Process for reducing formaldehyde content in the manufacturing of reconstituted wood panels, and reconstituted wood panel

Abstract

The present invention relates to the field of manufacturing construction materials, and specifically to the production of reconstituted wood panels. The process described comprises the steps of: (a) preparing wood chips; (b) preparing wood fibers or particles; (c) bonding the wood fibers or particles using a formaldehyde-based resin and a hydrogen sulfite-based chemical agent; and (d) pressing the wood fibers or particles, with the aim of improving production efficiency and reducing formaldehyde emissions from the final product, thereby complying with the emission standards regulated by certifying bodies. The objectives of the present invention are also achieved by a reconstituted wood panel manufactured using said process.

Description

"PROCESS FOR REDUCING FORMALDEHYDE CONTENT IN THE MANUFACTURE OF RECONSTITUTED WOOD PANELS AND RECONSTITUTED WOOD PANELS". Field of invention

[0001] The present invention relates to the field of manufacturing building materials, specifically to the production of reconstituted wood panels, comprising standard medium-density fiberboard (MDF) and Light (L-MDF) and Ultra Light (UL-MDF) variants, High-Density Fiberboard (HDF), and Medium-Density Particleboard (MDP), as well as High-Density Particleboard. The described process uses formaldehyde-based resins, more specifically urea-formaldehyde (UF) resin, and a chemical agent that acts as a resin curing catalyst and a hydrogen sulfite-based formaldehyde scavenger, aiming to improve production efficiency and reduce formaldehyde emissions from the final product, thus meeting the emission conditions regulated by national and international certifying bodies.In addition to its application in the furniture and construction industries, this technology is relevant to sectors that use reconstituted wood panels, such as the automotive and packaging industries, among others that may use reconstituted wood panels for other purposes. Background of the invention

[0002] There are some alternatives to the use of amines and ammonium salts as catalysts and formaldehyde scavengers described in the scientific and technical literature. However, none of them combines good scavenging power with catalytic power.

[0003] Document CN109111875A describes a curing accelerator for urea-formaldehyde resin with formaldehyde-reducing properties, which adopts an encapsulated structure. This structure is composed of a core (containing aliphatic amines, alcoholic amines, sulfanilurea, cyanamide, ammonium salts, among others) and a capsule wall, consisting of gelatin, chitosan, and acetic acid. The accelerator is designed to reduce the formaldehyde content in urea-formaldehyde resin and improve its curing, aiming to meet formaldehyde emission regulations for wood panels.

[0004] In comparison with the present invention, which uses a hydrogen sulfite-based chemical agent as an effective catalyst and formaldehyde sequestrant, the system presented in patent CN109111875A is more complex in terms of composition, involving a wider range of additives, which increases the cost and difficulty of implementation in production. The invention now proposed stands out. Due to its efficiency in reducing formaldehyde emissions by using fewer components and preserving the technological properties of the panels, the invention offers the possibility of operating with higher molar ratios and lower resin dosage, resulting in improved performance characteristics of MDF / HDF / MDP panels. Furthermore, it allows for more straightforward scalability in production, whereas patent CN109111875A requires more steps and manipulations. Therefore, the invention presents itself as a more practical and efficient solution.

[0005] Brazilian patent document BR 11 2017 002513 2 describes an aldehyde scavenger for urea-formaldehyde resin that includes a sulfite compound, an ammonium salt, free urea, and a liquid medium. The document specifies molar ratio ranges of formaldehyde to urea, aiming to reduce formaldehyde emissions and improve resin curing. Furthermore, the document proposes a composition using sulfite and ammonium salts in specific quantities, resulting in a scavenger that also exhibits storage stability.

[0006] Compared to the present invention, which uses a hydrogen sulfite-based chemical agent as an effective catalyst and formaldehyde sequestrant, the process in document BR 11 2017 002513 2 is more complex and depends of multiple components. The approach of the present invention offers a more simplified solution, efficiently replacing sequestering agents and catalysts with a hydrogen sulfite-based chemical agent, which not only reduces formaldehyde emissions but also maintains the technological properties of the panels. Furthermore, the inventiveness lies in its ability to operate within a wide range of formaldehyde-urea molar ratios, which increases the quality of the final product, simplifying the production process and making it more adaptable. Therefore, the technology of the present invention proves superior in its efficiency, simplicity, and preservation of the characteristics of the produced material.

[0007] Patent JP4102656 describes a scavenging agent for aldehydes, focusing specifically on capturing formaldehyde in aqueous solutions. This agent is composed of a double salt obtained by a neutralization reaction between sodium bisulfite and ammonia in a specific molar ratio. The objective of this agent is to exhibit effective formaldehyde capture properties, demonstrating prolonged effectiveness and preventing discoloration of wood materials such as particleboard and plywood.

[0008] In comparison with the invention now proposed, which uses a hydrogen sulfite-based chemical agent as a catalyst and formaldehyde sequestrant, patent JP4102656 presents a similar approach using hydrogen sulfite, but relies on the formation of a double salt. The approach of the present invention is more efficient, since it not only captures formaldehyde but also simplifies the production process by being able to operate with lower dosages of the hydrogen sulfite-based chemical agent in combination with formaldehyde-based resins. Furthermore, the invention is designed to maintain the technological properties of the panels, which is fundamental to the final product quality. Therefore, the technology of the present invention is superior due to its simplicity and effectiveness in maintaining the integrity of the produced material, as well as ensuring formaldehyde reduction without the need for more complex compositions.

