Volume 13 Issue 4

Hemicellulosic fractions isolated from agricultural wastes (rice straw and rice husk) were investigated using expansion pretreatment and subsequent alkali extraction, which is a method that combines the advantages of extrusion and milder steam explosion. The structure of the obtained hemicellulosic samples was determined by high-performance anion-exchange chromatography (HPAEC), Fourier transform infrared spectroscopy (FT-IR), 2D heteronuclear single quantum coherence nuclear magnetic resonance (NMR) spectroscopy, and thermogravimetric analysis (TGA). The expansion pretreatment resulted in a remarkable increase in the hemicellulose extraction efficiency from the rice straw compared with that of the controlled sample, while that from the rice husk was relatively unnoticeable. It was concluded from the FT-IR, molecular weight, sugar analysis, and NMR spectra results that the molecular weights of the hemicellulosic fractions extracted with this process significantly decreased and then rose, which was probably due to the prominent degradation and then generation of condensation substances. Moreover, the obtained hemicelluloses of the rice husk had a relatively more linear polymer structure than the rice straw. Considering the extraction efficiency and composition of each component, the expansion pretreatment was confirmed to be a promising method for the comprehensive separation and utilization of agricultural wastes.

Closed-system microwave-assisted extraction was applied to extract constituents from spruce bark, using 96.6% ethanol as an extractant. The influence of the time (1 min to 20 min), temperature (60 °C, 80 °C, and 100 °C), and liquid/solid ratio (8 mL/g dry bark to 12 mL/g dry bark) on the yield of extractives was studied. The effects of all three of the factors were explained. The results revealed that the optimum conditions were a liquid/solid ratio of 12.0 mL/g dry bark, extraction temperature of 100 °C, and extraction time of 13.4 min.

Oak wood (Quercus robur L.) was subjected to cyclic thermo-mechanical treatment (CTMT). The temperature of the press platens during the CTMT was either 100 °C or 150 °C. The equilibrium moisture content and the dimensional changes of the oak wood were examined when it was exposed to 9 to 98% relative humidity at 20 °C (± 2 °C). Densified oak wood had lower equilibrium moisture content than the non-densified wood for the relative humidity ranges examined. Furthermore, when the temperature of the thermo-mechanical modification was higher, the equilibrium moisture content of the wood was lower. Thermo-mechanical modified wood was characterised by higher swelling values in the radial direction than in the tangential direction. When the temperature of the CTMT was higher, the water absorption of the wood was lower. The number of treatment cycles significantly influenced the water absorption of the oak wood at its maximum saturation. After CTMT, changes were observed in oak wood, in particular, with regards to soluble substances in 1% NaOH and to chloroform-ethanol extractives.

Sodium xylenesulphonate (SXS) was evaluated in wood chip pretreatment in order to improve the quality and the properties of bleached eucalypt kraft pulp. First, the chips were subjected to pretreatment with SXS, and then the pretreated chips were cooked by the kraft process. The resulting pulp was subjected to oxygen-delignification and then to bleaching. Various bleached pulp properties, such as fiber morphology, physical, optical and mechanical strength, were measured. The pulp from the SXS pretreated chips had higher lignin removal efficiency in oxygen delignification, which resulted in higher bleachability and lower bleach consumption compared with the reference pulp. The physical and optical properties of the pulp from the SXS pretreated chips had higher drainability, capillarity water absorption, specific volume, roughness, and opacity versus the reference pulp. These observations indicated that the pretreated pulp has the potential to be used in tissue pulp grades. However, the pulp obtained from the SXS pretreated chips had lower mechanical strength properties than the reference pulp. In sum, SXS chip pretreatment can be used to produce a pulp that has high bleachability and is suitable for tissue grades.

To evaluate the influence of ultrasound-assisted extraction (UAE) on the physicochemical characteristics of wood, UAE and Soxhlet extraction (SE) were used to treat Eucalyptus. In UAE, ultrasound with a frequency of 40 kHz and an intensity of 360 W was performed at 60 °C for 30 min. Comparison of UAE samples with Soxhlet-extracted and untreated samples indicated that both the extraction and cavitation effects of ultrasound played a significant role in the efficient alteration of wood characteristics. Identification of extractives by gas chromatography-mass spectrometry (GC/MS) suggested the presence of more low- and high-volatility components in UAE, whereas SE mainly consisted of moderate-volatility components. In thermogravimetry (TG) analysis, UAE samples obtained the highest maximum mass-loss rate (-52.1%/min) at the lowest temperature (378.4 °C). Volatile profiles obtained by thermogravimetry-infrared spectroscopy (TG-FTIR) indicated that CO and CH4 increased, whereas CO2 and formic acid decreased during pyrolysis after UAE. The release of CO and methanol components was mainly influenced by extraction; however, the emission of CO2, CH4, and formic acid responded more strongly to the effects of ultrasound. Scanning electron microscopy (SEM) images revealed that the fracture of pit membranes and small protuberances on the surface of the residues reflected the effects of ultrasound.

