Particleboard three-layer

Table IV. Three-Layer Bark Extract Bonded Particleboard 3/8-Inch ...

Dost in 1971 reported on a study where redwood bark fiber was used in three-layer particleboard (44). Amount of bark in the furnish, by weight, was 0, 10, 20, and 30% hammemilled disk flakes or Pallmann flakes of redwood wood made up the remainder of the furnish. Urea formaldehyde resin was applied at three percentages. Test results showed surface smoothness and strength properties (MOR, MOE, and IB) decreased with increasing bark content in the boards. Water absorption decreased, but thickness swelling and linear expansion increased as the amount of bark increased. 

Results of the later studies showed bark-paraformaldehyde furnish as core of three-layer particleboard resulted in white fir boards meeting medium-density particleboard specifications for bending and internal bond strengths, as well as linear expansion (51). 

The thermal properties of composite boards were the subject of a recent report by Place and Maloney (58). Thermal conductivity tests were made on three-layer boards with surfaces of white pine wood flakes and cores of either Douglas-fir or grand fir bark. Density was varied at 34, 42, and 52 pounds per cubic foot. The composite boards containing bark proved to be better insulators than wood particleboard of comparable density. Douglas-fir bark cores had lower thermal conductivity than did grand fir. 

Figure 5. Strength of three-layer particleboard (20% surface chips) glued with hydroxymethylated bagasse lignin/commercial PF resin (67 33) and pressed at 170 to 180 °C for different times, 12% chip moisture content, final density 680 kg/m3.

Particleboard or mat-formed composite board is one of the products that can use recycled wood as a raw material. According to questionnaires, recycled wood used in the particleboard industry is estimated to be 20% of the total chips, and the amounts have been increasing. Laboratory scale particleboards were made using recycled P-chip and S-chip to evaluate chip quality. The results showed that the quality of P-chip was equal to that of ordinary chip. Hammer-milled particle from low grade chips can be used as a core material of particleboard. A new type of structural board with three-layer construction was proposed to expand the use of recycled wood chips. 

Using four types of wood furnish, i.e., Particle-a, -b, -cl, and -c2, particleboards were made in the laboratory. Eight types of board were made from these particles six types of homogeneous board and two types of three-layer board which had a 15 weight percent of each face layer and 70% of core layer. Furnish type and construction of PBs are shown in Table 2. Specifications for board manufacturing were as follows ... 

Specifications for board manufacturing were the same as mentioned in section 3.2. Construction of the board is shown in Table 3. Board-1 and board-5 were homogeneous board, and board-2, -3, and -4 were three-layer board. Board-1 was recycled wood particleboard and the board-5 was strand-board without orientation. 

Figure 7 shows the relationship between the face layer ratio and the modulus of elasticity (MOE) in bending of the composite boards. It was obvious that the MOE increased with an increasing face layer ratio of the composite board, because the elastic modulus of the strand layer was higher than that of the core layer with recycled wood particle. If a simple combination of different elastic bodies was introduced, the MOE of three-layer board can be predicted easily by a cubic equation of face layer ratio. It was thought that the MOE of the composite board shown in Figure 7 was predictable from the MOE data of recycled wood particleboard and strand-board. 

The MOE of three-layer board was also higher than that of commercial particleboard. This showed the possibility of manufacturing high performance panel from strands of domestic conifer and recycled wood particles. 

Duplicate 12 mm thick three layers particleboard 600 mm x 300 mm in dimensions were prepared in the laboratory using 7 Z UF resin solids total on oven dry pine wood chips. The glue mix used was as follows ... 

A three-layer particleboard was hand-formed in a metallic container with dimensions 220 mm x 220 mm x 80 mm. The total percentages of board mass were 20% for the upper face layer, 62% for the core layer and 18% for the bottom face layer. Boards were then pressed in a laboratory scale hot-press, controlled by a computer and equipped with a displacement sensor (LVDT), a load cell, thermocouples and pressure transducers. The mat was pressed at 195°C for 2.8 min to produce a board with a target density of 650 kg/m and with 17 mm thickness. 

Particleboard usually consists of a three-layered panel with two surface layers (outer layers) and one core layer (inner layer). The face furnish is usually thinner than that in the core. This permits the strength and stiflhess of the panel to be tailored and the faces to be produced with smooth surfaces. The American National Standard for Particleboard, ANSI A208.1, classifies particleboard by density, properties, and class, and is the voluntary particleboard standard for the North American industry (Table 3). 

Table 10.3.2. Properties of wood-face, bark-core, three-layer particleboards bonded with conifer bark tannins (173)...

A considerable amount of effort has gone into overcoming the sticking problems. One approach has been to manufacture a three-ply board in which the two outside layers utilize a conventional wood binder, such as a phenol-formaldehyde resin, and the internal layer is bound with an isocyanate adhesive.Deutsch Novopan GmbH of West Germany has commercialized such a process to manufacture exterior structural grade particleboard. A board prepared in this manner does not completely circumvent the potential problem of formaldehyde emissions, although they may be reduced relative to a board made solely with a formaldehyde adhesive. 

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