Structural analysis of heat-treated birch (Betule papyrifera) surface during artificial weathering

Effect of artificial weathering on the surface structural changes of birch (Betule papyrifera) wood, heattreated to different temperatures, was studied using the fluorescence microscopy and the scanning electron microscopy (SEM). Changes in the chemical structure of wood components were analyzed by FTIR in order to understand the mechanism of degradation taking place due to heat treatment and artificial weathering. The results are compared with those of the untreated (kiln-dried) birch. The SEM analysis results show that the effect of weathering on the cell wall of the untreated birch surface is more than that of heat-treated samples. The FTIR spectroscopy results indicate that lignin is the most sensitive component of heat-treated birch to the weathering degradation process. Elimination of the amorphous and highly crystallised cellulose is observed for both heat-treated and untreated wood during weathering. It is also observed that heat treatment increases the lignin and crystallised cellulose contents, which to some extent protects heat-treated birch against degradation due to weathering

Surface degradation of CeO2 stabilized acrylic polyurethane coated thermally treated jack pine during accelerated weathering

The thermally treated wood is a new value-added product and is very important for the diversification of forestry products. It drew the attention of consumers due to its attractive dark brown color. However, it loses its color when exposed to outside environment. Therefore, development of a protective coating for this value added product is necessary. In the present study, the efficiency of CeO2 nano particles alone or in combination with lignin stabilizer and/or bark extracts in acrylic polyurethane polymer was investigated by performing an accelerated weathering test. The color measurement results after accelerated weathering demonstrated that the coating containing CeO2 nano particles was the most effective whereas visual assessment suggested the coating containing CeO2 nano particles and lignin stabilizer as the most effective coating. The surface polarity changed for all the coatings during weathering and increase in contact angle after weathering suggested cross linking and reorientation of the polymer chain during weathering. The surface chemistry altered during weathering was evaluated by ATR-FTIR analysis. It suggested formation of different carbonyl byproducts during weathering. The chain scission reactions of the urethane linkages were not found to be significant during weathering

Enhancing exterior durability of jack pine by photo-stabilization of acrylic polyurethane coating using bark extract. Part 1: Effect of UV on color change and ATR–FT-IR analysis

Heat-treated wood is a value-added product but its exposure to various environmental factors leads to discoloration of wood surface due to the photochemical reactions. Discoloration has become an important economic problem for wood industries since product specifications are now more demanding. In addition, stricter environmental legislations necessitate the development of environmentally friendly transparent coatings with minimal use of chemicals which balances aesthetic and protection. In this study, the acrylic polyurethane coating was improved with the addition of natural antioxidant (bark extract) and lignin stabilizer alone or in combination to enhance the resistance of this coating to different weathering factors. An accelerated aging test was conducted with the aim of comparing the acrylic polyurethane coatings containing different additives with the commercially available pigmented solvent borne coating used by industry and organic UV absorbers. The modifications in chemical structure of coatings were characterized by ATR–FT-IR analysis. The color change data showed that the coating containing bark extract was the most effective and performed better than the industrial coating. However, the visual assessment showed that the coating containing bark extract and lignin stabilizer had the best performance. FT-IR analyses suggested that the chain scission reaction took place throughout the weathering but its effect was not significant for any of the coatings

Study of weathering behavior of jack pine heat-treated under different conditions

It is of considerable importance to investigate the influence of weathering on the degradation processes of heat-treated wood. Kiln-dried (untreated) jack pine (Pinus banksiana) and jack pine heat-treated at three different temperatures (190°C, 200°C, and 210°C) were exposed to artificial weathering for different periods in order to understand the degradation processes due to weathering. Before and after exposure, their color and wettability by water were determined. Structural changes and chemical modifications at exposed surfaces were also investigated using SEM, FTIR spectroscopy, and XPS. The results revealed that the photo-degradation of lignin and the presence of extractives play important roles in color change and wetting behavior of heat-treated wood surfaces during weathering. The structural changes also influence the wettability. The effects of weathering for woods heat-treated under different conditions were similar, but different from those for untreated wood

Study of weathering behavior of jack pine heat-treated under different conditions

It is of considerable importance to investigate the influence of weathering on the degradation processes of heat-treated wood. Kiln-dried (untreated) jack pine (Pinus banksiana) and jack pine heat-treated at three different temperatures (190°C, 200°C, and 210°C) were exposed to artificial weathering for different periods in order to understand the degradation processes due to weathering. Before and after exposure, their color and wettability by water were determined. Structural changes and chemical modifications at exposed surfaces were also investigated using SEM, FTIR spectroscopy, and XPS. The results revealed that the photo-degradation of lignin and the presence of extractives play important roles in color change and wetting behavior of heat-treated wood surfaces during weathering. The structural changes also influence the wettability. The effects of weathering for woods heat-treated under different conditions were similar, but different from those for untreated wood

Study of the degradation behavior of heat-treated jack pine (Pinus banksiana) under artificial sunlight irradiation

