The Effect of Talc on the Mechanical,Crystallization and Foaming Properties of Poly(Lactic Acid)

Poly(lactic acid) (PLA)/talc composites containing different contents of talc were prepared by melt blending. Multiple properties of the prepared composites were investigated including mechanical, rheological and crystallization as well as foaming properties. Tensile test results indicated that the mechanical properties of the composite with 3% wt. talc showed significant reinforcement and toughening effect. When the talc content reached 10%, Young's modulus of the composite was increased by 35% compared with pure PLA. The morphological results showed that the talc layers were partially delaminated and uniformly dispersed in the PLA matrix at low loading. Differential scanning calorimetry (DSC) and polarized optical microscopy (POM) results indicated that 3% wt. talc significantly increased the crystallinity of the PLA matrix. The thermogravimetric analysis (TGA) results demonstrated that the thermal stability of PLA/talc composites was enhanced as well. Moreover, talc at low loading could act as a plasticizer in the polymer flow, which was investigated by rheological tests. The batch foaming experiments revealed that 3% wt. talc loading had the most notable heterogeneous nucleation effect, with the cell size decreasing from 15.4 μm for neat PLA to 8.5 μm and the cell density increasing by 298%.     

Graphene Oxide–Carbon Nanotubes Hybrids: Preparation,Characterization, and Application in Phenol Formaldehyde Resin

Graphene oxide–carbon nanotubes hybrids were prepared by using methylene diphenyl diisocyanate as a bridging agent. The as-prepared hybrids were introduced in phenol formaldehyde resin to fabricate polymer-based composites. Fourier transform infrared spectroscopy, transmission electrical microscopy, and X-ray diffraction were performed to characterize the functional groups, morphologies, and crystal structure of the as-prepared hybrids, respectively. The experimental results showed that the carbon nanotubes were loaded on the surfaces of the graphene oxide and they were held together through chemical bonds. Moreover, the as-prepared hybrids could improve the mechanical properties of the matrix. When the as-prepared hybrids loading was 0.6 wt%, the tensile strength, Young's modulus, and elongation at break of the composites were 31.3%, 97.0%, and 75.0% more than the pure sample; in addition, the compression strength and modulus of the composites were 19.7% and 21.3% more than the pure sample, respectively.     

Thermally stimulated acoustic splitting of an elastic wave in polycrystalline niobium subjected to electron-beam remelting

The effect of temperature on the Young’s modulus of electron-beam-remelted polycrystalline niobium is studied in the temperature range 20–1000°C. The impurity content in the material is Ta<0.5 wt% and O₂<0.1 wt%. The acoustic split of the resonant frequency is found in the temperature range 60–180°C, which makes the determination of the Young’s modulus uncertain. Mechanisms behind the thermally stimulated splitting of an elastic wave and the behavior of the Young’s modulus over a wide temperature interval are discussed.     

Synthesis of nanoparticles and its effect on properties of elastomeric nanocomposites

Calcium carbonate (CaCO₃) nanoparticles (9, 15, and 21 nm) were synthesized by solution spray of CaCl₂ and NH₄HCO₃ with sodium lauryl sulfate (SLS) as a stabilizing agent, and their effect was studied on polybutadiene rubber (PBR) with variations in wt% loading (4, 8, and 12%). The results of PBR nanocomposites were compared with commercial CaCO₃ (40 μm) and fly ash (75 μm) filled PBR microcomposites. Properties such as tensile strength, young modulus, elongation at break, glass transition temperature, decomposition temperature, and abrasion resistances were determined. Profound effect in properties was observed, because nanometric size of CaCO₃ particles synthesized using solution spray technique. Maximum improvement in mechanical and flame retarding properties was observed at 8 wt% of filler loading. This increment in properties was more pronounced in 9-nm size CaCO₃. The results were not appreciable above 8 wt% of nanofillers because of agglomeration of nanoparticles. In addition, an attempt was made to consider modeling Young’s modulus of PBR–nano CaCO₃ which was predicted by modified Halpin–Tsai equation. It was observed that the predication by the Guth equation and modified Halpin–Tsai equation agreed very well with experimental, whereas the Halpin–Tsai equation can only applied to predict the modulus of rubber nanocomposites in the range of low addition of nanofiller, which agrees the Nielsen equation.     

