Water uptake, moisture absorption and wettability of beech veneer treated with N-Methylol melamine compounds and alkyl ketene dimer

 chemical reaction 
approx. 20%, much higher than those of the with hydroxyl groups of the cell wall (Nguyen 
other treatments. et al., 2007). 
 High WREs of mNMM-2 treatment can be 3.2. Sorption behavior at different relative 
explained by the location in the cell lumen of humidity 
the polymerized chemicals which cause less Wood is a hygroscopic material due to 
free space for water in capillary and close hydroxyl groups of cell wall polymers, 
penetration paths of water. Besides, paraffin especially cellulose. When dry-wood is 
proportion in these mNMM compounds also exposed to a humid environment, the wood 
resulted in considerable hydrophobic effect. In absorbs water vapor until its moisture content 
 JOURNAL OF FORESTRY SCIENCE AND TECHNOLOGY NO. 5 - 2017 147
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becomes sufficient high to be equilibrium with and swelling/shrinking of the treated wood in a 
the ambient atmosphere. This moisture specific humid environment depend on cell 
content, namely equilibrium moisture content wall bulking and covalent bonds of the reagent 
(EMCR), is approximately proportional to the with hydroxyl groups of the wood cell wall 
ambient relative humidity (RH) and (Rowell and Banks, 1985). Moreover, there is 
temperature (Skaar, C., 1998). As water vapor a direct relationship between the decrease in 
enters the wood cell wall, the space in the cell EMCR and the increase in resistance against 
wall is occupied, causing increase in fungal attack as discussed by Rowell (2005) 
dimension of the cell wall, as a result, the and Hill (2002). Therefore, the reduction in 
wood swells (Hill, 2006). EMCR and swelling/shrinking is one of the 
 With regard to wood modification, EMCR aims of wood modification. 
 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 Radial swelling 
 No Treatment EMCR (%) RS (%) 
 30% RH 65% RH 90% RH 30% RH 65% RH 90% RH 
 1 Control 4.62 13.60 18.42 0.84 2.79 3.74 
 STDEV 0.13 0.17 0.29 0.04 0.09 0.04 
 2 AKD 4.13 13.55 18.40 0.80 2.77 3.79 
 STDEV 0.16 0.15 0.29 0.04 0.09 0.10 
 3 NMM-1 4.10 12.37 16.72 0.61 2.27 3.09 
 STDEV 0.20 0.30 0.33 0.05 0.10 0.15 
 4 mNMM-2 3.69 12.64 17.01 0.70 2.52 3.40 
 STDEV 0.30 0.48 0.46 0.03 0.12 0.13 
 At 30, 65, 90% relative humidity (RH) and results from the esterification of AKD 
20°C, all the treated veneers (except AKD molecules with hydroxyl groups of wood 
treatments) showed slight reduction in EMCR cellulose and the orientation of alkyl chains 
and radial swelling (RS) compared to the due to heat effect. However, large AKD 
control veneers (Table 2). Thus, the chemicals particles could not penetrate and modify the 
more or less penetrated into the cell wall, cell wall; this was reflected by no cell wall 
deposited in micro voids, created covalent bulking. AKD could only form a hydrophobic 
bonds or cross-linking with hydroxyl groups of layer onto external and internal cell lumen 
the cell wall, these were reflected by radial surfaces. Consequently, AKD dispersion could 
bulking effect (RBE) as well. provide good water repellence in initial phases 
 AKD treated veneers could not impede of water submersion but not reduce EMCR and 
water sorption in the cell wall after a long RS in humid environment for the treated 
exposure in humidity climate. EMCR and RS veneers. 
