Influence of curing parameters on chemical fixation and water resistance of modified beech veneers

Forest Industry 
JOURNAL OF FORESTRY SCIENCE AND TECHNOLOGY NO. 2 - 2018 162
INFLUENCE OF CURING PARAMETERS ON CHEMICAL FIXATION 
AND WATER RESISTANCE OF MODIFIED BEECH VENEERS 
Trinh Hien Mai 
Vietnam National University of Forestry 
SUMMARY 
In this study, Beech (Fagus sylvatica. L) sliced veneers with dimension of 37 × 0.5 × 50 mm3 (rad × tang × 
long) were soxhlet extracted with water and organic solvents (cyclohexan and ethanol, 2 : 1, v/v), and then 
oven-dried prior to the chemical impregnation. Three chemicals used for veneer impregnation were: N-
methylol melamine (NMM - 1 - 10% solid content), fatty acid modified N-methylol melamine/paraffin 
compound (mNMM - 2 - 5% solid content), alkyl ketene dimer (AKD - 1% solid content). After 2 days of pre-
drying in room condition, the impregnated veneers were cured in a hot press with different parameters of 
temperature and time. Specifically, temperature: 130°C, 160°C; pressure: 1 N/mm2; pressing time: 5, 10 and 20 
min. The results indicated that influence of the hot pressing time and temperature on weight percent gain 
(WPG) and radial bulking effect (RBE), equilibrium moisture content (EMCR) and radial swelling (RS) in 
20°C, 65% relative humidity, and weight losses after extraction did not showed detrimental effects in case of 
the veneers cured by hot pressing at 5 min and 130°C in comparison to the other hot pressing parameters. 
Besides, water repellent effectiveness (WRE) of the treated veneers after soxhlet with organic solvents and 
water submersion presented optimum results for the veneers cured by hot pressing at 5 min and 130°C. In 
addition, reduced time and temperature for curing of veneers may inhibit ‘over-drying’ of veneers before gluing 
process in production of plywood. Hence, the time of 5 minutes and the temperature of 130°C were selected for 
curing by hot press of the impregnated veneers. Effects of curing parameters (by hot press) on properties of 
veneer modified with each chemical were discussed in detail in this paper. 
Keywords: Alkyl ketene dimer, beech (Fagus sylvatica. L) veneer, chemical fixation, equilibrium 
moisture content, N-methylol melamine, water repellent effectiveness. 
I. INTRODUCTION 
Beech (Fagus sylvatica. L) is one of the 
most important wood species used in veneer 
industry in European. According to the EN 
350: 2016, it is classified in durability class 5 
and treatability class 1. Beech is easily 
treatable but its low bioresistance and 
dimensional stability limit the area of 
application. Therefore, wood modification has 
been employed to improve durability for wood 
and wood-based products from beech. 
Furthermore, treatment processes of the veneer 
modification indicate some advantages which 
are less used chemical, more homogenous 
structure, shorter drying and curing periods as 
compared to those of the solid wood treatment 
(Wepner and Militz, 2005). In this study, beech 
sliced veneers were impregnated with 
chemicals from wood, textile and paper 
industry, then pre-drying and curing. Besides 
curing in a drying-oven, the impregnated 
veneers can be cured in a hot press. Curing in a 
hot press shows more obvious advantages than 
curing in a drying-oven such as: time saving, 
flat veneer makes itself easier for gluing 
process. In previous works of producing 
modified plywood, the impregnated veneers 
were cured in a hot press instead of a drying-
oven prior to gluing process (Wepner et al., 
2007; Dieste et al., 2009; Trinh, 2016). Time 
and temperature are two main factors of curing 
by hot press, affecting properties of the treated 
veneers. Thus, in this study, different 
parameters of hot press curing were applied on 
the impregnated veneers for testing of 
chemical fixation and water related properties. 
II. RESEARCH METHODOLOGY 
2.1. Veneer and chemical preparation 
Beech sliced veneers, free of heartwood, 
were cut in sizes of 37 × 0.5 × 50 mm3 (rad × 
tang × long). The quantity of veneers for each 
treatment was 20. 
