Condensation–addition‐type resole resins with phenyl ethynyl functions: Synthesis,characterization, and thermal properties

Novel phenolic resins bearing methylol and phenyl ethynyl functions and curing by both condensation and addition mechanisms were synthesized by the reaction of 3‐(phenyl ethynyl) phenol (PEP) with formaldehyde under alkaline conditions. Resins with varying relative concentration of the two functional groups were synthesized and characterized. The resins underwent a two‐stage cure, confirmed by both DSC and DMA analyses. The low‐temperature cure due to methylol condensation led to early gelation of the system. The ultimate curing through addition reaction of phenylethynyl group required heating at 275°C. The cured resins exhibited better thermal stability and anaerobic char yield in comparison to a conventional resole. The thermal stability and char‐yielding property showed a diminishing trend with enhanced methylol substitution. Resin with F/P ratio less than unity offered excellent thermal stability and anaerobic char yield. The thermal degradation of the cured resins occurred in two kinetic steps. Methylene groups favored the initial degradation, whereas the higher temperature carbonization process was independent of the network structure. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3371–3377, 2001     

Phosphorus-containing diamine for flame retardancy of high functionality epoxy resins. Part II. The thermal and mechanical properties of mixed amine systems

Bis(4-aminophenoxy)phenyl phosphonate (BAPP) was used in various ratios in combination with diethyltoluenediamine (DETDA) to investigate the effect of increasing phosphorous addition upon the thermal and mechanical properties of diglycidyl ether of bisphenol A (DGEBA) and tetra glycidyl dimethylenedianiline (TGDDM) based epoxy networks. Increasing phosphorous content was shown to decrease the temperature of the initial onset of degradation, while the char yield at 540 °C increased in both the nitrogen and air atmosphere. At 700 °C, however, the char formation was shown to be dependent upon the atmosphere with an oxidative environment promoting further chain scission, while a non-oxidative environment promoted char formation through crosslinking reactions. Increasing phosphorous content was found to produce only modest decreases in the glass transition temperatures, while no significant deleterious effects upon the mechanical and physical properties such as flexural properties and CTE were observed.     

A novel addition curable novolac bearing phthalonitrile groups: synthesis,characterization and thermal properties

Summary Novel phenolic novolac resins, bearing phthalonitrile groups anchored to benzene ring through phenyl azo linkage were realized by the coupling reaction between novolac and phthalonitrile diazonium salt. The diazo-coupling occurred to a maximun of about 61%. The apparent molecular weight, determined form GPC showed a downward drift with increase in degree of phthalonitrile substitution. Analysis using DSC technique indicated that the resin underwent curing in a temperature range form 290 to 320 °C . The curing occurred via addition polymerization of phthalonitrile groups. The thermal stability and anaerobic char yield of the polymers increased proportion to the crosslinking. The probable cure mechanics were discussed.     

Maleimide-epoxy resins: preparation, thermal properties, and flame retardance

Maleimide modified epoxy compounds were prepared through reacting N-(4-hydroxylphenyl)maleimide (HPM) with diglycidylether of bisphenol-A. Triphenylphosphine and methylethylketone were utilized in the reactions as a catalyst and a solvent, respectively. The resulting compounds possessed both oxirane ring and maleimide group. The kinetics of the curing reactions of the maleimide-epoxy compounds and amine curing agents, 4,4-diaminodipheylmethane (DDM) and dicyandiamide (DICY), were studied. Incorporation of maleimide groups into epoxy resins provided cyclic imide structure and high cross-linking density to the cured resins, to bring high glass transition temperatures (179 °C) and good thermal stability (above 380 °C) to the cured resins. High char yields in the thermogravimetric analysis and high limited oxygen index values (25.5-29.5) were also observed for the cured resins to impy their good flame retardance.     

Effects of oxidation and heat treatment of acetylene blacks on their electrochemical double layer capacitances

Correlations between the electrochemical double layer capacitances of various acetylene blacks modified by surface oxidation and heat treatment, and their morphologies are presented. The acetylene blacks were different from each other in primary structural unit size (equivalent to mean particle diameter). They were oxidized in air at 300 °C for 1 h to produce graphene sheets protruding from the surfaces of the spherical particles. In addition, the surfaces of the acetylene blacks were modified by heat treatments from 1000 °C to 2800 °C, which resulted in a morphological change from surfaces covered with protruding graphene sheets to ones wrapped with basal planes of graphite. Correlations between the capacitances of the acetylene blacks and the observed morphologies showed that the surface covered with protruding graphene sheets was roughly 10 times more effective in capacitive charging than the surface of graphite basal planes. Specifically, the surface specific capacitance of the edged-graphene-sheet-covering surface was 146 mF/m², while that of the basal-planes-wrapping surface was 16 mF/m². It was concluded that the capacitances of the acetylene blacks were mainly defined by surface morphology, which were in turn influenced by structural unit size and degree of oxidation.     

