Thermoplastic properties of coals carbonized at elevated pressures: effects of waste inorganic materials (GOB)

Thermal behaviour of coal-derived asphaltenes was investigated under atmospheric pressure by thermogravimetry (TG). The weight loss is rapid from 300 to 500°C and is slow above 500°C. The asphaltene comparatively low in molecular weight shows the greater weight loss. The temperature at which the differential thermogravimetry peak appears, T_m, correlates to the asphaltene aromaticity: the asphaltene comparatively high in aromaticity shows higher T_m. Of the residual asphaltene after heating up to 600°C, the obtained crystallite thickness through the c-axis direction (Lc₀₀₂) has a correlation with the molecular weight of the parent asphaltene: the parent asphaltene comparatively low in molecular weight produces residual asphaltene of larger Lc₀₀₂.     

Chemical structure of heavy oil from coal hydrogenation 1. Hydrogenation with zinc chloride catalyst

Oil product from the hydrogenolysis of a high-volatile bituminous coal was separated by solubility, fractionated by gel permeation chromotography and characterized by structural analysis. The average structural unit in the hexane-soluble, aromatic oil fraction consists of 1–3 aromatic rings with 0.3-0.5 of the ring carbons substituted by alkyl groups and oxygen containing groups. Molecular weights vary from 200 to 500. The larger molecular weight fractions have longer alkyl chains and lower carbon aromaticities. The molecules are mainly of single unit structures. The average structural units in asphaltene fractions contain from 2.5-4 aromatic rings, are of higher carbon aromaticities and contain shorter alkyl groups. The asphaltene molecules consist of two or more structural units, crosslinked together, and have molecular weights of 300–1400. The oxygen content of the fractions decreases with decreasing molecular weight. Increasing the amount of ZnCl₂ catalyst during hydrogenolysis resylts in an increased yield of lower-molecular-weight material, but no change in the structural properties of the product. This is interpreted to mean that ZnCl₂ is active in the scission of covalent bonds between structural units during liquefaction and that the hydrogenolysis reaction is mostly cleavage of crosslinks between structural units with minimal reaction of the units themselves.     

The chemical nature of a supercritical gas extract including comparison with other coal liquids

A supercritical gas extract of an Australian bituminous coal was separated into oil, asphaltene and pre-asphaltene. The oil was further separated by chromatography into three fractions. Average structure data for each fraction are reported based on NMR spectroscopy combined with elemental, molecular weight and functional group analyses. Unsubstituted alkyl chains (> C₈) were found in every fraction of the extract. The presence of n-alkanes, 1-alkenes and phenyl-n-alkanes were shown. The supercritical gas extract was compared with a flash pyrolysis tar and with hydrogenation liquids from the same coal. The supercritical gas extract and the flash pyrolysis tar had a similar distribution between oil, asphaltene and pre-asphaltene, but the oil, asphaltene and pre-asphaltene from the supercritical gas extract were less aromatic and contained fewer heteroatoms than these fractions from the flash pyrolysis tar. The supercritical gas extract has a higher H/C atomic ratio, higher heteroatom content and a higher percentage of carbon in long unsubstituted alkyl chains than hydrogenation liquids produced at 400°C and 450 °C. The oil/asphaltene ratio and the aromaticity of the oil and asphaltene from the supercritical gas extract were intermediate between those obtained for the two hydrogenation liquids.     

Hindered diffusion of asphaltenes through microporous membranes

The relationship between the diffusion coefficient of asphaltenes and pore size was studied experimentally using track-etched mica membranes. The asphaltenes were extracted from Kuwait atmospheric bottoms using criteria of n-pentane insolubility and tetrahydrofuran solubility at 25°C. Data were obtained for asphaltene fractions of narrow size range by using gel permeation chromatography to analyze the diffusion samples. The results show a very strong pore size effect on diffusion coefficient in the range 70–500 Å pore radius for asphaltenes whose GPC-equivalent polystyrene molecular weight is 3000 or greater. By properly accounting for the molecular size of the asphaltene fractions, we are able to obtain good agreement between the measured diffusion coefficients and those predicted from a hydrodynamic theory of hindered diffusion.     