Forest Industry 
JOURNAL OF FORESTRY SCIENCE AND TECHNOLOGY NO. 2 - 2018 163
Three chemicals were diluted with water to 
the different concentrations as follows: 
a) N-methylol melamine (NMM-1): 10% 
solid content (15.5% stock concentration) 
Madurit MW 840/75 WA (NMM-1) 
delivered by INEOS company, 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. 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 50oC to 
remove the bulk of water and 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 100oC, 
the time for reaction must last longer. 
b) Fatty acid modified N-methylol 
melamine/paraffin compound (mNMM-2): 5% 
solid content (13.2% stock concentration) with 
catalyst RB 1.9% (equal to 15% of mNMM-2 
stock solution w/w). 
Phobotex VFN (mNMM-2) delivered by 
Ciba company, 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 20oC. 
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 - 140oC and 
cured for 2 min at 160oC or 4 - 5 min at 150oC. 
c) Alkyl ketene dimer (AKD): 1% solid 
content (6.7% stock concentration) 
Basoplast AKD delivered by BASF 
company, 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. 
2.2. Treatment of the veneers 
The veneers were soxhlet extracted with 
water and organic solvents, and then oven-
dried prior to the chemical impregnation. 
Water extraction was performed with total 
running time of 6 h. Organic solvent 
(cyclohexan and ethanol, 2 : 1, v/v) extraction 
was carried out in the same way as the water 
extraction. After 2 days of pre-drying in room 
condition, the impregnated veneers were cured 
in a hot press with different parameters of 
temperature and time: 
- Temperature: 130oC, 160oC; Pressure: 1 
N/mm2 ; Time: 5, 10 and 20 min. 
Veneers impregnated with water served as 
control specimens. The test procedure is presented 
in figure 1. 
2.3. Chemical fixation and water related 
properties of the veneers 
Prior to the tests, the treated and control 
veneers were conditioned in a climate chamber 
at 20oC and 65% RH until constant weight. 
Then, 5 veneers from each treatment were 
oven-dried for determination of moisture 
content of the veneers at 20oC and 65% RH as 
the following: 
100(%)
1
1 
W
WW
M c (Equation 1) 
Where: 
W1: Oven-dry weight of veneers (g) after 
conditioning (the same as oven-dried weight 
after curing); 
Wc: Constant weight of veneer (g) conditioned 
in the climate chamber 20oC, 65% RH; 
M: Moisture content of veneer (%) at 20oC 
and 65% RH. 
Hence, the oven-dry weight of the other 15 
Forest Industry 
JOURNAL OF FORESTRY SCIENCE AND TECHNOLOGY NO. 2 - 2018 164
veneers after curing was calculated by 
extrapolation from the constant weight and 
moisture content of the veneers at 20oC and 65% 
RH, using Equation 2: 
100
100
1 
M
W
W c (Equation 2) 
The WPG and RBE of the treated and 
control veneers were determined as in 
Equation 3 and Equation 4, respectively: 
100(%) 1 
o
o
W
WW
WPG (Equation 3)
Where: 
WPG: Weight percent gain of the treated 
veneer (%); 
W1: Oven-dry weight of veneer after curing (g); 
Wo: Oven-dry weight of veneer before 
chemical impregnation (g). 
100(%) 1 
o
o
RD
RDRD
RBE (Equation 4) 
Where: 
RBE: Radial bulking effect of the treated 
veneer (%); 
RD1: Radial dimension of oven-dry veneer 
after curing (mm); 
RDo: Radial dimension of oven-dry veneer 
before chemical impregnation (mm). 
Similarly, EMCR and RS were calculated 
according to Equation 5 and Equation 6, 
respectively: 
100(%) 14 
o
R
W
WW
EMC (Equation 5) 
100(%)
1
14 
RD
RDRD
RS (Equation 6) 
Where: 
EMCR and RS: Equilibrium moisture 
content and radial swelling of the veneer (%); 
Wo: Oven-dry weight of the veneer before 
chemical treatment (g); 
W1 and RD 1: Oven-dry weight (g) and 
radial dimension (mm) of the veneer after 
curing (before conditioning); 
W4 and RD4: Weight (g) and radial 
dimension (mm) of veneer after conditioning. 
