Determination of the thermal modification degree of beech wood using thermogravimetry

Thermal modification is one of the environmental friendly wood preservation technologies. During this process, changes of the main woody cell wall components occur, which lead to improved dimensional stability, lower hygroscopicity and improvement in biological durability. Several chemical reactions which occur during thermal treatment of wood caused changes in wood properties. During TG measurements, thermal decomposition reactions, which was not completed during previous thermal modification process, continued in wood samples, meaning that more thermally treated samples exhibited lower mass losses in a certain or whole temperature range up to 600 °C. Therefore, mass loss, obtained within selected temperature range, could be used as a marker of previous thermal treatment. The aim of the present work is to evaluate suitability of a thermogravimetric method (TG) for determination of a degree of thermal treatment of beech wood. On the basis of thermally untreated sample and those which were thermally modified at 180, 190, 200, 210, 215 and 220 °C in the absence of oxygen, respectively, and with known values of mass loss during the modification processes, several calibration curves were constructed. They represent mass loss in a certain temperature range during TG measurement versus mass loss during previous thermal modification. In a temperature range from 130 to 300 °C and from 130 to 320 °C under nitrogen atmosphere, a linear dependence was observed; correlation coefficients R ² were 0.87 and 0.91, respectively. In wider temperature range and under air atmosphere, lower correlation coefficients were obtained. High correlation coefficient, higher than 0.95, was observed in a temperature range from 25 to 130 °C under both atmospheres. In this region, dehydration due to rehydration of thermally modified samples occurs. The results of this work were compared with those obtained for Norway spruce.     

Thermogravimetry as a possible tool for determining modification degree of thermally treated Norway spruce wood

Thermal treatment is one of environmental friendly wood modification processes, developed in order to improve wood’s natural durability and dimensional stability. Beside wood species, mainly isothermal temperature of heat-treatment and process duration affect these properties, which also correlate with the mass losses caused by the treatment. However, there is a lack of suitable external quality control methods. In this work thermogravimetry as a potential method for determining the degree of thermal modification is presented. Several calibration curves, representing the mass losses in a certain temperature range (the values obtained from the TG curves) compared to weight losses caused by previous heat-treatment (known values), were established for spruce wood samples modified at different isothermal temperatures (from 170 to 220 °C). Linear plot and good correlation factors (R ² = 0.95 and 0.96) were obtained for the TG mass losses from 130 to 280 °C and from 130 to 300 °C, both under nitrogen atmosphere. The predominant cause of mass loss in this temperature region was depolymerisation and thermal decomposition of hemicelluloses residues. Lower correlation factors were obtained under the air atmosphere and in the wider temperature range, respectively.     

Investigations of the reasons for fungal durability of heat-treated beech wood

It is generally accepted that thermal treatment of wood by mild pyrolysis (retification or torrefaction) improves its durability to fungal degradation. However, this property has recently been questioned in the literature and definitely needs further investigation. The increase in durability conferred by thermal treatment is generally explained by four hypotheses: the low affinity of heat-treated wood to water; the generation of toxic compounds during heating; the chemical modification of the main wood polymers and the degradation of hemicelluloses. This study was undertaken to understand the reasons for durability of heat-treated beech wood. In order to confirm or not the above mentioned hypotheses, the durability of heat-treated beech wood towards Coriolus versicolor was evaluated according to different parameters like mass loss, wettability or chemical composition. The heat treatment was carried out in a temperature range of 20-280 °C under inert atmosphere for 10 different temperatures. The results show clearly an important correlation between the temperature of treatment and the fungal durability. At the same time, there was insufficient evidence to support the hypothesis of improved decay resistance due to generation of fungicidal compounds or due to the hydrophobic character of wood. Finally, the most plausible hypothesis to explain improvement of wood durability concerns its chemical modifications. Indeed, degradation of hemicellulose associated with other chemical modifications appearing during treatment could be the origin of improved durability. There is a good correlation between decay resistance and mass loss measurements which are directly correlated to hemicellulose degradation.     