Soluble rigid rod-like polyimides and polyamides containing curable pendent groups

Soluble rod-like aromatic polyimides and polyamides containing curable pendent groups were synthesized. The polyimides (PIEANs) and polyamides (PAEANs) containing pendent enaminonitrile groups showed good thermal stability, and underwent curing reactions without the emission of volatile by-products above 300 °C to stable materials which were not soluble in any organic solvents. However, the polyimides (PIEONs) and polyamides (PAEONs) containing pendent enoxynitrile groups started to decompose around 300 °C, because of the instability of enoxynitrile groups. PAEONs underwent curing reactions around 420 °C in spite of the initial decomposition, but PIEONs exhibited only thermal degradation process. Thermal analyses of these polymers and the corresponding model compounds revealed that the curing of enaminonitrile groups proceeded via intermolecular crosslinking as well as intramolecular cyclization, while the enoxynitrile groups, known to undergo self-curing reaction, could not be cured by itself, and a reactive amine group was essential for the curing of the enoxynitrile groups.     

Aromatic phosphorodiamidate curing agent for epoxy resin coating with flame-retarding properties

Two organophosphorus-based diamines containing aromatic moieties has been synthesized and used as a curing and flame retarding agent for epoxy resin coatings. This agent functions not only as a crosslinking materials in the Epon 828 epoxy resin curing process but also as a fire retarding compound to produce thin films or composites upon curing. Phenyl phosphonic ethylene diamine diamide (PPEDD) was synthesized via condensation of phenylphosphonic dichloride (PPDC and ethylenediamine (EDA)). Likewise, phenyl phosphonic p-phenylene diamine diamide (PPPDD) was synthesized via condensation of PPDC and p-phenylenediamine (PDA). Kinetics studies of the curing reaction of the two phosphorodiamidates were carried out in comparison with the corresponding non-phosphorus containing reference crosslinking agents, EDA and PDA. Thermal stability of the cured epoxy were investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Moreover, flame retardant properties of the materials was investigated by limiting oxygen index (LOI) measurements. The results show that epoxy resin cured with phosphorodiamidate possesses higher thermostability than that of the non-phosphorus containing counterpart. This is evident by a significantly higher amount of char formed upon burning. More importantly, the LOI of 27 and 31 was observed in the PPEDD-cured epoxy resin and PPPDD-cured epoxy resin compared with those prepared from non-phosphorus curing agents (20 for EDA and 21 for PDA). This was obtained only with approximately 2–3 wt.% of phosphorus content.     

Synthesis of carbon nanocapsules and carbon nanotubes by an acetylene flame method

The fabrication of carbon nanocapsules and carbon nanotubes (CNTs) using an acetylene flame method was investigated. Carbon nanocapsules, a graphitic structure of nanoparticles with a hollow core, were synthesized using catalyst-free acetylene flames while CNTs were formed with the presence of cobalt-based catalysts in addition to acetylene flames. When the synthesis of these materials was carried out, the results showed that a massive amount of high-purity carbon nanocapsules with a particle size in the range of 15-30 nm can be produced with the acetylene flame method. The CNTs produced were multi-walled carbon nanotubes measuring a few micrometers in length and 20-30 nm in diameter. The acetylene flame method holds great potential for the cost-effective production of CNTs as well as carbon nanocapsules.     

Steam gasification reactivity of char from rapid pyrolysis of bio-oil/char slurry

A slurry of bio-oil and char originating from wood pyrolysis is a promising gasifier feed-stock because of its high energy density. When such a slurry is injected into a high temperature gasifier it undergoes a rapid pyrolysis yielding a char which then reacts with steam. The char produced by pyrolysis of an 80 wt% bio-oil/20 wt% char mixture at heating rates of 100-10,000 °C/s was subjected to steam gasification in a thermogravimetric analyzer. The original wood char from the bio-oil production was also tested. Gasification was conducted with 10-50 mol% steam at temperatures from 800 to 1200 °C. Reactivity of the slurry chars increased with pyrolysis heating rate, but was lower than that of the original chars. Kinetic parameters were established for a power-law rate model of the steam-char reaction, and compared to values from the literature. At temperatures over 1000 °C, the gasification rates appeared to be affected by diffusional resistance.     

