Water uptake, moisture absorption and wettability of beech veneer treated with N-methylol melamine compounds and alkyl ketene dimer
Forest Industry
WATER UPTAKE, MOISTURE ABSORPTION AND WETTABILITY
OF BEECH VENEER TREATED WITH N-METHYLOL MELAMINE
COMPOUNDS AND ALKYL KETENE DIMER
Trinh Hien Mai1, Nguyen Minh Hung2
1,2Vietnam National University of Forestry
SUMMARY
With Beech veneers being treated with 10% solid content of the chemicals from paper (Alkyl ketene dimer,
AKD), wood (N-methylol melamine, NMM-1) and textile industry (fatty acid modified N-methylol melamine,
mNMM-2), the results showed that the treatments with these chemicals considerably increased the water
repellence effectiveness (WRE) of veneers in the initial submersion phases; Then, WREs reduced significantly
from 4 h of immersion to water saturation state (full-water). Moreover, with the WREs at water saturation state
ranged from AKD (5.0%) to mNMM-2 (19.3%), there must be some certain chemical deposited in the cell
lumen and cell wall of the treated veneers. The water repellence of the treated veneers was stable after the
wetting-drying cycles. The chemicals NMM-1 and mNMM-2 that could react with hydroxyl groups or deposit
into the cell wall, may induce the reduction in equilibrium moisture content (EMCR) and radial swelling (RS)
for the treated veneers, while large AKD particles could not penetrate and modify the cell wall therefore did not
reduce EMCR and RS in humid environment for the treated veneers. Wettability of veneers treated with AKD,
NMM-1 and mNMM-2 was much lower than the untreated and control veneers.
Keywords: Beech, contact angle, equilibrium moisture content, veneer, water repellence effectiveness,
wettability.
(Inoue et al 1993, Deka and Saikia 2000, Gindl
et al 2004). In addition, water-based melamine
treated wood indicated the potential to increase
resistance against wood destroying fungi
(Rapp and Peek 1996, Lukowsky et al 1999)
and photochemical wood degradation caused
by weathering (Rapp and Peek 1999). Alkyl
ketene dimer (AKD) is widely used in the
paper industry as an internal sizing agent. The
hydrophobic effect of AKD is attributed to an
esterification with hydroxyl groups of wood
fibers and subsequent orientation of
hydrocarbon chains (Isogai and Taniguchi
1992, Hubbe 2006). Thus, the application of
AKD to wood and wood-based panels is
expected to result in an increased dimensional
stability; however, there have been only few
studies using AKD for wood modification.
I. INTRODUCTION
According to Borgin (1965), a truly water
repellent preservative for wood would prevent
water from being taken up by capillary system
and render cell wall inert to water. This can be
accomplished by impregnating the wood with a
hydrophobic material which may deposit in the
cell lumen, close the main penetration paths of
water, and/or penetrate and allocate into the
cell wall, resulting in bulking effect or cross-
links (Hill 2006; Rowell and Banks, 1985). On
the other hand, it is necessary to determine the
efficiency of water repellence after several
wetting-drying cycles to avoid misleading
comparisons.
Wood treated with melamine-based
compounds
brought
about
remarkable
improvements for solid wood, such as
enhanced water repellence and dimensional
stability (Inoue et al 1993, Pittman et al 1994,
Nguyen et al 2007), increased hardness,
modulus of elasticity and bending strength
In this paper, veneers treated with N-
methylol melamine and AKD chemicals were
investigated on water/moisture related
properties and their stability after cyclic tests.
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Water repellent effectiveness in submersion
tests, equilibrium moisture content and radial
swelling in different humid climates, contact
angle (wettability) are the crucial factors for
further consideration.
protect the wood against the formation of
cracks. In the second step, a sufficient
condensation of the resin is needed, if the
temperature is not up to 100°C, the time for
reaction must last longer (INEOS, 2006).