Studies of thermal oxidative degradation of polypropylene impact copolymer using the temperature rising elution fractionation method

Thermal oxidative degradation of polypropylene impact copolymer has been studied with its fractions obtained using the temperature rising elution fractionation method. The fractions were analyzed using ¹³C NMR, Fourier transform infrared and differential scanning calorimetry measurements, and the chemical structure, isotacticity, conformation and melting point were investigated. It is found that these fractions are composed of a homopolymer or a polymer blend of polypropylene, polyethylene and ethylene–propylene copolymer. The thermal oxidative degradation of each fraction was carried out at 130 °C, and the degradation progress was estimated by the change of molecular weight distribution (from gel permeation chromatography curves). The rate of degradation is found to be dominated by the content of tertiary C? H bonds (propylene unit) and the existence of 3₁ helix conformation corresponding to a crystalline polypropylene part in each fraction. The latter is more evident leading to the degradation reaction path with a lower activation energy. Copyright © 2007 Society of Chemical Industry     

Thermal behaviour of a supercritical gas extract of coal

The effect of temperature on the chemical structure of an extract prepared by supercritical extraction of a low-rank coal with toluene is described. The extract was heated in the absence of air at temperatures up to 400 °C and the products examined by solvent fractionation followed by ultimate analysis, ¹H nuclear magnetic resonance spectroscopy, OH measurements, molecular weight determinations and electron spin resonance spectroscopy. Temperatures up to 200 °C had little structural effect on the extract but by 300 °C radical condensation of asphaltene- and benzene-insoluble material into higher-molecular-weight compounds has occurred, although the structural types of the molecules remain unaltered. By 400 °C structural reorganisation into a disordered polyaromatic-insoluble char has taken place. Initially, molecules primarily condense at phenolic hydroxy sites to form oligomeric units.     

Reaction of Athabasca asphaltene with tetralin

Interaction of Athabasca asphaltene with a hydrogen-donating solvent such as tetralin at temperatures between 195 and 390 °C has been investigated. The reaction resulted in lowering the molecular weight of the treated asphaltene. At 390 °C, 50% of the original asphaltene was converted into pentane-solubles and the sulphur and oxygen contents were each depleted by about 40%. The results, which were interpreted in terms of thermal cleavage of sulphide bonds, are complementary to those obtained in the radical-ion electron-transfer reduction of the asphaltene with potassium in tetrahydrofuran. The negligible amount of coke formation at 390 °C proves the excellent stabilizing properties of tetralin in thermal reactions.     

Decomposition of poly(ethylene glycol) in nanocomposites

Poly(ethylene glycol) (PEG) has been widely used in studies of polymer–clay nanocomposites because it readily intercalates in smectite clays. Nanocomposites were formed from PEG with molecular weights (M_w) ranging from 300 to 20,000, as evidenced by expansion of the basal planar spacing of the clay (d₀₀₁) in X‐ray diffraction. However PEG with high molecular weight (≥ 10,000) readily underwent degradation during preparation of composites when heated at low temperature (60°C) due to oxidative attack. Molecular weight distribution determined by gel permeation chromatography showed that this degradation always happened with or without the presence of clay and it became more serious when the molecular weight was higher. The reduction in pH of aqueous PEG solutions after degradation increased with molecular weight. Since d₀₀₁ was independent of molecular weight over a wide range, such degradation cannot be detected by this method. Precautions against oxidative attack are therefore recommended to avoid decomposition when preparing PEG–clay nanocomposites. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 548–552, 2004     

Effect of the ultradrawing behavior of gel films of ultrahigh‐molecular‐weight polyethylene and low‐molecular‐weight polyethylene blends on their physical properties

This study examined the effect of the ultradrawing behavior of gel film specimens of ultrahigh‐molecular‐weight polyethylene (UHMWPE) and UHMWPE/low‐molecular‐weight polyethylene (LMWPE) blends on their physical properties. The concentration of a gel film approximated its critical concentration at a fixed drawing temperature; its achievable draw ratio was higher than that of other blend specimens with various concentrations. Noticeably, when about 5 wt % LMWPE was added to a UHMWPE/LMWPE gel film specimen, the achievable draw ratio of the gel film increased, and this contributed to an apparent promoting effect on its anticreeping properties and thermal stability. Therefore, when UL_B?0.9 was drawn to a draw ratio of 300, the anticreeping behavior was improved to less than 0.026%/day. Moreover, with respect to the thermal stability, when the same specimen was drawn to a draw ratio of 300, the retention capability of its storage modulus could resist a high temperature of 150°C, which was obviously much higher than the temperature of an undrawn gel film specimen (70°C). To study these interesting behaviors further, this study systematically investigated the gel solution viscosities, anticreeping properties, dynamic mechanical properties, thermal properties, molecular orientations, and mechanical properties of undrawn and drawn UHMWPE/LMWPE gel film specimens. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Electrochemistry of Biomass-Derived Materials I. Characterization,Practionation, and Reductive Electrolysis of Ethanol-Extracted Explosively-Depressurized Aspen Lignin

