Chemical Degradation Processes Research Articles

Simulation of in-Situ Chemical Membrane Degradation in the Presence of Fe and Ce Cations in Reinforced Fuel Cell Membranes

A PEM fuel cell’s durability and lifetime are affected by various degradation phenomena, among which chemical degradation of PEM material exerts the most damage. Chemical degradation of PEM occurs when reactive radicals such as hydroxyl (·OH) and hydroperoxyl (·OOH) are generated from the decomposition of hydrogen peroxide. The radicals chemically attack the main and side chains of the perfluorosulfonic acid-based PEM and change its internal chemical structure. This leads to excessive membrane thinning and pinhole formation that causes higher gas crossover and electrode shorting inside the PEM fuel cell1. The generation of harmful radicals accelerates in the presence of Fenton’s metal, such as iron (Fe)2. Evaluation of PEM fuel cell chemical degradation durability is performed using long-term pure chemical accelerated stress test (AST) under high temperature (T), low relative humidity (RH), and open circuit voltage (OCV) conditions3. Physical characterization of a membrane sample used in a fuel cell can help to visualize and assess damage incurred during an AST. These results, however, fail to encompass the formation rate of radicals and intermediate degradation products generated during the AST3. To overcome these issues, computational fluid dynamics models are developed that simulate the evolution of degraded products and predict the lifetime of PEM fuel cells4,5.The present work aims to develop an in-situ one-dimensional (1-D) transient chemical degradation model that describes reaction-transport phenomena within the membrane electrode assembly (MEA) in the presence of Fe and Ce cations. This work considers mechanically reinforced GORE-SELECT® 15 µm baseline (MemA) and chemically and mechanically reinforced 12 µm (MemB-Ce) membranes. The developed in-situ model simulates pure chemical AST operating conditions with variable Fe ion loading and follows the computational algorithms originally presented by Wong and Kjeang4. The model successfully predicted that side chain scission is followed by main chain unzipping, as reported in the literature6. The evaluation of the change in ionomer structure by chemical degradation was done by computing the temporal concentration profile of intermediate degraded ionomer species, hydrogen peroxide, and membrane thickness reduction. The 1-D model also encapsulates the concentration profile of Fe2+ and Fe3+ ions across the PEM and predicts their temporal distribution throughout the simulated AST duration under OCV conditions. It was observed that the MemA thickness decreased rapidly in the presence of Fe ions, as shown in Figure 1. The computational parameters and results were calibrated and validated using in-house AST results for MEAs with embedded Fe metallic particles, which were shown to completely dissolve during conditioning and hence treated as uniformly distributed Fe cations with an initial concentration of 900 ppm at the beginning-of-life7. The model identified a limiting Fe ion concentration limit of 100 ppm that accentuates the chemical attack. Experimentally, a low Fe concentration of 10 ppm was determined in the baseline MemA, which also reduced the membrane thickness within 1125 h of operation, as shown in Figure 1. It is known that cerium (Ce) ions can scavenge harmful radicals and increase the lifetime of PEM fuel cells8. The model, therefore, simulates the effectiveness of Ce ions in the MemB-Ce membrane and the temporal distribution of Ce3+/Ce4+ ions and shows a lower rate of membrane thickness reduction, as shown in Figure 1. The modelling framework was, therefore, able to predict PEM fuel cell lifetime in conjunction with the transport behaviour of both harmful and beneficial cations as well as their interactions during the chemical degradation process at OCV conditions. Keywords: PEM fuel cell, fuel cell durability, chemical degradation model, in-situ modelling, iron, cerium Acknowledgements This research was supported by the Natural Sciences and Engineering Research Council of Canada, Canada Foundation for Innovation, British Columbia Knowledge Development Fund, Western Economic Diversification Canada, Ballard Power Systems, and W.L. Gore & Associates. It was also undertaken in part thanks to funding from the Canada Research Chairs program. References J. Healy et al., Fuel Cells, 5, 302–308 (2005).S. Kundu, L. C. Simon, and M. W. Fowler, Polym. Degrad. Stab., 93, 214–224 (2008).Y. Singh, F. P. Orfino, M. Dutta, and E. Kjeang, J. Electrochem. Soc., 164, F1331–F1341 (2017).K. H. Wong and E. Kjeang, J. Electrochem. Soc., 161, F823–F832 (2014).R. B. Ferreira, D. S. Falcão, and A. M. F. R. Pinto, Int. J. Hydrogen Energy, 46, 1106–1120 (2021).L. Ghassemzadeh, K. D. Kreuer, J. Maier, and K. Müller, J. Phys. Chem. C, 114, 14635–14645 (2010).N. Kumar et al., ECS Meet. Abstr., MA2023-02, 1919–1919 (2023).S. M. Stewart, D. Spernjak, R. Borup, A. Datye, and F. Garzon, ECS Electrochem. Lett., 3, F19–F22 (2014). Figure 1

