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1.
Pyrolysis of lignocellulosic biomass leads to an array of useful solid, liquid and gaseous products. Staged degasification is a pyrolysis-based conversion route to generate value-added chemicals from biomass. Because of different thermal stabilities of the main biomass constituents hemicellulose, cellulose and lignin, different temperatures may be applied for a step-wise degradation into valuable chemicals. Staged degasification experiments were conducted with deciduous (beech, poplar), coniferous (spruce) and herbaceous (straw) biomass. Thermogravimetry was used to estimate appropriate temperatures for a two-stage degradation process that was subsequently evaluated on bench-scale by moving bed and bubbling fluidised bed pyrolysis experiments. Degasification in two consecutive stages at 250–300 °C and 350–400 °C leads to mixtures of degradation products that originate from the whole biomass. The mixtures that were generated at 250–300 °C, predominantly contain hemicellulose degradation products, while the composition of the mixtures that were obtained at 350–400 °C, is more representative for cellulose. Lignin-derived fragments are found in both mixtures. Yields up to 5 wt% of the dry feedstock are obtained for chemicals like acetic acid, furfural, acetol and levoglucosan. Certain groups of thermal degradation products like C2–C4 oxygenates and phenols are formed in yields up to 3 wt%. Highest yields have been obtained for beech wood. Staged degasification is a promising pyrolysis-based route to valorise lignocellulosic biomass. Clear opportunities exist to increase product yields and selectivities by optimisation of reactor conditions, application of catalysts and specific biomass pretreatments like demineralisation and pre-hydrolysis.  相似文献   

2.
The preparation of polyimide (PI) resin with high heat resistance and toughness is a significant challenge. In this study, thermoplastic PI (TPI) was used to toughen thermosetting PIs, and toughened PI (TPI/PI) blends were prepared. The modified PI resin system exhibited good thermal stability, excellent heat resistance, and high toughness. The results indicated that the TPI/PI blends maintained the curing behavior and characteristics of the PI oligomer. The Tg of the cured TPI/PI blend exceeded 395 °C, and the T5% values were in the range of 533–563 °C, suggesting excellent thermal stability and heat resistance. The maximum impact strength was increased by 46% compared with that of pure PI, indicating the excellent toughening effect of the TPI. Carbon fiber-reinforced PI composites were prepared using the toughening system as a matrix. The compression-after-impact values of the carbon fiber-reinforced PI composites were up to 190 MPa, indicating the excellent toughness of the materials.  相似文献   

3.
Thermoplastic polyurethane composites with an excellent dielectric constant and high thermal conductivity were obtained using CNT@BaTiO3 as a filler through a low-speed melt extrusion method. Before preparing the hybrid filler for the composite, the filler particles were surface modified to ensure that the outer surfaces could facilitate the reaction among particles to form the hybrid and ensure complete dispersion in the thermoplastic polyurethane matrix. After confirming the proper surface treatment of the filler particles using infrared spectroscopy, thermal degradation analysis and field emission scanning electron microscopy, they were used to prepare the composite materials at a processing temperature of 200 °C. The thermal stability, thermomechanical properties, mechanical properties, thermal conductivity, and dielectric properties of the composites were investigated. Compared to the neat thermoplastic polyurethane matrix, the prepared composite exhibited a higher thermal stability, approximately 300% higher storage modulus, higher tensile strength and elongation at break values, approximately three times higher thermal conductivity (improved from 0.19 W/(m.K) to 0.38 W/(m.K), and approximately five times larger dielectric constant at high frequencies (at 1 MHz a dielectric constant of 19.2 was obtained).  相似文献   

4.
Oxidative lime pretreatment increases the enzymatic digestibility of lignocellulosic biomass primarily by removing lignin. In this study, recommended pretreatment conditions (reaction temperature, oxygen pressure, lime loading, and time) were determined for Dacotah switchgrass. Glucan and xylan overall hydrolysis yields (72 h, 15 FPU/g raw glucan) were measured for 105 different reaction conditions involving three different reactor configurations (very short term, short term, and long term). The short-term reactor was the most productive. At the recommended pretreatment condition (120 °C, 6.89 bar O2, 240 min), it achieved an overall glucan hydrolysis yield of 85.2 g glucan hydrolyzed/100 g raw glucan and an overall xylan yield of 50.1 g xylan hydrolyzed/100 g raw xylan. At this condition, glucan oligomers (1.80 g glucan recovered/100 g glucan in raw biomass) and xylan oligomers (25.20 g xylan recovered/100 g xylan in raw biomass) were recovered from the pretreatment liquor, which compensate for low pretreatment yields.  相似文献   

