Influence of polyfurfuryl alcohol (PFA) loading on the properties of Nafion composite membranes

Composite membranes based on Nafion (N115) loaded with furfuryl alcohol (FA) were prepared by in situ acid-catalyzed polymerization technique, with the aim to improve the ionic conductivity of Nafion membranes. The functionalization, thermal stability, electrical properties and mechanical strength of N115-PFA composites was analyzed by means of Fourier transform infrared (FT-IR) attenuated total reflection (ATR) spectroscopy, small- and wide-angle X-ray scattering (SAXS/WAXS), thermogravimetric analysis (TGA), electrical impedance spectroscopy, dynamic vapor sorption (DVS) and dynamic mechanical analyser (DMA). The FA loading in the resultant composites had a positive correlation with the water uptake (W_u), water vapor uptake (W_vu), ionic conductivity and thermo-mechanical stability. At low polyfurfuryl alcohol (PFA) loading, these membranes displayed higher W_u and improved ionic and electrical properties. Further, the thermo-mechanical stability also gradually increased with the PFA loading. All the composites showed a well-defined glass transition temperature in DMA, which shifted to higher temperature with repeated PFA loading. Overall, the results indicate that the developed composite membrane are promising for low temperature polymer electrolyte membrane (PEM) fuel cells.     

New insights on the thermal degradation pathways of neat poly(furfuryl alcohol) and poly(furfuryl alcohol)/SiO2 hybrid materials

Poly(furfuryl alcohol)/SiO₂ hybrid material was prepared and properties characterized in comparison with those of neat poly(furfuryl alcohol) (PFA) thermoset. A morphological study conducted by transmission electron microscopy (TEM) on the hybrid material reveals well-dispersed silica nanoclusters. Combination of micro- and submicro-structural organizations between the organic and inorganic networks generates new thermo-mechanical performances. A study of relaxation process by dynamic mechanical analysis (DMA) gives some evidence of the nanoconfinement effect on the hybrid network. These restrictions on the molecular mobility lead to an increase of thermal stability of the PFA/SiO₂ material compared to the unfilled matrix. Thermogravimetric analyses (TGAs) coupled with GC-MS have permitted us to highlight a multi-step degradation pathway and chain scission reactions are proposed based on identified VOCs.     

The reaction of furfuryl alcohol resins with hexamethylenetetramine: A 13C and 15N high-resolution solid-state NMR study

The reactions between furfuryl alcohol (FA)/poly(furfuryl alcohol) (PFA) and hexamethylenetetramine (HMTA) have been studied by ¹³C and ¹⁵N high-resolution solid-state NMR techniques. Highly crosslinked polymer networks similar to those obtained from the thermal curing of FA resins under acidic condition are formed. Possible reaction pathways are postulated on the basis of changes of chemical structures during the curing; α-substituted furfurylamines are shown to be the initial intermediates. Their further reactions with FA/PFA, together with thermal decomposition, produce methylene linkages between furan rings, resulting in chain extension and crosslinking, which occurs at both the methylene linkages and the 3- or 4-C of furan rings. Various side-products such as amines, imines, amides, imides, and nitriles are also formed during the reactions, and some of these can remain in the resins up to 205°C. The crosslinked network can be heterogeneous with different structures on nanometer scales when higher oligomers of FA resins react with HMTA. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2233–2243, 1997     

Renewable resources as reinforcement of polymeric matrices: composites based on phenolic thermosets and chemically modified sisal fibers

