Research Articles

Lignin is an amorphous polymer that limits the enzymatic conversion of polysaccharides to fermentable sugars. Thus, a pretreatment that can enhance the accessibility of carbohydrates is a key step of successful biofuel conversion schemes. In this study, corn stover was fractioned into stem, cob, and leaf because their lignin is different. To elucidate the lignin changes, autohydrolysis, diluted acid, and alkali pretreatments were applied on the samples, followed by the isolation of cellulolytic enzyme lignin preparations. Alkaline nitrobenzene oxidation, 13C-Nuclear Magnetic Resonance (NMR), and 1H-13C heteronuclear single quantum coherence NMR were used to profile the lignin changes. The results indicated that corn stover lignin is a p-hydroxyphenyl-guaiacyl-syringyl-type lignin that incorporates p-coumarate and ferulate esters. The β-aryl-ether was the most abundant inter-unit linkage, followed by condensed linkages, e.g. pino-/syringaresinol, phenylcoumaran, and spirodienone. As for the non-pretreated samples, leaf lignin was more condensed than stem lignin and cob lignin. More lignin was removed by the alkali pretreatment due to more cleavage of β-aryl-ether linkages. As a comparison, more condensed linkages were generated by the acidic pretreatments. The decrease of the syringyl/guaiacyl ratio indicated that the residual lignin became more condensed and confirmed that guaiacyl and p-hydroxyphenyl units were more stable than syringyl units during the pretreatment.

Plywood can be used in the furniture industry and in civil construction due to its structural strength. However, for long useful life in construction, especially in tropical countries, it needs to undergo treatments against xylophagous organisms. The most common preservative treatment is the chemical chromated copper arsenate (CCA); there are alternatives, such as heat treatment, that do not use chemicals. The objective of this work was to evaluate the mechanical resistance of CCA and heat-treated plywood prepared at three different temperatures (160 °C, 180 °C, and 200 °C). Pinus taeda plywood with seven veneers and phenol-formaldehyde adhesive was produced and subjected to the preservative treatments. The results showed that the CCA treatment reduced the mechanical strength of the panels, while the heat treatment did not. Heat treatment also decreased panel hygroscopicity, indicating a better dimensional stability.

The density profile, mechanical properties, strength potential index, and microstructure changes of hybrid poplar were investigated before and after high-pressure (HP) treatments. The results of density profile indicated that a high uniform density distribution was developed inside the pressurized wood samples. The mechanical properties results showed that the HP treatments significantly increased (P < 0.05) the modulus of elasticity (MOE), the modulus of rupture (MOR), and the Brinell hardness (BH) of the densified wood at selected conditions. Of all the wood samples, the compressed wood at 150 MPa condition possessed the highest density and strength properties. Considering the variation in strength properties along with density, it can be concluded that the compression destruction degree of HP treatment was comparable with that caused by optimized thermal compression technique based on the strength potential index results. The integrity of wood cells presented in scanning electron microscopy results demonstrated the compression of wood cell wall achieved by HP treatment without causing any fractures, which further indicated that HP treatment is a less destructive compression technology. Based on this research, HP treatment has great potential to be applied in wood densification for commercial use.

The hemicellulose content in holocellulose was adjusted by an alkaline treatment. The effects of this treatment on the defibrillation efficiency of holocellulose nanofibrils (HCNFs) were investigated by wet disk-milling (WDM), along with their morphological and physical properties. In addition, the tensile properties of nanopaper sheets fabricated with these HCNFs were investigated. As the hemicellulose content decreased, the average diameter and the filtration time of the HCNFs decreased, whereas specific surface area and crystallinity index increased. An increase in the WDM time reduced the average diameter and crystallinity of the HCNFs and increased their filtration time and specific surface area. The tensile strength and elastic modulus of the nanopaper sheets increased with increased hemicellulose content and WMD time.

Durability is a very important property of currency and currency paper because currency is circulated in the public for a very long time. The effect of circulation time on the physical properties of currency was investigated. In addition, a crumpling treatment procedure was adopted to simulate the circulation of currency in public. The air permeance of currency that was subjected to eight rounds of crumpling treatment was compared with that of actual circulated currency. As the circulation time increased, the basis weight, thickness, air permeance, and b* value increased. On the other hand, the stiffness and the L* value decreased as the circulation time increased. Regarding the air permeance, the slope of the plot was greater than the slopes of other physical properties measured. Air permeance of the samples after the crumpling treatment was greater than that of the circulated currency, which indicated that the crumpling process resulted in more severe changes in air permeance than the crumpling that occurs during the actual circulation of currency.

