Physico-Mechanical Properties of Tropical Wood Treated with Novel Organotin (IV) Complexes

European Journal of Scientific Research

ISSN 1450-216X Vol. 89 No 4 October, 2012, pp.512-522

© EuroJournals Publishing, Inc. 2012

http://www.europeanjournalofscientificresearch.com

Physico-Mechanical Properties of Tropical Wood

Treated with Novel Organotin (IV) Complexes

Md. Masudur Rahman

Faculty of Resource Science and Technology, University Malaysia Sarawak

94300 Kota Samarahan, Sarawak, Malaysia

E-mail: masudaf2007@yahoo.com

Tel: +60 82 582990; Fax: +60 82 583160

Ismail Jusoh

Faculty of Resource Science and Technology

University Malaysia Sarawak, Sarawak, Malaysia

Md. Abu Affan

Faculty of Resource Science and Technology

University Malaysia Sarawak, Sarawak, Malaysia

Ahmad Husaini

Faculty of Resource Science and Technology

University Malaysia Sarawak, Sarawak, Malaysia

Sinin Hamdan

Faculty of Engineering, University Malaysia Sarawak

Sarawak, Malaysia

Md. Saiful Islam

Faculty of Engineering, University Malaysia Sarawak

Sarawak, Malaysia

Abstract

Physical and mechanical properties of wood are important criteria for selection and

designing of wood constructions. However, chemical treatment of wood sometimes may

alter its physical and mechanical properties. This study investigated the physical and

mechanical properties of tropical wood treated with novel organotin(IV) complexes. Three

selected tropical wood species namely Alstonia scholaris (pulai), Macaranga triloba

(mahang) and Hevea brasiliensis (rubberwood) were chemically treated with five newly

synthesized organotin(IV) complexes namely monomethyltin(IV) (MMT),

monophenyltin(IV) (MPT), dimethyltin(IV) (DMT), diphenyltin(IV) (DPT) and

dibutyltin(IV) (DBT) compounds with 2-acetylpyridine-N(4)-cyclohexylthiosemicarbazone

(APCT) ligand. Wood samples were treated with 1% concentration of organotin(IV)

complexes. Organotin(IV) complex reacted with hydroxyl group (-OH) of wood which was

confirmed through fourier transform infrared spectroscopic (FTIR) analysis. FT-IR spectra

of treated wood showed new absorption bands in the range of 594-606 cm-1

and 441-457

cm-1

due to Sn-C and Sn-N bond, respectively. A newly formed absorption band at range

Physico-Mechanical Properties of Tropical Wood Treated with Novel Organotin (IV) Complexes 513

549-569 cm-1

due to Sn-O bond was also observed in the treated wood sample spectra.

Wood densities increased following organotin (IV) treatment. Disubstituted organotin(IV)

complex treated wood density was higher than that of monosubstituted organotin(IV)

complex treated wood. The modulus of elasticity (MOE), modulus of rupture (MOR) and

compressive strength (CS) parallel to the grain of the treated wood samples decreased

following organotin(IV) treatment.

Keywords: Tropical Wood, Organotin (IV) Complex, Chemical Treatment, FTIR,

Mechanical Strength.

1. Introduction Wood is an extremely versatile material with a wide range of physical and mechanical properties

among the many species of wood (Winandy and Lebow, 1997). The widespread use of wood in the

construction industries has both an economic and an aesthetic basis. The ability to construct wood

buildings with a minimal amount of equipment has kept the cost of wood-frame building competitive

with other types of construction. However, as a naturally produced organic material, wood is subjected

to decay. Wood decay can be defined as changes in physical, mechanical and chemical properties of

wood caused by decay fungi. Although some wood are preferred in building and construction materials

for its natural durability but most tropical wood species are non durable or less durable which limits

their indoor and outdoor applications. Huge non-durable tropical wood species are abundantly

available in Southeast Asia (Chao and Lee, 2003; Deka et al., 2002).

The consumption of wood has been rapidly increasing year by year due to population increased.

