Effects of rosin sizing agent on the fixation of boron in styrax tonkinensis wood

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EFFECTS OF ROSIN SIZING AGENT ON THE FIXATION OF BORON 
IN STYRAX TONKINENSIS WOOD 
Nguyen Thi Thanh Hien1, Li Shujun2 
1Vietnam National University of Forestry 
2Northeast Forestry University, China. 
SUMMARY 
The aim of this study was to evaluate the effect of rosin sizing agent upon fixing boron in Styrax tonkinensis 
(Piere) wood treated with mixtures of 3% boric acid and 1% rosin sizing agent. After treatment, wood samples 
were also analyzed by scanning electron microscope observation and energy-dispersive X-ray spectroscopy 
(SEM-EDX). The results showed that all boron-rosin formulations impregnated Styrax tonkinensis wood evenly 
penetrated into the wood blocks. Boron-rosin treatment decreased by 16% the amount of boron leaching from 
treated wood samples compared with those from the samples treated with boric acid alone. The SEM-EDX 
analysis proved that the boron element was still in the cell lumens of boron-rosin treated wood blocks after 
leaching. Results indicated that rosin emulsion sizing agent can have an effect on the fixation of boron in wood. 
This signifies that using of rosin as fixing agents may contribute to lead to wood treated with boron based 
preservatives being more widely used. 
Keywords: Boron, boron-rosin, leaching resistance, rosin. 
I. INTRODUCTION 
Boron compounds exhibit good biocidal 
activities when used in wood preservative 
formulations. Nevertheless, they have limited 
utility in outdoor applications due to their high 
solubility in water which cause leaching from 
impregnated wood (Yalinkilic, 2000). 
Therefore, several xation systems to limit or 
decrease boron leachability from treated wood 
have been developed. For example a 
combination of boron with: glycerol/glyoxal, 
vinyl monomers, silanes, alkydes, tall oil 
derivates, protein, water repellent compound, 
lique ed wood, and montan wax emulsions 
(Köse et al., 2011; Obanda et al., 2008; Lesar 
et al., 2009, 2012; Sen et al., 2009; Temiz et 
al., 2008; Tomak et al., 2011). However, due to 
the high costs or a two-step treatment, the 
above-mentioned approach could have not 
been deployed in practice. 
Rosin is a product obtained from pines and 
some other plants. It is abundant, natural, and 
renewable. The major component of rosin is 
abietic acid, a partially unsaturated compound 
with three fused six-membered rings and one 
carboxyl group (Song, 2002). Therefore, it has 
a good hydrophobic property. Over the years, 
rosin was extensively applied in the paper 
industry as a sizing agent (Zhang, 2005). In our 
earlier investigations, the rosin sizing agent 
was used to impregnate poplar wood and the 
results showed that the rosin sizing agent can 
reduce the moisture absorption ability of 
poplar wood and contributes to improving 
wood decay resistance (Nguyen et al., 2012; Li 
et al., 2009, 2011). This paper presents results 
from a preliminary study to reduce the 
leachability of boron using a naturally dirived 
product - the rosin sizing agent to develop new 
formulations for wood preservation. 
II. RESEARCH METHODOLOGY 
2.1. Material preparations 
Styrax tonkinensis (Piere) wood was 
selected according to the Chinese standard GB 
1929 (2009) (same as ISO 3129). Wood 
specimens were cut from untreated Styrax 
tonkinensis sapwood into wood blocks with 
dimensions of 20 × 20 × 20 mm. Deficiency-
free cubes were selected for the tests. The 
weight differences of the chosen blocks did not 
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exceed 0.5 g. 
The anionic rosin emulsion sizing agent (R) 
was an industrial product and was supplied by 
Guangxi Wuzhou Arakawa Chemical 
Industries Co., Ltd. In this study, it was used to 
impregnate into wood at the concentration of 
1%. And 3% Boric acid (H3BO3) was provided 
by Tianjin Kermel Chemical Reagent Co., Ltd., 
was used as a preservative salts. It was also 
combined with the rosin emulsion sizing agent 
to impregnate wood. 
