Preparation and characterization of PLLA–ESO/surface-grafted silica nanocomposites

Various amounts of surface-grafted silica (g-SiO₂) and un-grafted (SiO₂) nanoparticles were solution blended with a copolymer of l-lactide and epoxidized soybean oil (PLLA–ESO) or PLLA. Chemical reaction between the low molecular weight (LMW) PLLA and surface of silica nanoparticles is confirmed by FTIR and TGA analyses. The amount of grafted LMW PLLA investigated by thermal gravimetric analysis (TGA) was about 14.9%–28.2% in weight. g-SiO₂ nanoparticles can be easily dispersed into PLLA–ESO matrix to form a uniform PLLA–ESO/g-SiO₂ composite. Thermal properties of PLLA–ESO/g-SiO₂ and PLLA/g-SiO₂ nanocomposites were subsequently investigated by the differential scanning calorimeter measurements (DSC). DSC analyses indicated that g-SiO₂ nanoparticles can serve as a nucleating agent for the crystallization of PLLA–ESO in the composites, while the melting temperature (T _m) and the glass transition temperature (T _g) of PLLA–ESO/g-SiO₂ nanocomposites seemed to be independent of loading of g-SiO₂ particles. The DSC curves of PLLA/g-SiO₂ nanocomposite obviously showed double melting peaks, while that of PLLA–ESO/g-SiO₂ nanocomposites only a single melting peak. PLLA–ESO/g-SiO₂ composites exhibited a higher tensile strength and elongation than that of PLLA–ESO/SiO₂ composites.     

Preparation and characterization of aluminum oxide–poly(ethylene-co-butyl acrylate) nanocomposites

This article describes the preparation and characterization of composites containing poly(ethylene-co-butyl acrylate) (EBA–13 and EBA–28 with 13 and 28 wt % butyl acrylate, respectively) and 2–12 wt % (0.5–3 vol %) of aluminum oxide nanoparticles (two types differing in specific surface area and hydroxyl-group concentration; uncoated and coated with, respectively, octyltriethoxysilane and aminopropyltriethoxysilane). A greater surface coverage was obtained with aminopropyltriethoxysilane than with octyltriethoxysilane. An overall good dispersion was obtained in the EBA-13 composites prepared by extrusion compounding. Composites with octyltriethoxysilane-coated nanoparticles showed the best dispersion. The addition of the nanoparticles to EBA–28 resulted in poor dispersion, probably due to insufficiently high shear forces acting during extrusion mixing which were unable to break down nanoparticle agglomerates. The nanoparticles had no effect on the crystallization kinetics in the EBA–13 composites, but in the EBA–28 composites the presence of the nanoparticles led to an increase in the crystallization peak temperature, suggesting that the nanoparticles had a nucleating effect in this particular polymer. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and characterization of pH-sensitive hydrogel microparticles as a biological on–off switch

The pH-responsive swelling and release behaviors of anionic P(MAA-co-EGMA) hydrogel microparticles having various MAA and EG contents were investigated as a biological on–off switch for the design of an intelligent drug delivery system triggered by external pH changes. When DC was used as a dispersion stabilizer, well-dispersed hydrogel microparticles having an average diameter of approximately 4 μm were obtained. There was a drastic change of the equilibrium weight swelling ratio of P(MAA-co-EGMA) hydrogels at a pH of around 5, which is the pK _a of PMAA. When the MAA content in the hydrogel increased, the swelling ratio increased at a pH above 5 due to the more electrostatic repulsion between the charged groups of MAA. The P(MAA-co-EGMA) hydrogel microparticles showed a pH-responsive release behavior. At low pH (pH 4.0) small amounts of Rh-B were released while at high pH (pH 6.0) relatively large amounts of Rh-B were released from the hydrogels. The difference in the released amount of Rh-B from the hydrogels between pH 4.0 and 6.0 decreased when the MAA content in the hydrogels decreased, which means that the pH-responsive release behavior of the P(MAA-co-EGMA) hydrogel microparticles is closely related to the pH-responsive swelling property of the hydrogel.     

Preparation and characterization of CeOx@MnOx core–shell structure catalyst for catalytic oxidation of NO

The CeOx@MnOx catalyst with a core–shell structure was prepared and used for catalytic oxidation of NO. It was found that CeOx@MnOx catalyst showed higher intrinsic catalytic activity than CeMnOx catalyst prepared by citric acid method. Based on the characterization results of N₂ adsorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), temperature-programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS), we may conclude that the excellent catalytic performance of CeOx@MnOx catalyst is related to its low crystallinity, good reducibility, and high concentrations of Mn^4 + and active oxygen species.     