Phobotex VFN (mNMM-2) delivered by
Ciba, is a fatty acid of modified N-methylol
melamine (methoxymethylen melamine and
paraffin). mNMM-2 is a white dispersion with
pH value from 4 - 6 at 20°C.
II. RESEARCH METHODOLOGY
2.1. Data base of the chemicals
2.1.1. Alkyl ketene dimer (AKD)
Basoplast AKD delivered by BASF, is a
fatty acid alkyl ketene dimer (AKD) in form of
a white dispersion with average pH value from
3.5 - 4.5. AKD is hydrophobization of paper,
especially when made under alkaline
conditions. AKD is widely used for liquid
containers, ink-jet printing paper, and many
other grades of paper and paperboard. AKD is
especially favored for products that need to
resist water over a long period (BASF, 2003).
2.1.2. N-methylol melamine (NMM)
mNMM-2 is a product for washfast and
water repellent finishes which can be used as a
finishing agent for textiles. mNMM-2 should
be combined with catalyst RB(aluminium salt)
to obtain optimal water repellent effect.
mNMM-2 can be diluted in cold water and
applied by padding at room temperature for
cotton fibers, then dried at 120 - 140°C and
cured for 2 min at 160°C or 4 - 5 min at 150°C
(Ciba, 2002).
Madurit MW 840/75 WA (NMM-1)
delivered by INEOS, is an N-methylol
melamine resin dissolved in water. NMM-1 is
a colorless and clear liquid with pH value from
10 - 11 at 20°C.
2.2. Veneer and chemical preparation
Beech (Fagus sylvatica L.) wood with
diameter of 60 cm, harvested in Northern part
of Germany, was selected for all experiments
in this study.
NMM-1 is used for impregnation of solid
wood with a solid content between 10 and
40%. The drying process of impregnated wood
includes two steps. In the first step, the
temperature during the first 24 h must be lower
than 50°C to remove the bulk of water and
Sliced beech veneers without heartwood
were prepared in sizes of 50 × 0.5 × 50 mm3
(rad × tang × long). The numbers of veneer
specimens are listed in the following table 1.
Table 1. Quantity of veneers for each treatment
Number of veneers per treatment
No
Experiments
50 × 0.5 × 50 (mm3)
1
2
3
Water uptake and cyclic tests
EMCR and radial swelling
Contact angle
10
10
10
30
Total veneers per treatment
Each chemical listed in section 2.1 was
diluted with water to get a 10% solid content
solution for each treatment. mNMM-2 was
mixed together with catalyst RB (15% of stock
solution of mNMM-2 (w/w).
2.3. Treatment of veneers
The veneers were oven-dried at (103 ± 2)°C
for 24 h, then transferred to a desiccator and
allowed to cool to ambient temperature over
silica gel. Prior to impregnation, each oven-dry
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veneer was weighted on a four-figure balance
and measured radial dimension using an
electronic micrometer accurate to ±0.01 mm.
After weighting and measuring, the veneers
were impregnated with the prepared solutions
mentioned in section 2.2 as soon as possible.
For comparisons, the beech veneers
impregnated with water served as control
specimens. The impregnation process included
two steps: vacuum of 60 mbar for 30 min and
followed by 2 h veneers being stored in the
solutions at atmospheric pressure. A complete
impregnation of the whole cross section is
guaranteed by this impregnation process
(Wepner et al., 2007). Excessive solutions on
surface of the wet veneers were removed
before pre-drying. Then, the veneers were pre-
dried at 40°C for 24 h and cured at 140°C for 2
h in a drying-oven. After cooling down in a
desiccator, weight and radial dimension of the
treated veneers after being cured were
recorded. The treated veneers were proceeded
with water/moisture related experiments as
described in Figure 1.