The cyclohexan and ethanol (2:1, v/v) 
extraction was carried out for 6 h with 5 
veneers per treatment. The weight loss (WLE) 
determination was calculated in the same way 
as in the water extraction (Equation 7): 
100(%)
1
31 
W
WW
WLE (Equation 7) 
Where: 
WLE: Weight loss after extraction (%); 
W1: Oven-dry weight of veneer after curing (g); 
W3: Oven-dry weight of veneer after extraction (g). 
Ten veneers per treatment were submersed 
one by one in a water bath at room temperature 
for the continuous times: 1 min, 10 min, 1 h, 2 
h, 4 h (submersion 1). The water uptake (WU) 
and water repellent effectiveness (WRE) were 
calculated following Equation 8 and Equation 9: 
100(%) 
o
ba
W
WW
WU (Equation 8) 
Where: 
WU: Water uptake (%); 
Wa: Veneer weight (g) after water submersion 
(1 min, 10 min, 1 h, 2 h, 4 h); 
Wb: Veneer weight before water submersion (g); 
Wo: Oven-dry weight of veneer before chemical 
impregnation (g). 
For comparison of the water uptake between 
the treated and the control veneers, water 
repellent effectiveness (WRE) was expressed 
as in Equation 9: 
100(%) 
control
treatedcontrol
WU
WUWU
WRE (Equation 9) 
Where: 
WRE: Water repellent effectiveness (%); 
WUcontrol: Water uptake of control veneer (%); 
WUtreated: Water uptake of treated veneer (%). 
Then, the veneers were continued with 
oven-drying, organic solvent extraction, 
submersion 2 or submersion 3 (similar like 
submersion 1) as described in Fig 1. The 
weight loss of the veneers was based on 
oven-dried weight after curing and oven-
dried weight after extraction or submersion 
as follows: 
Forest Industry 
JOURNAL OF FORESTRY SCIENCE AND TECHNOLOGY NO. 2 - 2018 165
100(%)
1
21 
W
WW
WL (Equation 10) 
Where: 
WL: Weight loss after extraction, 
submersion (%); 
W1: Oven-dry weight of veneer after curing (g); 
W2: Oven-dry weight of veneer after 
extraction, submersion (g). 
Figure 1. Test procedure of the veneers 
Drying veneers at 103°C, 24 h 
Vacuum/pressure impregnation 
Pre-drying at room temperature for 2 days 
Curing by hot press at the different parameters 
Conditioning veneers in a climate chamber at 20°C and 65% RH 
(20 veneers/treatment) 
Cyclohexan and 
Ethanol (2:1) 
extraction 1 for 6 h 
(5 veneers/treatment) 
Submersion 1 
(10 veneers/treatment) 
WRE1 
Drying at 103°C, 24 h 
(5 veneers/treatment) 
Weight loss 1 
Cyclohexane and Ethanol 
(2:1) extraction 2 for 6 h 
(5 veneers/treatment) 
Drying at 103°C, 24 h 
(5 veneers/treatment) 
Drying at 103°C, 24 h 
 (5 veneers/treatment) 
Weight loss 3 
Submersion 3 
(5 veneers/treatment) 
WRE3 
Submersion 2 
(5 veneers/treatment) 
WRE2 
Drying at 103°C, 24 h 
(5 veneers/treatment) 
Weight loss 2 
Drying at 103°C, 24 h 
(5 veneers/treatment) 
Drying 
at 103°C, 24 h 
(5 veneers/ 
treatment) M, 
WPG, RBE, 
EMCR, RS 
Water extraction, 6 h 
Cutting veneers (37 × 0.5 × 50) mm3 
Cyclohexan and ethanol (2:1) extraction, 6 h 
Forest Industry 
JOURNAL OF FORESTRY SCIENCE AND TECHNOLOGY NO. 2 - 2018 166
III. RESULTS AND DISCUSSION 
3.1. Weight percent gain and radial 
bulking effect 
The veneers were extracted with hot water, 
and then cyclohexane and ethanol (2:1, v/v) 
prior to the impregnation and hot pressing. The 
WPGs of the control veneers showed minor 
negative values because the extractives in the 
veneers were continued removing during the 
impregnation and hot pressing (Figure 2). 