[0009] Patent CN107090255B describes a compound curing agent for wood adhesives, which is made from a combination of several components, including ammonium chloride, urea, water, sodium bisulfite, ammonium persulfate, urotropin, sodium chloride, among others. This curing agent aims to reduce the pH of the adhesion, shortening the curing time of the adhesive used on wood panels.

[0010] In contrast, the invention now proposed uses a hydrogen sulfite-based chemical agent as a catalyst and formaldehyde sequestrant, simplifying the process by combining the curing and formaldehyde capture functions in a single component. While patent CN107090255B involves a complex formulation with several components that can complicate the production process, the approach of the present invention offers efficiency by reducing formaldehyde emissions without compromising the technological properties of the panels. The use of the hydrogen sulfite-based chemical agent in the present invention not only promotes the curing of urea-formaldehyde resins but also enables more effective control over emissions, ensuring a higher quality end product. Therefore, the technology of the present document stands out for its simplicity and effectiveness, offering a more practical and efficient solution for the wood panel industry. Objectives of the invention

[0011] A primary objective of the present invention is to reduce formaldehyde emissions through the use of a hydrogen sulfite-based chemical agent that reduces significantly reduced the free formaldehyde content of the panels, meeting regulatory emission standards.

[0012] A second objective of the present invention is to improve the effectiveness of the curing process. The action of the chemical agent not only sequesters formaldehyde, but also acts as an efficient catalyst in the curing of urea-formaldehyde resin, allowing for more stable production.

[0013] A third objective of the present invention is to simplify the formulation and production process by replacing multiple additives normally required to cure the resin and sequester formaldehyde with a hydrogen sulfite-based chemical agent.

[0014] A fourth objective of the present invention is to preserve the technological properties of the panels, ensuring that the use of the hydrogen sulfite-based chemical agent does not compromise their physical and mechanical characteristics, such as tensile strength, flexural strength, and swelling percentage, with minimum or maximum permitted values ​​established by international standards known to manufacturers of reconstituted wood panels.

[0015] A fifth objective of the present invention is to promote economic efficiency by reducing production costs through the replacement of additives from prior technology. by a hydrogen sulfite-based chemical agent and allow an increase in the formaldehyde / urea molar ratio (F / U) and, consequently, reduce the required resin dosage.

[0016] These objectives aim not only at improving the final product, but also at innovation in the wood panel industry. Brief description of the invention

[0017] The objectives of the present invention are achieved by a process for reducing formaldehyde emissions in the manufacture of reconstituted wood panels, using a thermosetting resin and a chemical agent comprising the following steps: (a) Preparation of wood chips; (b) Preparation of wood fibers or particles; (c) Bonding of wood fibers or particles using a formaldehyde-based thermosetting resin and a hydrogen sulfite-based chemical agent; (d) Pressing of wood fibers or particles.

[0018] The objectives of the present invention are also achieved by a reconstituted wood panel, manufactured by said process with reduced formaldehyde emissions during its use. The reconstituted wood panel may be made of wood fibers or wood particles produced by said process. Detailed Description of the Invention

[0019] Currently, the HDF, MDF, and MDP panel manufacturing industry faces a significant challenge related to formaldehyde emissions from the resins used. Formaldehyde is a chemical substance that presents occupational and environmental risks, and therefore its use is regulated by specific standards. Traditional methods for mitigating formaldehyde emissions in panels generally involve the use of additives such as amines and ammonium salts, which not only increase production costs but can also adversely affect the mechanical properties and durability of the panels.

[0020] Formaldehyde-based resins, such as urea-formaldehyde (UF), melamine-formaldehyde (MF), urea-melamine-formaldehyde (MUF), and phenol-formaldehyde (PF), widely used in the manufacture of reconstituted wood panels, have a chemical matrix that can release formaldehyde even when cured. Existing solutions that attempt to reduce these emissions may result in panels with lower mechanical strength and reduced moisture resistance, compromising the essential technological properties of the products.

[0021] The invention proposed here solves these problems in an innovative way by introducing an agent. A hydrogen sulfite-based chemical acts as a catalyst and formaldehyde scavenger. This compound works effectively, allowing the UF resin to cure without the need for additives that compromise the quality of the panel. The innovative features of the invention will be listed below.

[0022] - Significant Reduction in Formaldehyde Emissions: The use of the hydrogen sulfite-based agent allows for the capture of free formaldehyde during the curing process, as it combines formaldehyde-scavenging power with catalytic action.

[0023] - Process Simplicity and Efficiency: Replacing multiple additives with a single chemical agent simplifies the production process. This not only reduces material costs but also facilitates overall process quality control, making it more efficient. Ammonium sulfate, for example, is most effective as a catalyst only at high F / U molar ratios above 1.5. At low F / U molar ratios, ammonium sulfate lacks the acidifying power to promote the UF resin reaction. The hydrogen sulfite-based chemical agent, surprisingly, showed better catalytic effectiveness across a wide range of F / U molar ratios of the UF resin.

