28 Frequency of lathe check was presented as the number of lathe check per cm
length of veneer.
Figure 12 Veneer thickness 1, depth of lathe check 2 and length of lathe check 3 of poplar veneers’ loose side
3.3.2.3 Surface roughness measurement
A portable surface roughness tester TR200 was used for roughness evaluation of the samples. A total of 10 roughness measurements were conducted
according to JIS standard 2001 by using the roughness tester. Measurements were performed on each surface roughness test specimen across the grain orientation of
the veneer. Tracing speed, diamond tip radius, and tip angle were 0.5 mms
-1
, 5 μm and 90
o
, respectively. The length of tracing line was 15 mm and cut-off was 2.5 mm. The measuring force of the scanning arm on the surfaces was 4mN 0.4 g,
which did not put any significant damage on the surface. Measurements were repeated whenever the stylus tip fell into the pores. The calibration of the
instruments was checked in every 100 measurements by using a standard
reference plate with Ra values of 7 μm. Average roughness Ra values were recorded to evaluate surface roughness.
Figure 13 Contact angle of water a and PVAc as adhesive b on jabon veneers’
loose side 3.3.2.4 Measurements of contact angle
Water and PVAc were dropped by using pipette on loose side of veneer Figure 13. Video images were taken starting from initial drop up to 180 seconds
wetting. Then pictures were consecutively collected at every 10 seconds from the video images. Those single pictures were analyzed by motic image software to
measure their contact angles. Then, equilibrium contact angle was determined by segmented regression analysis using PROC NLIN on SAS software.
a b
1 3
2
29
3.3.3 Data Analysis
In this study, we analyzed the correlation between dependent variable equilibrium contact angle and independent variables frequency of lathe check
and Ra values by using multiple linear regressions. The model was as follow Y = α + β
1
X
1
+ β
2
X
2
where, Y
= equilibrium contact angle value α
= constant β
1
, β
2
= regressions coefficient X
1
= frequency of lathe check X
2
= Ra values Analysis of varianceANOVA of multiple linear regression were calculated
by minitab16 in order to obtain the effect of frequency of lathe check and surface roughness to equilibrium contact angle at 95 confidence level p0.05.
3.4 Results and Discussion
3.4.1 Variation of veneer thickness
Uniformity of veneer thickness is a very important factor affecting the quality of glue bond strength in LVL or plywood. The results presented in Figure
14a-c show that a slight thickness variations of rotary cut sengon, jabon and
poplar cultivars veneers are observed.
Figure 14 Variation of veneer thickness from pith to bark of sengon a, jabon b and poplar cultivars c
2.5 3
3.5
2 4
6 8
T hick
ness o
f ven
ee r
m m
Segmented rings from pith to bark Unboiled sengon
Boiled sengon a
2.5 3
3.5
1 2
3 4
5 6
7 8
T hick
ness o
f ven
ee r
m m
Segmented rings from pith to bark Unboiled jabon
Boiled jabon b
2.5 3
3.5
5 10
15 20
25 30
T hick
ness o
f ven
ee r
m m
Segmented rings from pith to bark Lambro
Soligo Taro
c
