Abstract
The effect of low pressure saturated vapor pre-steaming on restrained shrinkage strain, mechano-sorptive creep and the distribution of moisture content was investigated during conventional drying of wood discs. Mechano-sorptive creep was furthermore modelled by artificial neural network theory with five inputs, i.e., pre-steaming and drying temperatures, wood moisture content, relative humidity and distance from the pith. Results revealed that, pre-steaming partly reduced the variation of moisture content distribution along radial direction, increased restrained shrinkage strain in heartwood and decreased in sapwood and slightly decreased the mechano-sorptive creep. The neural network model provided reasonable prediction results, namely, the coefficient of determination for training, validation and test sets greater than 0.95. Keywords: Artificial neural network, Betula platyphylla, mechano-sorptive creep, restrained shrinkage strain, white birch discs
Highlights
Numerous studies have been carried out for the improvement of wood drying quality with various pretreatments, such as chemical modification, dry or wet heat treatment
The aim of this study is to explore the effect of pre-steaming on drying strains and moisture content (MC) distribution in wood during drying process, to understand the controlling mechanisms and to develop an artificial neural networks (ANN) model to predict mechano-sorptive creep in a non-destructive, swift and inexpensive way
The results show that pre-steaming could partly reduce the variation of MC from pith to bark in wood discs, that is reduce the moisture gradient in radial direction, and this will result in better drying quality
Summary
Numerous studies have been carried out for the improvement of wood drying quality with various pretreatments, such as chemical modification, dry or wet heat treatment The latter is exposing wood to saturated steam for a period of time just before drying begins (pre-steaming). Pre-steaming has been reported to increase dimensional stability (Fruhwald 2006) and wood permeability (Dashti et al 2012, Ratnasingam et al 2014), reduce moisture gradients within wood (Simpson 1976, Alexiou et al 1990b, Avramidis and Oliveira 1993), and alleviate drying defects (Chafe 1995, Chafe and Carr 1998). Some researchers argued that pre-steaming reduced drying time by increasing drying rate (Simpson 1975, Alexiou et al 1990a, Ratnasingam et al 2014), while others reported that presteaming reduced moisture content (MC) loss rate (Chafe and Ananias 1996). Avramidis and Oliveira (1993) concluded that pre-steaming had no clear influence on drying rate when hem-fir lumber was pre-steamed at 100°C for 5, 10, or 20 hours.
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