Volume 12 Issue 3

Hydrogels from alkali lignin were prepared and shown to display unique swelling. Variable lignin contents (6.25%, 10.00%, 12.50%, and 14.29%) were successfully grafted with both N,N’-methylenebisacrylamide (MBA) and acrylamide (AM). Ionic liquids such as 1-ethyl-3-methylimidazolium acetate ([Emim]Ac) were used to avoid harsh, unfriendly solvents. All materials were characterized using X-ray diffraction (XRD) FT-IR spectroscopy, scanning electron microscope (SEM), thermogravimetric analysis (TGA), and swellability. The swelling behaviors of the hydrogels were noticeably influenced by their lignin content. The degree of equilibrium swelling (the maximum swelling degree) decreased with increasing content of lignin. The highest swelling degree (1,650%) was obtained at 6.25 wt% lignin. Kinetics revealed that the swelling behaviors of hydrogels were well-fitted by the Schott model.

The dissolution of cellulose is an important pretreatment method required for some of its catalytic conversion processes. Morpholinium-based ionic liquids (ILs) are challenging solvent choices available for “greener” and “cheaper” dissolution of cellulose. In this study, morpholinium-based ILs were prepared, and their influencing factors were experimentally investigated. The unique bipolar chemical structure derived from oxygen (electron-rich center) and nitrogen (electron-poor center) considerably enhanced the Hammett acidity function (H0) of task-ILs. N-Methyl-N-allyl-morpholinium acetate IL showed the highest H0 (2.324) and polarizability power (1.096). The anion of ILs determined the hydrogen bond basicity (β). The acetate anion contributed to β (0.88) values. As to fluid properties, the morpholinium-based ILs exhibited much lower viscosity. The properties of ILs improved the dissolution efficiency. The cellulose was directly dissolved in morpholinium-based Ils, and no other derivatives were formed. The cations and the anions of ILs studied reacted with oxygen and hydrogen atoms on the hydroxyl groups of cellulose, respectively.

The combustion and thermal characteristics of fire retardant-treated pine (Pinus densiflora) were evaluated according to the KS F ISO 5660-1 (2003) standard, using a cone calorimeter. The specimens were treated with fire-retardant chemical compounds using pressure-impregnation equipment to reliably impregnate the compounds inside the wood. The heat release rate value of the fire retardant-treated wood specimens showed that the heat release time was delayed. A reduction of the total heat release value can indicate that fire was prevented from igniting in the materials during combustion. The microstructures of natural specimen and treated fire-retardant chemical compounds specimen were determined by scanning electron microscopy. It also confirmed that the pressure-impregnation processing method was effective in comparison to the other treatment methods.

The effects of torrefaction under an oxidizing atmosphere on the physicochemical properties of patula pine wood chips were studied. Raw and torrefied pine were characterized to evaluate the effect of temperature and residence time on biofuel properties, such as bulk density, equivalent Hardgrove grindability index (HGIeq), ultimate and proximate analyses, heating value, and fuel value index (FVI). In contrast, the torrefaction process was characterized by mass and energy yields, and by the energy-mass co-benefit index (EMCI). Torrefaction was performed in a rotary kiln at temperatures between 180 °C and 240 °C during residence times between 30 min and 120 min. The torrefaction process under an oxidizing atmosphere tended to increase the fixed carbon/volatile matter ratio (from 0.19 to 2.5), while the H/C and O/C atomic ratios decreased 73% and 55%, respectively. The best properties of wood reached in the experimental plan were obtained at 210 °C during 75 min. For this torrefaction condition, energy yield, FVI, and EMCI were 85.91%, 1.91 MJ/cm³, and 4.41%, respectively. Additionally, the lower heating value for torrefied pine (18.65 MJ/kg) was higher than for the raw material (17.76 MJ/kg), and the HGIeq was 17% greater, which resulted in a better grindability behavior.

The kinetics of cellulase saccharification of corn stover (CS) after pretreatment by lignin peroxidase (LiP) and H2O2 was modeled in this work. The Impeded Michaelis model was applied in fitting all experimental data. The model gave the initial activity and accessibility of the enzyme on the substrate (Kobs,0) and the gradual loss of enzyme activity (Ki). The maximum Ytrs (55.56%) was obtained at pH 4.7, 48.6 °C, a 1.5% cellulase, and 12.4:1 water-to-material ratio. The binary quadratic model provide a good fit of the data on Ytrs and of the model parameters Kobs,0 and Ki. The results showed that Ytrs was positively correlated with Kobs,0 and negatively correlated with Ki. This study laid a foundation for improving the cellulase saccharification efficiency of lignocellulosic biomass after pretreatment by H2O2 and LiP.

From the perspective of bio-refinery, sulfurous acid (H2SO3) treatment of lignocellulosic biomass is attractive because of its ability to act both as an acid catalyst and as a sulfonation agent. Therefore, its capability to hydrolyze polysaccharides (especially glucan) into monosaccharides was compared with two other acids, hydrochloric and sulfuric acids. The decomposition of methyl α-D-glucopyranoside (MGPα) in these three acids, hydrochloric, sulfuric, and sulfurous acids were studied. In addition, p-creosol and vanillyl alcohol were introduced to check whether it is possible to convert polysaccharides (such as hemicelluloses) into monosaccharides during the sulfurous acid treatment. The results showed that the decomposition of MGPα is much slower in H2SO3 than in HCl and H2SO4. The ligninsulfonic acid resulting from the lignin sulfonation reaction can be expected to improve the efficiency of hydrolysis of polysaccharides into monosaccharides during sulfurous acid treatment. Moreover, a higher actual yield of glucose was obtained in this case than in the other two acids.

The investigations presented in this article include a comparative study of static and fatigue four-point flexural tests performed for sandwich composites. The investigated composites consisted of a glass-epoxy laminate as a cladding material and core materials, such as synthetic foams and natural cork agglomerates, in different densities. The sandwich composites were prepared with the vacuum bagging method using the same resin, reinforcement, and additives. Although using cork agglomerate in sandwich composites instead of synthetic foam resulted in a decrease of the static flexural strength in such composites, it increased their resistance to fatigue cycles considerably and benefitted their eco-friendly image. However, only the reproducibility of all the factors in the production process and testing of composites allows a direct comparison of their test results to be made.