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

Forest Industry

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.

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.

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.

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

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

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exceed 0.5 g.

retention of each block. And the percentage of

actual retention to the theory retention was

regarded as the treatability of each preservative

formulation.

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

2.3. Leaching treated wood blocks

Leaching of boron was determined

according to the standard of the American

by Tianjin Kermel Chemical Reagent Co., Ltd., Wood Preservers’ Association E11 (AWPA

was used as a preservative salts. It was also

combined with the rosin emulsion sizing agent

to impregnate wood.

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.

2.2. Treating wood blocks

Before treatment, all sapwood blocks were

oven-dried at 103^oC 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:

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

GC

Theory retention, kg/m³=

10

(1)

V

Where G = W₂-W₁is 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

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element compositionwas determined by

regional analysis using an energy dispersive X-

ray spectrometer (EDX) combined with the

SEM.

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.

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

Table 1. Retention levels and treatability of wood samples treated with boron-rosin solutions

Theory Retention

(kg/m³)

Actual Retention

(kg/m³)

Treatability^a

(%)

Abbreviation

Concentrations

1

2

3

1% R + 3% H₃BO₃

3% H₃BO₃

1% R

26.15 (1.07)^b

17.12 (0.97)

6.47 (0.47)

25.20 (2.77)

16.74 (1.66)

6.01 (0.68)

96.41 (10.31)

97.74 (7.71)

92.97 (9.59)

Note：^aTreatability refers to the percentage of actual retention to the theory retention.

^bAll 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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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.

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%.

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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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.

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).

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

When the wood blocks treated with rosin alone, wood blocks treated with boron-rosin were

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).

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)

Element Wt%

BK

CK

OK

01.16

61.66

37.18

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).

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.

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

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

Revised

Accepted

: 22/3/2017

: 27/4/2017

: 10/5/2017

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