PEG quantification and examination of molecular weight distribution in wood cell walls

The amounts of polyethylene glycol (PEG) of a range of molecular weights (200–20000) and their mixtures in wood cell walls were estimated by preferential extraction of PEG from the cell lumens. PEG extracted by toluene over 1 h extraction periods was examined by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) spectroscopy. The assumption that a non-polar solvent would not extract PEG from the cell walls was shown to be invalid. Only about 0.07–0.08 g PEG per g dry wood was retained in wood after 12 h-toluene extraction and this value was not significantly affected by PEG molecular weight (MW). This relatively low cell wall content can result in as high as 50% cell wall bulking (CWB) which is dependent on MW. Samples treated with mixture of PEG MWs indicated preferential penetration of lower MW into cell walls.     

Solute diffusion into cell walls in solution-impregnated wood under conditioning process III: effect of relative humidity schedule on solute diffusion into shrinking cell walls

This study has focused on solute diffusing into cell walls in solution-impregnated wood under conditioning, process of evaporating solvent. The purpose of this paper was to clarify the RH- (relative humidity-) schedule that promotes the solute diffusion into shrinking cell walls during conditioning. The wood samples impregnated with a 20 mass% aqueous solution of polyethylene glycol (PEG1540) was conditioned with a temperature of 40?°C to the equilibrium point at the RH where the samples swelled maximally. The samples were subsequently conditioned at 40?°C under the schedules including four ways of RH-decrease steps where the cell walls shrunk. The amount of solute (PEGs) diffused into cell walls during the conditioning logarithmically increased with increasing the number of the RH-decrease steps. This was well explained by the theoretical model that describes the solute diffusion into shrinking cell walls. It is clarified from the model that the RH, or moisture content of the sample, should be decreased as gradually as possible to increase the total amount of diffused solute into shrinking cell walls, and that the amount of diffused solute is smaller for the lower moisture content. The model also suggests that effect of change in RH schedule on change in total amount of diffused solute does not depend on solute diffusivity in the sample under drying in a vacuum over phosphorous pentoxide, and that impregnated wood should be conditioned under natural convection rather than forced convection for promoting the diffusion into shrinking cell walls.     

Distribution of boron in wood treated with aqueous and methanolic boric acid solutions

The distributions of boron in Japanese cedar (Cryptomeria japonica D. Don) sapwood blocks treated with aqueous or methanolic boric acid [B(OH)₃] solutions were explored through Raman spectroscopy and prompt gamma-ray analysis (PGA). B(OH)₃ was the sole boron species observed in Raman spectra of the wood blocks treated with either solution. Plots of weight gain of the treated wood blocks versus boron concentration in treatment solutions were found to be linear. The results indicated that the methanolic solution makes it possible to impregnate wood with much larger amounts of boron than the aqueous solution. PGA confirmed that B(OH)₃ was highly enriched near the end grains of the treated wood blocks. Raman measurements suggested that boron content in the bulk of the wood block is not as large as expected from the weight gain of the treated wood blocks when an ordinary air-drying method is used. It was concluded that the aqueous solution impregnates the cell walls of wood with boron more easily than the methanolic solution. Part of this report was presented at the 55th (Kyoto, March 2005) and 56th (Akita, August 2006) Annual Meetings of the Japan Wood Research Society. This article follows the previous rapid communication “Analysis of boron in wood treated with boric acid solutions using Doppler broadening method of prompt gamma-rays.” J Wood Sci (2006) 52:279–281     

Evaluation of chemical treatments on dimensional stabilization of archeological waterlogged hardwoods obtained from the Thang Long Imperial Citadel site,Vietnam

In this article, the conservation of seven archeological waterlogged woods (WW) with polyethylene glycol (PEG) 4000, trehalose, and feather keratin was investigated. The results showed that the dimensional stability of WWs significantly improved after the different treatments. The anti-shrink efficiency values of the WWs treated with keratin ranged between 72.5 and 96.2% depending on the species and degree of wood degradation. These values varied from 82.4 to 96.9% for the WWs treated with PEG or trehalose. Microscopic observations showed that the chemically-treated woods maintained their original cell structures, forms, and shapes. It was also revealed that the reinforcement of cell walls by the feather keratin treatment was different from those observed for the PEG or trehalose treatments. It was observed that PEG and trehalose primarily filled the wood voids, while keratin predominantly absorbed on the cell walls and middle lamellae. Based on the improved dimensional stability of wood, shortened impregnation time, removability of chemical, and esthetic results obtained from the treatment, keratin showed a good performance in average as a preservation agent.     