Preparation and characterization of novel polyethylene/carbon nanotubes nanocomposites with core–shell structure

Preparation of novel polyethylene/carbon nanotubes (CNTs) nanocomposites with core–shell structure was presented. The method involved in situ ethylene polymerization in which nanotube surface was treated with Grignard Agent, followed by reacting with active transition metal compound, TiCl₄. The multiwalled carbon nanotubes (MWCNTs) supported catalysts polymerize ethylene to form polymer nanocomposite. MWCNTs were homogeneously dispersed within polymer matrix, and as expected, the resultant nanocomposites featured core–shell structure which was confirmed by HRTEM. For the nanocomposite, the microscopic examination of the cryogenically fractured surface not only ensured a good distribution of carbon nano-particles in the PE matrix but also revealed the ductile-like fracture. The Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were employed for the study of covalent sidewall functionalization and chemical bonding environment of MWCNTs, also indicated effective immobilization of titanium catalyst on the MWCNTs surface. The crystalline properties, dielectric property and thermal stability of the nanocomposites were determined by WAXD, impedance analyzer and TGA. The dielectric result showed a slight decline of the dielectric constant of the nanocomposites with increase of the polymerization time, and lower dielectric loss was also observed.     

Preparation and characterization of chitosan–zeolite composites

Double crosslinked chitosan–zeolite (CZ-2) and noncrosslinked chitosan–zeolite (CZ-0) composites were prepared and characterized by using Fourier transform infrared (FTIR) spectrometer, surface area analyzer, scanning electron microscope coupled with energy dispersive X-ray (SEM-EDX) spectrometer, thermogravimetric analyzer (TGA), X-ray diffraction analyzer (XRD) and carbon, hydrogen, nitrogen (CHN) analyzer. After crosslinking, CZ-2 showed a reduction in surface area and CHN content in comparison to chitosan, zeolite, and CZ-0. Crosslinking resulted in improved stability of CZ-2 in distilled water, acetic acid and NaOH as CZ-2 recorded the lowest percentage of swelling. XRD diffractograms confirmed the formation of composites as there was a marked difference in the peak intensity at 2θ = 19.8°. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and characterization of precursor derived TiN@Si–Al–C–N ceramic nanocomposites for oxygen reduction reaction

The development of efficient and durable catalysts is critical for the commercialization of fuel cells, as the catalysts’ durability and reactivity dictate their ultimate lifetime and activity. In this work, amorphous silicon-based ceramics (Si–C–N and Si–Al–C–N) and TiN@Si–Al–C–N nanocomposites were developed using a precursor derived ceramics approach. In TiN@Si–Al–C–N nanocomposites, TiN nanocrystals (with sizes in the range of 5–12 nm) were effectively anchored on an amorphous Si–Al–C–N support. The nanocomposites were found to be mesoporous in nature and exhibited a surface area as high as 132 m²/g. The average pore size of the nanocomposites was found to increase with an increase in the pyrolysis temperature, and a subsequent graphitization of free carbon was observed as revealed from the Raman spectra. The ceramics were investigated for electrocatalytic activity toward the oxygen reduction reaction using the rotating disk electrode method. The TiN@Si–Al–C–N nanocomposites showed an onset potential of 0.7 V versus reversible hydrogen electrode for oxygen reduction, which seems to indicate a 4-electron pathway at the pyrolysis temperature of 1000°C in contrast to a 2-electron pathway exhibited by the nanocomposites pyrolyzed at 750°C via the Koutecky–Levich plot.     

Synthesis and characterization of potassium humate–acrylic acid–acrylamide hydrogel

A novel potassium humate–acrylic acid–acrylamide (KHA–AA–AM) superabsorbent polymer was prepared from the reaction among leonardite potassium humate, acrylic acid and acrylamide by free radical initiating process using ammonium persulfate as the initiator and N, N′-methylene bisacrylamide as the crosslinker. Various effects of synthesis conditions on superabsorbent polymer were studied and the optimal reaction condition was obtained with crosslinker concentration 0.44–0.74 wt%, initiator concentration 1.12–2.22 wt%, n(KOH)/n(AA) 0.51–0.70, monomer concentration 10.95–12.59 wt%, graft reaction temperature 83 ± 1°C, monomer mole ratio of acrylic acid to acrylamide 1.42–2.30, and potassium humate content 17.54 wt%. Under the optimal conditions, the solution absorbency of KHA–AA–AM superabsorbent polymer to deionized water, tap water, 0.5% carbamide solution and 0.9% NaCl solution were 733–756, 161–284, 786–825, and 76–83 g/g, respectively.     

