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Medium-density fiberboard (MDF) appears uniform at first glance; however, the heat-pressing process creates layers of varying densities.
Medium-density fiberboard has good mechanical properties, a very smooth surface, excellent processing characteristics, and is a homogeneous board.
These excellent properties are due in part to the fibers that MDF is made of. An equally important factor behind MDF's impressive performance is the way those fibers are compressed into the board.
The wood raw material for medium-density fiberboard (MDF) ranges in size from cell fragments to fiber bundles, some of which are large, wood-like in size and are called chips; but even these are still much smaller than the particles used to make particleboard. The homogeneity of the layup is evident in Figure 1, which shows a medium-density fiberboard (MDF) mat after pre-pressing and trimming, but before hot pressing.
Wood fibers have an aspect ratio of approximately 100-in other words, they are 100 times longer than they are thick. This factor, combined with the very even distribution of the adhesive, partly explains why medium-density fiberboard (MDF) is stronger than particleboard.
The surface density of a typical medium-density fiberboard is about 1,000 kg/m3 (62.4 lb/ft3), which accounts for 1 to 2 mm of the board thickness. The density of the rest of the board is much lower, around 600 to 700 kg/m3.
This density distribution relative to weight imparts good bending properties, as surface stress is highest during bending. High surface density equates to good deformation resistance and high strength. Because the surface is dense, it is also scratch-resistant and has low permeability to liquids, significantly reducing surface treatment costs when painting and staining.
The advent of continuous presses has enabled manufacturers to fine-tune their density curves to meet specific customer requirements, thereby maintaining the reputation of medium-density fiberboard (MDF).