Intensive Spatiotemporal Characterization of the Tire Wear Toxin 6PPD Quinone in Urban Waters.

6PPDQ is a tire-derived contaminant toxic to coho salmon (LC50 = 41-95 ng/L) found widely distributed in urban environments. Most monitoring efforts have relied on relatively few discrete samples collected at select locations across rain events. Early work has revealed that 6PPDQ concentrations vary widely over time and space, raising questions about when and where to collect samples. Here, we employ condensed phase membrane introduction mass spectrometry, a high-throughput analysis approach to characterize spatiotemporal variability of 6PPDQ in urban streams. Analytical method detection limits of 0.3-8 ng/L and a duty cycle of 2.5 min/sample enabled high-throughput adaptive sampling. Temporal sampling revealed dynamic 6PPDQ concentrations, with significant changes occurring over minutes during peak rainfall. Spatial variability was characterized at multiple sites along three watercourses during the first significant precipitation of autumn 2023 on central Vancouver Island, B.C., Canada. Site-specific concentrations suggest attenuation of 6PPDQ after point source inputs by some combination of physical (dilution, sorption) or chemical (degradation) processes. This is the first report of an intensive sampling campaign describing the spatiotemporal distribution of 6PPDQ, highlighting the need for careful consideration of sampling strategies to evaluate the risk and impact of 6PPDQ in urban waterways.

Processing corn cob waste (Zea mays L) into bioethanol

Abstract As a country that requires large energy sources to meet its needs, Indonesia needs alternative energy sources to meet its energy needs. Bioethanol is an alternative energy source that can be produced using biomass which is rich in glucose, fiber and starch. Bioethanol in this research was produced through a chemical degradation process of corn cob powder using strong acid in the form of 0.3 M hydrochloric acid in three volume levels, namely 600 mL, 650 mL, and 700 mL followed by a biological degradation process using yeast for seven days. After three, five and seven days, water and bioethanol are separated through steam temperature differences. The amount of glucose contained in corn cob powder before hydrolysis was 27.25%. After hydrolysis, the largest percentage of glucose was obtained from hydrolysis with a volume of 600 ml of HCl, namely 14.7%. Likewise, the largest percentage of ethanol was also at the same volume on the fifth day of fermentation at 14%.

Environmental impact of the variations in solar reflectance index values of some selected dimension stones due to cyclic thermal shock

Natural stones are widely used environmentally appropriate building materials as dimension stone both for exterior cladding and floor coverings in urban areas. Depending on their solar reflectivity, these materials may absorb more solar radiation, especially with noontime summer sunlight exposure, which may cause both increasing cooling costs in commercial buildings and overheating of a city with the formation of urban heat islands. Solar reflectance index (SRI) is defined as the ability of a surface to reject solar heat which tends to change with physical, chemical and biological degradation processes by varying solar reflectance (SR) and thermal emissivity (TE) values. Weakening of the stone matrix structure by physical degradation mechanism, such as thermal shock (T-S) cycles mostly have significant impact on SRI. Within the scope of this study, SRI values were calculated before and after cyclic T-S by measuring the optical properties such as SR and TE values of 30 selected sedimentary and metamorphic originated carbonate-based natural stone types. The changes in surface properties such as color, roughness, and gloss, that may have an impact on the SRI values were also analyzed. In addition, a multivariate regression analysis was established to predict SRI value from such properties with a high degree of accuracy. Finally, it was found that, initial SRI values of 9 natural stone types (mostly metamorphic originated) have been increased considerably by cyclic T-S and tend to increase their ability to reduce urban temperatures by higher SRI values, one of the most important selection criteria in energy consumption for natural stones.