of AKD and paraffin treated veneers were N-methylol melamine (NMM) molecules 
equal or slightly higher as compared to those are believed to form three dimension network 
of the control veneers. It is assumed that in the cell wall (Lukowsky, 1999), hence micro 
hydrophobic properties of AKD treated wood voids in the cell wall could be filled with 
148 JOURNAL OF FORESTRY SCIENCE AND TECHNOLOGY NO. 5 - 2017 
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NMM resins. The quantity of NMM resin in The fatty acid modified N-methylol 
the cell walls mostly depends on molecular melamine (mNMM-2) treated veneers caused 
weight, degree of methylolation, solution moderate reduction in EMCR (1 - 1.4%) and 
concentration and method of impregnation RS (0.3 - 0.4%) in comparison to the control 
(Hansmann et al., 2006), the higher amount of veneers. This can be explained with the fact 
NMM in the cell walls, the more reduction in that a part of mNMM dispersions may 
EMCR and RS. penetrate into the cell wall; block micro voids 
 The NMM-1 treated veneers exhibited and create covalent bonds or cross linking with 
around 1.7% lower in EMCR and 0.6% lower hydroxyl groups of the wood cell wall. 
in RS compared to those of the control veneers 3.3. Contact angle 
at 90% RH and 20°C. Due to the deposition of The values of contact angle measured at the 
NMM-1 resin into the cell wall (with cell wall phase boundary between wood and liquid 
bulking), the empty space of micro voids is standard provide an issue point for the study of 
believed to be smaller; the ability for thermodynamic properties of wood surface. 
adsorption of water vapor was lessened, and, The values of this angle are used to calculate 
as a consequence, the EMCR and RS were surface free energy and reflect wettability of 
reduced. 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 after water drop was applied on veneer surface; 
angle of the untreated veneers reduced very and showed insignificant difference. Therefore, 
fast in the first 5 seconds, and then reduced wettability of AKD, NMM-1 and mNMM-2 
slowly to about 35° after 17 seconds. Congtact treated veneers presented much lower than the 
angle of the control veneers was much higher untreated and control veneers. 
than that of untreated veneers because hot IV. CONCLUSIONS 
press curing made veneers become more Beech veneers were impregnated with 10% 
hydrophobic. Contact angle values of AKD, solid content of the AKD, NMM-1 and 
NMM-1 and mNMM-2 treated veneers were mNMM-2 chemicals. High water repellence 
almost consistant during the first 20 seconds of the treated veneers resulted from the closing 
 JOURNAL OF FORESTRY SCIENCE AND TECHNOLOGY NO. 5 - 2017 149
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 water paths in lumen or blocking micro voids formaldehyde resin to improve the hardness of Norway 
 and/or hydroxyl groups of the cell wall as spruce wood. Journal of Applied Polymer Science, 
 93(4): 1900-1907. 
 discussed in details. The cycle after each 8. Gindl, W., Müller, U. and Teischinger, A. (2003) 
 submersion did not result in significant change Transverse compression strength and fracture of spruce 
 of WREs in the second, third and fourth wood modified by melamine-formaldehyde 
 submersion although weight loss of each impregnation of cell walls. Wood and Fiber Science, 
 35(2): 239-246. 
 treatment increased from the first cycle to the 9. Hill, C.A.S. and Papadopoulos, A.N. (2001) A 
 fourth submersion. Consequently, it can be review of methods used to determine the size of the cell 
 stated that, the water repellence of the treated wall micro voids of wood. Journal Institute Wood 
 veneers was stable after the wetting-drying Science, 90: 337-345. 
 10. Hill, C.A.S. (2002). How does the chemical 
 cycles. modification of wood provide protection against decay 
 Sorption behavior is related to the properties fungi? Presentation for Cost E22 - Finland. 
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 hydroxyl groups or deposit into the cell wall W. (2006) Artificial weathering of wood surfaces 
 induced the reduction in EMCR and RS for the modified by melamine formaldehyde resins. Holz als 
 treated veneers, while large AKD particles Roh-und Werkstoff, 64(3): 198-203 
 13. Hubbe, M.A. (2006) Paper's resistance to wetting 
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 modification of particleboard chips. Holz als Roh-und 
 wettability were in accordance with the water Werkstoff, 67(1): 37-45. 
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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 : 14/9/2017 
 Revised : 02/10/2017 
 Accepted : 10/10/2017 
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