电热竹木复合地板的制备工艺

以1~3层竹单板为面层材料,柳叶桉多层胶合板为基材,中间放置碳纤维电热纸,制备电热竹木复合地板,分析胶种、碳纤维电热纸品种、热压时间及面层竹单板层数等因素对地板的胶合强度及耐热尺寸稳定性的影响。结果表明,最优工艺因素组合为:采用改性三聚氰胺树脂胶和NL-110型电热纸,2层竹单板为面层,热压时间2.0 min/mm;在此条件下,既可提高地板的胶合强度,又可有效降低地板的收缩率,提高其耐热尺寸稳定性。     

实木复合地板的表层改性工艺

将表层橡木单板浸渍三聚氰胺树脂后,与桉木单板、三聚氰胺浸渍纸一次热压成型制作多层实木复合地板。采用正交试验方法,探讨橡木单板浸渍工艺及热压工艺对多层实木复合地板表面耐磨性等理化性能指标的影响。试验结果表明:浸渍温度对橡木单板浸渍质量增加率影响显著,浸渍浓度对橡木单板浸渍质量增加率影响一般显著,热压温度对多层实木复合地板的表面耐磨性能影响显著。在试验条件下,以浸渍时间20 min、浸渍浓度40%、浸渍温度45℃、热压温度145℃、热压时间0.8 min/mm、热压压力1.8 MPa和施胶量240 g/m2为较优工艺,压制所得多层实木复合地板的表面耐磨性能等理化性能较佳。     

热压压力及板材密度对竹木复合层积材顺纹抗压强度的影响

通过单因变量两因素重复试验,以毛竹竹篾和桦木单板为原料,使用酚醛树脂胶黏剂压制竹木复合层积材,分析热压压力及板材密度对竹木复合层积材顺纹抗压强度的影响,并利用扫描电子显微镜对竹木复合层积材的微观构造进行了观察.结果表明,在试验选定因素水平范围内,热压压力和板材密度对竹木复合层积材顺纹抗压强度影响显著,板材顺纹抗压强度随热压压力的升高先增大而后减小,且各水平间差异显著;不同密度对板材顺纹抗压强度的影响差异显著,板材的顺纹抗压强度随板材密度的增大而增大;在其他工艺参数相对不变的情况下,热压压力与板材密度的交互作用对板材顺纹抗压强度的影响并无显著的影响.扫描电镜照片显示,热压压力升至一定水平,板材内部结构受到一定程度的损伤.     

竹木碎料/纤维复合板热压工艺研究

选取热压温度、单位压力和热压时间作为工艺因素,对每个工艺因素选取3个不同水平,对竹木碎料/纤维复合板的热压工艺进行了研究.试验结果的极差和方差分析表明：在3个工艺因素中,单位压力对产品的各项性能指标的影响最显著,其次是热压时间,热压温度的影响相对较小.在此基础上优化出热压温度为130～140℃、热压单位压力2.6MPa,热压时间55s·mm^-1的工艺参数,对该工艺参数结果的预测和验证试验均表明所确定的工艺参数是合理的,可以获得较好的产品质量.     

不同因素对竹/木复合强化单板层积材MOE、MOR的影响

以杨木单板和竹帘为原料,采用低分子量水溶性酚醛树脂浸渍处理,通过干燥、组坯、热压等工艺制备竹木复合强化单板层积材。探讨了组坯方式、压缩率、热压温度、热压时间4个因素对竹木复合强化单板层积材弹性模量(MOE)和静曲强度(MOR)的影响。结果表明:表层为一层竹帘的竹木复合强化单板层积材的MOE和MOR较大,分别是13．43GPa、148．13MPa,与表层为杨木单板次表层为竹帘组坯方式相比分别增加了33．63％、56．16％。确定了竹木复合强化单板层积材较合理的制造工艺参数。     

