Effect of polarization switching on piezoelectric and dielectric performance of electrospun nanofabrics of poly(vinylidene fluoride)/Ca–Al LDH nanocomposite

At present, highly flexible, durable, and lightweight piezoelectric nanogenerators with high-power density and energy conversion efficiency are of great interest. The present study reports a new synthetic route for Ca–Al layered double hydroxide (LDH) nanosheets and incorporation of these two-dimensional nanosheets as filler material into poly(vinylidene fluoride) (PVDF) to produce composite nanofabrics by electrospinning. The polymorphism, crystallinity, and the interaction between PVDF and LDH were studied by Fourier transform infrared spectroscopy, X-ray diffraction, and differential scanning calorimetry techniques. The synergetic effect of PVDF–LDH interaction and in situ stretching due to electrospinning facilitates the nucleation of electroactive β phase up to 82.79%, which makes it a suitable material for piezoelectric-based nanogenerators. The piezoelectric performance of PVDF/Ca–Al LDH composite nanofabrics was demonstrated by hand slapping and frequency-dependent mechanical vibration mode, which delivered a maximum open circuit output voltage of 4.1 and 5.72 V, respectively. Moreover, the composite nanofabrics exhibited a high dielectric constant and low dielectric loss due to superior interfacial polarization at low-frequency region with LDH loading, promising its potential applications in electronic devices. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48697.     

Biodegradable poly(lactic acid)/cellulose-based superabsorbent hydrogel composite material as water and fertilizer reservoir in agricultural applications

The work presents a fully degradable superabsorbent composite material to be used in agricultural and horticultural applications. It is designed to retain and release fertilizer solutions to the soil in a controlled manner, permitting resource optimization. Because of its ability to absorb and release large amounts of saline water, a natural superabsorbent hydrogel derived from cellulose was chosen. Potassium nitrate was chosen to model the fertilizer. Poly(lactic acid) was added to the final composition in order to delay solution release. The composite material was obtained using easily available and low-cost starting materials and using a simple manufacturing process, using a standard mixer. After being analyzed for morphological (scanning electron microscopy), physical (X-ray diffraction), chemical (energy-dispersive X-ray spectroscopy), and thermal properties (thermogravimetric analysis and differential scanning calorimetry), the material was tested using two different Mediterranean cultivations (Pomodoro di Morciano di Leuca and Cicoria Otrantina) and two different kinds of soil (red and white soils). The analysis revealed different water release characteristics for different soils. These findings have been confirmed by measuring plant growth for both species, as well as fruit yield of the tomatoes. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47546.     

Thermal treatment of pyrolytic lignin and polyethylene terephthalate toward carbon fiber production

In this work, pyrolytic lignin (PL) was thermally co-treated with polyethylene terephthalate (PET) to produce carbon fiber precursor. The produced PL-PET precursors were thoroughly characterized and analyzed, and then being processed into carbon fiber. It was found that a novel precursor, rather than their physical blending, was formed by the thermal co-treatment, indicating there were strong interactions between PL and PET. The novel PL-PET precursors had enhanced thermal properties and rheological characteristics, therefore are more suitable for processing into better carbon fibers based on melt-spinning method. In this study, the precursor fibers derived from the co-treatment of PL and 5% PET were also stretched under tension during stabilization step to reduce the fiber diameter and improve molecular orientation. The resulting carbon fibers with an average diameter of 12.6 μm had the tensile strength of up to 1220 MPa. This work demonstrated that PET could be used to improve the processability and quality of lignin-based carbon fiber when it is chemically bonded with lignin-based precursor. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48843.     

QCM-D assay for quantifying the swelling,biodegradation, and protein adsorption of intelligent nanogels

Environmentally responsive nanomaterials have been developed for drug delivery applications, in an effort to target and accumulate therapeutic agents at sites of disease. Within a biological system, these nanomaterials will experience diverse conditions which encompass a variety of solute identities and concentrations. In this study, we developed a new quartz crystal microbalance with dissipation (QCM-D) assay, which enabled the quantitative analysis of nanogel swelling, protein adsorption, and biodegradation in a single experiment. As a proof of concept, we employed this assay to characterize non-degradable and biodegradable poly(acrylamide-co-methacrylic acid) nanogels. We compared the QCM-D results to those obtained by dynamic light scattering to highlight the advantages and limitations of each method. We detailed our protocol development and practical recommendations, and hope that this study will serve as a guide for others to design application-specific QCM-D assays within the nanomedicine domain. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48655.     

