Stavros Avramidis

University of British Columbia | UBC · Department of Wood Science

The mechanisms of moisture diffusion in wood are not yet fully understood, due to the complex and hierarchical structure of the wood cell wall constituents. To investigate this mechanism in this hierarchical structure, fractal geometry analysis was used as proper tool. The objective of this study is to develop a theoretical fractal moisture diffusi...

South Africa is a water scarce country with minimal natural forests. Plantation forest species such as the Mexican tropical hard pine, Pinus patula Schiede & Deppe ex Schltdl. & Cham. , was introduced into the country to satisfy local fibre demand. Today, the majority of pine plantations in South Africa are found in the Mpumalanga province. The pro...

This paper proposes the use of information fusion technology to identify different wood species by combining spectral and spatial information from hyperspectral images and terahertz (THz) spectra. The study utilized five species of coniferous wood as experimental samples. The hyperspectral and terahertz raw images and spectra acquired by the spectr...

The variation in seasonal conditions causes an impact on the wood–water relations and dimensional stability like shrinkage and swelling with solar drying technology, leading to discrepancies in drying qualities. To address this processing problem, we studied the pattern of drying kinetics and dimensional changes in four seasons and Northeast China....

Extractives have an impact on the processing and commercial value of wood. Ultrasound is an environmentally friendly technology commonly employed to reduce the extractive content and thus enhance the permeability of wood. This study aimed to understand the migration mechanism of extractives inside wood during ultrasonic treatment, which may help to...

The quality control of thermally modified wood and identifying heat treatment intensity using nondestructive testing methods are critical tasks. This study used near-infrared (NIR) spectroscopy and machine learning modeling to classify thermally modified wood. NIR spectra were collected from the surfaces of untreated and thermally treated (at 170 °...

Monitoring the moisture content uniformity in kiln-dried wood and preventing large gradients is vital as nonuniformity renders dried timbers susceptible to warpage and degrade. This research uses a gradient-boosting machine learning model to model kiln drying by providing a predictive approach to estimate moisture levels and gradients. A population...

Fast-growingwood is particularly favored as the lightweight material and has potential used in construction and furniture. However, dimensional instability, one of fast-growing wood’s inherent weaknesses, limits its utilization as solid wood products. In this study, fast-growing Ailanthus altissima wood was modified with 1,3-dimethylol-4,5-dihydrox...

Internal moisture distribution seriously affects timber shrinkage relations during drying, and it is also an essential parameter for testing the validity of a three-dimensional heat and mass transfer model. Here, we present an experimental study of 3D changes in moisture content at different stages during constant temperature and humidity drying of...

Understanding wood cell wall pore geometry and distribution is the basis for studying its macroscopic properties. This research investigated the pore fractal dimension using the pore size distribution of selected softwoods and hardwoods. Nitrogen gas analyzer was used to study the detailed structural parameters of wood pore size distributions and u...

Assistant/Associate Professor in Biofuels/Bioenergy/Biorefinery/Forest Products Biotechnology.

Drying is one of the most important processing steps in the production of timber and many of the wood composites. During this process, freshly cut timber, veneer, strands, or wood particles of various shapes and sizes are placed in specially designed chambers where under controlled ambient conditions most of the water present in the pores and cell...

In the native state of a tree, moisture can be present as a liquid solution in the cell lumen (specific for sapwood) and/or in the microstructure of the wood cell wall (bound moisture). In most wood products uses, moisture content has to be reduced significantly in order to match an in use target moisture content. This is carried out through the pr...

Monitoring the moisture content (MC) of wood and avoiding large MC variation is a crucial task as a large moisture spread after drying significantly devalues the product, especially in species with high green MC spread. Therefore, this research aims to optimize kiln-drying and provides a predictive approach to estimate and classify target timber mo...

Western hemlock (Tsuga heterophylla) is a prevalent coastal species in British Columbia (BC). Its wood has a high potential for thermal modification, a process that can affect numerous physical properties, including air permeability. The current study investigates the longitudinal air permeability of hemlock wood modified at three temperature level...

Understanding wood pore geometry and distribution is the basis for studying its macroscopic properties. This research investigated the pore fractal dimension using the pore size distribution of selected softwoods and hardwoods. Mercury intrusion porosimetry explored the detailed structural parameters of wood pore size distributions and assessed the...