5.
The formation of Ag–Au, Cu–Au, and Ag–Cu bimetallic particles on the surface of highly oriented pyrolytic graphite was studied by X-ray photoelectron spectroscopy. Samples with the core–shell structure of particles were prepared by sequential thermal vacuum deposition. The thermal stability of the samples was studied over a wide range of temperatures (25-400°C) under ultrahigh-vacuum conditions. The heating of the samples to ~250°C leads to the formation of bimetallic alloy particles with a relatively uniform distribution of metals in the bulk. The thermal stability of the samples with respect to sintering depends on the nature of the supported metals. Thus, the Ag–Au particles exhibited the highest thermal resistance (~350°C) under ultrahigh-vacuum conditions, whereas the Ag–Cu particles agglomerated even at ~250°C.  相似文献   

6.
Pyrolysis of tobacco, a complex biomass matrix, was investigated to further understand thermal decomposition processes that are accompanied by evaporation of relatively stable non-polymeric endogenous compounds. Pyrolysis of two types of tobacco, bright and burley were studied using thermo-gravimetry mass spectrometry (TG–MS) and field ionization mass spectrometry (FIMS) analyses. Tobacco contains biopolymers and many non-polymeric compounds. Unlike many biomass pyrolysis tars derived from wood or cellulose, tobacco pyrolysis tars can contain significant amounts of high molecular weight endogenous constituents such as waxes and terpenes that are transferred intact. The phenomenon of evaporation of high molecular weight non-polymeric compounds is illustrated by tobacco micro-sample pyrolysis in FIMS under vacuum (at a pressure of 10−4 Torr). These experiments indicate that the evaporation of relatively stable high molecular weight species occurs below about 220 °C generating 300 Da and higher molecular weight products; and, decomposition of tobacco biopolymers such as starch, cellulose, hemicellulose, lignin, and pectin occurs mostly at temperatures higher than 220 °C producing species mostly with molecular weight below 300 Da. Some of the high molecular weight compounds, such as stigmasterol (412 Da), α-tocopherol (430 Da), and solanesol (630 Da), were tentatively identified using the FIMS spectra.  相似文献   

7.
In this work, a polymeric composite was prepared from ethylene propylene diene monomer (EPDM) and silicone rubber (S) with additives of modified fumed silica (MFS), titanium dioxide (TiO2) and graphene. The dielectric and thermal performances of the EPDM-based composites were studied. An increase in the dielectric constant and AC dielectric breakdown strength was observed for the EPDM rubber composites containing MFS, TiO2, and graphene additives. In addition, the incorporation of the additives resulted7in a significant increase in the thermal stability (~30–50 °C) and thermal conductivity (~7–35%) of the composites. The combination of these various improvements gives suitable performance advantage to the polymeric composite for use in insulating applications.  相似文献   

8.
Hydrogen is regarded as the next-gen fuel for vehicles to avoid the emission of toxic gases, which needs a continuous monitoring of the concentration level. In the design of the H2 sensor, especially of flexible type, a sensing layer will be blended, which affects the sensing performance of the device. Based on this concern, the present investigation is carried out to understand the effect of the bending angle toward the sensing performance of bare and ZnO (n-type)-decorated Sb2O3 (p-type) nanobelt–based sensors for hydrogen gas. The sensing element was prepared by the thermal chemical vapor deposition followed by the drop-casting method. Furthermore, the role of the zinc precursor (molar concentration—1 M–3 M) on the preparation of ZnO-decorated Sb2O3 nanobelts was studied. Various techniques were used to confirm the formation of ZnO-decorated nanobelts such as X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), and Fourier transform infrared spectroscopy (FTIR). From these analyses, 1 M concentration of the zinc precursor shows uniform distribution of nanoparticles over the surface of Sb2O3 nanobelts. However, agglomeration was observed when the concentration of the zinc precursor increases from 1 M to 3 M. Later, the prepared nanobelts were deposited on the OverHead Projector (OHP) sheet by the doctor blade method for sensing hydrogen gas at 100 °C at a concentration of 1000–3000 ppm. In addition to it, the effect of the substrate bending angle (0°, 45°, 60°, and 90°) was analyzed at a fixed concentration of H2 gas (1000 ppm). From this study, it is clear that the highest sensing response was achieved for 1 M decorated nanobelts compared with bare as well as other concentrations because of uniform distribution of nanoparticles on the surface of nanobelts. Moreover, the prepared sample demonstrates better sensing performance with the bending of substrates, which suggests that the prepared sensor could be used for flexible electronic devices. The prepared nanobelts show a good H2 gas–sensing response even with bending of the substrates. The work suggests that the prepared sensor is applicable for flexible electronic devices.  相似文献   

