The effect of compression and incision on wood veneer and plywood physical and mechanical properties

ABSTRACT

Drying takes the largest share of energy in plywood production, and varying moisture content of veneers necessitates re-drying that often leads to over-dry veneers with deactivated surfaces, which may promote imperfect bonding. In order to decrease the drying time, reduce the need for re-drying of veneers, and improve the quality of plywood, birch and spruce veneers were subjected to pre-treatment by cold compression, incision, or a combination of the two. The effects of pre-treatment on the veneer and plywood quality were assessed by standard tests. Compression had a beneficial effect on water removal of the wettest veneers (spruce sapwood (SW) and birch), but some thickness reduction was observed in the veneers as well as the finished birch plywood. Compression led to thickness reduction of spruce veneers, but had no effect on SW plywood thickness likely due to higher viscoelasticity. Both compression and the combination of incising and compression levelled the moisture variation within the compressed stacks. Incision improved the modulus of elasticity of birch plywood, shear strength of SW plywood, and both bending and shear strengths of heartwood plywood. Higher surface pressure decreased the drying time of spruce SW in both plain compression and combined incision and compression pre-treatment.     

Comparative susceptibility of pine,spruce and larch to sapstain

Summary This study compared the susceptibility of five UK‐grown conifer species to colonization by sapstain fungi in two trials carried out in consecutive years. The conifers consisted of Sitka spruce (Picea sitchensis), Japanese larch (Larix kaempferi), Norway spruce (Picea abies), Scots pine (Pinus sylvestris) and lodgepole pine (Pinus contorta). Freshly cut 1‐m logs were exposed to the available inoculum of sapstain fungi from April to August in a woodland environment in the south east of England. Logs of each species were removed after 1‐, 2‐ and 4‐month exposure and sampled destructively to assess the amount of sapstain. In the second trial, per cent moisture content and concentrations of nitrogen, carbohydrate and phenolic compounds in the sapwood were also measured at the start and end of the trial. After 2 months, only the sapwood of both pine species had significant levels of sapstain; mean values of 37% and 19% for lodgepole pine (year 1 and year 2 respectively) and 12% and 1% for Scots pine. After 4 months, the levels of sapstain in both pine species exceeded 60% in both years. By contrast, very little sapstain developed in the other conifer species with maximum mean values of 10% for Norway spruce, 3.5% for larch and less than 1% for Sitka spruce. Overall, the moisture content of the logs decreased progressively in all species over the length of the trial. However, pine logs tended to retain higher levels of moisture throughout the trial compared with spruce or larch. The relatively higher moisture content of pine sapwood may be closer to the optimal moisture content that sapstain fungi require for infection and colonization, thereby contributing to the increased susceptibility of pine compared with the other conifer species. The pine logs also suffered from some colonization by bark beetles (Ips sexdentatus), which increased the inoculum potential and the opportunity for colonization by sapstain fungi. In addition, particular phenolic compounds in conifer sapwood may play a role in determining the resistance of some species to sapstain. Notably the most resistant species, Sitka spruce, was the only softwood that still retained detectable levels of phenolics in the sapwood to the end of the trial.     

The effect of girdling on the moisture content of small-sized trees

In this study, the effect of girdling on the moisture content of small-sized trees for heat energy production was clarified. The moisture content was measured for Scots pine (Pinus sylvestris), Norway spruce (Picea abies), and Downy birch (Betula pubescens) during two growing seasons after girdling. The trees were girdled at breast height for around 30 cm by removing the bark, phloem, and cambium from around the stem. At the beginning of the growing season the mean moisture content of the living Scots pine (P. sylvestris) and Norway spruce (P. abies) was 60%, and for Downy birch (B. pubescens) it was 50%. During the first growing season the effect of girdling on the moisture content was low, but during the second growing season the moisture content decreased significantly. The moisture content of the Norway spruce (P. abies) (23%) and Downy birch (B. pubescens) (33%) was at its lowest point at 14 months after girdling. There were no significant changes in the moisture content of the Scots pine (P. sylvestris) in this study. The results of this study can be used in basic research and in the development of energy wood production.     

