Volume 12 Issue 2

The heterologous expression of the gene LACP83 (encoding a laccase) from Pleurotus ostreatus in Escherichia coli was characterized. The laccase enzyme activity and kinetics of bacterial growth with an inducer (IPTG) and without inducer were determined. The maximum enzymatic activity was observed at 7 h post induction with a value of 3740 ± 342 U/L, which was similar to that reported for the native strain of P. ostreatus at 144 h of culture. Furthermore, the induction of laccase with IPTG reduced the specific growth rate of recombinant E. coli BL21 by approximately 50%. These results support the use this system for the recombinant production of the enzyme on an industrial scale.

The effects of hot air temperature on the drying properties of biomass brick during heat treatment were examined. Biomass brick was dried for 156 h at 30 °C to 80 °C and 50% relative humidity. The results showed that the moisture content and density of the brick during heat treatment were affected greatly by the hot air temperature. The moisture content was affected remarkably by the drying time. Drying shrinkage extents were affected noticeably by the drying time and air temperature. The moisture content and density after drying were decreased with increased time. The compression strength increased with the increased air temperature from 30 °C to 70 °C.

The influence of beech bark concentrations as filler in urea-formaldehyde (UF) adhesives was investigated relative to the composite forming process and selected properties of final 5-layer beech plywood. Beech bark was used as filler to lower the wood processing waste production and decrease formaldehyde emissions. A combination of UF adhesives filled with different beech bark concentrations as the adhesive was used. Three different concentrations of beech bark, 15 wt.%, 20 wt.%, and 25 wt.% were used in the experiment. Urea-formaldehyde adhesive filled with 20 wt.% technical flour was used as a reference sample. The effect of the filler was studied via its temperature profile during pressing, mechanical properties in bending, water absorption, thickness swelling, and formaldehyde emissions after pressing. The time needed to reach the temperature between the beech veneers, at least 105 °C, which was equal to the final temperature filler-adhesive-wood matrix cross-linking, was also investigated during the pressing process. The measurements of the free formaldehyde emissions showed that for samples with non-zero bark concentrations there was a decrease of formaldehyde emissions by at least 46%.

Properties were evaluated for particleboard made from polymethylene polyphenyl polyisocyanate (pMDI) binder and wheat straw treated with sodium hydroxide (NaOH) and ammonia hydroxide (NH3·H2O) solutions. The crystallinity (Xc) of wheat straw and board properties including internal bond strength (IB), thickness swelling after 24 h (24 hTS), modulus of rupture (MOR), and modulus of elasticity (MOE) were investigated. XRD indicated that the crystallinity of wheat straw was increased with the mass fraction range from 1% to 3%, and the bending properties of board were also improved. MOR and MOE were significantly (P < 0.05) improved, and a positive correlation with solution mass fraction was shown. Bending properties, especially MOE, were superior to the requirements in GB/T 4897-2015. IB of NaOH solution treated board was also significantly higher (P < 0.05), but results for IB of ammonia solution treated and 24 hTS for board treated with both solutions failed to meet the standard. Effects of the two solutions were not the same according to a t-test, and the effects of NaOH were better.

Wood modification is an efficient method to improve wood performance and expand the applications of wood material. In this study, a combination modification method of aluminum sol-gel and furfurylation was developed to improve the performance of poplar wood. Wood samples were characterized by Fourier transform infrared spectroscopy and field emission scanning electron microscopy. The properties of the treated wood, including thermal stability, water uptake, dimensional stability, and dynamic wettability were also evaluated. The thermogravimetric analysis results indicated that the incorporation of an aluminum-based gel could prevent furfurylated wood from thermal degradation by converting the gel into nano-Al2O3. The aluminum-based sol-gel apparently hindered furfuryl alcohol polymerization and reduced the weight percent gain of the samples; the anti-swelling efficiency of the treated wood was over 57% (with little decrease) due to crosslinking between the wood and aluminum-based gel. The water uptake and hydrophobicity of the modified samples were improved significantly in comparison to the control samples.

Plant surfaces provide an unlimited source of systems for the protection of their surface against the outer environment. These systems have continuously improved over the last 400 million years of evolution. Two of the most fascinating properties of these systems are superhydrophobicity and the self-cleaning ability of several plant species. These properties are most often achieved due to the hierarchical structure of the surface in combination with a deposited blend of epicuticular waxes. In this study, a layer of n-hexatriacontane was deposited on wood surfaces via thermal evaporation, and the self-assembly ability was investigated for various wood species with differently machined surfaces. The behavior of wax crystals was observed using scanning electron microscopy (SEM) and confocal microscopy. The impact on wettability was investigated by measuring contact angles and tilt angles. With wax deposition, a significant change of wettability was achieved, which was represented by the transition from hydrophilic to superhydrophobic surface behavior. The self-assembly ability of n-hexatriacontane resulted in an increased contact angle in all observed samples.

Biochars produced from rice straw, corn straw, and wheat straw under different pyrolysis temperatures were comprehensively characterized. The results indicated that the yields of the biochars decreased for all three biochar types with the increase in pyrolysis temperature from 250 °C to 600 °C. In addition, the carbon contents of the biochars increased, and the polar acidic functional groups decreased with the increase of the pyrolysis temperature. The hemicellulose and cellulose components likely decomposed at approximately 300 °C, and more condensed and ordered aromatic carbon structures were formed in the biochars with the increase in pyrolysis temperature. The results also indicated that these three types of biochars showed many similarities in elemental composition and structure. However, some differences were also observed. This work provides important baseline information for the production of biochars from crop residues with desired properties for environmental applications.