| Summary: | The localized properties of conventional pressed flakeboards were studied using simulated
approaches. There parallel experiments were performed in this study. Firstly,
Columns of trembling aspen flakes were assembled and pressed in wood particle mat in
order to simulate localized variations in a flakeboard. The flake columns were constructed
from 24, 32, 40 microtomed flakes. Powdered phenol formaldehyde resin was applied to
all flakes at the loading level of 1%. The flake assemblies were assessed in term of
bonding properties and dimensional stability. The thickness swell test were performed
using an image analysis system Three variables were studied (1) pressing condition; (2)
number of flakes in a flake assembly (density levels); (3) vertical layers in each flake
assembly. Secondly, the compression process of the flake columns were also monitored
the deformation process of the flake columns were also monitored using stress and strain
relationships using a computerized cold press. The deformed wood structures were
observed using a scanning electron microscope. The dimensional properties of flakes
compressed at different compaction ratios were also tested. Thirdly, the flow properties
of the powdered phenol formaldehyde resin was studied using a thermal mechanical
analyzer (TMA). A range of pressing forces and heating rates were applied to simulate
internal environmental conditions in flakeboard.
The results show that density of flake assemblies influences heat transfer, and also
positively affects bonding strength at the intermediate and core layers and thickness swell
values the face, intermediate and core layers. Outer layers generally have greater bonding
strength and thickness swell values than inner layers did. Moisture content affects bonding
strength and thickness for higher density flake assemblies at the face and intermediate
layers. This results from compression tested show that, at a higher CR, the thickness
swelling was mainly contributed to the balloon back of the cell lumens when compressed
wood was soaked in water condition. The results from (TMA) studies show that pressure and heating rate affect adhesive flow and greater adhesive flow occurred at the more rapid
heating rates.
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