The chemical characterization (functional group distribution) and spectroscopic properties (¹³C, ¹H, IR, UV-Vis) of a number of lignins obtained from ethanol extraction of explosively-decompressed aspen (Populus tremuloides) lignin (EEEDAL) are described. In this process mod is heated to ～240°C by direct steam and fiberized by sudden decompression. Both mechanical and chemical degradation occur which lead to a decrease of the molecular weight of all of the natural polymers. The lignin fraction is soluble in alcohols; it has a low number average molecular weight (925) and is very reactive. EEEDAL was subjected to fractionation by differential solubility prior to and after electrolyses on mercury cathodes at ?2.6 V vs. Ag/AgCl in methanol/tetraethyl-ammonium perchlorate. After recovery of 85–90% of the original weight of material used by precipitation with acid, followed by a series of extractions, the chemical and spectroscopic properties of each fraction were determined. The acid-insoluble fractions are more condensed than the acid-soluble fractions and have lower phenolic OH and lower aliphatic OH contents than the acid-soluble fractions. The acid-soluble fractions phenolic OH content approaches one per phenylpropane (5) unit of the Lignin. Electrolyses increase the amount of lower molecular weight, high phenolic content, acid-soluble lignins and changes the molecular weight distribution by decreasing the polydispersity of the resulting lignins. These low-molecular-weight lignins are chemically reactive (for instance, with formaldehyde) and can be used in the partial replacement of phenol in phenol-formaldehyde thermosetting resins.     

Thermosetting Polyetherimides: The Influence of Reactive Endgroup Type and Oligomer Molecular Weight on Synthesis,Network Formation,Adhesion Strength and Thermal Properties

The influence of the reactive endgroup on the synthesis, cure behavior and network properties of thermosetting polyetherimides was investigated. Reactive phenylethynyl, ethynyl and maleimide terminated etherimide oligomers were prepared and characterized. Optimal reaction conditions were established to produce fully endcapped oligomers with imidized structures and controlled molecular weight. The phenylethynyl and ethynyl endcapped systems were synthesized by ester-acid methods. The maleimide endcapped system utilized an amic-acid route. Phenylethynyl endcapped oligomers had good processibility and were thermally cured at high temperatures (350–380°C). The networks exhibited good thermal and hydrolytic stability and good adhesion strength, and are candidates for “primary'' bonding adhesives. In contrast, more reactive ethynyl and maleimide endcapped systems were prepared as “secondary'' bonding materials, which could be cured at temperatures lower than that of the T _g of the primary structure. Lap shear test results obtained from NMP-cast/methanol-extracted scrim-cloth-supported precursors confirmed that good adhesion to titanium at both room temperature and at 177°C was achieved when cured at 250°C-280°C. High glass transition temperatures and good thermal stability were achieved as determined by thermal analysis (DSC, TGA and DMA). Solvent extraction measurements confirmed that very high gel fractions were obtained, which is consistent with good chemical resistance.

The influence of molecular weight between crosslinks (Mc) on thermal and mechanical behavior was also investigated for 2,3,5,7 and 10k initial M _n values. Lower molecular weight oligomers exhibited lower T _g and cure temperatures, but higher cured network crosslink densities afforded higher T _g and higher gel fractions, but with reduced toughness.     

Phosphonium‐based layered silicate—Poly(ethylene terephthalate) nanocomposites: Stability,thermal and mechanical properties

PET‐clay nanocomposites were prepared using alkyl quaternary ammonium and phosphonium modified clays by melt‐mixing at 280°C using a micro twin screw extruder. The latter clays were prepared by synthesizing phosphonium surfactants using a simple one‐step method followed by a cation exchange reaction. The onset temperature of decomposition (T_onset) for phosphonium clays (>300°C) was found to be significantly higher than that of ammonium clays (around 240°C). The clay modified with a lower concentration (0.8 meq) of phosphonium surfactant showed a higher T_onset as compared to the clay modified with a higher concentration (1.5 meq) of surfactants. Nanocomposites prepared with octadecyltriphenyl phosphonium (C18P) modified clay showed a higher extent of polymer intercalation as compared with benzyltriphenylphosphonium (BTP) and dodecyltriphenylphosphonium (C12P) modified clays. The nanocomposites prepared with ammonium clays showed a significant decrease in the molecular weight of PET during processing due to thermal degradation of ammonium surfactants. This resulted in a substantial decrease in the mechanical properties. The molecular weight of PET was not considerably reduced during processing upon addition of phosphonium clay. The nanocomposites prepared using phosphonium clays showed an improvement in thermal properties as compared with ammonium clay‐based nanocomposites. T_onset increased significantly in the phosphonium clay‐based nanocomposites and was higher for nanocomposites which contained clay modified with lower amount of surfactant. The tensile strength decreased slightly; however, the modulus showed a significant improvement upon addition of phosphonium clays, as compared with PET. Elongation at break decreased sharply with clay. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Experimental study on the effect of molecular weight and chemical composition distribution on the mechanical response of high-density polyethylene