In contrast, however, the production of wood has been drastically decreasing. Due to this reason they

exist an imbalance between demand and supply of forest product (Tolunay et al., 2008). Declining

availability of the prime economic species in timber market has led to the investigation of lesser-used

species (Oluwafemi and Adegbenga, 2007; Kazemi, 2007). This situation has driven researchers to

look for alternative low-quality resources for value-added applications. One of the most effective way

is to apply suitable wood preservatives needed to improve low-quality resources in order to meet end-

use requirements (Wang et al., 2007; Zhang et al., 2006). Chemically treated wood typically have low

moisture absorption, high density and high resistance to decay, insects and ultra violet ray damage.

Izreen et al. (2011) showed that low density hardwood changed to good properties wood through

chemical impregnation which became highly resistant to fungal decay. Majority of commercial timbers

worldwide need to be treated before they can be utilized for various purposes (Sotannde et al., 2011).

Organotin(IV) compounds are chemical compounds based on tin with hydrocarbon

substituents. The chemistry of organotin(IV) compounds continues to be of interest due to their

interesting structural features and also because of their potentials as agricultural biocides, antitumor

agents and other biological activities which are currently being investigated by many researchers

(Singh and Kaushik, 2008; Benetollo et al., 2005). In recent years, organotin(IV) compounds have

been used extensively as agrochemical fungicides, biocides and antifouling agents (Hanif et al., 2010).

Trialkyltin compounds like TBTO (tri-n-butyltin oxide) and TBTN (tri-n-butyltin naphthanate) are

used as fungicides worldwide (Schweinfurth et al., 1991). These compounds are most effective against

wood decay fungi. Schweinfurth et al. (1991) also observed that the undiluted active ingredient of

TBTO was found to be severely irritating to the skin of rabbit and human. The application of the

compounds onto the skin of human showed severe reddening and slight swelling. This shows the

danger in using these trialkyltin compounds as fungicides. The precautions and safety of usage cannot

be guaranteed and strict supervision is needed if both these compounds were to be used. Although it is

very effective organotin(IV) compounds to treat wood but there have several disadvantages. Therefore,

TBTO is recommended only for aboveground use, such as mill work. It has been used as a marine

antifoulant, but this use has been almost eliminated because of the environmental impact of tin on

shellfish.

514 Md. Masudur Rahman, Ismail Jusoh, Md. Abu Affan,

Ahmad Husaini, Sinin Hamdan, and Md. Saiful Islam

Growing environmental awareness and new rules and regulations are forcing industries to seek

more ecological friendly wood preservatives for their products (Oksman et al., 2003). Wood is

considered an environmentally friendly material and it has become more and more controversial to use

chemical and poisonous substances as wood preservatives. Moreover there is now an increased

awareness of the hazards associated with the production and application of wood treatment chemicals

and the disposal of treated wood and unused solutions (Eaton and Hale, 1993). For this reason, it is

necessary to search for new wood preservatives which are environmentally friendly, more effective and

comparatively safe to use.

Since last decade, several wood preservatives such as CCA, ACQ, TBTO, TBTN have been

developed and currently used for building constructions, children’s play structures, decks, picnic

tables, etc. However, there is very limited information about the effects of chemicals on the mechanical

properties of tropical wood. Mechanical properties like modulus of rupture (MOR) determines the load

a beam will carry and the modulus of elasticity (MOE) measures of the resistance to bending, which

directly related to the stiffness of a beam, also a factor in the strength of a long column. Mechanical

properties, especially MOE and MOR are the primary criteria for the selection of wood materials

(Haygreen and Bowyer, 1989). Therefore, MOE and MOR values have crucial importance for

designing wood constructions. Thus, the effects of these new preservatives on mechanical properties of

wood have become an important issue and need to be investigated.

In a previous study, the authors reported the organotin(IV) complexes are effective in

protecting Alstonia scholaris (pulai), Macaranga triloba (mahang) and Hevea brasiliensis

(rubberwood) against white and brown rot decay fungi (Rahman et al., 2012). This study is

continuation and reports the effect of these newly synthesized organotin(IV) complexes on physical

and mechanical properties of tropical wood. Thus the objectives of this study was to investigate the

physico-mechanical properties of selected tropical wood species namely A. scholaris (pulai), M. triloba

(mahang) and H. brasiliensis (rubberwood) treated with novel organotin(IV) complexes.

