Total Degree Of Crystallinity Research Articles

Effects of nano-sized BaTiO3 on microstructural, thermal, mechanical and piezoelectric behavior of electrospun PVDF/BaTiO3 nanocomposite mats

Polyvinylidene fluoride (PVDF) is a good candidate for use in wearable electronics due to its flexibility, ease of processing, and ability to generate electrical charge in response to applied mechanical stress. In this work, low-density polyvinylidene fluoride (PVDF) nanocomposites containing nano-sized BaTiO3 with cubic symmetry were fabricated by electrospinning process, aiming to generate dominant electroactive β polar phase. The influence of nano-sized filler content on the microstructure, total degree of crystallinity, β phase content, and piezoelectric properties of the electrospun PVDF/BaTiO3 nanocomposites was systematically studied. The crystallinity and the thermal stability were evaluated using differential scanning calorimetry (DSC), x-ray diffraction (XRD) and thermogravimetric analysis (TGA). The content of evolved piezoactive β phase was determined by FTIR spectroscopy. It was shown that the electrospinning process is primarily responsible for very high content (up to 99.4%) of the developed piezoactive crystalline phase. High degree of crystallinity (up to 56.4%) was determined in PVDF/BaTiO3 nanocomposites, confirming the nucleation ability of the nanofiller. Maximum tensile strength of 55.5 MPa (127% higher than PVDF nanofiber mat) and maximum d33 coefficient of 18 pC N−1 were determined for the nanofiber mat containing 20 wt% BaTiO3. We believe that this work provides an important insight into the nanoparticles’ distribution and their agglomeration (SEM and TEM analyses) influence on the final properties of PVDF/BaTiO3 webs, generated via electrospinning.

High-performance flexible nanogenerators based on piezoelectric hBN- induced polyvinylidene fluoride nanofibers

Flexible piezoelectric nanogenerators (PENGs) are promising candidates for clean energy harvesting and powering electronics, especially for low-power modules. In this study, a PENG has been fabricated by incorporating functionalized mono-/few-layered hexagonal boron nitride nanosheets (F-hBNNS) in a polyvinylidene fluoride (PVDF) polymeric matrix. The synthesized 2D nanosheets are well characterized using different spectroscopic and microscopic methods. The analysis showed successful exfoliation of hBN, which indicated less than three layers of hBN after exfoliation and sulfonated and carboxylated functionalization on the surface. Also, the piezoresponse force microscopy (PFM) tests revealed a 3 times higher piezoelectric coefficient for F-hBNNS compared to that of the non-functionalized hBN with the same number of layers. The synthesized F-hBNNS with piezo-flexoelectric properties boosted the energy harvesting performance of the electrospun PVDF-based fibrous mats 5.5 times. The open-circuit output voltage test showed 23 V at 4 Hz with a power density of 1.93 μW/cm2 at a resistance loading of 16 MΩ in a simple finger tapping. The fabricated PENGs showed no decline in voltage output over 1000 cycles of bending-unbending of a robotic finger. It is proposed that the enhanced performance is due to (i) the synergistic effects of the flexoelectric and piezoelectric properties of synthesized F-hBNNS in the PVDF matrix and (ii) the manipulation of the crystalline structure of the PVDF chains, which is increased to 90% β-phase crystallinity with 49.03% total degree of crystallinity. This study shows the compatibility of the fabricated PENGs with the human body's biomechanics for being used as an efficient energy source for wearable devices with low power consumption.

Thermal and dielectric properties of PVDF/PEO/SiO2 nanodielectrics for flexible radioelectronic device technologies

Hybrid polymer nanocomposites (HPNCs) are innovative multifunctional materials, which are developed and intensively studied for their uses in the rapid evolution of flexible and lightweight device technologies. Accordingly, to contribute in this area, thermal properties of the crystal phases and the broadband radio frequencies dielectric dispersion and relaxation behaviour of the HPNC films based on poly(vinylidene fluoride) (PVDF)/poly(ethylene oxide) (PEO)/silica (SiO2) are formulated and studied by employing differential scanning calorimeter (DSC) and impedance/material analyzer (IMA). DSC thermograms of these semicrystalline HPNCs explained the wide range alteration in the crystals melting temperature of PVDF (153–167 ​°C) and PEO (59–72 ​°C) and the total degree of crystallinity (4–87%) with varying compositional ratio over the entire range of the PVDF/PEO blend host matrix and the dispersed amount of amorphous SiO2 nanomaterial up to 15 ​wt%. The dielectric dispersion behaviour of these HPNCs, at 20 ​°C, confirmed a non-linear decrease in permittivity with the increase of applied radio wave electric field frequency from 1 ​MHz to 1 ​GHz, which lies in the range of 6 to 2. At a fixed frequency, dielectric permittivity values exhibited an uneven variation with the increase of SiO2 amount and also the modification in the composition of polymer blend matrix in these composites. The analysis of dielectric loss spectra and relaxation processes revealed that these are low loss dielectrics and the presence of SiO2 nanoparticles in the polymer blend matrix impedes the chain segmental dynamics and the dipole reorientation. The electrical conductivity of these HPNCs enhanced in the range of 10−8 to 10−4 ​S/cm with the increase in frequency but it changed anomalously when the constituent amounts of the formulated composites are varied. The polymer crystals thermal properties and the dielectric and electrical conductivity dispersion behaviour of these materials are demonstrated with the consideration of polymer-polymer and polymer-nanoparticle hybrid interfaces and interactions. The experimental results evidenced the behaviour of PVDF/PEO/SiO2 films as tunable nanodielectrics with their compositions and could be used as insulator and dielectric substrate materials in the advances of flexible radioelectronics and energy storage devices.