2.2. Treating wood blocks 
Before treatment, all sapwood blocks were 
oven-dried at 103oC overnight, weighed to the 
nearest 0.01 g and recorded as W1. The blocks 
were then vacuum-treated with the treatment 
solution. The vacuum was applied for 30 min 
at 0.1 MPa before supplying the solution into 
the chamber. After the application another 30 
min at 0.1 MPa vacuum diffusion period 
followed. Then, the blocks were kept in the 
treatment solution at ambient conditions until 
complete saturation. The blocks were then 
individually removed from the solution, wiped 
lightly to remove solution from the wood 
surface, and immediately weighed to the 
nearest 0.01 g to determine the mass after 
impregnation (W2). The theory retention of 
each block was calculated using the following 
formula: 
10 = kg/m retention,Theory 3 
V
GC
 (1) 
Where G = W2-W1 is the weight in grams of 
the treating solution absorbed by the block, C 
is the weight (g) of preservative in 100 grams 
of treating solution, and V is the volume of the 
block in cubic centimeters. 
After calculating the retention, the treated 
samples were air-dried for 48 hours, and oven-
dried at 103 °C overnight, and then weighed to 
determine the dry weights of the wood blocks 
after treatment. The difference between the dry 
weights before and after treatment is the actual 
retention of each block. And the percentage of 
actual retention to the theory retention was 
regarded as the treatability of each preservative 
formulation. 
2.3. Leaching treated wood blocks 
Leaching of boron was determined 
according to the standard of the American 
Wood Preservers’ Association E11 (AWPA 
E11 2007). Twelve blocks per treatment were 
air-dried, then immersed in beakers of distilled 
water over which a vacuum was applied for 30 
min. Then the vacuum was released and the 
wood blocks were immersed in the distilled 
water. After 6 h, 24 h, 48 h, and 48-h intervals 
the leaching water was removed and replaced 
with an equal amount of fresh distilled water. 
Leaching was carried out for a total of 14 days. 
All leachates were collected and kept for boron 
analysis. 
2.4. Boron analysis 
In order to measure the contents of boron 
leached from the treated wood blocks, the 
leachates were analyzed by using the 
azomethine-H method described by John et al. 
(1975) and following American Wood 
Preservers’ Association standard method 
AWPA A2-07. 
2.5. Microscopic observation 
Small samples of dimensions 10 × 10 × 1 
mm were cut from the untreated control and 
the treated wood blocks, and located 3 mm 
from each radial, tangential, and transverse 
surface of the wood block. Each sample was 
mounted on a metal stub with adhesive, and 
then they were placed under vacuum and were 
sputter-coated with a thin layer (approximately 
20 nm thick) of gold. The samples were then 
observed with a scanning electron microscope 
(SEM, FEI Quanta 200, USA) at an 
accelerating voltage of 20 kV. Random 
observations were made on different structures 
to identify the existence of boron in the 
anatomical structure of the samples. The 
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element compositionwas determined by 
regional analysis using an energy dispersive X-
ray spectrometer (EDX) combined with the 
SEM. 
III. RESULTS AND DISCUSSION 
3.1. Retention results 
Retention levels of Styrax tonkinensis 
wood samples treated with boron-rosin 
solutions (as kilograms per cubic meter) and 
the actual percent retention of preservative 
formulations in wood blocks are recorded in 
Table 1. Total uptake of the treating solution in 
Styrax tonkinensis wood, including both rosin 
alone and in combination with boron, were 
relatively uniform. The actual retention of the 
rosin sizing agent alone or boron-rosin 
preservative was very close to theory retention. 
