Thursday, 20 October 2016

La relation entre les propriétés des panneaux de fibres de densité moyenne et les caractéristiques du bois - Collection des mémoires et thèses à l'Université Laval

Published Date
Wood composite products such as medium density fiberboard (MDF) are widely used in many applications (e.g. furniture, cabinet, door and window, etc.), and the production of MDF panels is increasing in the market place in recent years. Traditionally in Québec, the raw material for fiberboard manufacturing is spruce, pine, and fir (S-P-F) wood shavings and planings from natural stand. A deficiency in wood and fiber supply that is being experienced by wood composites industry requires extension and diversification in raw material. The changing resources, such as managed resource (e.g. plantation), fast-growing and short rotation resource (e.g. poplar, larch, etc.), undesirable resource (mainly plantations), underutilized resource (e.g. larch, birch, etc.), and in-forest resource (e.g. tops, bark), provide opportunities for such requirement in terms of more effective and economic use of raw material base. Thus, knowledge on the effects of raw material and process variables on fiberboard panel properties will enhance complete tree utilization, add value to each type of forest resources, and provide data needed for the successful conversion of this resource into high performance and valuable products. To address this issue, fiberboard panel properties in relation to raw material characteristics and process variables need to be studied. In the past decades, the relationships between composite panel properties and process variables have been thoroughly studied. However, how raw material affects fiberboard panel properties has not been well understood; this knowledge gap needs to be filled.
This study is concerned with the following subjects:
  1. Effect of juvenile wood on properties of black spruce MDF panels
  2. Effect of log position in the tree on properties of black spruce MDF panels
  3. Properties of MDF panels made from hybrid poplar clones
  4. Feasibility of using larch as raw material for MDF panel manufacturing
  5. Multivariate modeling of MDF panel properties in relation to wood fiber characteristics
Subject One: Adding Value to Low Quality Black Spruce Young Trees
Each year, intensive forest management and silvicultural practice produce millions of tons of young trees. Generally, young trees are not desired in many applications, for example, plywood, lumber, and construction, etc. since young trees contain a large proportion of juvenile wood. Compared to mature wood, juvenile wood has its unique characteristics, such as lower strength, lower specific gravity, thinner cell walls, higher longitudinal shrinkage, greater microfibril angle, etc. This encourages researchers to find proper uses for this undesirable forest resource on the basis of value-added end uses strategy.
Black spruce ( Picea mariana (Mill.) BSP.) is one of the most widely distributed conifers in North America. It is especially commercially important in Eastern Canada. Black spruce wood is highly valued for different end uses including pulpwood, lumber, construction, composites and a number of other end uses (Mullins and McKnight 1981). In Chapter II, study on the effect of juvenile wood on MDF panel properties was pursued. The raw materials for the panel making were black spruce fibers generated from 1-20, 21-40, and over 40 year-old wood. The information derived from this study is essential for proper utilization of managed black spruce forest resource as well as silvicultural practice products such as commercial thinnings.

Subject Two: Optimizing Black Spruce Log Allocation Strategy
Logs from a tree stem are usually allocated at sawmills for lumber conversion regardless of log position in the tree. As the forest industry is shifting toward value-added end uses, there is an increasing need to develop an optimal log allocation strategy, where logs are assigned to the best uses to maximize the value of the resource and to ensure the quality of final products. Properties of MDF panels made from black spruce ( Picea mariana (Mill.) BSP.) top, mid, and butt logs were studied in Chapter III. The outcome is helpful for black spruce log allocation strategy, also provides important information on economic utilization of in-forest resource such as tree tops.

Subject Three: Improving MDF Panel Performance through Tree Breeding
Hybrid poplar ( Populus spp.) is a fast-growing and short rotation hardwood species, which can be expected to produce a promising wood fiber source with high yields (Dix et al. 1999; Cisneroset al. 2000). Conventionally, the materials for papermaking and composite panel manufacturing come from softwood species such as pine, spruce, fir, etc. Due to the shortfall in softwood supply, forest products companies in Canada and the United States is more and more interested in fast-growing hardwood species as potential substitutions for softwood chips to sustain raw material supply.
The requirements of wood fiber characteristics for different end uses are diverse (Zhang et al. 1997). It has been known that wood and fiber properties (e.g. wood density and fiber cell wall thickness) can be affected by genetic control on hybrid poplar trees (Ivkovich, 1996; Law et al. 1997; Xing 2000; Cisneros et al. 2000; Savita 2001). Nevertheless, very little attention has been paid to genetic manipulation and selection of poplar trees for specific end uses. In Chapter IV, three hybrid poplar clones were studied as raw material for MDF panel manufacturing and the properties of MDF panels were evaluated. The effect of poplar clonal variation on MDF panel properties was examined. The significance of this study lies in the possibility of improving fiberboard panel performance through hybrid poplar tree breeding.

