Page 381 - Biosystems Engineering

358 Cha pte r T w e l v e

in the presence of sucrose. Increased stem growth was accomplished
by a decrease in Young’s elastic modulus in the growth zone but an
increased elasticity in mature tissue (Park et al. 2004). Increased (9 to
15 percent) cellulose content and alteration of hemicellulose composi-
tion was observed in antisense 4CL transgenic poplars as the result of
a drastic reduction (45 percent) of lignin content (Hu et al. 1999). This
research also showed an increased growth rate.
Research on genetic variations and control of hemicellulose content
are quite rare. Analyses of trees from a 6-year-old Eucalyptus species/
provenance trial in South Africa showed that variation in pentosan,
cellulose, and lignin contents among species was statistically significant,
as was that in pentosan and cellulose contents among provenances
within species (Clarke and Wessels 1995).

12.3.4 Durability
Lumber from most wood species usually lacks natural durability, and
this is of great concern for the building industry. Pine-dimensional
lumber is frequently treated with various chemicals for durability,
including copper–chrome–arsenate (CCA) pressure treatment for
outdoor and foundation application. Although this method is very
efficient, CCA is becoming less acceptable, even banned in some
applications, due to environmental concerns. Alternatives could be
found as genes that provide durability in other tree species may be
used for genetic engineering for higher durability.
The extraction of nonstructural hemicellulose sugars from wood
strands, prior to the production of oriented strandboard (OSB) is
expected to have a great impact on the stiffness and durability of
OSB. Hemicelluloses sugars are valuable resources for making other
by-products such as ethanol and polymers. Our recent study was to
extract hemicelluloses from southern yellow pine strands and using
the preextracted strands to produce enhanced OSB (Hosseinaei et
3
al. 2008). A total of 14 OSB panels with a 42-lb/ft target density were
made by the same hot-press parameters (200°C and 4 min). Four per-
cent of phenol–formaldehyde resin and 1 percent wax were used.
The results from this study indicated that weight loss of wood
strands and recovered sugars can be easily controlled by extraction
conditions, and all hemicelluloses can be removed from a strand
without damaging the strands. OSB panels made from extracted
strands have much better dimension stability and bending proper-
ties as compared to control panels. Water absorption and thickness
swelling of panels could be reduced to 51.8 and 37.8 percent,
respectively. All panels met the internal bonding requirements of
Canadian Standard Association standard. The mold susceptibility
of the panels made from preextracted strands was significantly
reduced as compared to control panels (Taylor et al. 2008). This sug-
gests that reduction and/or alteration of hemicelluloses through