructure. Controlling the architecture of multi-materials at different scales is still challenging and provides a great opportunity to broaden the range of functionalities in the field of ferroelectric-based ceramics. We used the potentialities of Spark Plasma Sintering (SPS) to control a number of key parameters regarding the properties: anisotropy, interfaces, grain size and strain effects. The flexibility of the wet and supercritical chemistry routes associated with the versatility of SPS allowed designing new ferroelectric composite ceramics at different scales. These approaches are illustrated through various examples based on our work on ferroelectric/dielectric composites.

Pyroelectric composites of triglycine sulfate (TGS)-polyvinylidene difluoride (PVDF) doped with graphene are studied. It is found that the graphene can effectively improve the polling efficiency and thermal property of the composites so that the infrared detective performance can be significantly improved. For example, by adding about 0.83 wt.% of graphene, the infrared detective property can be improved by more than 30%. It is also found that the size of the graphene plays a critical role on the property improvement. For example, the small-sized graphene prepared by ultrasonic exfoliation (UE) method is more effective than the big-sized graphene prepared by electrochemical exfoliation (EE) method.

The frequency-dependent percolation and scaling behavior of a variety of polymer/metal composites (PMC), based on polyvinylidene fluoride (PVDF) matrix and various types of fillers such as; metal/alloy particles of different sizes, prepared through cold/hot pressing process conditions have undergone investigation. The universal percolation behavior in the vicinity of percolation threshold ($f_c$), i.e., ${\sigma }_{\mathrm{\text{eff}}}(\omega ,f_{\mathrm{\text{con}}}\approx f_c)\propto {\omega }^x$ and ${\epsilon }_{\mathrm{\text{eff}}}(\omega ,f_{\mathrm{\text{con}}}\approx f_c)\propto {\omega }^{-y}$ is well satisfied, which suggests $f_c$ to be independent of frequency, where ${\sigma }_{\mathrm{\text{eff}}}$ and ${\epsilon }_{\mathrm{\text{eff}}}$ are the effective ac conductivity and effective dielectric constants of the composite and $\omega$ is the frequency of applied ac signal. The obtained experimental values of the exponents are consistent with the inter-cluster polarization model ($x=0.72$ and $y=0.28$), satisfying $x+y=1$. The widely used percolative equations are well fitted with the experimental results of all PMC at all values of the frequency. The value of $f_c$ is found to be independent of frequency of the applied signal, suggesting the studied PMC are real percolating systems. The critical exponents ($s$ and $s^{\prime }$) which characterize the divergence of ${\epsilon }_{\mathrm{\text{eff}}}$ and ${\sigma }_{\mathrm{\text{eff}}}$ in the vicinity of $f_c$ are found to decrease with the increase of frequency. The rate of decrease of ‘$s$’ and ‘$s^{\prime }$’ with increase of frequency is attributed to the method of preparation, size of the fillers, adhesiveness of polymer/filler and the rate of decrease of ${\epsilon }_{\mathrm{\text{eff}}}$ with frequency (due to the absence of different extents of contributions of various types of conventional polarizations).

Lead-free multiferroic composites of 1$-x$(K${}_{0.5}$Na${}_{0.5}$NbO${}_3-x$(Co${}_{0.6}$Zn${}_{0.4})$(Fe${}_{1.7}$Mn${}_{0.3})$O₄ (KNN-CZFMO), where $x$= 0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and 1.0, have been investigated for their structural, morphological, electrical, magnetic, dielectric and magneto-dielectric properties. Presence of KNN and CZFMO crystal structure in each composite has been confirmed from X-ray diffraction analysis (XRD). Cuboidal-shaped grains of KNN and spherical-shaped grains of CZFMO have been observed by scanning electron microscopy (SEM). The room temperature ferroelectric behavior as confirmed by polarization versus electric field ($P$–$E)$ hysteresis loops has been found to be decreasing with increasing CZFMO concentration. Increasing magnetic ordering with the increase in CZFMO concentration in the prepared composites has been observed by magnetization versus magnetic field ($M$–$H)$ hysteresis loops. The electrical conductivity of composites has been studied using Jonscher’s universal power law. The room temperature dielectric constant ($𝜀\prime )$ and dielectric loss (tan $\delta )$ have been observed to decrease with the increase in the frequency of the applied external electric field. The dielectric relaxation behavior has been observed using curve fitting analysis via the Havriliak–Negami relaxation model. Maximum value of the magnetodielectric (MD) effect $\sim$−11% at a frequency of 1 kHz with the applied magnetic field of 1 T has been achieved for 0.9 KNN−0.1 CZFMO ($x$= 0.1) composite in the present research work.

