Research Articles

Response surface methodology (RSM) based on the 2³ factorial central composite design (CCD) was used to optimize the biotechnological conditions for growth and protein production by a selected fungal strain Geotrichum candidum MIUG 2.15, by solid-state cultivation on a semisolid medium based on a mixture of paper residues, i.e. office paper, newspaper, and cardboard, mixed in a ratio of 1:1:1(w/w), supplemented with cheese whey waste and complex manure. Three independent variables, the solid:liquid ratio, the concentration of complex manure, and cultivation time, were evaluated to determine their correlative effect on biomass production and protein biosynthesis. The optimal conditions for obtaining a maximum protein yield of 9.53% w/w dry mass were the following: the complex manure concentration of 0.5%, the solid:liquid ratio of 1:5, and the growth time of 10 days.

In this article we studied the mechanism of wood drying using infrared (IR) heat transfer. Norway spruce (Picea abies (L.) Karst.) samples of 50 mm and 200 mm thickness were exposed to IR radiation, and the temperature and moisture profiles were recorded at the surface and at the core of the samples under controlled experimental conditions. It is proposed that the moisture transport in wood during drying is governed by osmotic effects. Based on such a hypothesis, the temperature stagnation was explained by a lower localized pressure at the core, which reduced the boiling point temperature of water. As moisture is drawn away due to osmosis from the central region, it cannot fill the empty lumens again; therefore, the pressure decreases locally. The evaporation of the internal moisture is brought about by a partial vacuum resulting in the disappearance of the liquid water.

The ability of natural and synthetic hinokitiol, as well as a water soluble derivative (hinokitiol sodium salt), to protect wood against fungal attack was examined. Synthetic and natural hinokitiol provided similar protection. All three materials exhibited similar antifungal activity against Aspergillus niger and Penicillium citrinum on yellow poplar wafers at concentrations of 1 mg/mL or greater. Fungal attack by Gloeophyllum trabeum or Trametes versicolor was completely inhibited in soil block tests in wood treated with any of the three extracts at concentrations of 20 mg/mL or greater. The water soluble hinokitiol sodium salt was highly susceptible to leaching, and blocks subjected to leaching had little resistance to fungal attack. The results suggest that further formulation development will be necessary to produce a water-soluble hinokitiol system that can resist leaching and retain biological activity.

This study optimized alkali pretreatment of sugarcane bagasse (SCB) and investigated the potential of alkali-pretreated SCB in producing cellulase and reducing sugar by a white-rot fungus, P. sanguineus, via solid state fermentation (SSF). The fermentability of the reducing sugar produced during SSF was examined by co-culturing yeast, Saccharomyces cerevisiae, with P. sanguineus. Central composite design (CCD) was applied to optimize the pretreatment based on reducing sugar yield obtained from enzymatic hydrolysis of the pretreated SCB. The model developed from CCD fitted the data well, and the optimized conditions for alkali pretreatment were 128 °C, 0.62 M NaOH, and 30 min with a reducing sugar yield of 97.8%. The alkali-pretreated SCB after washing and drying was cultivated with P. sanguineus during SSF. It was found that cellulase and reducing sugar can be produced simultaneously from this SSF system. The maximum cellulase activities determined from filter paper assay (FPase), carboxylmethylcellulase (CMCase) assay and β-glucosidase assay were 0.02 IU/mL, 0.11 IU/mL, and 0.13 IU/mL on day 8, day 3, and day 6 of cultivation, respectively. The maximum reducing sugar concentration of 19.9 mg/g pretreated SCB was obtained on day 4 of SSF. The reducing sugar produced was converted into ethanol upon the addition of yeast into the SSF system. Evidently, the reducing sugar acquired can be further utilized to produce other valuable products in subsequent processes.

Paper dust is a kind of cellulosic waste that is generated by converting operations in paper mills. It was derived to a low-grade cellulose acetate in this study. Papers made from recycled fiber were then impregnated with the resultant cellulose acetate. Effects of impregnation conditions on the paper properties were statistically investigated by employing central composite design (CCD) based response surface methodology (RSM). Four response variables, namely density, burst index, smoothness, and rate of surface wettability were analyzed. Polynomial estimation model of each response was developed as functions of three independent variables, which are pressing temperature (T), dipping time (D), and concentration of cellulose acetate (C). The paper which was impregnated based on the calculated optimum condition (T: 163 °C, D: 2.8 minutes, and C: 2.7 percent), possessed a density of 0.5450 g/cm3, rate of surface wettability of 0.012°/s, burst index of 2.84 kPa m2/g, and paper smoothness of 475 mL/min. There was no significant difference between the experimental values and the predicted values calculated from estimation models. The cellulose acetate impregnated Braille papers made from recycled fibre was found to have better properties than those of commercial Braille paper in terms of rate of surface wettability and burst index.