The actual percent retention of preservative 
solution containing rosin only or containing 
boric acid was 92.97% and 97.74%, 
respectively. However, when rosin sizing agent 
combined with boric acid to impregnate wood, 
the actual percent retention of presevative 
solution was 96.41%. Results indicate that the 
concentration of the solutions considered to 
impregnate Styrax tonkinensis wood using the 
impregnation method described did not 
influence the penetration of the preservative 
complexes into the wood blocks. Which could 
be proved by SEM analysis. 
Table 1. Retention levels and treatability of wood samples treated with boron-rosin solutions 
Abbreviation Concentrations 
Theory Retention 
(kg/m3) 
Actual Retention 
(kg/m3) 
Treatabilitya 
(%) 
1 1% R + 3% H3BO3 26.15 (1.07)
b 25.20 (2.77) 96.41 (10.31) 
2 3% H3BO3 17.12 (0.97) 16.74 (1.66) 97.74 (7.71) 
3 1% R 6.47 (0.47) 6.01 (0.68) 92.97 (9.59) 
Note：aTreatability refers to the percentage of actual retention to the theory retention. 
b All results are means of 24 samples. Standard deviations are in brackets. 
Figure 1. Boron released from the treated wood samples at different time intervals 
(BA: boric acid (H3BO3), R: rosin sizing agent) 
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3.2. Boron leaching 
The amount of boron ions released from the 
wood samples treated with boric acid solution 
alone or in combination with rosin at different 
time intervals are presented in Figure 1. The 
results show that a large amount of boron ions 
was leached out from the wood samples treated 
with boric acid alone. After 14 days of 
leaching, 1338 mg of boron was leached out 
from the samples. However, after 1% rosin 
sizing agent was added, the observed leaching 
of the boron was 1122 mg, in comparison to 
the treated samples with boric acid alone, the 
extent of boron leaching reduced was 16%. 
These results suggest that the rosin can 
contribute to improving boron fixation in wood. 
This was probably due to the hydrophobic 
property of rosin. After having penetrated into 
the wood blocks, the rosin molecules present in 
the cell lumen and forming an adhesive lm 
that covers the boron crystals (Nguyen et al., 
2013). During the leaching process, the rosin 
acted as a barrier that slowed down boron 
release from deep inside of the samples, which 
resulted in the reduction of the boron ion 
diffusing from wood during the leaching 
process. 
a) b) 
c) d) 
Figure 2. SEM images of tangential section of control wood block (a) and boric acid alone (b), 
rosin alone (c) and boron-rosin treated wood samples (d) 
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3.3. Microscopic observation 
Figure 2 shows the SEM images of the 
wood sample before and after treatment. 
untreated control and wood samples treated 
with boron-rosin solutions. It can be clearly 
seen that surface of wood cell wall of the 
control sample was extremely smooth and no 
preservative complexes was detected in any 
part of the untreaed control wood blocks (Fig. 
2a). When the wood blocks treated with only 
boric acid were observed, various crystal 
particles were found in the cell lumens (Fig. 
2b). The spot analysis using SEM-EDX proved 
that these particles contained B (Fig. 3ab). 
When the wood blocks treated with rosin alone, 
various spherical agglomerates were easily 
detected in the cell lumen (Fig. 2c). However, 
unlike the crystals in Figure 2b or spherical 
agglomerates in Figure 2c, various spherical 
agglomerates were easily detected in the cell 
lumen of the wood blocks treated with boron-
rosin formulation, these agglomerates were 
tightly adhered to the wood cell wall (Fig. 2d). 
The spectrum obtained from the spot analysis 
confirmed that these agglomerates contained 
the element B and they had a lower B content 
in comparison to that observed in the crystal 
particles (Fig. 3cd). This signifies easily 
penetrated into the wood blocks. 
