CHARACTERIZATION OF HEAT AND MASS TRANSFER IN THE MAT DURING THE HOT PRESSING OF MDF PANELS

The two objectives of this project were to determine gas permeability of the mat as a function of density, and to characterize panel properties and temperature and gas pressure evolution in the mat during hot pressing as a function of press closing strategy, panel density, and mat moisture content. Panels of 560 X 460 X 16 mm were made in a 600- X 600-mm laboratory press. The manufacturing parameters were the following: press closing strategy of 145, 155, and 165% of the target panel thickness after 30 s of pressing; initial mat moisture content of 10, 12, and 14%; and panel density of 650, 725, and 800 kg m -3 . Temperature and gas pressure were measured at the surface and core of the mat. The gas permeability of the panel was measured for panels of uniform densities of 400, 650, 900, and 1150 kg m -3 . Gas permeability decreased by a factor of 1000 when panel density increased from 400 to 1150 kg m -3 . The flexural properties increased with an increase in mat moisture content and panel density, and a decrease in press closing strategy. The internal bond increased with an increase in mat moisture content and panel density. Thickness swell decreased with an increase of panel density, and increased with an increase in press closing strategy. The time required to reach 100°C in the mat core decreased with a decrease in press closing strategy. The maximum gas pressure in the mat core was proportional to panel density. It also increased with mat moisture content for a press closing strategy of 165% and a panel density of 800 kg m -3 .

[1]  A. J. Bolton,et al.  The Permeability of Wood-Based Composite Materials. Part 1. A Review of the Literature and some Unpublished Work , 1994 .

[2]  M. Wolcott,et al.  Fundamentals of flakeboard manufacture: viscoelastic behavior of the wood component. , 1990 .

[3]  P. Winistorfer,et al.  Fundamentals of Vertical Density Profile Formation in Wood Composites. Part III. MDF Density Formation During Hot-Pressing , 2004 .

[4]  Wang Siqun,et al.  Fundamentals of vertical density profile formation in wood composites. Part II. Methodology of vertical density formation under dynamic conditions. , 2000 .

[5]  R. Geimer.  Dimensional stability of flakeboards as affected by board specific gravity and flake alinement , 1982 .

[6]  F. Kamke,et al.  Effects of wood-based panel characteristics on thermal conductivty , 1989 .

[7]  D. Smith.  Waferboard press closing strategies , 1982 .

[8]  A. J. Bolton,et al.  The Hot Pressing of Dry-formed Wood-based Composites - Part VI. The Importance of Stresses in the Pressed Mattress and their Relevance to the Minimisation of Pressing Time, and the Variability of Board Properties , 1989 .

[9]  C. Hse.  Properties of flakeboards from hardwoods growing on southern pine sites , 1975 .

[10]  Frederick A. Kamke,et al.  Characteristics of Phenol-Formaldehyde Adhesive Bonds in Steam Injection Pressed Flakeboard , 2007 .

[11]  John F. Siau,et al.  Wood--influence of moisture on physical properties , 1995 .

[12]  B. L. Bledsoe,et al.  Fundamentals of vertical density profile formation in wood composites. Part I. In-situ density measurement of the consolidation process. , 2000 .

[13]  Frederick A. Kamke,et al.  Fundamentals of flakeboard manufacture: internal-mat conditions. , 1988 .

[14]  S. Y. Zhang,et al.  Longitudinal and transverse permeability of balsam fir wetwood and normal heartwood. , 2000 .

[15]  P. Steiner,et al.  Compression behavior of randomly formed wood flake mats , 2007 .

[16]  Francis G. Wagner,et al.  A Model to Predict the Density Profile of Particleboard , 2007 .

[17]  J. Wilson,et al.  Parameters affecting dimensional stability of flakeboard and particleboard. , 1980 .

[18]  R. Geimer,et al.  Flakeboard Thickness Swelling. Part II. Fundamental Response of Board Properties to Steam Injection Pressing , 2007 .

[19]  P. E. Humphrey.  The Hot Pressing of Dry-formed Wood-based Composites. Part II. A Simulation Model for Heat and Moisture Transfer, and Typical Results , 1989 .

[20]  A. J. Bolton,et al.  The Hot Pressing of Dry-formed Wood-based Composites. Part III. Predicted Vapour Pressure and Temperature Variation with Time, Compared with Experimental Data for Laboratory Boards , 1989 .

[21]  A. J. Bolton,et al.  The Hot Pressing of Dry-formed Wood-based Composites - Part V. The Effect of Board Size: Comparability of Laboratory and Industrial Pressing , 1989 .

[22]  Wei Xu,et al.  Modulus of elasticity of wood composite panels with a uniform vertical density profile : A model , 2007 .

[23]  B. Riedl,et al.  Hot-pressing process optimization by response surface methodology. , 1999 .

[24]  F. Kamke,et al.  Gas pressure and temperature in the mat during flakeboard manufacture , 1988 .