[0024] - Maintenance of the Mechanical Properties of Panels: One of the main benefits of using the hydrogen sulfite-based chemical agent is that it demonstrates greater efficiency in scavenging formaldehyde compared to previous technologies, while preserving the technological properties of the panels (such as tensile strength, static bending, and swelling) to the standards desired for civil construction and furniture applications.

[0025] - Environmental and Health Benefits: The present invention not only minimizes formaldehyde emissions but also promotes sustainability in the panel manufacturing industry. The use of an effective sequestrant and the reduction in the use of additives make the final products safer for the environment and for consumers.

[0026] - Process Versatility: The process can be easily adapted to different production lines, being applicable not only to MDF, HDF and MDP, but also to other products that use formaldehyde-based resins, such as plywood and OSB (Oriented Strand Board).

[0027] The use of the hydrogen sulfite-based chemical agent can be extended to other formaldehyde-based resins such as melamine-formaldehyde (MF), melamine-urea-formaldehyde (MUF), and phenol-formaldehyde (PF). This allows manufacturers from various sectors to adopt the technology, expanding the reach and impact of the invention.

[0028] Therefore, the purpose of this invention goes beyond simply reducing formaldehyde; it establishes itself as a cutting-edge solution that balances efficiency, quality, and sustainability, comprehensively addressing the problems existing in the state of the art.

[0029] UF resins have urea and formaldehyde as their main components in water as a solvent. These two components are reacted under specific conditions of molar ratio F / U, pH, temperature, and reaction time. Methylation and condensation reactions are catalyzed by the action of hydronium ions (H3O+) or hydroxyl ions (OH-). - To adjust the pH, strong acids or bases are added, such as sodium hydroxide, hydrochloric acid, sulfuric acid, or acidic and basic salts, such as ammonium chloride and ammonium sulfate.

[0030] UF resins exhibit unique viscosity, molar mass distribution, and reactivity characteristics depending on the F / U molar ratio and synthesis conditions during the methylation and condensation steps. For each type of reconstituted wood panel, a specific resin is used in a specific dosage according to the desired density and thickness characteristics.

[0031] The UF resins used in reconstituted wood panels, according to the present invention, have an F / U molar ratio of 0.7 to 1.5, preferably 0.8 to 1.2, with a viscosity of 70 to 400 centipoise and a gel time of 50 to 150 seconds, preferably 60 to 120 seconds.

[0032] The present invention relates to a manufacturing process for reconstituted wood fiber panels, more specifically Medium Density Fiberboard (MDF) and Light (L-MDF) and Ultra Light (UL-MDF) variants, High Density Fiberboard (HDF) and Medium Density Particleboard (MDP), using formaldehyde-based resin, more specifically, urea-formaldehyde (UF) resin and a hydrogen sulfite-based chemical agent as a catalyst and formaldehyde sequestrant. This process not only improves the efficiency in panel production but also significantly reduces formaldehyde emissions, meeting stringent national and international regulatory standards.

[0033] The present invention stands out for its use of a hydrogen sulfite-based chemical agent, which acts on two fronts: as an efficient catalyst for curing UF resin and as an effective scavenger of free formaldehyde during the curing process. This combination is fundamental to guaranteeing the quality of the produced panels, maintaining their... Desirable technological properties, even with reduced formaldehyde doses in the resin.

[0034] The manufacturing process for reconstituted wood panels comprises four main stages, which will be described in detail below. Step (a): Preparation of the Wood Chips

[0035] The process begins with the preparation of the logs, which can be of different species, with Eucalyptus sp. and Pinus sp. being common choices. The logs are fed onto conveyor tables and pass through an industrial chipper.

[0036] Optionally, the logs can be debarked before chipping to remove the bark and obtain higher quality wood chips.

[0037] After crushing, the wood chips are sorted through sieves to separate fractions that are too large or too fine, ensuring they have the appropriate particle size.

[0038] The wood chips can be washed to remove dirt and impurities, increasing the purity of the fibers or particles.

[0039] At the end of this stage, the wood chips have a basic density of 400 to 600 kg / m³. 3 and moisture content between 20% and 50%. The particle size classification is 10-20% fraction Coarse (above 25mm), 70-85% medium fraction (between 15 and 25mm) and 5-10% fine.

[0040] The wood chips are transported on conveyor belts to storage silos. Step 2 - Preparation of fibers or particles

[0041] For each type of product there is a specific preparation method. For MDF and HDF, the wood chips undergo a cooking process followed by defibration, generating moist wood fibers. For MDP, the wood chips undergo a grinding process followed by drying, generating dry wood particles. Preparation of MDF and HDF fibers

[0042] The wood chips are fed into a preheater for cooking. The preheater consists of a vertical vessel where the wood chips are fed at the top via a plug screw, where saturated steam is injected at a pressure of 800 to 1,000 kPa. The wood chips remain in the preheater for 3 to 5 minutes (residence time), which facilitates subsequent defibrillation.