基于响应面法优化的竹丝饰面细木工板热压工艺

【目的】竹丝饰面细木工板是以三聚氰胺改性脲醛树脂(MUF)浸渍纸作为竹丝装饰材料与细木工板间胶合材料而制成的新型竹木复合材料。探讨热压过程中压力、温度和时间这三因素对竹丝饰面细木工板主要性能的影响,确定各因素的权重及最佳工艺参数。【方法】采用单因素试验法和响应面法,以热压过程中温度、时间和压力为试验因子,以表面胶合强度作为评价指标,在单因素试验的基础上,利用Box-Behnken中心组合试验和响应面分析法,进行最佳热压工艺条件优化设计。【结果】1)基于响应面法可获得竹丝饰面细木工板表面胶合强度的二次响应面回归方程模型,该回归模型方差极其显著,失拟项不显著。2)回归模型方差分析得到热压温度(X1)、热压时间(X2)和热压压力(X3)及其交互作用的P值排序为X2X3X1和X1X3X1X2X2X3,即在试验设定的区间内,热压三要素对竹丝饰面细木工板表面胶合强度影响大小为:热压时间热压压力热压温度。热压温度和热压压力的交互作用对竹丝饰面细木工板的表面胶合强度影响最大,热压温度和热压时间的交互作用次之,热压时间和热压压力的交互作用对表面胶合强度影响最小。3)利用DesignExpert 11优化得到的最佳工艺参数为:热压温度128.425℃,热压时间6.968 min,热压压力0.425 MPa;在实际工艺中设定热压温度128℃、热压时间7 min、热压压力0.43 MPa时制备的竹丝饰面细木工板的表面胶合性能为1.86 MPa,与预测值的相对误差不超过5%。【结论】竹丝饰面细木工板响应面模型的准确性和预测性良好,该研究结果可为竹丝饰面细木工板的生产制造提供理论依据。     

竹木复合建筑混凝土模板的工艺研究

以火车集装箱底板加工剩余物为原料,经过去贴面、磨砂等简单的处理后与杨木单板重组成一种层层交错结构的竹木复合建筑混凝土模板。用单因素实验方法,分析不同热压工艺参数下的静曲强度、弹性模量、含水率,从而确定热压温度、压力、时间的工艺参数范围。用正交实验法测试静曲强度、弹性模量、湿态胶合强度、密度等性能,并进行了方差分析和平均值分析。结果表明:与传统建筑混凝土模板制备方法相比,该工艺省去了去竹青、竹黄、竹节和软化等复杂的竹片材料制备方法。成品的竹材加工剩余物的体积利用率占竹木复合建筑混凝土模板的80%以上,同时节约了生产成本。通过极差分析,热压工艺因素对静曲强度、弹性模量、湿态胶合强度的影响程度都是:热压压力>热压时间>热压温度。通过平均值分析,最优热压参数为:3 MPa、50 s·mm^-1、135℃。     

热压温度及板材密度对竹木复合层积材顺纹抗压强度的影响

通过单因变量两因素重复试验,以毛竹竹篾和桦木单板为原料,使用酚醛树脂胶黏剂压制竹木复合层积材,分析热压温度及板材密度对竹木复合层积材顺纹抗压强度的影响。结果表明,在试验选定因素水平范围内,热压温度和板材密度对竹木复合层积材顺纹抗压强度影响显著,板材顺纹抗压强度随热压温度的升高而增强,但145℃与160℃两水平之间差异并不显著;不同密度对板材顺纹抗压强度的影响差异显著,板材的顺纹抗压强度随板材密度的增大而增大;在其他工艺参数相对不变的情况下,热压温度与板材密度的交互作用对板材顺纹抗压强度的影响并无显著的影响。     

竹丝模压刨花板的工艺优化研究

采用正交试验法对竹丝模压刨花板制造工艺与产品质量进行优化试验,探讨施胶量、热压温度、热压时间、板坯含水率工艺因素对竹丝模压刨花板物理力学性能的影响,并得到了较优的工艺参数.试验结果表明利用纤维状竹丝可以压制出高质量的竹丝模压刨花板.产品的主要物理力学性能为:密度0.8 g/cm3,弹性模量6 745.7 MPa,静曲强度54.39 MPa,内结合强度0.53 MPa,吸水厚度膨胀率11.3%.     

