myb22(1)-11

Vertical variation of density, flexural strength and stiffness of Persian silk wood

Variación longitudinal en densidad, resistencia a flexión y rigidez de la madera 'de seda' persa

Majid Kiaei1* and Mohammad Farsi1

1 Department of Wood and Paper Engineering, Sari Branch, Islamic Azad University. Sari, Iran.

* Corresponding author. mjd_kia59@yahoo.com

Abstract

The aim of this research was to investigate the effects of longitudinal position (stem height) and heart-sapwood on density, modulus of elasticity (MOE) and modulus of rupture (MOR) in bending for Persian silk wood (Albizzia julibrissin). Five normal trees were selected from the Guilan region, Iran. Samples for testing were prepared at four stem height levels (5%, 25%, 50% and 75% of total stem height) in both positions along radial direction (heartwood and sapwood). Analysis of variance results (Anova) indicated that the effects of longitudinal position (stem height) and heartwood-sapwood on the wood density, MOE and MOR were significant. The mean of wood density, MOE and MOR along longitudinal position from base to top decreased with height. The mean of wood density, MOR and MOE in sapwood are lower compared to the corresponding values for heartwood. The relationship between wood density and mechanical strength properties were analyzed by regression models. A positive correlation was found between wood density with MOE and MOR in both heartwood and sapwood.

Keywords: Albizzia julibrissin, modulus of elasticity, modulus of rupture, radial direction, stem height.

Resumen

El objeto de esta onvestigación fue estudiar los efectos de la posición en dirección longitudinal (altura del tronco) y del duramen y la albura sobre la densidad, el módulo de elasticidad (MOE) y el módulo de ruptura (MOR) en flexión para la madera de ‘seda’ persa (Albizzia julibrissin). Se recolectaron cinco árboles representativos de la región de Guilan, Irán. Se elaboraron especímenes para prueba a cuatro niveles de la altura del árbol (5%, 25%, 50% y 75% de la altura total del tronco) en ambos tipos de madera en la dirección radial (duramen y albura). Los resultados de los análisis de varianza (Andeva) indicaron que los efectos de la ubicación longitudinal (altura del árbol) y duramen y albura sobre la densidad de la madera, el MOE y el MOR fueron significativos. Los valores promedio de la densidad, MOE y MOR a lo largo de la posición longitudinal de la base a la copa disminuyeron con la altura. Los valores promedio de la densidad, MOR y MOE en albura son menores comparados con los del duramen. La relación entre la densidad de la madera y las propiedades mecánicas se analizaron por medio de modelos de regresión. Se encontró una correlación positive entre la densidad de la madera con MOE y MOR tanto en duramen como en albura.

Palabras clave: Albizzia julibrissin, modulus of elasticity, modulus of rupture, dirección radial, altura del árbol.

Introduction

In the living tree, the sapwood, in contrast with heartwood, is physiologically active, conducting water and nutrients from roots to leaves (Bamber, 1985; Hillis, 1987) and storing food materials (Bamber, 1985). The transformation of sapwood into heartwood is characterized by the death of parenchyma cells (Hillis, 1987), development of tyloses in the vessels of many species (Bamber, 1976) and the biosynthesis of nonstructural compounds, leading to an important accumulation of extractives and to the differences in physical and chemical properties between sapwood and heartwood (Sellin, 1994). Heartwood and sapwood in a tree vary with a large number of factors, including species, age, climate, rate of growth, foliage area, site quality and tree vitality, and have been the subject of several reviews (Pinto et al., 2004; Climent et al., 2002).

Heartwood and sapwood have different properties and their proportion within the tree will have a significant impact on the utilization of wood (Climent et al., 2002). For pulping, heartwood is at a disadvantage as its extractives can affect the process and product properties. For solid wood applications the different properties of heartwood and sapwood influence drying, durability, and aesthetic values for the consumer (Pinto et al., 2004; Morais and Pereira, 2007). When there is a large colour difference between sapwood and heartwood, selection of wood components by color also plays a significant role in some timber application (Dzifa et al., 2004).