Study of liquid photopolymer 3D printing resins exposed to accelerated aging for cultural heritage purposes

PurposeThis paper aims to study the suitability of a selection of 3D printing liquid photopolymer resins for their application in the cultural heritage context.Design/methodology/approachThe main concerns regarding the conservation and restoration of cultural assets are the chemical composition and long-term behavior of the new materials that will be in contact with the original object. Because of this, four different LED curing resins were exposed to an accelerated aging procedure and tested to identify the materials which demonstrated a better result. Some specific properties of the material (color, glossiness, pH and volatile organic compound emissions) were measured before and after the exposure.FindingsSome of the properties measured reported good results demonstrating a decent stability against the selected aging conditions. The main changes were produced in the colorimetric aspect, probably indicating other chemical reactions in the material. Likewise, a case study could be also executed to demonstrate the usefulness of these materials in the cultural field.Research limitations/implicationsIt is necessary to study in more detail the long-lasting behavior of the materials employed with these technologies. Further analysis should be carried out highlighting the chemical composition and degradation process of the materials proposed.Originality/valueThis paper contributes to the introduction of curing 3D printing resins in the restoration methodologies of cultural assets. For this, the study of a selection of properties represents the first stage to suggest or reject their use.

SHG behavior of the solid isomorphic compounds Ni- and Cu-5,10,15,20- tetraphenylporphyrinate. An experimental and theoretical study

We prepared and investigated the SHG behavior in the solid state of the two isomorphic Nickel and Copper 5,10,15,20-tetraphenylporphyrinate, that crystallize in the same acentric I4¯2d space group. The compounds were synthesized and characterized, and the Second Harmonic Generation (SHG) response of powdered samples was measured employing a 1.907 μm pulsed laser radiation. During laser irradiation, for both compounds, a gradual increase of the intensity of the SH signal was observed until, after a few minutes, it reached a plateau of about fifty times (for the Ni-TPP) or ten times (for the Cu-TPP) the initial value. We attempted to understand the origin of this phenomenon both through experimental analysis and theoretical calculations. Absorption and vibrational spectroscopies, in solution and solid state, combined with powder X-ray diffraction, both before and after irradiation, do not evidence any chemical degradation, phase transition or amorphization process. Theoretical calculations on little fragments of the Ni/Cu-TPP structure simulate appropriately the structural features of the complexes and their initial experimental SHG response. Magnetic balance measurement in the solid state before and after irradiation, in conjunction with DFT/B3LYP optimization of excited spin states and TDDFT calculations, highlight a change in the electronic and/or spin state due to the irradiation of the complexes.

Evaluation of effective cross-area of reinforced concrete wall considering chloride diffusion using ANN

Reinforced concrete structures are subject to exposure to chloride ions in the air, leading to chloride penetration, and carbonation attacks resulting from exposure to carbon dioxide. This chemical degradation process induces corrosion of reinforcing bars within concrete, significantly impacting durability. Structures situated in coastal areas, such as nuclear power plants, are particularly susceptible to rapid chloride penetration due to the high chloride concentration in the air. This study utilizes existing experimental data to forecast the chloride diffusion coefficient employing artificial neural network (ANN technology). The total number of experimental data was 535 gathered from 18 papers. Through analysis of the chloride coefficient and predicted degradation depth, the effective cross-sectional area of concrete is examined, and the deterioration of wall performance is forecasted.

Effects of Chemicals in Reporter Gene Bioassays with Different Metabolic Activities Compared to Baseline Toxicity.

