Fabrication and Physical Characterization of Biodegradable Poly(butylene succinate)/Carbon Nanofiber Nanocomposite Foams

Nanocomposites of biodegradable poly(butylene succinate) (PBS) and carbon nanofibers (CNFs) were prepared by three different methods, that is, solution blending, melt compounding, and solution and subsequent melt blending (SOAM) method, among which the SOAM method, where nano-scale fillers and polymer matrix are solution-blended and subsequently melt-mixed in a torque rheometer, is a two-step process for obtaining polymer nanocomposite. Dispersion of CNFs in the PBS matrix was characterized by FE-SEM, while thermal and mechanical properties were analyzed by thermogravimetric ananlysis (TGA) and universal test machine (UTM), respectively. The PBS/CNF nanocomposites were then converted to foams by employing a chemical blowing agent (CBA) in the melt. The presence of CNFs increased the melt viscosity of PBS so that the PBS/CNF nanocomposite foams were produced without modifying the chemical structure of the PBS. Nanocomposite foams prepared by the SOAM method showed higher physical properties compared with those prepared by the solution blending and the melt mixing. Cell size and blowing ratio increased with the increase in the CBA content, blowing temperature and time. Cell morphology of the nanocomposite foams was examined by optical microscopy, and the cell size distribution was also investigated.     

Morphology and Pore Size Distribution of Biocompatible Interconnected Porous Poly(L-lactic acid) Foams with Nanofibrous Structure Prepared by Thermally Induced Liquid–Liquid Phase Separation

Biocompatible, highly interconnected microporous poly(L-lactic acid) (PLLA) foams with nanofibrous structure, containing pores with average diameter below 1 μm and fibers with diameters of 10² nm scale, were prepared through the thermally induced liquid–liquid phase separation (TIPS) method consisting of quenching of the PLLA solution, freeze extraction with ethanol, and vacuum drying. Diverse foam morphologies were obtained by systematically changing parameters involved in the TIPS process, such as polymer concentration, solvent composition, and quenching temperatures. The morphology of different foams was examined by scanning electron microscopy to characterize the pore size and the pore size distribution. The results showed that most porous foams had a nanofibrous structure with interconnected open pores. In the case of using tetrahydrofuran (THF) as solvent, the higher the PLLA concentration, the smaller the average pore diameter and the narrower the pore size distribution. In the case of using the mixed solvents of THF/DOX (1,4-dioxane) with higher than 6/4 volume ratio, there appeared a maximum value of average pore diameter and a widest pore size distribution at 0.09 g/mL PLLA concentration. The average pore diameter of the foams increased with increasing DOX content in the mixed solvent and ranged from 0.2 to 0.9 μm depending on the process parameters. When the DOX content reached 60% by volume, the morphology of the foams contained some large closed pores with diameter ranging from 1 to 10 μm. By decreasing the quenching temperature, the average pore diameter of foams decreased and the pore size distribution became narrower. All the pore size distribution fit F-distribution equations.     

Epoxy/Silica Nanohybrids or Nanocomposites: Atomic Force Microscopy and X-ray Photoelectron Spectroscopy Investigation of the Processing–Structure–Property Relationships

The structural and morphological features influencing the glass transition temperature of epoxy/silica nanohybrid and nanocomposite materials containing 25–30 phr of nanoscale silica phases are discussed in this letter to answer the questions related to the processing–structure–property relationships. X-ray photoelectron spectroscopy and atomic force microscopy are used to study the surface chemical structure and morphology of epoxy/silica nanohybrids and nanocomposites. Nanohybrids are synthesized via in situ sol-gel process, while the respective nanocomposites are prepared by mechanical blending of preformed silica nanoparticles into epoxy resin. Differential scanning calorimetry is used to determine glass transition temperature of different materials. The surface analytical characterizations reveal that in situ sol-gel process is more suitable for producing organic–inorganic hybrid materials with superior glass transition temperature owing to the achievement of stronger interfacial compatibility and greater crosslink density. A number of other factors affecting glass transition temperature are explored and discussed with reference to surface chemistry, microstructure, and morphology of epoxy/silica nanohybrids and nanocomposites, respectively.     