Lignocellulosic materials can significantly contribute to the development of composites, since it is possible to chemically and/or physically modify their main components, cellulose, hemicelluloses and lignin. This may result in materials more stable and with more uniform properties. It has previously been shown that chemically modified sisal fibers by ClO(2) oxidation and reaction with FA and PFA presented a thin coating layer of PFA on their surface. FA and PFA were chosen as reagents because these alcohols can be obtained from renewable sources. In the present work, the effects of the polymeric coating layer as coupling agent in phenolic/sisal fibers composites were studied. For a more detailed characterization of the fibers, IGC was used to evaluate the changes that occurred at the sisal fibers surface after the chemical modifications. The dispersive and acid-base properties of untreated and treated sisal fibers surfaces were determined. Biodegradation experiments were also carried out. In a complementary study, another PFA modification was made on sisal fibers, using K2Cr2O(7) as oxidizing agent. In this case the oxidation effects involve mainly the cellulose polymer instead of lignin, as observed when the oxidation was carried out with ClO(2). The SEM images showed that the oxidation of sisal fibers followed by reaction with FA or PFA favored the fiber/phenolic matrix interaction at the interface. However, because the fibers were partially degraded by the chemical treatment, the impact strength of the sisal-reinforced composites decreased. By contrast, the chemical modification of fibers led to an increase of the water diffusion coefficient and to a decrease of the water absorption of the composites reinforced with modified fibers. The latter property is very important for certain applications, such as in the automotive industry.     

Synthesis of novel bismaleimide monomers based on fluorene cardo moiety and ester bond: Characterization and thermal properties

Two novel bismaleimide monomers based on fluorene cardo moiety and ester bonds, namely 9, 9-bis[4-(4-maleimidobenzoate) phenyl]fluorene (PEFBMI) and 9,9-bis[4-(4-maleimidobenzoate)-3-methylphenyl]fluorene (MEFBMI) were designed and synthesized. Their structures were confirmed by FTIR, ¹H-NMR, ¹³C-NMR spectroscopy and Elemental analysis. Both monomers obtained have excellent solubility in some organic solvents with low boiling point, including acetone, chloroform and dichloromethane. The curing process of the monomers were investigated by DSC, displaying that the melting point of the monomers were 157.1°C and 193.6°C respectively, and all processing windows exceed 30°C. DMA results showed the glass transition temperature of the cured PEFBMI/glass cloth composite was higher than 390°C while that of the cured PEFBMI composite was 349.2°C. TGA results indicated that the cured BMI resins have good thermal stability and their 5% weight loss temperatures were both higher than 410°C.     

Rigid biphenyl-contained epoxy resins with improved thermal resistant properties

Biphenyl-contained monomer of 1,4-bis[2-(3,4-epoxy cyclohexyl ethyl) dimethylsilyl] biphenyl(BP-Si H-EP) was prepared via hydrosilylation reaction of 1,4-bis(dimethylsilyl) biphenyl(BP-Si H) and 1,2-epoxy-4-vinylcyclohexane in the presence of Karstedt's catalyst. ~1H-NMR, ~(13)C-NMR and FTIR were used to characterize the structure of the obtained monomer. BP-Si H-EP was then cured by methyl hexahydrophthalic anhydride(Me HHPA) with 1-cyanoethyl-2-ethyl-4-methylimidazole as an accelerator. The polymerization behavior was studied by DSC. The results of DMA measurement demonstrate that the cured BP-Si H-EP/Me HHPA can maintain high storage modulus(1 GPa) in a wide range of temperature up to 176 °C. According to the damping factor curve of DMA, cured BP-Si H-EP/Me HHPA exhibits a high glass transition temperature(T_g) of 192 ° C, which is 20 ° C higher than that of cured 1,4-bis[2-(3,4-epoxy cyclohexyl ethyl)dimethylsilyl] benzene(DEDSB)/Me HHPA. TGA results show that cured BP-Si H-EP/Me HHPA has good thermal stability(T_(5% )= 339 ° C) due to the high heat-resistance of rigid biphenyl group. Moreover, the crosslinking density of cured BP-Si H-EP/Me HHPA should be lower than that of cured DEDSB/Me HHPA estimated from their chemical structures, which conflicts with the calculated results based on the rubber elasticity equation. The inconsistence indicates that the calculated crosslinking densities are not comparable, possibly owing to their differences in the rigidity of polymer chains and intermolecular interaction.     

