Method of production of wood agglomerated materials with reduced energy consumption

Abstract

The object of the invention is a method of production of particle boards and medium- density fibre boards (MDFs) produced by the dry methods. The new technology makes the boards of cold pressing using polyvinyl acetate, urea-formaldehyde and melamine-urea-formaldehyde glues and their mutual combinations. The particle or fibrous mat is pressed at 84°C - 105°C and maximum moisture content of 20% to the required thickness, after which it is cooled down intensively while maintaining the required thickness. After the board stabilisation, cold pressing is finished, and the prepared boards are taken out of the press. The production method reduces the energy consumption required for hot pressing by up to 100% and shortens the pressing time by up to 80%, depending on the cooling intensity of the boards in the press. It is an ecological way of producing boards with up to 100% representation of chips and fibres from waste agglomerated materials. Such boards using polyvinyl acetate adhesives meet the requirements of STN EN for physicomechanical properties and formaldehyde content in prepared boards for a dry environment for general purposes, including furniture.

Description

[0001] Method of production of wood agglomerated materials with reduced energy consumption

[0002] Technical field

[0003] Wood industry, furniture industry, waste economy, environment

[0004] Present status of the technique

[0005] Particle boards are produced from wooden particles based on natural wood with the possibility of repeated use of particles from waste agglomerated materials so that the amount of formaldehyde in prepared particle boards does not exceed the permitted standards. Urea-formaldehyde or melamine-urea-formaldehyde glue is applied onto dried wood chips which accumulate into a mat and are pressed in multi-stage discontinuous or continuous presses at the temperature of pressing plates of up to 250 °C for a period between 12.1 to 15.0 seconds per 1 mm of board thickness until the board is hardened (Albert de Mets, 1981 : Continuous operation press. US patent No. 4420299 A, Ahrweiler K.-H., Heimes B., DE, 1992: Means of production of particle boards and similar boards and double side conveyor press to reach this goal. CSFR-277188; also Blauhut W„ DE, 1993: CR-284211 , Kroll D„ 2003: Kontinuierliche arbeitende Presse, DE, EP 000001435288 B1 ). After pressing to the required temperature and moisture content, the boards are air-conditioned and formatted to the required dimensions.

[0006] Glues based on urea-formaldehyde resins and melamine-urea-formaldehyde resins with emission class E1 with an average emission of formaldehyde up to 6.5 mg per 100 g of medium-density fibreboards (MDFs) are used in the production of boards. (Weinkotz Stephan, 2015: Method for producing multi-layered lignocellulose materials having a core with unique properties and at least one upper and one lower cover layer, DE, WO 002016091797 A1 ; also Verfahren zur Herstellung von Lignocellulose-Werkstoffen, WO 002015104349 A2). Glues based on polyvinyl acetate did not harden during the given technological conditions and thus are unusable in this case. Agglomerated materials with zero formaldehyde presence can be produced using polyurethane glue. Using this glue concerning its price and production conditions is not ideal. (Erbreich M., Neubauer G., 2015: Verfahren zur Herstellung einer Kompositionwerkstoffplatte aus lignocellulosehaltigen Bestandteilen und Polyurethan). In the last few years, the main emphasis has been placed on the maximum recycling of agglomerated materials, especially during repeated production of particle boards and fibre boards where the amount of recycled material depends on formaldehyde content in such prepared boards with the use of urea-formaldehyde glues. The residual glue in recycled material and formaldehyde released from the material reduce the amount of utilisable recycled material for maximum tolerance value of formaldehyde content in board prepared using urea-formaldehyde glue.

[0007] The recycled material is cooked in water at a higher pressure to decrease the amount of residual formaldehyde. Certain chemicals can also be added to hydrolyse the glue. This process is accompanied by releasing water vapour and formaldehyde into the environment and creation wastewater containing formaldehyde and used chemicals. The advantage of repeated use of recycled material is thus reduced (Michanickl, A., Boehme, C., 2003: Method for recovering chips and fibres of bonded wood materials involves passing of steam through a vessel with such materials which have been soaked with a heated impregnation solution. DE 10144793; Sandison, M., 2002: Method for recovering wood fibre from compressed fiberboard scrap. Patent No. US 6413364, EP 1095182, also Pfleiderer Unternehmensverwaltung, 1994: Method of recycling wood materials. Patent No. EP 0581039, DE 4224629). The processing of recycled material can eliminate this deficiency based on the submitted patent application (Ihnat, V. et al., 2016: "Method for the preparation of pulp fibre from chip wood waste chipboard and oriented chipboard", PP 50072 - 2016) and in conjunction to technology proposed in this patent.