WPGs of the veneers treated with 5% solid 
content of mNMM-2 (catalyst RB) or 1% solid 
content of AKD did not change significantly 
when the temperature of the hot pressing 
increased from 130oC to 160oC. These WPGs 
did not depend on the pressing times (5 min, 
10 min, 20 min), either (Figure 2). 
WPGs of 10% NMM-1 treated veneers 
changed considerably when the temperature of 
the hot pressing increased from 130oC to 
160oC (WPGs were reduced from 22.6% to 
15.9%, relatively). 
Figure 2. Weight percent gain (WPG) and radial bulking effect (RBE) of the control and treated veneers 
Another experiment was processed to 
evaluate if the WPG of NMM-1 treated 
veneers reduced with increasing temperature of 
the hot pressing. 
Glass dishes containing 20 g of NMM-1 
stock solution were oven-dried for 24 h at 
different temperatures: 103oC, 120°C, 140°C, 
and 160°C. Then, these dishes were allowed to 
cool in desiccators to room temperature. 
Calculation of solid content was based on the 
weight of dried NMM-1 (solid, after drying) 
and the weight of NMM-1 stock solution 
(before drying) in each glass dish (w/w %). 
There were 3 replicates regard to each 
temperature. The results of this test are shown 
in table 1. 
Table 1. Solid content of NMM-1 stock solution at different temperatures 
Temperature (°C) 103 120 140 160 
Solid content (w/w %) 74.8 71.9 70.5 68.5 
Due to evaporation of some constituents in 
NMM-1 solution e.g. formaldehyde emission, 
the solid content of NMM-1 stock solution 
reduced with an increasing of oven-dried 
temperature. This is seen to be the reason for 
the decrease in WPG of NMM-1 treated 
veneers at higher temperature of the hot 
pressing besides loss in wood. 
-5
0
5
10
15
20
25
5 10 20
Pressing time (min)
W
e
ig
h
t 
p
e
rc
e
n
t 
g
a
in
 [
%
]
Control 130°C NMM-1 130°C mNMM-2 130°C AKD 130°C
Control 160°C NMM-1 160°C mNMM-2 160°C AKD 160°C
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Pressing time (min)
R
a
d
ia
l 
b
u
lk
in
g
 e
ff
e
c
t 
[%
]
Control 130°C NMM-1 130°C mNMM-2 130°C AKD 130°C
Control 160°C NMM-1 160°C mNMM-2 160°C AKD 160°C
5 10 20
Forest Industry 
JOURNAL OF FORESTRY SCIENCE AND TECHNOLOGY NO. 2 - 2018 167
With regard to above WPGs, only NMM-1 
treated veneers indicated a radial bulking 
effect (RBE, 1.9 - 2.7%), whereas the 
control, mNMM-2 and AKD treated veneers 
showed no RBE, even negative values 
(Figure 2). This bulking effect did not 
depend on the time or temperature of the hot 
pressing. Thus, longer pressing time or 
higher temperature did not enhance the 
deposition of these chemicals into the cell 
wall. Higher WPG and better penetration 
ability of melamine molecules into the cell 
wall resulted in bulking effect for NMM-1 
treated veneers. While low WPGs together 
with large particle sizes of mNMM-2 and 
AKD particles could be reasons for no 
bulking effect of the treated veneers. 
3.2. Equilibrium moisture content and 
radial swelling of the treated veneers at 
20°C and 65% RH 
As can be seen in figure 3, EMCR and RS of 
the veneers did not change when temperature 
and pressing time were changed. 
Only NMM-1 treated veneers exposed 
significantly lower EMCR and RS than the control 
veneers (2 - 3%). High dimensional stability of 
melamine resin treated wood under humid 
condition was confirmed in many previous studies 
(Deka and Saikia, 2000; Inoue et al., 1993; Pittman 
et al., 1994). EMCR and RS of the veneers treated 
with mNMM-2 and AKD were not clearly 
different from those of the control veneers. 
