Drainage of high-consistency fiber-laden foams

Lightweight lignocellulosic fibrous mate-
rials (LLFMs) offer a sustainable and biodegradable
alternative in many applications. Enthusiastic interest
in these materials has recently grown together with the
newly risen interest in foam forming. Foam bubbles
restrain fiber flocculation, and foam formed structures
have high uniformity. Moreover, the bubbles support
the fibrous structure during manufacturing enabling
the formation of highly porous structures. Mechanical
pressure cannot be applied in the manufacture of
LLFMs as the materials would lose their porous
structure. Water is therefore typically removed by a
combination of drainage and thermal drying. Thermal
drying of porous materials has been studied inten-
sively. However, there are only a few studies on the
drainage of fiber-laden foams. Thus, in this work, we
conducted a systematic analysis of this topic. Our
findings show that after drainage a stationary vertical
moisture profile similar to that of pure foams is
developed. Raising the initial fiber consistency was
found to increase the final fiber consistency of the
foam until the drainage ceased. Increasing mold height
was found to increase the final consistency consider-
ably. Without vacuum and heating, the shrinkage of
samples during drainage was only slightly higher than the volume of the drained water. Drainage rate and
final consistency increased clearly with increasing
vacuum, but simultaneously sample shrinkage
increased considerably. The best compromise was
obtained with a vacuum of 0.5 kPa, which increased
the final consistency by 60% without extra shrinkage.
Using warm foam and heating the foam during
drainage increased the final consistency considerably,
but this also led to significant shrinkage of the sample.