Treated and control veneers (after curing)
Weight and radial dimension
First submersion
(10 veneers/treatment)
WU, WRE
Conditioning in the climate
chambers: 30, 65, 90% RH
and 20°C
Conditioning in the
climate chambers: 65 %
RH and 20°C
(10 veneers/treatment)
EMCR, RS
(10 veneers/treatment)
Cycle 1
(10 veneers/treatment)
Determining
Contact angle
Second submersion
(10 veneers/treatment)
WU, WRE
Cycle 2
(10 veneers/treatment)
Third submersion
(10 veneers/treatment)
WU, WRE
Cycle 3
(10 veneers/treatment)
Fourth submersion
(10 veneers/treatment)
WU, WRE
Figure 1. Test procedure of the treated veneers
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2.4. Water submersion and cyclic tests
Water submersion
2.5. Cyclic tests
To evaluate the fixation of chemicals in the
treated veneers and the stability of the water
repellent effect under influence of wetting-
drying process; after each submersion, the
veneers were undergone a cyclic test based on
EN 321. Each cycle was carried out by
submersing the veneers in water (20 ± 2)°C for
(72 ± 1) h, freezing them at between -12°C and
-20°C for (24 ± 0.25) h; and then drying them
at (70 ± 1)°C for (72 ± 1) h. These cycles
might cause cracks on surface of the veneers,
Water repellent characteristic was evaluated
through water submersion tests; the veneer
specimens for these tests were described in
sections 2.2, 2.3 and Figure 1. For each
submersion test, 10 veneers per treatment were
submersed one by one in a water bath at room
temperature for continuous times: 1 min, 10
min, 1 h, 2 h, 4 h, and 24 h. After 24 h
submersion, water uptake was supported by
vacuum (100 mbar, 30 min), then the veneers
were stored in water at atmospheric pressure
overnight to reach full water uptake (water
saturation).
which
would
affect
water
uptake,
swelling/shrinking, and weight loss as well.
2.6. Sorption behavior
After given times had elapsde, the veneer
specimens were removed from the water bath,
dabbed off with tissue and weighted
immediately. The water uptake was calculated
according to Equation 1 (Donath, 2005).
Sorption behavior was evaluated with the
veneers described in sections 2.2 and 2.3. Ten
veneers from each treatment were conditioned
in different climates at 30, 65, 90 % relative
humidity (RH) and 20°C until the veneers
reached equilibrium moisture content (EMC).
EMC was considered to be reached when the
results of two successive weighting operations
within 24 h did not differ by more than 0.1%
of the weight of veneer. To avoid the reduction
in EMC simply due to increased weight of
veneer after the treatment, the EMCR
calculation was based upon the oven-dry
weight of the wood substance rather than the
treated wood. The EMCR and the radial
swelling (RS) are presented in Equation 3-4
(Hill, 2006)
Wa Wb
WU(%)
100
(1)
Wo
Where:
WU: water uptake;
Wa: veneer weight after water
submersion (1 min, 10 min, 1 h, 2 h, etc);
Wb: veneer weight before water
submersion;
Wo: oven-dry weight of veneer before
impregnation.
For comparison of the water uptake between
the treated and the control veneers, water
repellent effectiveness (WRE) was expressed
as in Equation 2 (Donath, 2005).
W2 W1
EMCR (%)
100
(3)
Wo
WUcontrol WUtreated
RD2 RD1
WRE(%)
100
(2)
RS
Where:
100
(4)
WUcontrol
RD
1
Where:
WRE: water repellent effectiveness;
WUcontrol : water uptake of control
EMCR and RS: equilibrium moisture
content and radial swelling of veneer;
Wo: oven-dry weight of veneer before
impregnation;
veneer;
veneer.
WUtreated : water uptake of treated
W1 and RD1: oven-dry weight and
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radial dimension of veneer after curing (before
conditioning);
were conditioned in a climate chamber at 65%
RH and 20°C until the veneers reached EMC
before measuring contact angle of the control,
treated and untreated veneer surface. Contact
angle between a distilled water drop and
veneer surface was criterion of the
measurement, point of view was horizontal.
The greater the angle, the more hydrophobic
surface and less wettability.
W2 and RD2: weight and radial
dimension of veneer after conditioning.