2. Materials and Methods 2.1. Preparation and Treatment of Wood Samples

In this study, three non-durable tropical wood species namely Alstonia scholaris (pulai), Macaranga

triloba (mahang) and Hevea brasiliensis (rubberwood) were chosen and collected from an old

secondary local forest of Sarawak, Malaysia. Heartwood was selected during cutting because it is the

most difficult to treat in most wood species. However, previous study (Jusoh et al., 2012) showed that

the heartwood of A. scholaris (pulai), M. triloba (mahang) and H. brasiliensis (rubberwood) are

treatable with organotin(IV) complexes. The boards were dried, planed, ripped and finally cut into

300x19x19 mm and 60x19x19 mm sized according to ASTM D-143 (1996) for bending test and

compression parallel to grain test, respectively. The cubes were conditioned at 60 ºC and 70% relative

humidity for four days until they reached a constant weight.

Five newly synthesized organotin(IV) complexes (Affan et al., 2011) were used as wood

preservatives. The compound monomethyltin [MeSnCl2(APCT)] (MMT) & monophenyltin

[PhSnCl2(APCT)] (MPT) of monosubstituted and dimethyltin [Me2SnCl(APCT)] (DMT), dibutyltin

[Bu2SnCl(APCT)] (DBT) & diphenyltin [Ph2SnCl(APCT)] (DPT) of disubstituted organotin(IV)

complexes were used in this study. 2-acetylpyridine-N(4)-cyclohexylthiosemicarbazone (APCT) was

used as ligand. One percent concentration of organotin(1V) complexes were prepared for treatment.

The organotin(IV) complexes were dissolved in solution of 20% dimethylsulphoxide (DMSO) and

80% distilled water.

Ten and six replicates of wood samples were used for untreated and treated wood samples,

respectively. Treatments were carried out according to the AWPA standard E10-91 (1991) with slight

modifications. All wood samples were placed inside the container containing the treating solution and

Physico-Mechanical Properties of Tropical Wood Treated with Novel Organotin (IV) Complexes 515

soaked for 2 h. The treatment schedule was done an initial vacuum of 100 mm Hg for 30 min followed

by 100 psi of pressure for 1 h and a final vacuum of 100 mm Hg for 30 min. After treatment, the wood

samples were taken out and the excess treating solutions on the surface of the wood samples were

wiped with tissue paper. The treated and untreated wood samples were cut into 19x19x19 mm to take

weight and volume which were used to calculate the density. The weight of wood samples after

conditioned before treatment (W1) and after treatment (W2) was recorded. The volume before treatment

(V1) and after treatment (V2) of the wood samples was determined using water displacement method.

2.2. FTIR Spectroscopy Analysis

Fourier Transform Infrared (FTIR) analysis was performed on Perkin Elmer Spectrum GX Fourier -

Transform spectrometer equipped with a micro sample holder. Potassium bromide (KBr) powder was

used to establish the background. Wood samples were air-dried prior to mixing with KBr. Spectra of

the samples were collected using diffuse Fourier transform infrared spectroscopic technique (DRIFT).

Spectra were collected for a total of 64 scans on 370 to 4000 cm-1

wavenumber range with a resolution

of 4 cm-1

. All spectra were displayed in absorbance and limited to 370 – 4000 cm-1

region.

2.3. Determination of Wood Density

Volume of the wood cubes was determined using water displacement method (Bowyer et al., 2003).

Air-dry wood density was calculated using the ratio of weight per unit volume at air-dry condition.

Air-dry density was calculated before and after chemical treatment and expressed in kg m-3

.

2.4. Mechanical Tests

In order to characterize mechanical properties, bending and compression parallel to grain tests were

carried out according to ASTM D-143 (1996) using a Shimadzu Universal Testing Machine having a

loading capacity of 300 kN. A cross head speed of 2 mm/min and span of 200 mm was used during

test. Clear, defect-free planks were ripped and cut to obtain sample size of 300 mm (L-longitudinal) x

19 mm (T-tangential) x 19 mm (R-radial) and 60 mm (L) x 19 mm (T) x 19 mm (R) for three point

bending test and compression parallel to grain test, respectively. Compressive strength was obtained

using the uniaxial compression test. The modulus of elasticity (MOE) and modulus of rupture (MOR)

were obtained from the three point bending test.

