Wood-based panel products

Progress in research and development in the wood-based industry and in the adhesive industry has shown many successes during the last decades. On the other hand, many industrial requirements still require considerable and important developments in this area. The main driving forces today are cheaper , quicker and more complex . The first two are caused by the heightened competition in the above-mentioned industries and the attempt to minimize costs while maintaining a certain level of product quality and performance. The key word more complex stands for new and specialized products and processes. Adhesives play a central role in wood-based panel production. The quality of bonding, and hence the properties of the wood-based panels, are determined mainly by the type and quality of the adhesive. Development in wood-based panels, therefore, is always linked to development in adhesives and resins. 

Forest products industries know that temperature increases in piles of sawdust and bark. In pulp and paper mills, self-heating develops in amassed tree chips. Paper rolls stacked hot tend to self-heat, as occasionally do stored bales of waste paper. The wood-base panel products particleboard, hardboard, and fiberboard self-heat after being stacked too hot in the factory. Where in structures the framing lumber, wood-base panels, and lignocellulosic insulation is heated by items such as steam pipes, temperatures tend to rise above that of the heat source. 

Wood-based panel products are usually bonded with synthetic adhesives based on condensates of phenol, resorcinol, urea, or melamine with formaldehyde. Particleboards and fiberboards can also be bonded with mineral binders like cement or gypsum. Wood adhesives derived from natural products have more... 

Wood-based panel products for exterior applications often require special finishes and special finishing practices (J, 69, 7J, 74, 96). Pretreatments and edge treatments are often required. 

Poliquin L (1998) Wood-based panel products special report a technology roadmap. Forintek Canada Corp, Vancouver, BC... 

Formaldehyde Emissions Hardwood Plywood and Certain Wood-Based Panel Products... 

Lines of demarcation between hardwood plywood, softwood plywood and certain other wood based panel products have become less distinct in recent years. One of the most important distinctions in respect to formaldehyde emission potential is that softwood plywood is typically bonded with phenol-formaldehyde while hardwood plywood is typically bonded with urea-formaldehyde. Phenol-formaldehyde adhesives are more stable and have less tendency to emit formaldehyde than do urea-formaldehyde adhesives. Some important features of hardwood plywood ... 

Press platens are made from stainless steel or chromium-plated brass and copper. The chromium layer preserves surface quahty longer than does ordinary steel. The MF laminates exhibit a remarkable set of characteristics. Because of their unusual chemical inertness, nonporosity, and nonabsorbance, they resist most substances, such as mild alkalies and acids, alcohols, solvents such as benzene, mineral spirits, natural oils, and greases. No stains are produced on MF surfaces by these substances. In addition to almost unlimited coloring and decorating possibilities, this remarkable resistance has resulted in the extensive use of MF laminated wood-based panel products for tabletops, sales counters, laboratory benches, heavy-duty work areas in factories and homes, wall paneling, and so on. 

Anonymous, Wood-based Panel Products Technology roadmap (Canadian Cataloguing in Publication Data), 1998, http //strategis.ic.gc.ca/trm. 

British Standards Institute, BS 6100 1992/Confirmed 1998. Glossary of Building and Civil Engineering Terms. Part 4 Forest Products, Section 4.1 Characteristics and Properties of Timber and Wood Based Panel Products. 

Both the wood-based panel industry and the adhesive industry show a high commitment to and great capability towards innovation. The best evidence for this is the considerable diversity of types of adhesives used for the production of wood-based panels. Well-known basic chemicals have been used for a long time for the production of the adhesives and their resins, the most important ones being formaldehyde, urea, melamine, phenol, resorcinol and isocyanate. The greater portion of the currently used adhesive resins and adhesives for wood-based panels is produced with these few raw materials. The how to cook the resins and the how to formulate the adhesive become more and more complicated and sophisticated and are key factors to meet today s requirements of the wood-based panel industry. 

Good-quality bonding and sufficient properties of the wood-based panels can be attained only if each of these three parameters contributes to the necessary extent to the bonding and production process. 

Shorter press times in a given production line for a certain type of wood-based panel can be attained, in the following ways ... 

