Volume 15 Issue 2

Wood-cement composites were considered as substitutes for wood or asbestos cement. This research is focused on the development, characterization, and durability of different wood-cement particle boards composed of wood waste [residual particles of pine species (Pinus spp.)], with silica fume or rice husk ash. The wood-cement panels produced by cold compression were evaluated for their physical and mechanical properties after accelerated and natural weathering for 28 and 91 days of curing, respectively. Results indicate that the performance of wood-cement panels containing the Pinus spp. residue was comparable to that of lignocellulosic aggregate in wood cement panels. Pine residue wood panels exhibited high levels of pozzolanic activity, suggesting that silica fume or rice husk ash could be used as a partial substitute in Portland cement. There was a significant loss of mechanical properties over time with both the reference panel and the panel produced with pozzolana. Although there was no direct correlation between the values of accelerated weathering tests and natural weathering tests, there was a larger degradation of the panels after 20 cycles of the accelerated weathering than that after 12 months of natural weathering. Morphology studies supported the observed results.

An adhesive for particleboards based on natural materials was prepared. Soy flour (38.9 wt%), magnesium oxide (MgO) (2.8 wt%), and a hydrolysate from an agricultural crop (13.9 wt%) were mixed with water and ground in a ball mill at 44% solids. The solubility and interaction of the soy flour proteins and the proteins contained in the plant hydrolysate were triggered by the strong basic environment created by MgO in the presence of water. The natural adhesive appeared to be thermally stable at temperatures from 130 °C to 240 °C, with unchanged mass and no major signals in the thermal analysis curves. These results, together with a viscosity of 510 Pa·s at 25 °C, suggested a good operability of the adhesive. Three-layered particleboards were manufactured with weight combinations of natural adhesive and polyamidoamine-epichlorohydrin (PAE) of 0%:100%, 33%:67%, 50%:50%, 67%:33%, and 100%:0%. The natural adhesive showed inferior internal bond strength and poor water resistance compared with urea-formaldehyde-bonded boards. Addition of the PAE significantly improved the internal bond and swelling, and for all the combinations these properties were comparable or, in most cases, better than in the urea-formaldehyde controls. All boards were formaldehyde-free, while the natural adhesive itself released no dangerous volatile substances.

Thermal treatments applied to lignocellulosic materials were found to induce internal chemical reactions, which modified the physical and mechanical properties and dimensional stability of the material. A 3-year-old basal section of bamboo (Guadua angustifolia Kunth), with no nodes and no skin, was subjected to a thermal treatment at temperatures which ranged from 160 to 200 °C for 1 to 4 h. The tensile stiffness showed a slight increase with temperature and time, while the tensile strength showed a notable increase at 160 °C for 2 h. There was a 5% difference in the equilibrium moisture content at 80% relative humidity between the untreated samples and the 200 °C, 4 h treatment.

A design for strap lap bond joints of wood powder/polyethylene composites (WP/PE) was proposed. The effects of combined treatment on surface properties of WP/PE and failure modes of WP/PE bonded by epoxy and acrylic ester were investigated. A finite element model of strap lap bond joints of WP/PE was established based on the elastoplasticity finite element method, and the effects of lap length and adhesive (epoxy and acrylic ester) on stress distributions and comprehensive displacements of strap lap bond joints of WP/PE were investigated. The results demonstrated that the bonding interface roughness of WP/PE was enhanced by the combined surface treatment. Active oxygen-containing functional groups were introduced to the sample surface. The finite element simulation results revealed that the Mises equivalent stress peaks and comprehensive displacements of strap lap bond joints were concentrated in lap zone ends and board connections, the stress distribution was independent of the lap length, and the Mises equivalent stress peaks and comprehensive displacements were independent of the adhesive.

Preliminary studies are presented showing to what extent nutrients available in the growth environment of Kombucha microorganisms affect the physical and mechanical properties of synthesized cellulose. With an increase in the amount of sucrose in the growth medium and with the presence of additional nutrients, peptone and tea extract, the thickness and strength of the biopolymer increased, while elongation was reduced. The best physical and mechanical parameters were obtained for bacterial cellulose from cultures with the addition of 10% sucrose and 0.25% peptone content. The increase in elongation correlated with the decrease in the degree of polymerization, which means that in media rich in nutrients, the number of molecules building the polymer decreases. The presented data is important in order to select ingredients that will help synthesize bacterial cellulose with the desired physio-mechanical properties.