Subject Four: Feasibility of Using Larch for Fiberboard Panel Manufacturing
Western larch ( Larix occidentalis ) and eastern larch ( Larix laricina ) are known as two major larch species grown in Canada. Western larch is often utilized in many applications (e.g. veneer, construction, and pulp, etc.), but eastern larch is an underutilized species. Studies show that some exotic larch species such as Japanese larch ( Larix leptolepis ) and European larch ( Larix decidua ) grew more rapidly and produced two to three times more wood and fiber than native species in the Lake States and southern parts of eastern Canada (Vallee and Stipanicic 1983; Fowler et al. 1988; Palmer 1991). Thus, the potential of using exotic larch in future sustainable fiber supply needs to be taken into account. Chapter V provides information on properties of MDF panels made from two exotic larch species and panels made from S-P-F wood chips were assessed as a control. Larch wood used as raw material in this study was a mix of two individual species Larix gmelinii and Larix sibirica with an approximate proportion of 4:1.

Subject Five: MDF Panel Properties in Relation to Wood Fiber Characteristics
There are a number of factors influencing the properties and performance of the final wood composite products (Maloney 1993). Processing parameters such as pressing schedule and platen temperature have been recognized to be critical in determining the properties of MDF panels because these factors can make a difference in panel vertical density profile. Vertical density profile plays an important role determining panel properties. On the other hand, characteristics of raw materials are also important. In Chapter VI, MDF panel properties in relation to wood and fiber characteristics were investigated via a black box method. In this study, MDF panels were manufactured from eleven wood species or types, which were black spruce ( Picea mariana (Mill.) BSP.) 1-20, 21-40, and over 40 year-old wood, black spruce ( Picea mariana (Mill.) BSP.) top, mid, and butt logs, hybrid poplar ( Populus spp.), larch ( Larix gmelinii and Larix sibirica ), and a mix of S-P-F wood chips. Modulus of rupture, modulus of elasticity, internal bond strength, linear expansion, thickness swell, and water absorption of these panels were measured as response variables. As predictor variables, various wood and fiber characteristics including wood density, wood and fiber pH and base buffering capacity, fiber arithmetic mean length and width, and fiber coarseness, etc. were measured as well. A consistent urea-formaldehyde (UF) resin content, pressing schedule (closure rate, pressing time, and opening time) and platen temperature were applied to the panels. The temperature at the center of each panel was recorded during hot-pressing, and the data show that the temperature exceeded 100 oC and was maintained at that temperature for one minute, which is sufficient for UF resin to be completely cured, especially at wood pH of 5 or lower. Multiple linear regression was performed to model the functional relationships between panel properties (response variables) and wood fiber characteristics (predictor variables). Ten dummy variables were created to identify the eleven wood species or types, and they were incorporated as into the regression analysis as predictor variables.

Fiber coarseness, arithmetic mean length, length weighted length, arithmetic mean width, and arithmetic fine percentage and length weighted fine percentage were measured using HiRes Fiber Quality Analyzer (FQA), located at ‘Centre spécialisé en pâtes et papiers’, Université du Québec à Trois-Rivières, Trois-Rivières, Québec, Canada. The pH and base buffering capacity of wood chips and fibers were determined by the Johns and Niazi’s method (1980). Since UF resin is acid catalyzed only base buffering capacity was measured. The percentages of fibers distributed in mesh size ranges of >3.240 mm2, 0.828-3.240 mm2, 0.281-0.828 mm2, 0.017-0.281 mm2, and smaller than 0.017 mm2 (The above mentioned mesh size is in accordance with 0-14 mesh, 14-28 mesh, 28-48 mesh, 48-200 mesh, and >200 mesh, respectively.) were determined using Bauer-McNett Classifier.

For further details log on website :
http://archimede.bibl.ulaval.ca/archimede/fichiers/23592/ch02.html

No comments:

Post a Comment