High-throughput cell-based bioassays are used for chemical screening and risk assessment. Chemical transformation processes caused by abiotic degradation or metabolization can reduce the chemical concentration or, in some cases, lead to the formation of more toxic transformation products. Unaccounted loss processes may falsify the bioassay results. Capturing the formation and effects of transformation products is important for relating the in vitro effects to in vivo. Reporter gene cell lines are believed to have low metabolic activity, but inducibility of cytochrome P450 (CYP) enzymes has been reported. Baseline toxicity is the minimal toxicity a chemical can have and is caused by the incorporation of the chemical into cell membranes. In the present study, we improved an existing baseline toxicity model based on a newly defined critical membrane burden derived from freely dissolved effect concentrations, which are directly related to the membrane concentration. Experimental effect concentrations of 94 chemicals in three bioassays (AREc32, ARE-bla and GR-bla) were compared with baseline toxicity by calculating the toxic ratio (TR). CYP activities of all cell lines were determined by using fluorescence-based assays. Only ARE-bla showed a low basal CYP activity and inducibility and AREc32 showed a low inducibility. Overall cytotoxicity was similar in all three assays despite the different metabolic activities indicating that chemical metabolism is not relevant for the cytotoxicity of the tested chemicals in these assays. Up to 28 chemicals showed specific cytotoxicity with TR > 10 in the bioassays, but baseline toxicity could explain the effects of the majority of the remaining chemicals. Seven chemicals showed TR < 0.1 indicating inaccurate physicochemical properties or experimental artifacts like chemical precipitation, volatilization, degradation, or other loss processes during the in vitro bioassay. The new baseline model can be used not only to identify specific cytotoxicity mechanisms but also to identify potential problems in the experimental performance or evaluation of the bioassay and thus improve the quality of the bioassay data.

Development of a Space Grease Lubricant with Long-Term-Storage Properties

Controlled vacuum environments as in space applications represent a challenge for the lubrication of tribological components. In addition to common space lubricant requirements like, e.g., low evaporation, a broad operational temperature range and a high stability during operation, long-term-storage (LTS) properties have gained increasing attention recently. The term addresses the time-dependent stability of a lubricant under static conditions, which can mean chemical degradation processes such as oxidation on the one hand, but also the physical separation of oil and thickener in heterogeneous lubricants like greases. Due to the extended storage periods of lubricated components on-ground but also during a space mission for several years, it has to be ensured that a lubricant is still functional after LTS. This article depicts the development of a space lubricant grease with LTS properties. Firstly, LTS requirements and methods for their assessment are discussed. In the following, a systematic approach towards the design of a grease formulation compatible with LTS is described. Finally, the manufacturing of prototype formulations and their broad characterization by means of LTS behaviour, outgassing, and tribological performance is presented.

Chemical and structural degradation of room temperature vulcanizing (RTV) silicone at high temperatures

Room temperature vulcanizing (RTV) silicone is an insulating adhesive used on thermal protection systems of space capsules. RTV materials experience significant heating during entry into an atmosphere. To understand the response of RTV materials in entry environments, RTV 511 and RTV 560 are heated in a mass spectrometer, a thermogravimetric analyzer, and a high-temperature flow tube furnace to understand the underlying chemical and structural degradation processes occurring during the decomposition of the two RTV materials. In addition, infrared spectroscopy is used to identify the functional groups and the polymer backbone configuration. X-ray computed tomography is used to create three-dimensional volumes of the decomposed samples to examine the structure of the degraded RTV materials. The three-dimensional volumes are also used to evaluate the permeability of degraded RTV materials. It is observed that both RTV materials decompose in three stages. Analysis of the three-dimensional volumes generated through X-ray computed tomography indicates that the decomposition begins with the formation of small cavities in both RTV variants. However, as the materials are subjected to higher temperatures, RTV 511 evolves into an outer solid layer with cavities inside, while the solid material in RTV 560 is distributed more homogeneously throughout the material, resulting in a structure with better mechanical integrity. Although most regions of both RTV variants are impermeable, certain regions of RTV 511 have a permeability that is two orders of magnitude higher than the permeability of the base heat shield material. The overall analysis indicates that the response of RTV materials to heat must be considered in the design and analysis of thermal protection systems.

