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Paraserianthes falcataria, a low-density wood species underwent viscoelastic thermal compression (VTC) treatment, which was the combination of pre-steaming and compression by hot-pressing, in order to increase its density and mechanical performance. The aim of this study was to evaluate the impact of VTC treatment on the density and moisture conten...
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... the completion of compression via hot-pressing, the laminas were conditioned for about 15 minutes before dimensions were measured. Measurements were 450 mm (length) × 100 mm (width) × 10 mm (thickness) after VTC process ( Figure 2). All laminas were stored in a room with temperature of 20 ± 5°C and relative humidity of 65%. ...
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... the completion of compression via hot-pressing, the laminas were conditioned for about 15 minutes before dimensions were measured. Measurements were 450 mm (length) × 100 mm (width) × 10 mm (thickness) after VTC process ( Figure 2). All laminas were stored in a room with temperature of 20 ± 5°C and relative humidity of 65%. ...
Citations
... However, a drawback these methods share is that the densified wood tends to swell back (shape recovery) when it is subjected to moisture after the process has been completed. Therefore more than two steps are normally necessary to reduce shape recovery, such as additional heating or cooling treatment after pressing, which increases the cost and time of the processing 7,8 . ...
A new two-step densification method for wooden materials entitled hot isostatic pressing (HIP) is proposed. This method has the advantage over previous densification methods that can achieved almost the full densification of wood, reaching values up to 1.47 kg/m³, which exceeds any value ever reported for a hardwood species. Furthermore, it can preserve about 35% of the original volume, in comparison to other methods which typically can preserve only 20% of the volume. Although not tested in this investigation, in principle, the HIP method should be capable of densifying any shape of wood including circular and tubular cross sections because the main densification mechanism is based on gas pressure that is equally exerted in the entire surface, rather than localized mechanical compression, which can only be effective with rectangular cross sections. In the first stage of the two-step proposed method, the compressive strength of the anatomical wood structure is reduced by delignification, and, in the second, a full densification is achieved by hot isostatic pressing under argon atmosphere. Three tropical hardwood species with distinct anatomical characteristics and properties were used to test the method. The HIP-densified wood’s microstructural, chemical, physical, and mechanical properties were assessed. Apart from the high densification values and volume preservation, the results indicate that proposed method was effective for all the tested species, showing homogenous density patterns, stable densification without noticeable shape recovery, and enhanced mechanical properties. Future research should test the HIP method in softwoods and consider the ring orientation in order to enhance the control of the densified geometry.
... Thermo-hydro mechanical (THM) treatment, which heavily relies on high-pressure steam injection, is a commonly utilized densification method in which wood is compressed in a closed chamber with high temperature saturated vapour [4]. VTC (viscoelastic-thermal compression) is a densification method that combines pre-steaming (softening) and hot-pressing to achieve densification without damaging the cellular structure of compressed wood [5][6][7]. ...
... The Janka hardness test, detailed in ASTM D IOP Publishing doi:10.1088/1755-1315/1053/1/012032 2 143 standards, is another standard approach for analyzing the hardness of wood materials [9]. Paraserianthes falcataria, also known as Batai wood, was classified as a light hardwood species with an average density of 360 kg/m 3 [7]. Glue-laminated timber comprises several layers of laminas glued together in a similar parallel direction, with at minimum three layers [8]. ...
... Unpenetrated adhesive would have been the main factor for the sudden peak attained between different layers, as shown in Figure 3. Prior studies on wettability properties of VTC modified Paraserianthes falcataria laminas suggested that highly viscous adhesive such as Polyvinyl Acetate (PVAc) might require a longer period to be diffused inside the laminas; due to the high viscosity value of the adhesive itself, as well as poor wettability properties of the densified laminas [5,7,8]. Furthermore, earlier study suggested that low-density zones have higher void area/open vessels, whilst high-density regions have collapsed vessels [5]. ...