Comparison of Eu(NO<Subscript>3</Subscript>)<Subscript>3</Subscript> and Eu(acac)<Subscript>3</Subscript> precursors for doping luminescent silica nanoparticles

In this study, we report the comparison between Eu³⁺-doped silica nanoparticles synthesized by Stöber method using Eu(NO₃)₃ or Eu(acac)₃ as precursors. The impact of different europium species on the properties of the final silica nanospheres is investigated in details in terms of size, morphology, reachable doping amount, and luminescence efficiency. Moreover, the results obtained for different thermal treatments are presented and discussed. It is shown that the organic complex modify the silica growing process, leading to bigger and irregular nanoparticles (500–800 nm) with respect to the perfectly spherical ones (400 nm) obtained by the nitrate salt, but their luminescence intensity and lifetime is significantly higher when 800–900 °C annealing is performed.     

Ionic transport studies in hyperbranched polyurethane/clay nanocomposite gel polymer electrolytes

In the present work, we report a novel nanocomposite gel electrolytes based on intercalation of hyperbranched polyurethane (HBPU) into organically modified montmorillonite for application in Li-ion batteries. The nanocomposites have been prepared by solution intercalation technique with varying clay loading. The formation of partially exfoliated nanocomposites has been confirmed by X-ray diffraction. Nanocomposites were soaked with 1 M LiCO₄ in 1:1 (v/v) solution of propylene carbonate and diethyl carbonate to get the required gel electrolytes. AC impedance analysis shows that ionic conductivity increases with the increase of clay loading and attains the highest value of 8.3?×?10^?3 S/cm for 5 wt.% clay concentration. Surface morphology of the nanocomposite electrolytes has been examined by SEM analysis. Improvement of electrochemical properties, viz., electrochemical potential window and interfacial stability, is also observed in the clay-loaded HBPU samples.     

Laser irradiation effects on the surface,structural and mechanical properties of Al–Cu alloy 2024

Laser irradiation effects on surface, structural and mechanical properties of Al–Cu–Mg alloy (Al–Cu alloy 2024) have been investigated. The specimens were irradiated for various fluences ranging from 3.8 to 5.5 J/cm² using an Excimer (KrF) laser (248 nm, 18 ns, 30 Hz) under vacuum environment. The surface and structural modifications of the irradiated targets have been investigated by scanning electron microscope (SEM) and X-ray diffractometer (XRD), respectively. SEM analysis reveals the formation of micro-sized craters along the growth of periodic surface structures (ripples) at their peripheries. The size of the craters initially increases and then decreases by increasing the laser fluence. XRD analysis shows an anomalous trend in the peak intensity and crystallite size of the specimen irradiated for various fluences. A universal tensile testing machine and Vickers microhardness tester were employed in order to investigate the mechanical properties of the irradiated targets. The changes in yield strength, ultimate tensile strength and microhardness were found to be anomalous with increasing laser fluences. The changes in the surface and structural properties of Al–Cu alloy 2024 after laser irradiation have been associated with the changes in mechanical properties.     

Study of Electrical Conductivity of Para-Toluene Sulfonic Acid Doped Polyaniline/Polyester-Based Polyurethane Blends in the S-Band Frequency Range

Conducting polymer blends were prepared using polyaniline doped with para- toluene sulfonic acid (PTSA-PANI) and a polyester polyol-based polyurethane (PU). The morphological, thermal and dielectric properties of the PTSA-PANI/PU blends in the frequency range of 1–5 GHz (S band) were investigated. It was found that the morphology of the samples was affected by the PTSA-PANI loading, resulting in the formation of agglomerates and pathways when above 10 wt%. The thermal stability of the composites was improved with increased PTSA-PANI loading. The electrical conductivity percolation threshold was obtained at 2.5% of PTSA-PANI loading and the electrical conductivity reached the value of 0.13 S/m at a PTSA-PANI loading of 30 wt%. The obtained results for the PTSA-PANI/PU blends prepared indicate a high potential for their successful use in electrical and electromagnetic applications.     

