Thermochemical behavior of Norway spruce (Picea abies) at 180–225 °C

Norway spruce (Picea abies) was heated for 2–8 h in the temperature range 180–225 °C, under a steam atmosphere. The chemical analyses of the treated feedstock samples indicated that during heating (total mass loss 1.5–12.5% of the initial DS) carbohydrates (hemicelluloses and cellulose) were clearly more amenable to various degradation reactions than lignin. In addition, major water-soluble products released from the feedstock material during the treatments were classified into several compound groups and changes in the relative mass portion of these groups were monitored by GC during a separate experiment. Received 20 December 1998     

Interaction between glycerin and wood at various temperatures from stress relaxation approach

In order to understand the reason why glycerin pre-treatment can accelerate the deformation fixation of compressed wood, the interaction between glycerin and wood at various temperatures was investigated in this study from stress relaxation approach. The compression stress relaxation curves of poplar (Populus cathayana Rehd.) samples impregnated with glycerin were measured at temperatures ranging from 25 to 180°C, together with the curves of oven-dry wood at temperatures between 100 and 180°C for comparison. The activation energy was calculated according to the Eyring’s absolute rate reaction theory. The results showed that temperature had very obvious effect on stress relaxation for both glycerin-treated wood (GTW) and oven-dry wood. The stress released very fast at higher temperatures. Glycerin showed an accelerating effect on stress relaxation. At temperatures exceeding 120°C, a complete relaxation of the stress could be expected. While for untreated wood, it cannot be reached until 160°C. By calculating the apparent activation energy (ΔE) of GTW at different temperatures, it is clear that two mechanisms are responsible for different temperature ranges. From 40 to 100°C, ΔE is only 8.24 kJ/mol, which corresponds to the hydrogen bonds formed between wood and glycerin molecules; from 120 to 180°C, ΔE reached 81.38 kJ/mol, which corresponds to the degradation of hemicelluloses or lignin, and during this process, new cross-linking would happen.     

Chemical changes of wood during steaming measured by IR spectroscopy

Black locust, poplar and spruce samples were steamed at 80°C and 120°C for 48 hours. IR difference spectra and the CIE Lab colour coordinates were measured for determining the chemical changes caused by the steaming. Steaming at 80°C caused only small changes in both IR spectra and colour. But steaming at 120°C produced intensive colour change and well-visible changes in IR spectra. The guaiacyl lignin in hardwoods underwent slight degradation but in spruce suffered substantial degradation during steaming at 120°C. The syringyl lignin absorbing around 1600 cm^?1 did not show any changes, indicating that it is more stable to steaming than guaiacyl lignin. The absorption decrease at 1175 cm^?1 indicated the cleavage of ether linkage in cellulose and hemicelluloses at both steaming temperatures.     

Antioxidant activity of liquors from steam explosion of <Emphasis Type="Italic">Olea europea</Emphasis> wood

The liquors from steam explosion of Olea europea wood carried out at temperatures in the range of 190–240°C were analysed for phenolic content, radical scavenging capacity and reducing power. Increased ethyl acetate solubles (EAS) and phenolics [as Gallic Acid Equivalents, (GAE)] extraction yield with increasing temperature were observed. At the higher temperature tested, up to 2.3 g EAS/100 g dry wood were obtained with 0.7 g GAE/100 g dry wood. The purity of the phenolic extracts was independent of the temperature (30 g GAE/100 g EAS). The lignin derived compounds increased steadily with temperature in the studied range, whereas the sugar decomposition products showed a maximum at 230°C. The radical scavenging capacity was slightly higher for the samples produced at the lowest temperature, and comparable to those of synthetic antioxidants. At 0.5 g/L the FRAP (Ferric Reducing Antioxidant Power) and Trolox Equivalent Antioxidant Activity (TEAC) values were equivalent to 1 and 2–3 mM ascorbic acid, respectively. EA extracts were less effective than Butylated hydroxyanisole (BHA) for protecting the oxidation in emulsions.     

