木材纤维与回收聚丙烯的热压复合工艺研究

研究了热压时间、热压温度、聚丙烯和偶联剂加入量等工艺因子对木材纤维和回收聚丙烯复合材料性能的影响。确定了压制密度为0．80g／cm3、10mm厚的木塑复合材料的最佳工艺条件为:热压温度175℃、热压时间8min、塑料加入量40％、偶联剂的加入量4％。在此条件下压制的木塑复合板材,物理力学性能中的内结合强度和吸水厚度膨胀率与中密度板的国家标准相比达到优等水平,静曲强度和弹性模量基本满足中密度板的国家标准要求。     

麦秸无胶碎料板制备工艺研究

以麦秸碎料为主要原料,采用漆酶水浴与干法两种不同处理方法压制麦秸无胶碎料板,研究热压温度、热压压力和热压时间对板材物理力学性能的影响。试验结果表明:影响麦秸无胶碎料板物理力学性能的主要因素是热压温度;水浴处理方法压制碎料板的物理力学性能优于干法压制的碎料板;漆酶水浴处理方法较优的热压工艺参数为漆酶用量43.6U/g,含水率10%,热压温度170℃,热压压力3~4MPa,热压时间20~25min。     

竹塑复合材料的制备工艺及其性能研究

以竹粉和高密度聚乙烯(HDPE)为主要原料,通过造粒、模压工艺制备竹塑复合材料,研究竹塑配比、相容剂用量、热压温度和热压时间对板材物理力学性能的影响.试验结果表明:相容剂用量和热压温度对板材力学性能影响显著,随着相容剂用量和热压温度的提高,板材各项力学性能呈上升趋势.综合生产成本、效率和节能等因素,确定最优工艺参数为竹塑配比7:3、相容剂用量6％、热压温度180℃、热压时间12min.     

麦秸/木材三层结构无机刨花板的制备工艺

以麦秸、木材碎料和无机胶黏剂制备麦秸/木材三层结构刨花板。研究麦秸与木材配比、板材密度、热压时间和温度对板材性能的影响。结果表明:随麦秸配比增加,板材抗弯性能降低,内结合强度增大,吸水厚度膨胀率(TS)减小;随密度增加和热压时间延长,板材力学性能增大,TS降低;随热压温度升高,板材力学性能先增大后减小,TS呈相反趋势。优化制板工艺为:碎料配比5:5,密度1.2g/cm~3,热压时间30min,温度100℃。     

木塑复合工艺因子对复合材料性能的影响

选用2种人工林木材(马尾松与杨木)和3种废弃塑料(聚乙烯、聚丙烯及聚苯乙烯)为原料,采用木材与塑料冷混-热压工艺,通过正交试验研究不同树种、木材组元形态、补强剂、塑料种类、板材密度及不同木塑混合比等复合工艺因子对木塑复合材料性能的影响.结果表明树种、木材组元形态、塑料种类、木塑复合比例、板材密度与补强剂等复合工艺因子对木塑复合材料性能有不同程度的影响;提高塑料在木塑复合材料中的比例也可以达到与添加酚醛补强剂同样或更好的结果;以杨木原料、细长刨花形态、聚丙烯塑料、板材密度为1g*cm-3等为最佳复合工艺因子,制成的复合材料性能达到或超过相关普通刨花板,包括室外结构用刨花板性能指标.     

地质聚合物-玉米秸秆皮复合碎料板的制备及性能研究

地质聚合物具有强度高、固化快等特点，作为新型无机胶凝材料在人造板制备中具有巨大的应用潜力。以玉米秸秆皮碎料为原料，偏高岭土基地质聚合物为胶黏剂，均匀组坯后经热压制备地质聚合物-玉米秸秆皮复合碎料板，重点探究了热压时间、热压温度、施胶量及密度对板材力学、耐水、导热及阻燃性能的影响。结果表明：当热压时间为120 s/mm、热压温度为170℃、密度为0.9 g/cm³、施胶量为40%时，所得板材静曲强度、弹性模量、内结合强度分别达到9.20、1 902.50、0.36 MPa,24 h吸水厚度膨胀率达到24.2%，烟密度等级(SDR)达到12.46，静曲强度和内结合强度符合GB/T 24312—2009《水泥刨花板》中合格品要求。     

生产工艺对巨尾桉/聚乙烯膜复合材料质量的影响

采用巨尾桉基材、胶合剂聚乙烯膜制备三层木塑复合材料,分析热压温度、热压时间、热压压力、施胶量这四个因素对复合材料胶合强度的影响。结果表明：在热压温度160℃、热压时间50s/mm、热压压力0.7MPa、施胶量为119g/m2的工艺条件下,巨尾桉/聚乙烯膜复合材料的胶合性能最优,能够达到II类胶合板标准。     

蓖麻秆制造人造板研究初探

分析了蓖麻秆的供应现状和蓖麻秆的原料特性,认为蓖麻秆用作人造板工业化生产是可行的;并在实验室试制了蓖麻秆刨花板和蓖麻秆纤维板,按照相关国家标准测试了板材的主要性能.结果表明,当脲醛树脂胶施胶量为12%、热压温度180℃、热压时间30 s/mm、板材密度为0.8g/cm3时,蓖麻秆刨花板的主要性能均能达到国家刨花板标准要求;当施胶量达到16%、热压温度180℃、热压时间30 s/mm、密度为0.86 g/cm3时,不添加防水剂的蓖麻秆纤维板除了吸水厚度膨胀率外,其余指标均能达到国家标准要求.     