Lignin was extracted from eucalyptus, Pinus koraiensis, and bagasse (representatives for hardwood, softwood, and Gramineae, respectively) black liquors to quantitatively distinguish the pollution loads caused by lignin. The results indicated that the actual common chemical oxygen demand (CODCr) of lignin was lower than the theoretical CODCr with an actual oxidative ratio of approximately 85%. The results also showed that 1 kg of lignin from eucalyptus, P. koraiensis, and bagasse could produce CODCr pollution loads of 1.476 kg, 1.540 kg, and 1.561 kg, respectively, which revealed the large contribution of lignin to the pollution load. Through the elemental analysis, infrared spectroscopy, and nuclear magnetic resonance analysis in the hydrogen and carbon spectra of the different lignin, it was found that guaiacyl structures in the lignin units can lead to a better thermal stability for P. koraiensis. Compared with the P. koraiensis and bagasse lignins, the eucalyptus lignin had a higher elemental oxygen content and lower molecular weight with mainly syringyl structures, which resulted in a higher reaction activity.

Tannin-based adhesives are alternative bio-based products that can be used in the wood panel industry instead of synthetic adhesives that contain formaldehyde. For the production of these adhesives, formaldehyde is utilized generally as a hardener as in its synthetic counterparts. In this study, adhesive formulations were prepared using eight different hardeners and tannin powder from Turkish red pine (Pinus brutia) barks. While the shortest gel time values in the adhesive formulations were identified in the samples prepared with formaldehyde and paraformaldehyde, the longest gel time was obtained in the formulation prepared with tris(hydroxymethyl)nitromethane. As a result of the dry bonding tests, the values closest to the commercial UF adhesive were found in descending order as paraformaldehyde, formaldehyde, hexamine glyoxal, and poly[(phenyl isocyanate)-co-formaldehyde] (pMDI). According to the wet bonding strength test results, the adhesive samples in which furfural, tris(hydroxymethyl)nitromethane, and benzaldehyde were used as hardeners did not achieve wet bonding strength. As a result of thermogravimetric analysis (TGA), commercial UF adhesive samples had dramatically lower thermal stability than all of the formulations prepared with tannin. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectral analysis revealed that new chemical bonds were established between the tannin and hardeners.

Using the Dou-gong brackets on the column of the Tianwang Palace in the Baosheng Temple from the Ming Dynasty as the research object, an experimental study was conducted on 15 groups of shaking table tests of a full-scale Dou-gong specimen made of Douglas fir. Through the analysis of dynamic magnification coefficient trends, the process of displacement characteristics of the Dou-gong in response to changes of vibration, and the rotary and sliding displacement values for each part of the Dou-gong at the largest deformation moments, major conclusions were drawn as follows. A higher vibration excitation intensity input resulted in a stronger damping effect of the Dou-gong model. The maximum deformation of each member had a strong correlation with the maximum deformation of the whole structure, among which the rotary deformation of the Lu-dou and Hua-gong occupied a dominant position. The Hua-gong with Ang, one special part of the Dou-gong, had relatively weak connection nodes during the tests; therefore more attention and relevant reinforcement measures should be taken on this part in the maintenance and conservation of cultural relics.

A biomass-based fly ash was fractionated and ground to produce fly ash adsorbents of various compositions and particle sizes. It was determined that grinding had no noticeable impact on the surface area and micropore volume of the fly ash, but it increased the mesopore volume of the fly ash remarkably. Isotherm analysis on the lignin and chemical oxygen demand (COD) removals from a thermomechanical pulping (TMP) pressate (i.e., spent liquor) was performed. It was determined that the adsorption process followed the Freundlich model, and the estimated maximum adsorption capacities for the lignin and COD on the fly ash were identified. The highest adsorption capacities for the COD and lignin were 204 mg fly ash/g TMP pressate and 149 mg fly ash/g TMP pressate, respectively, which were achieved under the treatment conditions of 298 K, 100 rpm when mixing the fly ash and pressate for 24 h. The potential impact of various physicochemical properties, such as the ionic strength and metals content of the fly ash, on the adsorption capacity for lignin and COD was also evaluated.

Graphene oxide (GO)-based nanofiltration (NF) membranes have simple fabrication and excellent performance in broad applications. However, the tight stacking of GO lamellae leads to low water flux. In this study, the interlamellar spacing of GO was increased by intercalating carboxyl-modified nano-crystalline cellulose (CCNC) to increase the membrane flux, which were prepared using vacuum filtration self-assembly. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images showed that GO and CCNC uniformly covered the holes of the substrate membrane. The maximum water flux of the CCNC-intercalated graphene oxide nanofiltration membrane was 12.74 L m⁻² h⁻¹ bar⁻¹, which is higher than most commercial nanofiltration membranes. The membrane attained high rejection rates for organic dyes with various charges (≥ 95% for sunset yellow (SY) and ≥ 90% for methylene blue (MB) and rhodamine B (Rh B)). In contrast, the negative GO-CCNC membrane showed a moderate rejection ratio for salt ions (e.g., 80.6% for Na₂SO₄ and 75.5% for MgSO₄). The antifouling property of the GO-CCNC nanofiltration membrane was tested using 1 g L^-1 bovine serum albumin (BSA) solution. The membrane intercalated with CCNC showed better antifouling performance. The pure water flux of the membrane was recovered by more than 90% by washing.