橡木贴面实木复合地板凹凸表面热压工艺研究

三聚氰胺浸渍橡木薄单板贴面实木复合地板是参考三聚氰胺浸渍纸贴面生产工艺生产出的表面凹凸实木复合地板。使用三聚氰胺胶黏剂、固化剂、渗透剂、脱膜剂（配比为500：1：1：1）混合液浸渍橡木薄单板,然后在真空度为0.08 MPa时保压浸渍5 min,在大气条件下放置30 min,取出后再放入90℃鼓风干燥箱中干燥10 min。浸渍完成的橡木薄单板与基材经热压成型为表面凹凸的实木复合地板。考虑热压温度、热压压力、热压时间对其凹凸表面成型的影响,每个因素取4个水平,制定因素水平表,选择正交表进行试验。对试验结果进行浸渍剥离及表面纹理深度的测量分析,得到最优的热压工艺条件为温度150℃、压力1.2 MPa、时间70 s。三聚氰胺浸渍的橡木贴面复合地板表面纹理、色泽、手感都更加接近自然。     

Growth of Phlebiopsis gigantea in wood of seven conifer species

Heterobasidion parviporum and Heterobasidion annosum are widely distributed root‐rot fungi that infect conifers throughout Europe. Infection of conifer stumps by spores of these pathogens can be controlled by treating fresh stumps with a competing non‐pathogenic fungus, Phlebiopsis gigantea. In this study, growth of three Latvian strains of P. gigantea and the biological control agent ‘Rotstop’ strain was evaluated in stem pieces of Norway spruce, Scots pine, lodgepole pine, Douglas‐fir, Weymouth pine, Siberian larch and Sitka spruce. The growth rates of one H. parviporum and one H. annosum isolate were also measured in the same stem pieces. The growth rate of P. gigantea varied greatly in wood of different conifer species. It was higher in the three pine species, lower in Norway spruce and lowest in Sitka spruce and Siberian larch, and in Douglas‐fir, this fungus did not grow. The largest area of wood occupied by P. gigantea was in lodgepole pine. Growth of Latvian isolates of P. gigantea in the wood of Pinus and Picea species was comparable to that of the Rotstop isolate. Consequently, stump treatment with local P. gigantea isolates should be recommended. However, our results suggest that Douglas‐fir stump treatment against Heterobasidion by P. gigantea may be ineffective and other stump treatment methods should be considered.     

Growth of Mixed Birch-Coniferous Stands in Relation to Pure Coniferous Stands at Similar Sites in South-eastern Norway

Mean age, mean and top heights and yield were studied in 20 mixed stands of birch ( Betula pubescens Ehrh. and B. pendula Roth) and Picea abies (L.) Karst. and nine mixed stands of birch and Pinus sylvestris L. in south-eastern Norway. Each mixed stand and the adjacent pure coniferous stand (control) were growing under the same site conditions and had not been commercially thinned. There were no significant differences in mean age at breast height or in top heights between birch and conifers in the mixed stands, while mean height was significantly higher for birch than for spruce. A growth index was calculated based on total volume and age at breast height. For the spruce sites the growth in young mixed stands (birch < 17 m) was superior to that of pure spruce, while the difference was insignificant in older stands. The growth index correlated positively with the ratio between generatively and vegetatively regenerated birch trees, and negatively with the age of the oldest species in the mixture and with site quality. For the pine sites there was no significant difference in the growth index between mixed birch-pine and pure pine stands. A mixture effect of birch on the volume yield of spruce or pine could not be demonstrated.     

Defoliation by the Needle-shortening Pine Gall Midge,Thecodiplosis brachyntera,on Pines in Central Sweden

An outbreak of the needle-shortening pine gall midge, Thecodiplosis brachyntera , occurred on Scots pine, Pinus sylvestris (L.) and lodgepole pine, P. contorta (Dougl.) in central Sweden during 1995-1998. The larval feeding of T. brachyntera kills current-year needles and heavy infestation causes severe defoliation. A pattern of fluctuating defoliation among years and sites was found on both pine species. Defoliation was evenly distributed in the crown of P. sylvestris during years of high as well as low infestation; apical whorls had as much defoliation as basal whorls. In P. contorta , however, there was a tendency for defoliation to be concentrated on branches in the most apical whorls. Growth ring increments on P. sylvestris with high levels of defoliation (71%) did not differ from trees with moderate levels (26%) of defoliation. Shoot lengths were significantly shorter, however, on heavily infested trees the year after defoliation.     