Thermal and flame retardant properties of epoxy resin cured by a novel phosphorus-containing 4,4′-bisphenol novolac curing agent

A novel flame retardant curing agent for epoxy resin (EP), i.e., a DOPO (9,10-dihydro-9-oxa-10-phosphaphenan-threne-10-oxide)-containing 4,4'-bisphenol novolac (BIP-DOPO) was synthesized and characterized by Fourier transform infrared (FTIR), ¹H NMR, ³¹P NMR spectroscopy, and gel permeation chromatography. The epoxy resin cured by BIP-DOPO itself or its mixture with a commonly used bisphenol A-formaldehyde novolac resin (NPEH720) was prepared. The flame retardancy of the cured EP thermosets were studied by limiting oxygen index (LOI), UL 94 and cone calorimeter test (CCT), and the thermal properties by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results show that the cured epoxy resin EPNP/BI/3/1, which contains 2.2% phosphorus, possesses a value of 26.2% and achieves the UL 94 V-0 rating. The data from cone calorimeter test demonstrated that the peak release rate, average heat release rate, total heat release decline sharply for the flame retarded epoxy resins, compared with those of pure ones. DSC results show that the glass-transition temperatures of cured epoxy resins decrease with increasing phosphorus content. TGA indicates that the incorporation of BIP-DOPO promotes the decomposition of epoxy resin matrix ahead of time and leads to higher char yield. The surface morphological structures of the char residues reveal that the introduction of BIP-DOPO benefits to the formation of a continuous and solid char layer on the epoxy resin material surface during combustion.     

Pyrolysis of lignin extracted from prairie cordgrass,aspen, and Kraft lignin by Py-GC/MS and TGA/FTIR

A study is undertaken to assess the effectiveness of lignin extracted from prairie cordgrass as a pyrolysis feedstock. The effects of variability of lignin source on fast and slow pyrolysis products are also investigated. To accomplish these goals, Py-GC/MS and TGA/FTIR are employed in the pyrolysis of three types of lignin: prairie cordgrass (PCG) lignin extracted from prairie cordgrass, aspen lignin extracted from aspen trees (hardwood), and synthetic Kraft lignin. Fast pyrolysis results from Py-GC/MS show that for PCG lignin, only ten of the detected compounds have relative peak area percentiles that exceed 2% and make up over 52% of the total area. For aspen lignin, excluding butanol that is used in the extraction process, only eight compounds are found to have relative peak areas exceeding 2% that make up over 52% of the total area. For Kraft lignin, only eight compounds exceeding 2% are found to make up more than 45% of the total area. Both techniques, Py-GC/MS and TGA/FTIR, indicate that PCG lignin releases more alkyls than aspen and Kraft lignin. TGA/FTIR results indicate that PCG lignin also releases by far the most light volatile products (<200 °C) while producing the least amount of char among the three types of lignin studied. These characteristics make PCG lignin a good choice in producing good quality bio-oil and thus decreasing upgrade requirements. Py-GC/MS results conclude that aspen lignin produces significantly more pyrolytic products than PCG lignin. This is indicative of the potential of aspen lignin to result in higher conversion rates of bio-oil than the other two lignins.     

Water absorption effects on hydrophilic polymer matrix of carboxyl functionalized glucose resin and epoxy resin

The effects of water absorption on hydrophilic polymer matrices based on carboxylic functionalized glucose (glucose maleic acid ester vinyl resin) and epoxy resins were studied as a function of curing temperature. The matrix cured at higher temperature shows compact crosslinks due to the higher concentration of ether bonds comparing to the matrix cured at the lower temperature. The polymer matrices cured at different temperatures were immersed in water at room temperature for 1000 h and the thermomechanical properties of the cured polymers were characterized using DMA and TGA. Two types of sorbed water were identified. Type I sorbed water contributed mainly to increasing the weight and to the decrease in T_g due to a plasticizer effect. Type II sorbed water was not removed after heating the polymer to 110 °C for an hour. Type II sorbed water causes changes in the mechanical properties of the polymers cured at different temperatures depending on the crosslinks of the matrix. The cured matrix at the higher temperature has the comparatively tight crosslinks in the network structure and the sorbed water molecule disturbed the polymer network resulting in the degradation of the matrix such as microcracks.     

