Antimicrobial activity and chemical profile of wood vinegar from eucalyptus (Eucalyptus urophylla x Eucalyptus grandis - clone I144) and bamboo (Bambusa vulgaris)

Microbial resistance to drugs is a public health problem; therefore, there is a search for alternatives to replace conventional products with natural agents. One of the potential antimicrobial agents is wood vinegar derived from the carbonization of lignocellulosic raw materials. The objectives of the present work were to evaluate the antibacterial and antifungal action of two kinds of wood vinegar (WV), one of Eucalyptus urograndis wood and another of Bambusa vulgaris biomass, and determine their chemical profile. The antimicrobial effect was assessed against Staphylococcus aureus, Pseudomonas aeruginosa, Salmonella enteritidis, Escherichia coli, Streptococcus agalactiae, and Candida albicans. The minimum inhibitory concentration and the minimum bactericidal and fungicidal concentrations were determined. Micrographs of the microorganisms before and after exposure to both kinds of wood vinegar were obtained by scanning electron microscopy. The chemical profile of the eucalyptus and bamboo vinegar was carried out by gas chromatography and mass spectrometry (GC/MS). Both types of WV presented significant antimicrobial activity, with the bamboo one having a higher efficiency. Both studied pyroligneous extracts seem promising for developing natural antimicrobials due to their efficiency against pathogens. GC/MS analyses demonstrated that the chemical profiles of both kinds of WV were similar but with some significant differences. The major component of the eucalyptus vinegar was furfural (17.2%), while the bamboo WV was phenol (15.3%). Several compounds in both WVs have proven antimicrobial activity, such as acetic acid, furfural, phenol, cresols, guaiacol, and xylenols. Together, they are the major in the chemical composition of the organic fraction of both WVs. Bamboo vinegar had a more expressive content of organic acids. Micrographs of microorganisms taken after exposure to both kinds of wood vinegar displayed several cell modifications. The potential of both types of wood vinegar as a basis for natural antimicrobial products seems feasible due to their proven effect on inhibiting the microorganisms' growth assessed in this experiment.

Char from the co-pyrolysis of Eucalyptus wood and low-density polyethylene for use as high-quality fuel: Influence of process parameters

Providing a valuable application to the under-utilized solid residue of co-pyrolysis of biomass and plastics could substantially improve economic and environmental sustainability of the process, thereby fostering circular economy. This study focuses on the variation of thermal and physiochemical characteristics of solid char, produced from the co-pyrolysis of waste low-density polyethylene (WLDPE) and Eucalyptus wood with varying pyrolysis temperatures from 300 to 550 °C, residence times of 90-150 min, and relative percentage of 33% and 25% (w/w) WLDPE in the feedstock. The highest values of yield (37%), energy density (1.25) and high heat value (31 MJ/Kg) were observed with the char produced at 300 °C. The physical inhibition caused by the overlaying plastic coating on the surface of the char below 450 °C resulted in the same. However, with the increase in temperature, increase in fuel ratio by 78-79% and fixed carbon content by 68-69% were observed. The highest concentrations of fixed carbon (39%), fuel ratio (0.81) along with the lowest O/C and H/C ratios (0.07 and 0.13) were observed with the chars produced above 450 °C depicting their high degree of carbonization. The fuel value indices of all the chars were > 500 GJ/m³ indicating their suitability as high-quality fuels. Significant influences of residence time and feedstock ratio were also observed on properties of the char. The analysis of variance and principal component analysis also depicted significant variations in the properties of the char produced below and above the temperatures of 450 °C due to the inhibitory and synergetic effects. While the chars produced at 300-350 °C could be used for combustion/co-combustion in coal-fired boilers, chars produced above 450 °C can be opted as household fuel due to their low losses of energy, water vapour, and smoke during combustion.