Curing temperature effect on mechanical strength of smokeless fuel briquettes prepared with molasses

Environmental acceptable smokeless fuel briquettes have been prepared with a low-rank coal and olive stone as biomass. The binder chosen for this study was molasses which acts with different roles, as chemical and matrix type. The effect of the curing temperature on these briquettes has been studied by Fourier transform infrared spectroscopy, temperature programmed decomposition (TPD) followed on-line by mass spectrometry and optical microscopy. TPD experiments help to predict the final properties of the briquettes more clearly than infrared spectroscopy. The aliphatic structures and methoxy groups as well as the hydrogen bonds decrease during the curing. On the other hand, the carboxylic groups tend to be formed due to the oxidation produced by the effect of curing temperature. In addition, the briquettes cured at 200 °C, 2 h showed the highest mechanical strength. These curing conditions also produce waterproof briquettes due to the presence of carboxylic groups which contribute to the stabilisation of the briquettes because of the formation of hydrogen bonds.     

Preparation and surface characteristics of low-temperature curing fluorinated cathodic electrodeposition coating

Fluorinated cationic cathodic electrodepositing (CED) resins were synthesized by copolymerization of several acrylic monomers including Zonyl. Water dispersible cationic blocked-diisocyanate (denoted as TId) was also synthesized from isophorone diisocyanate (IPDI), cationic triethanolamine (TEOA), and dimethylpyrazole as the cross-linker for the low temperature curing at 90–120 °C. The emulsion stability of the cationic fluorinated CED resin was improved by ionization of the cross-linker TId, showing a mean particle diameter of 140–150 nm and a narrow distribution. 0.5 wt% of curing catalyst dibutyltin dilaurate (DBTL) was enough to accelerate the curing reaction and the gel content of the TId cured fluorinated CED film was higher than 90 wt% after being cured at 130 °C for 40 min. The contact angle and XPS spectrum of the CED film demonstrated that the surface enrichment of C–F₂ and C–F₃ groups effectively reduced the surface tension of the fluorinated CED coating and its surface tension γ_sv is even lower than 15 mN m⁻¹ for PTFE. The preheating of the CED film above T_g but below curing temperature promoted this surface enrichment of the fluorinated groups. Thermal fragmentation of the fluorinated side chains in the CED resins was successfully avoided due to using TId for low temperature curing.     

Kinetics of tire derived fuel (TDF) char oxidation and accompanying changes in surface area

The oxidation behavior of tire-derived fuel (TDF) char has recently been studied by several groups. In the present study, TDF char oxidation has been examined between 670 and 825 K, at oxygen partial pressures ranging from 2 to 19.8 kPa. The order of reaction with respect to oxygen varied with burnoff, and was in the range 0.72-0.86. The activation energy of reaction ranged with burnoff from 138 to 150 kJ/mol. The reaction rate does not correlate well with BET surface area, but did correlate well with the surface area in pores ranging in size from 1.2 to roughly 7 nm in width. Pores smaller than 1.2 nm exist in the char, but appear not to be used or developed by the oxidation reaction. Results for chars that have been acid washed to remove some inorganic matter show lowered reactivity, and a distinctly different pattern of pore development with burnoff. This is, in turn, reflected in a very different pattern of reactivity change with burnoff for such materials.     

Synthesis of novel bisphenol containing phthalazinone and azomethine moieties and thermal properties of cured diamine/bisphenol/DGEBA polymers

A novel bisphenol(1,2-dihydro-2-(4-((4-hydroxy)phenyliminomethylidene)phenyl)-4-(4-((4-(4-hydroxy)phenyliminomethylidene)phenoxy)phenyl)(2H)phthalazin-1-one, DPP) and a diamine(1,2-dihydro-2-(4-aminophenyl)-4-(4-(4-aminophenoxy)phenyl)(2H)phthalazin-1-one, DAP) were synthesized and characterized. The novel epoxy polymers containing phthalazinone and/or azomethine moieties were prepared by binary polymerization of DAP (or DPP) with diglycidyl ether of biphenyl A (DGEBA) and ternary polymerization of hybrid curing agents, DAP/DPP (DAP and DPP under different molar ratios) with DGEBA. The cure behaviors of these new epoxy systems were studied by dynamic differential scanning calorimeter (DSC) and Infrared (IR) scans. Especially, the activation energy of DAP/DGEBA calculated by Kissinger and Ozawa methods were 73.8 and 77.4 kJ/mol, respectively. For ternary epoxy system, it was found that hybrid curing agents of DAP/DPP exhibited significant associated effect on their reactivity towards the oxirane group. Glass transition temperatures (T_g's) of these new epoxy polymers were all above 150 °C from the results of DSC, and the initial thermal decomposition temperatures (T_d,5%'s) and integral procedure decomposition temperatures (IPDT's) of these new epoxy polymers are above 350 and 850 °C, respectively from results of thermogravimetric analyses (TGA). These results show that new epoxy polymers containing phthalazinone and/or azomethine moieties exhibited excellent thermal properties. Especially, thermal properties of the ternary epoxy polymers could be modified by changing the content of DAP and DPP. The linear relationships between char yield (Y_c,wt%) and the structural compositions of these new polymers (weight percentage of phthalazinone, azomethine and nitrogen, C/H weight ratio) were built.     