The fluorescence characteristics of furfurylated wood studied by fluorescence spectroscopy and confocal laser scanning microscopy

The fluorescence of furfurylated wood was studied. Furfurylation of wood introduced fluorescent curing products into the cell walls. Fluorescent products were also found in the lumina if high loadings were used and/or if the wood contained cells with small radii. More intense fluorescence was obtained from lignin-rich parts of the compound cell wall (i.e., the middle lamella and the cell corners) than from the secondary cell wall if the wood was impregnated using furfuryl alcohol (FA), while impregnation using small poly(FA) oligomers showed no or only minor differences between different regions. The study also showed that when higher amounts of catalyst were added to the impregnation liquid, a red-shift in the fluorescence from the furfurylated wood was seen, corresponding to an increased conjugation length of conjugated poly(FA) formed within the wood cell wall. Longer conjugation length than within the cell wall was observed for the poly(FA) formed within the lumina. This indicates that the cell wall polymers restrict poly(FA) formation.     

Determining pore size distribution in wet earlywood cell wall by solute exclusion using total organic carbon technique (TOC)

Solute exclusion is a probe technique useful to determine the pore volume and pore size distribution of a cell wall network; however, accurate measuring of molecular probe concentration is critical. In this study, the concentration of polyethylene glycol (PEG) and glucose was measured by detection of their organic carbon using a total organic carbon (TOC) equipment. PEG and glucose concentration by TOC is based on the quantitative oxidation of the organic matter contained in the solution, and then, produced CO₂ is stoichiometrically correlated with the TOC value. In this work on Pinus radiata earlywood cell wall, the fiber saturation point was 0.72 mL/g and it was reached by a molecular probe size with a radius of gyration R _g = 5.96 Å. Moreover, the mean pore size present in the wood samples has a size equivalent to a molecular probe with a radius of gyration of 3.77 Å. Since TOC is based on the quantitative oxidation of the organic matter contained in the solution, it is essential to wash and rinse the wood samples to prevent that other carbon sources as extractives modify PEG and glucose concentration. Finally, the accuracy of TOC to determine the pore size distribution in the wet wood cell wall is subject to limitations of the solute exclusion technique.     

Measurement of cell wall penetration in wood of water-based chemicals using SEM/EDS and STEM/EDS technique

Summary The penetration of bulking chemicals (glycerol, PEG 200, PEG 1500 and pentaerythritol) into the cell wall of wood, Pinus sylvestris, has been studied. A number of different methods for determining the distribution of chemicals in the cell wall were used. Measurements of the increase in cell wall thickness showed that glycerol and PEG 200 resulted in greater cell wall bulking compared to PEG 1500 and pentaerythritol. Examination with SEM/EDS-linescan confirmed these results. However, the better resolution possible with the STEM/EDS-linescan revealed an inhomogenous distribution of the chemical in the cell wall. This is believed to be due to microcracks in the cell wall which are the result of the initial drying of the wood. This general damage to the cell wall could be the reason for the failure to find a stabilizing chemical and method. Received 10 February 1997     

The ultrastructure of cellulose from wood

Summary During the delignification of wood several processes overlap one another. One of these is the penetration of the wood samples by the delignifying solution. Penetration tests under different conditions show that there is almost no difference in the penetration depth of wood samples penetrated by diffusion only and of wood samples treated with pressure. In both cases the pits are closed during the flow of fluids. Vacuum treated samples show better penetration and most of the pits in these samples remain open. The distribution of fluids within the cell walls takes place in the intercellular spaces, in small openings in the compound middle lamella and in the secondary wall 1 as well as in very fine pores in the secondary wall 2. The penetration of a wood sample is greatly facilitated if the sample is mechanically injured. A slowly proceeding delignification with ethylene sulphite shows that the delignification obviously starts in the S 1 layer and proceeds from there towards the compound middle lamella and the S 2 layer. In the first stages of lignin removal the compound middle lamella is also attacked, the attack beginning at the border of the pit chambers.     