2.5. Analysis of Data

One-way analysis of variance was performed to determine the differences between mean values of

density, modulus of elasticity, modulus of rupture and compressive strength following different

organotin(IV) complexes by a computerized statistical program (SPSS-18.0). Further analyses of mean

comparisons were done using Tukey Multiple Comparison test.

3. Results and Discussion 3.1. Wood Density

Wood density is an indicator of wood quality including timber strength and stiffness (Bowyer et al.,

2003; Chave et al., 2009) and most relevant to structural design (Winandy and Lebow, 1997). Mean

wood density of untreated and treated wood samples with different organotin(IV) complexes are

summarized in Table 1.

516 Md. Masudur Rahman, Ismail Jusoh, Md. Abu Affan,

Ahmad Husaini, Sinin Hamdan, and Md. Saiful Islam

Table 1: Mean density (kg m

-3) of untreated and treated wood samples

Wood species Treating chemicals

Untreated MMT MPT DMT DPT DBT

Alstonia scholaris 357.04* a

(15.69)

359.32 a

(25.62)

360.87 a

(14.63)

363.58 a

(26.44)

365.22 a

(23.92)

366.16 a

(29.01)

Macaranga triloba 408.81 b

(16.85)

410.61 a

(23.15)

411.76 b

(22.07)

414.78 b

(25.18)

415.46 a

(17.69)

415.62 a

(23.55)

Hevea brasiliensis 655.52 c

(32.38)

658.99 b

(34.22)

663.27 c

(33.10)

664.12 c

(25.33)

663.68 b

(30.05)

665.59 b

(31.17)

Values in parenthesis is the standard deviation

*Means followed by a different letter within a column are statistically different at P < 0.05 using Tukey Multiple

Comparison test.

Mean densities of untreated A. scholaris, M. triloba and H. brasiliensi were 357, 409 and 656

kg m-3

, respectively which were significantly different between the wood species. These values are

comparable with densities obtained by Reyes et al. (1992). Malaysian Timber Industry Board (MTIB:

2010) reported the air-dry density of A. scholaris, M. triloba and H. brasiliensi wood are 210-500, 270-

495 and 560-640 kg m-3

, respectively. Wood density variation may occur within a species due to

location within the tree, site condition, genetic factor and age of tree (Fearnside, 1997; Izekor, et al.,

2010).

The density of treated wood cubes showed different increasing trend between the wood species

and chemicals. Among monosubstituted orgaotin(IV) complexes, MPT treated wood samples density

was higher than that of MMT treated wood samples. Whereas in disubstituted organotin(IV)

complexes, DBT treated wood density was higher than DMT and DPT treated samples for all treated

wood species. This effect might be due to the presence of bulky group in organotin(IV) complexes

(Affan et al., 2011).. The densities of disubstituted organotin(IV) treated wood samples were higher

than those of monosubstituted orgaotin(IV) treated wood samples. This effect might be due to the

presence of double alkyl or aryl group in disubstituted of organotin(IV) complexes (Affan et al., 2011).

3.2. Fourier Transform Infrared (FT-IR) Spectroscopy Analysis

Alstonia scholaris, Macaranga triloba and Hevea brasiliensis wood samples were treated with newly

synthesized five organotin(IV) compounds. The reaction mechanism between the hydroxyl part of

wood and organotin(IV) complexes is shown in scheme 1.

Scheme 1: Reaction of wood-hydroxyl with organotin(IV) complex

Physico-Mechanical Properties of Tropical Wood Treated with Novel Organotin (IV) Complexes 517

Treated wood samples were analyzed by FT-IR spectroscopy to authenticate the treating

chemicals were incorporated within the wood cell. The characterizations were performed on all species

of wood samples, but similar results were obtained. Thus only the result corresponding to DPT treated

and untreated A. scholaris wood spectra are given as a representative case shown in Figure 1.

Figure 1: IR spectra of untreated and treated Alstonia scholaris wood sample with diphenyltin(IV) complex.

