effects of adhesive and paraffin content on gas permeability of medium density fiberboard

in this study, medium density fiberboard (mdf), was produced by dry process using refined fibers from choob khazare caspian amol factory, with 3 levels of urea formaldehyde adhesive at 8, 10, and 12 percent, and 3 levels of paraffin at 0.5, 1, and 1.5 percent. from every treatment, cylindrical samples for permeability measurement with 13 mm in diameter, and 30 mm of height were cut using hole-saw. gas permeability of the boards was measured in two directions, parallel and perpendicular to the boards, as well as in central and marginal sections of the boards. results indicated that increase in adhesive content decreased gas permeability. in addition increase in paraffin content decreased gas permeability. gas permeability perpendicular to the boards showed greatest values. the highest value of gas permeability was measured to be 6.26 10-13 m3.m-1 with the lowest adhesive and the lowest paraffin content. the lowest value of gas permeability though was measured in the direction prependicular to the boards (0.38×10-13 m3.m-1) with the highest adhesive and paraffin contents. it can therefore be concluded that both adhesive and paraffin contents may decrease gas permeability. this would modify the previously belief that used to consider paraffin as a water proof agent in mdf composite and clarifies that water absorption and thickness swelling decrease may also be related to the lower permeability values.