Kinetics of Thermal Decomposition of Solid Propellant Based on Aluminum and Ammonium Perchlorate

Kinetic regularities of the mass loss and heat and-gas release were studied in the thermal decomposition of a solid propellant composed of aluminum, ammonium perchlorate, and a polymer binder. It was shown that, under heating from 40 to 340°C under permanent vacuum conditions, propellant samples decompose without ignition, with the limiting mass loss in the decomposition being 48%. When experiments were performed in air, the propellant formulation decomposes with sharp ignition, with the inflammation temperature (270–287°C) and amount of volatiles released by this instant of time (10–16 wt %) dependent on the heating rate. The kinetic regularities of the mass loss in the decomposition of a solid propellant were described in terms of the polychromatic kinetics model that assumes that the reaction system has ensembles of particles differing in reactivity. The distribution functions of the mass fractions of the propellant by activation energies of decomposition were calculated. The heat release kinetics in the decomposition of a propellant formulation in the temperature range 153–270°C in a closed evacuated system is described by a sum of equations for two parallel reactions: 1st-order reaction with a heat effect Q₁ = 200 ± 5 kJ kg^–1 and 1st-order autocatalysis with heat effect Q₂ = 1900 ± 50 kJ kg–1. The rate constants and the activation parameters of the process were determined.

     

Heat/mass transfer characteristics and nonisothermal drying kinetics at the first stage of biomass pyrolysis

Biomass pyrolysis can be divided into three stages: moisture evaporation, main devolatilization, and continuous slight devolatilization. This present study focuses on the heat and mass transfer characteristics of biomass in the first pyrolysis stage, which takes place in the range of room temperature to 150?°C. Thermalgravimetric experiments of rice husk and cotton stalk were performed by a synchronic thermal analyzer (TG/DSC). Four nonisothermal drying models were obtained from common isothermal drying models in order to describe the drying behavior of agricultural products. The moisture content of biomass decreased rapidly as the temperature increased and an apparent water loss peak was observed in the temperature range of 65?C75?°C. DSC could be regarded as the superposition of three parts: heat flow from moisture evaporation, heat flow from the heat capacity of unevaporated moisture, and heat flow from the heat capacity of dry base biomass. The heat requirements for the dehydration of 1?kg rice husk and cotton stalk were 251 and 269?kJ, respectively. Nonisothermal drying models were evaluated based on the coefficient of determination (R ²) and reduced chi-square (??²). Page model was found to be the best for describing the nonisothermal drying kinetics. The values of activation energy were determined to be 9.2 and 15.1?kJ/mol for rice husk and cotton stalk, respectively.     

Effects of temperature and holding time during torrefaction on the pyrolysis behaviors of woody biomass

Torrefaction is the thermal treatment techniques performed at relatively low temperature (<300 °C) in an inert atmosphere, which aims to improve the fuel properties attractively. In this study, woody biomass (Leucaena leucocephala) was torrefied at various temperatures and holding times and the pyrolysis behaviors of the torrefied wood were examined in detail by using TG-MS technique. It was found that the carbon content and the calorific value of the torrefied leucaena increased significantly when temperature and holding time during the torrefaction increased. From the TG-MS analysis, the pyrolysis behaviors of the torrefied leucaena were significantly different from those of the raw leucaena. The char yield at 800 °C for the torrefied leucaena was increased when increasing the holding time during the torrefaction. On the other hand, the tar yield during the pyrolysis decreased significantly with the increase in the holding time during the torrefaction. Through the results from the TG-MS analysis, it was concluded that the structure of leucaena was changed by the torrefaction at temperature below 275 °C and the cross-linking reactions occurred during the pyrolysis resulting in increase in char yields and decrease in tar yields. It was also suggested that the longer the holding time during the torrefaction, the more the cross-linking reactions proceed during the pyrolysis. The results obtained from the study provide the basic information for the pyrolyser and/or gasifier design by using torrefied biomass as a fuel.     