Electrospun antibacterial nanofibers: Production,activity, and in vivo applications

Electrospinning is an economical and relatively simple method to produce continuous and uniform nanofibers from almost any synthetic and many natural polymers. Because of the high specific surface area, tunable pore size, and flexibility, the nanofibrous membranes are finding an increasingly wide range of applications. Some particular attention has been devoted to antibacterial nanofibers for applications such as wound dressings. A variety of biocides, e.g., antibiotics, quaternary ammonium salts, triclosan, biguanides, (silver, titanium dioxide, and zinc oxide) nanoparticles and chitosan have been incorporated by various techniques into nanofibers that exhibit strong antibacterial activity in standard assays. However, the small diameters of the nanofibers also mean that the incorporated biocides are often burst released once the materials are submerged in an aqueous solution. Nevertheless, several strategies, such as core‐sheath structure of the nanofiber, covalent bonding of the biocide on the fiber surface and adsorption of the biocide in nanostructures, can be utilized to sustain the release over several days. This review summarizes recent development in the fabrication of antibacterial nanofibers, the release profiles of the biocides and their applications in in vivo systems. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40797.     

Production of reduced graphene oxide-based electrically conductive hydrogel by using modified chitosan

Herein, a new approach was applied to produce reduced graphene oxide (RGO)-based conductive hydrogel by using modified chitosan (CTS) as a primary constituent. A variety amounts of RGO (from 0 to 15%) were incorporated into the polymeric network generated by photopolymerization of CTS-graft-glycidyl methacrylate (CTS-g-GMA) and poly(ethylene glycol)diacrylate (PEGDA). The structures of hydrogels were confirmed by FT-IR, XRD, and SEM analyses. Water uptake capacity of hydrogels determined gravimetrically. L929 fibroblast cells were used for cytotoxicity test. According to conductivity measurements carried out by four-point probe technique, the highest conductivity (1.716 × 10⁻³ S/cm) was obtained when 10% RGO was encapsulated into the polymeric structure. From the results, it could be envisaged that electroconductive hydrogel (ECH) fabricated in this study could have a potential usage for biosensor applications in the future projects. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48008.     

Attempting to prepare a plastic scintillator from a biobased polymer

A new plastic scintillator was prepared from a renewable polymer source. It is composed of the mighty 2,5-diphenyloxazole and 1, 4-bis(2-methylstyryl)benzene molecules (PPO and bis-MSB), acting as primary and secondary fluorophores, respectively, together dissolved in a polylactic acid matrix—PLA. This polymer is indeed considered as the biomass-based equivalent of petroleum-derived plastics in terms of mechanical and optical properties. Subsequent to the bis-MSB emission, the emission wavelength is centered around 424 nm and the fluorescence decay time is in the nanosecond range. The material was fully characterized, and its scintillation performances were compared to a commercial PVT-based plastic scintillator: EJ-200. Like polystyrene- or polyvinyltoluene-based scintillators, the material displayed a good response linearity with the energy of the incident gamma-ray. However, the observed scintillation yield was rather modest, with a reported 500 ph/MeV value when excited with a gamma-ray-emitting ⁶⁰Co source. This preliminary test could pave the way to new and renewable polymers for unexpected applications such as nuclear physics. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48724.     

Lignin for Bioeconomy: The Present and Future Role of Technical Lignin

Lignin, the term commonly used in literature, represents a group of heterogeneous aromatic compounds of plant origin. Protolignin or lignin in the cell wall is entirely different from the commercially available technical lignin due to changes during the delignification process. In this paper, we assess the status of lignin valorization in terms of commercial products. We start with existing knowledge of the lignin/protolignin structure in its native form and move to the technical lignin from various sources. Special attention is given to the patents and lignin-based commercial products. We observed that the technical lignin-based commercial products utilize coarse properties of the technical lignin in marketed formulations. Additionally, the general principles of polymers chemistry and self-assembly are difficult to apply in lignin-based nanotechnology, and lignin-centric investigations must be carried out. The alternate upcoming approach is to develop lignin-centric or lignin first bio-refineries for high-value applications; however, that brings its own technological challenges. The assessment of the gap between lab-scale applications and lignin-based commercial products delineates the challenges lignin nanoparticles-based technologies must meet to be a commercially viable alternative.     