Fabrication and Thermal Characteristics of Liquid Crystalline Copolyester/OMMT Nanocomposite Films

Liquid crystalline copolyester (LCC)/organically modified-montmorillonite (OMMT) nanocomposite films were prepared by a solvent casting method with different OMMT contents, using p-chlorophenol as a solvent. Both LCC and LCC/OMMT were heat treated to obtain the smectic structure. To examine their internal structure and morphology, the prepared LCC/OMMT nanocomposite films were characterized by an X-ray diffraction method and TEM (transmission electron microscopy). The d-spacing of the silicate layers for each LCC/OMMT nanocomposite film was shifted, indicating that the OMMT particles were dispersed in the LCC matrix and formed intercalated structures. Thermal characteristics of the LCC/OMMT nanocomposite films were investigated by differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), and thermo-mechanical analysis (TMA). The gel-to-liquid crystal transition (T_c-lc) and degradation temperatures (T_d) of both LCC and LCC/OMMT nanocomposite films with different heat treatment time were examined. The T_c-lc and T_d of the LCC/OMMT were found to be enhanced compared with those of the LCC film, exhibiting their improved thermal characteristics.     

Thermal and Mechanical Properties of Poly(lactic acid)/Modified Carbon Black Composite

Poly(ethylene glycol) (PEG) was added as a plasticizer to the composite of poly(lactic acid) (PLA) and a modified carbon black (MCB). Among the three different molecular weight (M_n = 1000, 2000, 6000) PEGs used, PEG2000 promoted crystallization of PLA and enhanced the nucleation activity of MCB more efficiently than the other two. The crystallization rate of PLA/PEG2000/3 wt% MCB composite was three times that of PLA. Although a small decrease in tensile strength and modulus of elasticity of the composite was found as the PEG content increased, the elongation at break of the PLA/PEG/MCB composites significantly improved. When the PEG2000 content was 15 wt%, the elongation at break of the blend was 90%, 4.5 times that of the neat PLA.     

Fabrication of fluorographene nanosheets with high yield and good quality based on supercritical fluid-phase exfoliation

This article presents a novel and simple method of supercritical fluid-phase exfoliation to fabricate fluorographene (FG) nanosheets with high yield and good quality. After soaking with supercritical CO₂ and glycol at 10 MPa and 50 °C for 24 h, fluoride graphite powder was exfoliated by the intercalated CO₂ and glycol molecules during an abrupt depressurization step. Here, supercritical CO₂ acted as a penetrant and glycol acted as a “molecular wedge” to exfoliate fluoride graphite very well. The properties of FG nanosheets were detected by TEM, AFM, UV spectra, FTIR, XPS, Raman spectra, and XRD, which show the possibility of producing thickness-controlled FG nanosheets by varying numbers of supercritical CO₂ process and the high yield of pure FG nanosheets of 32 wt%, four times higher than that of the sample treated only by the traditional method of sonication. Its simplicity, high productivity, low cost, and short processing time make this technique suitable for large-scale manufacturing of FG nanosheets.     

High-Performance Poly(vinyl alcohol) Nanocomposites Filled with Individual Montmorillonite Nanolayers