Outdoor exposure of untreated Scots pine (Pinus sylvestris L.) and Norway spruce [Picea abies (L.) Karst.] wood samples

Abstract

Untreated Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) samples were exposed above ground in a durability test for 6 years. The samples consisted of three pieces of wood, 22×95×500 mm, screwed together; two pieces lengthwise with a third piece overlapping. Weight was measured, to calculate moisture content (MC), and samples checked regularly for cracks and fungal growth. Parameters investigated were heartwood/sapwood (pine), annual ring orientation (spruce), stand site, annual ring width and density. Stand site, annual ring width and density had no influence on MC or fungal growth for either pine or spruce. Spruce samples with vertical annual rings had fewer cracks than samples with horizontal annual rings. Pine sapwood samples had a high MC and a large amount of rot fungi, while heartwood had a lower MC and no rot. Most spruce samples were similar to pine heartwood, except from a few samples that had high MC and fungal growth. Those were all sawn from the outer part of the log. Therefore, it can be stated that spruce sawn from the inner part has almost the same properties as pine heartwood, while spruce from the outer part of the log has similar properties to pine sapwood.     

Modelling moisture content and dry matter loss during storage of logging residues for energy

Abstract

To achieve optimal utilisation of logging residues for energy, it is important to know how different handling and storage methods affect fuel properties. The aim of this study was to model how the moisture content and dry matter losses of logging residues develop during storage. Logging residues were collected from five different stands of spruce and pine during different seasons of the year and stored in the same location. The logging residues were stored in covered piles of bundled residues and loose residues. Only minor differences were found in the moisture content profiles between piles of bundles and loose residues. Logging residues located in the centre of both types of piles had considerably lower moisture content than the outer parts. The moisture content significantly affected dry matter loss, with the highest dry matter losses being found in the samples with the least favourable drying conditions. The dry matter losses varied between 1 and 3% per month. Significantly higher dry matter losses were found in the spruce bundles than in the pine bundles. Seasoned logging residues had the lowest dry matter loss, while the logging residues harvested and piled in the autumn had the highest loss.     

中山杉单板防腐处理对胶合板性能的影响

以CCA为木材防腐剂,对中山杉单板进行防腐处理,然后热压成胶合板。研究结果表明:中山杉单板经防腐处理后制造的胶合板含水率、密度、胶合强度要略高于未经防腐处理的中山杉胶合板,且含水率与胶合强度均达到I类胶合板要求。单板经防腐处理后的胶合板弹性模量、静曲强度差异不显著。不同方法处理单板对胶合板载药量影响很大,其中满细胞法最高,浸泡法和双真空法相近,涂刷法最低。     

脱脂与未脱脂马尾松胶合板的性能差异研究

采用热压方式对脱脂和未脱脂马尾松胶合板的性能进行研究。结果表明:在马尾松单板水煮脱脂过程中,随着脱脂时间的延长,其脱脂率逐渐加大,但脱脂速度相对降低。马尾松单板水煮脱脂在1~3 h内的脱脂率变化不大,脱脂效果与水煮时间关系不密切;在3~5 h内,单板脱脂率变化较大,脱脂率与水煮时间有密切关系。板坯热压的前3~4 min,未脱脂板坯的升温速度比脱脂板坯升温速度快;4 min后脱脂板坯的升温速度明显快于未脱脂板坯,而未脱脂板坯在较长时间内温度仅呈缓慢升高趋势。脱脂处理的马尾松胶合板在物理力学性能各个指标上都明显优于未脱脂处理的马尾松胶合板。     

Durability of thermally modified sapwood and heartwood of Scots pine and Norway spruce in the modified double layer test

In the present study, durability of untreated and thermally modified sapwood and heartwood of Scots pine and Norway spruce was examined using a modified double layer test. Base layer samples were partly on contact with ground where exposure conditions were harder than that in a double layer test above the ground. The base layer on ground contact gave results already after one year of exposure in Finnish climate, but the top layer of a double layer test element simulated more the situation of decking exposure.

Significant differences in durability and moisture content (MC) between the wood materials were detected after six years of exposure in the field. Thermally modified pine heartwood performed very well in all layers of the test element and only minor signs of decay were found in some of the base samples. Both sapwood and heartwood of thermally modified spruce were suffering only slight amounts of decay while thermally modified pine sapwood was slightly or moderately decayed. Untreated sapwood samples of pine and spruce were severely decayed or reached failure rating after six years in the field. Untreated heartwood samples performed clearly better. The highest MCs were measured from untreated and thermally modified pine samples. Thermal modification increased significantly the durability and decreased the MC values of all wood materials.     