[0043] After the cooking stage, the wood chips are discharged into a shredder. The shredder consists of two parallel discs, one stationary and the other rotating, which has segments with grooves in different directions. The spacing between the discs varies from 2 to 6. millimeters thick, the wood chips are fed into the center of the two discs as they exit the preheater. The rotation of the segmented disc performs the combined action of shear and friction as the chips follow the flow in a radial direction, resulting in the individualization of the wood fibers. Preparation of particles for MDP

[0044] The wood chips are fed into a shredding machine known as an industrial chipper, of the ring-fed chipper type, via mechanical conveyors. The ring-fed chips are adjusted to produce particles (fed chips) with a thickness of 0.5 to 0.8 millimeters. The particles are pneumatically conveyed to intermediate silos.

[0045] The moisture content of the particles must be reduced to 1 to 1.5% dry basis by means of a drying operation. A single-pass vertical drum dryer is commonly used, which may have a pre-drying circuit. The drying agent is usually hot combustion gas originating from biomass combustion or, alternatively, from fuel oil or natural gas originating from a boiler.

[0046] The dry particles are conveyed by mechanical transport to the top of oscillating screens that separate the particles into four fractions: (1) Coarse Particles (Oversize), which are reprocessed; (2) Medium Particles: (3) Fine Particles: which will make up the inner layer; (4) Powder: goes to the boiler for burning. The fine particles still undergo a grinding operation to adjust their size. Medium Particles have an equivalent diameter ranging from 1 to 4 millimeters and Fine Particles have an equivalent diameter ranging from 0.1 to 1.0 millimeters. Step 3 - Gluing

[0047] The bonding process involves applying resin, additives, and emulsion to the fibers (MDF / HDF) or particles (MDP). The application is done using various spray valves that uniformly spray the resin onto the fibers (MDF / HDF) or particles (MDP).

[0048] The most commonly used resins in the panel industry are those based on formaldehyde, such as urea-formaldehyde (UF), melamine-formaldehyde (MF), melamine-urea-formaldehyde (MUF), and phenol-formaldehyde (PF). UF resins are the least expensive, but produce panels with lower moisture resistance compared to MF, MUF, and PF. Bonds between urea and formaldehyde are highly susceptible to hydrolysis in the presence of moisture. Therefore, it is necessary to work with high F / U molar ratios to achieve greater moisture resistance. A high molar proportion of formaldehyde in UF resins is essential. to increase water resistance due to its role in increasing crosslinking density and improving the overall structural integrity of the resin. This results in a more robust network that can withstand moisture exposure.

[0049] Therefore, there is a search for solutions that improve moisture resistance and reduce formaldehyde emissions from panels produced with UF resin. However, most existing solutions compromise the technological properties of the panel. MDF and HDF bonding

[0050] In the case of MDF and HDF production, the resin is applied via spray valves during the pneumatic transport of the fibers in the sizing line (blow line) after exiting the preheater. The hydrogen sulfite-based chemical agent can be mixed with the resin or applied directly to the fibers via the spray valves.

[0051] After the resin is applied, the fibers go through a drying system using hot, dry air, ensuring that the residual moisture content of the fibers remains between 4% and 10%. The bonded fibers are carried by a stream of hot air to cyclones for separation and water removal. The temperature of the hot gas stream varies from 180 to 250°C, and the temperature of the gas stream with vapor at the cyclone outlet varies from 50 to 60°C. MDP gluing

[0052] In the case of MDP production, the resin is applied to the dry particles via spray valves in a sizing vessel equipped with mixing paddles at atmospheric pressure and ambient temperature. The hydrogen sulfite-based chemical agent can be mixed with the resin or applied directly to the particles.

[0053] Other compounds may be added in step (c) of sizing to improve panel performance, including emulsions, pigments, fillers and flame retardants, in a total dosage of up to 10 kg / m². 3 Made of wood.

[0054] Emulsions are those typically used in the manufacture of panels, comprising paraffins, waxes, vegetable oils, silanes, silicones, surfactants, among others. Fire-resistant agents include ammonium phosphate, aluminum hydroxide, boron and its compounds (such as boric acid and borax). Pigments include iron oxide (Fe2O3) for reddish coloration, carbon black to darken the panel, titanium dioxide (TiO2) to lighten the panel, methylene blue or malachite for green color. Fillers include calcium carbonate (CaCO3), kaolin, silica (SiO2).

[0055] After the sizing stage, the fibers (MDF / HDF) or particles (MDP) are sent to the mattress forming line, where they will be pressed into sheets or panels of reconstituted wood. Step 4 - Pressing the Fibers or Particles

[0056] In the MDF / HDF line, the dry, glued fibers are deposited homogeneously on a long mat forming a fiber mattress. In the MDP line, the dry, glued particles are deposited in three layers to form the particle mattress: (1) outer layer of fine particles at the bottom, (2) inner layer of medium particles, and (3) outer layer of fine particles at the top.

[0057] Next, the fiberboard (MDF / HDF) or particleboard (MDP) mat undergoes a pre-pressing operation. In this operation, the height of the mat is reduced by passing it through rollers without the application of heat. The aim is to remove air and improve heat transfer in the presses.

[0058] Optionally, the mattress can be sprayed with water containing release agents to improve its technological properties.

[0059] In the final stage, the formed fiberboard (MDF / HDF) or particleboard (MDP) mattress is subjected to pressing, which can It can be done using two types of presses: static multi-plate presses or continuous presses.