Filling poly(vinyl alcohol) (PVA) with clay, typically montmorillonite (MMT), has been proven to be an attractive option to meet the high-performance requirements of PVA-based materials. In previous reports MMT or organophilic MMT (OMMT) were directly used as fillers. As a result, both exfoliated and intercalated MMT structures coexisted in the resultant nanocomposites. However, there is still a large gap between these nanocomposites and ideally designed ones where individual clay nanolayers (CNLs) are expected to be uniformly dispersed in the PVA. With this in mind, an ameliorative solution casting process is proposed here to prepare PVA nanocomposites. For this purpose the CNLs were prepared ahead of time by exfoliation of MMT in water and then used as fillers. Assessment of the dispersion state of the CNLs in PVA revealed that they (≤5.0 wt%) were randomly and uniformly dispersed (down to the level of individual silicate layers) in and formed strong interfacial interactions with the PVA. This resulted in significantly enhanced physical properties of the resultant nanocomposites relative to neat PVA. In particular, a 104.7% increment in the yield stress was achieved with 5.0 wt% CNLs, much larger than the 15–70% increments of previous PVA nanocomposites using MMT or OMMT as fillers. Additionally, excellent optical clarity of the PVA was obtained for the nanocomposites.     

Electrochemical and structural properties of a polymer electrolyte system based on the effect of CeO<Subscript>2</Subscript> nanofiller with PVDF-co-HFP for energy storage devices

In the present work, a series of five different nanocomposite polymer electrolytes (NCPEs) have been reported with varying contents of ceria, CeO₂ nanofiller suitably incorporated within an optimized composition having 75:25 wt% ratio of poly(vinylidenefluoride-co-hexafluoropropylene) [(PVDF-co-HFP)] and zinc trifluoromethanesulfonate (ZnTf) in the form of films obtained by mean of solution casting technique with a general formula [75 wt% PVDF-co-HFP:25 wt% ZnTf]-x wt% CeO₂ where x = 1, 3, 5, 7, and 10, respectively. The chosen NCPE system is found to exhibit the maximum electrical conductivity of 3 × 10^?4 S cm^?1 for 5 wt% loading of CeO₂ nanofiller at ambient temperature. The observed conductivity enhancement has been attributed to the occurrence of an increase in the amorphous content as confirmed by X-ray diffraction (XRD) analysis. Detailed Fourier transform infrared (FTIR) spectral analysis has indicated the feasibility of complexation of the host polymer matrix with ZnTf salt and CeO₂ nanofiller. The incorporation of CeO₂ nanofiller has further increased the decomposition voltage of the polymer electrolyte from 2.4 to 2.7 V as revealed from the voltammetric studies performed on such NCPEs, thereby suggesting the suitability of these NCPE films with an enhanced electrical conductivity as new electrolytes in order to design and fabricate eco-friendly zinc rechargeable batteries and other electrochemical devices.     

Co-precipitation of asiatic acid and poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactide) using rapid expansion of subcritical solutions into liquid solvents

Poly(l-lactide) (PLLA) nanoparticles loaded with asiatic acid (AA) were successfully produced by rapid expansion of a subcritical solution into an aqueous receiving solution containing a dispersing agent. A mixture of carbon dioxide (CO₂) and ethanol (EtOH) with a weight ratio of 1:1 was used as the solvent for AA and PLLA. Two surfactants, Pluronic F127 and sodium dodecyl sulfate were employed. The former was found to be more effective for stabilizing AA-loaded PLLA nanoparticles, as a rapid expansion into a 0.1 wt% Pluronic F127 solution produced a stable nanosuspension consisting mainly of well-dispersed, individual nanoparticles. The effects of rapid expansion-processing conditions—AA to PLLA weight ratio and pre-expansion temperature (T_pre)—on the size and morphology of composite nanoparticles, and the loading capacity and entrapment efficiency of AA in PLLA nanoparticles, were systematically investigated. It was found that AA-loaded PLLA nanoparticles with a size range of 30–100 nm were consistently fabricated by rapid expansion at T_pre of 70–100 °C and AA to PLLA weight ratios of 1:2 and 1:4, and with a constant pre-expansion pressure of 330 bar. The T_pre and AA to PLLA weight ratio had no significant effects on the size of the nanoparticles. The AA to PLLA weight ratio is a controlling parameter for both the loading capacity and the entrapment efficiency of AA in PLLA nanoparticles. The loading capacity and entrapment efficiency increased from 8–11 to 16–21 wt%, and 38–57 to 50–62 wt%, respectively, when the AA to PLLA weight ratio changed from 1:4 to 1:2. However, increasing the T_pre from 70 to 100 °C decreased both the loading capacity and entrapment efficiency of AA in PLLA nanoparticles by ~20–30%.     