The uniformity of final moisture content within a drying timber batch is crucial. Lack of such uniformity leads to producing large percentages of over-dried and under-dried timber, resulting in significant quality degradation and value downgrade. This study aims to predict kiln-dried timber moisture content using its initial moisture value, timber...

The uniformity of final moisture content within a drying timber batch is crucial. Lack of such uniformity leads to undesirable moisture ranges, thus producing large percentages of over-dried and under-dried timber sub-populations, resulting in substantial quality degradation and value downgrade. Because it is an unmanageable task to collectively co...

Applications are invited for a faculty position at the Assistant Professor or Associate Professor level in the field of bioproducts biotechnology in the Department of Wood Science at the University of British Columbia. Preference will be given to visionary candidates who show promise or accomplishments in one or more of the following research stre...

Different mass timber structures require a specific range of wood moisture. Thus, moisture monitoring is a crucial quality control task during timber drying that impacts the properties and quality of the subsequent timber structures. Variations in the average and distribution of the final moisture can result in significant variations in the timber...

Kiln drying is admittedly a significant value-adding step in timber processing where the importance of predicting moisture within a dried batch cannot be overemphasized. This study predicts and characterizes the moisture variation in kiln-dried wood based on the initial and target moisture values using polynomial models. Four polynomial models are...

Machine learning (ML)-based models, decision tree and ANFIS, were used to predict the degree of surface checking and bending properties of 30-month weathered thermally modified timber. The results showed that the investigated initial board properties did not allow accurate predictions of surface checks. ML regression and clustering analysis confirm...

The effect of Thermo-Hydro-Mechanical densification on selected properties of western hemlock was investigated. The drive was to explore the possibility of using hemlock as a replacement for expensive hardwoods for flooring applications. Kiln-dried boards at about 12% moisture content were subjected to densification in a hot press. As a special tre...

This study investigated possibilities to predict the presence of internal checks in thermally modified Norway spruce timber after 2.5 years of weathering based on the initial properties of the boards. Machine-learning classification enabled sorting the input parameters based on their relative importance for accurate predictions. The parameters of t...

The nanoscale wood-water interaction strength, accessible sorption sites, and cell wall pore sizes are important factors that drive water sorption and the hysteresis phenomenon in wood. In this work, these factors were quantitatively studied using molecular simulations based on a cell wall pore model, previously developed by the authors. Specifical...

Predicting the properties of structural timber using a rapid and reliable non-destructive method is a critical quality control task in production. This study investigates using infrared spectroscopy for predicting the density, moduli of elasticity (MOE) and rupture (MOR) of two structural softwoods. Because the produced timber is sometimes planed d...

Applications are invited for a faculty position at the Associate Professor or Professor level in Sustainable Timber-Built Environment in the Department of Wood Science of the Faculty of Forestry at The University of British Columbia. A PhD degree in Structural Mechanics, Structural Engineering, Wood Science, Applied Science, or related field, and e...

Near infrared spectroscopy (NIRS) is a non-destructive method that has been used in wood property assessment. Preliminary studies have revealed its ability to predict wood density and mechanical properties, but with little attention given to the effect of surface quality and wood anisotropy. This study simulates sawmill conditions variable timber s...

Near-infrared spectroscopy (NIRS) is a suitable technique for characterizing many materials, including wood, and has been used to predict several wood properties. However, existing reports on this use of NIRS have paid little attention to the effect of wood surface condition and grain orientation. This study therefore used NIRS to assess wood densi...

A new opening for a graduate student in “Wood Physics or Drying” leading to a PhD degree is available at the Department of Wood Science, Faculty of Forestry, University of British Columbia, Vancouver, Canada. The ideal candidate will have a recently awarded research-based MSc degree in the areas of either wood physics or wood drying (Materials Sci...

This research was done to assess the feasibility of using a Non-Destructive evaluation tool such as Near Infrared Spectroscopy (NIRS) in predicting the wood properties of Pacific North-West Species (Western hemlock and Douglas-fir). We examined the effect of wood surface quality (rough and smooth) on NIRS predictions; where rough surfaced timbers g...

Whether water sorption hysteresis exists above 75 °C and the representation of its relationship with wood softening remains unclear. In this study, sorption hysteresis at three temperature levels, namely, 75, 90 and 99.5 °C, was investigated using accurately controlled conditioning chambers using powder samples from seven wood species. The dry mass...