[0060] The mattress enters a press (static or continuous), where high pressures of up to 30 MPa are applied for a period of 15 to 300 seconds at a temperature ranging from 120 to 260°C. The press is heated indirectly using steam or thermal oil.

[0061] This stage culminates in the resin curing reaction and the formation of reconstituted wood, which will be transformed into panels by sectioning the lateral and transverse edges using equipment called a "cross saw".

[0062] Medium-density fiberboard (MDF), and its Light (L-MDF) and Ultra-Light (UL-MDF) variants, have densities ranging from 550 to 800 kg / m³. 3 and high-density fiberboard (HDF) has a density greater than 800 kg / m³. 3 Reconstituted wood particleboard (MDP) has a density ranging from 550 to 650 kg / m³. 3 It can be manufactured with densities above 650 kg / m³. 3 .

[0063] Finally, the panels are transferred to a cooling station, where they complete the curing and stabilization process before proceeding to the finishing stages on calibrating sanders for thickness adjustment and cutting to different dimensions for commercialization.

[0064] The efficiency of the described process is based on the composition and characteristics of the materials that comprise it.

[0065] UF resin is chosen for its relatively low cost and its properties suitable for panel manufacturing. Its characteristics, such as the F / U molar ratio, viscosity, and gel time, are specified according to the type of panel to be produced. Panels produced by the process that is the subject of the present invention typically use UF resin with an F / U molar ratio of 0.7 to 1.5, preferably 1 to 1.5.

[0066] The hydrogen sulfite-based chemical agent comprises hydrogen sulfite salts of alkali or alkaline earth metals, such as sodium, potassium, magnesium or calcium, and organic ions, such as ammonium, methylamine or ethylamine, preferably comprising ammonium hydrogen sulfite salt, dissolved in a water-based solvent, in a mass ratio of 4 to 7 parts of hydrogen sulfite salt to 3 to 6 parts of water.

[0067] Typical dosages of formaldehyde-based resin and hydrogen sulfite-based chemical agent for the production of reconstituted wood panels according to the process of the invention are: 25 to 60 kg of formaldehyde-based resin and 0.1 to 6.5 kg of the hydrogen sulfite-based chemical agent. hydrogen sulfite base per cubic meter (m 3 ) of processed wood.

[0068] Typical dosages of formaldehyde-based resin and hydrogen sulfite-based chemical agent for the production of wood fiberboard (MDF), in its various forms standard MDF, L-MDF, UL-MDF and HDF, according to the process of the invention are preferably: 35 to 50 kg of formaldehyde-based resin and 2.5 to 4.5 kg of hydrogen sulfite-based chemical agent per cubic meter (m³). 3 ) of processed wood.

[0069] Typical dosages of formaldehyde-based resin and hydrogen sulfite-based chemical agent for the production of medium and high-density particleboard (MDP), according to the process of the invention, are preferably: 25 to 40 kg of formaldehyde-based resin and 1 to 4 kg of hydrogen sulfite-based chemical agent per cubic meter (m³). 3 ) of processed wood.

[0070] The hydrogen sulfite-based chemical agent, preferably ammonium hydrogen sulfite, acts as a catalyst for urea-formaldehyde resin and as a formaldehyde scavenging agent, allowing the resin to cure without the addition of other chemicals with catalytic action or additional formaldehyde scavengers.

[0071] Among bisulfite salts, ammonium hydrogen sulfite, along with its other components, qualifies as an excellent scavenger of free formaldehyde in formaldehyde-based resins and is effective as a catalyst, even at low dosages. Its use in panel manufacturing has demonstrated that the addition of other compounds commonly used as catalyst and scavenger additives, such as amines and ammonium salts, is unnecessary.

[0072] To guarantee the quality of the panels, several operational parameters are rigorously controlled during the manufacturing process. Specific conditions are applied to each type of product. The conditions applied to the processing of wood for the production of reconstituted wood panels, preferably of the MDF, HDF and MDP classes, using formaldehyde-based resin and a chemical agent based on a hydrogen sulfite salt, preferably ammonium hydrogen sulfite, are: Temperatures and Pressures:

[0073] Main Pressing: Temperatures between 120 and 250°C, with pressure from 0 to 30 MPa.

[0074] Pressing and Curing Time: Curing time varies from 20 to 250 seconds, depending on the thickness and type of panel.

[0075] Residual Moisture: The ideal residual moisture content after drying the fibers should be maintained between 1% and 10%, ensuring effective curing and the durability of the final product.

[0076] The invention can be widely applied in sectors that use reconstituted wood panels, such as: • Furniture Industry: Production of furniture and components with a lower environmental impact, due to the reduction of formaldehyde emissions. • Civil Construction: Use of MDF and MDP in internal structures, providing lightweight and resistant material. • Automotive Sector: Application in vehicle interiors, taking advantage of the acoustic and aesthetic properties of the panels. • Packaging: Development of boxes and packaging that require strength and lightness, with environmental concerns.

[0077] The advantages and benefits of the invention mentioned are relevant to various industries, especially in the manufacture of materials such as wood panels, where minimizing environmental impact and... Preserving the health of workers and consumers is becoming increasingly important.

[0078] Reducing formaldehyde emissions not only improves indoor air quality, but can also lead to greater product acceptance among health- and environmentally conscious consumers, creating a competitive advantage in the market.

