Particle boards, properties

Improvement in the particle board properties made by the process based on HNO3 surface activation and ammonium lignosul-fonate-furfuryl alcohol-maleic anhydride binder was reported to result from drying of the HNO3 treated chips (J90). 

Uses Industrial grade surfactant, emulsifier, for paper coatings, floor polishes, furniture polishes, fiberboard and particle board Properties Amber liq. sol. in IPA, perchloroethylene, xylene, cottonseed and paraffinic oil dens, 1,00 g/ml vise. 379 cs HLB 5 pour pt. -39 F 100% act. 

The phenoHc resins used for particle board are NaOH-catalyzed resoles of low viscosity and high water miscibility, similar to the Hquid resole adhesives used in plywood manufacture. The higher resin and caustic content of the board frequently necessitates the addition of hydrophobic agents such as wax emulsions to increase the barrier properties of the board. The adhesive is appHed to the particles in thin streams using high agitation to maximize material usage. Boards are cured in presses for 5—10 min at 150—185°C. 

Waferboard, a more recent wood constmction product, competes more with plywood than particle board. Waferboard and strand board are bonded with soHd, rather than Hquid, phenoHc resins. Both pulverized and spray-dried, rapid-curing resins have been successfully appHed. Wafers are dried, dusted with powdered resin and wax, and formed on a caul plate. A top caul plate is added and the wafers are bonded in a press at ca 180°C for 5—10 min. Physical properties such as flexural strength, modulus, and internal bond are similar to those of a plywood of equivalent thickness. 

Phenolic Resins. PhenoHc resins [9003-35 ] (qv) are thermosets prepared by the reaction of phenol with formaldehyde, through either the base-cataly2ed one-stage or the acid-cataly2ed two-stage process. The Hquid intermediate may be used as an adhesive and bonding resin for plywood, particle board, ftberboard, insulation, and cores for laminates. The physical properties for typical phenoHc laminates made with wood are Hsted in Table 1. 

Application of Laccase as a Radical Donor in Adhesives for Particle Boards. The properties of laccase with regard to lignin render it a candidate for application in technical processes. A two-component adhesive was formulated with lignin as the phenolic component and laccase as radical donor. The process is described in more detail elsewhere (1). 

Milled wood lignin was mixed with the crude enzyme solution of Tram-ties versicolor extracellular phenoloxidases produced on spent sulfite liquor in a ratio of approximately 2 1. This comprised the main part of the two-component bio-adhesive. Industrial particles were bonded with 15% bioadhesive under conventional pressing conditions to have 19 mm particle boards (40 x 50 cm) of the properties described in Table IV. The bonding reaction (crosslinking) took place in aqueous solution at room temperature. If conventional pressing technology is applied, the temperature should be elevated in order to maintain water evaporation within a reasonable press time. 

Table IV. Technological and Mechanical Properties of Biobonded Particle Boards Effect of Lignin Type, Enzyme Activity and Pressing Time...

In order to achieve results comparable to phenol-formaldehyde bonded particle boards which had densities in the range of. 71 to. 79 g/cc, densities of boards crosslinked with HDA were varied from. 77 to. 88 g/cc. Thus, using the same weight of flakes, boards prepared using the activated substrates exhibited similar properties but slightly higher densities. 

Anderson contributed a paper to the 1956 International Consultation on Insulation Board, Hardboard and Particle Board (26). In addition to a good review of the literature, the paper contained results of further experimentation using the barks of several more species as furnish for wet-process hardboard. New species included ponderosa pine, sugar pine, southern pine, pinyon pine, lodgepole pine, noble fir, and red oak. Ponderosa pine bark produced hardboard comparable to Douglas-fir bark in both strength and moisture resistance. The other species varied widely in these properties. 

There are also reports of the production of boards and moldings from plasticized wood particles, pulp or sawdust without adhesives (5,8,59,60). By compressing and heating to high temperatures, particle boards can be produced which have mechanical properties comparable to conventional resin bonded boards. However, their specific gravity is on the average about twice that of ordinary commercial products (59). 

The variety of wood products has increased enormously over the past decades as more adhesives have been found for bonding. The most important products in terms of volume are plywood, particle board, and fiber board. But adhesively bonded products range from tiny articles of jewelry to giant laminated timbers spanning hundreds of feet (5). The modification of adhesive properties to suit the different application requirements requires a sound understanding of the basic chemistry of adhesives. 

Table II. Some Properties of 1,6-Hexanediamine (HMDA) and Phenol—Formaldehyde-Bonded Particle Board...

Table HI. Effect of Species and Hydrogen Peroxide Concentration on the Properties of Particle Board...

Substitution of potassium ferricyanide for 1% of sulfur dioxide dissolved in calcium-base spent sulfite liquor was possible at a pH of about 2.0. An increase in pH stabilized the cross-linking mixture unless 4% of ammonium chloride (dry wood basis) was added. In this case particle board could be produced at a pH of 4.5, with properties equivalent to those produced at a pH of 2.0, i.e., with IB values of up to 82.0 psi and acceptable water resistance (JOS, 109). 

The nonconventionally produced particle board can offer several advantages. Some systems offer better water absorption and thickness swelling characteristics and/or low formaldehyde emissions. Reliance on agricultural by-products and independence from the international oil market represent additional attractions. The problems yet to be solved are mainly connected with abnormally high variability in the mechanical properties and generally inferior performance in the low density area. 

Table 1 Mechanical Properties of Particle Board and Plywood...

In order to confirm achievement of the necessary properties of the chip form and to compare it with lauan plywood and particle board, the various tests shown in Table 2 were performed. The conditions of the bending test are shown in Figure 4. 

The raw material for the particle board is scrap timber that has been cut into chips, and its final properties are to a large extent due to the nature of the adhesive used to bond the chips together, it is believed that for this reason the amount of dispersion of values is relatively small. In the case of lauan plywood on the other hand, the raw material is natural wood, so the dispersion in strength is relatively large but the wood fibers give only little dispersion in elongation results. 

Effect of undefibrated paper particles on board properties... 

In this study, the defibration is one of the key steps for the good board performance. In order to see the effect of the ratio of undefibrated paper particles (incomplete defibration) on the board properties, shredded paper particles (12x3 mm) before going through defibration process were artificially mixed with completely defibrated fibers, and the boards were manufactured. Figure 7 and 8 show MOR and MOE of the boards respectively. 

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