Decomposition and nutrient loss from prunings of different contour hedgerow species in tea plantations in the sloping highlands of Sri Lanka

Contour hedgerows of multipurpose tree species in the sloping tea lands of Sri Lanka are expected to reduce soil erosion and also add significant amounts of plant nutrients to the soil via periodic prunings. The objective of this experiment was to characterize the biomass decomposition pattern and quantify the amount of nutrients added through prunings of six tree species (Calliandra calothyrsus, Senna spectabilis, Euphatorium innulifolium, Flemingia congesta, Gliricidia sepium and Tithonia diversifolia) currently being used in hedgerows associated with tea. Withered leaf and stem prunings (50 g) were enclosed in 2-mm litter bags, placed at 5-cm depth and retrieved after one, three, six, nine and 12 weeks. Loss of initial dry weight, N, P and K was measured. Single exponential decay function adequately described both dry weight and nutrient loss. Tree species differed significantly in their rate of breakdown with decomposition constants (k) varying from 0.0299 to 0.2006 week⁻¹ for leaves and from 0.0225 to 0.0633 week⁻¹ for stems. Gliricidia showed the highest k for leaves with the rest in the following descending order: Senna > Tithonia ≥ Euphatorium > Calliandra > Flemingia. A similar pattern was observed for loss of all nutrients with Calliandra and Flemingia always having lower k values than the rest. Although N immobilization was not observed, immobilization of P and K was observed during the first week of incubation in some species, particularly in stem prunings. Annual biomass of prunings differed significantly between tree species in the following descending order: Calliandra > Senna > Flemingia > Tithonia > Gliricidia > Euphatorium. Calliandra added the greatest amount of nutrients annually to the soil with Euphatorium adding the least. Calliandra prunings provided the annual total K requirement and 49% of the N requirement of mature tea. However, none of the species provided more than 5% of the P requirement. It is concluded that among the tree species tested, Calliandra and Flemingia are the most suitable for contour hedgerows in tea plantations of this agroclimatic region because of their higher soil nutrient enrichment capacity and slower decomposition rates which would minimize leaching losses. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of Seed Weight and Seed Type on Early Seedling Growth of Pinus sylvestris under Harsh and Optimal Conditions

The effects of seed weight and seed type on seedling growth of Pinus sylvestris (L.) were studied by seeding individually weighed orchard and stand seed in different mixtures under harsh (direct seeding in field) and optimal (seeding in nursery) conditions. In the nursery experiment an increase in the seed weight from 3 to 7 mg increased the seedling height by 10-27% and total weight by 27-113%, and decreased the height/diameter ratio by 5-6% after 2 yrs. With elimination of seed weight effects, orchard seedlings were 2% taller than stand seedlings in year 2. Without elimination of seed weight effects, orchard seedlings were 7-13% taller. In the field experiment an increase in the seed weight from 3 to 7 mg increased seedling height by 18-65%, stem volume by 81-274% and the number of top-buds by 23-34% in year 5. After elimination of seed weight effects, orchard seedlings were 7-13% taller than stand seedlings and without elimination of seed weight effects 20-21% taller after 5 yrs. Even after elimination of both seed weight and genetic effects orchard seedlings were 3-9% larger than stand seedlings in the field experiment. In conclusion, the influence of seed weight and seed type on growth traits and slenderness is highly significant and the influence seems to be greater in harsh conditions.     

Modelling of adequate pretwist for obtaining straight timber

Abstract

Wood in general and wooden studs in particular are often distorted owing to uneven shrinkage during the drying process in the sawmill. Twist is often the most detrimental of all types of distortion, and it is caused by spiral grain in combination with variations in moisture content. For sawmills, the objective is to produce dried, straight boards, and one method of dealing with boards with excessive spiral grain is to sort them out and then dry them in a pretwisted position to obtain straight boards after drying. A model using the finite element (FE) method for the simulation of drying twist distortions was first calibrated against laboratory experiments in which boards were dried with and without restraints and pretwists. After the calibration, the FE results were compared with industrial test results for boards that were dried without restraints or with restraints with zero pretwist, i.e. straight restraints. The FE model used an elastic–ideally plastic material model to obtain permanent deformations. The calibration was to set the yield stresses so that there was a good match between FE results and results from the laboratory experiments. The comparison between the industrial test results and the FE results showed that the FE model is capable of realistic simulations of drying boards with and without restraints and presumably also pretwists.     