[0008] The process can also be applied in conjunction with waste from other renewable lignocellulosic materials (Losehand, Ch., 2014: Hochfestes Material aus nachwachsenden Rohstoffen und Verfahren zur Herstellung eines solchen Materials, DE 102014115506 A1 ; also Hofmann, M., Holm, A., Venschott, D., 2003: Holzwerkstoffplatte und Verfahren zu ihrer Herstellung, DE 000010326181 B4).

[0009] The technology of preparation of fibre boards MDFs by dry methods (marking based on STN EN 622-5) is carried out as preparation of lignocellulosic fibres by its defibration from wood chips when water and pressure are applied. Subsequently, the fibrous suspension is drained and dried in a drying unit to reach a water content of 4 % weight / weight. The subsequent technological processes are the same as in the case of particle board production. Dried fibre is coated with urea-formaldehyde glue or melamine-urea-formaldehyde glue; fibre is formed into the shape of a mat or carpet, which is subsequently pressed to reach a necessary pressure to obtain the required bulk density at the temperature of up to 250 °C. During heating, the ureaformaldehyde glue or melamine-urea-formaldehyde glue is hardened between 12.1 and 15.0 seconds per 1 mm of board thickness and thus, the board dimensions are stabilised. After the board conditioning, the board is formatted (Fessenbecker A., Leifeld F., Poulton S., Utecht J., DE, 2015: Method for producing wood fibres and wood fibre boards, EP 000003059056 A1 ; Lundgren G., Schedin K. et al., SE, 1994, Zpusob vyroby lignocelulozovych desek, OR 284373; also Roffael, E., Dix, B., 1995, Verfahren zur Herstellung von Holzspan- und Faserplatten, DE-OS 4428119). The glues based on polyvinyl acetate are unusable under the given technological conditions.

[0010] The basis of the technical solution

[0011] The basis of the invention consists of the use of lignocellulose properties. The lignocellulose in lignocellulosic materials (wood, straw, sugar cane, etc.) softens when temperature and water content increase. The degree of plastification increases with the gradual temperature increase. The basis of the invention joins the stated process of wood plastification with the opposite process of its cooling as one technological unit. By cooling, it is enabled to soften the pressed mat to stabilise so that after the pressing pressure is released, the wood particles do not spring back, and the board has a stable thickness and shape achieved during hot pressing. Thus, a board can be produced where glue does not have to harden during pressing. Instead, the glue can harden gradually during a period of 30 minutes or a more extended period, depending on other technological requirements. This process enables to use of entirely new and ecological glues in the production of lignocellulosic agglomerated materials, e.g. polyvinyl acetate adhesives, which were so far impossible to be used until now due to the need to harden the adhesive in the hot pressing process.

[0012] The listed properties of produced particle boards and fibre boards, which were produced by dry methods according to this invention, do meet the requirements of standard STN EN 312-3 for particle boards for use in a dry environment and the requirements based on STN EN 622-5 for fibre boards produced by dry means for general purposes to be used in a dry environment. The brackets listed values in Example 1 are standard-required values for particle boards and in Example 7 for fibre boards produced by dry means.

[0013] Examples of embodiments of the invention

[0014] Example 1

[0015] Preparation of particle boards without formaldehyde with a thickness of 16 mm is carried out using wood particles obtained from natural wood. Wet wooden particles are dried in a dryer to a moisture content of 1.9 %. The glue mixture is coated on oven-dried particles. This mixture consists of 10% Duvilax D3Rs and 0.8% paraffin in the form of 30% paraffin emulsion with 5% water for dry particles. Surface and central particles are used in a ratio of 1 :1 . The individual components of the glueing mixture are present in the same amount for surface and central particles. After applying the glue mixture, the moisture content in the mat before pressing reaches 14.6%, and the temperature of particles reaches 95 °C. Such particles are pressed to the required thickness of 16 mm under those conditions. After the board reaches the required thickness, it is immediately cooled down intensively and is pressed at a lower temperature until it reaches 70 °C. At the cold press temperature of 20 °C, it takes to reach the temperature is 125 seconds. The board can be subsequently conditioned on the turnstile and formatted. Such prepared wood-particle boards have the following final properties:

[0016] Bending strength - 17.42 N / mm2(13 N / mm2),

[0017] Elasticity modulus E - 1878 N / mm2(1600 N / mm2),

[0018] Tensile strength perpendicular to the board - 0.722 N / mm2(0.35 N / mm2).

