Selected properties of MDF and flakeboard overlaid with fiberglass mats

Abstract Nonwoven fiberglass face laminates have long been ap­plied to consolidated wood-basedcomposites to improve their performance and serviceability. In this study, fiberglass mats with 50 percent resin binder were applied as face laminates to unconsolidated wood fiber or flake mats, then hot-pressed to make overlaid medium density fiberboard and flakeboard. Fi­berglass reinforcementimprovedmechanical, surfacequality. and water-resistance properties. Such improvement could make fiberglass reinforcement during composite processing very attractive for enhancing the properties and durability of mat-formed engineered wood composites. This approach also might contribute to the future development of exterior wood composite products. T o promote the sustainability of wood as a natural re­source and to improve the structural efficiency of engineered wood composites, fiberglass has long been used to reinforce pre-formed wood composites. Research efforts to reinforce wood products with synthetic fibers started in the early 1960s. with investigations that focused on the flexural bending prop­erties of wood-fiberglass composite beams (Wangaard 1964, Biblis 1965). Since then, many researchers have taken advan­tage of the high strength of fiberglass to increase the strength and stiffness of wood-based composites; that is, laminated structural beam/lumber (Wangaard 1964; Biblis 1965; Row-lands et al. 1986; Tingley 1988, 1996), plywood (Biblis and Carino 2000), structural particleboard (Saucier and Holman 1975). hardboard (Steinmetz 1974, Smulski and Ifju 1987), and wood fasteners (Soltis et al. 1998). Most of these studies focused on the structural analysis of the behavior of rein­forced composites and the mechanical improvement provided by laminating fiberglass to wood products after production. Polyester woven fiberglass laminates were reported to have an average tensile modulus of rupture (MOR) of about 275.0 MPa and a modulus of elasticity (MOE) of 17.2 to 20.1 GPa (Biblis and Carino 2000). The incorporation of a relatively small volume of fiberglass was found to increase the bending MOE and MOR of reinforced wood composites significantly. Fiberglass reinforcement levels of 3.5 to 7.0 percent by vol­ume increased in-design bending strength from 10 to 20 per­cent (Spaun 1981). An economic feasibility study was performed for a manu­facturing process that used synthetic E-glass fiber, Douglas-fir veneer, and phenol-formaldehyde (PF) resin to produce re­inforced laminated veneer lumber (Laufenberg et al. 1984). The result of cash flow and secondary analyses using product prices and grades indicated the profitability of manufacturing high-yield structural components using fiberglass reinforced parallel laminated lumber. Although the improved structural performance of fiberglass-reinforced wood composites was impressive, few of these composites were marketed success­fully as a result of reluctance on the part prospective users of the product to switch and high price for perceived structural benefits of the strength reinforcement (Biblis and Carino 2000). In 2002, the consumption of medium density fiberboard (MDF) in the United States was 2.7 million cubic meters. an increase of about 14.6 percent from the previous year (How­ard 2004). Compared with other nonstructural panel products, MDF is expected to offer particularly strong growth in the near future because of its wide range of application in interior uses, such as furniture and cabinets. The use of MDF has been extended to other manufacturing industries as well. MDF shows superior surface quality. moulding and edge perfor­mance, and screw withdrawal retention. Because of its low formaldehyde emission and high dimensional stability. MDF is being developed using PF or diphenylmethane diisocyanate (MDI) resin binders. Increasingly, MDF is being used in building construction, but not as yet as a critical structural material. Improvements in strength and durability, however, may render MDF suitable as an exterior structural material. Structural flakehoard. such as sheathing and flooring, is the dominant material in the residential construction market. In 2004, the annual consumption of oriented strandboard (OSB) was about 20 million cubic meters in the United States (How­ard 2004). The annual production and consumption of OSB are expected to increase. Although existing wood composites exhibit many desirable characteristics as a renewable engineering material, their lack