Volume 55, Issue 2

The colour of Sapelli heartwood ( Entandrophragma cylindricum Sprague) is variable depending on habitat. In recent years an unusual pinkish-brown colour has been observed in commercial sawn timber of this species from Central Africa. Initial studies of Sapelli heartwood samples from various provenances have furthermore demonstrated pronounced differences in its decay resistance. Heartwood extractive composition varies considerably between provenances. Samples of Sapelli heartwood from the Central African Republic (RCA) contained 6.4% by weight of extractives compared with 12.5% for those from Cameroon and four other provenances investigated. UV microspectrophotometric analysis of heartwood extractives was used to localise phenolic extractives within wood cell walls and to identify their distribution at tissue level. The S 2 and S 3 wall layers of vessels and fibres in the heartwood were discriminated from sapwood by their high concentration of non-lignin phenolic extractives. These extractives in the cell walls were also found to be variable. As UV absorption properties show, the vessel and fibre secondary walls of Cameroon heartwood had a considerably higher concentration of extractives in comparison with samples from the RCA. In sapwood, the UV absorption levels for the fibre S 2 layer and the vessel S 3 layer were independent of the extraction procedure, suggesting the phenolic extractives in this part of the trunk were in low concentrations. Furthermore it is suggested that polyphenols constitute part of the cell wall matrix. The non-extractable phenolic content was found to be independent of provenances as demonstrated by wood from Cameroon and the RCA. The natural durability of Sapelli heartwood against fungal decay appears to be dependent on the extractive composition and on their concentration in the fibre tissue.

Leeuwenhoek's letter to the Royal Society of 27 March 1705, dealing with the anatomy of bark of cherry, birch, cinnamon, lime and cork oak is reviewed. It contains many detailed observations and illustrations of, i.a., ray dilatation, various types of phloem sclerenchyma, and annual rings in cork. This is another example of Leeuwenhoek's importance as an early plant anatomist.

Seasonal changes in the total amount (measured as ng cm −2 ) of endogenous indole-3-acetic acid (IAA) and abscisic acid (ABA) in the cambial region of Pinus densiflora Sieb. et Zucc. trees with crowns of different sizes were determined at different stem heights. The total amount of IAA varied seasonally in all trees and at all stem positions, being maximal in early summer (May or July). In a tree with a large crown, the total amount of IAA remained high after peaking and declined in autumn, whereas in a tree with small crown it decreased rapidly after peaking, in particular in the lower stem. The transition from earlywood to latewood occurred concurrently with the decrease in the total amount of IAA after it had peaked, suggesting the involvement of IAA in the control of latewood formation. Cessation of the production of tracheids also paralleled the decline in the total amount of IAA early in the growing season in the lower stem of the tree with a small crown, but not in the tree with a large crown. Thus, other factors in addition to declining IAA seem to be involved in halting the production of the tracheids. The total amount of ABA was lower than that of IAA in all trees and at all stem heights, and changes were not correlated with specific changes during the annual cycle of cambial activity and dormancy.

In trunks of Juglans nigra and the hybrid J. major × J. regia , the presence of non-structural carbohydrates, sucrose synthesizing and degrading enzymes, and their correlation with heartwood formation was investigated. Contents of starch and sucrose were highest in the youngest sapwood, decreased with increasing age of the tissue, and were absent in the heartwood. Pools of the monosaccharides glucose and fructose were low in the sapwood, and fructose was absent from the heartwood. Glucose transiently increased at the sapwood heartwood boundary in trunks of the hybrid. In black walnut stems, however, glucose started to accumulate within the transition zone and reached considerable amounts in the heartwood. Cold-adaptation in walnut wood was characterized by accumulation of soluble sugars. Sucrose formation was enabled by enhanced rates of sucrose-phosphate synthase (SPS, EC 2.4.1.14). Mid-winter starch-sugar interconversion was accompanied by increases in the activity of sucrose synthase (SuSy, EC 2.4.1.13; black walnut), or acid invertases (EC 3.2.1.26; hybrid). In the tissues undergoing heartwood formation, sucrose breakdown was enhanced from late summer until early winter. Sucrolysis was dominated by acid invertases with minor contribution of sucrose synthase. The catalytic activity of UDP-glucose pyrophosphorylase (EC 2.7.7.9), involved in the metabolization of the sucrose cleavage products, followed this seasonal trend and showed elevated activities from late summer until early winter. These data are further proof for the earlier made hypothesis (Hauch and Magel 1998) that the in situ synthesis of heartwood flavonoids relies on an interaction between primary (sucrose) and secondary metabolism. Flavonoids, however, constitute only a minor fraction in the heartwood of walnut and the bulk of heartwood phenolics seem to derive from transformation of phenolic precursors. Therefore, these recent findings together with earlier data are taken as evidence that more than one type of heartwood formation exists.

