Browsing by Author "Savov V."

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    Effect of Hot-Pressing Temperature on the Properties of Eco-Friendly Fiberboard Panels Bonded with Hydrolysis Lignin and Phenol–Formaldehyde Resin
    (2024-04-01) Valchev I.; Savov V.; Yordanov I.; Petrin S.; Antov P.
    Lignin is the natural binder in wood and lignocellulosic plants and is regarded as the main natural and renewable source of phenolic compounds. Its incorporation in the composition of fiberboards will enhance both the environmental performance of the panels and the complex use of natural resources. In recent years, the increased valorization of hydrolysis lignin in value-added applications, including adhesives for bonding fiberboard panels, has gained significant research interest. Markedly, a major drawback is the retention of lignin in the pulp until the hot-pressing process. This problem could be overcome by using a small content of phenol–formaldehyde (PF) resin in the adhesive mixture as an auxiliary binder. The aim of this research work was to investigate and evaluate the effect of the hot-pressing temperature, varied from 150 °C to 200 °C, in a modified hot-press cycle on the main physical and mechanical properties of fiberboard panels bonded with unmodified technical hydrolysis lignin (THL) as the main binder and PF resin as an auxiliary one. It was found that panels with very good mechanical properties can be fabricated even at a hot-pressing temperature of 160 °C, while to provide the panels with satisfactory waterproof properties, it is necessary to have a hot-pressing temperature of at least 190 °C.
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    Effect of Hot-Pressing Temperature on the Properties of Eco-Friendly Fiberboard Panels Bonded with Hydrolysis Lignin and Phenol–Formaldehyde Resin
    (2024-04-01) Valchev I.; Savov V.; Yordanov I.; Petrin S.; Antov P.
    Lignin is the natural binder in wood and lignocellulosic plants and is regarded as the main natural and renewable source of phenolic compounds. Its incorporation in the composition of fiberboards will enhance both the environmental performance of the panels and the complex use of natural resources. In recent years, the increased valorization of hydrolysis lignin in value-added applications, including adhesives for bonding fiberboard panels, has gained significant research interest. Markedly, a major drawback is the retention of lignin in the pulp until the hot-pressing process. This problem could be overcome by using a small content of phenol–formaldehyde (PF) resin in the adhesive mixture as an auxiliary binder. The aim of this research work was to investigate and evaluate the effect of the hot-pressing temperature, varied from 150 °C to 200 °C, in a modified hot-press cycle on the main physical and mechanical properties of fiberboard panels bonded with unmodified technical hydrolysis lignin (THL) as the main binder and PF resin as an auxiliary one. It was found that panels with very good mechanical properties can be fabricated even at a hot-pressing temperature of 160 °C, while to provide the panels with satisfactory waterproof properties, it is necessary to have a hot-pressing temperature of at least 190 °C.
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    Effect of Hydrolysis Regime on the Properties of Fibers Obtained from Recycling Medium-Density Fiberboards
    (2023-07-01) Savov V.; Antov P.; Panchev C.; Lubis M.A.R.; Lee S.H.; Taghiyari H.R.; Todorova M.; Petrin S.