9.
New hydrophobic protic ionic liquid, 2-butylaminoimidazolinium bis(trifluoromethylsulfonyl)imide (BAIM-TFSI), has been synthesized. The ionic liquid showed good thermal stability to at least 350 °C. The conductivity of BAIM-TFSI determined by electrochemical impedance method was found to be 5.6 × 10?2 S/cm at 140 °C. Homogeneous composite films based on commercial polyimide (PI) Matrimid and BAIM-TFSI containing 30–60 wt% of ionic liquid were prepared by casting from methylene chloride solutions. Thermogravimetric analysis data indicated an excellent thermal stability of PI/BAIM-TFSI composites and thermal degradation points in the temperature range 377 °C–397 °C. The addition of ionic liquid up to 50 wt% in PI films does not lead to any significant deterioration of the tensile strength of the polymer. The dynamic mechanical analysis results indicated both an increase of storage modulus E′ of PI/BAIM-TFSI composites at room temperature and a significant E′ decrease with temperature compared with the neat polymer. The cross-linking of the PI with polyetheramine Jeffamine D-400 allowed to prepare PI/Jeffamine/BAIM-TFSI (50%) membrane with E′ value of 300 MPa at 130 °C. The ionic conductivity of this cross-linked composite membrane reached the level of 10?2 S/cm at 130 °C, suggesting, therefore, its potential use in medium-temperature fuel cells operating in water-free conditions.  相似文献   

10.
A novel process using chemical, thermal, and enzymatic treatment for conversion of hulled barley into fermentable sugars was developed. The purpose of this process is to convert both lignocellulosic polysaccharides and starch in hulled barley grains into fermentable sugars simultaneously without a need for grinding and hull separation. In this study, hulled barley grains were treated with 0.1 and 1.0 wt.-% sulfuric acid at various temperatures ranging from 110 to 170 °C in a 63-ml flow-through packed-bed stainless steel reactor. After sulfuric acid pretreatment, simultaneous conversion of lignocellulose and starch in the barley grains into fermentable sugars was performed using an enzyme cocktail, which included α-amylase, glucoamylase, cellulase, and β-glucosidase. Both starch and non-starch polysaccharides in the pre-treated barley grains were readily converted to fermentable sugars. The treated hulled barley grains, including their hull, were completely hydrolyzed to fermentable sugars with recovery of almost 100% of the available glucose and xylose. The pretreatment conditions of this chemical, thermal, and enzymatic (CTE) process for achieving maximum yield of fermentable sugars were 1.0 wt.% sulfuric acid and 110 °C. In addition to starch, the acid pretreatment also retained most of the available proteins in solid form, which is essential for subsequent production of fuel ethanol and high protein distiller’s dried grains with solubles co-product.  相似文献   