Anti- O -methyltransferase (OMT) antiserum was prepared using a part of the OMT-histidine fusion protein expressed in transformed E. coli cells as antigens. Anti-peroxidase antiserum was prepared using artificially synthesized peptides. Immunocytochemistry revealed that OMT and peroxidase are localized in differentiating xylem cells of Populus euramericana . OMT labeling was observed in the cytosol and peroxidase labeling was observed in the ER or near the ER membrane.

The periodicity of the growth increment in six rubber wood ( Hevea brasiliensis Muell. Arg.) trees grown in Peninsula Malaysia was investigated continuously throughout three years using the pinning and the band-dendrometer method. The pinning and dendrometer data were analyzed for obtaining the correlation with the seasonal rhythm of radial growth and circumferential increments. The data of growth increments measured with the dendrometer continuously for three years indicated growth dormancy during the first three to five months (from January to March or May) each year in all the sample trees, in which annual ring-like features were observed. This means that rubber wood trees have an annual rhythm in the xylem growth. The boundary zone consisted of flattened wood fibers with thin walls, axial parenchyma cells, and small vessels. On the other hand, those obtained from the pinning method showed a vague growth dormancy around March every year. It seemed that growth measurement in tropical trees using the dendrometer is useful for detecting the growth rhythm of cambium.

A comparative study was carried out on fibre length and microfibril angle in Betula pendula Roth. Fibre length increased and microfibril angle decreased from pith to bark. Microfibril angle remained constant from the 15 th annual ring from the pith, to the outermost ring. Fibre length also reached a maximum length at this point although there were some differences at the 30 th ring from the pith.

Pinus sylvestris sapwood stakes were treated with various copper–containing waterborne and oilborne preservatives and exposed in ground for 31 years at Walpeup, Australia. Most of the waterborne preservative treatments contained basic copper carbonate and one or more of the following additives: arsenic pentoxide, pyridine, sodium pentachlorophenate, tannin and benzoic, boric, chromic, salicylic and sorbic acids. Basic copper carbonate and sulphate, at 0.95 kg m −3 of copper, protected the stakes from significant subterranean termite attack at a site in Australia providing a moderate termite hazard. Three additives (arsenic pentoxide at 0.95 kg m −3 , sodium pentachlorophenate at 0.93 kg m −3 and fluoride at 0.9 kg m −3 ) significantly improved the efficacy of basic copper carbonate when used at retentions of 1.7 to 2.0 kg m −3 of copper. The six waterborne preservative combinations that performed best (i.e. rating greater than 6.5 out of 8) against both the termite and decay hazards over the 31 year period contained basic copper carbonate (at least 1.79 kg m −3 of copper) plus arsenic pentoxide (at least 0.92 kg m −3 ). Three of the six combinations also contained chromic acid. The oilborne preservative combination performing best contained basic copper carbonate (1.33 kg m −3 ) and pentachlorophenol (6.64 kg m −3 ) in tall oil. A treatment containing a similar amount of pentachlorophenol in tall oil, but no basic copper carbonate was significantly less effective. Other treatments containing basic copper carbonate and pentachlorophenol in tall oil or the copper compound with sodium pentachlorophenate in oil emulsion performed well. The implications of these results for the current generation of copper-based preservatives are discussed.