[0079] A more streamlined manufacturing process not only saves costs but can also reduce production time, increasing delivery capacity and operational flexibility. This can be crucial in markets that require rapid responses to consumer demands.

[0080] Preserving the technological characteristics of the panels ensures that they meet essential quality and performance standards for applications in construction and interior design, where durability and functionality are paramount.

[0081] Choosing less toxic materials and reducing the use of chemicals not only improves the company's image in the market, but also meets a growing demand for sustainable products. This can result in an increase in consumers who prefer brands committed to environmentally friendly practices.

[0082] Thus, the present invention not only presents an innovation in the field of MDF, HDF and MDP panel manufacturing, but also provides a robust and sustainable solution to the challenges faced by the industry, ensuring the production of high-quality panels with a lower environmental impact. Examples of embodiments of the invention

[0083] In this section, we will discuss examples of embodiments of the invention, which relates to an innovative manufacturing process for reconstituted wood panels, such as MDF, HDF, and MDP panels. The preferred embodiment of the invention involves the use of UF resin adjusted according to the specific characteristics of each type of panel, aiming to minimize environmental impacts and maximize production efficiency.

[0084] Another preferred embodiment of the invention involves the production of MDF panels using UF resin with a formaldehyde-to-urea molar ratio (F / U) ranging from 0.7 to 1.5, and viscosity adjusted from 70 to 400 centipoise. By applying these parameters, we were able to significantly reduce formaldehyde emissions while ensuring the maintenance of the panel's technological and functional properties.

[0085] Regarding MDP, the preferred embodiment may include the use of wood particles with specific characteristics and dimensions, associated with a UF resin that, for example, may have a formaldehyde-to-urea molar ratio adjusted between 0.6 and 1.4, with a viscosity of 60 to 380 centipoises. This helps ensure that the panel has adequate strength and durability, while maintaining the sustainability of the process. Comparative Test Results

[0086] For Examples 1 through 8, wood fibers were prepared from eucalyptus wood chips with a basic density of 490 kg / m³. 3 , moisture content of 35% and particle size distribution of 14% coarse fraction (above 25 mm), 79% medium fraction (between 15 and 25 mm) and 7% fines - Step (a). The chips were preheated with saturated steam at 950 kPa for 4 minutes and defibrated - Step (b). The fibers were bonded in-line with UF resin at various molar ratios and dosages with the addition of catalyst / sequestrant at various dosages and emulsion at a dosage of 0.1 kg per cubic meter of wood. The fibers were dried in-line by a gas stream at 180°C, separated in a cyclone and sent for mat formation with 7% moisture content at 50°C - Step (c). The fiber mat was compacted in a pre-press and then pressed in a continuous press at 25 MPa for 120 seconds - Step (d).

[0087] The produced panels were analyzed for density, perpendicular tensile strength, swelling, and formaldehyde emission properties according to ABNT NBR 15316-2: 2019 standard. Example 1

[0088] A 15 mm thick medium-density fiberboard (MDF) panel was produced under the conditions described above, using UF resin with a F / U molar ratio of 1.05 at a dosage of 45.2 kg / m³. 3 wood with added ammonium sulfate (catalyst) and urea (sequestrant) at a dosage of 2.85 kg / m³ 3 Made of wood. This PD_1 panel had a density of 704 kg / m³. 3 , perpendicular traction of 6.3 kg / cm 2 , swelling of 13.2% and formaldehyde emission of 6.2 mg / 100g.

[0089] A 15 mm thick medium-density fiberboard (MDF) panel was produced under the conditions described above, using UF resin with a molar ratio F / U of 1.05 at a dosage of 45.2 kg / m³. 3wood, a chemical agent based on ammonium hydrogen sulfite, in a ratio of 7 parts salt to 3 parts water, at a dosage of 1.52 kg / m². 3 Made of wood (catalyst and sequestrant). This DX_1 panel had a density of 703 kg / m³. 3 , perpendicular traction of 6.7 kg / cm 2 , swelling of 12.0% and formaldehyde emission of 5.7 mg / 100g.

[0090] The DX_1 panel, produced according to the invention, exhibited technological properties that were better than or equal to those of the PD_1 panel. Example 2

[0091] A 15 mm thick medium-density fiberboard (MDF) panel was produced under the conditions described above, using UF resin with a molar ratio F / U of 1.11 at a dosage of 40.0 kg / m³. 3 of wood, ammonium sulfate (catalyst) and urea (sequestrant) at a dosage of 4.13 kg / m³ 3 Made of wood. This PD_2 panel had a density of 699 kg / m³. 3 , perpendicular traction of 6.1 kg / cm2 , swelling of 8.8% and formaldehyde emission of 8 mg / 100g.

[0092] A 15 mm thick medium-density fiberboard (MDF) panel was produced under the conditions described above, using UF resin with a molar ratio F / U of 1.11 at a dosage of 40.0 kg / m³. 3 wood, a chemical agent based on ammonium hydrogen sulfite, in a ratio of 7 parts salt to 3 parts water, at a dosage of 2.23 kg / m². 3 Made of wood (catalyst and sequestrant). This DX_02 panel had a density of 699 kg / m³. 3 , perpendicular traction of 7.1 kg / cm 2 , swelling of 8.4% and formaldehyde emission of 6.3 mg / 100g.