Natural degradation of polypyrrole nanowires in NaOH solutions and its degradation kinetics

The polypyrrole (PPy) nanowires doped with p-toluenesulfonate ions (PPy/pTS NWs) are prepared and degraded in aerated and deaerated NaOH solutions (CNaOH=0.02 - 0.5 M) for different times to examine their natural degradation behavior and kinetics. After degradation, the fluffy PPy/pTS NWs network film generally exhibits a uniform natural degradation state with apparent damaged areas on the nanowires' surface, decreased nanowire diameter, and increased film thickness. The electroactivity degradation of PPy/pTS NWs still follows the first-order degradation kinetics, like the bulk-structured PPy/pTS films. The natural degradation kinetics model established from the bulk-structured PPy films is proven to apply to PPy/pTS NWs. The rate equations for the chemical and electrochemical degradation of PPy/pTS NWs in NaOH solutions are determined. Additionally, it is confirmed that the electrochemical degradation process is the dominant factor, while CNaOH significantly impacts the chemical degradation process. The structural features of PPy/pTS NWs do not alter the chemical and electrochemical degradation processes but significantly accelerate the degradation rates. This research will contribute to our understanding of the degradation kinetics of PPy nanomaterials and support their practical applications.

Recent Trends and Advancement in the Removal of Persistent Organic Pollutants from Wastewater by Hybrid Electrocoagulation Chemical Degradation Processes

Recent Trends and Advancement in the Removal of Persistent Organic Pollutants from Wastewater by Hybrid Electrocoagulation Chemical Degradation Processes

Comparison between Chemical and Biological Degradation Processes for Perfluorooctanoic Acid

Perfluorooctanoic acid (PFOA) is a perfluoro compound that contains an eight-carbon perfluoroalkyl chain followed by a carboxylic acid function group. The C-F bound possesses a strong bond energy of approximately 485 kJ/mol, rendering PFOA thermally and chemically stable. It has found applications in water-resistant coating and is produced either by degrading other long-chain perfluorinated carboxylic acids or fluorotelomer alcohol. PFOA is challenging to further degrade during water treatment processes, leading to its accumulation in natural systems and causing contamination. Research has been conducted to develop several methods for its removal from the water system, but only a few of these methods effectively degrade PFOA. This review compares the most common chemical degradation methods such as photochemical, electrochemical, and sonochemical methods, to the cutting-edge biodegradation method. The chemical degradation and biodegradation methods both involve the stepwise degradation of PFOA, with the latter capable of occurring both aerobically and anaerobically. However, the degradation efficiency of the biological process is lower when compared to the chemical process, and further research is needed to explore the biological degradation aspect.

Challenges and Prospects of Sodium‐Ion and Potassium‐Ion Batteries for Mass Production

AbstractThe exponential growth of the lithium‐ion (LIB) market is causing a significant disparity between the supply chain and demand for its resources. In this regard, sodium‐ion and potassium‐ion batteries are promising alternatives to LIBs due to their low cost. However, the larger sizes of Na+ and K+ ions create challenges that prevent them from achieving energy densities comparable to LIBs while maintaining an acceptable cycle life. In this perspective, the aim is to evaluate the status of Na‐ion and K‐ion batteries and the challenges associated with them on both fundamental and commercial levels. The focus is on the structural instability arising from phase transitions during cycling, intricate chemical degradation processes, and potential avenues for enhancing their performance with a specific goal of improving their viability for grid‐scale energy storage. Materials production and abundance limitations for the chemistries of the state‐of‐the‐art materials and account for critical parameters from both the perspective of researchers and investors are analyzed. This analysis aims to provide insights into the strategic trade‐offs required to effectively implement the technology in real‐world applications, such as grid‐scale storage and other areas. Furthermore, the utilization of metals with low or no supply‐chain problems as an important aspect of these trade‐offs is considered.