One-Dimensional Nanostructures and Devices of II–V Group Semiconductors

The II–V group semiconductors, with narrow band gaps, are important materials with many applications in infrared detectors, lasers, solar cells, ultrasonic multipliers, and Hall generators. Since the first report on trumpet-like Zn₃P₂ nanowires, one-dimensional (1-D) nanostructures of II–V group semiconductors have attracted great research attention recently because these special 1-D nanostructures may find applications in fabricating new electronic and optoelectronic nanoscale devices. This article covers the 1-D II–V semiconducting nanostructures that have been synthesized till now, focusing on nanotubes, nanowires, nanobelts, and special nanostructures like heterostructured nanowires. Novel electronic and optoelectronic devices built on 1-D II–V semiconducting nanostructures will also be discussed, which include metal–insulator-semiconductor field-effect transistors, metal-semiconductor field-effect transistors, and p–n heterojunction photodiode. We intent to provide the readers a brief account of these exciting research activities.     

Design and characterization of PNVCL-based nanofibers and evaluation of their potential applications as scaffolds for surface drug delivery of hydrophobic drugs

In this work, nanofiber scaffolds for surface drug delivery applications were obtained by electrospinning poly(N-vinylcaprolactam) (PNVCL) and its blends with poly(ε-caprolactone) and poly(N-vinylcaprolactam)-b-poly(ε-caprolactone). The process parameters to obtain smooth and beadless PNVCL fibers were optimized. The average fibers diameter was less than 1 μm, and it was determined by scanning electron microscopy analyses. Their affinity toward water was evaluated by measuring the contact angle with water. The ketoprofen release behavior from the fibers was analyzed using independent and model-dependent approaches. The low values of the release exponent (n < 0.5) obtained for 20 and 42 °C, indicating a Fickian diffusion mechanism for all formulations. Dissolution efficiencies (DEs) revealed the effect of polymer composition, methodology used in the electrospinning process, and temperature on the release rate of ketoprofen. PNVCL/poly(N-vinylcaprolactam)-b-poly(ε-caprolactone)-based nanofibers showed greater ability to control the in vitro release of ketoprofen, in view of reduced kinetic constant and DE, making this material promising system for controlling release of hydrophobic drugs. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48472.     

Catalytic decomposition of methane for the simultaneous co-production of CO2-free hydrogen and carbon nanofibre based polymers

Through the catalytic decomposition of methane (CDM) it is possible to obtain in a single step both CO₂-free hydrogen and carbon nanostructures with a wide range of applications such as nanocomposite reinforcements. In this work, a Ni-based catalyst has been used to carry out the catalytic decomposition, obtaining an hydrogen concentration up to 47% (vol.) in the flue gas and carbon nanofibres (CNF). These structures have been inserted into two epoxy resins with different viscosity in order to study the influence of the CNF load in the electrical resistivity of the new materials prepared. As a result, the resistivity of these materials decreases up to 10⁶ Ω cm, values which avoid the electrostatic discharge and allow the electrostatic painting.     

A percolation threshold model that effectively characterizes the full concentration range for electrical-conducting polymer composites

The new percolation threshold model introduced in this study is a modification of Clingerman's model, which in turn is a modification of the model originally developed by Mamunya et al. Several of the original constants from Clingerman's and Mamunya's were consolidated, and most importantly, the concentration of the percolation threshold is not a required constant in the model. One extraordinary characteristic of this new model is that it is possible to separate this model into two different equations that separately describe the conducting filler component and the insulating matrix component. In general, this new percolation threshold model introduces five new calculated quantities on the S-shaped curve, including the calculated volume fraction of the percolation threshold. The capability of this new model was evaluated with three of Clingerman's polymer composite percolation threshold data sets involving electrical conductivity measurements. This new model did an excellent job of fitting the data extremely well over the whole concentration range. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47184.     