Studies on ignition and afterburning processes of KClO4/Mg pyrotechnics heated in air

Thermal behavior of KClO₄/Mg pyrotechnic mixtures heated in air was investigated by thermal analysis. Effects of oxygen balance and heating rates on the TG?CDSC curves of mixtures were examined. Results showed that DSC curves of the mixtures had two exothermic processes when heated from room temperature to 700?°C, and TG curve exhibited a slight mass gain followed by a two-stage mass fall and then a significant mass increase. The exothermic peak at lower temperature and higher temperature corresponded to the ignition process and afterburning process, respectively. Under the heating rate of 10?°C?min^?1, the peak temperatures for ignition and afterburning process of stoichiometric KClO₄/Mg (58.8/41.2) was 543 and 615?°C, respectively. When Mg content increased to 50%, the peak ignition temperature decreased to 530?°C, but the second exothermic peak changed little. Reaction kinetics of the two exothermic processes for the stoichiometric mixture was calculated using Kissinger method. Apparent activation energies for ignition and afterburning process were 153.6 and 289.5?kJ?mol^?1, respectively. A five-step reaction pathway was proposed for the ignition process in air, and activation energies for each step were also calculated. These results should provide reference for formula design and safety storage of KClO₄/Mg-containing pyrotechnics.     

Curing kinetics study of melamine–urea–formaldehyde resin

The influence of the preconditioning at different temperatures on the cure kinetics of melamine?Curea?Cformaldehyde resins coated on stone wool was investigated under acidic conditions using differential scanning calorimetry and thermogravimetry. The higher pre-treatment temperature was applied, to which resin-coated stone wool was exposed, the lower was the mass loss during the experiment. Kinetic model parameters were determined in two different manners, with the parameters being independent of preconditioning temperature and dependent on the latter. The apparent orders of reaction were approximately two (all of them being within the range 0.96?C2.33), which would imply that cross-linking predominantly proceeds via the bimolecular reaction of either melamine or urea and formaldehyde. Nonetheless, the apparent orders of reaction decreased as a function of preconditioning temperature. The apparent activation energies varied less with preconditioning temperature, assuming values between 64.2 and 78.5?kJ?mol^?1. The applicability of nth-order reaction kinetic models was consequently validated for two other dynamic thermal regimes.     

Kinetics and Equilibria of Synthesized Anionic Surfactant onto Berea Sandstone

We present static adsorption studies of anionic surfactants on crushed Berea sandstone. The maximum adsorption density was 0.9604 mg/g. The kinetics of adsorption process was modeled using pseudo-first-order and pseudo-second-order rate equations at 25°C and 70°C. The equilibrium adsorption process was validated using Langmuir and Freundlich adsorption models. In addition, the effects of different parameters that govern the effectiveness of these surfactants such as pH and temperature were also investigated. The kinetic study results show that the surfactant adsorption is a time dependent process. The apparent rate constant of adsorption process determined by the first-order kinetic model at 25°C and 70°C were 0.11768 and ?0.04513, respectively. The rate constant for pseudo-second-order kinetic model was 0.0086 at 25°C and 0.0101 at 70°C. The adsorption of anionic surfactant followed pseudo-second-order kinetic model. The Freundlich and Langmuir model constant were 1.6509 × 10^?4 and ?9.775 × 10^?5, respectively. The equilibrium results showed that the adsorption of anionic surfactant onto Berea sandstone was well described by Langmuir adsorption model. It was concluded that anionic surfactants performed better at higher pH and temperature.      

Influence of torrefaction on the devolatilization and oxidation kinetics of wood

Devolatilization and oxidation kinetics of torrefied wood have been studied by evaluating thermogravimetric curves measured in nitrogen and air at various heating rates. Samples consist of Norway spruce wood chips torrefied at several process temperatures and residence times. Data about untreated wood have also been obtained for comparison. Measured curves are well predicted by means of a five-reaction mechanism, consisting of three devolatilization reactions for the pseudo-components hemicellulose, cellulose and lignin and, in air, of two additional reactions for char devolatilization and combustion. The torrefaction pre-treatment only requires model modifications in the amounts of volatiles generated from the decomposition of pseudo-components, indicating that only their relative percentages and not their reactivities are modified. On the other hand, a slightly different thermal stability is found for the char generated from torrefied wood, which results in higher activation energy and lower reaction order for the oxidation step. Hence torrefaction conditions can affect the subsequent conversion characteristics of the char product.     