Heat-treated wood, a relatively new product treated at high temperatures of 180 to 260°C, possesses new versatile and attractive properties, which makes it popular for outdoor applications. It is of considerable importance to investigate the influence of sunlight on the weathering degradation processes. In order to understand the degradation processes, kiln-dried (untreated) and heat-treated (210˚C) jack pine woods (Pinus banksiana) were exposed to artificial sunlight irradiation for different periods. Before and after exposure, their color and wettability by water were determined. Structural changes and chemical modifications at exposed surfaces were also investigated using SEM, FTIR spectroscopy, and XPS. Degradation of middle lamellae, checking of cell wall and destruction of bordered pits were observed on heat-treated wood surfaces due to sunlight irradiation by SEM analyses. FTIR spectroscopy and XPS studies provided information about the behavior of functional groups of lignin during irradiation. The oxygen to carbon ratios revealed that the photo-degradation of lignin and presence of extractives played important roles in discoloration and wetting behavior of heat-treated wood surfaces during irradiation. The structural changes during irradiation also influenced wettabilty of the irradiated samples

Effect of TiO2-containing nano-coatings on the color protection of heat-treated jack pine

The UV protective coatings were developed by incorporating triazine derivative organic UV stabilizers into inorganic titania particles which were produced by sol–gel method. The objective of this study is to delay the color change of heat-treated wood subjected to outdoor conditions. The protective coatings were prepared in air at room temperature. The coatings were not further treated thermally after their application to heat-sensitive materials. Coatings were applied to heat-treated jack pine wood. Subsequently, accelerated aging tests were carried out using coated and uncoated jack pine samples. The color change of the wood samples was studied, and the results were compared. Also, the morphological analyses were done using XPS after having weathered the wood at different times

Changes in wettability of heat-treated wood due to artificial weathering

Effect of artificial weathering on the wettability of three heat-treated North American wood species (jack pine, aspen, and birch) is studied from the point of view of the structural and chemical changes taking place on the wood surface. Weathering increases wettability of all three heat-treated woods by water. Changes in wettability during artificial weathering differ according to heat treatment procedure and wood species and are likely due to combination of structural and chemical changes of the surfaces. Scanning electron microscopic analysis indicates that cracks form due to degradation taking place during weathering. As a result, water has easier entry into the cell wall, which consequently increases wettability. IR spectra suggest that the OH/CH2 ratio for heat-treated specimens is inversely proportional to the contact angle regardless of the type of wood species. The presence of cellulose-rich layer on wood surface and increasing amount of amorphous cellulose transformed from crystallized cellulose due to weathering result in increase in hydroxyl; consequently, it increases heat-treated wood wettability

Effectiveness of bark extracts and CeO2 nano particles as coating additives for the protection of heat-treated jack pine

High temperature heat-treatment of wood, which is value-added green product, is one of the alternatives to chemical treatment. It has better dimensional stability, thermal insulating properties and biological resistance compared to kiln dried wood. It also has dark brown color which is very important for decorative purposes. Unfortunately, this color changes during weathering. Developing a transparent and non-toxic coating for the protection of heat-treated wood against discoloration without changing its natural appearance is the main objective of this study. For this purpose, waterborne acrylic polyurethane base was chosen because of its durability against weathering and non-toxic nature. Natural antioxidants which are extracted from barks and CeO2 nano particles (alone or together with lignin stabilizer) were used as additives to develop different coatings. The protective characteristics of these coatings were compared with highly pigmented and toxic industrial coating under accelerated weathering conditions. The results showed that acrylic polyurethane coatings protected wood better compared to commercially available coating tested in this study. The chemical modifications during accelerated weathering of coated and heat-treated wood surfaces were monitored by XPS analysis and the morphological changes took place during weathering were studied by fluorescence microscope analysis

Effectiveness of bark extracts and CeO2 nano particles as coating additives for the protection of heat-treated jack pine

High temperature heat-treatment of wood for wood preservation is more beneficial compared to chemical treatment. There are several advantages of heat-treated wood compared to kiln dried wood due to the chemical modifications during high temperature heat-treatment. Heat-treated woods have improved dimensional stability, improved thermal insulating properties, and improved biological resistance. Also high temperature heat-treatment changes wood color to a dark brown color which is very important for decorative purposes. But unfortunately this color is not stable and it changes to grey or white depending on the wood species during weathering. Protection of heat-treated wood against discoloration due to weathering is the main objective of this study without changing its natural appearance. For this purpose waterborne acrylic polyurethane base was chosen for their high durability against weathering and non toxic nature. Since heat-treated wood is green product minimal use of chemicals during coating formulation was another very important factor. For this reason natural antioxidants were extracted from barks which are easily biodegradable and the source is renewable in nature. Also CeO2 nano particles were also used alone or together with lignin stabilizer to achieve a better protection against weathering on heat-treated jack pine. The protective characteristics of these coatings are compared with highly pigmented industrial coating under accelerated weathering condition. The results showed better protection of these acrylic polyurethane coatings compared to commercially available coatings used in this study. The chemical modifications during accelerated weathering of these coated heat-treated wood surface was monitored by XPS analysis and the morphological changes took place during weathering was studied by fluorescence microscope analysis