Preparation and Compatibility of EVM/TPU Blend

The preparation of EVM (ethylene‐vinyl acetate copolymer rubber)/TPU (thermoplastic polyurethane) blends with various ratios and their compatibility were investigated. The influence of mixing technology, filler type and content, the VA content in EVM (40 and 70 wt.%) and the addition of compatibilizers on the mechanical properties and the compatibility of the EVM/TPU blends were systematically studied.

The test results showed that in preparation of the blend, fillers should be added to the blend to improve the processability and that among the fillers used, silica showed the best reinforcing effect on the blends. The best parameters for blending EVM and TPU in a HAAKE rheometer was: mixing temperature 160°C, rotor speed 45 rpm and mixing time 15 min. The test results also showed that the compatibility of EVM 700 (VA=70%) with TPU was better than that of EVM400 (VA=40%). The addition of a compatibilizer EVM‐g‐MAH and EVM‐g‐FME improved the processability of the blends. The addition of EVM‐g‐MAH also improved the compatibility of EVM 700/TPU blend; both the mechanical properties and hot‐air aging properties of the blends were improved. However, the addition of EVM‐g‐FME did not improve the compatibility of EVM/TPU blends.     

Lightweight and thermally insulating aerogel glass materials

Glass represents an important and widely used building material, and crucial aspects to be addressed include thermal conductivity, visible light transmittance, and weight for windows with improved energy efficiency. In this work, by sintering monolithic silica aerogel precursors at elevated temperatures, aerogel glass materials were successfully prepared, which were characterized by low thermal conductivity [k ≈ 0.17–0.18 W/(mK)], high visible transparency (T _vis ≈ 91–96 % at 500 nm), low density (ρ ≈ 1.60–1.79 g/cm³), and enhanced mechanical strength (typical elastic modulus E _r ≈ 2.0–6.4 GPa). These improved properties were derived from a series of successive gelation and aging steps during the desiccation of silica aerogels. The involved sol → gel → glass transformation was investigated by means of thermo-gravimetric analysis, scanning electron microscopy, nanoindentation, and Fourier transform infrared spectroscopy. Strategies of improving further the mechanical strength of the obtained aerogel glass materials are also discussed.     

Preparation and Thermal Properties of Boron-Containing o-Cresol-Formaldehyde Resin/Octa(aminophenyl)-POSS Nanocomposites

The boron-containing o-cresol-formaldehyde resin (BoCFR) and octa(aminophenyl) polyhedral oligomeric silsesquioxane (OAP-POSS) were synthesized, and the BoCFR/OAP-POSS nanocomposite prepared via an in-situ method. The curing process of the resin was characterized by Fourier transform infrared (FTIR). The thermal properties and dynamic mechanical properties of the nanocomposites were investigated. The results show that the maximal mechanical loss temperature (T_p) increased with increasing OAP-POSS content. When the content of OAP-POSS was 10 wt% the T_p was over 200°C, 27°C higher than the pure BoCFR. The BoCFR/OAP-POSS nanocomposite had better thermal stablitity than the pure BoCFR. The residual weight of the o-cresol-formaldehyde resin was only 6.13 wt% at 600°C. But the residual weight of the pure BoCFR was 55.73 wt% at 600°C, and the residual weights of the BoCFR nanocomposites were all higher than pure BoCFR. The residual weight of the BoCFR nanocomposite was 63.2 wt% at 600°C and 21.83 wt% at 900°C when the OAP-POSS content was 10 wt%. The weight loss of BoCFR/OAP-POSS nanocomposite can be divided primarily into two temperature stages, from 430°C to 550°C and from 550°C to 900°C. The main thermal degradation reaction follows first order kinetics.     