A study on the variation of wood properties of Kyere wood indicated that the wood density and mechanical properties decreased along longitudinal position from the bottom up the stem. Site also had significant impact on the wood properties. Wood samples collected from the site with the highest mean annual rainfall had the least density and strength properties (Ayarkwa, 1998).

Albizia julibrissin or Persian silk tree is legume specie in the genus Albizia. The global distribution of this species is in the North Anatolian, northern Iran, Caucasus, Sinai, Japan, Cyprus, Yugoslavia, Bulgaria, and probably planted in Australia (Mozaffarian, 2003). There are two tree species in this genus, Albizia julibrissin that grow in temperate and cool temperate northern forests of Iran, and A. lebbeck grows only in tropical regions of Iran (Sabeti, 1975; Mozaffarian 1996). This species is used for making soap, hair shampoo and UV protectors and probably other compounds (Nehdi, 2011; Panahian and Rahnama 2010).

The information about the effect of longitudinal position on the wood different properties is not available for Albizzia julibrissin (silk wood) in Iran. Therefore, to use this material properly and efficiently, it is a requisite to know its different properties.

Objetives

The objectives of this study were: (a) to examine the variations of wood density and mechanical strength properties (MOE and MOR) along longitudinal position, (b) to compare wood properties between heartwood and sapwood, and (c) to determine the relationship between wood density and mechanical properties in Persian silk wood (Albizzia julibrissin).

Material and methods

Wood samples

Five silk trees (Albizzia julibrissin) from natural forests in the Guilan province in the north of Iran were sampled. Selected trees with straight trunks, normal branching and no disease or pest symptoms were felled. The age of silkwood trees was 36-42 years-old. The average air temperature is 11.6 °C and the total annual rainfall 700 mm/year in this region. The altitude of this region is 160 m asl.

Stem sectional discs were taken from each tree at different levels of total height (5%, 25%, 50% and 75%). The radial variation was studied by sampling in each wood disc at 2 positions (heartwood and sapwood). In this species, the heartwood shows a distinctive brown colour compared to the lighter coloured sapwood. The heartwood and sapwood area within the stem cross sectional area decreased with height. At the base height level, the heartwood area was generally higher than sapwood area and decreased afterwards until the top.

Wood density

Wood sampling method and the general requirements for physical tests were in accordance with the ISO standard 3129-E (1975). The ISO standard 3131-E (1975) was used to measure the wood density. The samples were oven-dried at 103 °C ± 2 °C to 0% moisture content for 24 h. After cooling in desiccators, the oven-dry weights of the specimens and theirs dimensions were measured. The values of the wood oven-dry density were calculated using the following equation (are oven-dry density (kg/m3), dried weight and dried volume, respectively):

Flexural strength properties

Static bending or flexural strength test were measured according to the ASTM–D143-94 standards. The dimensions of the samples were of 25 mm × 25 mm in cross-section and 410 mm in longitudinal direction. The length span was of 360 mm. Theprepared samples were then conditioned at the temperature of 20 °C ± 2 °C and at 65%±5% relative humidity until the specimens reached an equilibrium moisture content of about 12%. From the test results the modulus of elasticity (MOE) and modulus of rupture (MOR) were derived.

Statistics analysis

To determine the effects of longitudinal position and heartwood-sapwood on the wood density and mechanical properties analysis of variance (Anova) were conducted with the SPSS program. Also, a regression model was used to analyze the relationship between wood density and mechanical parameters (MOR and MOE) in heartwood and sapwood.

