Volume 12 Issue 3

Waste paper was studied as a potential source for lipid production using the oleaginous yeast Cryptococcus curvatus for the first time. Three common types of waste paper, office paper, newspaper, and cardboard, were directly hydrolyzed by an enzyme cocktail to generate sugar-rich and nitrogen-limited hydrolysates. When these hydrolysates were used without any auxiliary nutrients by C. curvatus, the lipid content and lipid yield were higher than 50% and 200 mg/g, respectively. The nitrogen-rich enzyme cocktail exerted no negative effects on lipid production. Moreover, the integrated processes of enzymatic hydrolysis and lipid fermentation achieved comparable lipid yield to the separate hydrolysis and lipid production process. The resulting lipid samples had similar fatty acid compositional profiles to those of vegetable oils, which suggested their potential for biodiesel production. These findings strongly supported waste paper as appealing substrates for lipid production via oleaginous yeast, which provided cost-effective waste paper-to-lipids routes for sustainable biodiesel production.

This study evaluates the microscopic changes of paulownia solid wood panels subjected to thermal compression via characterizing the changes in wood microstructure. The panels, with dimensions of 500 mm × 100 mm × 20 mm, were hot-pressed in a tangential direction by using a laboratory-type hot press at a temperature of either 150 °C or 170 °C and a pressure of 2 MPa for 45 min. Microscopic investigations conducted by light microscopy showed that slightly more damage occurred in the samples compressed at 170 °C and 2 MPa than at 150 °C and 2 MPa, and that the distribution of deformation in the panels was not uniform in the growth rings of the two treatment groups. The cell collapse was not observed in the microstructure of paulownia wood after the thermal compression. Cell shapes and their arrangement in the growth ring alongside loading direction were interpreted as effective factors governing the non-uniform distribution of damage and the lack of cell collapse in the microstructure.

Bamboo filament, a material often used for indoor decoration, should be treated with flame retardants for safe use. This study evaluated the effects of different boron fire retardants on the heat release and smoke release of bamboo filaments and untreated samples via a cone analysis. A thermogravimetric analyzer (TA) instrument was used to investigate the fire retardant mechanisms of the different boron compounds. The results showed that compared to the untreated samples, fire retardants that contained boric acid or borax effectively reduced the heat and smoke release from the bamboo filament. The effects of the different ingredients in the fire retardant on the combustion process were quite different. During the combustion process, borax displayed better performance for restraining the heat release rate than boric acid, while for the total amount of heat release and the smoke suspension performance, the result was the converse. The excellent synergistic effect could be obtained by a mixture that contained a reasonable proportion of boric acid and borax (Boric Acid:Borax = 1:1). In the pyrolysis process, boric acid had stronger catalytic dehydration, while the mass loss in the treated samples with boric acid or higher proportions of boric acid was less than the loss in the borax-treated samples.

Ethanol organosolv lignin separated from bamboo was depolymerized by low-power microwave radiation (~80 W) using ethanol as a swelling agent and formic acid as a hydrogen donor solvent. After increasing the temperature from 100 to 200 °C, the total amount of phenolic compounds in the products increased from 8.1% to 40.8%, and both the weight average molecular weight (Mw) and number average molecular weight (Mn) of the products from the lignin depolymerization decreased. With extended reaction time from 20 to 60 min, the total amount of phenolic compounds and molecular weight did not remarkably change. In addition, Fourier transform infrared (FT-IR) spectroscopy showed that oxidative fracture was the primary way that lignin depolymerized. The severity factor played an important role in converting lignin into small molecular substances, and the evaluation showed that the microwave temperature was more influential on the lignin depolymerization than the reaction time. Because depolymerization and repolymerization of fragments both occurred during the microwave radiation process, it is critical to inhibit repolymerization of degraded fragments for the efficient degradation of lignin. This study not only provides a theoretical basis for studying the mechanism of microwave-assisted lignin degradation but is also important for the determination of a cost-effective lignin depolymerization method.

Arundo donax was used to investigate the effect of the enzyme and substrate concentrations on hydrolysis, pre-hydrolysis and simultaneous saccharification and fermentation (PSSF), in comparison to simultaneous saccharification and fermentation (SSF). Hydrolysis was performed at 37 and 50 °C. At the highest biomass (10%) and enzyme (69.6 FPU/g cellulose) loadings, the highest glucose concentration (32.4 g/L) was obtained (at 50 °C). SSF resulted in a cellulose conversion (91.9%) and an ethanol concentration (19.8 g/L) higher than what was obtained using PSSF at 37 °C (86.9% and 18.8 g/L, respectively) and PSSF at 50 °C (81.6% and 17.7 g/L, respectively). A positive correlation between the cellulase concentration, cellulose conversion, and ethanol content was observed. In PSSF, the increase in the solids loadings caused a reduction in the % cellulose conversion, but the ethanol concentration in PSSF and SSF increased. SSF appeared to be the most advantageous process for bioethanol production from A. donax.

The low content of phenolic groups limits the application of lignin-based materials as biosorbents for the removal of metal ions. In this work, a novel gallic acid-grafted-lignin (GAL, 4.43 mmol/g hydroxyl group) biosorbent was designed by introducing gallic acid moieties to replace the hydroxyl groups of lignin. These grafted polyphenolic groups provide additional sites for the adsorption of metal ions. The structure of GAL was characterized by FT-IR, 31P NMR, and 13C NMR spectroscopy. The adsorption properties of GAL for Pb(II) ions were investigated under batch conditions. Kinetic and isothermal adsorption processes could be well-described by the pseudo-second order kinetic model and Langmuir isothermal model, respectively. The grafting of polyphenolic groups onto lignin increased the maximum adsorption capacity of the adsorbent for Pb(II) (119.1 mg/g). The adsorption thermodynamics indicated that the adsorption process was endothermic and spontaneous. In addition, GAL could selectively adsorb Pb(II) with a selectivity coefficient (k) at 1.89 in the presence of coexisting metal ions from aqueous solution. The high adsorption capacity and selectivity for Pb(II) by GAL, together with its environmental compatibility, enable this material to act as a promising biosorbent for removing heavy metal ions from polluted water.

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.