2.7. Contact angle measurement
Wettability of wood surface can be
determined through contact angle measurement
(
Deng and Abazeri, 1998; Jozef K, 2014)
. In
this study, ten veneers from each treatment
-
vi e
a)
b)
Figure 2. Contact angle of a surface
a) Contact angle measurement instrument
b) A distilled water drop on a veneer surface
Figure 3. Distilled water drop on a veneer surface
Drop Shape Analyzer, a high-quality system
solution for analysis
duration: 20 s; number of pictures per drop:
500; 1 picture/0.04s, contact angle is calculated
automatically.
of wetting and adhesion on solid surfaces was
used in this study with the contact angle
measurement instrument at HAWK University
of Applied Science and Arts in Germany.
Three distilled water drops were applied per
veneer (drop 0, drop 1 and drop 2). Drop
volume: 11µl; rate: 250 µl/min; exposure
III. RESULTS AND DISCUSSION
3.1. Water repellence effectiveness (WRE)
In general, as can be seen in Figure 5 - 7,
WREs of the first submersion were lower than
those of the second, third and fourth
submersion, especially in cases of dispersion
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treated veneers. This characteristic can be
explained by the following reasons:
(Figure 4) due to the formation of micro cracks
on the veneer surfaces caused by wetting-
drying cycles. Therefore, the relative value
WREs became higher with subsequent cycles.
Firstly, water uptake of the control veneers
increased from the first to the last submersion
120
100
80
60
40
20
0
Water
0
5
10
15
20
25
30
35
40
saturation
Water submersion time [h]
First submersion
Third submersion
Second submersion
Fourth submersion
Figure 4. Water uptake of the control veneers
Secondly, wetting-drying cycles are
supposed to encourage the process of ongoing
polymerization which leads the completion of
condensation and thus improves water
repellent effect (Donath, 2005; Lukowsky et
al., 1997; Mai and Militz, 2004).
empty voids, while water uptake occurred
slowly with the treated veneers because water
paths were occluded by the chemicals. Hence,
the treatments with these chemicals
considerably diminished the water uptake of
veneers in the initial submersion phases. The
WREs reduced significantly from 4 h of
immersion to water saturation state (full-
water), thus, the treatments mostly inhibited
the speed of water uptake. Moreover, with the
WREs at water saturation state ranged from
AKD (5.0%) to fatty acid modified N-methylol
compound mNMM-2 (19.3%), there must be
some chemicals deposited in the cell lumen
and cell wall of the treated veneers and
therefore caused lower full-water uptake in
comparison to that of the control veneers.
As can be seen in Figure 5 - 7, WREs of the
treated veneers within each submersion were
high (up to 80%) in the initial submersion
phases of 1 min, 10 min, 1 h, 2 h, 4 h and then
lessened gradually in the submersion phases of
24 h. As expected, after vacuum support and
soaking in water overnight (24 h), WREs (at
water saturation) got the lowest values. Within
the first 4 h of submersion, water uptake
occurred rapidly with the control veneers
(Figure 4) because water penetrated easily into
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Alkyl ketene dimer (AKD treatment)
80
70
60
50
40
30
20
10
0
Water
saturation
0
5
10
15
20
25
30
35
40
-10
Water submersion time [h]
First submersion
Third submersion
Second submersion
Fourth submersion
Figure 5. Water repellent effectiveness of AKD treated veneers
Alkyl ketene dimer (AKD) is used in paper
The WREs of the first submersion were
significantly lower than those of the latter
submersions (Figure 5), this can be explained
by the leaching of cationic starch which is used
as a stabilizer (emulsifier) and has hydrophilic
effect. The WREs at water saturation of four
times of soaking were almost equal (2.4 - 5%),
meaning that there were only small amounts of
AKD emulsion permanently deposited in the
cell lumen. High values of WRE in the initial
phases of the submersions may be due to the
fact that AKD particles form a hydrophobic
surface coating on the treated veneers as the
findings from Suttie et al. (1998).
industry as an internal sizing agent.