Online monitoring of synthesis and curing of phenol-formaldehyde resol resins by Raman spectroscopy

The synthesis and curing of phenol-formaldehyde resol resins were monitored online by Raman spectroscopy. The synthesis of the resins (F/P 2.0, alkalinity 4.5 wt%) was studied at rising temperature (40-90 °C) for 90 min and at constant temperatures (80 °C, 90 °C, 100 °C, and 110 °C) for 120 min. The progress of the curing was investigated isothermally (80 °C, 90 °C, 100 °C, and 110 °C) for 120 min for three resins with different degrees of condensation. The synthesis and curing of the resins were started in the reactor and the advancement of the methylolation and condensation reactions was followed through the window of the reactor in the wave number region of 2000-400 cm⁻¹ with use of a fiber optic probe for the data collection. The Raman spectra of six model compounds (formaldehyde, phenol, 2-hydroxybenzyl alcohol, 4-hydroxybenzyl alcohol, 2-benzylphenol, and 4-benzylphenol) were analyzed to facilitate the interpretation of the spectra of the resins. The consumptions of free phenol and free formaldehyde, as well as the progress of the methylolation and condensation reactions were easily monitored by following the changes in intensity of the characteristic Raman bands. The results for the cured resins obtained by Raman spectroscopy were in good agreement with the structures and residual reactivities studied by CP/MAS ¹³C NMR spectroscopy and differential scanning calorimetry (DSC), respectively. The results of the study show Raman spectroscopy to be a promising tool for the online monitoring and control of phenol-formaldehyde resol resin synthesis and curing; in addition, Raman spectroscopy offers an effective and fast method for structural study of the solid state resins.     

Influence of the concentration of ethanol and the interaction of compounds in the pyrolysis of acetylene and ethanol mixtures

The pyrolysis of acetylene, ethanol and acetylene-ethanol mixtures in the 975-1475 K temperature range has been studied. The purpose of this work is to analyze the variation of soot and gas products coming from the pyrolysis of acetylene when adding increasing amounts of ethanol. Gas and soot products coming from the pyrolysis of 30,000 ppm of acetylene and different concentrations of ethanol (0-20,000 ppm) have been identified and quantified, and the influence of the amount of ethanol added has been analyzed. Analyses are supported on model calculations run with Chemkin using a detailed gas phase chemical kinetic mechanism, including subsets for acetylene and ethanol reactions and PAH formation and consumption reactions. In addition, the sum of the soot obtained from the individual pyrolysis of acetylene and ethanol is compared with the results coming from the pyrolysis of the corresponding acetylene-ethanol mixtures in order to analyze the interaction when they react jointly. Experimental results highlight the importance of the relative concentration acetylene/ethanol in the mixtures. Moreover, the results show that adding very small concentrations of ethanol, i.e. up to 600 times lower than acetylene concentration, leads to a diminution on the production of soot from the pyrolysis of acetylene.     

Decomposition and gasification of pyrolysis volatiles from pine wood through a bed of hot char

Pine wood was pyrolyzed in a fixed bed reactor at a heating rate of 10 °C and a final temperature of 700 °C, and the resultant volatiles were allowed to be secondarily cracked through a tubular reactor in a temperature range of 500-700 °C with and without packing a bed of char. The thermal effect and the catalytic effect of char on the cracking of tar were investigated. An attempt was made to deconvolute the intermingled contributions of the char-catalyzed tar cracking and the char gasification to the yields of gaseous and liquid products. It was found that the wood char (charcoal) was catalytically active for the tar cracking at 500-600 °C, while at 650-700 °C, the thermal effect became a dominant mode of the tar cracking. Above 600 °C, the autogenerated steam gasified the charcoal, resulting in a marked increase in the yield of gaseous product and a significant change in the gas composition. An anthracite char (A-char), a bituminous coal char (B-char), a lignite char (L-char) and graphite also behaved with catalytic activities towards the tar cracking at lower temperature, but only L-char showed reactivity for gasification at higher temperature.     

