Page 84 - Kutnar, Andreja, et al., eds., 2015. Proceedings of the 1st COST Action FP1307 International Conference - Life Cycle Assessment, EPDs, and modified wood. University of Primorska Press, Koper.

ditions
–
samples
have
a
gluebond
strength
higher
than
1
MPa
or
wood
failure
percentage
was

high
enough
per
EN
314-­‐2
(Fig.
2).
Gluebond
strength
decreased
as
treatment
temperature
and

percentage
of
treated
veneers
in
plywood
composition
increased.
Control
samples
composed
of

untreated
veneers
(5U)
showed
the
highest
average
gluebond
strength
with
a
value
of
1.603
MPa.

The
plywood
(5T)
composed
only
of
veneers
treated
at
215
°C
had
the
lowest
gluebond
strength

with
a
value
of
0.837
MPa.

Figure
2:

Average
gluebond
shear
strength
of
plywoods
after
immersion
in
water
for
24
h
at
20
°C

After
immersion
in
water
for
24
h
at
20
°C,
wood
failure
of
samples
was
between
39.36
%
and

82.14
%
with
average
of
62.37
%.
Increasing
the
pretreatment
temperature
of
samples
for
use
in

outdoor
conditions
and
high
humidity
lead
to
a
decrease
of
gluebond
strength.
This
gluebond

strength
drop,
apart
from
decreasing
of
mechanical
properties
of
wood,
was
probably
caused
by

weakening
of
glue-­‐wood
relation.
The
decrease
of
average
wood
failure
percentage
from
62.37
%

(EN
636-­‐1:
dry
conditions)
to
16.56
%
(EN
636-­‐2:
high
humidity
conditions)
and
13.31
%
(EN
636-­‐3:

outdoor
conditions)
supports
this
statement.
These
results
are
in
agreement
with
Fioravanti
et
al.

(2013)
who
reported
that
gluebond
strength
of
MUF
adhesive
decreased
64
%
in
plywood
for
high

humidity
conditions,
as
compared
to
plywood
for
dry
conditions.

Increased
gluebond
strength
may
be
achieved
by
better
adhesive
penetration
into
the
wood

before
glue
setting
by
using
lower
pressing
temperature
and
longer
pressing
time.
In
addition
to

better
plywood
dimensional
stability
and
more
attractive
appearance,
such
plywood
would
be
of

higher
quality.

References

Fioravanti
M.,
Goli
G.,
Negro
F.,
Cremonini
C.,
Zanuttini
R.

2013.
Effect
of
heat
treatment
on
mechanical

properties
and
bonding
quality
of
poplar
plywood
glued
with
MUF
resin.
13th
internacional
scientific

conference
on
hardwood
processing,
Florence,
Italy:
227-­‐231

Lovrić
A.,
Zdravković
V.,
Furtula
M.
2014.
Influence
of
thermal
modification
on
colour
of
poplar
(Populus
x

euramericana)
rotary
cut
veneer.
Wood
research
59,
4:
661-­‐670

Zdravković
V.,
Lovrić
A.,
Stanković
B.
2013.
Dimensional
stability
of
pluwood
panels
made
from
thermally

modified
poplar
veneers
in
conditions
of
variable
air
humidity.
Drvna
industrija,
64,
3:
175-­‐181

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