Hybrid nanostructured materials with tunable magnetic characteristics

Novel titanium oxide (TiO₂) nanoparticles were fabricated via a modified propanol drying step. These nanoparticles were loaded with anti-cancer drug paclitaxel (PTX) to yield PTX-TiO₂ nanocomposites. The nanocomposites were characterized for their size and surface morphology employing nanoparticle tracking analysis (NTA) and scanning electron microscopy (SEM). The SEM images showed spherical particles with smooth surface and narrow size distribution of ~30–40 nm, which was also supported by NTA analysis data. The drug loading efficiency of the air-dried nanoparticles was observed to be ~63.61 % while those prepared through propanol-induced drying step showed ~69.70 %, thereby demonstrating higher efficiency of the latter. In vitro pH-dependent release of the loaded PTX was observed with higher release at acidic pH compared with physiological pH. Cell uptake studies suggested of time-dependent internalization of nanocomposites with significant improvement in uptake by increasing incubation time from 2 to 24 h, as evidenced by flow cytometry. Further, the cell viability as a measure of anti-cancer activity revealed that cell viability upon exposure to PTX only was 40.5 % while that of PTX-TiO₂ nanocomposite showed 21.6 % viability after 24 h, suggesting better anti-cancer efficacy of nanocomposites. Apoptosis studies revealed that cells treated with PTX-TiO₂ nanocomposites possessed more amount of apoptotic bodies as compared to those treated with PTX only.     

Properties and Preparation of Chitosan/Silanol Quaternary Ammonium Modified Silica Hybrids Using Sol–Gel Process

Chitosan/modified silica nanocomposites, with a sol–gel process being used to prepare a silanol quaternary ammonium modified silica possessing antimicrobial activity, were investigated, as well as the thermal properties, morphology, optical, mechanical, antimicrobial, and adsorption properties of this type of nanocomposite. Grafting of the modifier onto nanosilica was confirmed through the Fourier transform infrared (FTIR) spectra. X-ray diffraction patterns indicated that the chitosan structure was not disrupted from the incorporation of the modified silica. Fracture surfaces with no clear micro-phase separation were observed by scanning electron microscopy (SEM), which indicated the good interaction of chitosan and the modified silica. The organic modifier tended to cause the aggregation of the modified silica at higher content on a submicron scale based on transmission electron microscopy (TEM) analysis, which might be due to a decrease of the stability factor originating from the negative charges on silica. With the introduction of modified silica, the optical transmittance decreased at higher organic modifier content in agreement with TEM analysis. The elongation at break remained largely unchanged, but tensile strength and Young's moduli deteriorated in modified silica filled systems in comparison with pure silica filled systems. The introduction of the organic modified silica gave a higher antibacterial activity. All nanocomposites were capable of chelating Cu (II) as well as Fe (III) at a different degree. Thus, the prepared chitosan/modified silica nanocomposites exhibited both antimicrobial and chelating properties.     

Hyperbranched Polyimide-Silica Hybrid Materials: Synthesis,Structure, Dynamics,and Gas Transport Properties

A series of organic–inorganic hybrid materials were prepared from a hyperbranched polyimide precursor (hyperbranched polyamic acid), tetramethoxysilane, and/or 3-glycidyloxypropyl-trimethoxysilane via a sol-gel process. The hyperbranched polyimide-silica hybrids, whose polyimide moieties were based on commercially available monomers 4,4′,4^″-triaminotriphenylmethane and 4,4′-oxydiphthalic anhydride taken in molar ratio 1:1, contained from 10 to 30 wt% silica. Their morphology and dynamics were characterized by using scanning electron microscopy, differential scanning calorimetry, dynamic mechanical analysis, laser-interferometric creep rate spectroscopy, and wide-angle X-ray diffraction. Attention was also focused on the relation between morphology/dynamics and gas transport properties of these materials.     

Aromatic Polyimide/MWCNT Hybrid Nanocomposites: Structure,Dynamics, and Properties

Two series of hybrid polyimide (PI)/multiwalled carbon nanotube (MWCNT) nanocomposites were prepared including COOH-functionalized or pristine nanotubes, and their structure, morphology and dynamics/mechanical properties at 20°C–500°C were studied using WAXD (Wide-angle X-ray diffraction), AFM (Atomic force microscopy), TEM (transmission electron microscopy), DSC (Differential scanning calorimetry), DMA (Dynamic mechanical analysis), CRS (creep rate spectroscopy) techniques, and stress–strain testing. The impact of nanofiller loadings of 0.125, 0.25, 0.5, or 1 wt% relative to PI was evaluated. Specific changes in the matrix morphology and different quality of nanotube dispersion in the nanocomposites with amorphous and semicrystalline matrices were determined. The best nanotube dispersion was observed in the composites with 0.5 wt% MWCNT-COOH. A peculiar high temperature dynamics, different for amorphous, and semicrystalline matrices, was revealed in these nanocomposites. The most dramatic changes in high temperature dynamics and a pronounced dynamic heterogeneity as well as substantially enhanced mechanical properties at room temperature were revealed in the case of a semicrystalline PI matrix. The results were treated in terms of the synergistic impact of nanotubes and matrix crystallites on dynamics in the intercrystalline regions of PI (“combined constrained dynamics effect”) and the peculiar interfacial dynamics.     