Low-temperature gasification of a woody biomass under a nickel-loaded brown coal char

Catalytic gasification of a woody biomass, Japanese cypress, was investigated under a prepared nickel-loaded brown coal (LY-Ni) char in a two-stage fixed-bed reactor. The nickel-loaded brown coal was prepared by ion-exchange method with a nickel loading rate of 8.3 wt.%. Nickel species dispersed well in the brown coal, and the LY-Ni char via devolatilization at 600 °C showed a great porous property with a specific surface area of 382 m² g^− 1.The LY-Ni char was confirmed to be quite active for the Japanese cypress volatiles gasification at a relatively low-temperature range from 450 to 650 °C. For example, at 550 °C, 16.6 times hydrogen gas and 6.3 times total gases were yielded from the catalytic steam gasification of Japanese cypress volatiles under the LY-Ni char, compared with the case of non-catalyst. The biomass tar decomposition showed a dependence on catalyst temperatures. When the catalyst temperature was higher than 500 °C, Japanese cypress tar converted much efficiently, high gas yields and high carbon balances were obtained.     

Phenolic resins with phenyl maleimide functions: Thermal characteristics and laminate composite properties

Phenolic resins bearing varying concentrations of phenyl maleimide functions were synthesized by copolymerizing phenol with N‐(4‐hydroxyphenyl)maleimide (HPM) and formaldehyde in the presence of an acid catalyst. The resins underwent a two‐stage curing, through condensation of methylol groups and addition polymerization of maleimide groups. The cure characterization of the resin by dynamic mechanical analysis confirmed the two‐stage cure and the dominance of maleimide polymerization over methylol condensation in the network buildup process. The kinetics of both cure reactions, studied by the Rogers method, substantiated the earlier proposed cure mechanism for each stage. Although the initial decomposition temperature of the cured resin was not significantly improved, enhancing the crosslink density through HPM improved thermal stability of the material in a higher temperature regime. The anaerobic char yield also increased proportional to the maleimide content. Isothermal pyrolysis and analysis of the char confirmed that pyrolysis occurs by loss of hydrocarbon and nitrogenous products. The resins serve as effective matrices in silica‐ and glass fabric–reinforced composites whose mechanical properties are optimum for moderately crosslinked resins, in which failure occurs through a combination of fiber debonding and resin fracture. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1664–1674, 2001     

Evaluation of structural features of chars from pyrolysis of biomass of different particle sizes

The structural features of chars derived from pyrolysis of mallee wood of different particle sizes in a novel fluidized-bed/fixed-bed reactor have been investigated. Raman spectroscopy was used for structural evaluation of chars. Spectra were curve-fitted with 10 Gaussian bands representing typical structural features of the chars. The temperature had a significant influence on the evolution of char structure and thus the total Raman peak area between 800 and 1800 cm^− 1 is seen to decrease significantly with increasing pyrolysis temperature for all chars. On the other hand, the ratio I_D/I_{(Gr + Vl + Vr)} between the band intensities of condensed aromatic ring systems (> 6 rings) and amorphous char structures with small aromatic ring (3-5 rings) systems is seen to increase with increasing temperature. The particle size of biomass has a great role in char structure at fast heating rate (> 1000 °C/s) pyrolysis although it has no effect on char structure at slow heating rate pyrolysis (0.17 °C/s). However, in the bigger biomass particle, the structure of char prepared under fast heating rate pyrolysis is similar to that of the structure of char prepared under slow heating rate pyrolysis.     

Drastic changes in biomass char structure and reactivity upon contact with steam

An Australian cane trash biomass was pyrolysed by heating at a slow heating rate to 700-900 °C in an inert gas atmosphere. The chars were then gasified in situ with steam. Our results indicate that the gasification of char with steam, even only for 20 s when the char conversion was minimal, resulted in drastic reduction in the intrinsic reactivity of char with air at 400 °C. The decreases in the char reactivity were not mainly due to the possible volatilisation of inherent catalysts during gasification in steam. Instead, the FT-Raman spectroscopy of the chars showed that the gasification of char with steam resulted in drastic changes in char structure including the transformation of smaller ring systems (3-5 fused rings) to large ring systems (?6 fused rings). It is believed that the intermediates of char-steam reactions, especially H, penetrated deep into the char matrix to induce the ring condensation reactions.