It is commonly accepted that the fire retardant mechanism of boric acid is a physical mechanism achieved by the formation of a coating or protective layer on the wood surface at high temperature. Although a char-forming catalytic mechanism has been proposed by some researchers, little direct experimental support has been provided for such a chemical mechanism. In this paper, new experimental results using thermal analysis, cone calorimetry (CONE), and gas chromatography–Fourier transform infrared spectroscopy (GC–FTIR) analysis are presented and the fire retardant mechanism of boric acid on wood is discussed. Basswood was treated with boric acid, guanylurea phosphate (GUP), and GUP–boric acid. Treated wood was then analyzed by thermogravimetry (TG/DTG), differential thermal analysis (DTA), CONE, and GC–FTIR analysis. Thermogravimetry showed that the weight loss of basswood treated with boric acid was about three times that of untreated or GUP-treated wood at 165°C, a temperature at which GUP is stable. The DTA curve showed that boric acid treated basswood has an exothermal peak at 420°C, indicating the exothermal polymerization reaction of charring. CONE results showed that boric acid and GUP had a considerable synergistic fire retardant effect on wood. The GC–FTIR spectra indicated that compounds generated by boric acid treated wood are different than those generated by untreated wood. We conclude that boric acid catalyzes the dehydration and other oxygen-eliminating reactions of wood at a relatively low temperature (approximately 100–300°C) and may catalyze the isomerization of the newly formed polymeric materials by forming aromatic structures. This contributes partly to the effects of boric acid on promoting the charring and fire retardation of wood. The mechanism of the strong fire retardant synergism between boric acid and GUP is due to the different fire retardant mechanisms of boric acid and GUP and the different activation temperatures of these two chemicals.

https://www.fpl.fs.fed.us/documnts/pdf2004/fpl_2004_wang002.pdf

Chemical mechanism of fire retardance of boric acid on wood

A conductive PVDF-Ni membrane with superior rejection, permeance and antifouling ability via electric assisted in-situ aeration for dye separation

The synthesis of 1,4-naphthoquinone derivatives is of great interest since these compounds exhibit strong activity as antimalarial, antibacterial, antifungal and anticancer agents. A series of 50 naphthoquinone derivatives was synthesized and evaluated for antibacterial and antifungal activity against Escherichia coli, Pseudomonas aeruginosa, Enterococcus faecalis, Staphylococcus aureus, Candida krusei, Candida parapsilosis and Cryptococcus neoformans using the broth microdilution method. The Candida species were the most susceptible microorganisms. Halogen derivatives of 1,4-naphthoquinone presented strong activity, e.g., 2-bromo-5-hydroxy-1,4-naphthoquinone, which exhibited inhibition at an MIC of 16 µg/mL in S. aureus, and 2-chloro-5,8-dihydroxy-1,4-naphthoquinone, with an MIC of 2 µg/mL in C. krusei. These compounds showed higher activity against fungi, but the antibacterial activities were very low. The study of structure–activity relationships is very important in the search for new antimicrobial drugs due to the limited therapeutic arsenal.

/pdf/synthesis-antibacterial-and-antifungal-activities-of-2a623r96t7.pdf

Synthesis, antibacterial and antifungal activities of naphthoquinone derivatives: a structure–activity relationship study

The use of thermally modified timber for structural purposes is of increasing interest. In order to guarantee sufficient reliability in terms of load bearing capacity and fitness for use the strength and stiffness properties of this modified wood have to be assessed. Industrially produced, thermally modified structural timber members made of beech (Fagus sylvatica L.) were subject of the tests presented in this paper. Bending, tension parallel and perpendicular to grain and compression parallel and perpendicular to grain properties were determined. The derived mechanical properties were benchmarked to the European EN 338 strength class system for structural timber. It turned out that the used strong thermal treatment of the raw material resulted in a significant reduction of most of the strength properties. However, stiffness properties were not affected. In particular the strength properties perpendicular to grain suffered a lot due to the thermal modification whereas compression strength parallel to grain was unchanged. The main drawbacks found along the experiments were a pronounced brittle behaviour of the specimens and big variations in strength. For the determination of strength values it is proposed not to use correlations as provided in European standards but to test and state these properties discretely. On the basis of these results a general use of strongly thermally modified beech as structural timber cannot be recommended. However, for selected purposes, like e.g., for structural facade elements or for columns, the use of this material might be an option.

/pdf/mechanical-properties-of-thermally-modified-beech-timber-for-3srrkrfvvm.pdf

Mechanical properties of thermally modified beech timber for structural purposes

Nickel (Ni) is a ubiquitous and highly important heavy metal. At low levels, Ni plays an essential role in plants such as its role in urease, superoxide dismutase, methyl-coenzyme M reductase, hydrogenase, acetyl-coenzyme A synthase, and carbon monoxide dehydrogenase enzyme. Although its deficiency in crops is very uncommon, but in the past few years, many studies have demonstrated Ni deficiency symptoms in plants. On the other hand, high levels of applied Ni can provoke numerous toxic effects (such as biochemical, physiological, and morphological) in plant tissues. Most importantly, from an ecological and risk assessment point of view, this metal has narrow ranges of its essential, beneficial, and toxic concentrations to plants, which significantly vary with plant species. This implies that it is of great importance to monitor the levels of Ni in different environmental compartments from which it can enter plants. Additionally, several abiotic stresses (such as salinity and drought) have been reported to affect the biogeochemical behavior of Ni in the soil-plant system. Thus, it is also important to assess Ni behavior critically under different abiotic stresses, which can greatly affect its role being an essential or toxic element. This review summarizes and critically discusses data about sources, bioavailability, and adsorption/desorption of Ni in soil; its soil-plant transfer and effect on other competing ions; accumulation in different plant tissues; essential and toxic effects inside plants; and tolerance mechanisms adopted by plants under Ni stress.

