Hardwood plywood paneling

Particleboard decking and hardwood plywood wall panels can represent 80% to 90% of the total exposed surface of formaldehyde containing wood based products in new mobile homes. Kitchen cabinets, vanities, shelving and other built-ins are primarily made from industrial particleboard, MDF or hardwood plywood panels. 

The U.S.Department for Housing and Urban Development s rule 3280.308 established formaldehyde emission standards for particleboard and hardwood plywood paneling used in mobile homes. These standards took effect February 11, 1985. The certification program under this rule requires each manufacturer to develop a quality control in-plant testing program that relates to tests conducted in a large scale environmental chamber. 

Determining Formaldehyde Emission from Wood Products" FTM-2 - 1983 (16). In this method, particleboard and hardwood plywood paneling are tested under the following conditions ... 

Figure 9 presents chamber data of only one set of hardwood plywood paneling performed at different loading and air change rates. 

In addition, the effect of ventilation rate on chamber concentration is different for each wood product type, i.e. particleboard, medium density fiberboard, hardwood plywood paneling. 

Figure 9. Effect of air change rate and loading on chamber formaldehyde concentration - hardwood plywood paneling.

Two Product Loading - Particleboard And Hardwood Plywood Paneling. 

The H.U.D. formaldehyde standards of 0.2 ppm and 0.3 ppm for hardwood plywood paneling and particleboard, respectively, were chosen because the combination of these products at their specific loadings and air change rate would result in a chamber concentration of less than 0.4 ppm. This assumption was based on four studies. 

Upon completion of the chamber test, the hardwood plywood paneling or particleboard is removed and 12 each 7.00cm x 12.7 cm specimens are randomly cut from each board loaded into the chamber. For the surface monitor (FSEM) and the small scale test chamber(SSTC), one 30.5cm X 30.5cm board is cut from each board loaded in the chamber. These samples are immediately tested by the Equilibrium Jar for particleboard or the Two Hour Desiccator or FSEM or SSTC for all wood product types. The values obtained from each test are averaged and are then compared to the chamber concentration observed for that loading and air change rate. 

Figure 14 provides a graphical representation of 27 chamber tests conducted on a variety of veneer, print, a paper overlay finished hardwood plywood paneling. Even though it is not shown, a breakdown by different product type did not affect the correlation by anymore than 5%. As with particleboard, the cloud of points below 0.2 ppm represents current production made to meet the H.U.D. hardwood plywood paneling standard (0.2 ppm chamber). The group of points between 0.24 and 0.36 ppm chamber are from earlier chamber studies needed to define the curve. 

Figure 14. Correlation of 2 hour desiccator to chamber for hardwood plywood paneling.

Hour Desiccator for G-P hardwood plywood paneling correlates to the large scale test chamber. 

The primary adhesive used ia hardwood plywood is urea—formaldehyde (UF) mixed with wheat flour as an extender to improve spreadabiUty, reduce penetration, and provide dry-out resistance. A catalyst may also be added to UF resias to speed the cure or to cause the UF to cure. Scavengers also may be added to reduce formaldehyde emissions from finished panels. If more water-resistance is requited using a UF bond, small amounts of melamine maybe added, producing a melamine—urea—formaldehyde (MUF) adhesive. 

Lay-up proceeds by laying down the veneer which is to be the back surface of the panel. Then a sufficient number of pieces of core veneer are passed through the glue spreader to form the next layer of cross-oriented veneer. The glue spreader commonly used in hardwood plywood manufacture is a roU coater in which a pair of opposing mbber roUs are coated with a thin layer of adhesive. As the veneer is passed between the roUs, the adhesive is transferred to the surfaces of the veneer. Adhesive is appHed only to the cross-pfles and in sufficient quantity to provide a continuous layer on both opposing faces of veneer. Thus, in the case of a three-ply panel, only the core layer is spread with adhesive and in that of a five-ply panel, the second and fourth layers both of which are cross-pfles, are spread with adhesive. Then the top surface veneer, which is normally the decorative surface, is placed on the assembly. 

Uses and Treatments of Hardwood Plywood. Most early appHcations of hardwood plywood were those where the hardwood plywood was better adapted to the use than soHd wood. One of the most important early uses was in curved or formed parts, an appHcation particularly suited to the use of veneers which could be molded into intricate shapes during the pressing and bonding process. Then, as furniture manufacturers realized the inherently superior stabiHty of plywood compared to soHd wood, lumber-core or plywood panels began to be used for most flat-panel constmctions in furniture. 

Thin hardwood plywood in the range of 4.5—6.0 mm (3/16—1 /4 in.) was normally a three-ply constmction with a thin, medium-quaHty back ply, a thicker lower value core, and another thin, high quaHty decorative face veneer. These panels were used as wall paneling, door facings, or for fumiture/cabinet appHcations requiring thin panels. Currently, only relatively small quantities of these types of panels are produced in the United States. 

Plywood is also divided into softwood and hardwood plywood products. The classification depends on the type of wood the face pHes are made from. The principal appHcation for 1 cm and thicker hardwood plywoods are cabinets and furniture. The thinner grades are used to make paneling and doorskins, which represent approximately 56% of the total hardwood plywood products. The total market in 1989 was estimated to be 2.1 biUion. 

Approximately one million metric tons of urea-formaldehyde resin are produced annually all over the world. More than 70% of this urea-formaldehyde resin is consumed by the forest products industry. The resin is used in the production of an adhesive for bonding particleboard (61% of the urea-formaldehyde used in the industry), medium-density fiberboard (27%), hardwood plywood (5%), and as a laminating adhesive (7%) for bonding furniture case goods, overlays to panels, and interior flush doors, for example. 

In the April, 1975, issue of Plywood Panel magazine, we find reported square feet, quarter inch basis, domestic hardwood plywood manufactured in this country was approximately 3.5 billion and softwood plywood was 27.5 billion. This means 89 percent of the total plywood produced was softwood plywood, and 97 percent of this production was glued with phenol-formaldehyde resin adhesives, according to the American Plywood Association. This leaves 11 percent domestic hardwood plywood which was 95 percent glued with urea-formaldehyde resin adhesives,... 

Hot press plates heated to about 250° Fahrenheit for urea hardwood plywood and 300° Farenheit for phenolic bonded softwood plywood are closed under pressure at 150 - 200 pounds per square inch. The hot presses may vary from ten openings to as many as fifty openings capable of pressing one or two thin panels per opening. 

The types of adhesives suitable for laminating beams are restricted by the conditions of application and by their end-use requirements. A wider choice of adhesives for plywood depends on whether softwoods or hardwoods are used, whether they are required for internal or external exposures, or whether they are to be used for ornamental or structural purposes. Thus phenol-formaldehyde types would be used for marine or exterior construction uses urea-formaldehyde types would be advantageous for cold pressing, or melamine-urea adhesives might be preferred for hardwood plywood, or lumber-core panels used in furniture production. 

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