University of British Columbia Faculty of Forestry Department of Wood Science Assistant Professor of Teaching (Tenure-Track) Wood Products Design and Manufacturing

ASSISTANT PROFESSOR IN SUSTAINABLE BUSINESS MANAGEMENT OF NATURAL RESOURCES (DEADLINE: AUGUST 31, 2020) Job Summary Applications are invited for a faculty position at the Assistant Professor level (tenure-track) in Sustainable Business Management of Natural Resources in the Department of Wood Science, Faculty of Forestry, University of British Col...

Heat treatment (HT) is thought to degrade wood surface wettability and cause gluing problems; this study focused on wettability and surface strength of the surface layer on heat-treated wood. The outer and inner surfaces formed by removing the 1-, 2- and 3-mm surface layers of heat-treated poplar on the tangential section were investigated. Dynamic...

In this study, a method suitable for on-line rapid species classification of western hemlock and amabilis fir (hem-fir) green mix of timber was developed and tested with the use of near infrared spectroscopy (NIRS) and chemometrics. The spectra of 600 wood specimens obtained from each species were collected over the wavelength range of 350–2500 nm....

This study explores the application of near-infrared spectroscopy (NIRS) and least-squares support vector machines (LS-SVM) for in-line determination and classification of green timber mix with respect to species and moisture content (MC). In total, 1200 sapwood and heartwood samples (hem-fir mix) with radial, tangential, and transverse sections ar...

This research focuses on exploring commercial heat treatment on western hemlock product quality for potentially new applications and markets for this abundant Pacific Northwest coast softwood species. In this regard, flatsawn and quartersawn kiln-dried hemlock boards were subjected to the ThermoWood® process in a commercial unit at three temperatur...

Methods suitable for the determination and classification of green timber mix (western hemlock and amabilis fir), with respect to species and moisture content, were developed and tested using near infrared spectroscopy and chemometrics. One thousand two hundred samples were distributed into a calibration set (720 samples) and a prediction set (480...

In continuation of our former study on a novel combined treatment of nitrogen–phosphorus fire retardant and thermomechanical densification on wood, this study focuses on the dynamic wettability and the bonding strength. The contact angle was measured using the sessile drop method and the surface energy was calculated according to the van Oss method...

To enhance compression stability and fire retardancy of densified wood, a new modification method i.e., combined nitrogen–phosphorus (NP) fire retardant pre-impregnation with surface thermo-mechanical densification is used to fabricate a certain thickness of functionalized surface layer on poplar. This combined treated wood is investigated via vert...

Visible and near-infrared (VIS–NIR) spectroscopy was used for classifying and predicting the properties of thermally modified Western hemlock wood. The speci-mens were treated at 170 °C, 212 °C, and 230 °C. The dimensional reduction was performed using linear discriminant analysis, and the resulted dataset was used for wood classiication using the...

Owing to technical difficulties, experimental assessment of wood cell wall pore size distribution (PSD) in the hygroscopic range still remains challenging. Here, a “trial-and-error” approach was proposed to calculate such distribution through bridging experimental and simulated sorption isotherms presented by the authors in the past. Two main assum...

Fibre direction cylindrical specimens from the sapwood and heartwood areas of Paulownia wood were heat treated at 180, 190, and 200°C split in eight groups of ten specimens each. Air and water permeability were measured, thereafter. Results demonstrated that heat treatment had a positive effect on air permeability both in sapwood and heartwood spec...

This study investigated using the stress wave method to predict the properties of thermally modified wood by means of an adaptive neuro-fuzzy inference system (ANFIS) and neural network (NN) modeling. The stress wave was detected using a pair of accelerometers and an acoustic emission (AE) sensor, and the effect of heat treatment (HT) on the physic...

The effect of nano-wollastonite and Aspergillus niger fungus on permeability of historical and common paper was studied here. Specimens were immersed in aqueous wollastonite nano-suspension (NW) at 10, 20, 30, and 40% concentration, and their permeability was finally compared with that obtained from control specimens. Permeability of each specimen...

Classification of thermally modified wood (TMW) allowing the distinction between different processing temperatures and the corresponding changes in wood properties is a crucial task in TMW grading. In this study, stress wave evaluation technique was used to classify the heat treatment level. Accordingly, an acoustic emission (AE) sensor and a pair...

Classification of thermally modified wood is a critical assessment and control task that assures the quality of thermally treated wood. Machine learning methods can be used for identifying the optimal feature(s) for wood classification. In this study, the performance of artificial neural networks (ANN), support vector machines (SVM), and naïve Baye...