11.
Hot-compressed water (HCW) is among several cost-effective pretreatment processes of lignocellulosic biomass for enzymatic hydrolysis. The present work investigated the characteristics of HCW pretreatment of rice straw including sugar production and inhibitor formation in the liquid fraction and enzymatic hydrolysis of pretreated material. Pretreatment was carried out at a temperature ranging from 140 to 240 °C for 10 or 30 min. Soluble oligosaccharides were found to constitute almost all the components of total sugars in the liquid fraction. The maximal production of total glucose at 180 °C and below accounted for 4.4–4.9% of glucan in raw material. Total xylose production peaked at 180 °C, accounting for 43.3% of xylan in raw material for 10-min pretreatment and 29.8% for 30-min pretreatment. The production of acetic acid increased at higher temperatures and longer treatment time, indicating more significant disruption of lignocellulosic structure, and furfural production achieved the maximum (2.8 mg/ml) at 200 °C for both 10-min and 30-min processes. The glucose yield by enzymatic hydrolysis of pretreated rice straw was no less than 85% at 180 °C and above for 30-min pretreatment and at 200 °C and above for 10-min pretreatment. Considering sugar recovery, inhibitor formation, and process severity, it is recommended that a temperature of 180 °C for a time of 30 min can be the most efficient process for HCW pretreatment of rice straw.  相似文献   

12.
Cordierite-based ceramics were fabricated from Moroccan natural halloysite clay by using a simple and low-cost manufacturing method. To this end, peridotite and halloysite samples, collected from Beni Bousera and Melilla sites, Morocco, were used as raw materials for ceramics manufacturing. A starting mixture was prepared (76.08 wt% of clay and 23.92 wt% of peridotite), molded and heated to the desired temperature (1250, 1300 and 1350 °C) to fabricate cordierite ceramic specimens. Both raw materials (peridotite and halloysite) and final ceramics were analyzed using routine characterization techniques including chemical analysis by XRF, mineralogical analysis by XRD, thermogravimetric analysis, and morphological characteristics using scanning electron microscopy (SEM). The prepared ceramics were investigated regarding their mineralogical composition, thermal and technological properties, chemical resistance, and microstructural characteristics. Our results indicated that peridotite sample is mainly composed of silica (40.25 wt%) and magnesia (38.05 wt%) while halloysite is consisted essentially of silica (38.00 wt%) and alumina (34.13 wt%). This was confirmed by XRD, TG-DTA and FTIR analyses. The prepared ceramic specimens at different sintering temperatures (i.e., 1250, 1300 and 1350 °C) have regular cylindrical forms, displaying good ceramic properties. This is consolidated with the main technological tests including porosity (4.56–3.11%), bulk density (2.45–2.78 g/cm3), shrinkage (6.51–10.31%), indirect tensile strength (20.35–27.60 MPa), and low linear thermal expansion coefficient (3.05–2.18 × 10?6/°C). Cordierite specimen prepared at 1350 °C provided the best ceramic sample with the highest technological properties, good chemical resistance and thermal properties. Thus, naturally abundant halloysite and peridotite deposits are potential candidates for cordierite-based ceramic manufacture. Therefore, the achieved results have provided cost-effective ceramic bricks with physical, thermal and mechanical properties that are favorable to be used as refractory bricks.  相似文献   

13.

Nowadays application of radiation shielding structures grows over the world. Nuclear buildings represent one of the most complicated radiation shielding structures; that is why a particular type of concrete is required to withstand different conditions during their lifespan. Unique properties such as the behaviour under elevated temperatures, radiation shielding, and thermal stability properties are essential to guarantee the fire resistance safety of nuclear buildings. However, some gaps are still there, warranting further investigation, particularly the thermal stability and fire-resistance properties of the heavyweight concrete. The properties are mechanical, physical, and deformation properties of concrete after being subjected to elevated temperature. This paper investigated the fire resistance properties of three concrete mixes. There were magnetite-based concrete, basalt-based concrete, and quartz-based concrete. Compressive and flexural strength, spalling, mass loss, porosity, and scanning electron microscopy were measured for the three concrete types after being subjected to different temperature steps at 20, 150, 300, 500, and 800 °C. The three types of concrete showed different fire resistance properties. Magnetite-based concrete has better heat/fire resistance than basalt- and quartz-based concrete; there was no significant change up to 500 °C, and explosive spalling occurred at 800 °C. Correspondingly, the maximum change in porosity and reduction in the compressive and flexural strength occurred at 300 °C, which indicates the good thermal stability of magnetite-based concrete. Concerning basalt-based and quartz-based concretes, cracks were observed at 500 °C, and cracks with colour change and small spalling were initiated at 800 °C. Therefore, the maximum growth in the porosity and the high reduction in the compressive and flexural strength in basalt-based concrete occurred at 800 °C. Likewise, the extreme change in the porosity occurred at 500 °C, and the drastic reduction in the compressive and the flexural strength in the quartz-based concrete was relatively high at 500 °C and 800 °C. The SEM observations and analysis obtained the appearance of microcracks, voids and degradation of C-S-H in different concrete mixes at 500 and 800℃.

