Page 81 - 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.
P. 81
act
of
thermal
treatment
on
moisture-‐dependent
elasto-‐plastic
behaviour
of
beech
Straže
A.1,
Fajdiga
G.1,
Pervan
S.2,
Gorišek
Ž.1
1
University
of
Ljubljana,
Biotechnical
Faculty,
Jamnikarjeva
101,
SI-‐1000
Ljubljana,
Slovenia;
ales.straze@bf.uni-‐lj.si
2
University
of
Zagreb,
Faculty
of
forestry,
Svetošimunska
25,
HR-‐10000
Zagreb,
Croatia
Keywords:
thermo-‐modified
wood,
elasto-‐plasticity,
compression
test,
moisture
content
Strength
and
stiffness
alteration
are
important
properties
of
thermally
treated
wood,
and
vary
with
anatomical
direction
of
wood,
testing
method,
and
wood
species.
Since
wood
density
is
commonly
decreased
after
thermal
treatment
(Poncsak
et
al.
2006),
one
might
expect
a
similar
trend
with
material
strength
and
stiffness.
However,
the
reduction
of
hydrogen
bonding
and
a
decrease
in
free
accessible
hydroxyl
groups
are
often
present
in
thermally
treated
wood
(Boonstra
and
Tjeerdsma
2006),
and
lead
to
a
decrease
in
equilibrium
moisture
content
(EMC)
(Esteves
and
Pereira
2009).
There
is
a
known
negative
correlation
between
moisture
content
(MC),
and
strength
and
stiffness
(Ozyhar
et
al.
2013).
While
there
is
a
positive
correlation
between
wood
density
and
MC,
which
is
influenced
by
mass
loss
during
thermal
treatment.
It
is
expected
that
there
will
be
various
strength-‐stiffness
properties
of
thermally
treated
wood
when
exposed
to
varied
climatic
conditions.
The
relationship
of
mechanical
properties
of
wood
and
wood
MC
after
thermal
treatment
is
therefore
researched.
Ten
radially
oriented
beech
wood
boards
(Fagus
sylvatica
L.)
of
32
mm
thickness
and
2
m
length,
having
no
visible
defects,
were
split
into
two
halves
for
the
control
(C)
and
thermally
treated
board
samples
(TT).
Industrial
thermal
treatment
in
an
unsaturated
steam
atmosphere
(Patm
=
1.2
bar)
was
performed
at
Evolen
company
(HR)
on
TT
board
samples
with
a
pre-‐drying
phase
(T
=
105
°C),
a
stepwise
heating
phase,
heating
at
maximum
temperature
of
210
°C,
followed
by
cooling
and
conditioning
(20
°C
/
65
%
RH).
Prismatic
compression
wood
specimens
(L×R×T
=
20
mm
×
20
mm
×
20
mm)
were
made
in
a
series
(n
=
8)
from
each
unmodified
and
thermally-‐treated
board
halves.
Adsorption
behaviour
was
studied
at
room
temperature
(20
±
0.1
°C)
by
putting
one
specimen
of
a
series
to
equilibrate
at
a
single
relative
humidity
(RH),
having
a
range
from
0
%
to
97
%.
Transverse
(T)
and
longitudinal
(L)
displacement-‐
controlled
compression
tests
were
conducted
on
equilibrated
specimens
using
a
Universal
Testing
Machine
(Zwick
Z100),
where
Young’s
moduli
MOE,
proportional
limit
stress
σPL,
and
ultimate
strength
σmax
were
determined.
The
thermal
treatment
generally
improved
the
hygroscopicity
of
beech
wood
(∆EMC
=
-‐50
%),
more
pronounced
at
upper
hygroscopic
range,
and
reduced
wood
density,
where
the
mean
oven-‐
69
of
thermal
treatment
on
moisture-‐dependent
elasto-‐plastic
behaviour
of
beech
Straže
A.1,
Fajdiga
G.1,
Pervan
S.2,
Gorišek
Ž.1
1
University
of
Ljubljana,
Biotechnical
Faculty,
Jamnikarjeva
101,
SI-‐1000
Ljubljana,
Slovenia;
ales.straze@bf.uni-‐lj.si
2
University
of
Zagreb,
Faculty
of
forestry,
Svetošimunska
25,
HR-‐10000
Zagreb,
Croatia
Keywords:
thermo-‐modified
wood,
elasto-‐plasticity,
compression
test,
moisture
content
Strength
and
stiffness
alteration
are
important
properties
of
thermally
treated
wood,
and
vary
with
anatomical
direction
of
wood,
testing
method,
and
wood
species.
Since
wood
density
is
commonly
decreased
after
thermal
treatment
(Poncsak
et
al.
2006),
one
might
expect
a
similar
trend
with
material
strength
and
stiffness.
However,
the
reduction
of
hydrogen
bonding
and
a
decrease
in
free
accessible
hydroxyl
groups
are
often
present
in
thermally
treated
wood
(Boonstra
and
Tjeerdsma
2006),
and
lead
to
a
decrease
in
equilibrium
moisture
content
(EMC)
(Esteves
and
Pereira
2009).
There
is
a
known
negative
correlation
between
moisture
content
(MC),
and
strength
and
stiffness
(Ozyhar
et
al.
2013).
While
there
is
a
positive
correlation
between
wood
density
and
MC,
which
is
influenced
by
mass
loss
during
thermal
treatment.
It
is
expected
that
there
will
be
various
strength-‐stiffness
properties
of
thermally
treated
wood
when
exposed
to
varied
climatic
conditions.
The
relationship
of
mechanical
properties
of
wood
and
wood
MC
after
thermal
treatment
is
therefore
researched.
Ten
radially
oriented
beech
wood
boards
(Fagus
sylvatica
L.)
of
32
mm
thickness
and
2
m
length,
having
no
visible
defects,
were
split
into
two
halves
for
the
control
(C)
and
thermally
treated
board
samples
(TT).
Industrial
thermal
treatment
in
an
unsaturated
steam
atmosphere
(Patm
=
1.2
bar)
was
performed
at
Evolen
company
(HR)
on
TT
board
samples
with
a
pre-‐drying
phase
(T
=
105
°C),
a
stepwise
heating
phase,
heating
at
maximum
temperature
of
210
°C,
followed
by
cooling
and
conditioning
(20
°C
/
65
%
RH).
Prismatic
compression
wood
specimens
(L×R×T
=
20
mm
×
20
mm
×
20
mm)
were
made
in
a
series
(n
=
8)
from
each
unmodified
and
thermally-‐treated
board
halves.
Adsorption
behaviour
was
studied
at
room
temperature
(20
±
0.1
°C)
by
putting
one
specimen
of
a
series
to
equilibrate
at
a
single
relative
humidity
(RH),
having
a
range
from
0
%
to
97
%.
Transverse
(T)
and
longitudinal
(L)
displacement-‐
controlled
compression
tests
were
conducted
on
equilibrated
specimens
using
a
Universal
Testing
Machine
(Zwick
Z100),
where
Young’s
moduli
MOE,
proportional
limit
stress
σPL,
and
ultimate
strength
σmax
were
determined.
The
thermal
treatment
generally
improved
the
hygroscopicity
of
beech
wood
(∆EMC
=
-‐50
%),
more
pronounced
at
upper
hygroscopic
range,
and
reduced
wood
density,
where
the
mean
oven-‐
69