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 tempera...

The effect of heat treatment at 50 and up to 150°C was studied on dowel-shape specimens prepared from beech (Fagus orientalis), poplar (Populus nigra), and fir (Abies alba) wood. Specimens were cut into two diameter sizes (18 and 25 mm) to explore the effect of diameter size on permeability. Separate sets of specimens from each size and species wer...

X-ray computed tomography (CT) scanning of sawmill logs is associated with costly and complex machines. An alternative scanning solution was developed, but its data have not been evaluated regarding detection of internal features. In this exploratory study, a knot detection algorithm was applied to images of four logs to evaluate its performance in...

The effect of thermal modification (TM) on the color of western hemlock wood and its physical and mechanical properties were investigated. The focus of this study was the prediction of material properties of thermally modified wood based on the color change via the "group method of data handling (GMDH)" neural network (NN). The NN was trained by co...

Although many properties of plantation wood are greatly enhanced by heat treatment, large quantities of volatile organic compounds (VOCs) are released from this process, resulting in potential problems for the environment and human health. Volatile byproducts were collected from Populus tomentosa wood that was treated at 160, 180, 200, and 220 °C f...

Radio frequency heating combined with convection (RF/C) drying of larch boxed-heart square timber and its influence on drying kinetics such as rate, moisture content distribution, and stresses was explored. Results revealed that RF heating increased the drying rate and in RF/C drying was twice as high as in conventional drying. Below fiber saturati...

Wood cell wall pores are essential for understanding nanostructure and subsequent application to wood processing and new product design. CO2 and N2 sorption isotherms were used to explore nanopores in dried cell walls of Douglas-fir, aspen and western red cedar heartwood specimens. The total cell wall pore volume was estimated as sum of detected mi...

This paper presents the physical mechanisms involved in the migration of bound water (diffusion) in wood. It explains the phenomena of isothermal and non-isothermal moisture diffusion under steady-state and unsteady-state conditions and briefly examines the effect of various wood and ambient parameters that affect the value of the diffusion coeffic...

A spreadsheet for the numerical simulation of one-dimensional unsteady-state nonisothermal moisture diffusion in solid wood in the transverse direction below the fiber saturation point was developed in this work. Calculations for solving a pair of partial differential equations describing the moisture diffusion based on a finite-difference method w...

Elastic strain is one of the most important parameters associated with drying stresses. The research presented in this paper attempts to develop an artificial neural network based model for predicting elastic strain in white birch (Betula platyphylla Suk) disks during drying as a function of temperature, moisture content, relative humidity and dist...

The detection and analysis of drying-induced stresses in wood are of fundamental importance for quality evaluation and grading of kiln-dried lumber, and thus, various such procedures have been developed commercially. In this paper, a softwood drying-induced stress evaluation concept was proposed that is based on the drying rheology and wood mechano...

Hydrothermal–mechanical (HTM) treatment is a combined action of temperature, moisture, and mechanical loads. Various kinds of HTM processes have been developed to produce eco-friendly modified wood products. Among these modification technologies, a combination of surface densification and hydrothermal post-treatment is a promising option that can b...

The intention of this exploratory study was to determine whether near-infrared spectroscopy, combined with multivariate statistical modeling, could become a swift and accurate tool for identifying sub-alpine fir within a typical spruce-pine-fir (SPF) lumber mix in the green chain of a sawmill. This need arises from the difficulty encountered in the...

The use of X-ray computed tomography (CT) scanning of logs in sawmill has become a reality in the last few years, usually with rather costly and complex machines resembling medical scanners. However, a scanning solution has been developed that is less costly and more robust, and therefore more suited for sawmill needs. The rather coarse data from t...

Poplar wood was modified by a combination of thermo-mechanical densification (TMD) and heat treatment (HT) process at five temperatures ranging from 170 to 210°C. A new two-step conditioning method (CM) is suggested, in the course of which the modified wood is submitted to 50°C/99% RH→25°C/65% RH, where RH means relative humidity in the climate cha...

Several machine learning models were used to predict interior spruce wood density using data from open-pollinated progeny testing trial. The data set consists of growth (height and diameter which were used to estimate individual tree volume) and wood quality (wood density determined by X-ray densitometry, resistance to drilling, and acoustic veloci...