A fast-growing tree species, Paraserianthes falcataria , possessed low value in density. Therefore, it was subjected to a densification treatment, i.e., viscoelastic-thermal compression (VTC), to enhance its density and mechanical performance. The objective of this study was to investigate the correlation between the density profile and hardness of VTC-modified glue-laminated timber. The laminas underwent VTC, whereby five different pre-steaming durations were applied, ranging from 0-30 minutes prior to forming into glue-laminated timber panels. The panels were cut into pre-determined test pieces and subjected to density determination using an X-ray densitometer and hardness test in the tangential direction using the ball indentation method. The correlation analysis found that increasing density slightly enhanced the hardness of the tangential surface of the glue-laminated timber test pieces, whereby the Pearson’s correlation values, r were .074 (0 minutes, non-densified), .154 (0 minutes, densified), -.027 (10 minutes, densified), .088 (20 minutes, densified), and .225 (30 minutes, densified). Nevertheless, the associations were found to be statistically insignificant because the p-values were greater than 0.05, thus suggesting densification treatment did not enhance hardness.
Heat treatment is a modification method that can alter the polymeric components of wood (cellulose, hemicellulose and lignin). Densification technology has emerged as one of the promising technologies capable of improving the properties of low-density wood. In this study, the effects of heat treatment and densification on moisture content, density, and morphological features of low-density Paraserianthes falcataria laminas were examined. Laminas were heat-treated (100°C, 120°C and 140°C for 1 hour) and compressed at 50% compression ratio. Non-heat-treated laminas, on the other hand, were compressed at 40-60% compression ratios. The changes in pores area, moisture content and density of the heat-treated and densified laminas were identified. The lowest moisture content for heat-treated laminas was at 120°C. Laminas with 60% compression ratio were observed to have the highest deformed pores, where it increased the density of the laminas. In summary, heat treatment and densification affected the properties of the laminas. Heat treatment at high temperatures resulted in decreased density and moisture content, while increasing the compression ratio during densification increased the density. The results suggest that combining heat treatment and densification could be a viable method for improving the properties of low-density wood.
A new two-step densification method for wooden materials is proposed. This method achieved wood that was virtually non-porous and fully densified exceeding any value ever reported for a hardwood species. In the first step, the compressive strength of the anatomical wood structure is reduced by delignification, and, in the second, a full densification is achieved by hot isostatic pressing under argon atmosphere. Three tropical hardwood species with distinct anatomical characteristics and properties were used to test the method. The HIP-densified wood's microstructural, chemical, physical, and mechanical properties were assessed. The results indicate that proposed method was effective for all the tested species, obtaining a material that it is mostly non porous, shows homogenous density patterns, preserves the original volume, features great stability and it has enhanced mechanical properties. Therefore, the HIP wood densification may be a promising densification technique since it overcomes several limitations faced by previous wood densification methods.
Wood delignification is a straightforward process of great interest in the development of advanced materials and products for sustainable applications. This process can reduce the stiffness of the wood cell wall by using selective chemical reagents that remove lignin/hemicellulose and thus facilitate its modification in combination with other treatments. This study aimed to compare the efficiency and uniformity of the partial delignification process using the sodium hydroxide and sodium sulfite (NaOH/Na 2 SO 3 ) mixed aqueous solution in the three hardwood species Brosimum utile (Sande), Carapa guianensis (Andiroba), and Dipteryx oleifera (Choiba). These are important tropical tree species, providing essential material for the wood industry. The effects and distribution of the solution were studied based on the variations exhibited by the center and ends of the delignified woods, using chemical composition analysis techniques, FT-IR spectra, optical microscopy, and scanning electron microscopy (SEM). The process allows the partial chemical removal of lignin/hemicellulose in different non-uniform proportions between the center and the ends of the woods under study. The lignin/hemicellulose removal ratios varied widely between the different wood species. The density of delignified wood did not vary significantly after treatment. The modulus of rupture (MOR) and modulus of elasticity (MOE) of delignified wood decreased. The results suggested that denser tropical wood requires the adjustment of the process variables while the proposed method can treat less dense tropical woods. Partially delignified tropical hardwood can be used to develop advanced materials and products for diverse applications.
