Differential response of heartwood and sapwood to heat treatment. Part 1: Strength properties

Abstract

The transition from sapwood to heartwood is characterised by several changes including increasing acidity. On the basis of the strong correlation, which has been established between strength reduction and wood acidity during heat treatment, the differences in the response of heartwood and sapwood strength properties were investigated. Heartwood and sapwood samples obtained from one board of Scots pine (Pinus sylvestris) were heat-treated and their strength properties compared. There was 15.8% and 3.3% reduction in modulus of elasticity in the heartwood and sapwood respectively while the loss in modulus of rupture is 32.9% and 15.6% in the heartwood and sapwood respectively. The lower reductions in the strength properties in the sapwood compared to the heartwood indicate that the former is less amenable to heat treatment than the latter. This is probably due to the higher acidity of the former, which could have resulted in higher degree of degradation, higher cellulose crystallinity and consequently higher strength reduction. Therefore the effects of heat treatment on wood especially the strength properties depends on the proportions of heartwood and sapwood.

Keywords

HEARTWOOD SAPWOOD HEAT TREATMENT MODULUS OF ELASTICITY MODULUS OF RUPTURE

Get full access to this article

View all access options for this article.

References

Bergstrom

. 2003. Chemical and structural changes during heartwood formation in Pinus sylvestris. Forestry, 76(1): 45–53.

Bhuiyan

M. T. R.

; Hirai

and Sobue

2000. Changes of crystallinity in wood cellulose by heat treatment under dried and moist conditions. Journal of Wood Science, 46(6): 431–436.

Bootle

K. R

. 1983. Wood in Australia. Types, properties and uses. McGraw-Hill Book Company Sydney, 443pp.

Dwianto

; Morooka

and Norimoto

. 1998. The compressive stress relaxation of albizia (Paraserienthes falcate Becker) wood during heat treatment. Mokuzzai Gakkaishi. 44(6): 403–409.

Garrote

; Dominguez

and Parajo

J. C.

2001. Study on the deacetylation of hemicelluloses during the hydrothermal processing of Eucalyptus wood. Holz als Rob und Werkstoff. 590: 53–59.

Geissen

and Du

Q. P

. 1995. Influence of heat treatment on the accuracy of wood moisture content determina-tion by electrical resistance-type meters. Holz als Roh und Werkstoff. 53(5): 303–307.

Hanger

; Huber

; Lackner

; Wimmer

and Feltner

2002. Improving the natural durability of heat-treated spruce, pine and beech. Holzforschung und Holzverwertung. 54(5): 92–93.

Hodgin

D. A.

and Lee

A. W. C

. 2002. Comparison of strength properties and failure characteristics between fire-retardant-treated and untreated roofing lumber after long-term exposure: A South Carolina case study. Forest Products Journal, 52(6): 91–94.

Kamdem

D. P.

; Pizzi

and Triboulot

M. C.

2000. Heat-treated timber: potentially toxic byproducts presence and extent of wood cell wall degradation. Holz als Roh und Werkstoff, 58(4): 253–257.

10.

Kamdem

D. P.

; Pi77i

and Jermannaud

2002. Durability of heat-treated wood. Holz als Roh und Werkstoff, 60(1): 1–6.

11.

Kim

G. H.

; Yun

K. E.

and Kim

J. J.

1998. Effect of heat treatment on the decay resistance and the bending properties of radiata pine sapwood. Material und Organismen, 32(2): 101–108.

12.

Kubojima

; Okano

and Ohta

. 2000. Bending strength and toughness of heat-treated wood. Journal of Wood Science, 46(1): 8–15.

13.

Manninen

A. M.

; Pasanen

and Holopainen

J. K.

2002. Comparing the emissions between air-dried and heat-treated Scots pine wood. Atmospheric Environment, 36(11): 1763–1768.

14.

Nogi

; Yamamoto

and Okuyama

. 2003. Relaxation mechanism of residual stress inside logs by heat treatment: choosing the heating time and temperature. Journal of Wood Science. 49(1): 22–28.

15.

Obataya

; Tanaka

, Norimoto

and Tomita

. 2000. Hygroscopicity of heat-treated wood. I. Effects of after-treatments on the hygroscopicity of heat-treated wood. Mokuzai Gakkaishi. 46(2): 77–87

16.

Obataya

and Tomita

. 2002. Hygroscopicity of heat-treated wood. II. Reversible and irreversible reductions in the hygroscopicity of wood due to heating. Mokuzai Gakkaishi. 48(4): 288–295.

17.

Papp

A. O.

and Sailer

. 2001. Oil-heat-treatment of wood-process and properties. Drvna Industrija. 52(2): 63–70.

18.

Sailer

; Rapp

A. O.

; Leithoff

and Peek

R. D.

2000. Upgrading of wood by application of an oil-heat treatment. Holz als Roh und Werkstoff. 58(1/2): 15–22.

19.

Santos

J. A

. 2000. Mechanical behavior of Eucalyptus wood modified by heat. Wood Science and Technology. 34(1): 39–43.

20.

Tejada

; Okuyama

; Yamamoto

and Yoshida

. 1997. Reduction of growth stresses in log by direct heat treatment: Assessment of a commercial scale opera-tion. Forest Products Journal. 47(9): 86–93.

21.

Tejada

; Okuyama

; Yamamoto

; Yoshida

; Imai

and Itoh

. 1998. Studies on the softening point of wood powder as a basis for understanding the release of residual stresses in logs. Forest Products Journal. 48(7 — 8): 84–90.

22.

Udaka

and Furuno

. 2003. Change in crystalline structure of compressed wood by treatment with a closed heating system. Mokuzai Gakkaishi, 49(1): 1–6.