The Influence of Elevated Temperatures on Selected Properties of Rubberwood

1. The Influence of Elevated Temperatures on Selected Properties of Rubberwood 1,2 Sik H.S., 2 Sarani Z., 2 Sahrim Hj. A., & 1 Choo K.T. 1Forest Research Institute Malaysia (FRIM) 2 Universiti Kebangsaan Malaysia (UKM)

2. Introduction • Rubberwood - Hevea brasiliensisor rubber trees of Euphorbiaceae family. • Plantation timber- harvested when latex production is no longer economically viable. • Wooden furniture, mostly rubberwood, accounted for 80% of total furniture exports of 7.25 billion ringgit (USD 2.07 billion) in 2006. • Drying - Reduce the moisture content in freshly sawn timber / dry timber down to the equilibrium moisture content (emc) that it will attain in service.

3. Elevated temperature drying of tropical hardwoods is still unknown in Malaysia and other tropical hardwoods producing region. • Drying at elevated temperature is accomplished at dry-bulb temperatures of 100 °C or higher. • Currently, more than 95% of the drying mills in Malaysia are based on conventional low temperature-heated system.

4. Elevated-temperature Drying? • time and cost saving practice • reduce drying time; • allow “just-in-time” production that leads to lower inventory cost and smaller plant sites; • lower energy consumption and probably fewer deformations enhancing the properties of throughput dried timbers To improve the performance of drying operation, towards achieving a more energy-and-cost efficient system.

5. Objectives • Investigate the influence of elevated temperatures on specific properties of tangential and radial sawn rubberwood compared to conventionally dried material in a laboratory experimental kiln

6. Methodology • Simulated Drying using Experimental Kiln : • 60 ºC (control) • 100 ºC • 120 ºC • 130 ºC • 140 ºC • 150 ºC • Initial moisture content : 62.36 – 64.13 % • Monitoring of drying activities up to 24 hours for elevated drying.

7. Results and Findings • Physical properties • Mechanical properties • Timber stress at elevated drying temperatures • Low molecular sugars content

8. W W T T Cross section flat sawn quarter –sawn Source : USDA Handbook A. Physical Properties Shrinkage in wood • Wood Shrink – to achieve dimensional stability • Shrinkage in Transverse direction :

9. W T FIGURE 1. Shrinkage in Quarter Sawn Rubberwood Cross-section of a quarter –sawn timber

10. W T FIGURE 2. Shrinkage in Flat Sawn Rubberwood Cross-section of a flat sawn timber

11. Shrinkage in Longitudinal direction • Excessive shrinkage along length • presence of tension wood. tension wood normal wood

12. Specific Gravity Specific gravity of rubberwood at green and after drying at different temperatures.

14. Rubberwood Timber y 150 ºC 100 ºC Typical honeycombing/ internal checks formation • Drying stresses • – the shell of a board undergoing drying initially shrinks more • than the core compressive stress collapse. • Collapse in Wood ( Capillary tension) • Crucial, especially at elevated drying temperature

15. Pinched-In Prong Test 60 ºC 120 ºC 140 ºC 150 ºC Degree of pinched-in of all test pieces were generally in permissible range of 1 to ≤ 3mm after conditioned for 24 hours at room temperature

16. B. Mechanical Properties Compared to 60°C ( control) : • MOR was higher in 100°C, 120°C, 130°C • MOE was higher in 100°C, 120°C, 130°C and 140°C • Compressive strength was higher in all elevated temperatures (highest in 100 °C) • Hardness value was higher in all elevated temperatures (highest in 140 °C) • Shear strength was higher in all elevated temperatures (highest in 140 °C)

17. Increase of MOR values are significant in 100 °C- and 120 °C-dried samples

18. Increase of MOE values are insignificant; reduction is significant at 150°C

19. Increase in compression parallel to grain is significant at 95% confidence interval for all temperatures.

20. Increase in hardness values is significant at 95% confidence interval for all temperatures.

21. Increase in shear strength is only significant (P< 0.05) for 140 °C-dried samples

22. C. Influence of temperature on the redistribution of LM sugars in rubberwood Note : Air dry condition : ambient temperature at 25 – 32°C

23. Conclusion • The incremental shrinkages of rubberwood measured at elevated temperatures indicates the requirement for increase shrinkage allowances, or green sawn size target. • In tangential sawn, where drying stresses are more significant than in radial, more regular and positive increase of shrinkage in thickness is noticed. • Abnormal shrinkage in longitudinal direction was detected, due to the occurrence of tension wood, commonly found in rubberwood.

24. The relative mechanical strength of rubberwood dried at elevated temperatures up to 130 °C increased when compared to conventional-dried sawn. • Redistribution of hydrolysed low molecular sugar (LMS) during drying is more prominent at elevated temperature. • The incidence of collapse and honeycomb did not occur in elevated-temperature drying up to 150°C. • Rubberwood is able to withstand drying stresses at high temperatures, thus tolerable of drying at elevated temperatures up to 150ºC.

25. Thank you