Electrokinetic and antibacterial properties of needle like‐TiO2/polyrhodanine core/shell hybrid nanostructures

The aim of this study was to fabricate needle like‐TiO₂/polyrhodanine nanostructures by polymerizing rhodanine monomer on the TiO₂ nanoparticles' surfaces and investigate their antibacterial activities. The structural, thermal, morphological, surface and electrical properties of non‐covalently functionalized nanoparticles were characterized by using FTIR, XPS, elemental analysis, TGA, XRD, SEM‐EDX, TEM, contact angle, and conductivity measurements. Characterization results confirmed the formation of needle like‐TiO₂/polyrhodanine (PRh) core/shell hybrid nanostructures. Alterations on the surface and electrokinetic properties of the materials were characterized by zeta (ζ)‐potential measurements with the presence of various salts and surfactants. The ζ‐potential of needle like‐TiO₂ was observed to increase from ?7.6 mV to +28.4 mV after forming a core/shell needle like‐TiO₂/PRh nanocomposite structure and with the presence of cetyltrimethyl ammonium bromide (CTAB) surfactant. Thereby colloidally more stable dispersions were formed. Antibacterial properties of needle like‐TiO₂/PRh were also tested against Staphylococcus aureus, Klebsiella pneumoniae, and Escherichia coli by various methods and they showed good antibacterial activity. The highest killing efficiency was determined for needle like‐TiO₂/PRh against E. coli by colony‐counting method as 0.95. TEM experiments also showed the immobilizations of the nanoparticles on E. coli and revealed the interactions between E. coli and the nanoparticles. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41554.     

Thermoplastic and moisture-dependent behavior of lignin phenol formaldehyde resins

Bonding kinetics of thermosetting adhesives is influenced by a variety of factors such as temperature, humidity, and resin properties. A comparison of lignin-based phenol formaldehyde (LPF) and phenol formaldehyde (PF) adhesive in terms of reactivity and mechanical properties referring to testing conditions (temperature, moisture of specimen) were investigated. For this purpose, two resins were manufactured aiming for similar technological resin properties. The reactivity was evaluated by B-time measurements at different temperatures and the development of bonding strength at three different conditions, testing immediately after hot pressing, after applying a cooling phase after hot pressing, or sample conditioning at standard climate. In addition, the moisture stability of the two fully cured resins was examined. The calculated reactivity index demonstrated that LPF requires more energy for curing than PF. Further results indicate that lignin as substituent for phenol in PF resin has a negative impact on its moisture resistance. Additionally, the known thermoplastic behavior of lignin could also be detected in the behavior of the cured resin. This behavior is relevant for the adhesive in use and necessitates a cooling phase before testing the bonding strength development of lignin-based adhesive systems. © 2019 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48011.     

Toughening of thermoset green zein resin: A comparison between natural rubber-based additives and plasticizers

Zein-based brittle thermoset green resin was toughened using sorbitol, natural rubber fibers (NRF), and epoxidized natural rubber fibers (ENRF). NRF and ENRF were electrospun directly into zein slurry. Chemical, thermal, and mechanical properties of zein resin containing NRF (Zein/NRF) and ENRF (Zein/ENRF) were compared with those of sorbitol-plasticized zein. NRF was found to be immiscible in zein and Zein/NRF resins showed two distinct glass transition temperatures (T _g), whereas Zein/ENRF specimens showed significant increases in both T _g and degradation temperature (T _d) due to crosslinking between zein and epoxidized natural rubber. ENRF was more effective in enhancing fracture toughness of zein than NRF or sorbitol. Increased ENRF loading to 15 wt % showed significant increase in toughness with minimal decreases in strength and Young's modulus. Sorbitol and NRF were unable to improve the toughness of zein resin significantly. Environment-friendly zein/ENRF resin with higher fracture toughness developed in this study would be suitable in many applications including green composites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48512.     

Recent advances in flexible sensors for wearable and implantable devices

Flexible devices are emerging as important applications for future display, robotics, in vitro diagnostics, advanced therapies, and energy harvesting. In this review, we provide an overview of recent achievements in flexible mechanical and electrical sensing devices, focusing on the properties and functions of polymeric layers. In the order of historical development, sensing platforms are classified into four types: electronic skins for robotics and medical applications, wearable devices for in vitro diagnostics, implantable devices for human organs or tissues for surgical applications, and advanced sensing devices with additional features such as transparency, self‐power, and self‐healing. In all of these examples, a polymer layer is used as a versatile component including a flexible structural support and a functional material to generate, transmit, and process mechanical and electrical inputs in various ways. We briefly discuss some outlooks and future challenges toward the next steps for flexible devices. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1429–1441, 2013     

Poly(lactic acid)–thermoplastic starch–cotton composites: Starch-compatibilizing effects and composite biodegradability