This article aims to appraise the effect of microstructure comprising molecular weight distribution and chemical composition distribution on the mechanical properties of high-density polyethylene (HDPE). HDPE resins were synthesized using several titanium–magnesium-supported Ziegler–Natta catalysts in the industrial gas phase reactor under the same polymerization condition. Gel permeation chromatography and crystallization elution fractionation (CEF) were conducted on the resins to characterize the molecular weight and comonomer distribution. Crystallization, thermal and rheological behavior were evaluated following differential scanning calorimetry, polarization light microscopy, and rheometric mechanical spectrometry. The resins with higher soluble fraction in trichlorobenzene below 80°C (highly branched low molecular weight chains) exhibited longer crystallization time based on the crystallization kinetic obtained from the Avrami model. Rheological determination of the molecular weight between entanglements (M_e) and the average lamella thickness based on the Gibbs–Thomson equation revealed that the entanglement density and impact strength decreased, and the average lamella thickness increased with an increase in the ratio of CEF eluted fraction below 80°C to the crystallizable fraction in the range of 80–90°C.     

The Chemical and Physical Structure of Peat Bitumens

Peat bitumen obtained by solvent extraction of Irish high moor peat was subjected to chemical, structural and rheological characterisation. The bitumen was fractionated on the basis of solubility in n-heptane, toluene and ethyl acetate into wax, resin and asphaltene; each of these major constituent groups was further separated into sub-fractions by column chromatography using solvents of increasing polarity. All materials were chemically characterised by C, H, N and O content and infra-red spectroscopy. Molecular size distribution of the materials was determined by gel permeation chromatography and vapour pressure osmometry. Heats of fusion, measured using the differential scanning calorimeter, indicated that crystalline species were concentrated in the wax fraction. The rheological properties of the bitumen were investigated between 10 and 50°C, and the fractions were examined at 20°C. Following analysis as yield pseudoplastic fluids, flow behaviour was described in terms of yield stress, flow and consistency indices. The measured flow parameters were examined in the light of the structural implications of the calorimetry and the results of the chemical analysis. Carboxylic acids and esters which are found principally in the wax fraction are considered to be the dominating rheological influence in the bitumen, affecting physical behaviour through their ability to crystallise at low temperature and thus mechanically hinder flow, and through secondary bonding increasing viscosity in the liquid phase.     

Estimation of aliphatic H/C ratios for coal liquefaction products by spin-echo 13C n.m.r.

The direct estimation of aliphatic H/C ratios for coal liquefaction products using a part-coupled spinecho (PCSE) ¹³C n.m.r. method is described. The method, which enables proportions of aliphatic C, CH, CH₂ and CH₃ groups to be deduced, has been applied to a low molecular weight (<200) aromatic fraction of hydrogenated anthracene oil (HAO) and to higher molecular weight (?280) aromatic and asphaltene fractions of supercritical gas (SCG) extracts and a hydrogenation residue (pitch). Aliphatic H/C ratios for these occur in the range 1.9-2.3, the SCG extract fractions having the highest values because they contain significantly more CH₃ and less CH than the HAO and pitch fractions.     

Molecular aggregation in poly(vinyl chloride)

PVC synthesized in a bulk polymerization at ?25°C was fractionated by preparative GPC. The eluent THF solutions consist largely of dissociated molecules. Following precipitation into methanol, recovered PVC fractions contain aggregated molecules and are partially insoluble in THF. The soluble portions produce distorted chromatograms characteristic of molecular aggregation. The aggregate fraction increases with molecular weight. Heating recovered PVC fractions at 90°C in THF was adequate to dissociate the aggregates. Following recovery, fractions of PVC do not show crystalline x-ray diffraction patterns. The PVC fractions were crystallizable by subsequent annealing at 150°C to approximately 15% crystallinity, largely independent of molecular weight.     