Results

Wood density

Average and standard deviation of wood density along longitudinal position in hartwood and sapwood are listed in table 1. The analysis of variance (Anova) indicated that the longitudinal position and heartwood-sapwood did affect significantly wood density. The interaction effects between longitudinal position and heartwood-sapwood were not significant on wood density (Table 2). The mean of wood density along longitudinal position from the base upward decreased in heartwood and sapwood. The relationship between longitudinal position and wood density in heartwood (R2=0.459) is stronger than in sapwood (R2= 0.431). The average of wood density in heartwood is higher compared to the sapwood (439 kg/m3 vs 394 kg/m3).

Table 1. The variation of wood properties in different stem height levels for silk wood.

MOE (GPa)

MOR (MPa)

Density (kg/m3)

Longitudinal
position (%)

Wood

6.14 (0.50)

60.08 (2.53)

494.4 (39.16)

5

Heartwood

5.63 (0.54)

54.62 (3.61)

437.6 (40.13)

25

5.41 (0.59)

53.20 (3.77)

425.2 (40.32)

50

4.95 (0.36)

51.21 (3.46)

400.4 (29.64)

75

5.53 (0.67)A

54.78 (4.69)A

439.4 (50.68)A

Average

0.403

0.492

0.459

R2

5.36 (0.47)

54.86 (3.38)

440 (38.62)

5

Sapwood

5.13 (0.60)

49.66 (1.24)

391.8 (37.17)

25

4.54 (0.38)

48.73 (1.41)

375.5 (24.61)

50

4.15 (0.57)

47.23 (2.15)

369.2 (26.03)

75

4.80 (0.70)B

50.12 (3.61)B

394.1 (42.23)B

Average

0.468

0.626

0.431

R2

5.75 (0.64)d

57.47 (3.96)d

467.2 (47.29)d

5

Total

5.38 (0.62)c

52.14 (3.66)c

414.7 (44.71)c

25

4.97 (0.65)b

50.97 (3.61)b

400.3 (41.49b

50

4.55 (0.62)a

49.22 (3.49)a

384.82 (31.78)a

75

Uppercase and lowercase letters respectively show significant differences among longitudinal position and between heartwood-sapwood.

Table 2. F-value (in Anova results) for wood properties along longitudinal position

MOE

MOR

Density

Variable

100.088**

133.075**

83.343**

Heart-sapwood (A)

49.634**

77.417**

52.165**

Longitudinal position (B)

1.225ns

0.465ns

1.026ns

A × B

MOR

Average and standard deviation of MOR along longitudinal position in hartwood and sapwood are listed in table 1. The analysis of variance (Anova) indicated that the longitudinal position and heartwood-sapwood did affect significantly MOR. The interaction effects between longitudinal position and heartwood-sapwood were not significant on MOR (Table 2). The mean of MOR along longitudinal position from the base upward decreased in heartwood and sapwood. The relationship between longitudinal position and MOR in heartwood (R2= 0.492) is weaker than in sapwood (R2= 0.626). The average of MOR in heartwood is higher compared to the sapwood (54.78 MPa vs 50.12 MPa).

MOE

Average and standard deviation of MOE along longitudinal position in hartwood and sapwood are listed in table 1. The analysis of variance (Anova) indicated that the longitudinal position and heartwood-sapwood did affect significantly MOE. The interaction effects between longitudinal position and heartwood-sapwood were not significant on MOE (Table 2). The mean of MOE along longitudinal position from the base upward decreased in heartwood and sapwood. The relationship between longitudinal position and MOE in heartwood (R2=0.403) is weaker than in sapwood (R2= 0.468). The avaerage of MOE in heartwood is higher compared to the sapwood (5.53 GPa vs 4.80 GPa).

Relationship among wood properties

The dependence of static bending properties (MOE and MOR) on the oven-dry density was modeled using simple regression models (Figs. 1 and 2). These relationships in sapwood (R2 density-MOR = 0.368, R2 density-MOE = 0.174) are higher compared to the heartwood (R2 density-MOR = 0.139, R2 density-MOE = 0.138).

Figure 1. The relationship between wood density and modulus of elasticity (MOE) in heartwood and sapwood.