This work presents the results of study of the electrophysical properties of composite polymer ceramics (1$-x)$[KNN-LTSN]–$x$PVDF at $x$ = 25 vol.% and $x$= 50 vol.% in the temperature range of $T$ = 20–160${}^{\circ }$C and frequency range of $f$ = 2 × 10¹–2 × 10⁶ Hz. The concentration dependence of piezomodules of the studied materials has been analyzed as a function of temperature. X-ray measurements have also been carried out. A model of description of revealed dielectric parameters dispersion in the material is presented. The nonclassical modified Havriliak–Negami model written for complex electrical conductivity has been used to describe the temperature–frequency properties. It is shown that the dielectric spectra of the studied composites include three relaxation processes in the temperature ranges of 40–80${}^{\circ }$C, 80–120${}^{\circ }$C and 120–150 ${}^{\circ }$C, which were confirmed by the dynamics of changes in the dependences of ${\gamma {}^{\prime }}^{(}f)$, tg$\delta (f)$, ${M{}^{\prime }}^{(}f)$, $M^{\mathrm{\prime \prime }}$($f$) and $M\mathrm{\prime \prime }$($M\prime )$. All three processes are almost exactly described by this model and well correlated with the studies by other researchers of the composites based on PVDF. The results of this work show that the use of such experimental model is suitable for describing the complex dielectric spectra of any nonlinear dielectrics including composite materials.

A novel category of polyphenylene oxide/high-impact polystyrene (PPO/HIPS) alloy was used as the polymer matrix (abbreviated as mPPO) and loaded with different volume fractions (0, 10, 20, 30, 40, 50 vol.%) of MgTiO₃–Ca${}_{0.7}$La${}_{0.2}$TiO₃ (abbreviated as MTCLT) ceramics to prepare composites by injection molding. Its micromorphology, density, dielectric, thermal and mechanical properties were analyzed in detail. The experimental results show that the composites possess a compact microstructure because HIPS increases the fluidity of PPO. Due to the excellent dielectric properties of both mPPO and MTCLT, the composites have an extremely low dielectric loss. The realization of the high ceramic filler fraction greatly limits the thermal expansion of the polymer chain by introducing the interphase, so that the coefficient of thermal expansion of the composite material could be as low as 21.8 ppm/${}^{\circ }$C. At the same time, the presence of ceramic particles could reinforce the mechanical property of the composites. When the ceramic filler fraction is higher than 20 vol.%, the bending strength of the composite material is around 110 MPa. When the ceramic filler fraction is 40 vol.%, the composite possesses the best comprehensive performance. The dielectric constant is 6.81, the dielectric loss is 0.00104, the thermal expansion coefficient is as low as 25.3 ppm/${}^{\circ }$C, and the bending strength is 110.4 MPa. Due to its excellent properties, this material can be a good candidate in the field of microwave communication.

The paper deals with Dielectric Behaviour, Complex Impedance Spectroscopy and Magnetoelectric effect in La_0.7Sr_0.3MnO₃(LSMO) and BaTiO₃ (BT) Composites. The LSMO and BT are synthesized by hydroxide co-precipitation route. The nanocomposites are prepared by two series x LSMO + (1-x) BT + 2 wt % Bi₂O₃, for x = 0.05, 0.1, 0.15 and 0.2 ……series 1. x LSMO + (1-x) BT + 3 wt % Bi₂O₃, for x = 0.05, 0.1, 0.15 and 0.2 ……series 2. and sintered at T_s=1000°C and 1080°C. The composites are termed as LSMO-BT. The paper reports the crystal structure, micro-structural analysis, dielectric constant, complex impedance spectroscopy and magnetoelectric properties of LSMO-BT composites. It has been observed that the ε_r passes through a broad maximum at T ~ 124° C, which is nearly the ferroelectric transition temperature of BT. Both ε_r and ε_rmax increases as x increases from 0.05 to 0.2. The ε_r' and ε_r'' decreases sharply for all the compositions at low frequencies. This feature is typical of the presence of interfacial polarization. The variation of 4πMs is almost linear with x, the 4πMs increases with x as well as sintering aid. The 4πMs of respective compositions reduce as the sintering temperature is increased. The value of α increases for increase in sintering temperature as well as increase in wt % of the sintering aid. The magnitude of α is in the range as reported earlier for composites based on BT.

This paper deals with the adhesion strength of laminated bamboo composites fabricated only from steam-exploded bamboo plates by using a hot-pressing method. The adhesion strength of laminated bamboo composites were evaluated by a short beam bending teats. The effects of molding conditions on the shear strength were examined by changing the molding temperature, time, and pressure. The optimum molding conditions of the laminated bamboo composites are 140°C, 30 min. and 10 MPa among the conditions investigated. The maximum shear strength of the laminated bamboo composites was approximately 46 MPa, and this value is comparable to that of single plate bamboo composites without lamination.