Improving sample preparation to investigate lignin intensity of xylem at the cellular level by confocal Raman microspectroscopy of Populus tomentosa

Confocal Raman microspectroscopy(CRM)is an important tool for analyzing the compositional distribution of cell walls in situ.In this study,we improved the sample preparation method using paraffin-embedded sections combined with hexane dewaxing to obtain high resolution Raman images.We determined that the cell wall components of fiber cells were different from those of ray cells and vessel cells in the xylem of Populus tomentosa.Acetyl bromide and CRM methods produced similar trends when the difference in lignin intensity in the xylem region was compared between transgenic PtrLac4 and wild-type P.tomentosa.However,CRM proved more useful to analyze the lignin distribution in each cell type and distinguished the detailed difference in lignin intensity at the cellular level.Thus,CRM proved to be a useful in situ method to rapidly analyze the spatial variation of lignin content in the xylem of woody plants.     

Etching of wood surfaces by glow discharge plasma

This research tests the hypothesis that plasma will cause differential etching of wood cell walls because of variation in the susceptibility of aromatic and aliphatic polymers to degradation by plasma. Wood was exposed to glow discharge plasma, and scanning electron microscopy and chromatic confocal profilometry were used to examine etching of cell walls. Plasma etched cell walls and made them thinner, but the middle lamella was more resistant to etching than the secondary wall. Plasma created small voids within the secondary wall, which were separated by thin lamellae connected to the middle lamella and tertiary wall layers. Larger voids were created in cell walls by the etching of bordered and half-bordered pits. Etching of the uppermost layer of cells at wood surfaces occurs first and when large voids are created in the walls of these cells then significant plasma etching of the underlying cells occurs. Etching of wood cell walls can be quantified using confocal profilometry, and using this technique a strong relationship between applied plasma energy and volume of cell wall etched by plasma was observed. It is concluded that all of wood’s polymers can be degraded by plasma even though cell wall layers that are rich in lignin are etched more slowly than other parts of the cell wall.     

Comparison of the effect of chemical and mechanical treatment of end-grain surfaces on adhesive bond strength

Abstract

End-grain surfaces of spruce wood specimens that were planed with a microtome knife were chemically modified by treatment with bleaching reagents, namely sodium hypochlorite and peracetic acid, and the effect of the surface modification on bond strength of end-grain joints was studied. The chemically treated samples were compared with sawn surfaces, microtome-planed specimens that were additionally irradiated by light, and surfaces that were solely planed with a microtome knife. Significantly higher bond strength compared with the microtome-planed specimens was observed for the sawn specimens and for hypochlorite-modified samples. These findings were ascribed on the one hand to an increased surface roughness resulting from the mechanical process of sawing leading to an enlargement of the bonding area. On the other hand, during the etching process with sodium hypochlorite a pulp of cell walls and cell wall fragments was formed, leading to a partially closed surface which prevented overpenetration of adhesive into the opened cells.     

Studies on holocellulose and alpha-cellulose from spruce wood using cryo-ultramicrotomy part 2: The influence of heavy metal salt impregnation and the dimensions of delignified cell wall layers

Summary Delignified samples of spruce wood were impregnated with various heavy metal salts and afterwards cut on a cryo-ultramicrotome. In the electron microscope a different swelling of the cell walls and different staining effects depending on the impregnated salt were observed. The thickness of the cell wall layers was determined in holocelluloses containing different amounts of residual lignin and in holocelluloses impregnated with various heavy metal salts. From the results it can be seen that the swelling state of the wall layers is determined by the competitive processes of swelling and loss of substance. Metal salt impregnations cause different swelling states of the wall layers. Some of the salts show a specific deposition within the cell wall which is interpreted as a chemical affinity to polyoses.Supported by Deutsche Forschungsgemeinschaft. The assistance of Miss U. Schwartz with the preparation is greatly appreciated.     

Ultrastructural analysis of the differentiation process of secondary xylem vessel element in Populus deltoides

Using electronic microscopy, ultrastructural changes were observed during differentiation in a secondary xylem vessel element (VE) in Populus deltoides. Results showed that morphological development of VE differentiation was successively divided into three stages. First was primary cell wall outspread (the initial stage), where the VE was highly vacuolated and the protoplasma distributed along the cell wall. Second was secondary cell wall construction (the pivotal stage), where substances accumulated before the tonoplast broke, and the VE organelle was distinct. Golgi bodies and vesicles, which were associated closely with synthesis and transportation of secondary cell wall substances, were also abundant. After the tonoplast broke, these substances accumulated faster. Simultaneously, the protoplasm was disaggregated and the agglomerated chromatin was distributed over the margin of the nucleus, showing the typical characteristics of programmed cell death (PCD). During secondary cell wall formation, no cell wall substances accumulated between the terminal cell walls of neighboring VEs. In addition, terminal cell wall substances were disaggregated in the post secondary cell wall formation. Later, when the remnant terminal cell wall was broken in the third stage, perforation occurred. Thus, for these successive stages of VE differentiation, the critical stage, when differentiation was not reversible, was at the start of secondary cell wall formation with succeeding VE differentiation similar to a typical PCD process.     