Figure 2. The relationship between wood density and modulus of rupture (MOR) in heart wood and sapwood

Discussion

The wood density, MOE and MOR in heartwood is higher compared to sapwood. These differences are related to the chemical properties in herawood and sapwood. Significant amount of extractives are deposited in the hearwood, up to two or three times more than in sapwood (Panshin and de Zeeuw, 1980). Our observation of silkwood behavior are in accodance with the studies of Panshin and de Zeeuw (1980) (“Type 4 woods: specific gravity of the wood exhibit a general decrease from pith to bark in the stem”. Examples of North American hardwoods: Fagus sylvatica, Liriodendrum tulipifera, Populus spp., Prunus serotina and Quercus falcata), Morais and Pereira (2007; Eucalyptus globulus Labill.) and Pinto et al., (2004; a conifer, Pinus pinaster Ait). Panshin and de Zeeuw (1980) also point out that “among the hardwoods there is almost even division between reported increases and decreases in specific gravity from pith to bark”.

Within-tree wood density and mechanical properties decreased along the stem, from the base upwards; however, wood density, MOE and MOR was the highest at 5% of total tree height. Similar patterns of wood density and mechanical properties variation in the longitudinal direction have also been reported by several researchers: Panshin and de Zeeuw (1980. “Static bending properties… decrease upward in the stem for Pinus resinosa Ait. and Shorea almon Foxw.); Ayarkwa (1998; Pterygota macrocarpa K. schum); and Kord et al., (2010; Populus euramericana). This may be due to the fact that butt log of the same tree has more mature wood than the top log which consists mainly of juvenile wood (Panshin and de Zeeuw, 1980). Juvenile wood is explained by Kolzlowski (1971) and Larson (1969) as being the results of the relative abundance of growth regulators and carbohydrates in the cambial zone near the crown. Juvenile wood density and mechanical properties were lower than that of mature wood. The lower density and strength properties of the wood near the top may be due to the thin walls of the cells of the wood, the lower cellulose content and crystallinity of the wood compared with that of the matured wood in the log at the butt (Zobel and Sprague, 1998).

Positive relationship was found between wood density and mechanical strength properties in heartwood and sapwood. Also, the relationship between wood density and MOE is weaker than the relationship between wood density and MOR in heartwood and sapwood. A similar trend has also been reported by several researchers for various species (Zhang, 1997; Zobel and Van Buijtenen, 1989). Wood density had important role on the variation of mechanical properties.

Conclusions

In the present research, the wood density and mechanical properties of heartwood and sapwood in silkwood were determined. The following conclusions were drawn from the study:

1. The analysis of variance (ANOVA) indicated that the longitudinal position and heartwood-sapwood did affect significantly wood density, MOR and MOE.

2. The interaction effects between longitudinal position and heartwood-sapwood were not significant on wood density, MOR and MOE.

3. The average of wood density, modulus of elasticity (MOE) and modulus of rupture (MOR) along longitudinal position from base to the top were decreased. The mean of wood density, MOE and MOR in heartwood is higher than sapwood for Silk wood.

4. There are positive relationship between wood density and mechanical properties (MOE and MOR) in heartwood and sapwood.

References

Ayarkwa, J. 1998. The influence of site and longitudinal position in the tree on the density and strength properties of the wood of Pterygota macrocarpa K. schum. Ghana Journal of Forestry 6:34-41

Bamber, R.K. 1985. The wood anatomy of eucalypts and papermaking. Appita Journal 38:210–216.

Bamber, R.K. 1976. Heartwood, its function and formation. Wood Science and Technology 10:1–8.

Climent, J., M.R. Chambel, E. Perez, L. Gil and J. Pardoa. 2002. Relationship between heartwood radius early radial growth, tree age, and climate in Pinus canariensis. Canadian Journal of Forestry Research 32(1):103-111.