Fabrication of carbon/silica hybrid materials using cationic polymerization and the sol-gel process

Silica particles with different morphology have been functionalized with carbon shells by different synthetic procedures. In the key step, the bare silica particles are functionalized by a specific cationic surface polymerization with furfuryl alcohol (FA). The polyfurfuryl alcohol (PFA)/silica hybrid particles have been also post-functionalized with maleic anhydride (MSA) by a Diels Alder reaction. Simultaneously occuring cationic polymerization of FA and sol-gel process with TEOS has been used for producing interpenetrating carbon-silica hybrid materials. The thermal transformation of the PFA component on silica into the carbon phase has been carried out under argon atmosphere in a temperature range from 700°C to 900°C. The influence of the former morphology of the silica on the homogenity of the resulting carbon layer is shown by zetapotential measurements and electron microscopic investigations.     

Thiourethane‐based thiol‐ene high Tg networks: Preparation,thermal, mechanical,and physical properties

Thiourethane‐based thiol‐ene (TUTE) films were prepared from diisocyanates, tetrafunctional thiols and trienes. The incorporation of thiourethane linkages into the thiol‐ene networks results in TUTE films with high glass transition temperatures. Increases of T_g were achieved by aging at room temperature and annealing the UV cured films at 85 °C. The aged/annealed film with thiol prepared from isophorone diisocyanate and cured with a 10,080‐mJ/cm² radiant exposure had the highest DMA‐based glass transition temperature (108 °C) and a tan δ peak with a full width at half maximum (FWHM) of 22 °C, indicating a very uniform matrix structure. All of the initially prepared TUTE films exhibited good physical and mechanical properties based on pencil hardness, pendulum hardness, impact, and bending tests. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5103–5111, 2007     

Optical Study of Chitosan-Ofloxacin Complex for Biomedical Applications

Chitosan ofloxacin complex was prepared in isopropyl alcohol under mild conditions. The ionic complexation between chitosan and ofloxacin was confirmed by Fourier transform infrared (FTIR), and nuclear magnetic resonance (NMR) spectroscopy. The crystallinity, thermal, surface morphology and optical properties were evaluated by X-ray diffraction (XRD) analysis, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), ultraviolet-visible (UV-Vis) spectroscopy, photoluminescence (PL) spectroscopy and second harmonic generation (SHG) studies, respectively. Absorption of the complex was high (10⁶cm^?1) with an optical band gap of 3.80 eV. The chitosan-ofloxacin complex may be considered as a novel optical material from biomedical application point of views. It may find applications as biosensors and environmentally sensitive membranes and artificial membranes.     

Catalytic polymerization and facile grafting of poly(furfuryl alcohol) to single-wall carbon nanotube: preparation of nanocomposite carbon

A nanocomposite carbon was prepared by grafting a carbonizable polymer, poly(furfuryl alcohol) (PFA), to a single-wall carbon nanotube (SWNT). The SWNT was first functionalized with arylsulfonic acid groups on the sidewall via a method using a diazonium reagent. Both Raman and FTIR spectroscopies were used to identify the functional groups on the nanotube surface. HRTEM imaging shows that the SWNT bundles are exfoliated after functionalization. Once this state of the SWNTs was accomplished, the PFA-functionalized SWNT (PFA-SWNT) was prepared by in situ polymerization of furfuryl alcohol (FA). The sulfonic acid groups on the surface of the SWNT acted as a catalyst for FA polymerization, and the resulting PFA then grafted to the SWNTs. The surfaces of the SWNTs converted from hydrophilic to hydrophobic when they were wrapped with PFA. The formation of the polymer and the attraction between it and the sulfonic acid groups were confirmed by IR spectra. A nanocomposite carbon was generated by heating the PFA-SWNT in argon at 600 degrees C, a process during which the PFA was transformed to nanoporous carbon (NPC) and the sulfonic acid groups were cleaved from the SWNT. Based upon the Raman spectra and HRTEM images of the composite, it is concluded that SWNTs survive this process and a continuous phase is formed between the NPC and the SWNT.     