[0093] The DX_2 panel, produced according to the invention, exhibited technological properties that were better than or equal to those of the PD_2 panel. Example 3

[0094] A high-density fiberboard (HDF) panel with a thickness of 2.7 mm was produced under the conditions described above, using UF resin with a F / U molar ratio of 0.9 at a dosage of 41.9 kg / m³ of wood, ammonium sulfate (catalyst), and urea (sequestrant) at a dosage of 0.77 kg / m³ of wood. This PD_3 panel exhibited a density of 896 kg / m³, perpendicular tensile strength of 5.5 kg / cm², swelling of 40%, and formaldehyde emission of 7.7 mg / 100g.

[0095] A high-density fiberboard (HDF) panel with a thickness of 2.7 mm was produced under the conditions described above, using UF resin with a molar ratio F / U of 0.9 at a dosage of 41.9 kg / m². 3 wood, a chemical agent based on ammonium hydrogen sulfite, in a ratio of 7 parts salt to 3 parts water, at a dosage of 0.58 kg / m². 3 Made of wood (catalyst and sequestrant). This DX_3 panel had a density of 900 kg / m³. 3 , perpendicular traction of 5.5 kg / cm 2, swelling of 40% and formaldehyde emission of 7.2 mg / 100g.

[0096] The DX_3 panel, produced according to the invention, exhibited technological properties that were better than or equal to those of the PD_3 panel.

[0097] For Example 4, wood particles were prepared from eucalyptus chips with a basic density of 490 kg / m³. 3, 35% moisture content and particle size distribution of 18% coarse fraction (above 25 mm), 73% medium fraction (between 15 and 25 mm) and 9% fines - Step (a). The chips were crushed in an industrial knife ring miller. The particles were dried in a rotating drum with hot gas, reaching a residual moisture content of 2%. The dried particles were separated into four fractions using an oscillating sieve. The coarse particle fraction was reprocessed, and the powder fraction was sent to a boiler. The medium particle fraction underwent a further separation step to reach a particle size of 3 mm (D50). The fine particle fraction was sent to mills to reach a particle size of 0.5 mm (D50) - Step (b). The medium and fine particle streams were sent to a rotary gluing machine where they received different dosages of UF resin with the addition of catalyst / sequestering agent in varying dosages and emulsion at a dosage of 0.1 kg per cubic meter of wood.The bonded particles were sent to form the mattress - Step (c). The particle mattress was... compacted in a pre-press and then pressed in a continuous press at 25 MPa for 100 seconds - Step (d).

[0098] The MDP panels were analyzed for density, perpendicular tensile strength, swelling, and formaldehyde emission properties according to ABNT NBR 14810-2: 2018 standard. Example 4

[0099] A medium-density particleboard (MDP) panel with a thickness of 15 mm was produced under the conditions described above, using UF resin with a molar ratio F / U of 1.06 in the outer layer and 1.25 in the inner layer at a dosage of 30.3 kg / m³ of wood, ammonium sulfate (catalyst) and urea (sequestrant) at a dosage of 1.10 kg / m³ of wood. This PD_4 panel presented a density of 630 kg / m³, perpendicular tensile strength of 5.4 kg / cm², swelling of 20.3%, and formaldehyde emission of 8.0 mg / 100g.

[0100] A medium-density particleboard (MDP) panel with a thickness of 15 mm was produced under the conditions described above, using UF resin with a molar ratio F / U of 1.06 in the outer layer and 1.25 in the inner layer at a dosage of 30.3 kg / m³ of wood, and a chemical agent based on ammonium hydrogen sulfite, in a proportion of 7 parts salt to 3 parts water, at a dosage of 0.9 kg / m³. 3 of wood (catalyst and sequestrant). This DX_4 panel featured density of 630 kg / m³ 3 , perpendicular traction of 5.5 kg / cm 2 , swelling of 20.0% and formaldehyde emission of 6.5 mg / 100g.

[0101] The DX_4 panel, produced according to the invention, exhibited technological properties that were better than or equal to those of the PD_4 panel.

Claims

CLAIMS 1. Process for reducing formaldehyde content in the manufacture of reconstituted wood panels, characterized by using a formaldehyde-based resin and a chemical agent, comprising the following steps: (a) Preparation of wood chips; (b) Preparation of wood fibers or particles; (c) Bonding of wood fibers or particles with formaldehyde-based resin and hydrogen sulfite-based chemical agent; (d) Pressing of glued wood fibers or particles.

2. Process, according to claim 1, characterized in that said hydrogen sulfite-based chemical agent acts as a catalyst for the curing reaction of formaldehyde-based resin and as a scavenger of free formaldehyde.

3. A process according to any one of claims 1 or 2, characterized in that said hydrogen sulfite-based chemical agent comprises hydrogen sulfite salts of alkali or alkaline earth metals, such as sodium, potassium, magnesium or calcium, and organic ions, such as ammonium, methylamine or ethylamine, dissolved in a water-based solvent, in a mass ratio of 3 to 6 parts salts to 7 to 4 parts water-based solvent.

4. Process, according to any one of claims 1 to 3, characterized in that said hydrogen sulfite-based chemical agent comprises ammonium hydrogen sulfite salt.

