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Binderless composite panels are manufactured from wood or non-wood lignocellulosic particles as well as fibers bonded together without using any adhesives. They have recently attracted increasing attention due to their numerous advantages, such as being eco-friendly and the possibility to use agricultural wastes, as well as resulting in the low production cost given that adhesives are not required in the production process. However, low dimensional stability and internal bond strength of the final products are two of the challenges commonly faced. Several studies have been conducted to develop a technique that will allow binderless boards with high dimensional stability. Some techniques or manufacturing processes include hot-pressing, steam or steam-exploded pretreatment, followed by the hot-pressing process, and steam-injection hot-pressing. Since the heat or steam treatment used during the manufacture of compression wood and that of binderless boards are almost same, it is presumed that their dimensional stability mechanisms are also similar. There are a number of ideas offered to explain the mechanisms of self-bonding on binderless boards. These include the thermal softening of the cell wall matrix as well as degradation or decomposition of the chemical components of lignocellulosic materials generating stable free radicals and reactive sites, which then will form cross-linking between polymers in the cell wall. Meanwhile, internal stress relaxation is still infrequently used as a mechanism for dimensional stability in binderless boards. On the other hand, it has been demonstrated that internal stress relaxation plays a significant role in the dimensional stability of compression wood. Therefore, it is suggested that the low-thickness swelling in binderless boards is, among others, caused by internal stress relaxation stored in the cell wall. Therefore, this study aims to review and collect data to clarify the above assumption. It is essential to verify the self-bonding mechanisms of binderless boards to further enhance their performance and promote industrialization. [ABSTRACT FROM AUTHOR]

The objectives of this study were to evaluate some of physical and mechanical properties of rubberwood (Hevea brasiliensis) as function of microwave heat treatment process. The specimens were heat treated at three temperature levels of 150 °C, 180 °C, and 220 °C for 20 min in a small microwave oven connected to a computer. Bending characteristics, namely modulus of elasticity (MOE), modulus of rupture (MOR) as well as hardness of the samples were tested. Dimensional stability in the form of swelling and water absorption of the specimens were also determined. Based on the findings in this work it appears that microwave can be used successfully for heat treatment of rubberwood. Overall mechanical properties of the samples were adversely influenced by the treatment. MOE, MOR and hardness values of the samples treated at a temperature of 220 °C had 2.37, 3.69, and 2.12 times reduced than those of control samples, respectively. Dimensional stability of the heat treated samples as a result of 2-h and 24-h water soaking improved. Micrographs take from scanning electron microscope (SEM) and transmission electron microscope (TEM) revealed that certain amount of damage took place in the cellwall of the treated specimens. Overall discoloration on the samples due to microwave heat treatment was found insignificant. [ABSTRACT FROM AUTHOR]

The objective of this work was to determine effect of heat treatment and compression on some of the mechanical properties of Cappadocian maple (Acer c.) samples. Bending, compression and shear strength along with Brinell hardness of defect free specimens compressed using temperature levels of 120°C, 140°C, and 160°C were evaluated. Based on findings in this work densification of the samples resulted in 59%, 16%, 12%, 28% 145% and 174% increase for modulus of rupture, modulus of elasticity, shear strength, compression strength, hardness in radial and tangential grain orientations, respectively. It seems that data determined in this study would provide basic information on better utilization of Cappadocian maple. The densification process significantly increased the strength properties of specimens. The ideal temperature level was determined as 120°C for the highest bending, shear and compression strength values while the samples exposed to 160°C had the highest radial and tangential hardness values for densified samples. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate some of the properties of densified eastern redcedar as function of temperature and pressure. Surface quality, adhesive bondline shear strength, hardness, and color changes of the samples compressed using different temperature levels ranging from 100 °C to 180 °C were investigated. Based on the findings in this work, surface roughness of compressed specimens decreased with increased temperature. Overall adhesive bondline shear strength of the samples decreased as compared to that of control specimens as a result of compression. It appears that densified samples exposed to a temperature of 180 °C had significantly darker surface than those of the others, based on color measurement. Data found in this work provide some basic information for more efficient use of underutilized species such as eastern redcedar. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the effect of heat treatment on physical and mechanical properties including oven-dry density, weight loss, swelling, shrinkage, and hardness of southern red oak ( Quercus falcata Michx.). The samples were treated at a temperature level of 190 °C for 3 h and 8 h. After heat treatment of the specimens, their dimensional stability in the form of swelling and shrinkage were determined by soaking them in water for 2 and 24 h. Hardness of samples as function of heat treatment was also measured using Janka hardness (ASTM D 1037–12). Tangential, radial and longitudinal swelling values of the samples exposed to 8 h heat treatment and soaked in water for 2 h were 0.245%, 0.236%, 0.098%, respectively. Corresponding values for the control samples were 0.504%, 0.455%, 0.135%. Overall hardness of the specimens was adversely influenced due to heat treatment. Based on the findings in this study shrinkage and swelling of the samples improved as a result of heat exposure. It appears that heat treatment would be a viable method to enhance dimensional stability of red oak for more effective utilization where enhanced hygroscopicity of such species is desired. [ABSTRACT FROM AUTHOR]