Cellulose Structural Changes during Mild Torrefaction of Eucalyptus Wood

The changes in the cellulose structure of eight Eucalyptus species (E. botryoides, E. globulus, E. grandis, E. maculata, E. propinqua, E. rudis, E. saligna and E. viminalis) in a mild torrefaction (from 160 °C to 230 °C, 3 h) were studied in situ and after cellulose isolation from the wood by solid-state carbon nuclear magnetic resonance (¹³C NMR), wide angle X-ray scattering (WAXS), Fourier transform infrared spectroscopy (FTIR) and by analytic pyrolysis coupled with gas chromatography and mass spectrometry (Py-GC/MS). Changes in molecular weight were assessed by viscosimetry. A small decrease in cellulose crystallinity (ca. 2%–3%) was attributed to its amorphization on crystallite surfaces as a result of acid hydrolysis and free radical reactions resulting in the homolytic splitting of glycosidic bonds. The degree of the cellulose polymerization (DPv) decreased more than twice during the heat treatment of wood. It has been proposed that changes in the supramolecular structure of cellulose and in molecular weight during a heat treatment can be affected by the amount of lignin present in the wood. The limitations of FTIR and Py-GC/MS techniques to distinguish the minor changes in cellulose crystallinity were discussed.

Technologies for Eucalyptus wood processing in the scope of biorefineries: A comprehensive review

Eucalyptus is the most widely planted type of hardwoods, and represents an important biomass source for the production of fuels, chemicals, and materials. Its industrial benefit can be achieved by processes following the biorefinery concept, which is based on the selective separation ("fractionation") of the major components (hemicelluloses, cellulose and lignin), and on the generation of added-value from the resulting fractions. This article provides a in-depth assessment on the composition of Eucalyptus wood and a critical evaluation of selected technologies allowing its overall exploitation. These latter include treatments with organosolvents and with emerging fractionation agents (ionic liquids and deep eutectic solvents). The comparative evaluation of the diverse processing technologies is carried out in terms of degree of fractionation, yields and selectivities. The weak and strong points, challenges, and opportunities of the diverse fractionation methods are identified, focusing on the integral utilization of the feedstocks.

High Purity and Low Molecular Weight Lignin Nano-Particles Extracted from Acid-Assisted MIBK Pretreatment

A simple and economical biorefinery method, organosolv methyl isobutyl ketone (MIBK) pretreatment assisted by Lewis acid ferric trichloride hydrolysis, was proposed for fractionating the lignin from extractive-free Eucalyptus powder at the nanoscale, accompanied by another product furfural, derived from hemicellulose. Under the conditions (180 °C, 1 h) optimized based on the best yield of furfural, 40.13% of the acid-insoluble lignin (AIL) could be obtained with a high purity of 100%, a low molecular weight of 767 (M_n) and improved thermostability. The extracted lignin was characterized by its chemical structure, thermostability, homogeneity, molecular weight, and morphology as compared with milled wood lignin (MWL). The results showed significant variations in chemical structures of the extracted lignin during the pretreatment. Specifically, the aryl ether linkage and phenylcoumarans were broken severely while the resinols were more resistant. The G-type lignin was more sensitive to degradation than the S-type, and after the pretreatment, H-type lignin was formed, indicating the occurrence of a demethoxylation reaction at high temperature. Moreover, the lignin nano-particles were identified visually by AFM and TEM images. The dynamic light scattering (DLS) showed that the average diameter of the measured samples was 131.8 nm, with the polydispersity index (PDI) of 0.149. The MIBK-lignin nano-particles prepared in our laboratory exhibit high potentials in producing high functional and valuable materials for the application in wide fields.