[0019] Example 2

[0020] Wood particleboards with a thickness of 16 mm are prepared using wood particles obtained like in Example 1 . Urea-formaldehyde glue Kronores CB 1100 F is coated in 10 % of glue per dry particle with 5% of hardener DAM 390 per dry glue. In addition to the listed components, the glue mixture also contains 0.8% paraffin per dry weight of the chips in the form of a 30% paraffin emulsion with the addition of 5% water per dry weight of the chips. After coating the glue mixture, the particle temperature is 100 °C. Such boards are pressed at the given conditions of Example 1 to the required thickness of 16 mm and are subsequently cooled. The time pressing in cold press at the initial temperature of 20 °C takes 135 seconds for a board to cool down to 65 °C. The board is subsequently conditioned on the turnstile and formatted. Finally, the strength properties have the following values:

[0021] Bending strength - 18.05 N / mm2,

[0022] Elasticity modulus E - 1947 N / mm2,

[0023] Tensile strength perpendicular to the board - 0.86 N / mm2.

[0024] Example 3

[0025] Preparation of particle boards with a thickness of 16 mm is carried out according to Example 2 using melamine-urea-formaldehyde glue Kronores CB 4004 F with an addition of 6 % hardener DAM 390 per dry glue. Other additions and the composition of particles are similar to Example 2. After coating the glue mixture, the board's temperature reaches 100 °C. Such boards are pressed to the required thickness of 16 mm in the same way as listed in Example 1 and are subsequently cooled. The time pressing in cold press at the initial temperature of 20 °C takes 135 seconds for a board to cool down to 65 °C. Further board processing is carried out according to Example 1 . The final strength properties have the following values:

[0026] Bending strength - 19.9 N / mm2(13 N / mm2),

[0027] Elasticity modulus E - 2030 N / mm2(1600 N / mm2),

[0028] Tensile strength perpendicular to the board - 0.97 N / mm2(0.35 N / mm2).

[0029] Example 4

[0030] 100% of wood particles obtained from waste particle boards and non-formaldehyde glue Duvilax D3RS is used according to Example 1 for particle board preparation. The formaldehyde content in the prepared board is not higher than in the original recycled board because glue with zero formaldehyde content is added. The board prepared according to Example 1 has properties similar to Example 1 .

[0031] Example 5

[0032] Wood particles obtained from waste particle boards are mixed with wood particles produced from natural wood in a ratio of 1 :1. For the prepared mixed particles - surface particles as well as central particles, 10% of a mixture of Duvilax D3RS and urea-formaldehyde glue Kronores CB 1100 F together with 5 % hardener DAM 390 per dry glue Kronores in the proportion of 20% with additives of glue mixture components are applied according to Example 1. After coating of glue mixture, the board is prepared according to Example 1 . The formaldehyde content determined by the perforating method is 5.2 mg / 100g of board. The prepared board has the following properties:

[0033] Bending strength - 21 .34 N / mm2,

[0034] Elasticity modulus E - 2262 N / mm2,

[0035] Tensile strength perpendicular to the board - 0.93 N / mm2.

[0036] Example 6

[0037] The preparation of fibre boards (MDFs) produced by the dry method with zero formaldehyde content with a thickness of 16 mm is carried out using wood fibre obtained from natural wood. Wet wood fibres are dried until their moisture content is 1.6%. The glue is coated in the proportion of 15 % dry glue Duvilax D3RS on dry wood fibre and 1 .2% paraffin on dry wood fibre in the form of 30% paraffin emulsion with the addition of 4% water. After the glue mixture application, the temperature reaches 95 °C. The fibrous mat is pressed at the given conditions to a required thickness of 16 mm. After obtaining the required thickness, the board is immediately cooled intensively and pressed until it reaches 65 °C. At the press temperature of 20 °C, reaching this temperature is 135 seconds. The board is subsequently conditioned and formatted. Such prepared boards have the following properties:

[0038] Bending strength - 23.35 N / mm2(20 N / mm2),

[0039] Tensile strength perpendicular to the board - 1 .92 N / mm2(0.55 N / mm2), Elasticity modulus - 2225 N / mm2(2200 N / mm2).

[0040] Example 7

[0041] Preparation of wood fibre boards (MDFs) produced by the dry method with a thickness of 16 mm is carried out according to Example 6 with the use of ureaformaldehyde glue Kronores CB 1100 F in the amount of 13% dry glue per dry wood fibre with an addition of 5% hardener DAM 390 on dry glue and 3% water. After applying the glue mixture, the moisture content of the wood fibre in the mat before pressing reaches 11.5%, and the temperature of the wood fibre reaches 100 °C. Such mat is pressed to the required thickness of 16 mm and immediately cooled in the cold press while maintaining the 16 mm thickness. The pressing time in cold press to reach the temperature of 65 °C at the initial temperature of cold press at 20 °C reaches 135 seconds. The board is subsequently conditioned and formatted. Finally, such prepared boards have the following properties:

[0042] Bending strength - 21 .98 N / mm2(20 N / mm2),

[0043] Tensile strength perpendicular to the board - 1 .73 N / mm2(0.55 N / mm2), Elasticity modulus - 2254 N / mm2(2200 N / mm2).