Preparation and properties of core–shell silver/polyimide nanocomposites

A new series of core–shell structured silver/polyimide (PI) nanocomposites was prepared by in situ polymerization followed by the chemical imidization of poly(amic acid) (PAA, precursor of PI) at a low temperature. The TEM images showed that the silver cores of the nanocomposites were encapsulated with homogeneous shells with thickness of 4 and 8 nm at silver contents of 90 and 60 %, respectively. The shell thickness was controlled by varying the content of PAA. FTIR spectroscopic analysis indicated that the imide ring formation occurred after the chemical imidization. The Ag/PI nanocomposites showed excellent thermal stability and exhibited only 10 % weight loss at 300 °C in the air. Moreover, percolation was observed at silver weight fractions close to the critical value, and the maximum dielectric permittivity of the nanocomposites was 120, which is about 40 times higher than that of pristine PI.     

Preparation and characterization of electrospun polyurethane–polypyrrole nanofibers and films

Polyurethane (PU)–polypyrrole (PPy) composite films and nanofibers were successfully prepared for the purpose of combining the properties of PU and PPy. Pyrrole (Py) monomer was polymerized and dispersed uniformly throughout the PU matrix by means of oxidative polymerization with cerium(IV) [ceric ammonium nitrate Ce(IV)] in dimethylformamide. Films and nanofibers were prepared with this solution. The effects of the PPy content on the thermal, mechanical, dielectric, and morphological properties of the composites were investigated with differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), Fourier transform infrared (FTIR)–attenuated total reflection (ATR) spectroscopy, dielectric spectrometry, and scanning electron microscopy. The Young's modulus and glass-transition temperatures of the composites exhibited an increasing trend with increases in the initially added amount of Py. The electrical conductivities of the composite films and nanofibers increased. The crystallinity of the composites were followed with DSC, the mechanical properties were followed with DMA, and the spectroscopic results were followed with FTIR–ATR spectroscopy. In the composite films, a new absorption band located at about 1650 cm⁻¹ appeared, and its intensity improved with the addition of Py. The studied composites show potential for promising applications in advanced electronic devices. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis,characterization and photocatalytic activity of CdS–montmorillonite nanocomposites

Nanocomposites based on cadmium sulfide (CdS) and Na-montmorillonite (Na⁺-Mt) were prepared by a hydrothermal method using Cd[NH₂CSNH₂]SO₄ complex as precursor of CdS which was derived from cadmium sulfate and thiourea. These nanocomposites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR) and X-fluorescence (XF). The nanocomposites consist of nanosized CdS pillars, which tend to increase in size as the amount of complex precursor increases. The CdS crystals have a hexagonal symmetry. The photocatalytic activity of the obtained CdS–Mt nanocomposites is improved significantly compared to that of the Mt and pure CdS. The resulting CdS–Mt nanocomposites could degrade methylene blue and rhodamine 6G under near UV–visible irradiation.     

Preparation and characterization of polyhedral oligomeric silsesquioxane–titania aerogels

The novel polyhedral oligomeric silsesquioxane (POSS)–titania aerogels which contain different contents of titania were successfully prepared by the sol–gel process and subsequently supercritical drying with carbon dioxide. All the aerogels are monolithic and the densities of those aerogels are low. The FTIR spectra of the aerogels showed the resulting POSS–TiO₂ composite aerogels had homogeneous Si–O–Ti bonds. The microstructure, surface composition and thermal stability were measured by FESEM, XPS and TGA. With the increasing of titania contents, the aggregated particles of the aerogels in the microstructure got larger and larger. The texture of the aerogels was measured by XRD and nitrogen adsorption/desorption and showed that they were amorphous and had high surface area (>500 m²/g).     

On the oxidation–reduction kinetics of palladium

The oxidation–reduction kinetics of Pd was investigated on polycrystalline Pd foils using XPS and sputter‐depth profiling over a wide range of temperatures. The observed behavior can be explained in terms of a desorption‐controlled process at lower temperatures (T > 230° C) and a diffusion‐controlled process at higher temperatures (T > 450° C). In the intermediate range (230 < T < 450°C) a transition between the two processes is observed which gives rise to a pronounced shoulder in the reduction time trace. The interpretation is qualitatively confirmed using a simple mathematical model for a coupled bulk diffusion/surface reaction system. This revised version was published online in July 2006 with corrections to the Cover Date.     