The objective of this work was to evaluate the effect of heat treatment and compression on the swelling and surface roughness of Southern red oak (Quercus falcate Michx.) and Southern pine (Pinus taeda L.). Specimens were exposed to temperature levels of 110 °C or 200 °C for 8 h before they were compressed using 2.5 MPa pressure for 5 min. Swelling values of the control and heat-treated samples in three grain orientations were evaluated by soaking them in water for 48 h. A stylus method was employed to determine the surface characteristics of the samples. Three main roughness parameters, namely mean arithmetic deviation of profile (Ra), mean peak-to-valley height (Rz), and maximum roughness (Rmax) were used to evaluate the effect of heat treatment on surface characteristics of the samples. Oak and pine specimens had 39.8% and 28.7% lower tangential swelling values, respectively, than those of control samples as a result of exposure to a temperature of 200 °C. Heat treatment did not make any significant difference on surface quality. Micrographs taken from cross sections of the specimens revealed that there was some cell distortion and modification due to heat treatment as well as compression. Combination of heat treatment and compression can be considered an alternative method to improve certain physical properties of these two species. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate the effect of heat treatment on surface roughness and hardness of four wood species, namely black alder (Alnus glutinosa L.), red oak (Quercus falcata Michx.), Southern pine (Pinus taeda L.) and yellow poplar (Liriodendron tulipifera). Samples were exposed to heat treatment schedules having two temperature and exposure levels of 120°C and 190°C for 3 and 6h, respectively. Average hardness value of red oak samples exposed to a temperature of 190°C for 6h was 41.7% lower than that recorded before the heat treatment. Temperature of 190°C produced 7.9% lower hardness values for black alder with the increased exposure time from 3h to 6h. No significant differences were found between same type of Southern pine and yellow poplar specimens before and after the heat treatment in terms of their hardness values. Among the four species considered in this study red oak having the most porous anatomical structure showed the roughest surface. An improvement in surface quality (Ra) with 7.46% with extending exposure time from 3h to 6h at the temperature level of 190°C was noticed. However all four types of wood species kept in the oven at 190° for 6h presented smoother surface quality. It was found that increased temperature from 120°C to 190°C for both exposure times showed significant differences from the surface quality of nontreated samples at 95% confidence level. The anatomical structure of samples was also observed by scanning electron microscope (SEM) and some damage of the cell wall was determined due to heat treatment. The findings of this study demonstrated that heat treatment resulted in adverse effect on hardness characteristics of the samples. It appears that strength losses can be limited through alternative modified heat treatment techniques. On the other hand, surface quality of the samples from all species was enhanced as a result of heat treatment. Therefore such heat treatment would be considered to improve surface quality of the sample for furniture applications where smooth surfaces are ideal adding potential value on wood material to be used more effectively in furniture manufacturing. [ABSTRACT FROM AUTHOR]

Highlights: [•] Heat treatment reduced strength properties of the samples. [•] Hardness of the samples reduced with increasing exposure time. [•] Roughness of both species did not make any significant difference as a result of heat treatment. [•] Shear strength of the samples reduced due to heat treatment. [Copyright &y& Elsevier]