Figure 3. Equilibrium moisture content (EMC) radial swelling (RS) 
of the control and treated veneers at 20°C and 65% RH 
Compared to the veneers cured in a drying-
oven (Trinh and Nguyen, 2017), EMCR and RS 
of the veneers cured in the hot press were 
reduced in case of NMM-1 treatment due to 
higher WPG. On the contrary, EMCR and RS 
of mNMM-2 treated veneers cured in a hot 
press were higher than those cured in a drying-
oven because of the lower WPG. While AKD 
treated veneers always showed the same EMCR 
and RS values as the controls in both cases 
cured in an oven and a hot press machine, 
regardless of WPG. 
3.3. Water repellent effectiveness 
WRE 1 is the water repellent effectiveness 
of submersion 1 (as depicted in figure 1). This 
is the submersion of the veneers after curing 
and conditioning at 20°C and 65% RH. 
Similarly, WRE 2 is the water repellent 
8
9
10
11
12
13
14
15
5 10 20
Pressing time (min)
E
q
u
il
ib
ri
u
m
 m
o
is
tu
re
 c
o
n
te
n
t 
[%
]
Control 130°C NMM-1 130°C mNMM-2 130°C AKD 130°C
Control 160°C NMM-1 160°C mNMM-2 160°C AKD 160°C
1.0
1.5
2.0
2.5
3.0
5 10 20
Pressing time (min)
R
a
d
ia
l 
s
w
e
ll
in
g
 [
%
]
Control 130°C NMM-1 130°C mNMM-2 130°C AKD 130°C
Control 160°C NMM-1 160°C mNMM-2 160°C AKD 160°C
Forest Industry 
JOURNAL OF FORESTRY SCIENCE AND TECHNOLOGY NO. 2 - 2018 168
effectiveness of submersion 2 for the dried-
veneers after undergoing submersion 1. WRE 3 
was used for the dried-veneers after submersion 
1 and an organic solvent extraction. 
 A B C 
Figure 4. Water repellent effectiveness (WRE) of the veneers treated with 10% solid content of 
NMM-1, cured in a hot press (A: WRE 1, B: WRE 2, C: WRE 3) 
As described in figure 4, WRE 1 of 10% 
NMM-1 treated veneers was higher than WRE 
2 and WRE 3, regardless of hot pressing 
parameters (time and temperature). These 
results showed the same tendency as NMM-1 
treated veneers cured in a drying-oven when 
submersed in water after the cycles (Trinh and 
Nguyen, 2017). This can be explained by the 
leaching of NMM-1 after submersion 1. The 
WRE 3 was not reduced significantly 
compared to the WRE 2 because the veneers 
treated with NMM-1 resulted in no weight loss 
through cyclohexan and ethanol extraction. 
 A B C 
Figure 5. Water repellent effectiveness of the veneers treated with 5% solid content of mNMM-2 
(catalyst RB), cured in a hot press (A: WRE 1, B: WRE 2, C: WRE 3) 
Like the oven-cured veneers, WRE 2 and 
WRE 3 of 5% mNMM-2 treated veneers (with 
catalyst RB) were improved compared to WRE 
1 (Figure 5) most probable because hydrophilic 
compounds in the formulation were removed 
through submersion 1 and ongoing 
0
10
20
30
40
50
60
70
80
90
0 50 100 150 200 250
Water submersion time [min]
W
R
E
 1
 -
 N
M
M
-1
 [
%
]
130°C, 5 min 160°C, 5 min
0
10
20
30
40
50
60
70
80
90
0 50 100 150 200 250
Water submersion time [min]
W
R
E
 2
 -
 N
M
M
-1
 [
%
]
130°C, 10 min 160°C, 10 min
0
10
20
30
40
50
60
70
80
90
0 50 100 150 200 250
Water submersion time [min]
W
R
E
 3
 -
 N
M
M
-1
 [
%
]
130°C, 20 min 160°C, 20 min
0
10
20
30
40
50
60
70
80
90
0 50 100 150 200 250
Water submersion time [min]
W
R
E
 3
 -
 m
N
M
M
-2
 [
%
]
130°C, 20 min 160°C, 20 min
0
10
20
30
40
50
60
70
80
90
0 50 100 150 200 250
Water submersion time [min]
W
R
E
 1
 -
 m
N
M
M
-2
 [
%
]
130°C, 5 min 160°C, 5 min
0
10
20
30
40
50
60
70
80
90
0 50 100 150 200 250
Water submersion time [min]
W
R
E
 2
 -
 m
N
M
M
-2
 [
%
]
130°C, 10 min 160°C, 10 min
Forest Industry 
JOURNAL OF FORESTRY SCIENCE AND TECHNOLOGY NO. 2 - 2018 169
condensation occurred during the drying 
process. There was high weight loss due to the 
organic extraction; however, the WRE 3 was 
not lower than the WRE 2. 