Thermal,Mechanical, and Rheological Characterization of Polylactic Acid/Halloysite Nanotube Nanocomposites

Halloysite nanotube (HNT) clay and biodegradable polylactic acid (PLA) nanocomposites were fabricated by a melt-blending method with five different clay levels (1, 3, 5, 7, and 9 wt%). The effect of HNT loading on the thermal and mechanical properties of the PLA/HNT nanocomposites was examined by thermogravimetric analysis and universal tensile testing, respectively. Morphological characteristics were investigated by transmission electron microscopy. The composites' melt rheological characteristic analyses were conducted using a rotational rheometer in both steady-shear and oscillatory dynamic testing modes. The data were found to be well-analyzed using the Carreau model, Cox–Merz rule, modified Cole–Cole plot, and van Gurp–Palmen plot.     

Synthesis of modified multi-walled carbon nanotube poly(benzimidazole-imide) composites: assessment of morphological and thermo-mechanical properties

A fully aromatic poly(benzimidazole-imide) (PBI) containing triazole side units and amine-modified multi-wall carbon nanotube (MWCNT)/PBI composites were fabricated via a polymerization process of monomer reactants and solution mixing with ultrasonication excitation. The polymer and composites were characterized by field emission scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction. According to the microscopic characterizations, the MWCNTs homogeneously dispersed in the composites. The mechanical properties of the composite films were also measured by tensile test. The test results evidently indicated that the Young’s modulus increased by about 60.0% at 1 wt% CNT loading, and further modulus growth was observed at higher filler loading. The composite films hold preferable thermal stability the same as the pure PBI. The improvement of the mechanical and thermal properties was attributed to the incorporation of the surface modified CNTs. For CNT-reinforced polymer composites, strong interfacial adhesion and uniform dispersion of CNTs are more crucial factors for improving such properties.     

The Effect of Structure of the Clay Modifier on the Morphology and Properties of Polystyrene/Clay Nanocomposites Prepared via In Situ Suspension Polymerization

Polystyrene (PS)/organoclay nanocomposites were prepared via free radical suspension polymerization. Two kinds of organoclay were used, labeled KT and KD, modified by trimethyloctadecyl ammonium (TM) and dimethyldioctadecyl ammonium (DM) ions, respectively. Nanocomposites containing various amounts of both of the organoclay nanoparticles (1, 3, and 5 wt%) were prepared. The wide angle X-ray diffraction (WAXD) results revealed intercalation in both of the nanocomposites. The greatest improvement in thermal stability of the nanocomposites was achieved with 5 wt% of organo-MMT for both of the clays. The nanocomposite containing 3 wt% of KT organo-MMT showed the greatest improvement of storage modulus. When the organoclay content exceeded 3 wt%, the storage moduli decreased compared to the nanocomposite filled with 3 wt% of the organoclay. D-spacing calculations using Bragg's law and WAXD data showed that the KT and KD nanoparticles were intercalated within the PS matrix, but with different extents of intercalation. The styrene conversions of the as-polymerized nanocomposite samples were obtained by a gravimetric method. The results showed that conversion decreased with incorporation of organoclay in the reaction recipe. Particle size was also increased by increasing nanoclay content.     