    Unlike the recycling of particleboards, the recycling of medium-density fiberboards (MDF) is not a widespread industrial practice, and currently, most waste MDF panels are landfilled or incinerated after the end of their life cycle. Therefore, it is of great importance to develop cost-effective methods for MDF recycling. The extraction of resins used for bonding the panels, mostly urea–formaldehyde (UF) resins, is carried out mainly with hydrolysis. Hydrothermal hydrolysis is a more environmentally friendly and cheaper recycling technique compared to acid hydrolysis and allows obtaining a high yield of recycled fibers. The aim of this research work was to investigate and evaluate the effect of hydrolysis regime applied on its efficiency and on the properties of the recycled MDF fibers. For this purpose, thermal hydrolysis was carried out in an autoclave with saturated steam as a heat carrier. The main novelty of the research is the preliminary preparation of the recyclable MDF in samples with dimensions close to those of pulp chips. The effect of hydrolysis regime characteristics, i.e., process time and temperature on the properties of recycled MDF wood fibers, was studied. The hydrolysis temperatures used were 121 °C (saturated steam pressure of 0.2 MPa) and 134 °C (saturated steam pressure of 0.3 MPa); for each temperature, three durations were applied—30, 45, and 60 min. After hydrolysis, the resulting fiber fraction was refined using a hammer mill. The fractional and elemental composition of the recycled fibers obtained were evaluated. The hemicellulose content after each hydrolysis treatment was also determined. The chemical oxygen demand (COD) was defined as an indicator of wastewater contamination and as an indirect indicator of the quantitative yield of the process. The results revealed no significant changes in the elemental composition of the recycled fibers, and the hydrolysis regimes used showed no decrease in pentosan content. The recycled MDF fibers exhibited similar fiber morphology and fractional composition, being shorter than fibers from industrial pulp. The increased temperature and time of hydrolysis resulted in a significant increase in COD values. Based on the obtained results, with a view to the slightest contamination of wastewater (as determined by COD), the most promising hydrolysis regime was at a temperature of 121 °C and a time of 30 min. It should be emphasized that for a confirmation of this statement, the properties of MDF panels fabricated with fibers recycled in different regimes should be subsequently investigated.
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    Effect of the Adhesive System on the Properties of Fiberboard Panels Bonded with Hydrolysis Lignin and Phenol-Formaldehyde Resin
    (2022-05-01) Savov V.; Valchev I.; Antov P.; Yordanov I.; Popski Z.
    This study aimed to propose an alternative technological solution for manufacturing fiberboard panels using a modified hot-pressing regime and hydrolysis lignin as the main binder. The main novelty of the research is the optimized adhesive system composed of unmodified hydrolysis lignin and reduced phenol–formaldehyde (PF) resin content. The fiberboard panels were fabricated in the laboratory with a very low PF resin content, varying from 1% to 3.6%, and hydrolysis lignin addition levels varying from 7% to 10.8% (based on the dry wood fibers). A specific two-stage hot-pressing regime, including initial low pressure of 1.2 MPa and subsequent high pressure of 4 MPa, was applied. The effect of binder content and PF resin content in the adhesive system on the main properties of fiberboards (water absorption, thickness swelling, bending strength, modulus of elasticity, and internal bond strength) was investigated, and appropriate optimization was performed to define the optimal content of PF resin and hydrolysis lignin for complying with European standards. It was concluded that the proposed technology is suitable for manufacturing fiberboard panels fulfilling the strictest EN standard. Markedly, it was shown that for the production of this type of panels, the minimum total content of binders should be 10.6%, and the PF resin content should be at least 14% of the adhesive system.
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    Effect of the Adhesive System on the Properties of Fiberboard Panels Bonded with Hydrolysis Lignin and Phenol-Formaldehyde Resin
    (2022-05-01) Savov V.; Valchev I.; Antov P.; Yordanov I.; Popski Z.
    This study aimed to propose an alternative technological solution for manufacturing fiberboard panels using a modified hot-pressing regime and hydrolysis lignin as the main binder. The main novelty of the research is the optimized adhesive system composed of unmodified hydrolysis lignin and reduced phenol–formaldehyde (PF) resin content. The fiberboard panels were fabricated in the laboratory with a very low PF resin content, varying from 1% to 3.6%, and hydrolysis lignin addition levels varying from 7% to 10.8% (based on the dry wood fibers). A specific two-stage hot-pressing regime, including initial low pressure of 1.2 MPa and subsequent high pressure of 4 MPa, was applied. The effect of binder content and PF resin content in the adhesive system on the main properties of fiberboards (water absorption, thickness swelling, bending strength, modulus of elasticity, and internal bond strength) was investigated, and appropriate optimization was performed to define the optimal content of PF resin and hydrolysis lignin for complying with European standards. It was concluded that the proposed technology is suitable for manufacturing fiberboard panels fulfilling the strictest EN standard. Markedly, it was shown that for the production of this type of panels, the minimum total content of binders should be 10.6%, and the PF resin content should be at least 14% of the adhesive system.
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    Optimization of the hot-pressing regime in the production of eco-friendly fibreboards bonded with hydrolysis lignin
    (2022-11-26) Valchev I.; Yordanov Y.; Savov V.; Antov P.