Interrelations between soil respiration and its thermal stability

Biological transformation of organic matter in soil is a crucial factor affecting the global carbon cycle. In order to understand these complex processes, soils must be investigated by a combination of various methods. This study compares the dynamics of biological mineralization of soil organic matter (SOM) determined via CO₂ evolution during an 80-day laboratory incubation with their thermo-oxidative stability determined by thermogravimetry (TG). Thirty-three soil samples, originating from a wide range of geological and vegetation conditions from various German national parks were studied. The results showed a correlation between the amount and rate of respired CO₂ and thermal mass losses of air-dried, conditioned soils occurring around 100?°C with linear coefficients of determination up to R ²?=?0.85. Further, correlation of soil respiration with thermal mass losses around 260?°C confirmed previous observations. The comparison of TG profiles from incubated and non-incubated soils underlined the importance of thermal mass losses in these two temperature intervals. Incubated soils had reduced thermal mass losses above 240?°C and conversely an increased mass loss at 100?C120?°C. Furthermore, the accurate determination of soil properties by TG such as soil organic carbon content was confirmed, and it was shown that it can be applied to a wider range of carbon contents as was previously thought. It was concluded that results of thermal analysis could be a helpful starting point for estimation of soil respiration and for development of methods revealing processes in soils.     

Study of artificially degraded woods simulating natural ageing of archaeological findings

Simulation of waterlogged archaeological woods was carried out by immersion of fir and chestnut wood samples into sea water at different temperatures (room temperature and 40°C). The effects of metals in contact with woods were simulated by inserting in some specimens of the two types of wood copper or iron nails, the most important metals from the archaeological point of view. The effects of this ageing simulation on woods were studied by different characterization methods. At first we have performed gravimetric analyses, controlling the mass increase of immersed wood in function of the time of immersion and the temperature of the bath. Then, thermogravimetry, differential thermal analysis, differential scanning calorimetry in oxygen flux were used. The alteration of wood was observed by means of the peak temperatures of DTA, DTG and DSC variation and by the mass losses observed during heating, evaluated on the basis of the measured thermal data. The samples were woods powder obtained by milling. Complementary characterization of the woods was performed by evaluating the crystallinity of cellulose by means of X-ray powder diffraction. The change in colour of woods during ageing was checked by means of spectrophotometric measurements in the visible region. X-ray fluorescence was used to investigate the penetration of metals into wood samples. An artificial ageing treatment with NaOH and O₃ was also performed. Finally, a comparison between the effects of artificial alteration realised in our specimens and natural degradation observed in archaeological woods, was performed.     

Release of Terpenes from Fir Wood during Its Long-Term Use and in Thermal Treatment

Building structures made from fir wood are often attacked by wood-destroying insects for which the terpenes it contains serve as attractants. One of the possibilities for extending the lifetime of structures is to use older wood with a lower content of terpenes and/or thermally modified wood. The study evaluated the levels of terpenes in naturally aged fir wood (108, 146, 279, 287 and 390 years) and their decrease by thermal treatment (the temperature of 60 °C and 120 °C, treatment duration of 10 h). Terpenes were extracted from wood samples by hexane and?analyzed by gas-chromatography mass-spectrometry (GC-MS). The results indicate that recent fir wood contained approximately 60 times more terpenes than the oldest wood (186:3.1 mg/kg). The thermal wood treatment speeded up the release of terpenes. The temperature of 60 °C caused a loss in terpenes in the recent fir wood by 62%, the temperature of 120 °C even by >99%. After the treatment at the temperature of 60 °C the recent fir wood had approximately the same quantity of terpenes as non-thermally treated 108 year old wood, i.e., approximately 60-70 mg/kg. After the thermal treatment at the temperature of 120 °C the quantity of terpenes dropped in the recent as well as the old fir wood to minimum quantities (0.7-1.1 mg/kg). The thermal treatment can thus be used as a suitable method for the protection of fir wood from wood-destroying insects.     