Effect of liquid crystal ionomer intercalated montmorillonite nanocomposites on PEO/PLA solid polymer electrolytes

A series of solid polymer electrolytes (SPEs) based on poly (ethylene oxide)/polylactic acid (PEO/PLA) with liquid crystal ionomer (LCI) intercalated montmorillonite (MMT) nanocomposites (LCI-MMT) has been prepared by solution blending method. The effects of LCI-MMT on the structural, crystallization, thermal, and ionic conductivity properties of solid polymer electrolytes have been analyzed. It is demonstrated that the incorporation of LCI-MMT into the blend suppressed the crystallinity of PEO and increased the crystallinity of PLA. The maximum ionic conductivity is found to be in the range of 1.05?×?10^?5 S/cm for 0.5 wt% LCI-MMT, which is higher than that of the LCI-MMT-free polymer electrolyte (5.36?×?10^?6 S/cm) at room temperature.     

Comparing the Effect of Sodium-Based and Calcium-Based Crosslinkers on the Swelling,Mechanical and Rheological Properties of Chitosan/Gelatin/Starch Films

Abstract

In this research chitosan/gelatin/starch films with a 47.5/47.5/5.0 (vol.%) composition were prepared by a solution casting method. To improve the mechanical and rheological properties of the chitosan-based films, two types of chemical crosslinkers, sodium triphosphate (STP) and calcium triphosphate (CTP), were used and the effects of these crosslinkers on the mechanical properties, swelling, water vapor transmission rate (WVTR) and the rheological-mechanical spectroscopy (RMS) of the films were investigated. For each crosslinker, two concentrations (0.05 and 0.1?wt% solutions) were used. The tensile test results showed that the samples with 0.05?wt% of STP or 0.1?wt% of CTP, had the best performance in enhancing the tensile strength and modulus of the films. The swelling tests indicated that 0.05?wt% of STP had the lowest swelling, and the performance with 0.1?wt% of CTP was also good. The results of the WVTR tests revealed that 0.05?wt% of STP and 0.1?wt% of CTP had the least and the most WVTR, respectively. Also, antibacterial tests were evaluated for the films based on an inhibition zone technique, and the results showed that the films containing the STP crosslinker has the best antibacterial activity. The RMS results indicated that the rheological properties of the films were enhanced by incorporating the crosslinkers, especially 0.1% concentration of CTP, into the film formulations.     

On-the-fly green generation and dispersion of AgI nanoparticles for cloud seeding nuclei

This study reports on an on-the-fly green synthesis/dispersion of silver iodide (AgI) nanoparticles from the combustion of AgIO₃/carbon black (CB)/nitrocellulose (NC) composites, which could be used as a candidate for a cloud-seeding pyrotechnic. Films were formed by direct electrospray deposition of a mixture of synthesized silver iodate with CB and NC. The decomposition pathways of AgIO₃/CB and AgIO₃/CB/NC were evaluated by temperature jump time of flight mass spectrometry (T-jump TOFMS) and XRD, showing that AgI particles and CO₂ are released from the reaction between AgIO₃ and CB without other toxic residuals. The flame propagation velocity of AgIO₃/CB/NC films increases with the increasing of particle mass loading of AgIO₃ and CB and peaks at 40 wt%, which is much higher than that of an AgI/AP/NC film. The mean diameter of the resultant AgI nanoparticles is from 51 to 97 nm. The mass loading of AgIO₃ and CB was found to play a major role in size control of the AgI nanoparticles.     

Ionic transport properties of PVdF-HFP-MMT intercalated nanocomposite electrolytes based on ionic liquid, 1-butyl-3-methylimidazolium bromide

Ionic conductivity and transport properties of polyvinylidenefluoride–co-hexafluoropropylene– montmorillonite intercalated nanocomposite electrolytes based on ionic liquid 1-butyl-3-methylimidazolium bromide have been studied for various concentrations of montmorillonite clay. Ionic conductivity of the order of 10^?3?S?cm^?1 at room temperature with thermal stability up to about 235 °C has been obtained for the electrolyte system. The electrolyte system has superior properties at 5 wt% of clay loading with highly amorphous morphology as seen from selected area electron diffraction micrograph. Scanning electron microscope studies show that the electrolyte system has highly porous morphology and the ionic liquid is trapped in the pores. Dielectric properties of the electrolyte system have been studied to investigate the relaxation processes occurring in the system. Variation of real part of dielectric permittivity with frequency shows two relaxation processes occurring in the system, slow at low frequency and fast at high frequency. Kohlrausch exponential parameter has been calculated from modulus formalism, and the values show that the distribution of conductivity relaxation times becomes narrower with increasing clay loading.     

