Medium-density fiberboard (MDF) is one of the most used and versatile wood composites. Most of its use has been focused on interior applications. Adhesives such as p-MDI (polymeric methyl diphenyl diisocyanate) provide MDF with a better performance against moisture, but resistance against decay is also required for outdoor use. A mix of wood fibers, p-MDI, and 0.75%-1.5% of ZB was made to produce MDF that could be qualified for this use. Samples of the material were tested following the AWPA (American Wood Protection Association) E-26: Standard field test for evaluating wood preservatives for interior applications (UC1 and UC2) to validate the formulation. The samples were tested for 60 months in the Michigan Tech Wood Protection Group test site at Maunawili, HI. After testing, the ZB samples performed better against termites than MDF with no ZB, Douglas-fir, and Southern pine. The results allowed passing the International Code Council (ICC) acceptance criteria for exterior composite trim with ZB preservative by a non-pressure process (AC424). This allowed for the approval and commercialization of MDF containing ZB (now Armorite®) for its use in outdoor applications.

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