Hydrophobic effect of AKD is attributed to an
esterification with hydroxyl groups of wood
fiber
and
subsequent
chains
orientation
(Hubbe,
of
hydrocarbon
2006;
Hundhausen et al., 2009). However, AKD is
unlikely to penetrate into the cell wall because
its dispersion size is about 1 µm (Neimo, 1999)
whereas micro void diameter in the cell wall
does not exceed 2 nm (Hill and Papadopoulos,
2001). As a result, AKD may only deposit in
the cell lumen and modify surfaces of the cell
lumen, not modify the cell wall.
N-methylol melamine (NMM-1 treatment)
80
70
60
50
40
30
20
10
0
Water
0
5
10
15
20
25
30
35
40
saturation
Water submersion time [h]
The first submersion
The third submersion
The second submersion
The fourth submersion
Figure 6. Water repellent effectiveness of NMM-1 treated veneers
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As can be seen in Figure 6, unlike the other
treatments, the treatments with NMM-1 resins
showed WREs of the first submersion not
lower than those of the latter times, except at
24 h of soaking. The WREs at water saturation
reduced gradually from the first submersion
(14%) to the last one (7%), this can be explained
by cracks and leaching of NMM-1 in the treated
veneers through the wetting-drying cycles.
dimensional network to provide mechanical
fixation in the cell walls (Lukowsky, 1999)
although there was an evidence for covalent
bonds between melamine resin and wood
components given by Troughto and Chow
(1968). Because of these reasons, water flow
and water vapor diffusion are impeded both in
the cell wall and the cell lumen of the treated
veneers. WRE and dimensional stability were
achieved quite high in the experiments of the
wood impregnated with melamine resins (Deka
and Saikia, 2000; Inoue et al., 1993).
Penetration and deposition of NMM resin
into the cell lumen and cell wall were reported
by many scientists (Gindl et al., 2004; Gindl et
al., 2003; Rapp et al., 1999). In addition, it is
believed that NMM molecules form 3-D
Fatty
acid
modified
N-methylol
melamine/paraffin (mNMM-2 treatment)
80
70
60
50
40
30
20
10
0
Water
saturation
0
5
10
15
20
25
30
35
40
Water submersion time [h]
First submersion
Third submersion
Second submersion
Fourth submersion
Figure 7. Water repellent effectiveness of mNMM-2 treated veneers (catalyst RB)
As depicted in Figure 7, water repellence of
mNMM-2 treated veneers was very high from
the second submersion like AKD treatments.
The WREs at water saturation state reached
approx. 20%, much higher than those of the
other treatments.
addition, it is assumed that some active
ingredients of mNMM compounds could
penetrate into the cell wall and cause micro-
pore blocking and undergo chemical reaction
with hydroxyl groups of the cell wall (Nguyen
et al., 2007).
High WREs of mNMM-2 treatment can be
explained by the location in the cell lumen of
the polymerized chemicals which cause less
free space for water in capillary and close
penetration paths of water. Besides, paraffin
proportion in these mNMM compounds also
resulted in considerable hydrophobic effect. In
3.2. Sorption behavior at different relative
humidity
Wood is a hygroscopic material due to
hydroxyl groups of cell wall polymers,
especially cellulose. When dry-wood is
exposed to a humid environment, the wood
absorbs water vapor until its moisture content
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becomes sufficient high to be equilibrium with
the ambient atmosphere. This moisture
content, namely equilibrium moisture content
(EMCR), is approximately proportional to the
ambient relative humidity (RH) and
temperature (Skaar, C., 1998). As water vapor
enters the wood cell wall, the space in the cell
wall is occupied, causing increase in
dimension of the cell wall, as a result, the
wood swells (Hill, 2006).
and swelling/shrinking of the treated wood in a
specific humid environment depend on cell
wall bulking and covalent bonds of the reagent
with hydroxyl groups of the wood cell wall
(Rowell and Banks, 1985). Moreover, there is
a direct relationship between the decrease in
EMCR and the increase in resistance against
fungal attack as discussed by Rowell (2005)
and Hill (2002). Therefore, the reduction in
EMCR and swelling/shrinking is one of the
aims of wood modification.