Prediction of the optimum veneer drying temperature for good bonding in plywood manufacturing by means of artificial neural network

Veneer drying is one of the most important stages in the manufacturing of veneer-based composites such as plywood and laminated veneer lumber. Due to the high drying costs, increased temperatures are being used commonly in plywood industry to reduce the overall drying time and increase capacity. However, high drying temperatures can alter some physical, mechanical and chemical characteristics of wood and cause some drying-related defects. In this study, it was attempted to predict the optimum drying temperature for beech and spruce veneers via artificial neural network modeling for optimum bonding. Therefore, bonding shear strength values of plywood panels manufactured from beech and spruce veneers dried at temperatures of 20, 110, 150 and 180 °C were obtained experimentally. Then, the intermediate bond strength values based on veneer drying temperatures were predicted by artificial neural network modeling, and the values not measured experimentally were evaluated. The optimum drying temperature values that yielded the highest bonding strength were obtained as 169 °C for urea formaldehyde and 125 °C for phenol formaldehyde adhesive in beech plywood panels, while 162 °C for urea formaldehyde and 151 °C for phenol formaldehyde in spruce plywood panels.     

Numerical and experimental study of moisture-induced stress and strain field developments in timber logs

When solid wood dries from a green condition to a moisture content used for further processing, moisture-induced fracture and stresses can occur. The drying stresses arise because of internal deformation constraints that are strongly affected by the cross-sectional moisture gradient differential shrinkage and the inhomogeneity of the material. To obtain a better understanding of how stresses develop during climatic variations, the field histories of stresses (and strains) in cross sections in their entirety need to be studied. The present paper reports on experiments and numerical simulations concerned with analysing the development of strains and stresses during the drying of 15-mm-thick discs of Norway spruce timber log. The samples were dried at 23 °C and relative humidity of 64 % from a green condition to equilibrium moisture content. The moisture gradient in the longitudinal direction was minimised by use of thin discs simplifying the moisture history of the samples studied. The strain field history was measured throughout the drying process by use of a digital image correlation system. Numerical simulations of the samples agreed rather well with the experimental strain results obtained. The stress results also indicated where in the cross section and when fractures could be expected to occur during drying. More optimal drying schemes showed markedly reduced stress generation.     

Estimation of shrinkage coefficients in radial and tangential directions from CT images

The aim of the present work was to use the displacement information generated from the spatial alignment in order to compute wood shrinkage in the radial and tangential directions in computed tomography (CT) images, and to compare the results with those obtained with computer-aided design software on the same images. To estimate the shrinkage coefficients from tomography images, wood specimens in the green state, equilibrium moisture content 15% and 8% state and oven dry condition were scanned. Specimens were taken from Norway spruce and Scots pine logs. The root-mean-square-error calculations showed acceptable small differences between the two measuring methods, which means that the algorithm is a useful tool for estimating the shrinkage coefficients in radial and tangential direction from CT images. This provides an image processing tool to monitor the dimensional changes during the drying and heat treatment process.     

Isolation and characterisation of water soluble polysaccharides from Norway spruce and Scots pine

Water soluble polysaccharides from Norway spruce, Scots pine, and Siberian larch were compared. For all species the total amount of polysaccharides isolated from the heartwood was higher than that from the sapwood. The heartwood polysaccharides had a high content of galactose and arabinose units, and some glucuronic acid units, suggesting the presence of acidic arabinogalactans. The total amounts of recovered water-soluble arabinogalactans were 1.9 mg/g for spruce heartwood, 5.3 mg/g for pine heartwood, and as much as 106 mg/g for larch heartwood. The other water-soluble polysaccharides were mainly glucomannans. The average ratio of Gal:Ara:GlcA in the water-soluble arabinogalactans of spruce heartwood was about 4.3:1:1, pine heartwood about 4.5:1:0.2, and larch heartwood about 6.7:1:0.1. The corresponding molar ratios then being about 3.6:1:0.8 for spruce, 3.8:1:0.2 for pine, and 5.6:1:0.08 for larch. Thus, the content of glucuronic acid units was especially high in the spruce heartwood arabinogalactans. The content of arabinose was slightly higher in spruce and pine than in larch heartwood arabinogalactans.     

玉米淀粉改性UF树脂胶合高含水率单板

采用半酯化的玉米淀粉与脲醛树脂(UF)共聚改性,探讨加入量、脲醛树脂的量比、混合比、热压条件等对胶液的黏度、稳定性、固化时间及胶合质量的影响.结果表明:当单板含水率提高到16%～18%时,用改性UF树脂生产的多层胶合板,其物理力学性能指标达到GB/T 9846.1～12-88中Ⅱ类胶合板的要求,并大幅度地降低了胶合板的制造成本.     

