Experimental and numerical analysis of poplar thermodegradation
Abstract
Wood heat treatment (WHT) is an eco-friendly preservation process to improve material
properties, such as dimensional stability and durability. This value-added technique had a huge
development in the last decades and, concerning heating rate and treatment duration, presents
similar operating conditions to slow pyrolysis. The treatment is conducted within an inert
atmosphere (nitrogen or vacuum) with a temperature ranging between 180 °C and 240 °C and is
characterized by a low heating rate in the order of 0.25 to 1 °C min-1. Due to heat effect, wood
polymers undergo a thermodegradation characterized by a mass loss. This parameter
characterizes treatment progress and is used as a quality control indicator. The present study
aims to analyze the effect of treatment intensity (operating temperature for a given process
duration) on thermodegradation of a hardwood species (Poplar, Populus nigra). Experiments were
performed within a conduction oven under nitrogen on large scale boards (25 x 11 x 2.5 cm). Five
temperatures were studied in a stablished range between 200-240 °C with a slow heating rate of
1 °C min-1 and 10 h of treatment duration. A maximum mass loss of 21.02 wt% was observed at
the higher temperature (240 °C). The lower mass loss value 6.19 wt% was recorded for the
experiment performed at 200 °C. Based on measured data, a numerical model for instantaneous
mass loss prediction during thermal process has been developed. A two-step kinetic mechanism
was adopted to simulate reaction rate of wood components degradation. The reaction rates from
numerical results agree with observations reported in literature showing a more pronounced
thermodegradation when treatment temperature increases. A comparison between experimental
and numerical results allows the model’s accuracy evaluation.