Biogeochemical behavior of nickel under different abiotic stresses: toxicity and detoxification mechanisms in plants

Electrical and electromagnetic shielding wood-metal composite was prepared by using electroless nickel plating. The effects of solution amount, plating time and plating temperature on surface resistivity and electromagnetic shielding effectiveness were investigated. And P content, microstructure and surface feature of layers obtained at different temperatures were analyzed by energy dispersion spectrometer (EDS), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that layers with higher electro-conductivity and electromagnetic shielding effectiveness were obtained under the optimum conditions that plating solution was 500 mL, plating time was 30 min and plating temperature was 62°C. The results showed by EDS analysis that P content increased gradually in a small extent with plating temperature increased. It was showed by XRD and SEM analysis that layers plated at different temperatures were all microcrystalline structure and uniform and successive, which had noticeable metal luster. Those indicated that plating temperature had little influence on microstructure and surface feature under pH value invariable.

Preparation of electromagnetic shielding wood-metal composite by electroless nickel plating

Wood is a kind of porous natural material with very poor electro-conductivity, and it has almost no function of electromagnetic shielding. The method of electroless nickel plating was used to produce wooden material with electrical and effective electromagnetic shielding properties. Ni−P alloy layer was obtained on wood surface. The surface feature of plated wood veneer was observed by SEM and the surface composition and microstructure of the layer under different conditions were investigated by EDS and XRD respectively. Mean-while, the relevant surface resistivity and electromagnetic shielding effectiveness were measured. Correlations of the phosphorous content in the layer to the structure of Ni−P alloy, electro-conductivity and electromagnetic shielding of plated veneers were discussed. SEM photos showed that the surface of electroless nickel plated veneers were covered with Ni−P alloy layer entirely, which made wood veneers more like metal. At the same time, the results showed that with the decreasing of the phosphorous content in the layer, the microstructure of Ni−P alloy layer transformed to be microcrystalline and electro-conductivity and electromagnetic shielding effectiveness were imrpoved. When the phosphorous content was less than 2.37wt pct in the layer, the microstructure of Ni−P alloy layer was microcrystalline structure and its surface resistivity and electromagnetic shielding effectiveness were nearly 0.5 Ω/⊥ and 55–60dB respectively.

Surface characteristics of electroless nickel plated electromagnetic shielding wood veneer

The structures of the solid state products formed by the partial combustion of Korean pine wood treated with fire-retardant FRW were analyzed by microscopic FTIR. The volatile pyrolytic products of basswood (Tilia amurensis) specimens treated with FRW and its components guanylurea phosphate and boric acid were analyzed by GC-FTIR. The pyrolytic and charring process, the effects of fire-retardant, and the structural characteristics of the pyrolytic products were discussed. It was concluded that upon heating and by the catalysis of FRW and its decomposition products reactions of wood took place successively, namely the dehydration of polysaccharide, the elimination of acetic acid from hemicellulose, the degradation of polysaccharide, the degradation of lignin, the polymerization of the pyrolytic products of wood, reactions of oxygen-element-elimination of aliphatic polymers and the structural change of the latter to form aromatic structures, and charring. The pyrolysis process of wood was altered and the yield of volatile pyrolytic products was decreased by FRW treatment.

Study on the fire retardant mechanism of fire-retardant FRW by FTIR.

Juglone was extracted from Juglans mandshurica bark via vacuum-assisted steam stripping. The extract was characterized by Fourier transform infrared spectroscopy (FTIR), 1 H nuclear magnetic resonance (NMR), and gas chromatography/mass spectrometry (GC-MS). The extraction process was easy to perform and produced excellent yields (0.22 g juglone/1 00 g of bark) of a high purity extract (96.42% juglone). The yield was much higher than that of previous studies. The biological activity of the extract was assessed in vitro against Aspergillus niger, Paecilomyces variotii, Trametes versicolor, Gloeophyllum trabeum, Postia placenta, and Chaetomium globosum. Juglone showed good antifungal activity with the first four fungi listed, even at concentrations as low as 500 ppm; poor activity was shown with the last two fungi listed. The results suggest that juglone has promise as a natural wood protectant; further studies are planned.

Li Jian

Papers

Preparation of electromagnetic shielding wood-metal composite by electroless nickel plating

Surface characteristics of electroless nickel plated electromagnetic shielding wood veneer

Study on the fire retardant mechanism of fire-retardant FRW by FTIR.

Effect of juglone from Juglans mandshurica bark on the activity of wood decay fungi.

A study on the fire retardancy of FRW fire retardant for wood by cone calorimeter.