A review of wood thermal pretreatments to improve wood composite properties

The objective of this paper is to review the published literature on improving properties of wood composites through thermal pretreatment of wood. Thermal pretreatment has been conducted in moist environments using hot water or steam at temperatures up to 180 and 230 °C, respectively, or in dry environments using inert gases at temperatures up to 240 °C. In these conditions, hemicelluloses are removed, crystallinity index of cellulose is increased, and cellulose degree of polymerization is reduced, while lignin is not considerably affected. Thermally modified wood has been used to manufacture wood–plastic composites, particleboard, oriented strand board, binderless panels, fiberboard, waferboard, and flakeboard. Thermal pretreatment considerably reduced water absorption and thickness swelling of wood composites, which has been attributed mainly to the removal of hemicelluloses. Mechanical properties have been increased or sometimes reduced, depending on the product and the conditions of the pretreatment. Thermal pretreatment has also shown to improve the resistance of composites to decay.     

Spectrochemical characterization by FT-Raman spectroscopy of wood heat-treated at low temperatures: Japanese larch and beech

Test samples of Japanese larch (Larix leptolepis) heartwood and Japanese beech (Fagus crenata) sapwood were heated for 22 h at constant temperatures (50°–180°C) under three water content conditions. Raman spectra of the samples were recorded before and after the heat treatments, and spectral changes in the range from 1000 cm⁻¹ to 1800 cm⁻¹ were evaluated using the difference spectrum method. For both wood species, the Raman band intensity at 1655–1660 cm⁻¹ due mainly to the C=C and C=O groups in lignin clearly decreased with increasing heat-treatment temperature (HTT). The spectral change was thought to reflect the progress of condensation reactions of lignin molecules during the heat treatment. Moreover, the decrease in band intensity was considerably facilitated by the presence of water in the cell wall, suggesting that the condensation is closely related to the softening of lignin. From the spectral changes in the wavenumber region of 1200–1500 cm⁻¹, it was considered that wood constituents are partially decomposed at the higher HTT. Part of this article was presented at the 53rd Annual Meeting of the Japan Wood Research Society, Fukuoka, March 2003     

Dynamic viscoelastic behavior of wood under drying conditions

In this study heartwood from a Chinese fir [Cunninghamia lanceolata (Lamb.) Hook] plantation was treated using a high-temperature drying (HTD) method at 115°C, a low-temperature drying (LTD) method at 65°C, and freeze vacuum drying (FVD), respectively. The dynamic viscoelastic properties of dried wood specimens were investigated. The measurements were carried out at a temperature range of −120 to 250°C at four different frequencies (1, 2, 5, and 10 Hz) using dynamic mechanical analysis (DMA). We have drawn the following conclusions: 1) the storage modulus E′ and loss modulus E″ are the highest for HTD wood and the lowest for FVD wood; 2) three relaxation processes were detected in HTD and LTD wood, attributed to the micro-Brownian motion of cell wall polymers in the non-crystalline region, the oscillations of the torso of cell wall polymers, and the motions of the methyl groups of cell wall polymers in the non-crystalline region in a decreasing order of temperatures at which they occurred; and 3) in FVD wood, four relaxation processes were observed. A newly added relaxation is attributed to the micro-Brownian motions of lignin molecules. This study suggests that both the HTD and the LTD methods restrict the micro-Brownian motion of lignin molecules somewhat by the cross-linking of chains due to their heating history. __________ Translated from Journal of Beijing Forestry University, 2008, 30(3): 96–100 [译自: 北京林业大学学报]     

Carbonization mechanism of bamboo（phyllostachys） by means of Fourier Transform Infrared and elemental analysis

Bamboo was carbonized at different temperatures ranging from 200℃ to 600℃.The dependence of the change of hemicellulose,cellulose,and lignin on the temperature was investigated by means of elemental analysis and Fourier Transform Infrared (FTIR) spectra of the residual solid products.The results showed:(1)Below 200℃,hemicellulose in bamboo wasdecomposed and a large amount of hydroxyl groups are dislocated from hemicellulose and cellulose,accompanied by the evolution of water to escape.(2)200℃-250℃,cellulose in bamboo was brastically decomposed whereas the net structure of lignin keep stable,with the except of the dislocation of methoxyl groups from lignin.(3)250℃-400℃,the net structure of lignin collapse,up to 400℃,followed by that the more position in aryl groups are substituted.(4)For bamboo carbonization,the aromatization of residual carbon has approximately completed at the temperature as high as 600℃.But the fusion of aromatic rings possibly does not occur.     