[0044] Example 8

[0045] The preparation of fibre boards (MDFs) prepared by dry method with a thickness of 16 mm is carried out using wood fibres obtained from natural wood and wood fibre from waste MDF boards. Wet wood fibre is mixed in 70% waste and 30% natural fibre ratios. It is dried in a drier until a moisture content of 1.6% is reached. 15% of glue is applied on the dried mixed fibres, which consists of 30 % urea-formaldehyde glue Kronores CB 1100 F with the addition of 5 % hardener DAM 390 on dry glue and 70 % of Duvilax D3RS. 1.2 % of paraffin in the form of 30 % paraffin emulsion and 3 % water on dry mixed wood fibres is added to the glue mixture. After applying the glue mixture, the board is prepared according to Example 6. The amount of formaldehyde determined with perforating method is 4.9 mg / 100g of board. Such prepared MDF boards have the following parameters:

[0046] Bending strength - 26.14 N / mm2(20 N / mm2),

[0047] Tensile strength perpendicular to the board - 1 .98 N / mm2(0.55 N / mm2), Elasticity modulus - 2258 N / mm2(2200 N / mm2).

[0048] Industrial applicability

[0049] Applicability of the invention is in the wood industry, furniture industry, waste economy and environment.

[0050] The invention enables to:

[0051] 1 . Produce ecological particle and fibre boards prepared by the dry method for indoor environments based on polyvinyl acetate glues with zero formaldehyde content suitable for subsequent furniture production.

[0052] 2. Produce ecological particle and fibre boards produced by the dry method for indoor environments with decreased energy consumption by up to 100 %, which is necessary during pressing on a hot press. For hot pressing of 1 tonne of particle board, 381 kWh / t of energy is consumed (company Dieffenbacher), which at a price of 0.1 € / kWh represents 38.1 Eur / t. Within Europe, 39 million tonnes of particle and fibre boards (MDFs) are produced per year (FAOstat), total consumption of 14,859,000,000 kWh. At the stated price of electricity, energy worth 1 ,485,900,000 EUR will be saved. Method of production of ecological particle and fibre boards produced by dry methods with the use of polyvinyl acetate, urea-formaldehyde and melamine- urea-formaldehyde with shortening the time of pressing from 12.10 s / mm to 3.75 s / mm of thickness depending on the intensity of press cooling. Method of production of particle and fibre boards produced by dry methods with up to 100% ratio of waste raw materials which meet requirements for formaldehyde content in a prepared board for indoor environment with the use of polyvinyl acetate glues and also combining them with urea-formaldehyde and melamine-urea-formaldehyde glues. By recycling particle boards and MDF boards, native wood is also saved. With the price of coniferous wood 27 € / m3and the price of hardwood 42 € / m3, at a ratio of 1 :1 , an average price of 35 € / m3= 58.8 € / t is saved with 100% use of recycled wood. With the annual production of 39 million tonnes of particle boards and MDF boards, wood worth 2,293,000,000 million EUR can be saved.

Claims

Claims1. The method of production of particle boards and medium-density fibre boards obtained from dry methods with the use of wood particles or wood fibres from natural wood obtained by conventional methods, in the amount according to the required bulk density of produced boards between 450 kg / m3and 1100 kg / m3and by use of a surface coating of glue amounting at 4.0% to 20.0% weight / weight of dry glue to dry wood particles, characterised in that, at the minimum temperature of 84°C and the maximum wood particle moisture content of 20 % weight / weight the particle or fibrous mat is pressed to the requested thickness and is intensely cooled down to board thickness to attain the temperature of lower than 70°C in the middle of board crosssection while pressing it to the required thickness while maintaining this thickness at this temperature and this moment cold pressing is finalised, and the prepared boards are taken out of the press and is further processed by the common methods.

2. The method of production of particle boards and medium-density fibre boards, according to claim 1 , is characterised in that the used glue is polyvinyl acetate glues, also preferably urea-formaldehyde and melamine-urea-formaldehyde glues, as well as their mutual combination.

3. The method of production of particle boards and medium-density fibre boards, according to claims 1 and 2, is characterised in that the wood chips or wood fibre obtained from waste agglomerated wood materials such as chipboards, mediumdensity fibreboards and oriented strand boards as well as from natural wood are used and mixed in a ratio between 0% and 100% weight / weight by the common methods.