Hydrothermal and organic-chemical treatments of eucalyptus biomass for industrial purposes

This study aimed to evaluate the promising feasibility of the hydrothermal pre-processing of eucalyptus wood and eucalyptus bark under organosolv and organic acid conditions to produce a highly concentrated cellulose feedstock. For that, particulate samples of both biomasses were heated in water solutions containing from 0 to 50%_vol/vol of ethanol and from 0 to 50 mmol.L^-1 of oxalic acid at temperatures between 140 and 180 °C. Significant differences on the thermal degradation profiles were observed for both biomasses indicating the partial hydrolysis converted them into a more homogeneous solid fraction with higher contents of cellulose. It was also observed a significant variation of the glycan content from approximately 39 to 76% for wood particles, whereas the variation for bark was from 32 to 50%. In general, the proposed pre-processing route was considered potentially feasible to concentrate the cellulose/glycan contents of eucalyptus biomasses for subsequent industrial utilization.

Combining autohydrolysis and ionic liquid microwave treatment to enhance enzymatic hydrolysis of Eucalyptus globulus wood

The combination of autohydrolysis and ionic liquid microwave treatments of eucalyptus wood have been studied to facilitate sugar production in a subsequent enzymatic hydrolysis step. Three autohydrolysis conditions (150 °C, 175 °C and 200 °C) in combination with two ionic liquid temperatures (80 °C and 120 °C) were compared in terms of chemical composition, enzymatic digestibility and sugar production. Morphology was measured (using SEM) and the biomass surface was visualized with confocal fluorescence microscopy. The synergistic cooperation of both treatments was demonstrated, enhancing cellulose accessibility. At intermediate autohydrolysis conditions (175 °C) and low ionic liquid temperature (80 °C), a glucan digestibility of 84.4% was obtained. Using SEM micrographs, fractal dimension (as a measure of biomass complexity) and lacunarity (as a measure of homogeneity) were calculated before and after pretreatment. High fractals dimensions and low lacunarities correspond to morphologically complex and homogeneous samples, that are better digested by enzyme cocktails.

Biosynthesis of silver nanoparticles using pre-hydrolysis liquor of Eucalyptus wood and its effective antimicrobial activity

Herein, we described for the first time, biosynthesis of silver nanoparticles (AgNPs) using pre-hydrolyzed liquor of Eucalyptus wood under ambient conditions. The pre-hydrolyzed liquor containing a high amount of metabolites such as polyphenols, hemicelluloses and its derivatives are mainly assisted for the reduction and stabilization process of Ag+ ions to AgNPs. The formation of AgNPs is monitored by recording the UV-vis spectrophotometer for surface plasmon resonance (SPR) peak observed at ∼415nm. The intensity of SPR increased linearly with increasing the reaction time at ambient condition. X-ray diffraction (XRD) pattern of AgNPs reveals the formation of face-centered cubic structure. Field emission electron microscopy (FESEM) and transmission electron microscopy (TEM) images show the spherical shaped particles and narrow size distribution with an average diameter of 25-30nm. The elemental analysis by energy dispersive X-ray (EDAX) analysis confirms the presence of Ag as the major amount and is found to be 82%. Analysis of the fourier transform infrared (FT-IR) spectra of the NPs revealed the presence of phytoconstituents from pre-hydrolyzed liquor adsorbed on the surface of AgNPs. Moreover, in vitro, antimicrobial activity is found to be effective for as-synthesized AgNPs on tested bacteria (viz., P. aeruginosa, S. aureus and E. coli) followed by fungus (C. oxysporum, P. chrysogenum, C. albicans and A.niger). Thus, these results suggest the use of biosynthesized AgNPs as effective growth inhibitors for various biomedical applications.

PAHs in corn grains submitted to drying with firewood

Grain drying using firewood as fuel for air heating, with direct fire, is still widely used in Brazil. The combustion of organic material, such as wood, can generate polycyclic aromatic hydrocarbons (PAHs) which are known to have carcinogenic potential. In the present work corn grain drying was carried out at three drying air temperatures: 60°C, 60/80°C and 80°C. Following the drying process, the presence and quantification of PAH in the corn grains was investigated. After extracting the PAHs of the matrix, the material was subjected to analysis by gas chromatography with mass detector. he results showed the presence of seven compounds: fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo(a)anthracene and chrysene.