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

2 Introduction  Rubberwood - Hevea brasiliensis or 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  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  Simulated Drying using Experimental Kiln : 60 ºC (control) 100 ºC 120 ºC 130 ºC 140 ºC 150 ºC  Initial moisture content : – %  Monitoring of drying activities up to 24 hours for elevated drying. Methodology

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

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

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

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

11 Shrinkage in Longitudinal direction tension woodnormal wood Drying Temperature (°C) QuatersawnFlatsawn Excessive shrinkage along length presence of tension wood.

12 Specific Gravity Specific gravity of rubberwood at green and after drying at different temperatures. Temperature (°C) Specific Gravity at Green Specific Gravity after Drying Increase of Specific Gravity (%)

13

14 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 Rubberwood Timber y 150 ºC100 ºC Typical honeycombing / internal checks formation

ºC60 ºC120 ºC140 ºC Prong Test 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 Pinched-In

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 Temperature (°C) Air dry mm mm Case : Core0.4 : : 1 1 : : 1 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