Initial reactions in sapwood of Norway spruce and Scots pine after wounding and infection by Heterobasidion parviporum and H. annosum

The xylem surface of seedlings, stem material and roots of Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) were inoculated with strains of Heterobasidion annosum s. str. and H. parviporum s. str. The depth of necrosis in wounded spruce increased at a linear rate for at least seven weeks of incubation, but the rate of necrotic spread was significantly faster in infected wounds. In wounded pine the necrosis was maintained at a more superficial level for several weeks. Both spruce and pine sapwood were initially infected by hyphae of both species. In spruce, the hyphae advanced at a constant rate behind the necrotic front. On the contrary, after 1–2 weeks living H. parviporum hyphae were rare in pine rays. Heterobasidion annosum hyphae survived in pine rays, phloem and tracheids, despite a heavy accumulation of phenolics and resins and were able to penetrate into the sapwood at a linear rate although slower than infections in spruce. Histochemistry and quantitative estimates demonstrated that peroxidase activity was initially higher in spruce sapwood than in pine. Within three days of incubation, the activity in spruce sapwood disappeared concurrently with deepening necrosis. However, in pine, in both control and infected samples, there was a significant increase in peroxidase activity in the area surrounding the superficial necrosis, up to the wound surface and in the cambium and phloem around the wound. After wounding and infection, the content of soluble protein increased significantly in wood of older trees but not in seedlings. Infection resulted in an increased formation of lipophilic extractives in both spruce and pine but to a significantly greater degree in the latter, whereas the amount of hydrophilic compounds decreased in both. High‐performance liquid chromatography (HPLC) analyses of lipophilic extracts showed that inoculation of pine with the two species of Heterobasidion increased the amounts of pinosylvin, its monomethylether and several other phenolics as also resinous compounds. The results obtained may be relevant in explaining the known higher resistance of Scots pine to H. parviporum.     

Growth and Wood Properties of Sitka Spruce (Picea sitchensis (Bong.) Carr.) in Nursing Mixtures Established on Nitrogen-deficient Mineral Soils

Rate of growth and wood properties of Sitka spruce (Picea sitchensis (Bong.) Carr.) were investigated in triplet mixtures with lodgepole pine (Pinus contorta Loud.) (Alaskan provenance) and Japanese larch (Larix kaempferi (Lamb.) Carr.), established on nitrogen-deficient, iron pan soils. These ?nursing? mixtures were compared with pure stands of Sitka spruce that had been either regularly or periodically fertilized with nitrogen. Japanese larch promoted a growth rate in Sitka spruce greater than that achieved in the lodgepole pine-nursed spruce and equivalent to the two pure spruce treatments over the duration of the experiment (current age 28 yrs). Growth of regularly fertilized pure Sitka spruce was not significantly greater than that of periodically fertilized pure spruce. Alaskan lodgepole pine controlled branch size on the lower part of the spruce stems more effectively than the other treatments, although this may have been a function of tree size. Branch characteristics of Japanese larch-nursed spruce, however, were similar to those of the pure spruce treatments. Japanese larch caused an imbalance in crown development in the spruce, although it is unclear from the present study whether this will have an influence on stem and wood quality by the end of the rotation. Overall, the evidence from this study suggests that Japanese larch is an effective nurse of Sitka spruce on nitrogen-deficient iron pans, maintaining a rate of growth similar to that of pure Sitka spruce periodically fertilized with nitrogen and higher than that observed in spruce nursed by Alaskan lodgepole pine.     

ACQ-D中山杉防腐胶合板加工工艺研究

笔者研究了中山杉防腐胶合板的加工工艺。以ACQ-D为木材防腐剂,分别用不同方法对单板进行防腐处理,然后热压成胶合板。结果表明:中山杉防腐胶合板密度要高于未经防腐处理的普通中山杉胶合板,且中山杉防腐胶合板含水率与胶合强度均达到室外用胶合板I类要求。胶合板弹性模量、抗弯强度、顺纹抗压强度普遍偏低。不同方法处理单板对胶合板载药量影响很大,其中满细胞法最高,浸泡法和双真空法相近,涂刷法最低。     

Some factors influencing susceptibility to discoloring fungi and water uptake of Scots pine (Pinus sylvestris), Norway spruce (Picea abies) and Oriental spruce (Picea orientalis)

Abstract

The heartwood and sapwood from Scots pine (PS), Norway spruce (PA), and Oriental spruce (PO) were tested for susceptibility to discoloring fungi and water uptake. In addition, annual ring width and density were measured. The methods used were Mycologg for testing growth of fungi and a modified version of EN 927-5 to investigate water uptake. For pine, the heartwood showed a lower water uptake and no discoloring fungi growing in the tests. The heartwood had a significantly higher density and smaller annual ring width than the sapwood. In PA the heartwood had significantly lower discoloration than sapwood. The total water uptake in g/m² was significantly higher in sapwood, but not the calculated moisture content. As for wood properties, the density was significantly higher in sapwood compared to heartwood, although there were no differences in annual ring width. Regarding PO, differences in water uptake could be seen between sapwood and heartwood although the densities were similar. These results show that susceptibility to discoloring fungi and water uptake is hard to correlate to a single inherent property when looking at different wood species.     