Figure 4 shows SEM images corresponding 
spectrum of tangential sections of treated wood 
blocks after leaching. For wood blocks treated 
with boric acid alone, after leaching no crystal 
particles was detected by SEM observation 
(Fig. 4a). This revealed that after leaching, 
boric acid seemed to be completely leached out 
from treated wood. However, when the leached 
wood blocks treated with boron-rosin were 
observed, the spherical agglomerates were still 
detected in the cell lumens (Fig. 4b). In 
addition, the spot analysis using SEM-EDX 
proved that these agglomerates contained the 
element B (Fig. 4cd). This signi es that the 
rosin formed an adhesive lm to cover the 
boron crystals and the resulting boron was 
xed into the wood blocks. 
a) b) 
c) d) 
Figure 3. SEM images (left) and corresponding spectrum (right) of tangential section of unleached 
wood blocks treated with boric acid alone (a,b) and boron-rosin solution (c,d) 
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a) b) 
c) d) 
Figure 4. SEM images and corresponding spectrum of tangential section of leached wood blocks 
treated with boron alone (a) and boron-rosin solution (b, c, d). 
IV. CONCLUSIONS 
This study evaluated the effect of rosin 
sizing agent on the fixation of boron in styrax 
tonkinensis wood. The results showed that 
using rosin alone or in combination with boric 
acid solution to impregnated Styrax tonkinensis 
wood by the impregnation method described 
did not influence the penetration of the 
preservative complexes into the wood blocks. 
The rosin sizing agent had have a certain effect 
on the fixation of boron in wood. The amount 
of boron ions released from the samples treated 
with the boron-rosin solution reduced by 16% 
compared with those from the samples treated 
with boric acid alone. The SEM-EDX analysis 
of the wood blocks treated with boron-rosin 
formulation confirmed that the preservative 
complexes containing B still existed in the cell 
lumens of wood, even after leaching. The use 
of rosin as fixing agents may contribute to lead 
to wood treated with boron based preservatives 
being more widely used. 
Acknowledgements 
The authors are grateful for the support of 
the Vietnam National University of Forestry. 
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ẢNH HƯỞNG CỦA KEO NHỰA THÔNG 
ĐẾN KHẢ NĂNG CỐ ĐỊNH BORON TRONG GỖ BỒ ĐỀ 
Nguyễn Thị Thanh Hiền1, Li Shujun2 
1Trường Đại học Lâm nghiệp 
2Trường Đại học Lâm nghiệp Đông Bắc, Trung Quốc 
TÓM TẮT 
Mục đích của nghiên cứu này là đánh giá ảnh hưởng của keo nhựa thông đến khả năng rửa trôi của boron từ gỗ 
Bồ đề được xử lý bởi hỗn hợp của 3% axit boric và 1% keo nhựa thông. Các mẫu gỗ sau khi xử lý được quan 
sát và phân tích bằng một phổ kế tán sắc năng lượng tia X kết hợp với kính hiển vi điện tử (SEM-EDX). Kết 
quả cho thấy rằng tất cả các công thức boron - nhựa thông được ngâm tẩm vào gỗ Bồ đề đều thẩm thấu tốt vào 
các mẫu gỗ thí nghiệm. Gỗ được xử lý bởi công thức kết hợp boron-nhựa thông đã giảm 16% lượng boron bị 
rửa trôi so với khi chỉ sử dụng axit boric để xử lý. Kết quả phân tích SEM-EDX cũng đã chứng minh nguyên tố 
B vẫn tồn tại trong khoang tế bào của gỗ được xử lý bởi boron-nhựa thông sau khi rửa trôi. Kết quả đã cho thấy 
rằng dung dịch keo nhựa thông có một ảnh hưởng nhất định đến khả năng cố định boron trong gỗ. Điều này gợi 
ý rằng sử dụng nhựa thông để làm chất cố định có thể góp phần nâng cao khả năng sử dụng của gỗ được xử lý 
bởi các hợp chất chứa boron. 
Từ khóa: Boron, boron-nhựa thông, kháng rửa trôi, nhựa thông. 
Received : 22/3/2017 
Revised : 27/4/2017 
Accepted : 10/5/2017