RU2484955C2 - Method of making wood-fiber boards - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to woodwork, wasteless processes and ecology. Proposed method comprises grinding of process wood chips in two steps and adding additives to and ground bark to wood-fiber mass in amount of 6-16% of absolutely dry fiber mass. First, bark is ground to 0.05-0.8 mm-particle size and soaked in water at 60-100°C for, at least, 2-4 h at weight ratio of 1:10-1:14. Then, wood fiber carpet is made to form boards to be pressed, tempered and conditioned.

EFFECT: lower costs and emission of formaldehyde.

2 cl, 2 tbl

Description

The invention relates to non-waste and low-waste resource-saving technologies in the production of fiberboards (hardboard) from hardwood, as well as the environment and provides for the disposal of bark in the woodworking industry.

Bark refers to production waste that has not found wide industrial use. The reason for this situation is the special anatomical structure of the cortex and its high humidity, increased ash content. At the same time, a huge amount of bark is formed during the processing of wood and does not find further use in the technological process. From 6 to 20% of the total volume of round timber is accumulated annually at the wood processing enterprises of the bark. The bark is practically not used, a small part of the bark is used for the production of fuel briquettes or is used for burning, and the rest is taken to landfills for burial.

Despite the fact that numerous studies are being conducted and there are developments by domestic and foreign authors on the use of bark, including in the production of plate materials, these developments have not been found to be practical. This is due to the fact that woodworking enterprises have large volumes of higher-quality wood waste (lumpy sawmill waste, furniture and carpentry waste, technological raw materials), which make it possible to obtain both fiberboard and particleboard without additional costs for the development of new technology.

SverdNIIPdrevom developed a method for producing measles slabs, without adding wood fiber and binders, in which it is possible to obtain slabs with a tensile strength under static bending of up to 20 MPa, and swelling in 24 hours is 15%. The technological process of obtaining such plates requires a pressing temperature of 157-167 ° C and a pressure of 5-6 MPa [1].

Due to the low strength, such plates are not widely used.

A known method of producing a composition based on birch bark and melt oil or mealy pitch as a binder component. Birch bark, divided into bark and forehead, crushed to a size of 0.1-50 mm, is used in an amount of up to 99%. In addition, the wood base can be made only from birch bark, or only from bast, or from a mixture of birch bark and bast at a given ratio of components. Tall oil or tall pitch in an amount of up to 25% can be used as a binder component [2].

A known method of using crushed birch bark without synthetic binders for the production of plates with a density of 350 to 800 kg / m ³ [3]. In this case, birch bark is used, crushed to a fraction of 40-5000 microns, and the filler is predominantly made from cellulose fibers in the following proportions of total dry weight, wt.%: Birch bark - 60-95, cellulose fiber - 5-40%. Before forming the carpet, the filler is moistened to a moisture content of 18-20% and mixed with crushed bark, the carpet is formed with a thickness equal to 200-300% of the thickness of the finished plate. Thus formed carpet is pressed at a temperature of 160-180 ° C. The pressing time is 0.5-0.8 minutes per 1 mm of thickness.

The disadvantage of these methods is the lack of equipment and process organization schemes for the production of products from the proposed compositions.

A known method of manufacturing plates from the bark of deciduous or coniferous trees [4]. The bark is crushed, sieved, removing bark particles above and below the required size. The prepared bark is impregnated with a 5-20% solution of polystyrene or methyl methacrylate in ethyl acetate until the polymer content in the plate is 10-25%. After the impregnation is complete, the solvent (ethyl acetate) is removed for recovery. Plates are formed by compression pressing at the polymer melting temperature (for polystyrene + 180 ± 5 ° С, for polymethyl methacrylate + 170 ± 5 ° С) and specific pressure 10 ± 0.5 MPa. The exposure time under pressure is 0.3-0.5 min per 1 mm of the thickness of the finished plate. The finished plates are cooled under pressure to a temperature of about 110 ° C, after which the plates are removed from the mold.