Polyelectrolyte Nanocomposite Membranes,Based on Chitosan-phosphotungstic Acid Complex and Montmorillonite for Fuel Cells Applications

A polyelectrolyte complex (PEC) of chitosan and phosphotungstic acid (PWA) was prepared and characterized as a proton-conducting membrane for direct methanol fuel cell (DMFC) applications. Fourier transform infrared spectroscopy showed the presence of stable PWA in PEC. To reduce the methanol permeability, several amounts of montmorilonite (MMT) nanoclays (trade name: Cloisite Na) were introduced to the system. The X-ray diffraction patterns of nanocomposite membranes proved the nanoclay layers were exfoliated in the membranes at loading weights of MMT lower than 3 wt%. Proton conductivity and methanol permeability were measured. According to the selectivity parameter—ratio of proton conductivity to methanol permeability—PEC containing 2 wt% MMT (PEC/2 wt% MMT) was identified as the optimum composition. Finally, DMFC performance tests were investigated at 70°C and 5 M methanol feed and the optimum membrane showed higher maximum power density in comparison with Nafion 117. The results indicated the optimum nanocomposite membrane is a promising polyelectrolyte membrane (PEM) for DMFC applications.     

Morphology and Mechanical Properties of Acrylonitrile-Butadiene-Styrene (ABS)/Polyamide 6 (PA6) Nanocomposites Prepared via Melt Mixing

Acrylonitrile-butadiene-styrene (ABS)/polyamide 6 (PA6) blends containing various amounts of organomontmorillonite (OMMT) were prepared using a twin-screw extruder followed by injection molding. The effect of OMMT on the microstructure and properties of the ternary nanocomposites is investigated by wide-angle X-ray diffraction (WAXD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and mechanical properties testing. The results showed the OMMT platelets were preferentially located and exfoliated in the PA6 phase, but some were located at the interface of the ABS and PA6 phase. The effect of the addition of the OMMT on the morphology and mechanical properties was also evaluated. SEM revealed that the dimensions of the dispersed PA6 droplets were greatly reduced when the concentration of the OMMT was less than 4 phr. The domain size was less than the neat ABS/PA6 blends with the increasing of the OMMT content. It was suggested that the OMMT can compatibilize the ABS/PA6 blend. In addition, the flexural strength and modulus increased with increasing OMMT content, but the tensile strength became maximal at 3 phr OMMT. The OMMT had a negligible effect on the impact strength of the ABS/PA6 blend nanocomposite.     

Dielectric,thermal, and electrochemical properties of PVC/PEMA blended polymer electrolytes complexed with zinc triflate salt

A new solid polymer electrolyte system based on poly (vinyl chloride) (PVC) and poly (ethyl methacrylate) (PEMA) containing zinc triflate [Zn(CF₃SO₃)₂] salt obtained in the form of thin film specimens using solution casting technique has been examined by means of complex impedance analysis, thermogravimetry (TG) and differential scanning calorimetric (DSC) studies, linear sweep voltammetry (LSV) and cyclic voltammetric (CV) measurements. The relevant mechanism of zinc ion transport involved in the case of the present polymer blend electrolyte viz., [PVC (30 wt%)/PEMA (70 wt%)] : x wt% [Zn(CF₃SO₃)₂] (where x = 10, 15, 20, 25, 30, and 35, respectively) has been evaluated in terms of AC impedance method, dielectric and electrical modulus formalisms. The optimized composition of the chosen blended polymer electrolyte system having 30 wt% loading of zinc triflate salt exhibited a single glass transition temperature (T _g) and possessed appreciable levels of thermal and electrochemical stability for possible utilization in zinc batteries.