Highlights: [•] Samples with rougher surface resulted in higher shear strength values. [•] Overall surface roughness of the samples improved as a result of heat treatment. [•] Stylus type equipment can be used to evaluate surface roughness of such samples. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this work is to investigate the effect of heat treatment on swelling, hardness and surface quality of samples from four species, namely mindi (Melia azedarch L.), mahogany (Swietenia macrophyla), red oak (Quercus falcate Michx.) and Southern pine (Pinus taeda L.). Specimens were exposed to temperature levels of 130°C and 200°C for 2 and 8h. Swelling values of the control and heat treated samples were evaluated by soaking them in water for 2h. Surface quality and hardness of the species were also determined using a stylus technique and Janka hardness, respectively. Based on the findings in this study dimensional stability of all four types of samples improved with heat treatment. Surface quality of the specimens was also significantly enhanced by exposing them to heat. Micrographs taken from scanning electron microscope revealed that there was some distortion and modification of the cells due to heat treatment. Overall hardness of the samples was adversely influenced by heat treatment. It seems that properties of the species evaluated in this investigation were more pronounced with increasing temperature and time span. [Copyright &y& Elsevier]

Heat treatment effects on surface properties of wild cherry (Prunus avium) including surface roughness, glossiness, and color stability were evaluated. Samples were exposed to a temperature of 212 °C for 1.5 and 2.5 h. A stylus type profilometer, glossmeter, and spectrophotometer were employed to determine surface characteristics of heat-treated specimens. Glossiness and surface roughness values of the samples decreased with heat treatment compared to those of control specimens. The glossiness and values of surface roughness decreased for the samples with all treatment combinations. The samples had significant discoloration as a result of heat exposure. Color difference of the specimens increased as a result of all treatment schedules. [ABSTRACT FROM AUTHOR]

Abstract: The objective of the study was to investigate the influence of heat treatment and exposure time on surface roughness, wettability, shear strength and hardness of rubberwood, Eastern redcedar and red oak samples. The anatomical structure of each species was also observed using scanning electron microscope (SEM). All specimens were exposed to two different temperature levels, namely 120°C and 190°C for 2 and 8h. Red oak samples had the most enhanced surface quality along with less wettability characteristics followed by rubberwood and Eastern redcedar specimens as function of increased heat exposure. On the other hand, it appears that heat exposure adversely affected shear strength and hardness properties of all three types of samples. These two properties of heat treated samples had reduction values ranging from 52.7% to 69.4% and 10.8% to 33.3%, respectively as compared to those of control samples. [Copyright &y& Elsevier]

Abstract: The objective of this study was to evaluate effect of heat treatment and compression on some properties of Eastern redcedar (Juniperus virginiana) including bonding strength, hardness and surface quality. Specimens were exposed to three temperature levels of 120°C, 160°C and 190°C for 6h before they were compressed using 2.5MPa pressure for 5min. Polyvinyl acetate (PVAc) bonded specimens showed 23.6% reduction in their shear strength when they were exposed to a temperature of 120°C. Such strength reduction values were 44.4% and 64.1% for the specimens exposed to temperature levels of 160°C and 190°C, respectively. The lowest average Janka hardness value of 214.08kg was determined for the samples exposed to a temperature of 190°C while those treated with a temperature of 120°C had the highest hardness value of 397.73kg. It appears that combination of heat treatment and compression enchanced overall surface quality of the samples in the form of their roughness determined using stylus type equipment. [Copyright &y& Elsevier]

Abstract: The objective of the study is to investigate the influence of heat treatment on shrinkage, density, surface roughness, water absorption, diffusion coefficient, swelling and shear strength of eastern redcedar (Juniperus virginiana L.) samples. The anatomical structures of samples are also observed by scanning electron microscope (SEM). Specimens are exposed to temperature levels of 120°C, 160°C and 190°C for time spans of 2 and 8h. Based on the results of this study, dimensional stability in the form of shrinkage of the samples is improved by 2.68%, 1.40% and 1.49% for tangential, longitudinal and radial grain orientations as function of heat treatment, respectively. Heat treatment also enhances surface quality of the samples based on numerical values determined from stylus type of equipment. Water absorption, swelling values and diffusion coefficient of the samples are also reduced with heat treatment. Samples exposed to heat treatment have lower shear strength values, ranging from 25.12% to 52.67%, than those of control samples. It appears that all properties evaluated in this work are affected more pronouncedly as temperature and exposure time is increased. [Copyright &y& Elsevier]