Effects of seed water content and storage temperature on the germination parameters of white spruce, black spruce and lodgepole pine seed

The effect of seed water content (WC) (2–3, 5–6 and 22–25%, on a fresh weight basis), storage temperature (+4, −20, −80 and −196°C) and storage duration (6, 12, 24, 48 and 60 months) on the germination of white spruce (Picea glauca (Moench) Voss), black spruce (Picea mariana (Mill.) B.S.P.) and lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) seed was investigated. Germination of white spruce control (untreated) seeds and seeds adjusted to 2–3% and 5–6% WC declined after 48 months of storage at −80 and −196°C, with a further decline at 60 months at −20, −80, −196°C. Germination remained high when control white spruce seeds and seeds with 2–3, 5–6% WC were stored at +4°C, over all storage durations. Generally, black spruce and lodgepole pine exhibited high germination at all storage temperatures at 2–3% and 5–6% WC as well as the control (untreated) seed, for up to 60 months in storage. Germination declined for all three species when seed was conditioned to 22–25% WC. This loss in germination was partially recovered in white spruce seed stored at +4, −20 and −80°C after storage durations of 24, 12 and 48 months, respectively, and in black spruce seeds stored at −20 and −196°C after storage durations of 24 months. Mean germination time (MGT) was relatively constant for all species, under all conditions, except for seed conditioned to 22–25% WC, where MGT increased for white spruce seed stored 48 months at −80 and −196°C, and for black spruce seed stored 24 months at +4 and −80°C and 60 months at −196°C. These results show that the optimal storage temperatures are 4°C for white spruce, and 4, −20, −80, and −196°C for black spruce and lodgepole pine, and 2–6% water content is optimal for all 3 species at these temperatures.     

Variation in litter decomposition-temperature relationships between coniferous and broadleaf forests in Huangshan Mountain,China

A study was conducted to identify the differences in the decompositions of leaf litter, lignin and carbohydrate between coniferous forest and broadleaf forest at 20℃ and 30℃ in Huangshan Mountain, Anhui Province, China. Results showed that at 20℃ mass loss of leaf litter driven by microbial decomposers was higher in broadleaf forest than that in coniferous forest, whereas the difference in mass loss of leaf litter was not significant at 30℃. The temperature increase did not affect the mass loss of leaf litter for coniferous forest treatment, but significantly reduced the decomposition rate for broadleaf forest treatment. The functional decomposers of microorganism in broadleaf forest produced a higher lignin decomposition rate at 20℃, compared to that in coniferous forest, but the difference in lignin decomposition was not found between two forest types at 30℃. Improved temperature increased the lignin decomposition for both broadleaf and coniferous forest. Additionally, the functional group of microorganism from broadleaf forest showed marginally higher carbohydrate loss than that from coniferous forest at both temperatures. Temperature increase reduced the carbohydrate decomposition for broadleaf forest, while only a little reduce was found for coniferous forest. Remarkable differences occurred in responses between most enzymes （Phenoloxidase, peroxidase, !5-glucosidase and endocellulase） and decomposition rate of leaf litter to forest type and temperature, although there exist strong relationships between measured enzyme activities and decomposition rate in most cases. The reason is that more than one enzyme contribute to the mass loss of leaf litter and organic chemical components. In conclusion, at a community scale the coniferous and broadleaf forests differed in their temperature-decomposition relationships.     