With regard to wood modification, EMCR
Table 2. Equilibrium moisture content and radial swelling of the control and treated veneers (10%
solid content of the chemicals) at different relative humidity and 20°C
Equilibrium moisture content
EMCR (%)
Radial swelling
RS (%)
No
1
Treatment
30% RH
65% RH
13.60
0.17
90% RH
30% RH
0.84
65% RH
2.79
90% RH
3.74
Control
STDEV
AKD
4.62
0.13
4.13
0.16
4.10
0.20
3.69
0.30
18.42
0.29
0.04
0.09
0.04
13.55
0.15
18.40
0.29
0.80
2.77
3.79
2
STDEV
NMM-1
STDEV
mNMM-2
STDEV
0.04
0.09
0.10
12.37
0.30
16.72
0.33
0.61
2.27
3.09
3
0.05
0.10
0.15
12.64
0.48
17.01
0.46
0.70
2.52
3.40
4
0.03
0.12
0.13
At 30, 65, 90% relative humidity (RH) and
20°C, all the treated veneers (except AKD
treatments) showed slight reduction in EMCR
and radial swelling (RS) compared to the
control veneers (Table 2). Thus, the chemicals
more or less penetrated into the cell wall,
deposited in micro voids, created covalent
bonds or cross-linking with hydroxyl groups of
the cell wall, these were reflected by radial
bulking effect (RBE) as well.
results from the esterification of AKD
molecules with hydroxyl groups of wood
cellulose and the orientation of alkyl chains
due to heat effect. However, large AKD
particles could not penetrate and modify the
cell wall; this was reflected by no cell wall
bulking. AKD could only form a hydrophobic
layer onto external and internal cell lumen
surfaces. Consequently, AKD dispersion could
provide good water repellence in initial phases
of water submersion but not reduce EMCR and
RS in humid environment for the treated
veneers.
AKD treated veneers could not impede
water sorption in the cell wall after a long
exposure in humidity climate. EMCR and RS
of AKD and paraffin treated veneers were
equal or slightly higher as compared to those
of the control veneers. It is assumed that
hydrophobic properties of AKD treated wood
N-methylol melamine (NMM) molecules
are believed to form three dimension network
in the cell wall (Lukowsky, 1999), hence micro
voids in the cell wall could be filled with
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NMM resins. The quantity of NMM resin in
the cell walls mostly depends on molecular
weight, degree of methylolation, solution
concentration and method of impregnation
(Hansmann et al., 2006), the higher amount of
NMM in the cell walls, the more reduction in
EMCR and RS.
The fatty acid modified N-methylol
melamine (mNMM-2) treated veneers caused
moderate reduction in EMCR (1 - 1.4%) and
RS (0.3 - 0.4%) in comparison to the control
veneers. This can be explained with the fact
that a part of mNMM dispersions may
penetrate into the cell wall; block micro voids
and create covalent bonds or cross linking with
hydroxyl groups of the wood cell wall.
The NMM-1 treated veneers exhibited
around 1.7% lower in EMCR and 0.6% lower
in RS compared to those of the control veneers
at 90% RH and 20°C. Due to the deposition of
NMM-1 resin into the cell wall (with cell wall
bulking), the empty space of micro voids is
believed to be smaller; the ability for
adsorption of water vapor was lessened, and,
as a consequence, the EMCR and RS were
reduced.
3.3. Contact angle
The values of contact angle measured at the
phase boundary between wood and liquid
standard provide an issue point for the study of
thermodynamic properties of wood surface.
The values of this angle are used to calculate
surface free energy and reflect wettability of
wood surface (Jozep, 2014).
