Effect of two relative humidity environments on the performance properties of MDF, OSB and chipboard

The static strength, stiffness and fatigue life of MDF, OSB and chipboard have been measured in a 65%RH environment and a 85%RH environment. Chipboard is commonly utilised as a flooring material and OSB is also used in structural applications, for example floor decking and webs of I-beams. The mean static strengths of MDF, OSB and chipboard at 65%RH were 47.9 MPa, 27.9 MPa and 21.0Mpa, respectively, compared with 34.59 MPa, 21.70 MPa and 10.61 MPa at 85%RH. However, MDF has mostly been used in non-structural applications, such as furniture, so its resistance to fatigue loads as a structural panel is of considerable interest. In a 65%RH environment dynamic modulus values showed that whilst MDF and chipboard exhibit similar stiffness values (4 GPa), OSB is approximately 50% stiffer. However, at 85%RH MDF was the stiffest of the three materials, followed by OSB and chipboard. The fatigue life performance of all three panel products was markedly lower at 85%RH compared with 65%RH. Overall, the high RH environment had a noticeably detrimental effect on the MOE (modulus of elasticity), MOR (modulus of rupture) and fatigue lives of OSB and chipboard. This is attributed to these panels retaining more of the original characteristics of the original wood, i.e. larger particle sizes (flakes/chips) compared with the homogeneous fibrous composition of MDF.