40 and depth of lathe check tended slightly fluctuate from pith to bark. These results
were occurred in all wood species that were used in this study. In general, 3 mm sengon and jabon veneers from 5 years old boiled sengon
and jabon logs had better veneer quality lower lathe check frequency, better surface roughness however better wettability than unboiled logs. In most of
samples, frequency of lathe check and surface roughness were correlated negatively with equilibrium contact angle except for boiled jabon.
41
4 THE EFFECT OF LATHE CHECK AND JUVENILITY ON FAST GROWING SPECIES LVL GLUE BOND AND BENDING
STRENGTH
4.1 Introduction
With the emergence of a rapidly grown plantation timber resource throughout the world, a larger proportion of available timber will be found in the
form of juvenile wood. To be able to use juvenile wood, it is first required that a working knowledge of the juvenile wood component be gained. This knowledge
will then allow the manufacturing sector to modify existing procedures and techniques to more fully utilize this juvenile material for the production of high
performance LVL.
Sengon Falcataria molluccana and Jabon Anthocephalus cadamba as fast growing wood species widely planted Indonesia, have short cutting cycle 5 to
7 years. Based on this research see Chapter 2, they contained 100 of juvenile wood by the age 7 years old. The boiling treatment prior to peeling could
decrease lathe check frequency of 3 mm veneer, decrease Ra values the veneer surface become smoother, however their wettability was higher compared to
unboiled veneers see Chaper 3.
Poplar Populus spp and douglas-fir Pseudotsuga menziesii, contained 52 and 77 of juvenile wood portion see Chapter 2. Poplar logs did not need
any treatment prior to peeling. Juvenile veneers were higher than mature veneers, in terms of lathe check frequency and surface roughness. However in terms of
contact angle, the juvenile veneers were lower than that of mature veneers see Chapter 3. Douglas-fir is easily machined and dried and also its peeling and
gluing properties are good CIRAD 2011. It is known as one of the wood species widely utilize as laminated veneer lumber. Since they are being used in the
laminated veneer lumber industry, their bonding quality became important to be analyzed
The quality of veneer, such as moisture content, density, lathe checks, and surface roughness would influence the bonding strength of the veneers Dundar et
al. 2008. Among these factors, lathe check is one of the important factors on the
bonding strength. The bonding strength decreases, probably because of the presence of important lathe checks. Also, the veneers with lathe checks require
much more glue spread because of the degradation of veneer surface topography Daoui et al. 2011. Veneers with lathe checks can also cause excessive resin use
and may result in resin-bleed through the inside of veneer.
Some researchers have published physical and mechanical properties of LVL manufactured from softwood as well as hardwood of different species
Ranta-Maunus 1995, Shukla and Kamdem 2007. The reported values for LVL are normally higher than those obtained for other traditional wooden products,
which may be explained by the fact that large defects can be avoided when logs are cut into thin veneers and these are laid and glued parallel to the grain Ranta-
Maunus 1995. In addition to its very good mechanical behavior, LVL exhibits other advantages common to all wooden materials such as those related to
environmental aspects Shukla and Kamdem 2007. Using fast growing wood species for LVL production can help to solve the problems linked to the shrinkage
42 of raw materials for construction and to the protection of natural forests. The
impact of juvenile wood on LVL using southern yellow pine and Douglas-fir was discussed in depth in a study by Kretschmann et al. 1993. This study found that
juvenile wood could reduce the structural integrity of an LVL product when significant quantities of juvenile wood were used. Douglas-fir LVL seemed to be
more influenced by the inclusion of juvenile wood compared to the southern yellow pine. Finally, it was also found that the inclusion of juvenile wood did not
significantly influence the amount of warp found in the LVL studs. Kretschmann et al
. 1993 also showed that the ratio between Douglas fir LVL from juvenile and mature veneers is 0.8 for strength and stiffness. Langum et al. 2009
reported that flexural stiffness and strength in solid Douglas-fir increase with increasing distance from pith to bark. Therefore the juvenility effect on LVL
bending strength was important to be analyzed.
Wang et al. 2003 indicated that veneer peeled from low value red maple logs may be used to manufacture high quality LVL products. This could be done
with the incorporation of low density wood species as core layer and high density wood species as surface layer, where a superior end product can be produced
without compromising the strength and quality of high commercial value wood species. Low strength and stiffness values of juvenile wood are well known in
wood science. LVL was produced as a possible means to reduce the overall structural problems inherent in poorer quality timber Koch 1966. This potential
reduction is made possible by laminating veneers of high stiffness in the outer layers, due to the transformed section modulus, lower stiffness veneers may be
used in the central core of the LVL product. Since the core does not require the same stiffness as the outer layers Bodig and Jayne 1993. Harding and Orange
1998 stated that on radiata pine, the lay-up pattern of the loose side with tight side produces a LVL with a significantly lower stiffness than for a pattern that
matches the loose side with the loose side. By strategically placing selected veneer sheets within the composite, it is possible to manufacture a wood-base
product that has well-controlled physical and mechanical properties Wang et al. 2003. Daoui et al. 2001 recommend carefully selecting the veneers to be used
in composing LVL. The effect of different layout on glue bond and bending propertied in sengon and jabon LVL was analyzed in this study.
LVL presents the inconvenience of using a large amount of adhesive during its manufacturing, which can be up to 20 of its total mass Daoui et al. 2011.
According to De Melo and Del Menezzi 2014, the adhesive is a component with significant technical and economic implications with regard to the utilization of
wood products and its cost can be half the product price. Echols and Currier 1973 found better results on bending strength of solid wood than on 5-ply, and
better results on 5-ply than on 7-ply Douglas-fir LVL. Therefore, increasing veneer thickness on poplar and douglas-fir LVL can enable a decrease in adhesive
use for these panels.
MOE LVL could be measured by dynamic and static modulus of elasticity. Dynamic analysis is a simple and efficient way of characterizing the BING
Module of Elasticity MOE of many materials, including wood Brancheriau and Bailleres 2002; Bucur 2006. Using various species of wood, sample dimensions
and growth conditions, several studies have shown a strong linear correlation between the dynamic and static modulus of elasticity Biblis et al. 2004; El-
