Research Articles

Luffa cylindrica plant fiber is a new biodegradable engineering material. However, the dynamic behaviors of these new green materials or their composites should be explored to consider them for practical applications. The dynamic characteristics including modal behavior and the elastic and sound isolation properties of luffa-based bio-composite plates were explored in this study. Structural frequency response function measurements were conducted using a few luffa bio-composite plates to identify their modal behavior. The modal frequencies and loss factors of the luffa bio-composite plates were identified by analyzing the frequency response function measurements using a few modal analysis methods such as half-power, circle-fit, and line-fit. The same luffa bio-composite structures were modelled using a finite element formulation with damping capability, and the elastic moduli of the composite plates were identified. In addition, the transmission loss levels of the same luffa composite samples were measured using the impedance tube method. The results showed that luffa composite structures have considerably high stiffness (elasticity modulus: 2.5 GPa), damping levels (loss factor: 2.6%), and transmission loss level (25 to 30 dB for a 1 cm thickness), and their mechanical properties are promising as an alternative disposable material for noise and vibration control engineering applications.

To investigate the fire-retardant properties of intumescent fire-retardant coatings of wood modified by different zeolites, tests were conducted by a cone calorimeter with poplar samples whose surfaces were covered by an intumescent fire-retardant coating modified by 3A, 4A, 5A, 13X zeolites, respectively. Results indicated that the ignition time (TTI) of the intumescent fire-retardant coating modified by 3A zeolite was prolonged 120 s, while the total smoke production (TSP) increased 60.1% as compared with the untreated group. The intumescent fire-retardant coating modified by the 13X zeolite had a smaller smoke production rate (SPR) and was the last to reach the peak-SPR. Its TSP remained in a very low state until 410 s and decreased 25%. Thus, 3A zeolite and 13X zeolite were of complementarily synergistic effects on improving the fire-retardant properties of an intumescent fire-retardant coating for wood. This paper suggested the alternative types of zeolites for flame-retardant coatings.

Arundo donax is a cane species with high growing productivity, and it is becoming an important source of biomass. The main objective of this study was to obtain fibreboards with high mechanical performance from A. donax without any added adhesive. Boards made without adhesive are free from formaldehyde emissions and consume no fossil resources. The characteristics of the obtained boards depended on the original material, steam explosion pre-treatments, and forming conditions (pressure, temperature, and pressing time). Production parameters were optimized. The effect of forming pressure on the physical and mechanical properties density, elastic modulus (MOE), modulus of rupture (MOR), tensile strength perpendicular to the faces (IB), thickness swelling, and water absorption of the obtained boards was studied. The European Norms (EN) methodologies were used to test the board specifications. Density, MOE, and MOR were modelled by a double reciprocal function. TS and WA were modelled with a reciprocal function in X. The boards obtained met and sometimes exceeded the requirements of these standards for the most demanding structural use.

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.