A quantitative method for the production of 3,3′,4,4′-tetra-O-methylellagic acid was developed. Ellagic acid was fully methylated under nitrogen and in air using dimethyl sulphate and 25% guanidinium methoxide in N -methyl- 2 -pyrrolidone. The synthesis of a range of polymer precursors derived from 3,3′,4,4′-tetra-O-methylellagic acid are outlined, including the previously unreported 2,3,4,2′,3′,4′-hexamethoxy-6,6′-diphenoyl-dichloride, 2,3,4,2′,3′,4′-hexamethoxy-6,6′-diisocyanato-diphenyl, 2,3,4, 2′,3′,4′-hexamethoxy-6,6′-diamino-diphenyl, 2,3,4,2′,3′,4′-hexamethoxy-6,6′-dihydroxymethyl-diphenyl and 2,3,4,2′,3′,4′-hexamethoxy-diphenyl-6,6′-dialdehyde.

Density and microfibril angle (MFA) of tension wood and normal wood were assessed in the sapwood and heartwood, from three provenanaces of 10-year-old Eucalyptus globulus Labill. Density was measured using a modified saturation method that also enabled the calculation of the extractives lost during saturation. Microdensity and MFA were determined by SilviScan 2, a rapid X-ray densitometry and X-ray diffraction system developed at CSIRO. Significant differences were found in density and extractives between provenances and also density between the sapwood and adjacent heartwood from each provenance. This result may explain some of the drying differences between provenances found in an earlier study (Washusen and Ilic 2000). Sapwood samples with high percentages of tension wood fibres had high density and a significant positive correlation was found between microdensity and tension wood fibre percentage. MFA was found to be very low in normal wood in the sapwood, where most tension wood was found, so tension wood could not be identified by MFA. The positive association between tension wood and wood density suggests that caution should be taken when selecting trees for high wood density in tree improvement programs.

Residual lignins have been isolated by enzymatic hydrolysis from sulfite, kraft, ASAM and soda/AQ/MeOH pulps obtained both of spruce and beech wood. The protein content of the samples were in the range of 2 to 61 % and the carbohydrate content fluctuated roughly between 1 and 12 %. Seven of the isolates have been submitted to analytical pyrolysis (Py-GC/MS) aiming at the determination of the lignin composition in terms of 4-hydroxy-phenylpropane, guaiacylpropane, and syringylpropane units, referred to in the following as H, G, and S units. Pyrolysis of proteins leads mainly to phenol, cresol, and indole. Phenol and cresol of protein origin may influence seriously the H content determination of lignins. However, the contribution of protein to this compounds can be corrected successfully based on the intensity of the indole peak in the pyrograms. Nevertheless, the pyrolysis results should not be over-interpreted concerning the H contents in the case of samples heavily contaminated with proteins. As analytical pyrolysis overestimates the S content in a similar manner as the chemical degradation techniques do, an empirical correction equation was used to approximate the “true”" S content. Py-GC/MS gave systematic and reproducible differences between the residual lignins on the one hand, and the MWLs, which have been pyrolysed for comparison, on the other hand. The fingerprinting ability of analytical pyrolysis, the G/S ratios of beech residual lignins, and the unusual properties of ASAM residual lignins with their high S contents are discussed.

The effect of two different wood modification treatments on the lignin of Norway spruce wood was studied by means of cellular UV-spectroscopy. The modification treatments chosen were acetylation using acetic anhydride and a two step hydrothermal treatment. Small cross sectional thin slides from the wood surface were taken and were subsequently analysed using a UV-micro-spectro-photometer. The modified samples were compared with a non-treated control sample. The results revealed changes in the absorption spectra of lignin after both modification treatments. Spectra of the compound middle lamella (CML) of acetylated wood revealed a decrease in the lignin-specific absorption maximum at 280nm, which is considered to be caused by superficial leaching of lignin due to acetylation. The retarding effect of acetylation on UV-degradation of wood is discussed. In hydrothermal-treated wood the 280nm maximum was increased within the S2 layer. This maximum remained almost unchanged in the CML while a lower maximum was observed at about 330nm. Changes in the chromophoric behaviour of lignin are probably caused by de-masking reactions within the S2 layer resulting from hydrolysis of carbohydrates and side chain reactions. Both treatments lead to a severe decrease in absorption at the lower end of the spectrum towards 250nm which is possibly attributed to changes or even splitting of biphenyls.