不同工艺参数对UF工业大麻秆刨花板性能的影响研究

工业大麻秆是一种优质的轻质非木质原料,利用脲醛树脂为胶黏剂可以制备出性能优良的刨花板产品.笔者主要分析不同的工艺参数,包括密度、热压时间、热压温度和施胶量对板材性能的影响.研究结果表明,密度和施胶量对板材性能的影响要比热压温度和热压时间明显,随着板材密度、热压温度和热压时间的增加,板材的力学性能大多先增加后减小;而随着施胶量的增加,板材的力学性能呈增加趋势.在目标密度0.55 g/cm3,施胶量10％,热压温度130℃或170℃条件下,板材的力学性能可达到国标普通刨花板的标准要求;当目标密度等于或高于0.65 g/cm3、施胶量等于或高于12％、热压温度在140～ 160℃、热压时间在20 ～ 45s/mm之间时,除TS外,板材的其他力学性能可达到国标室内装饰和家具用材的标准要求,并可与相同工艺条件下,目标密度为0.75 g/cm3的木质刨花板的各项性能相媲美.可见,工业大麻秆是一种优质的非木质原料,利用该原料在低温条件下制备低密度的刨花板是可行的.     

混凝土模板用复合竹碎料板工艺研究

用正交试验法研究了施胶量、热压温度和热压时间3个因素对复合竹碎料板物理力学性能的综合影响．结果表明：热压温度是影响板材物理力学性能的主要因素．较佳工艺参数为，施政量12％，热压温度150℃，热压时间22min，板材物理力学性能能满足混凝土模板材料性能的需要．     

Browsing Damage on Pine (Pinus sylvestris and P. contorta) by a migrating moose (Alces alces) Population in Winter: Relation to Habitat Composition and Road Barriers

In Scandinavia, moose (Alces alces L.) sometimes cause severe browsing damage to economically-important pine. Moose-vehicle accidents have spurred construction of fences along roads, and these may interfere with moose migration between summer and winter ranges, or the road alone may be a barrier. If this happens and moose build up along roads, landowners may suffer economically. Therefore, this study investigated whether roads, fences or other factors influence the use of young pine stands by moose. Eighty stands along roads in northern Sweden were evaluated in which individually-browsed branches were counted on 9972 pines. Moose browsing was not significantly related to birch (Betula pendula Roth, B. pubescens Ehrh.) density, nor did it differ between pines (Pinus contorta Douglas or P. sylvestris L.). However, increased pine density, site productivity and proximity to a highway were associated with increased browsing. Further large-scale studies are needed to understand moose habitat selection and the effects of roads.     

Effects of Root Freezing on the Physiology and Growth of Picea glauca,Picea mariana and Pinus banksiana Seedlings Under Different Soil Moisture Regimes

The root systems of 2-yr-old Picea glauca, Picea mariana and Pinus banksiana seedlings were submitted to various frost temperatures during an artificial frost to induce different levels of root damage. Frost-damaged and control seedlings were placed in a greenhouse under high and low soil moisture regimes. Seedling growth and physiology were evaluated periodically. Seedling survival was reduced when root damage reached levels of 60-80%. Root systems of all three species showed partial to total recovery by the end of the experiment. In general, root freezing damage caused reductions in seedling growth, with these reductions becoming less significant over time. Root damage had little to no effect on black spruce and jack pine seedling physiology, while white spruce CO 2 uptake decreased with increasing root damage. Shoot nitrogen content of all three species decreased slightly with increasing root damage.     

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.     

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.     

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.     

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.     

Stand Structure in Pine,Spruce and Deciduous Forests: A Comparison Between Finnish and Russian Karelia

This study investigated the stand structure in pine, spruce and deciduous forests in the border district of Finland and Russia. A total of 46 mature forest stands was selected as pairs, the members of each pair being as similar as possible with respect to their forest site type, age, moisture and topography. The stands were then compared between the two countries by means of basal areas and number of stems. The proportions of dominating tree species were 2-12% lower, and correspondingly the proportions of secondary tree species higher, in Russian forests. The density of the forest stock was also higher in each forest type in Russia. The forests in the two countries differed most radically in terms of the abundance of dead trees. The amount was two to four times higher in Russian deciduous and spruce forests, and in pine forests the difference was 10-fold. The stand structures indicated that Russian coniferous stands, in particular, were more heterogeneous than intensively managed pine and spruce stands in Finland.     

Growth and Terminal Bud Formation in Picea abies Seedlings Grown with Alternating Diurnal Temperature and Different Light Qualities

The root collar diameter and the height:diameter ratio are of particular importance in container-grown seedlings where a high density in the containers may produce spindly seedlings. Temperature regimes and light quality are known to affect plant growth. The aim of this study was to identify responses in Picea abies (L.) Karst. seedlings grown with light providing different red:far-red ratios and under temperature regimes with alternating day (DT) and night temperature (NT) from negative (DT < NT) to positive (DT > NT) difference (DIF) between DT and NT. Experiments were conducted in controlled environment chambers and in a daylight phytotron. Only limited thermoperiodic responses appeared in P . abies seedlings with respect to seedling height and dry weight accumulation. The formation of terminal buds, however, was clearly delayed in seedlings grown at negative DIF. The results indicate a requirement for day extension light that is high in far-red, to prevent terminal bud formation under natural short-day conditions. An extended study should be conducted to clarify the minimum level of light intensity and the optimal light quality needed to prevent terminal bud formation under natural short-day conditions.     

CAD与建筑设计的关系

本文分析了CAD在设计中引起的正面和负面影响,并进行了系统的阐述,从而使设计者在应用中能够保持客观的态度。