A simplified model on vertical density profile and shrinkage ratio of virgin and charred medium density fibreboard

摘要

This work is part of a wider scope of research on developing comprehensive pyrolysis model for medium density fibreboard (MDF) in fires. A simplified model is developed to predict the vertical density profile of virgin MDF. The model shows that vertical density profile can be reproduced using a second order conic curve. Several sets of experimental data are used to validate the model with promising results that are presented. Further investigation shows that the density difference between surface and core densities tends to maintain constant within a range of 300 to 450kg/m~3. Moreover, the model can predict the mean density with an error less than 30 kg/m~3. Typical MDF panels were experimentally charred using thermogravimetric analysis and cone calorimetry to investigate the shrinkage and density of char. The actual char density is measured as 330 kg/m~3 with a uniform density distribution along the char layer thickness. A model is developed to predict the shrinkage ratios. The restraining effect caused by surface deformation will lead to different vertical and horizontal shrinkage ratios. The volume reductions at vertical and horizontal directions are experimentally measured as 40% and 20% for the two tested MDF panels, which is comparable with the model predictions.