 A B C 
Figure 6. Water repellent effectiveness of the veneers treated with 1% solid content of AKD, 
cured in a hot press (A: WRE 1, B: WRE 2, C: WRE 3) 
WRE of 1% AKD treated veneers was 
slightly reduced from submersion 1 to 
submersion 3 (Figure 6) due to leaching of 
AKD, the tendency is different from 10% 
AKD treated veneers cured in drying-oven 
(Trinh and Nguyen, 2017). This might be 
explained by leaching effect of hydrophilic 
emulsifier (cationic starch) in 10% AKD 
treated veneers. 
Water repellence of the veneers treated with 
10% NMM-1, 5% mNMM-2 (catalyst RB) or 
1% AKD was stable after the extraction with 
water and organic solvents. For these 
chemicals, curing at 130°C brought better 
results of WREs. 
3.4. Fixation of the chemicals 
Figure 7. Weight loss after cyclohexane and 
ethanol extraction of the control and treated veneers 
Figure 8. Weight loss after submersion 1 and 
submersion 2 of the control and treated veneers 
In this study, the fixation of the chemicals 
(N-methylol melamine and ADK) in the 
treated veneers was reflected by different 
weight losses after cyclohexane and ethanol 
extraction, water submersion. The weight 
losses after cyclohexane and ethanol extraction 
1 (weight loss 1) of the control and NMM-1 
treated veneers showed negative values for all 
processes. In contrast, the weight loss 1 of 
mNMM-2 (catalyst RB) and AKD treated 
veneers was quite high, even more than 50% 
comparable to their WPGs. There was 
0
10
20
30
40
50
60
70
80
90
0 50 100 150 200 250
Water submersion time [min]
W
R
E
 1
 -
 A
K
D
 [
%
]
130°C, 5 min 160°C, 5 min
0
10
20
30
40
50
60
70
80
90
0 50 100 150 200 250
Water submersion time [min]
W
R
E
 2
 -
 A
K
D
 [
%
]
130°C, 10 min 160°C, 10 min
0
10
20
30
40
50
60
70
80
90
0 50 100 150 200 250
Water submersion time [min]
W
R
E
 3
 -
 A
K
D
 [
%
]
130°C, 20 min 160°C, 20 min
-3
-2
-1
0
1
2
3
4
5
Pressing time (min)
W
e
ig
h
t 
lo
s
s
 1
 [
%
]
Control 130°C NMM-1 130°C mNMM-2 130°C AKD 130°C
Control 160°C NMM-1 160°C mNMM-2 160°C AKD 160°C
5 10 20
-1
0
1
2
3
4
5 10 20
Pressing time (min)
W
e
ig
h
t 
lo
s
s
 2
 [
%
]
Control 130°C NMM-1 130°C mNMM-2 130°C AKD 130°C
Control 160°C NMM-1 160°C mNMM-2 160°C AKD 160°C
Forest Industry 
JOURNAL OF FORESTRY SCIENCE AND TECHNOLOGY NO. 2 - 2018 170
insignificant difference of weight loss 1 
between the different hot pressing processes of 
the veneers (Figure 7). 
Weight loss 2 of the control, NMM-1 and 
AKD treated veneers were low (less than 
1.0%). As compared to the WPG, weight loss 2 
of NMM-1 was very small while weight loss 2 of 
mNMM-2 treated veneers was high (Figure 8). 
