A simple method to eliminate drying collapse of liquid-filled porous palm wood

Abstract

Relatively large drying collapse has restricted the utilization of low-density oil palm wood (OPW), an agricultural waste in the palm oil industry, for several decades. This work reports a simple pretreatment that allows OPW from all sections of the trunk having a thickness of up to 0.2 m to be severely kiln-dried up to the temperature of 200 °C without any drying defects and with relatively low drying shrinkage. Lightweight characteristics and mechanical, thermal and acoustic properties of the dried OPW are maintained. The pretreatment process involves water impregnation of fresh OPW followed by freezing the OPW below the eutectic temperature of sap (water–sugar) of about −10 °C before kiln drying. This strategy creates localized microcracks at the pit cavities that connect between the parenchyma cells. These microcracks allow the short-range flow of intercellular liquid at atmospheric pressure to compensate for the negative capillary pressure of the intracellular liquid inside the parenchyma cell cavity during drying. A fraction of the intercellular liquid plays a crucial role in the formation of microcracks during freezing and the reduction of cell collapse during drying. The technique is also found to be applicable to the drying of the porous trunk of other palm species.

Keywords:

• Oil palm wood
• impregnation
• freezing
• drying
• capillary pressure
• cell collapse

Acknowledgments

The authors gratefully acknowledge Jaipet Tomad, Nopparat Sangtong and Taweesin Wongprot at the Center of Excellence in Wood and Biomaterials, Walailak University, Thailand for helping set up the kiln-drying equipment and Asst. Prof. Dr. Buhnnum Kyokong for useful discussions.

Disclosure statement

The authors have applied for petty-patent entitled “A method for reducing a collapse of oil palm wood during drying”: Thailand (Filing Date: 27 May 2020, Application No. 2003001129), Malaysia (Filing Date: 03 May 2021, Application No. UI2021002432) and Indonesia (Filing Date: 10 May 2021, Application No. S00202103493) pending to Thailand Science, Research and Innovation and Walailak University, Thailand.

Additional information

Funding

This work was supported by the Thailand Science, Research and Innovation and Timber Engineering of Krabi Co., Ltd., Muang, Krabi, Thailand (Grant No. PHD60I0038); and the Walailak University research fund (Grant No. WU60602).