Styrene Butadiene Rubber/Epoxidized Natural Rubber (SBR/ENR50) Nanocomposites Containing Nanoclay and Carbon Black as Fillers for Application in Tire-Tread Compounds

Nanocomposite vulcunizates based on a SBR/ENR50 (50/50%wt) rubber blend containing nanoclay (5 or 10 phr) with and without carbon black (CB 20 phr) were prepared by melt blending in an internal mixer. The compound containing 35 phr carbon black (only) was prepared as a reference sample. Microstructure of nanocomposite samples was investigated by using X-ray diffraction (XRD), melt rheo-mechanical spectroscopy (RMS), and scanning electron microscopy (SEM). The XRD patterns revealed that the distance between the clay layers were increased by adding CB to the nanocomposite samples; they caused better diffusion of chains between the layers and resulted in an intercalated structure. The RMS results also indicated the formation of the filler-filler networks. SEM images of fracture surfaces showed the presence of much roughness in the samples containing both nanoclay and CB compared to the other samples. The results obtained from application of the Flory–Rhener equation showed a high crosslink density for the sample with 10 phr nanoclay and 20 phr CB. Dynamic mechanical behavior, mechanical properties, and abrasion resistance of the nanocomposites were evaluated. The results indicated that the sample containing 10 phr nanoclay and 20 phr CB had an increased dynamic elastic modulus, reduced maximum loss factor (tanδ)_max,, and an improved tensile strength and abrasion resistance compared to the reference sample. Also, this sample showed the lowest maximum loss factor, at 50–60°C, so it can be a candidate for tire-tread application.     

Preparation and Properties of Poly(ethylene terephthalate)/Silica Nanocomposites

A kind of poly(ethylene terephthalate) (PET)/Silica nanocomposite (PETS) was synthesized via in situ polymerization using the compatibility between silica nanoparticles and ethylene glycol (EG). Transmission electron microscopy (TEM) micrographs revealed that the silica nanoparticles were well dispersed in the PET matrix, the particle size was about 10 nm with narrow distribution, and there existed strong interaction between the particles and the polymer chains. Differential scanning calorimetry (DSC) results indicated that the thermal properties of PETS with 2 wt% silica (PETS‐2) are different from those of pure PET (PETS‐0). The properties of the as‐spun fibers show that the tenacity and LASE‐5 (load at a specified elongation of 5%) of PETS‐2 were higher than those of PETS‐0, while the heat shrinkage of PETS‐2 was lower than that of PETS‐0. We suggest that the increasing of crystallinity and the strong interface interaction of the nanocomposite caused the fibers of PETS‐2 to not only have higher tenacity and LASE‐5 but also to have lower heat shrinkage.     

Foaming and Damping Properties of Ethylene Vinyl-Acetate Copolymer/Polylactic Acid Blends

With ethylene vinyl-acetate copolymer (EVM) and polylactic acid (PLA) blends as the matrix, dicumyl peroxide (DCP) as the curing agent and azodicarbonamide (AC) as the foaming agent, EVM/PLA foamed blends were prepared by compression molding. The effects of different amounts of AC, DCP, and silica, as well as varying foaming time, on the cell structure and damping properties of the EVM/PLA-foamed blends were examined by scanning election microscopy (SEM) and dynamic mechanical analysis (DMA). The results showed that the cell size and damping properties varied little with increasing AC content in the compounds; however, the cell size declined slightly as DCP increased and the damping properties rose slightly, exhibiting an optimum set of properties at 5 phr of DCP. The cell size declined dramatically and damping increased significantly as the foaming time was increased. Moreover, both suddenly increased after 5 min foaming. It was found that the damping properties of the foamed materials increased with decreasing cell size and increasing number of cells. The cell size also decreased and damping properties increased as the silica content was increased. The silica interacted more strongly with EVM than with PLA.     