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14.

In this study, tetradecanol–palmitic acid/expanded perlite composites containing carbon fiber (TD-PA/EP-CF CPCMs) were prepared by a vacuum impregnation method. Binary eutectic mixtures of PA and TD were utilized as thermal energy storage material in the composites, where EP behaved as supporting material. X-ray diffraction demonstrated that crystal structures of PA, TD, EP, and CF remained unchanged, confirming no chemical interactions among raw materials besides physical combinations. The microstructures indicated that TD-PA was sufficiently absorbed into EP porous structure, forming no leakage even in molten state. Differential scanning calorimetry estimated the melting temperature of TD-PA/EP-CF CPCM to 33.6 °C, with high phase change latent heat (PCLH) of 138.3 kJ kg−1. Also, the freezing temperature was estimated at 29.7 °C, with PCLH of 137.5 kJ kg−1. The thermal cycling measurements showed that PCM composite had adequate stability even after 200 melting/freezing cycles. Moreover, the thermal conductivity enhanced from 0.48 to 1.081 W m−1 K−1 in the presence of CF. Overall, the proposed CPCMs look promising materials for future applications due to their appropriate phase change temperature, elevated PCLH, and better thermal stability.

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15.
Two different multi-porous epoxy thermosets (MPETs), bi-functionality of DGEBA and tri-functionality of TGTPM, were prepared foremost for the interaction of template concentration and epoxy functionality under several physical properties. By performing an automated mercury porosimeter test, we found out template concentration was critical to the amount of voids/pores. Meanwhile, epoxy functionality decided the formation of porous structure through SEM. Comparing with TGTPM MPETs system, the DGEBA MPETs system with 20 wt% template displayed appreciable Tg and tan δ properties while the phenomenon exhibited higher thermal stability property. Additionally, thermal conductivity patterns show the DGEBA MPETs system is a remarkable material of thermal resistance. However, it reduces optical clarity, dielectric permittivity and mechanical strength according to the UV-visible spectroscopy, LCR meter, and DMA, normally. Therefore, we can understand that template concentration and epoxy functionality are key factors of physical degradation and stability in porous epoxy materials.  相似文献   

16.

The preliminary studies on thermal behavior of differently aged natural resins from Russia (Khatanga), Dominican Republic (El Valle), Colombia and Poland (Jantar) were performed. Thermal stability and behavior under elevated temperature were investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC), while the differences in the structure and composition by FT-IR spectroscopy. Analyzed resins show different thermal effects during heating suggesting that possible post-reactions and structural changes occurred. TG results indicated that Dominican, Russian and Colombian resins present relatively high thermal stability under air conditions in the range of 228–300 °C, whereas the mass loss of 5mass% at about 217 °C was observed for Baltic amber. During DSC experiments, the analyzed resins expose thermal events which make impossible determination of glass transition temperature in a raw sample. The results indicate that both TG and DSC cannot be considered as methods for age dating of natural resins and more advanced techniques should be applied. Careful analysis of FT-IR data in the carbonyl region may provide additional information about the composition and history of the natural resin.

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17.
A novel co-precipitation and annealing route to the large-quantity synthesis of boron nitride nanotubes (BNNTs), using amorphous boron powder, iron nitrate nonahydrate (Fe(NO3)3·9H2O) and urea (CO(NH2)2) as the raw materials, was demonstrated. An intermediate Fe(OH)3·B was firstly prepared through a co-precipitation process and then annealed in flowing ammonia atmosphere at 1200 °C. It was found that the heat treatment at 800 °C during the annealing process could favor the growth of BNNTs. The BNNTs had an average diameter of 70 nm and possessed bamboo and quasi-cylindrical structures. The annealing temperature greatly affected the formation of BNNTs. Only BN particles could be obtained at lower temperature (e.g. 1100 °C), whereas thorn-like nanosheet-decorated BNNTs were fabricated at higher temperature (e.g. 1300 °C). A combination mechanism of solid–liquid–solid (SLS) and vapor–liquid–solid (VLS) model was suggested to be responsible for the growth of BNNTs.  相似文献   