4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 370.0

0.0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100.0

cm-1

%T cyclohexyl

Tra

nsm

itta

nce

Wavenumber

OH

Sn-NSn-O

C=N

C-S N-N

C-S

Sn-C

Treated

Untreated

The IR spectra of untreated wood clearly showed the absorption band at 3406-3415, 2903-2917

and 1730-1742 cm-1

due to OH, CH and CO stretching vibrations, respectively. These absorption bands

are due to the hydroxyl group in cellulose, carbonyl group in hemicellulose and carbonyl aldehyde in

lignin (Ismail et al. 2002). Zhang and Kamdem (2000) also observed that hemicellulose and lignin are

the bonding sites for copper. On the other hand the formation of new bond like tin carbon (Sn-C), tin

oxygen (Sn-O) and tin nitrogen (Sn-N) bond by the fixation of organotin(IV) compound within the

wood cell was confirmed by the FT-IR spectroscopy analysis of treated wood. In the spectra of

organotin(IV) treated A. scholaris, M. triloba and H. brasiliensis wood, a new absorption band at 594-

606 cm-1

, 561-569 cm-1

and 441-457 cm-1

are assigned to the stretching mode of ν(Sn-C), ν(Sn-O) and

ν(Sn-N), respectively. A new ν(Sn-O) linkage indicating the tin(IV) coordinated with oxygen of OH

after deprotination in wood cell which suggesting the fixation of organotin(IV) within the wood cell

(Yin et al., 2007; Mendes et al., 2006).

Moreover IR spectra of treated wood clearly showed the presence of the characteristics of

cyclohexyl, C=N, C-S and N-N bond at 2929-2937, 1542-1559, 1242-1255 & 829-836 and 1011-1034

cm-1

, respectively (Rebolledo, 2005; Elvy et al., 1995; Haque et al., 2009; Covolan et al., 1997). The

absorption band of OH group also shifted towards lower wave number (3415 to 3375-3395 cm-1

) with

narrowed band intensity, which gives further evidence of the reaction of cellulose OH groups with

organotin(IV) compound and formed new Sn-O bond (Hortling et al., 1997; Tolvaj and Faix, 1995). IR

spectra results confirmed that the newly synthesized selective organotin(IV) compound incorporated

within the cell of selected tropical wood species.

518 Md. Masudur Rahman, Ismail Jusoh, Md. Abu Affan,

Ahmad Husaini, Sinin Hamdan, and Md. Saiful Islam

3.2. Bending Strength of Organotin (IV)-Treated Wood

The effects of organotin (IV) complexes on bending properties (MOE and MOR) of A. scholaris, M.

triloba and H. brasiliensis are illustrated in Figure 2 and 3, respectively. Mean MOE and MOR of

untreated A. scholaris, M. triloba and H. brasiliensi was 4021, 4400 & 8026 MPa and 41, 56 & 85

MPa, respectively. These values are comparable to mean MOE and MOR of wood reported by Islam et

al. (2012) and Malaysian Timber Industry Board (MTIB: 2010).

Figure 2: Modulus of elasticity (MOE) of untreated and treated wood samples (different letter within a wood

species are statistically different at P<0.05 using Tukey Multiple Comparison test).

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

Alstonia scholaris Macaranga triloba Hevea brasiliensis

MO

E (

MP

a)

Wood species

Untreated MMT MPT DMT DPT DBT

a

bab ab

a

ab ab

aaa

aa

b

a

abab

ab ab

Figure 3: Modulus of rupture (MOR) of untreated and treated wood samples (different letter within a wood

species are statistically different at P<0.05 using Tukey Multiple Comparison test).

0

10

20

30

40

50

60

70

80

90

Alstonia scholaris Macaranga triloba Hevea brasiliensis

MO

R (

MP

a)

Wood species

Untreated MMT MPT DMT DPT DBT

b

a

abab ab ab

b

a

ababab ab

aa

a

aa

a

The variation regarding MOE and MOR may occur within a species due to location within the

tree, site condition, genetic factor and age of tree (Josue, 2004; Izekor et al., 2010). The MOE and

MOR of treated wood sample was lower for all treating organotin(IV) complexes in all wood species.