Thermogravimetric analysis of cellulose insulation and determination of activation energy of its thermo‐oxidation using non‐isothermal,model‐free methods

The aim of the work was to determine the effect of heating rate on initial decomposition temperature and phases of thermal decomposition of cellulose insulation. The activation energy of thermo‐oxidation of insulation was also determined. Individual samples were heated in the air flow in the thermal range of 100°C to 500°C at rates from 1.9°C min^?1 to 20.1°C min^?1. The initial temperatures of thermal decomposition ranged from 220°C to 320°C, depending on the heating rate. Three regions of thermal decomposition were observed. The maximum rates of mass loss were measured at the temperatures between 288°C and 362°C. The activation energies, which achieved average values between 75 and 80.7 kJ mol^?1, were calculated from the obtained results by non‐isothermal, model‐free methods. Copyright © 2014 John Wiley & Sons, Ltd.     

Kinetic parameters of unsaturated polyester resin modified with poly(ε -caprolactone)

The mineral sabugalite (HAl)_0.5[(UO₂)₂(PO₄)]₂⋅8H₂O, has been studied using a combination of energy dispersive X-ray analysis, X-ray diffraction, dynamic and controlled rate thermal analysis techniques. X-ray diffraction shows that the starting material in the thermal decomposition is sabugalite and the product of the thermal treatment is a mixture of aluminium and uranyl phosphates. Four mass loss steps are observed for the dehydration of sabugalite at 48°C (temperature range 39 to 59°C), 84°C (temperature range 59 to 109°C), 127°C (temperature range 109 to 165°C) and around 270°C (temperature range 175 to 525°C) with mass losses of 2.8, 6.5, 2.3 and 4.4%, respectively, making a total mass loss of water of 16.0%. In the CRTA experiment mass loss stages were found at 60, 97, 140 and 270°C which correspond to four dehydration steps involving the loss of 2, 6, 6 and 2 moles of water. These mass losses result in the formation of four phases namely meta(I)sabugalite, meta(II)sabugalite, meta(III)sabugalite and finally uranyl phosphate and alumina phosphates. The use of a combination of dynamic and controlled rate thermal analysis techniques enabled a definitive study of the thermal decomposition of sabugalite. While the temperature ranges and the mass losses vary due to the different experimental conditions, the results of the CRTA analysis should be considered as standard data due to the quasi-equilibrium nature of the thermal decomposition process. The online version of the original article can be found at     

Improvement of Structural and Thermal Stabilities of PVC and Wood/PVC Composite by Zn and Pb Stearates,and Zeolite

Three different chemical stabilizers were introduced into neat PVC and a wood/PVC composite (containing 50 phr wood flour) to improve their thermal and structural stabilities. The changes in CIE yellowness index, polyene index, %wt loss, and decomposition temperature (T_d) were monitored. The effects of type and content of thermal stabilizers, thermal ageing time, and the presence of wood flour were our main interests. The experimental results suggested that the additions of Zn and Pb stearates into PVC and wood/PVC composite could improve the thermal stability of the PVC. At the test temperature of 177°C, the additions of Zn and Pb stearates could improve the thermal stabilities of PVC by retarding the upzipped reaction and by reducing the conjugated double bonds in PVC, Pb stearate being the most suitable for thermally stabilizing the PVC. Around the T_d range (～264°C), the addition of Zn stearate reduced the T_d value of PVC whereas that of Pb stearate had no effect on the change in T_d value. Zeolite loading could shift the T_d value of the PVC from 264 to 280°C. The addition of wood particles increased the polyene content and decreased the decomposition temperature of the PVC. The effect of wood flour on the thermal and structural changes of PVC overruled that of thermal stabilizer loading.     