5. Process, according to any one of claims 1 to 4, characterized in that the resin is a formaldehyde-based thermosetting resin.

6. Process, according to any one of claims 1 to 5, characterized in that said thermosetting resin is selected from among the following resins: Urea-Formaldehyde, Melamine-Formaldehyde, Melamine-Urea-Formaldehyde or Phenol-Formaldehyde.

7. Process, according to any one of claims 5 or 6, characterized in that said thermosetting resin is Urea-Formaldehyde.

8. Process, according to any one of claims 1 to 7, characterized in that the wood is of the genus Eucalyptus sp. or Pinus sp.

9. Process, according to any one of claims 1 to 8, characterized in that the chip preparation step (a) comprises crushing the wood into wood chips and, optionally, washing of the wood chips and / or peeling of the logs before shredding.

10. Process according to any one of claims 1 to 9, characterized in that, in step (c), the bonding of the fibers or particles comprises the application of resin at a dosage of 25 to 60 kg / m³. 3 wood and addition of a hydrogen sulfite-based chemical agent at a dosage of 0.1 to 10 kg / m³. 3 Made of wood.

11. Process, according to any one of claims 1 to 10, characterized in that, in step (b), for the preparation of the fibers, the chips are cooked in a preheater under steam at a pressure of 800 to 1,000 kPa and a residence time of 3 to 5 minutes.

12. Process, according to claim 11, characterized in that, in step (b), preheated chips are fed into a defibrator that separates the fibers by means of the action of two discs, one static with a smooth surface and the other circular with segments with reliefs in different directions that combine simultaneous mechanical shearing and friction action.

13. Process according to claim 12, characterized in that, in step (c), the bonding of the fibers comprises the application of thermosetting resin by means of of sprinkler valves at a dosage of 35 to 50 kg / m³ 3 wood and addition of a hydrogen sulfite-based chemical agent at a dosage of 2.5 to 4.5 kg / m². 3 Made of wood.

14. Process according to claim 13, characterized in that, in step (c), the spun fibers are subjected to drying by a hot gas stream at a temperature of 180 to 250°C and separated from the gas stream enriched with vapor in cyclones with a residual moisture content between 1% and 10%.

15. Process, according to any one of claims 1 to 10, characterized in that, in step (b), the chips are crushed in an industrial ring-knife type milling machine producing particles with a thickness of 0.5 to 0.8 millimeters.

16. Process according to claim 15, characterized in that, in step (b), the particles are subjected to a drying process until they reach a moisture content of 1.0 to 1.5% on a dry basis.

17. Process according to any of the claims 16, characterized in that, in step (b), the particles are separated by size in oscillating sieves into four fractions: (1) coarse, which are reprocessed, (2) medium, with a diameter of 1 to 4 millimeters. (3) fine, further subjected to grinding operations, reaching a diameter of 0.1 to 1.0 millimeter, and (4) powder, which then goes on to be burned in a boiler.

18. Process according to claim 17, characterized in that, in step (c), the bonding of the medium and fine fraction particles comprises the application, in separate vessels, of thermosetting resin by means of spray valves at a dosage of 25 to 40 kg / m³. 3 wood and addition of a hydrogen sulfite-based chemical agent at a dosage of 1 to 4 kg / m².3 Made of wood.

19. Process, according to any one of claims 1 to 18, characterized in that, in step (d), the glued wood fibers or particles are distributed on conveyors, forming a mat, which is pre-pressed to remove air and proceeds to multi-plate presses or continuous presses, wherein the pressure applied during resin curing is up to 30 MPa for a period of time from 15 to 300 seconds at a temperature ranging from 120 to 260°C.

20. Process, according to any one of claims 1 to 19, characterized in that the reconstituted wood panel is produced with wood fibers pressed to an average density varying from 550 to 800 kg / m³. 3 (MDF and variants) or in high density above 800 kg / m³ 3 (HDF), or with wood particles, pressed at a medium density of 550 to 650 kg / m³ 3 (MDP) and even high densities above 650 kg / m³ 3 .

21. Process, according to any one of claims 1 to 20, characterized in that, in the sizing step (c), the addition of the hydrogen sulfite-based chemical agent is carried out by means of independent spray valves on the fibers or particles immediately after application of the formaldehyde-based resin.

22. Process, according to any one of claims 1 to 21, characterized in that, in the sizing step (c), the hydrogen sulfite-based chemical agent is mixed with the resin in a mixing vessel before the resin is sprayed.

23. Reconstituted wood panel characterized by being manufactured by the process as defined in any one of claims 1 to 22.

24. Reconstituted wood panel, according to claim 23, characterized by comprising the following dosage ranges for fiberboard panels (MDF, variants and HDF): formaldehyde-based resin from 35 to 50 kg / m³. 3of wood and a hydrogen sulfite-based chemical agent at a dosage of 2.5 to 4.5 kg / m² 3 Made of wood.

25. Reconstituted wood panel, according to claim 23, characterized by comprising the dosage ranges for particleboard (MDP): formaldehyde-based resin from 25 to 40 kg / m³. 3 of wood and a hydrogen sulfite-based chemical agent at a dosage of 1 to 4 kg / m² 3 Made of wood.