Changes in ultrastructure of Picea abies needles following severe long‐term winter frost

An uncommonly harsh winter occurred in Finland in 1986/1987, when the minimum monthly temperatures were lower than ‐30°C in December, January and February. This study reports the development of visible symptoms, changes in electrolyte leakage and ultrastructure in Picea abies needles from a rural and an industrial area during this period. The first frost‐induced visible symptoms, entirely or partially greyish needles, appeared in late February following a mild spell. Gradually the discoloured needles turned reddish‐brown and most of the injured needles were shed before the onset of the new season growth. Electrolyte leakage, measured as relative conductivity (RC %), showed substantially higher wintertime values (RC ca 75%) in greyish needles compared with healthy looking green needles (RC ca 30%). Light microscopy showed contracted protoplasts and collapsed cell walls in the greyish part of the needle. The main ultrastructural symptoms in all the samples were the withdrawal of plasma membrane from the cell wall, darkening of the cytoplasm, disappearance of the tonoplast (and central vacuole), contraction of the protoplast and finally collapse of the cell walls and total disintegration of the protoplast. There were no qualitative differences in the frost‐induced visible or structural symptoms between the rural and industrial area.     

Immunolocalization of (1,4)-beta-galactan in tension wood fibers of poplar

The occurrence and distribution of (1,4)-beta-galactan in wood cells of poplar (Populus trichocarpa Torr. & A. Gray x P. koreana Rehder) were studied by immunolabeling with a monoclonal antibody (LM5) specific to this carbohydrate epitope. Immunofluorescence microscopy revealed exclusive binding of the LM5 antibody to tension wood fibers, indicating the specific presence of (1,4)-beta-galactan in cell walls of this wood cell type. Higher magnifications achieved with the fluorescence microscope and additional immunogold electron microscopy showed that the binding of the LM5 antibody was mainly restricted to a narrow cell wall area between the gelatinous G-layer and the secondary cell wall. This labeling pattern strongly suggests a role of (1,4)-beta-galactan in cross-linking the G-layer and secondary cell wall. Furthermore, the exclusive localization of (1,4)-beta-galactan in tension wood strengthens the view that this carbohydrate epitope can be considered a highly specific marker of reaction wood formation in mechanically stressed trees.     

TEM/FE-SEM studies on tension wood fibres of Acer spp., Fagus sylvatica L. and Quercus robur L.

Tension wood (TW) fibres from maple, beech and oak were analysed with special emphasis on the cell wall fine structure and deposition of aromatic compounds within the gelatinous layer (GL). For this purpose, transmission electron microscopy (TEM) was applied after section staining with potassium permanganate. There was evidence for the occurrence of aromatic compounds in the GLs of fibres of all three species. Some GLs showed a concentric sub-layering. Hence, conclusions about the biosynthetic activities during cell wall formation in TW could be derived. Additional information about structural characteristics of TW fibres were obtained by means of field emission electron microscopy. High-resolution micrographs of cell walls were used for measurements of diameter and microfibril angle (MFA) of cellulose aggregates (CAG). CAG of 7 nm were observed although their diameter varied greatly in the GLs. MFA in the secondary wall of TW was slightly smaller than in opposite wood. The microscopic methods provided complementary ultrastructural and topochemical information on tension wood fibres. The subcellular localisation of aromatic compounds and the observations of the ultrastructural morphology will contribute to the understanding of origin and functionality of TW and its characteristic GL.     

