Medium-density fiberboards

Plywood furniture core panels, also about 19 mm (3/4 in.) thick, were normally made of a number of layers of relatively thick, 1.5—3.0 mm (1 /16—1 /8 in.) lower value wood veneers combined with thin surface pHes of the decorative veneer. These assembhes were laid-up from glued veneers and then pressed while the bonding occurred. Both lumber core and plywood core have been almost totally displaced in recent years by particleboard or medium-density fiberboard, both discussed herein. This change resulted from the increasing availabiHty and improved finishing characteristics of composites and from decreasing suppHes of core lumber or veneer of suitable quaHty. 

Production, Processing, and Shipment. Medium-density fiberboards (MDF) are panels made of fibrous raw material and used ia most of the same appHcations as particleboard. MDF products generally have more smooth surfaces and edges than particleboards and are thus preferred for some uses, even though the manufacture of MDF is more cosdy and the product is significantly more expensive. 

Medium-Density Fiberboard (MDF), ANSI A208.2-1994, American National Standards Institute, New York, 1994. 

Medium-density fiberboard (MDF) a flat pressed wood composite panel composed of randomly oriented wood fibers obtained by thermomechanical wood pulping and bonded by hot-pre.ssing by using thermosetting adhesive resins. The panel has generally a density of approximately 850 kg/m- and the average amount of resin solids in the board core section is between 11 % and 14% on dry wood. 

Adhesives based on isocyanate (especially PMDl, polymethylene diisocyanate, more exactly polymeric 4,4 -diphenylmethane diisocyanate) have been used for more than 25 years in the wood-based panel industry [88], but still have a low market value in the wood-working industry compared to systems based on UF-, MUF- or PF-resins. The main application is the production of waterproof panels, but also the production of panels from raw materials that are difficult to glue, like straw, bagasse, rice shells or sugar cane bagasse. They can be used as adhesives for wood-based products like particleboard, oriented strandboard (OSB), laminated strand lumber (LSL), medium-density fiberboard (MDF) or... 

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. 

Particleboard, 62% medium density fiberboard, 19% hardwood plywood, 5% glass fiber roofing mats, 4% molding compounds, 3% miscellaneous, 7%... 

Almost any substrate that will be powder coated, whether it is metal, medium-density fiberboard (MDF), or some other material, requires some kind of surface freafmenf. Surface preparafion (prefreafmenf) of wood and more specifically, MDF preparation consist of sanding, removal of confami-nanfs, and board condifioning. MDF boards fhaf will be coafed by UV curable powders should have a moisture content of 49%. If is also a common practice fo preheaf MDF boards prior to application of fhe UV powder. Mefal surfaces are always cleaned by washing and usually freated by a phosphafe primer. Conductive plastics are washed and dried and then coated without any further treatment. Nonconductive plastics are made conductive by applying a primer coat or treated by plasma or flame. ... 

Wood and wood composites Solid wood as well as particleboard and medium-density fiberboard (MDF) are suitable substrates for powder coating. They tend to emit volatiles such as entrapped air and moisture, and therefore require curing temperatures below 100°C (212°F) and preferably nof higher than 80°C (144°F). A typical curing procedure for MDF is in Table 7.8. 

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. 

Fig. 6. The dry-process hardboard (and medium-density fiberboard) process.

Baumann, M.G.D., Batterman, S.A. and Zhang, G.-Z. (1999) Terpene emissions from particleboard and medium-density fiberboard products. Forest Products Journal, 49 (1), 49-56. 

Koontz, M.D. and Hoag, M.L. (1995) Volatile organic compound emissions from particleboard and medium density fiberboard. Measuring and Controlling Volatile Organic Compounds and Particle Emissions from Wood-Processing Operations and Wood-Based Products, Proceedings No. 7301, Forest Products Society, WI, pp. 76-87. 

One of today s fastest growing segments of the wood composition board industry is production of medium density fiberboard (MDF) using a dry process similar to that used for particleboard. First mention of the possibility of utilizing bark for MDF came in a presentation by Brooks in 1971 (43). He described a process in which a homogenous board with superior properties could be made from such raw materials as mixed, unbarked hardwood pulp chips unbarked pine chips, if bark content was less than 30% forest thinnings, branches, and so on and hardwood bark. Furnish was prepared by double-disk pressurized refiners. Brooks concluded a plant could be built to operate on 100% hardwood bark. 

So far this year, two reports have been published on the effect of bark in medium-density fiberboard. The first by Woodson (61) covered the bark of three southern hardwoods, sweetgum, southern red oak, and mockernut hickory percentage of bark in the whole-tree furnish was 13.4, 20.0, and 18.6%, respectively. Urea-melamine formaldehyde binder was added at 8-10%, and wax at 1%. Test results showed inclusion of bark decreased tensile and bending strengths by 16-18%, MOE by 10-14%, and IB by 8%. Linear expan sion was not affected significantly by bark. Thickness swelling was improved in two of the three species. Woodson concluded good quality, medium-density fiberboard could be made from barky chips. 

Wood Adhesives. Melamine-modified wood adhesives are used in various wood products such as plywood, particle board, medium-density fiberboard (MDF), truck and railcar flooring, furniture doors and wooden salad bowls and trays. 

Borax pentahydrate is an effective flame retardant for wood/cellulosic materials in terms of surface flammability. However, due to the Na20 moiety, it can promote smoldering combustion in cellulose. Thus, in cellulosic material and wood products, it is commonly used in combination with boric acid, which is an effective smoldering inhibitor. For example, the treatment of wood fibers with a partially dissolved boric acid and borax pentahydrate slurry (-1.75% by wt. of boron) results in Medium Density Fiberboard (MDF) that is claimed to pass the ASTM E-84 Class 1 surface flammability standard.12 The additional examples of using borax pentahydrate and boric acid combination are presented in Section 9.2.2.1. 

In the study of Hietaniemi et al. [76], the model reproduced well most of the experiments conducted on spruce, but the calculated HRR was sensitive to the back-face boundary condition in the SBI test and the observed decay in the HRR in the cavity experiment was not captured by the model. Modeled HRR for medium density fiberboard closely matched room/corner test data, whereas HRR in the SBI test was not reproduced as closely. The HRR of the PVC wall carpet was reproduced reasonably well in the SBI test, but was overpredicted in the room corner test, probably owing to the discrepancy between the back-face boundary condition in reality and in the model. For the upholstered chair, FDS underestimated the time to ignition and the peak HRR compared with experimental data for both the furniture calorimeter and ISO room cases. Finally, for the polyethylene-sheathed cables in the 6 m cavity, the modeled HRR matched the experimental data fairly closely. In general, the results of Hietaniemi et al. [76] are encouraging. 

Compressed Intermediate or medium density fiberboard (includes laminated paperboards and homogeneous boards) 0.40-0.80 25-50 Structural use and heat insulation as sheathing base for plaster and siding, interior paneling, containers, underflooring... 

More recently, vaporous FA treatment has been applied to the improvement of dimensional stability of medium-density fiberboard (MDF) (36). Among... 

Medium-density fiberboard (MDF) has been of much interest as the most promising reconstituted product. MDF can be utilized not only for interior materials and furniture but for construction materials. One of the inferior properties of MDF is the dimensional instability when exposed to humid condition. It is also quite often invaded by wood-degrading organisms. 

Table 18 Antiswelling Efficiency (ASE) of Formalized Medium-Density Fiberboards (MDF), and Their Weight Loss (WL) After 12 Weeks Decay Tests, After 9 Months Soil Burial Test, and After 9 Weeks Termite Test...

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