The effect of alternating temperature on the rest break process of male flowers of Cryptomeria japonica D. Don

In order to develop a model for predicting the period of male flower anthesis in Cryptomeria japonica, it is requisite to clarify the rest break process in male flowers. In this study, the effect of alternating temperatures in a daily cycle on rest break was investigated using twigs bearing male flowers from three clones of C. japonica. Four temperature treatments with the same daily mean of 8°C were applied to sample twigs over a period of 35 days: (1) 8°C constant (TR-A); (2) 7°–10°C alternating (TR-B); (3) 5.5°–13°C alternating (TR-C); and (4) 4°–16°C alternating (TR-D). After treatment, the sample twigs were forced to bloom at a constant temperature of 16°C, and the cumulative effective temperatures (CETs) required for anthesis were compared. While the CETs for anthesis were the same for TR-A and TR-B, that for TR-C was significantly higher. After TR-D, almost no male flower bloomed, indicating that this treatment was ineffective in breaking rest. When considering these results on an hour basis, it was a reasonable interpretation that 13°C had no effect on breaking rest while the temperatures below 10°C were all equally effective. On the other hand, temperatures of 16°C or above were considered to have an antagonizing effect that cancels the effects of chilling temperatures below 10°C. These results suggest that the effects of high temperatures during the daytime in chilling periods should be properly incorporated into a model of the process by which rest of male flowers is broken.     

Optimal germination condition by sulfuric acid pretreatment to improve seed germination of Sabina vulgaris Ant.

Understanding the germination traits of plants is important not only for understanding natural regeneration processes but also for developing seedling production techniques for planting. Sabina vulgaris Ant. is a common species used for reforestation in semi-arid areas of the Mu-Us Desert, in Inner Mongolia, China, but its extremely low germination rate, both in situ and in vivo, is a bottleneck for seedling production. Sulfuric acid pretreatment was applied to improve germination, and the germination rate was compared for different soaking time (10, 30, 60, 90, and 120 min), different temperatures (10, 15, 20, 30, and 35°C) and under different lighting conditions (dark and light). Sulfuric acid treatment gave a high germination rate, reaching 60% at 30 days after sowing. However, the non-treated seeds produced no germination. The optimal treatment time in sulfuric acid was 120 min. Germination after sulfuric acid treatment increased at incubation temperatures from 10 to 30°C, but decreased at 35°C. Incubation at 25–30°C gave maximum germination of more than 50%. Light treatment had little effect on germination. Pretreatment with sulfuric acid improved water absorption by the embryo by creating cracks and cavities in the seed coat tissue. These results indicated that S. vulgaris seeds have physical dormancy caused by their hard seed coats, which prevents absorption of water into the embryo. A combination of pretreatment with sulfuric acid and incubation at 25–30°C was most effective in improving the germination of S. vulgaris seeds.     

Molecular sieving behavior of carbonized wood: selective adsorption of toluene from a gas mixture containing α-pinene

The adsorption properties of wood carbonized at various temperatures were investigated using a mixed gas containing toluene and α-pinene. Hinoki (Chamaecyparis obtusa) samples carbonized at 500°–1100°C were exposed to gas mixtures of toluene and α-pinene at 20°C. The samples carbonized at 500°–700°C only adsorbed toluene, whereas those carbonized at 800°–1100°C adsorbed both toluene and α-pinene. Analysis of the surface structure of the carbonized wood by nitrogen adsorption at liquid nitrogen temperature indicated that the sample carbonized at 700°C had micropores mainly 0.6 nm in diameter and few mesopores, whereas the samples carbonized at 900°C and 1100°C had mesopores and micropores larger than 0.8 nm in diameter. With the sample carbonized at 700°C, the flat-shaped toluene molecules could probably penetrate into the narrower pores, 0.8 nm in diameter, whereas the bulky globular-shaped α-pinene molecules could not. Carbonization at temperatures higher than 900°C probably enlarged the pore size and thereby reduced the selectivity of adsorption. The results revealed that wood carbonized below activation temperature has a unique flat-pore structure that seems to work as a kind of molecular sieving carbon, successfully removing only the harmful volatile organic compound (VOC), toluene, and leaving behind a pleasant aroma of α-pinene in the atmosphere.     

