Study on dimensional stability of fiberboard and its products in hygrothermal environments

In this paper, a dynamic vapor sorption analyzer in conjunction with the Dino-Lite Edge Digital Microscope was utilized to study the moisture sorption and thickness variation characteristics of the surface and core layers of impregnated paper coated fiberboards (IPCF) and its substrate high density fiberboards (HDF) at different temperatures. Results showed that the equilibrium moisture content (EMC) of both the surface and core layers of IPCF was reduced by the impregnated paper coating, and their dimensional stability as well as dimensional recovery performance after swelling was enhanced. A different phenomenon from previous studies was observed, the EMC of both the surface and core layers of IPCF and HDF increased with the increase of temperature. It can be affirmed that this phenomenon is not related to capillary condensation water. In addition, both the surface and core layers of IPCF and HDF exhibited moisture sorption hysteresis and swelling hysteresis during the moisture sorption cycle, both of which showed opposite responses to temperature. The sorption hysteresis and swelling hysteresis were affected by the degree of melamine-urea–formaldehyde (MUF) resin crosslinking and porosity, respectively. The higher the crosslinking degrees of the MUF resin in fiberboard, the greater the absolute hysteresis; swelling hysteresis is negatively correlated with porosity.