The impact of ray and vessel features on the radial air permeability and liquid penetration was compared between poplar (Populus nigra) tension and normal wood. Air permeability was measured by the falling-water volume-displacement method. To measure liquid penetration, specimens were saturated with safranin solution by the full-cell process at low...

The Pacific Coast Hemlock (PCH) or “hemfir” is a dominant species mix in British Columbia that is difficult to kiln dry hence, many mills are quite conservative with their drying schedules. Furthermore, mills tend to dry hemfir with no green moisture content pre-sorting thus promoting high moisture differences within and between dried timbers. In t...

Molecular simulation has been successfully applied to sorption and hysteresis studies of various nanoporous materials, revealing underlying mechanisms that neither theoretical nor experimental approaches can achieve. In this work, the grand canonical Monte Carlo approach is used in a simplified wood-water system to simulate sorption isotherms and h...

The Preisach model, the mathematical form of the independent domain model, has been used tο describe water sorption hysteresis in wood for over 20 years, however, its geometric interpretation has not been fully explored. In this work, it is demonstrated that the geometric interpretation can be used to explain the five experimental hysteresis patter...

The origin of sorption hysteresis in the wood-water system is still under debate. In nanoporous-fluid systems, in general, hysteresis is explained as the manifestation of metastable states in a single pore-fluid system and that is further complicated by the pore connectivity. Cell walls are considered as micro-mesoporous materials and capillary con...

An optimum artificial neural network and a partial least square with discriminant analysis regression were developed and tested for accuracy in distinguishing two wood species by using near-infrared (NIR) spectrum. A mixed population of kiln-dried wood boards of western hemlock (Tsuga heterophylla (Raf.) Sarg.) and amabilis fir (Abies amabilis (Dou...

The bioincising impact of Physisporinus vitreus and Xylaria longipeson the porous structure, and permeability of Douglas- fir containing compression wood was investigated. Fungal cultivation was carried out at 25°C and 85% relative humidity in an incubator for three time periods, namely, 15, 30 and 45 days. Safranin solution was injected into wood...

Quality evaluation and grading of thermally treated wood products are of fundamental importance to their commercial utilization. The combined impacts of conventional drying, thermal post-treatment and transverse dimensions of lumber over the residual stresses and shape deformations of larch (Larix gmelinii) wood were examined. Larch specimens with...

Pinewood nematode (Bursaphelenchus xylophilus) mortality was investigated after ultrasonic treatment at 20 and 40 kHz frequency. Experiments were conducted with infected small wood specimens that were ultrasonically treated for 1, 3, 5 and 7 hours and two variable temperature conditions, namely, a gradually increasing from ambient to a maximum of 7...

The skill in optimized lumber drying lies in controlling the rate of evaporation to match the rate at which moisture is reaching the surface; the aim is to minimize the moisture gradient without damaging the lumber. Adjustable speed drives have proven themselves as a method for reducing energy consumption by reducing fan speed in the later stages o...

Needle fir (Abies nephrolepis) wood was surface densified at two compression ratios (16.1 and 21.7 %), two hot-pressing temperatures (160 and 180 °C) for a pressure holding duration of 10 min. Subsequently, it was thermally treated at two temperatures (180 and 200 °C) for 1 h. The equilibrium moisture content responses and radial swelling strain ra...

Dielectric heating and drying are important nontraditional technologies for the phytosanitation and quality dehydration of wood products. Unit operation optimization requires, among others, knowledge of the variable dielectric properties of wood so that an optimum dielectric generator matching wood impedance is maintained throughout the process. Fo...

In this paper we tested if the value of the radiofrequencies (RF) heating rate during pasteurization of two green softwoods, namely, red cedar and pine, can be estimated by means of an artificial neural networks model that is solved using the Monte Carlo method (MCM). Based on the proposed approach, the value of the RF heating rate was predicted re...

The change of microfibril angle (MFA) in wood cell wall was assessed after drying at 60°C and 70°C to a target moisture content (MC) of 8% or 15%. Despite literature contradictions about the effect of drying on MFA, this study showed that drying increased significantly the MFA, possibly as a result of lateral deformation of cellulose microfibrils d...

Wood is a common material used for the manufacture of many products, and submerged wood, in particular, has been used in niche markets and musical instruments. In order to examine if submerged wood in British Columbia, Canada, would be appropriate for use as musical instruments, a study was performed in 2007 on submerged wood from Ootsa Lake, Briti...