Panel products

All of the above treatments, unless deliberately superficial, are not easy to apply to lumber because of the lengthy time for diffusion and reaction, or because of the difficulties in achieving effective penetration. In recent years, therefore, interest has also centred on improving the dimensional stability and durability of reconstituted panels hardboard, particleboard, medium density fibreboard and new derivatives. 

SHAKTI CHAUHAN ROBERT DONNELLY CHIH-LIN HUANG RYOGO NAKADA YIN YAFANG AND JOHN 

Context is everything. It informs, clothes and gives shape to the simplest idea. In isolation wood quality has little meaning only where set against a particular set of end use requirements is it possible to categorize the desired wood characteristics and properties that a particular product needs. 

Discussion of the influence of time for forest praetices is deferred until later. At this stage it is useful to consider further this tenuous thread linking the forest resource to consumer desires and needs, as examination brings clarity - or at least systematic order - to the concept of wood quality. 

---

Insulation Boa.rd. The panel products known as insulation board were the earliest commodity products made from fibers or particles in the composite panel area. These are fiber-base products with a density less than 500 kg/m. Early U.S. patents were obtained in 1915 and production began soon thereafter. The initial production used wood fiber as a raw material, but later products were made of recycled paper, bagasse (sugar cane residue), and straw. Schematics of the two major processes still ia use are shown ia Figure 4. 

Production, Processing, and Shipment. Hardboards and hardboard siding are fiber-base panel products having densities in the 500—1000-kg/m range. Two density classes are made medium density at 500—880 kg/m and high density, >880 kg/m . Hardboards are generally thin products, 2.5—9.5 mm in thickness, whereas the siding products are usually 11.1—12.7 mm in thickness. 

After humidification, the products are trimmed to size and stacked. The stacks are then moved to the next processing step and many of the secondary treatments of hardboard will take place at the panel production site. These latter may include the following ... 

Then, in the early 1980s the concept of OSB was realized in the constmction and operation of large-size mills. OSB is a panel product made from wood strands and somewhat like plywood in that the strands on the two faces are oriented in the long direction of the panel and the core strands are oriented in the cross-panel direction. The use of orientation yields panels having exceUent directional properties, much like plywood, and thus an exceUent and economical stmctural sheathing material is created. 

Some fabrication processes, such as continuous panel processes, are mn at elevated temperatures to improve productivity. Dual-catalyst systems are commonly used to initiate a controlled rapid gel and then a fast cure to complete the cross-linking reaction. Cumene hydroperoxide initiated at 50°C with benzyl trimethyl ammonium hydroxide and copper naphthenate in combination with tert-huty octoate are preferred for panel products. Other heat-initiated catalysts, such as lauroyl peroxide and tert-huty perbenzoate, are optional systems. Eor higher temperature mol ding processes such as pultmsion or matched metal die mol ding at temperatures of 150°C, dual-catalyst systems are usually employed based on /-butyl perbenzoate and 2,5-dimethyl-2,5-di-2-ethyIhexanoylperoxy-hexane (Table 6). 

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. 

Robson, D.J., In 1st Furopean Panel Products Symposium, Proceedings, Llandudno, Wales, 1991, pp. 203-210. 

Nitric acid is one of the three major acids of the modem chemical industiy and has been known as a corrosive solvent for metals since alchemical times in the thirteenth centuiy. " " It is now invariably made by the catalytic oxidation of ammonia under conditions which promote the formation of NO rather than the thermodynamically more favoured products N2 or N2O (p. 423). The NO is then further oxidized to NO2 and the gases absorbed in water to yield a concentrated aqueous solution of the acid. The vast scale of production requires the optimization of all the reaction conditions and present-day operations are based on the intricate interaction of fundamental thermodynamics, modem catalyst technology, advanced reactor design, and chemical engineering aspects of process control (see Panel). Production in the USA alone now exceeds 7 million tonnes annually, of which the greater part is used to produce nitrates for fertilizers, explosives and other purposes (see Panel). 

Developments in glued laminated structures and panel products such as plywood and chipboard raises the question of the durability of adhesives as well as wood. Urea-formaldehyde adhesives are most commonly used for indoor components. For exterior use, resorcinol adhesives are used for assembly work, whilst phenolic, tannin and melamine/urea adhesives are used for manufactured wood products. Urea and casein adhesives can give good outdoor service if protected with well-maintained surface finishes. Assembly failures of adhesives caused by exudates from some timber species can be avoided by freshly sanding the surfaces before glue application. 

Fig. 9-6 Cost comparison of panel production using TCM program that shows blow molding with the lowest product cost.

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. 

Among lignocellulosic panel products, fiberboard (called fiber insulation board in earlier decades) seems to have caused more fires than the denser products hardboard, particleboard, and plywood. Fiberboard self-heats more because it conducts less of the generated heat out of the... 

Uie recycling of wood waste is also increasingly being used, where timber products at the end of life are usually reduced by chipping, or fibre production, and the resultant material is then reused in reconstituted wood products. Strict monitoring and control are required in order to ensure that inappropriately treated waste is not included in the feedstock stream for recycling wood. The use of recycled wood in reconstituted products is rising rapidly for example, in the UK, the panel products industry used 400 000 tonnes of recycled wood in 1999, and this had risen to 932000 tonnes by 2002 (UK Forestry Commission data 2003). 

Timar, M.C., Maher, K., Me, M. and Mihai, M.D. (1999b). High performance wood-fibre/plastic composites by chemical modification. In Proceedings of the Third European Panel Products Symposium, Hague, 1., Griffiths, S., Loxton, C., McLauchlin, A., Mayhead, G. and Tomkinson, J. (Eds.), pp. 352-358. 

MDF Medium-density fiberboard. A composite panel product manufactured from wood fibers and s)mthetic resin binders bonded together under heat and pressure the fibers and resin form a homogeneous board with consistent properties in each direction. 

ASTM (1999), Annual Book ofASTM Standards, ASTM Method D 1037-99, American Society for Testing and Materials, Committee D7 on Wood, Subcommittee D07.03 on Panel Products, West Conshohocken, PA. 

The particleboard industry has grown rapidly since its beginning in Europe during the Second World War. The original development was in response to the demand for an inexpensive panel product which could be produced from low-quality wood unsuitable for plywood. In the mid 1950 s the particleboard industry was established in the United States not in response to a demand for the product but in response to the availability of cheap residues generated by planer mills and sawmills. 

Hume, G. 2005. Fire retardant composite panel product and a method and system for fabricating same. U.S. Patent Appl. 2005/0249934. 

It is worthwhile to review the U.S. market size for the four principal resins currently used in wood-panel products today (4 )- These are phenol-formaldehyde (PF), urea-formaldehyde (UF), melamine-formaldehyde (MF), and resorcinol-formaldehyde (RF) (Table III). When these production figures are compared to the quantities of lignin potentially available (Table II), it is immediately obvious that all wood adhesives could be replaced by only a very small fraction of the lignin produced annually during chemical woodpulping processes. 

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... 

Formulations for particleboard and plywood adhesives based on combinations of diisocyanates and compounds from renewable resources like tannins, starch, and proteins have been developed and tested at the Fraunhofer-Institute. All in all, the results of gluing tests indicated the potential for using diisocyanates combined with natural polymers for adhesive purposes where each natural product used alone will fail. More attempts will be necessary to find precise mixtures to produce successful adhesives for panel products. The development of adequate particleboard and plywood glue formulations based on diisocyanates and natural polymers has to be accompanied by more sophisticated technologies than those used in conventional production processes. The results presented here may give some hints on how these technologies can evolve. 

---