Possibilities for Waste Wood Products

Opportunities for environmentally friendly wood products, adhering to the concept of sustainable development, what are the possibilities for waste wood products

In the future, forestry and forestry-related industries will become the focus of discussions about the main challenges of the future. One of the great challenges facing mankind is the development of a sustainable society. Such a society would require the use of renewable materials, significant reductions in the use of non-renewable natural resources, and significant reductions in environmental impact, including significant reductions in greenhouse gas emissions.

One way to reduce CO₂ emissions is to use more wood products and extend the life of these products so that the carbon is stored for longer. Another possibility is to replace energy-intensive materials with wood, and wood-based products. . Forest resources and wood products can play an important role in long-term strategies for sustainable development and mitigating human impact on the environment.

Renewable materials

Replacing non-renewable materials with wood products is critical to the development of a sustainable society, and new knowledge is needed to demonstrate how to design and implement resource-efficient wood products processes with low environmental impact.

In the future, wood products must also be improved to holistically consider and optimize all life cycle stages - production, operation, retrofit and end-of-life.

The development of hydrothermal power and hydrothermal mechanical technologies and wood processing processes, including the energy and material chain from forests to final services, can play a key role in this regard.

In order for wood to compete with other materials in a broad sense, it is not enough to rely solely on the environmental advantages of wood, which according to calculations based on life cycle assessment criteria has lower CO2 emissions. Wood must also be competitive in terms of technical properties, providing not only high material utilization during use, but also competitive economic output.

Some hydrothermal electrical or hydrothermal mechanical processes have high material utilization and low energy consumption, and therefore have economic advantages compared to processing other materials.

The technical and environmental performance of TH or THM treated wood products is not always as competitive as products from other materials and therefore needs improvement. The results of TH or THM treatment in different areas show that the properties of wood: shape stability, strength, surface hardness and durability can be improved.

Potential application areas for TH or THM products are being identified in the construction industry and furniture manufacturing. Extend the life of wood products by improving durability and stability. TH and THM treatments are now generating great interest in industry as a basis for improving the inherent properties of wood and developing new product market portfolios.

TH and THM processing concepts

TH is applied to wood to enhance its properties, dissipate internal stress, dry and soften the wood. Common heat treatment processes include wood drying at high temperatures, drying of wood-based composites or plywood products.

In contrast, THM is mainly used for wood shaping and mold processing, improving wood quality through densification, embossing and wood bending, etc.

Some of these technologies have been around for a long time, and the results of TH or THM machining depend on whether the process is open or closed. In an open system, it is difficult to adequately control process parameters, such as the moisture content of the elements, whereas in a closed system, all parameters involved in the treatment process, such as media type, time, temperature, and humidity, can be accurately controlled.

A traditional example is the thermal degradation of wood, which can have completely different results with or without air.

Usually heating without air is called pyrolysis, such as making charcoal in a closed system, while heating with air is called combustion, which can be complete or incomplete.

Different TH and THM processes can be performed as open or closed processes and often give completely different results.

heat treatment

Heat treatment processes have been around for a long time and include several different methods. In ancient Africa, indigenous people prepared a stick by placing a sharp stick into red-hot coals and then hitting the burnt end with a stone, repeating the process many times until the end became sharp and hard.

The heat treatment process can also change the acoustic properties of wood, which may be of particular interest in musical instrumentation. In most industrialized processes today, heat treatment involves temperatures between 150 and 260°C and treatment times ranging from minutes to hours.

The goals of treating wood are to achieve dimensional stability and increase resistance to biodegradation. The heat treatment process can also be carried out by compressing the wood in the axial or transverse direction. This process is in most cases carried out in a vacuum, in air or using inert gases. Preheated oil can also be used.

In this case, the oil acts as a heat transfer medium and also excludes oxygen from the wood. Due to the severe degradation of wood materials, wood heat treatment exceeding 300°C is of limited practical value. Accelerated aging of wood is a heat treatment process that uses lower temperatures, that is, it is processed in the range of 100-150°C. In most cases, this is done under controlled relative humidity and pressure.

During the 20th century, there were several reports on heat treatment of wood, primarily observing high-temperature drying of wood with discoloration, better dimensional stability, and less hygroscopicity.

To minimize oxidation and its impact on strength, and to achieve rapid heat transfer, they used a method of heating the wood beneath the surface of the molten metal.

When wood is heated in air, the loss in strength per unit of shrinkage efficiency is greater than when the wood is heated with the air excluded. Based on this discovery, a product called Staywood was developed, although heating can improve the dimensional stability of compressed wood and remove important properties such as shape memory.

But the strength of the wood dropped to unacceptable levels and the product was never commercialized. When the wood is heated in steam or water, it degrades faster than when heated in dry conditions. To empirically optimize the thermal stabilization conditions of oak, beech, spruce and pine, a heat treatment method called Feuchte-Wärme-Druck was developed.

The optimal treatment of pine under such conditions is a humidity of 20-30% and a temperature of 160°C for 15 hours in a closed container. Under such conditions, pine has considerable resistance to brown rot fungi. ability, and the decrease in strength is negligible.

Heat treatment significantly affects wood properties such as hygroscopicity, decay resistance, durability, strength and dimensional stability.

In order to increase the understanding of the chemical changes that occur in heat-treated wood, many studies have been conducted to elucidate the chemical degradation of wood components during heat treatment, while a series of chemical reactions occur. These reactions are both endothermic and exothermic, making it almost impossible to determine the onset temperatures of the different reactions, further complicating the analysis due to the interactions between reactions involving different components.