The peculiar SHG behaviour of Co-5,10,15,20-tetraphenilporphyrinate in the solid state. An experimental and theoretical study

We prepared and investigated the SHG behavior in the solid state of the Cobalt 5,10,15,20-tetraphenylporphyrinate that crystallizes in the acentric I4¯2d space group. The compound was synthesized and characterized, and the Second Harmonic Generation (SHG) response of a powdered sample was measured through a 1.907 μm pulsed laser radiation. During laser irradiation, a gradual increase of the intensity of the SH signal was observed until, after a few minutes, it reached a plateau of about fifty times the initial value. We attempted to understand the origin of this peculiar SHG behavior, both through experimental analysis and theoretical calculations. Mass spectrometry, absorption, emission, and vibrational spectroscopies in solution combined with powder X-ray diffraction analysis in solid state, both before and after irradiation, do not evidence any chemical degradation, phase transition or amorphization process. Theoretical calculations on little fragments of the Co-TPP structure simulate appropriately the structural feature of the complex and its initial experimental SHG response. UV–VIS and EPR spectra collected in the solid state before and after irradiation, in conjunction with DFT/B3LYP optimization of excited spin states and TDDFT calculation, highlight a change in the electronic and/or spin state due to the irradiation of the complex.

Enzyme activities and heavy metal interactions in calcareous soils under different land uses

This study was carried out to examine the interaction of enzyme activities, microbial biomass carbon, and CO2 respiration with heavy metals under different land uses in terms of quality and sustainability of the soil. There is a statistically significant positive correlation between dehydrogenase enzyme activity and Mn, Pb, Cd, and Co, while it was negative between Cr. There was a positive correlation between catalase enzyme activity and Mn and Pb and between urease and Co. The higher interaction of dehydrogenase activity with heavy metals, which is included in the endo enzyme group, has been explained as a much stronger effect of heavy metals on living microorganisms and endoenzymes than extracellular enzymes stabilized on clay minerals and organic matter. The high clay content of the soil is thought to reduce some of the negative effects of heavy metals on enzymes. The results of this study may be good indicators of enzyme activities, especially dehydrogenase, catalase, and urease, for soil health and quality, chemical degradation and restoration processes, and ecosystem functioning in soils contaminated or to be contaminated with heavy metals. It shows that the activities of these enzymes are very sensitive and can decrease rapidly in case of high concentrations of heavy metals.

Examining a Year-Long Chemical Degradation Process and Reaction Kinetics in Pristine and Defect-Passivated Lead Halide Perovskites

As a promising solar energy harvesting technology, solution-processed metal halide perovskites (MHPs) are of great current interest in developing low-cost and efficient photovoltaic cells. Despite their excellent optoelectronic properties and the nascent advancements in compositional tailoring and interfacial engineering to develop high-performance MHPs, issues associated with the long-term environmental stability of these materials are yet to be addressed. Here we examine the moisture-induced cascade degradation reactions over a year for methylammonium lead iodide (MAPbI3)- and formamidinium-rich [Cs0.05(MA0.17FA0.83)0.95Pb(Br0.17I0.83)3] formulations at 40 and 85% relative humidity (RH) in the air. The transformative reactions at 85% RH lead to chemical degradation process in both MA-rich and FA-rich perovskites, yielding to the different organic and inorganic byproducts within a few hours, but the exposure to 40% RH retains the longevity of these materials up to several months. The defect passivation by the tetrapropylammonium cation (TPA+) imparts enhanced stability of MAPbI3 particles, irrespective of the exposure conditions to water vapor. By resolving thin-film morphology at sub-nanometer to nanometer resolution using solid-state (ss)NMR spectroscopy and X-ray diffraction techniques, kinetics of degradation reactions and structural insights into the inorganic/organic interfaces and degradation products are obtained and compared. Our findings provide mechanistic details into the cascade degradation reactions in pristine and defect-passivated MHPs, enabling guidance for novel passivating and interfacial engineering strategies to further improve the robustness of the MHPs with respect to environmental stressors.

