Kiln Drying of Acacia mangium Willd Wood: Considerations of Moisture Content before and after Drying and Presence of Wet Pockets

Abstract

Acacia mangium is an important plantation species cultivated in Costa Rica and other tropical countries worldwide. However, wood uses have been limited due to drying-related problems such as high initial moisture content (MC_i) and high variability in final moisture content (MC_f). The objective of this study was to investigate the causes of these problems. Climatic conditions where trees grow, tree height, grain pattern, drying schedules, distance from pith, and sapwood or heartwood presence were considered. Results showed an average MC_i of 127% ranging from 58 to 186%. MC_i variation was influenced by climatic conditions, tree height, and grain pattern. Average MC_f was 19%, ranging from 9 to 52%. Lack of MC_f uniformity after drying is influenced by tree height, drying schedule, and the interaction of both factors. Wet pockets were also found to develop during drying. Lumber from trees growing in humid tropical climates subjected to a low relative humidity drying schedule as well as rift-sawn or double rift-sawn lumber was likely to develop wet pockets.

Keywords:

• Costa Rica
• Kiln dry
• Moisture uniformity
• Tropical wood
• Wet pockets

ACKNOWLEDGMENTS

We thank the Vicerrectoría de Insvestigación y Extensión of Instituto Tecnológico de Costa Rica for financial support, and Ganadera Barsa S.A for providing the raw materials and facilities for this study.

Notes

^a Plantation characteristics were obtained from two temporary plots established in the plantation.

TBS = Dry bulb temperature; EMC = equilibrium moisture content; MC = lumber moisture content.

NC = not considered in the model, MC_i = initial moisture content, MC_f = final moisture content, ΔE = change of color.

*Statistically significant at α = 0.05. **Statistically significant at α = 0.01.

NC = not considered in the model, MC_i = initial moisture content, MC_f = final moisture content, ΔE = change of color.

*Statistically significant at α = 0.05. **Statistically significant at α = 0.01.

^a Standard deviation.

^b Minimum and maximum moisture content values.

^c Moisture content monitored in six kiln samples in different locations.

*Statistically significant at α = 0.01.