This study investigated some physical and mechanical properties of experimental particleboard panels manufactured from different parts of oil palm including bark, leaves, fronds, and trunk consisting of mid-part and core-part using phenol formaldehyde adhesive. Two types of panels with target densities of 0.80 and 1.0 g/cm 3 were manufactured using pressure levels of 5 and 12 MPa, respectively. Both types of panels were pressed at a temperature of 180°C for 20 min. The findings indicated density and pressure level had an influence on the overall properties of the panels. Samples from the core-part had the highest modulus of rupture (MOR) values followed by those panels made from fronds and bark particles. Such samples satisfied MOR characteristics for particleboard type 13 listed in the Japanese Standard. Similarly, panels made from mid-part and leaves also showed satisfactory MOR values for particleboard type 8 based on the same standard. All panels met the IB strength requirement for type 8 except panels made from leaves made at a target density of 1.0 g/cm 3 pressed at 12 MPa. None of the samples satisfied the thickness swelling requirements. The scanning electron microscopy and Fourier transform infrared spectroscopy study indicated positive effect of the resin on interfacial bonding between the particles. Different parts of oil palm may have potential to manufacture exterior particleboard panels with acceptable strength properties. Dimensional properties of the samples need to be enhanced by using different chemicals such as wax or application of various treatments including heat treatment. [ABSTRACT FROM AUTHOR]

Abstract: Heat treatment is widely used to improve the dimensional stability of wood and wood products. The objective of this study was to evaluate effects of heat treatment on mechanical properties of hazelnut wood (Corylus colurna L.). Samples were exposed to temperature levels of 120°C, 150°C, and 180°C for time spans ranging from 2 to 10h Mechanical properties including compression strength, modulus of elasticity, modulus of rupture, Janka-hardness, impact bending strength, tension strength perpendicular to grain, tension strength parallel to grain, shear strength, and cleavage strength of heat-treated samples were determined. Maximum reduction values of 68.11%, 64.97%, and 58.75% were found for Janka-hardness in radial, tangential, and tension strength parallel to grain for the samples exposed to 180°C for 10h, respectively. Overall results showed that treated samples had lower mechanical properties than those of the control samples. Statistically significant difference was determined (p =0.05) between mechanical properties of the control samples and those of treated at 180°C for 10h. [Copyright &y& Elsevier]

The objective of this work was to investigate the effect of heat treatment on swelling, hardness, and surface quality of four wood species, namely black locust (Robinia pseudoacacia L.), common alder (Alnus glutinosa L.), Western prickly juniper (Juniperus oxycedrus L.) and plum (Prunus domestica L.). Samples were exposed to temperature levels of 130 and 160 °C for 3 and 7 h. Surface quality and hardness of the specimens were determined using a stylus technique and Janka hardness, respectively. Based on the findings in this work overall dimensional stability of all four species improved with heat treatment. Surface quality of the samples was also enhanced due to heat exposure. Scanning electron micrographs revealed that some distortion and cell modification took place as a result of heat treatment. Furthermore, hardness of the samples was adversely influenced by the heat exposure. It appears that the properties of all samples exposed to a temperature of 160 °C for 7 h were more pronounced than those treated with a temperature of 130 °C for 3 h. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this study was to determine the effect of heat treatment on bonding strength of the samples from four different species, namely Scotch pine, oriental beech, white oak and Uludag fir woods. The samples were exposed to three temperature levels of 120°C, 150°C and 180°C for time periods of 2 and 6h. Based on the findings in this work white oak samples had the highest average roughness (Ra ) and maximum roughness (R max) values of 9.49μm and 48.9μm, respectively. It appears that heat treatment enhanced overall surface quality of the samples. [Copyright &y& Elsevier]