18.
Polyarylates derived from 4,4″-dihydroxy-meta-terphenyl (DHmTP) were prepared by the phase-transfer catalyzed, two-phase polycondensation with aromatic diacid chlorides. The resulting polymers were crystalline, solvent resistant, and produced brittle films. Copolymers with bisphenol-A were also synthesized using isophthaloyl diacid chloride. At low to moderate levels of DHmTP in the copolymers (25–75%), the materials had high glass transition temperatures (186–201°C), good solvent resistance, and gave tough, clear films. Terpolymers of DHmTP and BPA with 50:50 isophthaloyl and terphthaloyl diacid chloride were prepared with not much improvement over Ardel D-100®. All the DHmTP-polyarylates had good thermal stability (5% weight loss in air > 415–460°C) and had a high % char (20–48%). © 1994 John Wiley & Sons, Inc.  相似文献   

19.
《印度化学会志》2023,100(4):100966
In the present study, tribological and corrosion behaviour of electroless Ni–B–W (ENB-W) coatings prepared from stabilizer-free baths and deposited on AISI 1040 steel substrates were examined. Three distinct coating bath temperatures (85 °C, 90 °C, and 95 °C) were varied for coating deposition. The coatings showed nodular morphology. Thermogravimetric study of ENB-W coatings revealed improved thermal stability attained at 95 °C bath temperature. The microhardness of ENB-W coating was 645, 690, and 720 HV100 at bath temperatures of 85 °C, 90 °C, and 95 °C respectively. The inclusion of W to Ni–B coating enhanced the hardness by ∼150 HV100. On a pin-on-disc tribometer, wear test was conducted. The precipitation of Ni (111) and its borides occurred post sliding wear at high temperatures (300 °C). Ni (111) crystallite size decreased because of high temperature sliding wear at 300 °C with an increase in coating bath temperature. With a reduction in crystallite size at high temperatures, both wear rate and COF decreases. The scratch hardness and first critical load of failure of the coatings was determined using a scratch tester. Using potentiodynamic polarization, corrosion resistance of ENB-W coatings in 3.5% NaCl was investigated. ENB-W coatings could provide shielding to AISI 1040 steel from corrosion. Though the corrosion resistance is poor with respect to lead stabilized coatings.  相似文献   

20.
Aqueous crosslinked microparticle dispersions were prepared from a copolymer of d,l-lactic acid, 1,4-butanediol, and itaconic acid with a thermomechanical method. The copolymer was prepared in one step polycondensation reaction using Sn(Oct)2 as a catalyst. A polymer with Mn of 2800 g mol?1 and a molecular weight distribution of 1.41 was obtained (as determined by SEC), that contained double bonds introduced by the itaconic acid monomer units (6 mol-%, as determined by NMR). Crosslinking ability of the prepared copolymer was demonstrated in bulk by adding a thermal initiator and altering amounts of ethylene glycol dimethacrylate (EGDMA) crosslinking agent into molten polymer at 60–150 °C. A crosslinked gel was formed in less than 15 min at 80 °C when 10 wt.% of EGDMA was added and benzoyl peroxide (BPO) was used as the initiator. Aqueous dispersions were prepared of the non-crosslinked copolymer with a thermomechanical method that involved slow addition of aqueous polyvinyl alcohol (PVA) solution into molten copolymer at 60 °C under shear. Dispersions were prepared with 10 wt.% of EGDMA and 2 wt.% of BPO. Crosslinking of the dispersed microparticles was achieved by heating the dispersions at 80 °C for 30 or 60 min. The dispersions were characterized by SEM, DSC, TGA, FT-IR, solid state NMR, and gel content measurements. The effect of crosslinking was clearly seen in SEM images of films cast from the dispersions. The films cast from non-crosslinked dispersions had smooth morphology whereas in films cast from crosslinked dispersions separate spherical particles were observed. During the crosslinking reactions, glass transition temperatures increased (as determined by DSC), thermal stability of the samples increased (as determined by TGA), and the gel content of the samples increased.  相似文献   

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