A study on Xingkai Lake pine gall rust

The Xingkai Lake pine (Pinus takahasii Nakai) gall rust caused byCronartium quercuum(Berk.) Miyabc: Shirai is a serious stem rust in the northeast region of China. The alternate host is oak (Quercus mongolica Fisch). Germination of both acciospores and urediospores was optimal at 12°C and occurred over a range of temperatures, from 4°C to 32°C. Teliospores germinated optimally at 16–18°C and over a range of 8–28°C. All spores germinated best under natural light and dark conditions. Direct light inhibited germination even when followed by darkness. The incubation periods of urediospores and teliospores in inoculation experiments were 6–16 days and 3–33 days respectively. Anatomical studies ofCronartium quercuum galls showed that rust hyphae freely ramify through the intercellular spaces within parenchymatous tissues of the cortex, phloem, cambium and xylem. Hyphae are perennial; large haustoria arc cylindrical with rounded or blunt ends. Among the 12 fungicides tested for control of the rust, pine-tar, pine-tar: diesel oil (1:1, 1:3, 1:5), 75% Bravo emulsion and 70% Mancozeb emulsion applied to the galls produced satisfactory results.     

Oxidation of bleached wood pulp by TEMPO/NaClO/NaClO2 system: effect of the oxidation conditions on carboxylate content and degree of polymerization

Oxidation of bleached wood pulp by the TEMPO/NaClO/NaClO₂ system was carried out at pH 3.5–6.8 and 25°–60°C with different amounts of NaClO, and investigated in terms of effects of the reaction conditions on carboxylate content and degree of polymerization (DP) of the oxidized pulp. Oxidation was accelerated by the addition of NaClO, when carried out at pH 6.8 and 40°–60°C. Addition of NaClO of more than 0.5 mmol per gram of the pulp was effective to accelerate the oxidation. Carboxylate content of pulp oxidized under such conditions increased to approximately 0.6 mmol/g within 6 h. Although DP of the oxidized pulp gradually decreased with oxidation time, no significant differences in DP of oxidized pulps were found at oxidation temperatures between 25° and 60°C, and DP values of more than 900 were maintained after oxidation for 54 h at 60°C.     

Nickel-catalyzed carbonization of wood for coproduction of functional carbon and fluid fuels I: production of crystallized mesoporous carbon

Japanese larch wood loaded with nickel (1%–4%) alone or with nickel and calcium (0.25%–1.5%) was carbonized at 800°–900°C for 0–120min with a heating rate of 5°–20°C min⁻¹ in a helium flow of 5.8−46.4 ml STP cm⁻² min⁻¹ to examine the influence of these variables on the crystallization of carbon (the formation of T component) and the development of mesoporosity. From the obtained results, reaction conditions suitable for effective production of carbon with the dual functions of adequate electroconductivity and adsorption capacity in liquid phase were established, thereby explaining the factors that govern the process. It was also confirmed that mesopore having a diameter of about 4 nm was selectively produced at the cost of specific (BET) surface area in parallel with the formation of T component. This result provided good insight into how the simultaneous dual function could be realized.     

The influence of acetosolv pulping conditions on the enzymatic hydrolysis of Eucalyptus pulps

Eucalyptus globulus wood was subjected first to HCl–catalysed delignification with 70% acetic acid under conditions realizing an incomplete 3 × 3 × 3 factorial design (HCl concentration 0, 0.025 or 0.05%; temperature 120, 140 or 160 °C; reaction time 1, 2.5 or 4 h), and then to enzymatic hydrolysis. The hydrolysis kinetics conformed to both Ghose's empirical model and a biexponential equation. The biexponential fit implies the presence of both readily and reluctantly hydrolysed cellulose fractions, and the fitted coefficients show hydrolysis yield to depend largely on the digestibility of the latter. Multiple regression of performance variables on pulping conditions showed that neither the rate nor the extent of hydrolysis is greatest for pulps with minimum lignin or xylose contents; we attribute this circumstance to the condensation and precipitation of lignin under severe pulping conditions, which protects the cellulose of the pulp from enzymatic attack. Received 20 June 1998     

Alkaloid variations in Catharanthus roseus seedlings treated by different temperatures in short term and long term