Poly(lactic acid) (PLA) is a biodegradable, brittle, and high-cost polymer, which can be applied over structural components and green packaging. In this study, we reinforced PLA with natural cotton (10 wt %) and thermoplastic starch (TPS; 3 wt %) to obtain a biodegradable and lower cost composite. TPS was incorporated in three distinct ways: it was blended, coated, and blended and coated. In this study, we investigated the compatibilization of TPS in the improvement of matrix-reinforcement adhesion and increase in the tensile behavior without a compromise in biodegradation. The samples were investigated with thermal analysis, dynamic mechanical thermal analysis, tensile testing, scanning electron microscopy, confocal laser scanning microscopy, and hydrolytic degradation. The results show that the coupling effect was more pronounced in the PLA_TPS–cotton_TPS (hybrid system with PLA and cotton) hybrid system. This formulation presented a higher glass-transition temperature, thermal stability, storage modulus, wettability, and ductility. The TPS addition improved the adhesion between the matrix and starched cotton fiber and retarded abiotic biodegradation. These properties will allow for green applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47490.     

Quickly self-healing hydrogel at room temperature with high conductivity synthesized through simple free radical polymerization

The use of conductive self-healing hydrogels in electronic devices not only reduces replacement and maintenance costs but also prolongs their lifetime. Therefore, developing hydrogels with autonomous self-healing properties and electronic conductivity is vital for the advancement of emerging fields, such as conductors, semiconductors, sensors, artificial skin, and electrodes and solar cells. However, it remains a challenge to fabricate a hydrogel with high conductivity that can be healed quickly at room temperature without any external stimulus. In this work, we report an effective and simple free radical polymerization approach to synthesizing a hydrogel using modified rGO and acrylate monomers containing abundant ion groups. The hydrogel exhibits excellent electronic conductivity, extremely fast electronic self-healing ability, and excellent repeatable restoration performance at 25 °C. The conductivity of the hydrogel reaches 27.2 S/m, the hydrogel recovers its original shape, and scoring scratched on the surface totally disappears after holding at 25 °C for 40 s. This conductive, room-temperature self-healing hydrogel takes unique advantage of supramolecular chemistry and polymer nanoscience and has potential applications in various fields such as self-healing electronics, artificial skin, soft robotics, biomimetic prostheses, and energy storage. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47379.     

Design of polyurethane fibers: Relation between the spinning technique and the resulting fiber topology

Properties or characteristics of fibers are affected by their topology. In fact, these topologies are found to have significant impacts in the functionalities of many applications. Hence, in this study, the relations between the spinning techniques and the topology of the resulting fibers are studied with the aim to provide a guideline for future reference where fibers with certain topology can be fabricated to suit specific applications. For this purpose, polyurethane is chosen to be the raw material to fabricate the fibers due to its versatility to be applied in various fields. The surface morphology, structures, and alignments of the fibers are studied. It is found that the polymer solution properties largely influence the mechanisms in the spinning process and can significantly affect the topology of the fibers. For instance, viscous solutions enable the spinning of coiled and smooth fibers, whereas conductive solutions encourage the splaying of the solution jet which results in the spinning of straight fibers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47706.     

Biocompatible shape-memory poly(vinyl chloride) with a tunable switching temperature via a plasticization effect

Biocompatible shape-memory poly(vinyl chloride) (PVC) with a tunable switching temperature (T_s) was fabricated via the incorporation of an environmentally friendly plasticizer of 1,2-cyclohexane dicarboxylic acid diisononyl (DINCH). It was revealed that both of the shape-memory effect (SME) and T_s were significantly influenced by the plasticization effect. With the addition of DINCH, the shape-fixing ratio (R_f) showed a slight reduction, whereas the shape-recovering ratio (R_r) was greatly enhanced, and T_s was decreased from 90 to 47 °C. PVC with 40 phr plasticizer realized an excellent SME with an R_f of 97.0% and a R_r of 90.1%; this resulted from the formation of an efficient shape-memory network via the physical crosslinking of the amorphous chains with crystals and rigid chain entanglements. In addition, the blood compatibility of the DINCH-plasticized PVC was evaluated, and the results indicate that it was of great potential for biomedical applications. Therefore, in this study, we successfully developed a new shape-memory polymer and provided a promising strategy for achieving SME with tunable T_s. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47992.