Solute diffusion into cell walls in solution-impregnated wood under conditioning process IV: effect of temperature on solute diffusivity

This study has focused on solute diffusing into cell walls in solution-impregnated wood under conditioning, process of evaporating solvent. The amount of the diffusion is known to be determined by the solute diffusivity and the solute-concentration difference between cell walls and cell cavities. Purpose of this paper was to clarify the effect of temperature only on the solute diffusivity that is directionally related to the thermal vibration of the solute molecule. The cross-cut block of hinoki (Chamaecyparis obtusa), polyethylene glycol (PEG1540), and water was employed as wood sample, solute, and solvent, respectively. The sample impregnated with a 20 mass% solution was conditioned at 20, 35, or 50 °C to finish the solute diffusion evaluated using the dimension of the sample that was conditioned followed by drying in a vacuum. To unify the solute-concentration difference, for all temperatures, the equilibrium moisture content was unified and the solvent-evaporation rate was controlled in three ways during conditioning. The solute diffusivity was higher in order of 35, 50, and 20 °C, which was evaluated by the solute diffusion at the same evaporation rate. It is clarified that the diffusivity increases with increasing the dimension of cell walls rather than with increasing the thermal vibration of solute molecule.     

Dimensional stabilization of wood with water soluble fire retardant bulking chemicals compared with polyethylene glycol-1000

Summary Mono and diammonium acid phosphate, ammonium sulfamate, and sodium silicate were compared with polyethylene glycol-1000 as bulking dimension stabilizing agents using Engelmann spruce cross sectional wafers. Limiting antiswell efficiencies are equal to the volume fraction of chemical in a saturated solution. The experimental antiswell efficiencies due to bulking are the percent increase in the dry cross sectional area of the wafers caused by deposition of dry chemical within the cell walls divided by the percent swelling in water. These values for the phosphates, the sulfamate, and the polyethylene glycol approach the limiting values from solubility indicating that chemical continues to diffuse into the cell walls as the wood is dried to virtually attain a saturated solution within that structure. The sodium silicate gave an apparent negative antiswell efficiency as collapse of the fibers on drying exceeded the actual bulking. Antiswell efficiencies between 0 and 30% relative humidity, 0 and 90% relative humidity and 30 and 90% relative humidity were in general still lower. This is largely due to the treated systems taking up more water than the controls, especially at the higher relative humidity. Antiswell efficiencies for the mono ammonium acid phosphate ranged from 20 to 27%, for the diammonium acid phosphate from 28 to 37%, the ammonium sulfamate from 51 to 66% and the polyethylene glycol from 63 to 77%.Paper No. 4245 of the Journal Series of North Carolina State University Agricultural Experiment Station, Raleigh, North Carolina     

Early stages of bordered pit formation in radiata pine

Summary The development of bordered pit sites in the cambium of Pinus radiata D. Don was studied using light and electron microscopy. No primary pit fields occur in the fusiform initials and no plasmodesmatal connections were seen in radial walls of undifferentiated cambial cells or differentiating tracheids. Thin areas bounded by a thick rim appear in the radial walls of these cells once enlargement is under way. They appear to result from a redistribution of wall material which, it is suggested, is brought about by some agent which penetrates the primary wall. The thin areas, which are the sites of bordered pits, are common to the cells joined by the affected wall, and the rim which protrudes symmetrically into each cell provides a template on which the border is subsequently formed. This mechanism would explain how symmetrical pit pairs can be formed in the absence of plasmodesmata.     

Ultraviolet resistance and other physical properties of softwood polymer nanocomposites reinforced with ZnO nanoparticles and nanoclay

Wood polymer nanocomposites (WPNCs) based on nano-ZnO and nanoclay were prepared by impregnation of melamine formaldehyde–furfuryl alcohol copolymer, 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU), a cross-linking agent and a renewable polymer obtained as a gum from the plant Moringa oleifera under vacuum condition. Fourier transform infrared spectroscopy (FTIR) and X-ray diffractometry (XRD) studies were employed for the characterization of modified ZnO and WPNCs. The change in crystallinity index (CrI) value of the cellulose in wood and the distribution of ZnO nanoparticles in composites were determined using FTIR and XRD. Scanning electron microscopy and Transmission electron microscopy showed the presence of nanoparticles and nanoclay in the cell lumen or cell wall of wood. An enhanced UV resistance property was shown by the treated wood samples as judged by lower weight loss, carbonyl index, lignin index, cellulose CrI values, and mechanical property loss compared to the untreated wood samples. Wood polymer composites treated with 3 phr each of nanoclay, ZnO, and the plant gum showed an improvement in mechanical properties, flame-retarding properties, thermal stability, and lower water uptake capacity.