Figure 9. Weight loss after submersion 1, cyclohexane and ethanol extraction, and submersion 3 
of the control and treated veneers 
For the control and NMM-1 treated veneers, 
weight loss 2 and weight loss 3 were not 
considerably different, because these veneers 
did not get weight loss through the extraction 
with cyclohexan and ethanol. On the contrary, 
weight loss 3 of mNMM-2 and AKD treated 
veneers was significantly higher than weight 
loss 2 (Figure 9). 
There were no influences of hot pressing 
time and temperature on weight losses of the 
control, NMM-1 and AKD treated veneers. 
Weight losses of mNMM-2 treated veneers 
were lower at the higher hot pressing 
temperature (160°C), however, WRE 3 of 
mNMM-2 treated veneers was higher for the 
veneers pressed at 130°C. 
IV. CONCLUSIONS 
Regardless of the chemical treatments, 
water repellent effectiveness of the treated 
veneers after soxhlet with organic solvents 
and water submersion imparted optimum 
results for the veneers cured by hot pressing 
at 5 min and 130°C. The influence of the hot 
pressing time and temperature on WPG and 
radial bulking, EMCR and radial swelling, 
and weight loss after extraction did not 
showed detrimental effects in case of the 
veneers cured by hot pressing at 5 min and 
130°C in comparison to the other hot 
pressing processes. Hence, the time of 5 
minutes and the temperature of 130°C were 
selected for curing by hot press of the 
impregnated veneers. 
The applied concentrations of the selected 
chemicals NMM-1 (10% solid content), 
mNMM-2 (5% solid content, catalyst RB 
1.9%), AKD (1% solid content) have been 
shown to bring about sufficient water repellent 
effect for the treated veneers. 
REFERENCES 
1. Deka, M. and Saikia, C.N. (2000). Chemical 
modification of wood with thermosetting resin: effect on 
dimensional stability and strength property. Bioresource 
Technology, 73(2): 179-181. 
2. Dieste, A., Krause, A., Bollmus, S. and Militz, H. 
(2009). Gluing ability of plywood produced with 
DMDHEU-modified veneers of Fagus sp., Betula sp., 
and Picea sp. International Journal of Adhesion and 
Adhesives, 29: 206-209. 
3. EN 350:2016 Durability of wood and wood-
based products - Testing and classification of the 
durability to biological agents of wood and wood-
based materials. 
4. Inoue, M., Ogata, S., Nishikawa, M., Otsuka, 
Y., Kawai, S. and Norimoto, M. (1993). Dimensional 
stability, mechanical-properties, and color changes of 
a low-molecular-weight melamine-formaldehyde 
-1
0
1
2
3
4
5
6
5 10 20
Pressing time (min)
W
ei
g
h
t 
lo
s
s 
3
 [
%
]
Control 130°C NMM-1 130°C mNMM-2 130°C AKD 130°C
Control 160°C NMM-1 160°C mNMM-2 160°C AKD 160°C
Forest Industry 
JOURNAL OF FORESTRY SCIENCE AND TECHNOLOGY NO. 2 - 2018 171
resin impregnated wood. Mokuzai Gakkaishi, 39(2): 
181-189. 
5. Pittman, C.U., Kim, M.G., Nicholas, D.D., 
Wang, L.C., Kabir, F.R.A., Schultz, T.P. and Ingram, 
L.L. (1994). Wood enhancement treatments 1. 
Impregnation of Southern yellow pine with melamine-
formaldehyde and melamine-ammeline-formaldehyde 
resins. Journal of Wood Chemistry and Technology, 
14(4): 577-603. 
6. Trinh Hien Mai (2016). Effect of veneer curing 
process on bonding quality of modified plywood. 
Journal of Forest Science and Technology, Vietnam 
National University of Forestry, ISSN 1859-3828, 
Volume 3, 2016. 
7. Trinh Hien Mai, Nguyen Minh Hung (2017). 
Water uptake, moisture absorption and wettability of 
Beech veneer treated with N-methylol melamine 
compounds and alkyl ketene dimer. Journal of Forest 
Science and Technology, Vietnam National University of 
Forestry, ISSN 1859-3828, Volume 5, 2017. 
