Page 77 - 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. 77
el
moisture
sorption
model
explaining
parallel
kinetics
of
transient
wood
moisture
content
Wim
Willems
Grote
Bottel
7a,
5753
PE
Deurne,
Netherlands,
FirmoLin
Technologies
BV,
w.willems@firmolin.eu
Keywords:
Wood
moisture
sorption
isotherm,
PEK
model,
Sorption
site
occupancy
model,
Water
chemical
potential,
Water
clusters,
Polymer
relaxation
Wood
moisture
sorption
isotherms
are
thought
to
contain
valuable
information
for
the
characterisation
of
modified
wood
and
its
performance
in
service.
Many
alternative
physical
models
of
equilibrium
wood
moisture
sorption
fit
and
explain
the
sigmoid
shape
of
the
adsorption
isotherm.
On
the
other
hand,
when
other
phenomena
of
wood
moisture
are
considered,
these
models
reveal
serious
shortcomings,
such
as
in
the
transient
moisture
content.
Qualitatively,
a
fast
and
a
slow
kinetic
component
has
been
identified,
tentatively
assigned
to
mass
diffusion
and
polymer
relaxation
respectively
(Hill
et
al
2012).
In
this
contribution,
a
new
moisture
sorption
model
is
presented,
based
on
a
thermodynamic
model
of
the
bonding
configuration
of
water
within
the
cell
wall.
Wood
moisture
at
low
humidity
is
argued
to
be
bound
to
two
hydroxyl-‐groups
of
the
wood
cell
wall,
whereas
at
high
humidity
one
extra
water
molecule
will
cluster
at
an
already
adsorbed
molecule.
It
is
shown
that
the
fast
and
slow
components
of
the
transient
moisture
content
are
consistent
with
molecular
processes
in
the
model.
A
closed-‐form
expression
for
the
sigmoid
adsorption
isotherm
based
on
the
sorption
model
is
given.
The
model
satisfies
the
principles
of
wood
moisture
sorption,
described
in
previous
work
of
the
author
(Willems
2014a,b),
that
the
wood
moisture
content
can
be
factored
into
a
density
of
accessible
sorption
sites
and
a
statistical
occupancy
of
these
accessible
sites.
The
latter
occupancy
factor
is
directly
controlled
by
the
water
vapour
humidity
and
temperature,
independent
of
the
density
of
water
sorption
sites.
References
Hill,
C.
A.,
Keating,
B.
A.,
Jalaludin,
Z.,
Mahrdt,
E.
2012.
A
rheological
description
of
the
water
vapour
sorption
kinetics
behaviour
of
wood
invoking
a
model
using
a
canonical
assembly
of
Kelvin-‐Voigt
elements
and
a
possible
link
with
sorption
hysteresis.
Holzforschung,
66,
1:
35-‐47
65
moisture
sorption
model
explaining
parallel
kinetics
of
transient
wood
moisture
content
Wim
Willems
Grote
Bottel
7a,
5753
PE
Deurne,
Netherlands,
FirmoLin
Technologies
BV,
w.willems@firmolin.eu
Keywords:
Wood
moisture
sorption
isotherm,
PEK
model,
Sorption
site
occupancy
model,
Water
chemical
potential,
Water
clusters,
Polymer
relaxation
Wood
moisture
sorption
isotherms
are
thought
to
contain
valuable
information
for
the
characterisation
of
modified
wood
and
its
performance
in
service.
Many
alternative
physical
models
of
equilibrium
wood
moisture
sorption
fit
and
explain
the
sigmoid
shape
of
the
adsorption
isotherm.
On
the
other
hand,
when
other
phenomena
of
wood
moisture
are
considered,
these
models
reveal
serious
shortcomings,
such
as
in
the
transient
moisture
content.
Qualitatively,
a
fast
and
a
slow
kinetic
component
has
been
identified,
tentatively
assigned
to
mass
diffusion
and
polymer
relaxation
respectively
(Hill
et
al
2012).
In
this
contribution,
a
new
moisture
sorption
model
is
presented,
based
on
a
thermodynamic
model
of
the
bonding
configuration
of
water
within
the
cell
wall.
Wood
moisture
at
low
humidity
is
argued
to
be
bound
to
two
hydroxyl-‐groups
of
the
wood
cell
wall,
whereas
at
high
humidity
one
extra
water
molecule
will
cluster
at
an
already
adsorbed
molecule.
It
is
shown
that
the
fast
and
slow
components
of
the
transient
moisture
content
are
consistent
with
molecular
processes
in
the
model.
A
closed-‐form
expression
for
the
sigmoid
adsorption
isotherm
based
on
the
sorption
model
is
given.
The
model
satisfies
the
principles
of
wood
moisture
sorption,
described
in
previous
work
of
the
author
(Willems
2014a,b),
that
the
wood
moisture
content
can
be
factored
into
a
density
of
accessible
sorption
sites
and
a
statistical
occupancy
of
these
accessible
sites.
The
latter
occupancy
factor
is
directly
controlled
by
the
water
vapour
humidity
and
temperature,
independent
of
the
density
of
water
sorption
sites.
References
Hill,
C.
A.,
Keating,
B.
A.,
Jalaludin,
Z.,
Mahrdt,
E.
2012.
A
rheological
description
of
the
water
vapour
sorption
kinetics
behaviour
of
wood
invoking
a
model
using
a
canonical
assembly
of
Kelvin-‐Voigt
elements
and
a
possible
link
with
sorption
hysteresis.
Holzforschung,
66,
1:
35-‐47
65