Effect of filler content on the stress relaxation behavior of fly ash/polyurea composites

In this study, fly ash/polyurea (FA/PU) composites of various fly ash volume fractions were fabricated. The time-domain stress relaxation behaviors of pure polyurea and the FA/PU composites were measured by dynamic mechanical analysis (DMA) in tension mode at various temperatures. Both temperature and volume fraction of fly ash can affect the segmental motion of polyurea as well as the interaction between fly ash hollow spheres and polyurea matrix, which constitutes the intrinsic mechanism of stress relaxation. Master curves of relaxation modulus were constructed and compared for PU and FA/PU composites. A model was proposed to relate the relaxation modulus and volume fraction of fillers based on three-parameter fractional derivative model and Mori-Tanaka model. The numerical predictions obtained from the model are found to be in good agreement with the experimental results.     

Polypropylene as a potential matrix for the creation of shape stabilized phase change materials

Phase change materials, based on isotactic polypropylene (PP) blended with soft and hard Fischer−Tropsch paraffin wax respectively, were studied in this paper. DSC, DMA, TGA and SEM were used to determine the structure and properties of the blends. While paraffin waxes in the blend changed state from solid to liquid, the PP matrix kept the material in a compact shape. Strong phase separation was observed in both cases, which was more pronounced in the case of soft paraffin wax. Despite the fact that both grades of paraffin wax are not miscible with PP due to different crystalline structures, it was shown that the hard Fischer−Tropsch paraffin wax is more compatible with PP than the soft one. Both waxes plasticized the PP matrix. TGA showed that PP blended with the hard Fischer−Tropsch wax degrades in just one step, whereas blends containing soft paraffin wax degrade in two distinguishable steps. SEM exposed a completely different morphology for the two paraffin waxes and confirmed the lower compatibility of PP and soft paraffin wax. The soft and hard characters of the waxes were manifested in the viscoelastic properties, where the blends containing soft paraffin wax exhibited a lower elastic modulus than pure polypropylene, whereas the hard Fisher−Tropsch paraffin wax solidified the matrix. However, both kinds of blends were able to sustain the dynamic forces applied by the DMA within five cycle runs implying good shape stability.     

In-site mineralization of amorphous calcium carbonate particles: A facile and efficient approach to fabricate poly(l-lactic acid) based hybrids

The aim of this investigation is to obtain a polymer-based hybrid material with biodegradability, biocompatibility, and good mechanical properties and this object was realized via. in-situ introduction of the unmodified calcium carbonate (CaCO₃) into a poly(l-lactic acid) (PLLA) matrix. As verified by the measurements from scanning electron microscopy (SEM), optical microscopy, dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA), the hybrid films which possesses a uniform dispersion of calcium carbonate CaCO₃ in nano-meter scale, mechanically robustness and thermal stability could be fabricated by a mineralization-alike process. For example, the storage modulus increases from 441 MPa of neat PLLA to 1034 MPa of hybrid film containing 2% (w/w) CaCO₃. In addition, the hybrid films display a significant improvement in its UV-exposure resistance.     