Figure 8. Contact angle of the control, untreated and AKD, NMM treated veneer
As can be seen in the Figure 8, contact
angle of the untreated veneers reduced very
fast in the first 5 seconds, and then reduced
slowly to about 35° after 17 seconds. Congtact
angle of the control veneers was much higher
than that of untreated veneers because hot
press curing made veneers become more
hydrophobic. Contact angle values of AKD,
NMM-1 and mNMM-2 treated veneers were
almost consistant during the first 20 seconds
after water drop was applied on veneer surface;
and showed insignificant difference. Therefore,
wettability of AKD, NMM-1 and mNMM-2
treated veneers presented much lower than the
untreated and control veneers.
IV. CONCLUSIONS
Beech veneers were impregnated with 10%
solid content of the AKD, NMM-1 and
mNMM-2 chemicals. High water repellence
of the treated veneers resulted from the closing
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formaldehyde resin to improve the hardness of Norway
spruce wood. Journal of Applied Polymer Science,
93(4): 1900-1907.
8. Gindl, W., Müller, U. and Teischinger, A. (2003)
Transverse compression strength and fracture of spruce
water paths in lumen or blocking micro voids
and/or hydroxyl groups of the cell wall as
discussed in details. The cycle after each
submersion did not result in significant change
of WREs in the second, third and fourth
submersion although weight loss of each
treatment increased from the first cycle to the
fourth submersion. Consequently, it can be
stated that, the water repellence of the treated
veneers was stable after the wetting-drying
cycles.
wood
modified
by
melamine-formaldehyde
impregnation of cell walls. Wood and Fiber Science,
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TÍNH HÚT NƯỚC, HÚT ẨM VÀ THẤM ƯỚT BỀ MẶT CỦA VÁN MỎNG
GỖ BEECH (Fagus sylvatica L.) BIẾN TÍNH VỚI CÁC HỢP CHẤT
CÓ CHỨA N-METHYLOL MELAMINE VÀ ALKYL KETENE DIMER
Trịnh Hiền Mai1, Nguyễn Minh Hùng2
1,2Trường Đại học Lâm nghiệp
TÓM TẮT
Kết quả xử lý ván mỏng gỗ Beech với các hóa chất từ công nghiệp giấy (alkyl ketene dimer, AKD), công
nghiệp gỗ (N-methylol melamine, NMM-1) và công nghiệp dệt (fatty acid modified N-methylol melamine,
mNMM-2) ở hàm lượng rắn 10% cho thấy khả năng chống hút nước trong giai đoạn đầu khá cao; Sau đó giảm
đáng kể từ 4 giờ sau khi ngâm đến khi ván đạt trạng thái bão hòa nước. Khả năng chống hút nước ở trạng thái
bão hòa nước thay đổi từ 5% (AKD) đến 19,3% (mNMM-2), do đó có một lượng hóa chất nhất định tích tụ
trong ruột tế bào và vách tế bào của ván mỏng được xử lý với các hóa chất trên. Khả năng chống hút nước của
ván mỏng được xử lý hóa chất ổn định qua các chu kỳ ngâm nước – sấy khô. Hóa chất NMM-1 và mNMM-2
có khả năng phản ứng với nhóm hydroxyl hoặc tích tụ trong vách tế bào làm giảm độ ẩm thăng bằng và tỷ lệ
trương nở theo phương xuyên tâm của ván mỏng biến tính, trong khi đó các hạt AKD có kích thước lớn không
thể di chuyển vào vách tế bào để biến tính do đó không làm giảm độ ẩm thăng bằng và tỷ lệ trương nở theo
phương xuyên tâm. Khả năng thấm ướt của ván mỏng xử lý với AKD, NMM-1 và mNMM-2 thấp hơn nhiều so
với ván mỏng đối chứng và ván không xử lý.
Từ khoá: Độ ẩm thăng bằng, góc tiếp xúc, gỗ Beech, khả năng chống hút nước, tính thấm ướt, ván mỏng.
Received
Revised
Accepted
: 14/9/2017
: 02/10/2017
: 10/10/2017
JOURNAL OF FORESTRY SCIENCE AND TECHNOLOGY NO. 5 - 2017
151
12 trang
20/04/2022
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