Impacts of changing climate on the productivity of Norway spruce dominant stands with a mixture of Scots pine and birch in relation to water availability in southern and northern Finland

A process-based ecosystem model was used to assess the impacts of changing climate on net photosynthesis and total stem wood growth in relation to water availability in two unmanaged Norway spruce (Picea abies) dominant stands with a mixture of Scots pine (Pinus sylvestris) and birch (Betula sp.). The mixed stands were grown over a 100-year rotation (2000-99) in southern and northern Finland with initial species shares of 50, 25 and 25% for Norway spruce, Scots pine and birch, respectively. In addition, pure Norway spruce, Scots pine and birch stands were used as a comparison to identify whether species' response is different in mixed and pure stands. Soil type and moisture conditions (moderate drought) were expected to be the same at the beginning of the simulations irrespective of site location. Regardless of tree species, both annual net canopy photosynthesis (P(nc)) and total stem wood growth (V(s)) were, on average, lower on the southern site under the changing climate compared with the current climate (difference increasing toward the end of the rotation); the opposite was the case for the northern site. Regarding the stand water budget, evapotranspiration (E(T)) was higher under the changing climate regardless of site location. Transpiration and evaporation from the canopy affected water depletion the most. Norway spruce and birch accounted for most of the water depletion in mixed stands on both sites regardless of climatic condition. The annual soil water deficit (W(d)) was higher on the southern site under the changing climate. On the northern site, the situation was the opposite. According to our results, the growth of pure Norway spruce stands in southern Finland could be even lower than the growth of Norway spruce in mixed stands under the changing climate. The opposite was found for pure Scots pine and birch stands due to lower water depletion. This indicates that in the future the management should be properly adapted to climate change in order to sustain the productivity of mixed stands dominated by Norway spruce.     

Competitive Interactions between Norway Spruce and Scots Pine at Gisburn Forest, NW England

Species mixtures, although promising for improving the growthof spruce on nitrogendeficient sites, carry a risk of competitionfrom the admixed nurse species. The mixture of Scots pine (Pinussylvestris) and Norway spruce (Picea abies) planted at GisburnForest in 1955, in which nutritional benefits have been observed,provided a unique opportunity to study competition between thesespecies. Pure plots of both species as well as the mixture werereplicated in three blocks, allowing the effects of interplantingon the survival and mean diameter of each species to be testedstatistically. Further, the grouped arrangement of the speciesin mixed plots presented a variety of competitive configurationsbetween the two species. Instead of demonstrating the nursing benefit of pine to spruce,comparisons of mean diameters in pure and mixed stands indicatedthat spruce suffered and pine benefited from their interplantingat this site. Frequency distributions of tree diameters confirmedthat spruce tended to be suppressed in mixture and pine dominant.Neighbour analysis revealed that spruce were significantly smallerwhen adjacent to pine and that this effect was mainly due tothe larger size of pines. The increased height of spruce atthis site, previously attributed to a nutritional benefit conferredby pine, was probably due to competition for light from an overtoppingnurse. Nurse varieties must be carefully selected if they areto promote rather than suppress the growth of crop trees.     

Micromorphology and topochemistry of extractives in Scots pine and Norway spruce thermomechanical pulps: a cytochemical approach

Due to the increasing demand for Norway spruce as prime raw material for high-yield pulping, recent interest has focused on Scots pine as an alternative. However, the intrinsic properties of Scots pine, particularly the high amounts of extractives and the fiber properties, have been considered a disadvantage for thermomechanical pulping. A study was therefore conducted on the variations in the spatial distribution and redistribution of lipophilic extractives in spruce and pine wood and thermomechanical pulp (TMP) using cytochemical staining methods and chemical analysis. Chemical analyses showed chips from pine thinnings and sawmill slabs to contain three to five and two to three times, respectively, more extractives than found in spruce; in particular, the amount of triglycerides differed significantly. Results from staining techniques on the abundance and distribution of extractives (i.e., fats) between pine and spruce correlated with amounts detected by Fourier transform infrared spectroscopy and gel permeation chromatography. Cytochemical observations revealed information pertaining to species-specific distribution and redistribution of extractives among TMP fines and fibers and indicated the presence of a molecular film of extractives. Results indicate that the high concentrations of extractives in pine ray parenchyma are released during TMP processing and are redistributed onto the surfaces of the pulps, negatively affecting energy usage during primary refining.