The formation and stability of furans formed from pentoses and hexoses were studied in acetic acid/formic acid mixtures which are applied in the FORMACELL pulping process. For comparison, acetic acid/water mixtures with and without addition of HCl were included in the study. The investigations demonstrated that furfural can be obtained in high yields from xylose and xylan. Hexoses are converted to hydroxymethylfurfural (HMF), acetoxymethylfurfural (AMF) and furfural. Here, the water content of the reaction mixture influences the ratio of HMF and AMF in the solution. Stability studies revealed that furfural and HMF exhibit a high stability in acetic acid/formic acid mixtures. This explained the high furfural yields previously published for acetic acid pulping. The long-time stability of furans was investigated for 275 days at room temperature. No significant losses occurred suggesting that organic acids act as radical scavengers inhibiting oxidative degradation.

To determine more accurately the amount of polyflavanoids in tannin extracts from radiata pine bark, which react with formaldehyde, it is important to elucidate chemical structures of (﹢)-catechin-formaldehyde reaction products (Stiasny precipitates). The Stiasny value of 106.4% for (﹢)-catechin was obtained from the reaction with formaldehyde under strong acid conditions. This value is almost identical to the value calculated from the Stiasny precipitates, which were formed in the ratio of two molecules of (﹢)-catechin to three molecules of formaldehyde. The solid-state 13 C NMR spectrum was measured to elucidate the structures of the Stiasny precipitates, and analysed on the basis of the chemical shifts of (﹢)-catechin. The NMR results indicate that C-6 and C-8 in the A-ring are bonded by methylene bridges to form polymers, and also form methylene bridges with C2′, C5′ or C6′ in the B-ring of a catechin unit. Consequently, the reaction products of (﹢)-catechin-formaldehyde under strong acid conditions (Stiasny precipitates) are (﹢)-catechin-polymers, which consist of two moles of (﹢)-catechin and three moles of formaldehyde. The methylene bridges are formed mostly between A-rings, and less frequently, between A- and B-rings and between B-rings of the catechin units.

Thermomechanical (TMP) and chemo-thermomechanical pulps (CTMP) were prepared from spruce under different pulping conditions. The fibres were dried at 70 °C and medium density fibreboards (MDF) were made therefrom in pilot plant scale using urea-formaldehyde resins as a binder. The results of testing the physical-mechanical properties reveal that the pulping temperature has a significant influence on the thickness swelling and water absorption of the boards. MDF prepared from fibres produced at high pulping temperature (180 °C) generally show lower thickness swelling and water absorption than MDF made from fibres produced at low pulping temperature (140°C and 160 °C). However, high pulping temperature may have a negative effect on the internal bond strength of the boards. In general, CTMP leads to MDF with higher internal bonding strength compared to those derived from TMP. In addition, the influence of different drying conditions (150 °C and 170 °C) of TMP and CTMP on the physical-mechanical properties of MDF was assessed. MDF made from CTMP showed lower thickness swelling when dried under high temperature.

The pulp and paper industry in China has been growing rapidly as the nation's population and economy have grown. As a result, there has been a huge demand for pulp and paper raw materials. China has a long tradition for using non-wood raw materials for pulp and paper due to its limited forest resources and rich supply of agricultural residues and non-wood plants. Agricultural residues, such as rice straw and wheat straw, are traditional raw materials for China's paper industry. Massive plantation of bamboo provides an increasingly important source of raw material for pulp and paper. Problems with non-wood fiber include collection and transportation, storage and handling, washing, bleaching, papermaking, and chemical recovery. Small mills, primary users of non-wood fiber, are typically deficient in pollution control and subject to government closure. This paper reviews non-wood fibers commonly used in China's pulp and paper industry. By increased knowledge of use of non-wood fibers, wood suppliers can plan for access to the growing Chinese market.