Bending creep behavior of medium density fiberboard and particleboard during cyclic moisture changes

Bending creep behavior of four types of medium density fiberboard (MDF) and two types of particleboard during cyclic moisture changes was investigated in this study. Tests were made at 20 degreesC with three cyclic relative h umidity changes between 65% and 95% under the 10% short-term breaking stres s. The effect of moisture content (MC) change on initial compliance and mec hano-sorptive (MS) compliance was examined. The results indicated that rela tive deflection and total compliance of the samples increased over the hist ory of cyclic moisture changes, and their magnitudes varied with board type s. Melamine- and phenol-resin bonded boards had smaller relative deflection and total compliance than did urea-resin bonded boards. Both relative defl ection and total compliance increased in adsorption and showed reduction in desorption. Initial compliance followed a linear relation with MC and had some influence on total compliance behavior under moisture cycles. NIS comp liance increased in adsorption while showing slight reduction or increase i n desorption. The first adsorption led to the largest NIS compliance, follo wed by subsequent adsorption. With increasing MC change, MS compliance incr eased linearly in the first adsorption, while it increased nonlinearly in t he subsequent adsorption. The MS compliance coefficient K-M was product-dep endent. Resin type appeared to be an important factor influencing the varia tions in K-M. In this study, urea-resin bonded boards had a greater K-M com pared to melamine- and phenol-resin bonded boards.