Upgrading of woody biomass by torrefaction under pressure

In this study, the upgrading by torrefaction of leucaena, woody biomass, at 200–250 °C under volumetric pressure up to 4 MPa was examined. It was found that the yield of torrefied leucaena decreased with the increase in torrefaction temperature, whereas at the same temperature the yield of torrefied leucaena increased with the increase in torrefaction pressure. From the elemental analyses, the higher carbon content in torrefied leucaena can be achieved by the rising of torrefaction pressure. As large as 92.6% of carbon was recovered in the torrefied leucaena prepared at 250 °C and 4 MPa. On the other hand, the oxygen content decreased to 31.1% for the leucaena torrefied at 250 °C and 4 MPa. The higher heating value (HHV) of leucaena torrefied at high pressure increased significantly when compared to that of leucaena torrefied at atmospheric pressure. As large as 94.3% of energy yield was achieved with the mass yield of 74.4% for the torrefaction at 250 °C and 4 MPa. From the subsequent pyrolysis and combustion in TGA, leucaena torrefied under pressure showed the difference of weight decreasing curves comparing to that of leucaena torrefied at atmospheric pressure. It was found that the weight of leucaena torrefied at high pressure started to decrease at temperature lower than 200 °C. The char yield at 800 °C for the leucaena torrefied at high pressure increased with the increase in torrefaction pressure. These results suggested that the structure of leucaena was changed by the torrefaction under pressure and the cross-linking reactions during the pyrolysis were enhanced by the pressure during the torrefaction resulting in increase in char yields. The substantial increase in char combustion rate was also found for leucaena torrefied under pressure.     

Kinetic study of the pyrolysis of neoprene

Kinetics of neoprene thermal decomposition has been performed under dynamic conditions at different heating rates, between 5 and 80 °C/min in a TG apparatus. The same kinetic model has been applied simultaneously to runs performed at different heating rates and different atmospheres allowing a good correlation of the weight loss data. A mechanism based on three independent reactions has been used to model the thermal decomposition. The first reaction is of an order close to two, and the other two reactions are of order below one, similar to other plastic materials. Different alternatives for the mathematical treatment for fitting TG data were considered. The accuracy of the calculated kinetic parameters was studied by means of a sensibility analysis.     

Kinetics of Thermal Dissociation of Ammonium Metavanadate

The solid products of thermal decomposition of ammonium metavanadate can be used as catalysts in many important processes, and a knowledge of the dynamics of these processes is therefore essential. The thermal dissociation of ammonium metavanadate was studied under non-isothermal conditions in air atmosphere. This process occurred in three steps under the applied experimental conditions, and was associated with the elimination of ammonia and water below 330°C and with the formation of nitrogen oxides above 330°C. The kinetics of particular stages of (NH₄)₂OV₂0₅ decomposition was evaluated from the dynamic mass loss data by means of the integral method, with applycation of the Coats and Redfern approximation. The first stage of decomposition to ammonium hexavanadate is governed by a random nucleation model, the second step by a three-dimensional diffusion or contracting volume model, and the last stage again by a random nucleation model. The apparent activation energies found for the particular stages were 144.97, 378.31 or 184.40 and 260.65 kJ mol^?1, respectively.     

Thermal tools in the evaluation of decayed and weathered wood polymer composites prepared by in situ polymerization

This study aims to apply thermal tools in the evaluation of decayed and weathered wood polymer composites prepared by in situ polymerization with and without cross-linkers. Pinewood samples were impregnated with methyl methacrylate using glycidyl methacrylate and methacrylic acid as cross-linkers by vacuum/pressure. The polymerization was carried out in an oven at 90 °C for 10 h using benzoyl peroxide as catalyst. All samples were exposed to decay and artificial weathering tests. The characterization was performed by mass loss, color changes, optical images, wettability, thermogravimetric analysis (by means of DTG) and differential scanning calorimetry analyzes. The mass loss was higher in untreated wood in comparison with the composites, ~2.5–10 times. Cross-linked composites showed the highest resistance to fungal biodeterioration. The reduction in L*, chroma and b* confirmed loss of original yellow tones and increase in dark and dull tones of samples. The wettability was very affected by irregularities of the samples’ surface. Only DTG showed a shifting in the temperature of thermal events related to polysaccharides and lignin after exposure to decay and weathering. DTG was the best thermal technique for evaluation of decaying and weathering of wood composites.