Particle board bonding preparation

It was originally hoped that free radicals formed by oxidative activation of the wood surface would join via oxidative coupling to form covalent bonds (Figure 2). The particle board was prepared by... 

Amino Resins. Amino resins (qv) include both urea- and melamine—formaldehyde condensation products. They are thermosets prepared similarly by the reaction of the amino groups in urea [57-13-6] or melamine [108-78-1] with formaldehyde to form the corresponding methylol derivatives, which are soluble in water or ethanol. To form plywood, particle board, and other wood products for adhesive or bonding purposes, a Hquid resin is mixed with some acid catalyst and sprayed on the boards or granules, then cured and cross-linked under heat and pressure. 

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. 

Plastic laminated sheets produced in 1913 led to the formation of the Formica Products Company and the commercial introduction, in 1931, of decorative laminates consisting of a urea—formaldehyde surface on an unrefined (kraft) paper core impregnated with phenoHc resin and compressed and heated between poHshed steel platens (8,10). The decorative surface laminates are usually about 1.6 mm thick and bonded to wood (a natural composite), plywood (another laminate), or particle board (a particulate composite). Since 1937, the surface layer of most decorative laminates has been fabricated with melamine—formaldehyde, which can be prepared with mineral fiUers, thus offering improved heat and moisture resistance and allowing a wide range of decorative effects (10,11). 

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. 

Primary benefits of the second-generation acrylics included increased toughness and impact strength of metal-to-metal bonds, as well as the ability to bond metal surfaces, even oily metal surfaces, with little or no surface preparation. The products were also shown to be capable of effective performance as 100% solids alternatives to solvent cements in application such as plastic pipe bonding and decorative lamination of vinyl and high-pressure laminates to metals and particle board [2]. 

Preparation of Hot-Melt and Self-Bonded Boards. Reaction conditions for benzylation are dependent on wood species and specimen size. For Akamatsu particles, pretreatments and reaction conditions are as follows wood is first oven-dried at 105°C for 24 h and then immersed in 40% sodium hydroxide solution for 1-2 h at room temperature. These particles are then squeezed to remove excess sodium hydroxide and reacted with benzyl chloride at 120°C for 1-2 h. Benzylated particles are then washed in water and any unreacted reagent is removed by squeezing. Particles are then washed further in a mixture of water-methanol (1 2 v/v) and air-dried for 48 h at 20 C. In general, benzylation of softwood species is more difficult than for hardwoods, and the reactivities of wood from fast-growing trees, i.e., willow or monocotyledons,... 

Duplicate one-layer laboratory particleboards of dimensions 350 mm x 310 mm x 16 mm were prepared by adding 10% total resin solids on dry wood particles. The boards were pressed at a maximum pressure of 28 kg/cm followed by a decrease in pressure first to 15 kg/cm and last to 5 kg/cm, at a press temperature of 195°C and for a total press time of 7.5 min. Shorter press times were also used (see Table 3). The target average density for all the panels was 680-700 kg/m. The panels, after light surface sanding, were tested for dry internal bond (l.B.) strength according to European Norm EN 314 [21]. 

In fabrication of printed circuit boards (Goh 1994), a resin formula is prepared and impregnated with fibreglass and other particles. This is baked to form a panel or a board. Lamination involves metallic copper being bonded to the board in (sandwiched) layers. Each side of the laminate is cleaned, photoprinted and etched to form the electrical circuits. Solder plating is done, and the boards are drilled and cut to the required sizes. Finally, the boards are marked and tested. 

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