Effects of the wood species, number of teeth, and adhesive type were studied relative to the moment capacities of box joints under tension and compression loadings, which is commonly used in case type solid wood furniture. For this purpose, L-type specimens were prepared from Scotch pine (Pinus sylvestris L.), poplar (Populus sp.), and fir (Abies sp.). Polyvinyl acetate (PVAc) and polyurethane (PU) adhesives were used in the preparation of joints. Tension and compression tests with 360 samples were performed under static loading. According to the results, the highest moment capacities were obtained for Scotch pine under tension, and poplar specimens under compression. With respect to the number of teeth, the highest moment capacities were obtained with 12-tooth joints under both tension and compression loadings. For adhesive types, the specimens glued with PVAc gave better results in both tension and compression. In manufacturing of solid wood based case-type furniture, the higher number of teeth resulted in a slightly better performance; however, the results with the 4-tooth structure was not too far from 8-tooth. Furthermore, it was concluded that Scotch pine as a substance and PVAc as adhesive could be recommended.

An aqueous mixture of hydrophilic and hydrophobic cross-linked copolymers was prepared and coated on the surface of filter paper to improve the water and oil resistances. The mixture was mainly composed of sodium alginate and hydroxyl-terminated polydimethylsiloxane (PDMS)-tetramethoxysilane (TMOS) cross-linked network. The results indicated that the resistances to both water and oil of the resulting paper were significantly enhanced. The water contact angle results demonstrated that the mixture enhanced the hydrophobic properties of the coated paper greatly with water contact angles higher than 110°, and the coated paper showed excellent oil resistance with a Kit number as high as 10.

α-Amylase, which was isolated from Geobacillus stearothermophilus SR74, has shown its potential to be used in industrial applications. However, its expression in the Pichia pastoris expression system with the alcohol oxidase 1 promoter (PAOX1) requires high methanol consumption and is time-consuming. This study aimed to express SR74 α-amylase in an alternative yeast system, using Meyerozyma guilliermondii strain SO, which was isolated from a spoiled orange (SO) under the regulation of a formaldehyde dehydrogenase promoter (PFLD). Qualitative screening showed that strain SO possessed a native amylase grown on YPD-starch plate at 30 °C. The recombinant SR74 α-amylase was further quantified and validated using the Western blot test. It was confirmed that SR74 α-amylase was expressed by strain SO extracellularly with a size of 59 kDa. Optimization in a shake flask showed that the recombinant SR74 α-amylase, which was regulated by PFLD, was successfully produced (26 U/mL) without any external inducer in the YPT medium after 24 h of cultivation. In conclusion, strain SO was able to produce SR74 amylase without methanol in one-fifth the fermentation time of P. pastoris. Further optimization of the expression may be done to improve the yield, as this methanol-free host is still underexplored.

Cationic polyacrylamide emulsions prepared with ultra-high concentration (CPAME-uhc) have the advantages of fast dissolution, convenient operation, and low transportation cost. In order to further improve the molecular weight, solubility, and temperature/salt resistance of CPAME-uhc, in this study the preparation process of CPAME-uhc was optimized, and the effects of solubilizing agents and functional monomers on solubility and temperature/ salt resistance of CPAME-uhc were evaluated. Finally, the flocculation performance of CPAME-uhc on papermaking wastewater was examined. The results showed that the molecular weight of CPAME-uhc can be increased to 14 to 15 million by process optimization, and the solubility of CPAME-uhc can be greatly increased by adding urea and Na2SO4. The temperature/salt resistance of CPAME-uhc can be improved by adding 2 wt% N,N-dimethylacrylamide, 2 wt% N-vinylpyrrolidone, and 5 wt% sodium 2-acrylamide-2-methylpropionate, based on the total monomer weight. When CPAME-uhc was added to papermaking wastewater the removal percentages of chemical oxygen demand (COD) and suspended solid (SS) were 95% and 93%, respectively. This study provides a useful reference for the preparation, optimization and application of CPAME-uhc.

Pectinase was immobilized on magnetic regenerated cellulose microspheres using cationic polyacrylamide (CPAM) or polyethyleneimine (PEI) via electrostatic adsorption. PEI-immobilized enzyme (PEI-EMCB) had higher activity (2711 U/g) than CPAM-immobilized enzyme (CPAM-EMCB). The time course of PEI-immobilized enzyme catalytic reaction was similar to the free form. PEI-EMCB reached its maximal activity at pH 4.8, while the optimal pH for CPAM-EMCB was the same with the free form (4.4). CPAM3-EMCB was most tolerant to pH variation, which can be possibly ascribed to the high molecular weight of CPAM3. After immobilization, the optimum temperature for the enzyme declined from 45 °C to different degrees. PEI-EMCB exhibited good storage stability with 67% of the initial activity maintained after 7 days and with moderate reusability. The magnetic properties of the regenerated cellulose beads provided convenience for the immobilized enzyme to be used and recycled. The results indicate a potential route for utilization of cellulose as enzyme support via a simple method.