Adhesives and resins are one of the most important raw materials in wood-based panels. Thus, each question concerning the life cycle assessment and the recycling of bonded wood panels does bring into question the adhesive resins used. This includes, for example, the impact of the resin on various environmental aspects such as waste water and effluents, emission of noxious volatile chemicals during production and from the finished boards, or the reuse for energy generation of wood panels. The type of resin has also a crucial influence on feasibility and efficiency for several material recycling processes. 

Emission of volatile noxious chemicals from wood-based panels during their production can be caused by chemicals inherent to wood itself, like terpenes or free acids, as well as by volatile compounds and residual monomers of the adhesive. The emission of formaldehyde as well as free phenol effluents is a matter of concern. 

Adhesives based on isocyanate (especially PMDl, polymethylene diisocyanate, more exactly polymeric 4,4 -diphenylmethane diisocyanate) have been used for more than 25 years in the wood-based panel industry [88], but still have a low market value in the wood-working industry compared to systems based on UF-, MUF- or PF-resins. The main application is the production of waterproof panels, but also the production of panels from raw materials that are difficult to glue, like straw, bagasse, rice shells or sugar cane bagasse. They can be used as adhesives for wood-based products like particleboard, oriented strandboard (OSB), laminated strand lumber (LSL), medium-density fiberboard (MDF) or... 

For the production of wood-based panels various adhesives are in use like aminoplastic resins (UF, MU(P)F), phenolic resins (PF) or isocyanate (PMDI). The proper choice of the adhesive depends on the required properties of the wood-based panels, on the working conditions during the production as well as often on the costs for the adhesive system this not only means the net price of the adhesive but the overall costs of the gluing system including glue spread factor. 

The properties of wood-based panels are determined in principle by three influence parameters (1) wood component (2) adhesive (3) production conditions. Only if all three parameters are appropriately considered, can proper bonding results can achieved. 

During the production of wood-based panels, part of the adhesive penetrates into the wood surface. An overpenetration causes starved glue lines, whereas a low penetration limits the contact surface between wood and the adhesive low penetration often is the consequence of bad wetting behavior. 

Lignocellulosics reach temperatures around 80 C in many ways besides. For example, planer shavings and peat insulation around hot pipes or in walls of dry kilns easily attain 100 C, and forest product industries stack still hot wood-base panels at temperatures around 80 C. In many cases the temperatures of the hot materials later on rose above the initial 80 or 100"C, first to levels of smoldering combustion, and finally to those of open flames. In air-exposed and ventilated materials oxidation could cause the heating above 80 or 100 C, but inside tight packs of panels pyrolysis must have been the heat source. 

Brown (1999b) reported formaldehyde and VOC emissions from new, unfinished particleboard and MDF (both using urea formaldehyde resins) in Ausbalia. Formaldehyde emissions over the first three weeks exhibited first-order decay behavior that predicted little to no formaldehyde emission after 6 months. However, further emission measurements at 8 months showed the products sbll emitted formaldehyde at approximately one-half the new product rate (also further unpublished measurement at 2 years showed the same emission rate as at 8 months). It was concluded that the wood-based panels emitted formaldehyde by a double-exponen-ttal model, the early- to late-term emissions including the free formaldehyde in the products but the long-term emissions consisbng of only the formaldehyde... 

Table 11.2 shows 2003 production of both sawn timber and wood panels for various regions of the world. Structural panel production is dominated by North America, mainly because structural panel products have enjoyed a dominant position in residential construction. The United States is a substantial manufacturer of softwood plywood for domestic production but only 10% is exported whereas half that volume is imported as tropical hardwood plywood. Europe manufactures and uses comparatively little plywood and OSB. Instead the region relies on its own lower quality domestic wood resources for the manufacture of other wood-based panels, e.g. particleboard and fibre-based board. Amazingly, panel production in Asia equals that of lumber, reflecting the inter-regional China-centric supply chain. 

The overall picture is of the wood-based panels sector continuing to grow as products are developed that meet new customer requirements. The processes have demonstrated an adaptability to different fibre sources, both in form and in species that has allowed plants to be established in most parts of the world, primarily to meet local demand, but also with a significant export component to those areas where fibre supplies are fully committed. 

Young S (2005) Emissions from wood-based products a world update on regulations and trends. Proceedings of the Asia-Pacific Wood-Based Panels Conference, Shanghai, Paper 15... 

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