The disadvantage of this method is that to create the required strength of the obtained products using synthetic polymers in a volatile solvent, the removal of which requires a separate stage of distillation of the toxic solvent, which requires explosion-proof equipment. In addition, the proposed polymers are scarce and expensive and worsen the environmental situation in the shops and in the whole enterprise.

A known wood board and a method of manufacturing these boards, using wood bark without the use of synthetic binders [5]. To prepare the carpet press composition, plant material — bark — is taken and subjected to hydrolysis at a temperature of 170-180 ° C for 2 hours, after which the mass is dried to a moisture content of 8% and first compressed at a temperature of 20 ° C and a pressure of 15 MPa, and then pressed at a temperature of 160 ° C and a pressure of 15 MPa. Duration of pressing 1 min per 1 mm of the thickness of the finished plate. After hot pressing, the plastic is cooled in a press without relieving pressure.

A disadvantage of the known solution is that its implementation requires the stage of hydrolysis and the stage of cooling of the finished plastic in the press without relieving pressure, which complicates the technology as a whole and increases the cost of production. In addition, the range of manufactured plates is limited by the high density of products.

A known method for the production of fiberboard wet. The method provides for the separation and washing of technological chips; grinding wood chips in two steps; the introduction into the wood fiber mass of additives: phenol-formaldehyde resin, paraffin emulsion, and sulfuric acid; carpet tint; hot pressing; hardening; conditioning and format cutting of the resulting plates [6].

The disadvantage of this method is that in the production of fiberboard from hardwood, the resin content in relation to the mass of absolutely dry fiber should be at least 1.3%. The technological process for the production of fiberboard allows the use of feedstock with a bark content of not more than 15% (in wood chips from knots up to 20%) by weight of the wood chips. Limiting the amount of bark in wood chips reduces the possibility of using bark in woodworking plants. With an increase in the proportion of bark in the total fiber mass, both the appearance of the finished product and its quality characteristics deteriorate, which leads to the need to use a larger amount of binder, which increases the cost and toxicity of the boards.

Thus, the existing methods of using bark in the production of boards and wood compositions either worsen the physical and mechanical characteristics while observing the existing technology, or increase the toxicity of the boards, or require the use of new equipment, new costly technologies for the production of finished products using bark. And technologies that allow the use of bark in fiberboard, in an amount exceeding 15%, without compromising the physical and mechanical characteristics, do not exist.

The invention solves the problem of recycling bark, improving the environmental condition of industrial sites of woodworking enterprises; efficient use of wood, reducing the consumption of absolutely dry fiber for the production of fiberboard; reduce toxicity and cost of finished products by reducing the consumption of a binder in the production of fiberboard from hardwood.

The technical result of the invention is the development of a simple and cheap method of utilization and processing of bark in the production of fiberboard from hardwood, improving the physical and mechanical characteristics of fiberboard, reducing the emission of formaldehyde from plates and reducing the cost of production.

The specified technical result is achieved due to the fact that in the method for the production of hardboard from hardwood, including the grinding of technological chips in two stages, the introduction of additives - phenol-formaldehyde resin, paraffin emulsion and precipitant, carpet formation and pressing, with the introduction of additives, bark is additionally introduced into the amount of 6-16% by weight of absolutely dry fiber. The crust is pre-crushed to a fraction size of 0.05-0.8 mm and soaked for 2-4 hours in hot water at a temperature of 60-100 ° C with a mass ratio of bark to water of 1: 10-1: 14.

As a bark, you can use pine bark, or birch bark, or fir-fir bark.

The specified technical result is achieved by grinding to a certain fractional composition of the crust, soaking it with hot water and using this composition as a strengthening additive in the production of fiberboard. The optimal amount of bark introduced into the wood pulp should be in the range from 6 to 16% by weight of the raw unbarked feed in a completely dry state. The sequence of technological operations and modes of operation of the equipment are similar to those in the production of fiberboard by the wet production method.

The use of bark in an amount of less than 6% and more than 16% affects the physical and mechanical characteristics of fiberboard.