Climent, J., M.R. Chambel, L. Gil and J. Pardoa. 2002. Vertical heartwood variation patterns and prediction of heartwood volume in Pinus canariensis SM. Forest Ecology and Management 174(1-3):203-211.

Dzifa, A., H. Bailleres, A. Stoke and K. Kokou. 2004. Proportion and quality of heartwood in Togolese teak (Tectona grandis). Forest Ecology and Management 189(1-3):37-48.

Hillis, W.E. 1987. Heartwood and tree exudates, Springer-Verlag, Berlin.

Kolzlowski, T.T. 1971. Growth and development of trees, Vol. II. Academic Press. New York. 86 p.

Kord, B., A. Kilashaki and B. Kord. 2010. The within-tree variation in wood density and shrinkage, and their relationship in Populus euramericana. Turkish Agriculture and Forestry 34:121-126.

Larson, P.R. 1969. Wood formation and concept of wood quality. Bulletin No. 74, Yale University School of Forestry. New Haven.

Mosaffarian, M. 1996. A dictionary of Iranian plants names. Latin, English, Persian. Farhang Moaser. 22 p.

Mosaffarian, M. 2003. Trees and shrubs of Iran. Farhang Moaser publication. Iran. 382 p.

Morais, M.C and H. Pereira. 2007. Heartwood and sapwood variation in Eucalyptus globulus Labill. Trees at the end of rotation for pulpwood production. Annals of Forest Science 64(6):665-671.

Nehdi, I. 2011. Characteristics, chemical composition and utilisation of Albizia julibrissin seed oil. Industrial Crops and Products 33:30-34.

Panahian, G.H. and K. Rahnama. 2010. Fasarium wilts on native silk trees (Albizia Julibrissin Durz) in the north of Iran, Gorgan. International Journal of Agronomy and Plant Production 1(1):1-5.

Panshin, A. and C. de Zeeuw. 1980. Textbook of Wood Technology. 4th ed. McGraw-Hill. New York.

Pinto, I.H. Pereira and A. Usenius. 2004. Heartwood and sapwood development within maritime pine (Pinus pinaster Ait) stems. Trees 18:284-294.

Sabeti, S. 1975. Trees and shrubs of Iran. Tehran University Press. p:25-26

Sellin, A. 1994. Sapwood-heartwood proportion related to tree diameter, age, and growth rate in Picea abies, Canadian Journal of Forestry Research 24:1022–1028.

Zhang, S.Y. 1997. Wood specific gravity-mechanical property relationship at species level. Wood Science and Technology 31:181-191.

Zobel, B.J. and J. Sprague. 1998. Juvenile wood in trees. Springer-Verlag. New York.

Zobel, B.J. and J.P. van Buijtenen. 1989. Wood variation: Its causes and control. Springer-Verlag. Berlin, Heidelberg, New York.

Manuscrito recibido el 7 de agosto de 2014.

Aceptado el 19 de noviembre de 2015.

Este documento se debe citar como:

Kiaei, M. and M. Farsi. 2016. Vertical variation of density, flexural strength and stiffness of Persian silk wood. Madera y Bosques 22(1):169-175.

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Madera y Bosques, Vol. 24, Núm. 1, Primavera 2018, es una publicación cuatrimestral editada por el Instituto de Ecología, A.C. Carretera antigua a Coatepec, 351, Col. El Haya, Xalapa, Ver. C.P. 91070, Tel. (228) 842-1835, http://myb.ojs.inecol.mx/, mabosque@inecol.mx. Editor responsable: Raymundo Dávalos Sotelo. Reserva de Derechos al Uso Exclusivo 04-2016-062312190600-203, ISSN electrónico 2448-7597, ambos otorgados por el Instituto Nacional del Derecho de Autor. Responsable de la última actualización de este Número, Reyna Paula Zárate Morales, Carretera antigua a Coatepec, 351, Col. El Haya, Xalapa, Ver., C.P. 91070, fecha de última modificación, 25 de abril de 2018.

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