Banana fiber strands–reinforced polymer matrix composites

Banana fiber (BF)-reinforced low-density polyethylene (LDPE) unidirectional composites were fabricated by the compression molding process with 40 wt% fiber loading. The fibers were modified with methylacrylate (MA) mixed with methanol (MeOH) along with 2% benzyl peroxide under thermal curing method at different temperatures (50–90 °C) for different curing times (10–50 min) in order to have better compatibility with the matrix. The effect of fiber surface modification on the mechanical properties (tensile and impact properties) of the composites were evaluated. Monomer concentration, curing temperature, and curing time were optimized in terms of polymer loading and mechanical properties. The mechanical properties were found to be improved based on the improved interaction between the reinforcement and the matrix. Optimized BFs were again treated with 2–5 wt% starch solutions and composites made of 4% starch treated BF showed the highest mechanical properties than that of MA treated composites. Scanning electron microscopy (SEM) was performed to get an insight into the morphology of the composites. Water uptake and soil degradation test of the composites were also investigated.     

The physical,mechanical, thermal and barrier properties of starch nanoparticle (SNP)/polyurethane (PU) nanocomposite films synthesised by an ultrasound-assisted process

This article reports on the ultrasound-assisted acid hydrolysis for the synthesis and evaluation of starch nanoparticles (SNP) as nanofillers to improve the physical, mechanical, thermal, and barrier properties of polyurethane (PU) films. During the ultrasonic irradiation, dropwise addition of 0.25 mol L^-1 H₂SO₄ was carried out to the starch dispersion for the preparation of SNPs. The synthesized SNPs were blended uniformly within the PU matrix using ultrasonic irradiation (20 kHz, 220 W pulse mode). The temperature was kept constant during the synthesis (4 °C). The nanocomposite coating films were made with a regulated thickness using the casting method. The effect of SNP content (wt%) in nanocomposite coating films on various properties such as morphology, water vapour permeability (WVP), glass transition temperature (Tg), microbial barrier, and mechanical properties was studied. The addition of SNP to the PU matrix increased the roughness of the surface, and Tg by 7 °C, lowering WVP by 60% compared to the PU film without the addition of SNP. As the SNP concentration was increased, the opacity of the film increased. The reinforcement of the SNP in the PU matrix enhanced the microbial barrier of the film by 99.9%, with the optimal content of SNP being 5%. Improvement in the toughness and barrier properties was observed with an increase in the SNP content of the film.     

Preparation and Characterization of Poly(Vinyl Alcohol) (PVA)/SiO2, PVA/Sulfosuccinic Acid (SSA) and PVA/SiO2/SSA Membranes: A Comparative Study

Abstract

New organic–inorganic nanocomposites based on PVA, SiO₂ and SSA were prepared in a single step using a solution casting method, with the aim to improve the thermomechanical properties and ionic conductivity of PVA membranes. The structure, morphology, and properties of these membranes were characterized by Raman spectroscopy, small- and wide-angle X-ray scattering (SAXS/WAXS), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), water uptake (Wu) measurements and ionic conductivity measurements. The SAXS/WAXS analysis showed that the silica deposited in the form of small nanoparticles (～ 10?nm) in the PVA composites and it also revealed an appreciable crystallinity of pristine PVA membrane and PVA/SiO₂ membranes (decreasing with increasing silica loading), and an amorphous structure of PVA/SSA and PVA/SSA/SiO₂ membranes with high SSA loadings. The thermal and mechanical stability of the nanocomposite membranes increased with the increasing silica loading, and silica also decreased the water uptake of membranes. As expected, the ionic conductivity increased with increasing content of the SSA crosslinker, which is a donor of the hydrophilic sulfonic groups. Some of the PVA/SSA/SiO₂ membranes had a good balance between stability in aqueous environment (water uptake), thermomechanical stability and ionic conductivity and could be potential candidates for proton exchange membranes (PEM) in fuel cells.