Propargyl silicon‐cyclopentadiene oligomeric resin with high temperature resistance

Multiple propargyl substituted cyclopentadiene was synthesized by phase transfer reaction between cyclopentadiene and propargyl bromide in an aqueous solution mediated by sodium hydroxide. It was found that propargylated cyclopentadiene (PCp) could be thermally cured with a mass loss of ca 28%, while the cured material showed a high char yield of ca 76% at 900°C. In order to overcome the processing problems of PCp, a condensation reaction between PCp di‐anion and dimethyldichlorosilane was performed to make a silicon‐PCp (SiPCp) oligomeric resin. SiPCp resin has an acceptable processability, attributed to its organosolubility, low viscosity, and broad processing window. SiPCp resin can readily undergo thermal cure via addition polymerization of ethynyl groups in the temperature range of 170–270°C with an exothermic maximum at ca 240°C, and the mass loss upon cure was less than 5%. Evidenced by the results of dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) in a nitrogen atmosphere, the cured SiPCp resin exhibited stable thermo‐mechanical properties up to 320°C, and possessed an anerobic char yield of ca 77% at 900°C. The results of TGA in air atmosphere revealed the higher oxidation resistance of SiPCp resin. Copyright © 2008 John Wiley & Sons, Ltd.     

Polyurethane Networks Nanoreinforced by Polyhedral Oligomeric Silsesquioxane

Summary: Octaaminophenyl polyhedral oligomeric silsesquioxane (OapPOSS) was used as a crosslinking agent together with 4,4^′‐methylenebis‐(2‐chloroaniline) to prepare polyurethane networks containing POSS. Fourier transform infrared spectroscopy (FT‐IR), dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) were employed to characterize the POSS‐reinforced polyurethane. The POSS‐containing PU networks displayed enhanced glass transition temperatures (T_gs) and the storage moduli of the networks of the glassy state and rubber plateaus were also observed to be significantly higher than that of the control polyurethane although only a small amount of POSS was incorporated into the systems. The results can be ascribed to the significant nanoscale reinforcement effect of POSS cages on the polyurethane matrix. TGA results showed the thermal stability was also improved with incorporation of POSS into the system.

Dynamic mechanical spectra of PU and PU nanocomposites containing POSS.     

Synthesis and characterization of ultraviolet light-curable resin for optical fiber coating

UV-curable polydimethylsiloxane epoxy acrylate (PSEA) and polyethylene glycol urethane acrylate (PGUA) were synthesized and characterized by ¹H-NMR and FTIR spectra. PGUA, PSEA and trimethylolpropane triacrylate (TMPTA) were mixed in different proportions to modify the properties of blends to prepare optical fiber coating. Formulation was optimized by the orthogonal table. When the proportion was PGUA:PSEA:TMPTA=10:4:3, it was used for a single coating (OFC-6). However, the proportion PGUA:PSEA:TMPTA=8:3:2 was used for a primary buffer coating. The rheological behavior and the selection of photoinitiators for OFC-6 were also discussed. The photopolymerization of OFC-6 was inspected by the FTIR spectrum. Results show OFC-6 film is completely cured after irradiated 5 s. The thermal behaviors of the cured film were also investigated by TGA, DMA, etc.     

Excited Semiconductor Clusters: Magic Source

In this paper, we review the preparation and properties of CdS-like clusters as well as their important applications in several nanostructures. The clusters created by the reaction of S^2? ions generated by the decomposition of thioglycolic acid (TGA) and Cd²⁺ ions play important roles for the construction of novel nanocrystals (NCs), the assembly of the NCs, and the formation of nanostructures including 1D solid and tubal fibers, 2D dendritic morphology, and 3D crystals. The formation and property of the clusters depended strongly on the molar ratio of TGA and Cd²⁺ ions in solutions. When aqueous CdTe NCs coated with a hybrid SiO₂ shell containing the clusters, they revealed a drastic increase in photoluminescence (PL) efficiency (from 28 to 80 %) and temperature-dependent PL. These excellent PL properties were ascribed to the clusters very closed to CdTe cores. This is confirmed through the observation of a lengthening of the Auger recombination lifetime by a factor of ~3.5 in the presence of the clusters. The size of the clusters determined the PL properties of the hybrid SiO₂-coated NCs and those fibers. Because of their high PL, these biofunctional materials could provide a platform for various applications.