Preparation of α-mannoside hydrogel and electrical detection of saccharide-protein interactions using the smart gel-modified gate field effect transistor

The purpose of this study was to detect saccharide-protein interaction capitalizing on the gel-modified field effect transistor [FET]. A lectin-sensitive polymer gel that undergoes volume changes in response to the formation of molecular complex between ''pendant'' carbohydrate and a ''target'' lectin concanavalin A [Con A] was synthesized. It was revealed that direction and magnitude of the gel response (swelling or deswelling) could be readily designed depending on composition and network density of the gel. The Con A-sensitive polymer gel has shown the ability to transduce the detection of saccharide-protein interactions into electrical signals for FET.PACS: 87.85.jf, bio-based materials     

Polyurethaneurea–silica nanocomposites: Preparation and investigation of the structure–property behavior

Nanocomposites consisting of thermoplastic polyurethane–urea (TPU) and silica nanoparticles of various size and filler loadings were prepared by solution blending and extensively characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), thermal analysis, tensile tests, and nanoindentation. TPU copolymer was based on a cycloaliphatic diisocyanate and poly(tetramethylene oxide) (PTMO-2000) soft segments and had urea hard segment content of 20% by weight. TPU/silica nanocomposites using silica particles of different size (29, 74 and 215 nm) and at different loadings (1, 5, 10, 20 and 40 wt. %) were prepared and characterized. Solution blending using isopropyl alcohol resulted in even distribution of silica nanoparticles in the polyurethane–urea matrix. FTIR spectroscopy indicated strong interactions between silica particles and polyether segments. Incorporation of silica nanoparticles of smaller size led to higher modulus and tensile strength of the nanocomposites, and elastomeric properties were retained. Increased filler content of up to about 20 wt. % resulted in materials with higher elastic moduli and tensile strength while the glass transition temperature remained the same. The fracture toughness increased relative to neat TPU regardless of the silica particle size. Improvements in tensile properties of the nanocomposites, particularly at intermediate silica loading levels and smaller particle size, are attributed to the interactions between the surface of silica nanoparticles and ether linkages of the polyether segments of the copolymers.     

Preparation and characterization of wood-fiber-reinforced polyamide 6–polypropylene blend composites

In this study, we used lithium chloride (LiCl) as a modifier to decrease the melting temperature (T _m) of polyamide 6 (PA6), and then, we fabricated wood-fiber-reinforced PA6–polypropylene (PP) blend composites via hot pressing. From crystallization analysis, the composites exhibited a lower T _m and a lower processing temperature compared to PA6. Color and Fourier transform infrared analyses showed that severe thermal degradation and discoloration of the composites could be prevented by the incorporation of LiCl. LiCl had positive effects on the mechanical properties of the final product and the interfacial compatibility among PA6, PP, and wood fiber. The flexural strength increased by 8.5%. In addition, both maleic anhydride grafted PP and wood fiber improved the mechanical properties. The flexural strengths increased by 7.9 and 40%, respectively. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47413.     

Preparation and structural properties of Fe3O4–polyimide hybrid nanocomposites

Polyimide films in which magnetic Fe₃O₄ nanoparticles are uniformly distributed are prepared. Before the preparation of the Fe₃O₄–polyimide composites, pure magnetite nanoparticles (Fe₃O₄) have been synthesized in water by co-precipitation (from ferric chlorides). Its surface was firstly modified with the 3-aminopropyl triethoxysilane. The prepared polyimide–Fe₃O₄ nanocomposite films were characterized for their structure, morphology, and thermal behavior employing Fourier transform infrared spectroscopy, scanning electron micrograph, X-ray diffraction, and thermal analysis (DTA/TGA/DSC) techniques.     

Preparation and characterization of ultrafine ZrB2–SiC composite powders by a combined sol–gel and microwave boro/carbothermal reduction method

A combined sol–gel and microwave boro/carbothermal reduction technique was investigated and used to synthesize ultrafine ZrB₂–SiC composite powders from raw starting materials of zirconium oxychloride, boric acid, tetraethoxysilane and glucose. The effects of reaction temperature, molar ratios of n(B)/n(Zr) and n(C)/n(Zr+Si) on the synthesis of ultrafine ZrB₂–SiC composite powders were studied. The results showed that the optimum molar ratios of n(B)/n(Zr) and n(C)/n(Zr+Si) for the preparation of phase pure ultrafine ZrB₂–SiC composite powders were 2.5 and 8.0, respectively, and the firing temperature required was 1300 °C. This temperature was 200 °C lower than that require by using the conventional boro/carbothermal reduction method. Microstructures and phase morphologies of as-prepared ultrafine ZrB₂–SiC composite powders were examined by field emission-scanning electron microscopy (FE-SEM) and transmission electron microscope (TEM), showing that SiC grains were formed evenly among the ZrB₂ grains, and the grain sizes of ZrB₂ in the samples prepared at 1300 °C for 3 h were about 1–2 μm. The average crystalline sizes of these two phases in the as-prepared samples were calculated by using the Scherrer equation as about 58 and 27 nm, respectively.