Among the five organotin(IV) complexes, only DMT treated A. scholaris and M. triloba wood samples

MOE and MOR significantly lower than that of untreated samples. But in H. brasiliensis didn’t

significantly affect following treatment. Hydrolysis of hemicellulose in the cell wall would be

Physico-Mechanical Properties of Tropical Wood Treated with Novel Organotin (IV) Complexes 519

responsible for the reduction in MOE and MOR of the treated samples (Hillis, 1984). The MOE and

MOR in treated H. brasiliensis were not affected as much as MOE and MOR in A. scholaris and M.

triloba wood samples. This might be due to the higher density and hardness of H. brasiliensis than A.

scholaris and M. triloba. This effect in wood properties is obvious and may be due to the disturbance

within the wood fibre (LeVan and Winandy 1990) and chemical interaction as confirmed in FTIR

result.

The highest and lowest mean MOE and MOR was 7973 & 2913 MPa and 82 & 30 MPa in

MPT treated H. brasiliensis and DMT treated A. scholaris wood species, respectively. Hiziroglu

(1997) observed that static bending properties of CCA-treated rubberwood reduced as pressure

treatment time increased compare to untreated sample. Yildiz et al. (2004) also showed that almost

10% decrease in MOE and 12% decrease in MOR of yellow pine wood samples treated with CCA

compare to untreated one. Green et al. (2007) stated that wood preservatives can negatively affect on

MOE and MOR of wood and may reduced the strength up to 30%.

3.3. Compression Test Analysis

The compressive strength (CS) parallel to the grain for treated and untreated wood samples are

summarized in Figure 4. Mean CS values of untreated A. scholaris, M. triloba and H. brasiliensi were

22, 26 and 35 MPa, respectively. According to Malaysian Timber Industry Board (MTIB: 2010), the

air-dry compression parallel to grain of A. scholaris and H. brasiliensi are 25 and 32 MPa,

respectively. This variation may occur within a species due to site condition, genetic factor, age of tree

(Fearnside, 1997; Izekor et al., 2010).

Figure 4: Compressive strength (CS) of untreated and treated wood samples.

0

10

20

30

40

50

60

70

80

90

MP

a

Treating chemicals

Hevea brasiliensis

Macaranga triloba

Alstonia scholaris

The CS of treated wood sample was lower for all treating organotin(IV) complexes in all wood

species. Green et al. (2007) stated that wood preservatives can affect compressive strength parallel to

grains and reduced from 0 to 20%. The highest (35 MPa) and lowest (18 MPa) CS was observed in

MPT treated H. brasiliensis and DMT treated A. scholaris wood species. Disubstituted organotin(IV)

treated wood samples showed higher decreasing tendency than that of monosubstituted organotin(IV)

treated in all wood species. This effect might be due to the presence of double alkyl or aryl group in

disubstituted of organotin(IV) complexes. The more retention values in disubstituted organotin(IV)

treated wood samples showed highly reduced on CS compare than that of monosubstituted

organotin(IV) treated wood samples (Rahman et al., 2012; Green et al., 2007).

520 Md. Masudur Rahman, Ismail Jusoh, Md. Abu Affan,

Ahmad Husaini, Sinin Hamdan, and Md. Saiful Islam

4. Conclusions The purpose of this study was to determine the effects of new preservatives, i.e. MMT, MPT, DMT,

DPT and DBT complexes on density, MOE, MOR and CS of A. scholaris, M. triloba and H.

brasiliensi. In this study it was observed that density of all treated wood samples had higher compare

to untreated wood sample. Disubstituted organotin(IV) treated wood density was higher than

monosubstituted organotin(IV) treated wood density in all wood species. A newly formed Sn-O bond

was observed in all treated wood sample. FT-IR spectra showed tin compounds bind with wood cell

suggest the newly synthesized organotin(IV) compounds are incorporated within the wood cell of all

selected tropical wood species. Hemicellulose and lignin play the important role in bonding tin. The

decreases in MOE, MOR and CS of the wood treated with disubstituted organotin(IV) complexes was

much higher than those of monosubstituted organotin(IV) treated wood. The MOE and MOR of DMT

treated A. scholaris and M. triloba wood was significantly lower compare to untreated wood samples.

In contrast, MPT treated wood samples showed least effect on MOE, MOR and CS among all selective

organotin(IV) complexes.

5. Acknowledgement This work was supported by the University Malaysia Sarawak (UNIMAS) under a research grant No. E

14052 F07 49 791/2011(01). The authors would like to expresses their sincere thanks to all staff from

the Faculty of Resource Science and Technology, UNIMAS for the technical support provided.

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