The effects of press pressure on glue line thickness (GLT) and properties of laminated veneer lumbers (LVLs) manufactured from half-round sliced I-214 hybrid poplar clone veneers with phenol formaldehyde adhesives were determined. The results showed that press pressures significantly influenced GLT and properties of LVLs. Results of higher specific gravity, thickness swelling ratio, and mechanical properties, but lower GLT and water absorption ratio were attributed to higher press pressure uses. Optimum properties were obtained by using a press pressure of 10 kg cm-2 in relation to GLT and properties of LVLs. Significant relationships were found between GLT and mechanical properties. GLT may provide reliable information to determine wood bonding quality and may be used for non-destructive evaluation of mechanical properties of wood composites in the future.

Bamboo is a very interesting bioresource for use as a building material because of its properties of strength in combination with low density. However, its susceptibility to fungi and insects is problematic for its usage. Thermal modification is used in Vietnam to improve the durability and dimensional stability of bamboo. The thermal modification causes many changes related to the physical properties of bamboo, e.g., mass, color, and equilibrium moisture content (EMC). All these changes are dependent on the modification conditions (modification temperature and duration). The mass loss (ML), the color difference (DE*ab), and the reduction of EMC (DEMC) were due to the thermal modification increase with higher temperature and/or longer duration. Therefore the temperature had greater influence than the modification duration. The changes were slight at 130 °C (ML: 0,3…0,6 %; DE*ab: 3…5; DEMC: 0,5…0,8 % ), moderate at 180 °C (ML: 1,5…4 %; DE*ab: 21…37; DEMC: 3,6…4,4 %), but very strong at 220 °C (ML: 14…16 %; DE*ab: 46…51; DEMC: 5,6…5,7%). There are close correlations between the changes mentioned above.

A computational approach was used to analyze the FTIR spectra of a wide range of treated and untreated lignocellulosic biomass (coconut husk, banana trunk, sago hampas, rice husk, and empty fruit bunch). The biomass was treated with strong sulphuric acid and NaOH, respectively. A total of 87 spectra were obtained in which the absorption bands were de-convoluted automatically, generating a peak table of 87 rows and 60 columns. Square roots were taken of the peak values, with further standardization prior to Principal Component Analysis (PCA) for data exploration. In a scores plot, the treated and untreated biomass were distinguishable along the two main axes, PC1 and PC2. Examining the absorption bands corresponding to lignocellulosic components indicated that the acid pretreatment had resulted in dissolution and degradation of hemicelluloses and lignin, confirmed typically by disappearance of bands. The alkali treatment however was not as rigorous as the acid treatment, as some characteristic bands of hemicelluloses and lignin were enhanced, suggesting condensation of the degraded polysaccharides. The computer-assisted analysis of the FTIR spectra allowed efficient and simultaneous comparisons of lignocellulosic compositions present in various treated and untreated biomass. This represents an improvement relative to the conventional methods, since a large dataset can be handled efficiently and individual peaks can be examined.

The effects of processing conditions such as pressure, temperature, and holding time on the flexural properties of bagasse and bamboo biodegradable composites were investigated. Each sample of bagasse or bamboo was mixed with a corn-starch-based biodegradable resin and fabricated by a hot press forming method. The cross-sectional structure of the bagasse fiber was found to be porous and compressible, while that of bamboo was found to be more solid. The relationship between flexural strength, flexural modulus, and pressure in bagasse fiber was apparently different from that of bamboo due to the differences in the cross-sectional structure. In bagasse, the flexural strength and flexural modulus increased with the increase in pressure, whereas in bamboo those properties decreased. In bagasse, an increase in pressure made the fibers into a more compressed structure, increasing their flexural properties. In rigid bamboo, an increase in pressure caused the resin to extrude between fibers, and this resulted in lower flexural properties. At temperatures above 170 °C, the resin depolymerized thermally and the degree of polymerization decreased. Thus, the flexural modulus and strength decreased gradually with increase in holding temperature in both bagasse and bamboo composites. Furthermore, a maximum fiber volume fraction existed for both bagasse and bamboo plastic composites in the approximate range of 75% to 80%.

The effect of joint size on the loading capacity of wood single lap joints was studied with an orthogonal experimental design. The maximum load, modulus of elasticity, and modulus of rupture were the three mechanical indexes used to evaluate wood joint quality. A simulation model of bending tests was established using the finite element method. The stress distributions of the joints were analyzed; the peak stripping stress was reduced with an increase in gluing length and thickness. The increase in the corresponding experimental values of maximum load was in agreement with this conclusion. The joint force for various loading positions was simulated, and the peak stress was lowest at the location with the maximum offset. Therefore, the bending capacity of the wood joints can be improved by changing the loading position. Nondestructive fast Fourier transform (FFT) testing of the bending vibration was used to obtain the dynamic elastic modulus. A significant correlation existed between modulus of elasticity and modulus of rupture. Finite element simulation analysis and nondestructive testing are all effective methods for quality evaluation of wood joints, and they can be applied to the design and testing of wood joints.