利用改性胶粘剂制备玉米秸秆皮层刨花板的工艺研究

在分析比较了玉米秸秆皮、穰化学成分的基础上,采用正交试验方法,分析热压时间、热压温度、成板密度和施胶量几个因素对刨花板物理力学性能指标的影响。结果表明,玉米秸秆皮层刨花板优化制备工艺为：热压温度150℃,热压时间5min,成板密度0．70g／cm3,施胶量12％。     

软木聚结材料生产工艺的研究

为降低生产成本,采用MDI和VAE的混合胶压制软木聚结板.通过正交试验分析MDI和VAE混合质量比、施胶量、热压温度和时间对软木聚结板性能的影响.结果表明,在MDI中加入一定量的VAE,对软木聚结板的主要性能无显著影响;最佳工艺为:MDI和VAE质量比0.15,施胶量10%,热压温度150 ℃,热压时间30 min.     

吸声保温玉米秸秆穰板制备及性能研究

以疏解后的玉米秸秆穰丝为基材,异氰酸酯为胶黏剂,均匀组坯后经热压制备成吸声保温玉米秸秆穰板。通过单因素试验分别探究了施胶量、热压温度板材密度、厚度对玉米秸秆穰板吸声、导热和压缩性能的影响。结果表明:综合板材的性能和生产成本,优化工艺为施胶量2%、热压温度140℃、密度0.10 g/cm3,所得板材吸声性能达到GB/T 16731—1997的Ⅲ级标准,压缩强度满足GB/T 25975—2010中的要求,属高效保温材料。     

轻质豆秸刨花板工艺的研究

从UF胶制造轻质豆秸刨花板的初步研究,分析了板的密度、施胶量、热压时间等工艺因子对板性能的影响。试验结果表明,利用豆秸制造轻质刨花板是完全可行的,其产品主要物理力学性能为:密度0.483 g/cm 3、吸水厚度膨胀率11.2 % 、内结合强度0.303 MPa、静曲强度8.98 MPa,均达到日本JISA 5908 的技术指标。     

API压制稻秸秆人造板的初步研究

围绕着稻秸秆人造板的发展现状.结合我国稻秸秆人造板的应用情况,以及在稻秸秆人造板生产工艺中存在的问题,通过对稻秸秆原料结构特性的了解及对所用胶黏剂的改进,经过大量的实验和相关资料的查询,最终确定了在稻秸秆人造板密度750kg/m~3、板厚15mm,热压压力2.5MPa不变的条件下进行正交试验。经试验结果分析表明,试验时间、试验温度和施胶量对稻秸秆人造板的各项性能影响显著。最终得出在热压时间为18min、热压温度为165℃、施胶量为6%(单位质量的秸秆)的条件下压制的稻秸秆人造板符合国家标准GB/T 21723—2008麦(稻)秸秆人造板行业标准中的各项要求。     

基于共磨技术制备无胶复合秸秆人造板的研究

为提高农业剩余物秸秆的综合利用,以秸秆和大豆为主要原料,研究通过共磨技术利用材料自身的自黏性制备无胶复合秸秆人造板。通过正交试验研究热压时间、热压温度、预处理时间三因素对无胶复合秸秆人造板性能的影响,并进一步利用木片改性秸秆的综合性能。结果表明:热压时间参数为12 min/mm,热压温度160℃,预处理时间8 d为较佳工艺参数,且木片添加量为30%～50%时可以获得性能较好的无胶复合秸秆人造板性能。     

豆秸刨花板工艺的研究

对豆秸刨花板的制造工艺以及利用杨木单板、三聚氰胺浸渍纸对豆秸刨花板进行覆面处理进行了初步研究。分析了板的密度、施胶量、热压时间、热压温度 4个变量因子对豆秸刨花板性能的影响。试验结果表明用豆秸制造刨花板是完全可行的 ,其产品主要物理力学性能 :密度 ( ρ) 0 80g/cm3、静曲强度 (MOR) 1 9 9MPa、内结合强度 (IB) 0 45MPa、吸水厚度膨胀率 (TS) 3 3 %均达到了GB/T4 897- 92中的技术指标。贴面处理后的豆秸刨花板 ,其静曲强度、弹性模量均有较大提高。     

秸秆板贴面用异氰酸酯胶的改性

通过对异氰酸酯(API)主剂进行改性,从而减少交联剂的用量,降低API胶黏剂的生产成本。将改性API胶黏剂用于秸秆板薄木贴面的试验表明,当主剂、交联剂、填料之比为100∶4∶30,热压温度为60~110℃时,秸秆板的贴面效果达到相关国标要求。     

Ⅱ型淀粉基API热压工艺参数的研究

对所开发的满足三种不同用途的Ⅱ型淀粉基API胶黏剂,通过正交试验确定该胶的最佳应用条件。结果表明,最佳的热压工艺参数为热压温度115℃,单位压力1.2MPa,热压时间3.5min(0.8min/mm板厚)。     

热压工艺与竹席竹帘胶合板性能的关系

通过正交试验方法对竹席竹帘胶合板热压工艺与产品质量的关系进行了分析，在试验基础上，对不同的热压工艺进行了比较，经过优化，确定最佳热压条件为；热压温度１３０℃－１４０℃，每毫米板厚的保压时间为８０ｓ，最高热压压力为３．５ＭＰａ，通过重复试验，证明该工艺是正确的和可行的，可以获得良好的产品质量。     

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.     

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.     

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.     

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。     

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.     

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.