Potential to harness superior nutritional qualities of exotic baobabs if local adaptation can be conferred through grafting

Baobab leaves form an important part of the local diet in Sahel countries and elsewhere in Africa. Existing leaf nutritional data and agroforestry performance information are based solely on Adansonia digitata L., the baobab of continental Africa. The introduction potential of Adansonia species from the center of diversity in Madagascar and from Australia remains untapped. To assess this potential, the mineral contents and B₁ and B₂ vitamin levels of dried baobab leaves were determined for five-year old trees of A. digitata, A. gibbosa (A. Cunn.) Guymer ex D. Baum, A. rubrostipa Jum. & H. Perrier (syn. A. fony Baill.), A. perrieri Capuron and A. za Baill. grown in an introduction trial in Mali. Nutritional data were evaluated against survival and vigor to identify promising germplasm. Leaf vitamin and crude protein contents were highest in the Madagascar species, especially A. rubrostipa (B₁ 88 mg 100 g⁻¹, B₂ 187 mg 100 g⁻¹, protein 20.7% dry weight). However, the local species far outperformed the introductions in survival, tree height, basal diameter and resistance to termites. We suggest grafting as a way of harnessing the vigor of well-adapted local baobab varieties to the superior nutritional profiles of A. rubrostipa and others. Cross-species grafting tests in Adansonia were successful, thus creating new agroforestry possibilities with different scion/rootstock combinations.     

Boron in forest trees and forest ecosystems

This review critically examines the role of boron (B) in forests in view of recent findings on B nutrition and the continuing occurrence of B deficiency. Many perceptions about the role of B in plants and its uptake and mobility have been altered since the last review on B in forest trees in 1990. Now there is evidence for a fundamental role of B in the formation of the pectic structure in primary cell walls in plants, and further roles in membrane function are being explored. In plants, channel-mediated B uptake, active B uptake and B uptake by mycorrhizas have been shown, B transporters have been identified, and B retranslocation has been shown. We explore these findings and their consequences on forest trees and on ecosystems that they dominate. Particular emphasis is placed on B retranslocation and B in mycorrhizal symbiosis, given their importance in trees.     

Survival and Growth of Picea abies Regeneration after Shelterwood Removal with Single- and Double-grip Harvester Systems

Three stands in Sweden were followed for 7 yrs to study the survival and growth of Norway spruce [Picea abies (L.) Karst.] regeneration after shelterwood removal with single- and double-grip harvester systems. The height of all seedlings within circular plots was recorded before and after final cutting. The tallest seedling and one randomly selected seedling on each circular plot were permanently marked and their annual height growth was measured each year during the period 1993-1999. No significant differences between single- and double-grip harvester systems were found with respect to their effects on regeneration density, survival or annual height growth. The annual height growth of the individual seedlings after shelterwood removal was significantly correlated with seedling height before shelterwood removal. Significant differences were found in annual height growth between seedlings with high and low vitality. Logging damage did not affect the annual height growth. Several practical conclusions were drawn. First, the choice of harvester system does not affect seedling height growth or survival after shelterwood removal. Secondly, the removal of a 200 m³ shelterwood with 200 stems ha^-1 does not seem to constitute a serious problem for seedling survival and growth. Finally, estimated vitality and seedling height both seem to be fairly good predictors of postrelease survival and growth.     

Development of Pinus sylvestris Main Stems Following Three Different Precommercial Thinning Methods in a Mixed Stand

Reducing competition by point cleaning may be an attractive alternative to conventional precommercial thinning in forestry. In this study, survival and development of main stems of Scots pine (Pinus sylvestris L.) following point cleaning were examined in a mixed stand of mainly Scots pine and birch (Betula pendula Roth and Betula pubescens Ehrh.) in northern Sweden. Treatments studied were: no precommercial thinning, conventional precommercial thinning, point cleaning of all secondary stems, and point cleaning of only the secondary stems that were higher than the main stem, within a radius of 0.8 m from the main stem, respectively. A randomised complete block design with three replicates was used. Measurements taken 13 growing seasons after these treatments showed that conventional precommercial thinning was the best treatment for retaining Scots pines as main stems. However, conventional precommercial thinning resulted in the poorest timber quality of the remaining Scots pines in terms of stem taper, thickest branch diameter and relative live crown height. In conclusion, point cleaning has to be followed by a complementary cleaning operation if the objective is to retain Scots pines as main stems in such mixed stands.