8. Wepner and Militz (2005). Fungal resistance, 
dimensional stability and accelerated weathering 
performance of N-methylol treated veneers of Fagus 
sylvatica. Proceeding of the second European 
conference on wood modification. 
9. Wepner, F., Krause, A. and Militz, H. (2007). 
Weather resistance of N-methylol treated plywood 
panels. Proceedings of the 2nd International Symposium 
on the Veneer Processing and Products, Vancouver, 
B.C, Canada, 305-314. 
ẢNH HƯỞNG CỦA THÔNG SỐ CHẾ ĐỘ XỬ LÝ NHIỆT 
ĐẾN SỰ CỐ ĐỊNH LẠI CỦA HÓA CHẤT VÀ KHẢ NĂNG CHỐNG HÚT NƯỚC 
CỦA VÁN MỎNG GỖ BEECH BIẾN TÍNH 
Trịnh Hiền Mai 
Trường Đại học Lâm nghiệp 
TÓM TẮT 
Trong nghiên cứu này, ván mỏng lạng từ gỗ Beech (Fagus sylvatica. L) với kích thước 37 × 0.5 × 50 mm3 (XT 
× TT × DT) đã được lọc rửa qua thiết bị soxhlet bằng nước nóng và các dung môi hữu cơ (cyclohexan và 
ethanol, tỷ lệ thể tích 2:1), sau đó ván mỏng được sấy khô trước khi ngâm tẩm với các dung dịch hóa chất biến 
tính. Ba loại hóa chất đã được sử dụng để biến tính ván mỏng là: N-methylol melamine (NMM-1 - sử dụng ở 
hàm lượng rắn 10%), fatty acid modified N-methylol melamine/paraffin (mNMM-2 - sử dụng ở hàm lượng rắn 
5%), alkyl ketene dimer (AKD - sử dụng ở hàm lượng rắn 1%). Ván mỏng sau khi tẩm hóa chất biến tính được 
hong phơi 2 ngày ở điều kiện phòng rồi xử lý nhiệt (curing) trong máy ép nhiệt với các thông số chế độ ép 
(nhiệt độ và thời gian) khác nhau. Cụ thể: nhiệt độ: 130°C, 160°C; áp suất: 1 N/mm2; thời gian ép: 5, 10, 20 
phút. Kết quả nghiên cứu cho thấy: thời gian ép 5 phút và nhiệt độ ép 130°C không gây ảnh hưởng xấu đến tỷ 
lệ tăng khối lượng (WPG) và tỷ lệ tăng kích thước chiều tiếp tuyến (RBE), độ ẩm thăng bằng (EMCR) và tỷ lệ 
trương nở chiều tiếp tuyến (RS) (trong môi trường 20°C, độ ẩm 65%), và tỷ lệ tổn hao khối lượng (WL). Bên 
cạnh đó, khả năng chống hút nước của ván mỏng biến tính sau khi bị lọc rửa qua thiết bị soxhlet với các dung 
môi hữu cơ và các lần ngâm nước cho kết quả tốt nhất trong trường hợp ván mỏng được xử lý nhiệt ở chế độ: 
thời gian ép 5 phút và nhiệt độ ép 130°C. Hơn thế nữa, giảm thời gian và nhiệt độ của quá trình xử lý nhiệt 
trong máy ép nhiệt có thể ngăn chặn được hiện tượng “sấy quá” của ván mỏng trước khi tráng keo để sản xuất 
ván dán. Do đó, thời gian ép 5 phút và nhiệt độ ép 130°C đã được lựa chọn để xử lý nhiệt ván mỏng trong máy 
ép nhiệt. Ảnh hưởng của thông số chế độ xử lý nhiệt (bằng máy ép nhiệt) đến các tính chất của ván mỏng biến 
tính với mỗi loại hóa chất đã được thảo luận chi tiết trong bài báo. 
Từ khóa: Alkyl ketene dimer, độ ẩm thăng bằng, khả năng chống hút nước, N-methylol melamine, sự cố 
định lại của hóa chất, ván mỏng gỗ beech (Fagus sylvatica. L). 
Received : 26/01/2018 
Revised : 30/3/2018 
Accepted : 05/4/2018