A study was conducted to investigate the effects of high temperature on variations of alkaloid metabolism in C. roseus seedlings in Key Laboratory of Forest Plant Ecology, Northeast Forestry University, Heilongiang, China. 60-day-old C. roseus seedlings with 3-4 pairs of leaves were incubated in chambers with temperature of 30℃ and 40℃for short-term heat shock experiment and 20℃, 25℃ and 35℃ for long-term experiment. The contents of vindoline, catharanthine, vinblastine and vincristine in C. roseus leaves and root were checked at different temperatures in short term （1-6 h） and long term （1-16 d）. Results showed that under short-term heat shock, the contents of vindoline, catharanthine and vinblastine in leaves of the seedlings were higher at 40℃ than at 30℃, but after 6 h treatment, the contents of vindoline and catharanthine under the two temperatures came to the same level. Catharanthine was exclusively distributed in C. roseus roots and its content was increased by 40% after two hours incubation at 40℃, while increased slowly at 30℃ incubation and reached the highest value at 6 h. In the Long-term experiment, concentrations of monomeric alkaloids catharanthine and vindoline were higher at 20℃ than at 25℃ and had a sharp increase under the condition of 35℃. While for dimeric alkaloid, it showed that the higher the temperature, the earlier the peak value of vinblastine content appears. Vincristine had a continuous enhancement and attained 0.027 mg.g^-1 at 16th day under 35℃ condition which was higher than those in the other conditions. It was concluded that high temperature could promote the accumulation of different alkaloids in C. roseus and the accumulation characteristic is highly related to treatment time.     

Effects of high temperature kiln drying on the practical performances of Japanese cedar wood (Cryptomeria japonica) II: Changes in mechanical properties due to heating

Japanese cedar wood specimens were steamed at 80°, 100°, and 120°C over 14 days, and their equilibrium moisture content (M) at 20°C and 60% relative humidity, longitudinal dynamic Young’s modulus (E), bending strength (σ _max), and breaking strain (ε _max) were compared with those of unheated specimens. Steaming for a longer duration at a higher temperature resulted in a greater reduction in M, σ _max, and ε _max. The E of wood was slightly enhanced by steaming at 100°C for 1–4 days and 120°C for 1–2 days, and thereafter it decreased. The slight increase in the E of sapwood was attributable to the reduction in hygroscopicity, while sufficient explanation was not given for a greater increase in the heartwood stiffness. Irrespective of the steaming temperature, the correlations between M and the mechanical properties of steamed wood were expressed in terms of simple curves. M values above 8% indicated a slight reduction in E and s max, whereas M values below 8% indicated a marked decrease in the mechanical performances. In addition, the e max decreased almost linearly with a decrease in the value of M. These results suggest that hygroscopicity measurement enables the evaluation of degradation in the mechanical performances of wood caused by steaming at high temperatures.     

Reactions between Cr(VI) and wood and its model compounds

Wood, macromolecular and simple model compounds, were reacted with CrO₃ or K₂CrO₄ aqueous solutions. Extracted lignin, guaiacol, vanillin, vanillyl alcohol and homovanillyl alcohol were chosen as model compounds for lignin, whilst cellulose, gum Ghatti, xylan, extracted hemicellulose from pine, methyl-β-D-glucopyranoside and methyl-β-cellobioside were used as models for wood polysaccharides. The kinetics of the reduction reactions of Cr(VI) were monitored using UV-Vis spectroscopy and the results obtained for several temperatures are discussed. In general terms, wood, lignin and lignin model compounds reduced Cr(VI) faster and to a greater extent than polysaccharides or simple sugar molecules. Moreover, lignin model compounds were reduced even faster than lignin. Simple sugars showed a reduction pattern similar to that of cellulose. Extracted hemicellulose revealed to be a poorer reductant while gum Ghatti was the strongest among the polysaccharides. As expected, CrO₃ aq. behaved as a more powerfull oxidant than K₂CrO₄ aq. for these substances. Even at 100 °C, sugars or polysaccharides did not seem to be oxidised by K₂CrO₄ aq. 0.01 M. These results suggest that, because of the differences in reactivity, lignin reacts preferentially when wood is treated with Cr(VI)-containing formulations, like those which are applied in wood preservation treatments.