    This research was aimed at studying the potential of using residual lignin from acid hydrolysis as a binder in manufacturing eco-friendly, dry-process fibreboards. For that purpose, a modification of the adhesive system and hot-pressing regime was conducted. The adhesive system applied was composed of 2 % phenol-formaldehyde (PF) resin and 10 % hydrolysis lignin (based on the dry fibres). The PF resin does not only act as a binder but generally contributes to the even distribution and good retention of the main binder – hydrolysis lignin. A specific hot-pressing cycle was used. In the first stage, the pressure was 1.0 MPa, followed by an increased pressure of 4.0 MPa, and subsequent cooling. The purpose of the initial lower pressure was softening the lignin and reduction of the material moisture content. The effect of the second stage of hot-pressing on the properties of eco-friendly fibreboards was investigated. It was determined that the fibreboards produced with 2 % PF resin and 10 % hydrolysis lignin have similar physical and mechanical properties to those of the control panels, produced with 10 % PF resin at a standard hot-pressing cycle. The findings of this work demonstrate that residual hydrolysis lignin can be effectively utilized as a binder in the production of eco-friendly, dry-process fibreboards with acceptable physical and mechanical properties.
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    Optimization of the hot-pressing regime in the production of eco-friendly fibreboards bonded with hydrolysis lignin
    (2022-11-26) Valchev I.; Yordanov Y.; Savov V.; Antov P.
    This research was aimed at studying the potential of using residual lignin from acid hydrolysis as a binder in manufacturing eco-friendly, dry-process fibreboards. For that purpose, a modification of the adhesive system and hot-pressing regime was conducted. The adhesive system applied was composed of 2 % phenol-formaldehyde (PF) resin and 10 % hydrolysis lignin (based on the dry fibres). The PF resin does not only act as a binder but generally contributes to the even distribution and good retention of the main binder – hydrolysis lignin. A specific hot-pressing cycle was used. In the first stage, the pressure was 1.0 MPa, followed by an increased pressure of 4.0 MPa, and subsequent cooling. The purpose of the initial lower pressure was softening the lignin and reduction of the material moisture content. The effect of the second stage of hot-pressing on the properties of eco-friendly fibreboards was investigated. It was determined that the fibreboards produced with 2 % PF resin and 10 % hydrolysis lignin have similar physical and mechanical properties to those of the control panels, produced with 10 % PF resin at a standard hot-pressing cycle. The findings of this work demonstrate that residual hydrolysis lignin can be effectively utilized as a binder in the production of eco-friendly, dry-process fibreboards with acceptable physical and mechanical properties.
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    Structural application of eco-friendly composites from recycled wood fibres bonded with magnesium lignosulfonate
    (2020-11-01) Antov P.; Jivkov V.; Savov V.; Simeonova R.; Yavorov N.
    The pulp and paper industry generates substantial amounts of solid waste and wastewater, which contain waste fibres. The potential of using these recycled wood fibres for producing eco-friendly composites that were bonded with a formaldehyde-free adhesive (magnesium lignosulfonate) and their use in structural applications was evaluated in this study. Fibreboards were produced in the laboratory with a density of 720 kg·m−3 and 15% magnesium lignosulfonate gluing content, based on the dry fibres. The mechanical properties (bending strength, modulus of elasticity and internal bond strength), physical properties (thickness swelling and water absorption) and formaldehyde content were determined and compared with the European Standards requirements for wood-based panels. In general, the laboratory-produced panels demonstrated acceptable mechanical properties, such as bending strength (18.5 N·mm−2) and modulus of elasticity (2225 N·mm−2), which were higher than the minimum requirements for type P2 particleboards and equal to the requirements for MDF panels. The moisture properties, i.e., thickness swelling (24 h) and water absorption (24 h) significantly deteriorated. The free formaldehyde content of the laboratory-produced composites (1.1 mg/100 g) reached the super E0 grade (≤1.5 mg/100 g), which allowed for their classification as eco-friendly, low-emission wood-based composites. The L-type corner joints, made from the developed composites, demonstrated significantly lower bending capacity (from 2.5 to 6.5 times) compared to the same joints made from MDF panels. Nevertheless, the new eco-friendly composites can be efficiently utilised as a structural material in non-load-bearing applications.