The effects of different kinds (cotton stalk, rice husk, and sawdust) and proportions (0%, 10%, 20%, and 30% based on weight) of biomass and operating conditions (temperature and excess air coefficient) were evaluated relative to the ash deposition characteristics during the co-firing of Huang Ling (HL) coal with biomass. The experiments were performed in a drop-tube furnace. The chemical compositions and mineral phase characteristics of the collected ash particles were analyzed using scanning electron microscopy with energy dispersive X-ray (SEM-EDX) and X-ray diffraction (XRD), respectively. The results showed that the most severe agglomeration, from co-firing coal with cotton stalk, was due to the higher content of alkali metals, especially K. The amount of K in the ash increased with an increasing proportion of cotton stalk, and ultimately, agglomeration was more serious. When the combustion temperature increased from 1050 °C to 1300 °C, the dystectic solid compounds were transformed into eutectic compounds. The increased excess air coefficient accelerated the sulfur reaction, but did not relieve the heavy sintering. Consequently, limiting the content of biomass in the fuel blends, maintaining a lower combustion temperature, and a suitable level of excess air were determined to be necessary for the co-firing of coal and biomass.

Liquid hot water (LHW) and alkali-promoted LHW pretreatments of wheat straw were comparatively studied at temperatures from 100 °C to 180 °C to investigate their ethanol production and pentose recovery. An amount of 4.52 g/L ethanol was obtained by fermentation from the synergistic substrate treated with LHW under optimal temperature (140 ºC) and enzymatic hydrolysis (EH). Under these conditions, the recovery rate of pentose was 48.8% and 58.1% for xylose and arabinose, respectively. After the pretreatment and bioconversion processes, 20.3% cellulose, 10.5% xylan, and 19.5% lignin remained solid. The alkali promoter introduced into LHW enhanced the bioconversion efficiency of the substrate, which resulted in 5.82 g/L ethanol, and 57.5% xylose and 59.0% arabinose recovery, respectively. The results from this study contributed an effective manner for co-production of ethanol and pentose, enlarging the utilization efficiency of carbohydrates.

The effects of chemical pretreatments (dilute H2SO4, dilute NaOH, and NH4OH) and biological pretreatments (Coriolus versicolor and Daedalea quercina) on the enzymatic hydrolysis of Eucalyptus were investigated. The results showed that Eucalyptus obtained from different regions possess similar chemical compositions and that the optimum particle sizes for reducing sugar production were 60- to 80-mesh. Contrary to the negative influences of a dilute H2SO4 pretreatment, an alkali pretreatment showed positive effects on Eucalyptus saccharification. This phenomenon may had been attributed to the efficient removal of lignin and the stronger structural damage during the alkali pretreatment process. In comparison with the chemical pretreatments, a higher reducing sugar yield could be achieved from the biological pretreated Eucalyptus. The highest reducing sugar yield of 97.14 mg/g was obtained from the Guangxi (GX) Eucalyptus that was pretreated with Daedalea quercina.

The aim of this study was to investigate the changes that occur in the molecular form and surface morphology of aged biochar and to explore the dynamics of aging in various types of soil. For this purpose, the biochar was rice hull heated to 500 °C for 30 min. Approximately 15% of fresh biochar was incubated in either acidic red soil, weak alkaline sandy soil, or alkaline coastal solonchak for 1 and 13 months. Aged biochars incubated without soil were also prepared. The characteristics of fresh biochar and aged biochar were analyzed in terms of elemental composition, specific surface area, and pore size, together with scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The results for aged biochar relative to fresh biochar included: (1) decreased carbon and nitrogen contents; (2) reduced pH values which tended to be neutral; (3) reduced porosity and specific surface area (Brunauer-Emmett-Teller, BET), depending on incubation environment; and (4) increased oxygen-containing functional groups on the surface. In general, the surface characteristics of the aged biochar were changed and varied with soil type.

The lipophilic colloidal substances (CS) in papermaking white water mainly originate from sizing agents applied during paper manufacturing operations and wood extractives, such as resin acids and fatty acids. In this study, the aqueous dispersions of sodium resinate and sodium stearate were used to simulate the colloidal substances concentrated in white water. The aggregation process and mechanism of pitch deposits developed from soluble colloidal particles were investigated by the determination of turbidity and zeta potential of colloidal substances simulacra dispersions as a function of Ca2+ concentration, as well as through morphological observation, structural characterization, and contact angle measurement of calcium-induced pitch deposits. The results showed that the micelles with hydrophilic groups extending in the water could be formed when the colloidal substances accumulated to a certain concentration. The Ca2+ can exchange Na+ of colloidal substance micelles, and hydrophobic pitch deposits can then be produced by either particle-particle collision or “layer by layer” adsorption with addition of Ca2+, or by both of the mechanisms mentioned above. The complete destabilization of the colloidal substance simulacra occurred when the Ca2+ concentration reached 5 mmol/L. The initial contact angles of water on the surfaces of calcium resinate and calcium stearate discs were 90.2° and 96.0°, respectively.