The effect of the mass ratio of hard and soft segments on some properties of thermoplastic poly(ester‐siloxane)s

AbstractA series of thermoplastic elastomers based on soft polydimethylsiloxane (PDMS) and hard poly(butylene terephthalate) (PBT) segments was synthesized using a two‐step transesterification reaction in the melt. The molar mass of the soft PDMS component was constant (M̄nPDMS = 1056 g mol−1) while the starting reaction mixture compositions were varied to obtained copolymers with a mass ratio of hard to soft segments in the range from 70/30 to 40/60. The structure and composition of the copolymers was verified by 1H NMR spectroscopy. It appeared that there was a pronounced molar mass maximum when the PBT content of the copolymers was approximately 60 mass%, whereas all samples were considerably inhomogeneous with respect to the distribution of the lengths of the hard segments. Differential scanning calorimetry (DSC) thermograms showed that the melting and crystallization temperature increased with increasing PBT content, as did the total degree of crystallinity, which was confirmed by wide‐angle X‐ray scattering (WAXS) analysis. Thermogravimetric analysis (TGA) performed in nitrogen gave subtle differences for samples of different composition, including that of the PBT homopolymer, whereas in oxygen these differences were more pronounced in the way the thermo‐oxidative stability of the obtained copolymers decreased with decreasing PBT content. Finally, it was shown that the hardness depended directly on the PBT content, ie the higher the PBT content, the greater the hardness of the corresponding copolymer. Copyright © 2004 Society of Chemical Industry

Thermal and shrinkage behaviour of stretched peroxide-crosslinked high-density polyethylene

The thermal shrinkage of stretched crosslinked high-density polyethylene (HDPE) was investigated with the aim to produce heat shrinkable materials. The heat shrinkable property was achieved by a process of heating–stretching–cooling by aid of tensile machine on crosslinked HDPE obtained by compounding with various amount of peroxide. Effect of stretching ratio and stretching temperature on thermal and shrinkage behaviour at varying peroxide contents was investigated. The results showed that crosslinking hindered the crystallization process by decreasing the melting and crystallization temperatures as well as the total degree of crystallinity. The stretching ratio had no significant effect on shrink temperature but rather on ultimate shrinkage. The stretching temperature had relatively significant influence on the shrink temperature. Crosslinked HDPE stretched at above melting point (140 °C) had higher shrink temperature as compared to those stretched at lower temperature (90 °C). These effects could be reasonably explained by Hoffman theory and changes in crystallites size and total amount of crystallinity.

Dynamic FT-IR Analysis of the Crystallization to the Planar Zigzag Form for Syndiotactic Polypropylene

The polymorph and crystallization process for syndiotactic polypropylene (sPP) formed around at 0 °C after quenching from the melt has been dynamically investigated by infrared spectroscopy. The observation is carried out at constant temperatures between -5 and 15 °C after quenching into ice-water from the melt. Just after quenching into ice-water from the melt, the specimen is completely in the noncrystalline state with trans-rich sequences. When the samples are kept below 0 °C, only the planar zigzag form (form III) is crystallized in a few hours. Above 5 °C, in addition to the planar zigzag form, form I with the t 2 g 2 conformation is simultaneously formed. Just above the glass transition temperature (around -5 °C), the trans-rich chains are aggregated and developed to form form III. Above 5 °C, the trans-gauche transition is accelerated, and then the helical form with t 2 g 2 conformation is crystallized as form I. The total degree of crystallinity is not so high, because further crystallization is promoted in the noncrystalline region when the sample is left at room temperature after reaching the equilibrium state at each crystallization temperature.

Aspects of the structure of grafted polycrylonitrile on liquid-phase graft polymerization to polycaproamide fibres

The relationship between the main parameters of the structure of polycaproamide (PCA) fibre and the structure of grafted PAN has been investigated by IR spectroscopy and X-ray structural analysis. The influence of the orientation of the PCA crystallites, the type of their crystalline modification and the total degree of crystallinity on the structure of PAN in the copolymer has been studied. Graft polymerization with the method of initiation used increases the degree of crystallinity and the size of the PCA crystallites. The orientation of these crystallites after garfting increases. It is shown that the process of structuring of PAN does not depend on the type of crystalline modification of PCA. Oriented PAN crystallites appear directly in the course of polymerization of acrylonitrile on the PCA fibre and their advent is determined by the matrix influence of the PCA crystallites.