This means that analyzes involving isolated derivative reactions of individual components may be very different from what actually occurs inside the wood, with interactions not only between components within the wood but also between the wood and the treatment atmosphere. Thermal degradation rates of different components of wood are different, with hemicellulose being the highest, cellulose being lower, and lignin being the lowest.

In general, hardwoods are less thermally stable than softwoods, which is attributed to differences in hemicellulose content and composition.

Due to the loss of water-soluble hemicellulosic sugars during heat treatment and their conversion into less hygroscopic furan-based polymers, the equilibrium moisture content is reduced to approximately half that of untreated wood.

During the early stages of weight loss, the hemicellulose polymers decompose, while the cellulose remains unchanged, and during the thermal treatment of wood, autocatalytic reactions of the cell wall components lead to a transformation of the chemical structure.

It is known that during heat treatment of wood under humid conditions, carbonic acid is initially formed due to the cleavage of the acetyl groups of hemicellulose.

Depending on the acid concentration and temperature, hemicellulose hydrolyzes into oligomeric and monomeric structures, with greater weight loss in hardwood than in softwood, probably due to the higher content of acetate acetyl groups in hardwood. Acetic acid is released during heat treatment, which promotes acid hydrolysis.

Subsequent dehydration of the monomeric sugar units to form aldehydes, the pentose sugars to furfural, and the hexasaccharide units to hydroxymethylfuranal have been shown to be accompanied by reduced moisture absorption.

Along with increased dimensional stability and durability, modification also results in color changes and the development of strong odors. In heat treatment of wood above 150°C, strength is reduced, and in mechanical tests the failure modes of heat-treated wood are mostly brittle.

During heat treatment, the density of wood decreases by 5-15%, which of course affects strength, but does not explain the overall decrease in strength. The decrease in strength is due to the degradation of the cell wall matrix due to the degradation of hemicellulose polymers.

General guidelines for strength reduction are 5-10% reduction in hardness, 10-20% reduction in flexural strength, 5-20% reduction in elastic modulus, and 30-80% reduction in impact flexural strength, which means that heat treatment in its current form Timber is not suitable for load-carrying purposes.

Heat-treated wood may be suitable for above-grade outdoor applications due to its greater durability and dimensional stability.

When heat-treated wood is left outdoors, its brown color will quickly fade and eventually turn gray, indicating photolysis and lignin loss from the exposed portions of the wood surface.

Heat treatment provides little or very poor protection against blue rot. Regarding whether heat treatment reduces the susceptibility of wood to surface cracking when exposed to the outdoors: "The extent of cracking due to dimensional changes is reduced compared to natural wood".

In contrast, heat-treated pine and spruce surfaces are just as susceptible to cracking as unmodified wood when exposed to the outdoors.

The tendency of wood to crack during the weathering process is strongly related to the direction of the growth rings of the wood cross-section. To avoid cracking when the wood is used outdoors, wood should be selected with growth rings oriented perpendicular to the exposed wood surface.

The main reason for the differing opinions on the tendency of cracking when exposed to the outdoors is that heat-treated wood is not recommended for use in contact with the ground, due to the lower equilibrium moisture content of heat-treated wood and the partial degradation of the wood components.

For example, most of the hemicellulose is depolymerized and the susceptibility to biodegradation by brown rot fungi is reduced. Due to less degradation of lignin during heat treatment, the protective effect against white rot fungi is poor.

White rot fungi primarily attack the lignin in wood, making aged wood more stable than fresh wood and having better acoustic properties. The natural aging of wood refers to the structural and chemical changes that occur over time when wood undergoes routine changes such as climate and ultraviolet radiation, and does not undergo biodegradation processes.

Generally speaking, as wood ages over hundreds of years, its stiffness and strength increase, but the wood becomes more brittle and less resistant to stretching. The acoustic quality of aged wood is improved, changes that are different from those caused by chemical and thermal treatments.

Regarding the natural aging process of wood at low temperatures, where the temperature is below 50 degrees, there is little or only slight change in the physical, mechanical and chemical properties of the wood during the aging process.

Using FTIR-ATR and UV resonance Raman spectroscopy techniques, it was concluded that time itself does not affect the chemical properties of wood during the aging process. Other factors such as UV rays, humidity, insect or fungal attack and the source of the wood can influence these changes.

Sustainable wood processing is important for future opportunities in environmentally friendly wood products.

Increasing sustainability, sustainable wood processing can reduce reliance on natural forests and promote the sustainable use of forest resources through rational management and regenerative forestry practices.

This helps protect ecosystems, maintain biodiversity, and reduce the negative impact of deforestation on global climate change and reduce carbon emissions. Wood is a renewable material.

At the same time, it has carbon-fixing properties, which can significantly reduce carbon emissions by choosing sustainable wood and using energy-efficient processing methods.

Manufacturing environmentally friendly wood products can be an important way to reduce greenhouse gas emissions and promote a circular economy, and sustainable wood processing can promote the development of a circular economy.

By increasing the recycling and reuse rate of wood waste, resource waste can be minimized and the service life of products can be extended. This practice can reduce the need for raw materials and reduce environmental pressure.

Innovative wood products, sustainable wood processing also encourages the development of innovative wood products. Through technological innovation and process improvement, more environmentally friendly and high-quality wood products can be produced, such as environmentally friendly furniture, building materials, and decorations. These products have good degradability and regeneration properties and meet people's needs for sustainable lifestyles.

As the global awareness of environmental protection increases, the market demand for environmentally friendly wood products continues to grow, through the use of sustainable wood processing and production of environmentally friendly wood products. Enterprises can improve their market competitiveness and gain more business opportunities and consumer recognition. Sustainable wood processing provides huge future opportunities for environmentally friendly wood products. This practice not only helps protect forest resources and the environment, but also creates economic benefits and sustainable development prospects for enterprises.