Degradation of Diethyl Phthalate by HO• and SO4• – in the Aqueous Phase: Mechanisms, Kinetics, and Toxicity

The chemical degradation processes of diethyl phthalate (DEP) induced by HO• and SO4• – in aqueous solution were studied in a theoretical way. Not only radical addition and H-abstraction reactions but also single-electron transfer processes of DEP were considered. The thermodynamic and kinetic results indicate that the more favorable pathways are the H abstraction occurring in aliphatic side chains for all HO•/SO4• –-initiated degradation reactions of DEP. Subsequent reaction mechanisms of crucial primary intermediates were taken into account. At 298 K, the total rate constants for DEP degradation reactions induced by HO• and SO4• – are 2.34 × 109 and 1.24 × 108 M–1 s–1, respectively. They are in accordance with the experimental data. In comparison to SO4• –, HO• has higher reactivity toward DEP in the research temperature range of 273–303 K. Considering the impact on the water eco-environment and human health, DEP and its 10 products have no bioaccumulation potential, but most products are developmentally toxic, except for (Z)-ethyl-2,5-dioxopent-3-enoate. Moreover, (Z)-ethyl-2,5-dioxopent-3-enoate is acutely toxic to fish; phthalic acid is mutagenicity positive; and we should pay more attention to them in the future.

The Return of the Smell: The Instability of Lignin’s Odor

Lignin is a major constituent of renewable plant resources. Its complete utilization is therefore a key element in a biobased economy. Lignin products can fail to be accepted commercially if they release volatile organic compounds, since they must conform to emission standards, and consumers must not reject them due to a repulsive smell. We therefore investigated low-odor kraft lignins for the stability of their volatile profiles, both on the long and the short term. With an increase in temperature, the emitted amount of volatile compounds increased, while the types of volatiles remained unchanged. The activation energy for the release was found to be in the area of physical desorption. It is therefore unlikely that chemical degradation processes contribute to the release of volatiles up to a temperature of 100 °C, and lignin can in principle be deodorized without degradation. Humidity had a stronger effect on the release of volatiles than temperature. When the relative humidity exceeded 60% or liquid water was added to a lignin powder, the detected volatiles multiplied. While we were unable to elucidate the underlying mechanism, our observations indicate a physical release, which is probably caused by the displacement of adsorbed organic molecules by water. Based on these findings, the influence of high-humidity conditions and elevated temperature must be taken into account during the development of lignin-based products to guarantee their stability.

Soil chemical attributes in areas under conversion from forest to pasture in southern Brazilian Amazon

The south of the Brazilian Amazon is one of the largest cattle-producing regions in Brazil, however, most of the pastures are in low fertility soils. Thus, cattle breeders compensate for the low production of pastures, increasing the size of the areas, generating more deforestation and burning. These practices increase the chemical degradation process of Amazonian soils, making them increasingly infertile when improperly managed. With this, the objective of the work was to evaluate the impacts caused in the chemical attributes of soils, in areas under forest-to-pasture conversion, in the south of the Brazilian Amazon. The study was carried out in the district of União Bandeirantes, in an area of forest and two areas with pastures (brachiaria and mombaça grass). In the field, soil samples were collected at two depths (0.00–0.10 and 0.10–0.20 m), to carry out chemical analyzes. Further, uni, bi and multivariate statistical analyzes were carried out, besides geostatistical analyzes were carried out to study spatial variability and management zones. The conversion of forest to pasture increased the pH and exchangeable bases levels, reducing the availability of exchangeable aluminum and potential acidity, however, it induces losses of phosphorus and organic carbon from the soil. Among the pasture environments, the mombaça grass area presented higher fertility. Greater spatial variability of chemical attributes was observed in the environment with mombaça grass, indicating greater heterogeneity in the distribution of attributes in the area. We attribute this behavior to the higher grazing intensity and the micro-reliefs in the area that direct the flow of water and nutrients.