Absorption and emission spectra of Athabasca asphaltene in the visible and near ultraviolet regions

Absorption, excitation and emission spectra in the visible and ultra-violet region were recorded at room temperature for Athabasca (Alberta, Canada) asphaltene and five of its fractions separated according to molecular weight (MW) by gel permeation chromatography (g.p.c.) on Bio-Beads SX-1. Strong concentrations effects were observed on the profiles of all the excitation and emission spectra at concentrations higher than 5.0 mg l⁻¹. The proper excitation and emission spectra were taken at concentrations lower than 5.0 mg l⁻¹ where the profiles are independent of concentration. All the spectra obtained were broad, structureless bands with the exception of that of the lowest MW fraction, which shows the sharp Soret band characteristic of the vanadyl porphyrin complex. The absorbance of the whole asphaltene was found to be equal to the weighted sum of absorbances of the fractions at a given wavelength and a given weight concentration. This additive property was not observed among the intensities in the emission spectra. The profiles of all the excitation and absorption spectra are identical throughout the asphaltene fractions, suggesting that the basic absorbing chromospheres are the same throughout the fractions and independent of MW of the fractions. In addition the absorption spectra are not significantly affected by the Tyndall scattering. From the examination of absorptivity and the position of the absorption band, the average number of aromatic rings in the average absorbing chromophores throughout the fractions was found to consist of approximately two to three. The fluorescence spectra, on the other hand, show a very rapid decrease of intensity at a constant weight concentration and a gradual shift of the band maxima toward longer wavelength with increasing number average MW. The origin of the fluorescence band is considered to be exciplexes. The average rate of non-radiative processes decreases steadily with decreasing MW from fraction 1 to fraction 5. The influence of various solvents was explored on the absorption, excitation and emission spectra of the lowest MW (1200) asphaltene fraction.     

Correlation between structural evolution and rheological properties for polycarbonate in the molten state

In this work, multiple rheological and molecular structure characterization methods are utilized to investigate the melt post-polycondensation (MPP) process of polycarbonate (PC) at high temperatures (260–300°C) under a nitrogen atmosphere. We find some unexpected phenomena that the complex viscosity of PC melt rise rapidly and it reaches an extraordinarily high value of about 10⁶ Pa·s during the MPP process of 10 h at 300°C. Dissoluble PC and insoluble gel residue are separated and both fractions are analyzed by gel permeation chromatography, ¹H-NMR, and pyrolysis-gas chromatography mass spectrometry. Results show that the molecular weight of dissoluble PC significantly increases at the early stage of the reaction (less than 1 h). After that, it continues to reduce due to the occurrence of branching reactions and degradation reactions caused by high temperature reactions for a long time. Chemical structure analysis indicates that the same two branched structures are discovered in both dissoluble PC and insoluble gel residue, the changes in structures indicate that no new structures are formed during the crosslinking reaction. According to this study's results, we clearly understand the correlation between the rheological properties and structural changes for PC in the MPP progress.     

Radiation-induced seeded copolymerization of tetrafluoroethylene with propylene. I. Effects of agitation and dose rate

Seeded copolymerization of teterafluoroethylene with propylene by radiation was studied by semibatch experiment at a constant pressure of 25 kg/cm², a temperature of 40°C, and at various dose rates and monomer compositions in polymer particles. The polymerization rate and polymer molecular weight are in the ranges of 5.6–58.7 g/h.L-H₂O and 4.6 × 10⁴–1.6 × 10⁵, respectively. The polymerization rate increases with agitation speed up to 300 rpm and slightly decreases above 500 rpm. The polymer molecular weight is the highest at 300 rpm. The polymerization rate and polymer molecular weight increase with tetrafluoroethylene fraction. At lower tetrafluoroethylene fraction, the polymerization rate is proportional to the 0.7–0.9 power of the dose rate and the polymer molecular weight is almost independent. The dose rate effects are explained by considering that first-order termination by degradative chain transfer to propylene is predominant at a lower tetrafluoroethylene fraction. Decrease in the dose rate dependence of the polymerization rate and increase in that of the polymer molecular weight with the tetrafluoroethylene fraction are due to the increase in second-order termination by recombination.     

Chemical composition and structure characterization of distillation residues of middle-temperature coal tar

The distillation residues of middle-temperature coal tar (DRMCT) were separated into saturate, aromatic, resin and asphaltene fractions by using the combination of solvent extraction and columnchromatography separation.The isolated four fractions have been further characterized through the combination of elemental analysis,Fourier transform infrared (FTIR) spectra, proton nuclearmagnetic resonance spectrum(1HNMR) and molecular weight analysis. The analysis results confirm the view that the saturate fraction from DRMCT was mainly composed of long-chain alkanes and almost all of the heteroatoms (S, N and O) were existed in aromatic structures.The asphaltene fraction had the highest molecular weight, the most amount of heteroatom (especially oxygen)and was the most condensed with shortest alkyl side chains among all the fractions. In addition, for the heavier components, the resin and asphaltene fractions from DRMCT contained lower ratio of H/C, lower molecular weight and higher aromaticity degree when compared with crude oils.