65 the veneer thickness on the stiffness or strength is positive. This result was in line
with Echols and Currier 1973. The use of thick veneers appears to be not penalizing to LVL bending strength for this species in the range of parameters in
use. Consequently, the idea of using thicker veneers to reduce the adhesive consumption without altering their mechanical properties has promising prospect.
4.8 The correlation between MFA and fiber length of fast growing wood
species and bending properties
The results in Chapter 2 stated that MFA values tended to decrease from pith to bark. MFA values of sengon near pith and near bark were 71° and 29°,
respectively. While MFA values of jabon were 72° near pith and 28° near bark. MFA values of douglas-fir juvenile and mature wood were 45° and 28°,
respectively. While MFA values of ‘soligo’ poplar cultivars were 59° near pith
and 15° near bark. The decrease of MFA value would lead to the increase of static MOE. The percentage gain of static MOE LVL between juvenile near pith
to mature wood near bark for sengon, jabon, ‘soligo’ and douglas-fir were 12, 36, 13 and 14, respectively. According to Kretschmann 1997, wood
composites properties of loblolly pine depend for a part on MFA of wood fiberparticles in used. In general, small MFA values ensure high mechanical
properties. The longitudinal stiffness of cell wall is determined by MFA. The properties of cell wall material specifically MFA and the amount of cell wall
density both affect the mechanical properties of wood MOE longitudinal. Hence, both MFA and density can be related to wood stiffness, either theoretically
or experimentally Xu et al. 2004.
Moreover, because of its fiber characteristics, juvenile wood has significantly lower strength and stiffness, more longitudinal shrinkage, and less
radial and tangential shrinkage than mature wood Pearson and Gilmore 1971; Bendtsen 1978; Bendtsen and Senft 1986. Results on Chapter 2 regarding fiber
length of sengon near pith and near bark were 770 and 1336 µm, respectively. While jabon fiber lengths were 753 µm near pith and 1642 µm near bark. The
fiber lengths of ‘soligo’ were 1058 µm near pith and 1348 µm near bark. Douglas-fir fiber lengths for juvenile and mature wood were 1200 and 3359 µm,
respectively. The increase of fiber length was followed by the increase of MOR LVL made of juvenile veneers to mature veneers. The percentage gain MOR
LVL between juvenile near pith to mature wood near bark for sengon, jabon,
‘soligo’ and douglas-fir were 10, 27, 22 and 10, respectively. This trend was also observed by Kiaei et al. 2013 who found that there was a relationship
between MOR of Pinus eldarica solid wood and tracheid length R
2
=0.47
4.9 Conclusion
The glue bond strength, MOE and MOR of sengon and jabon LVL increased from pith to bark. The advantage of using veneers from poplar mature wood was
proved with an improvement of 15 to 20 on average for mechanical properties, with almost the same panel weight. Douglas-fir LVL made of mature veneers had
higher bending strength compare to LVL made of juvenile veneers. Utilization of
66 mature veneers in producing douglas-fir LVL appears to improve bending strength
from 7 to 22. Boiling treatment prior to peeling in 75°C water for 4h and application of
type II layout have successfully increase glue bond and bending strength of sengon and jabon LVL. The glue bond strength, MOE and MOR of sengon and
jabon LVL were decreased as the frequency of lathe check increased. The increase of glue bond increased sengon and jabon LVL bending strength.
The use of thicker veneers in poplar and douglas-fir LVL, reduced the use of adhesive, and simplified and accelerated the production of panels without altering
their mechanical properties. The sample position did not give significant effect on static MOE, SMOE and density of poplar LVL. The dynamic MOE, MOR and
SMOR of poplar LVL for flatwise were always a little higher. LVL made of 3mm veneers of douglas-fir has lower bending strength compared to LVL made of
5.25mm veneers. The sample position did not give significant effect on all parameters measured of douglas-fir LVL
Some cultivars have a real potential for structural applications ‘Lambro’,
‘Soligo’, ‘Alcinde’, ‘Brenta’ and ‘Taro’, some should be used with careful sample selection ‘Lena’, ‘Trichobel’, ‘Mella’, ‘Koster’ and ‘Dvina’, while
‘Polargo’, ‘A4A’, ‘I-214’ and ‘Triplo’ should be excluded. The resonance technique is a reliable tool for estimating LVL MOE and
avoiding destructive test. It is particularly useful for poplar and douglas-fir.