Grinding the crust to a fraction size of less than 0.05 is not economically feasible, and more than 0.8 mm leads to a decrease in physical and mechanical characteristics and a deterioration in the appearance of the plates.

The soaking of crushed bark in hot water at a temperature of 60-100 ° C and a mass ratio of 1: 10-1: 14 for 2-4 hours is determined experimentally and leads to the best physical and mechanical characteristics of the plates.

For examples, fiberboards were made according to GOST 4598-86 “Wood-fiber boards of the wet production method” with a content of crushed pine, birch and spruce-fir bark from 6 to 16% in the laboratory of wood processing, pulp and paper and chemical wood technology of the Lesosiberian branch of Siberian State University .

Example 1

Technological wood chips from hardwood with a bark content of 15% were subjected to grinding in two steps (diffuser, refiner). The degree of grinding of the mass in the first stage of 11 DS, in the second 22 DS, the index of the fractional composition was 33 g. For the manufacture of 1 sample (plate), a wood-fiber mass with an absolute dry fiber content of 207 g was taken

The pine bark was crushed to a fraction size of 0.05 mm. For crushing the bark, a mill using the dry grinding method was used. The crushed bark was soaked in hot water with a mass ratio of 1:10 at a temperature of 100 ° C and kept for 2 hours.

Phenol-formaldehyde resin was added to the resulting wood pulp in an amount of 1% by weight of absolutely dry fiber (2.07 g of standard concentration), a paraffin emulsion in an amount of 1% of paraffin to absolutely dry fiber (2.07 g), sulfuric acid was used as a precipitant (0.7% concentrated sulfuric acid; 1.45 g) and 6% pine bark (12.42 g at a moisture content of 8%).

Carpet casting and plate pressing were carried out on laboratory equipment in accordance with the selected mode for the production of solid fibreboard wet production method. The temperature of the press plates was 183 ° С, the pressing pressure in the spin phase was 6 MPa, in the drying phase 1 MPa, in the hardening phase 5 MPa, the pressing time was 1.79 min per 1 mm of the thickness of the finished plate .

After pressing, the plates were quenched for 4 hours at a temperature of 150 ° C. Physico-mechanical characteristics of the plates were determined according to GOST 19592-80 “Wood-fiber boards. Test Methods. "

Examples 2-6 - a method of producing fiberboard analogously to example 1.

Examples 7-12 - a method of producing fiberboard analogously to example 1. As the bark, birch bark was used.

Examples 12-18 - a method of producing fiberboard analogously to example 1. As the bark, fir-fir bark was used.

The conditions for the process of obtaining fiberboard according to examples 1-18 are shown in table 1.

Table 1 The conditions for the process of obtaining fiberboard N example The mass of absolutely dry fiber, g The amount of crushed bark,% The size of the crust fraction, mm Soaking time, hour Soaking temperature, ° С Mass ratio, bark: water one 2 3 four 5 6 7 Pine bark one 207 6 0.05 2 one hundred 1:10 2 202 8 0.08 2 70 1:12 3 198 10 0.1 four 60 1:14 four 194 12 0.06 2 60 1:10 5 189 fourteen 0.5 3 70 1:10 6 185 16 0.8 2 70 1:14

Continuation of table 1 one 2 3 four 5 6 7 Birch bark 7 207 6 0.8 2 70 1:10 8 202 8 0.09 3 80 1:12 9 198 10 0.1 3 one hundred 1:11 10 194 12 0.2 3 one hundred 1:14 eleven 189 fourteen 0.05 2 60 1:14 12 185 16 0.8 four 70 1:13 Spruce-fir bark 13 207 6 0.8 2 60 1:12 fourteen 202 8 0.5 2 70 1:14 fifteen 198 10 0,07 3 one hundred 1:10 16 194 12 0.4 four 80 1:12 17 189 fourteen 0.05 3 70 1:13 eighteen 185 16 0.1 3 70 1:12

Table 2 shows the values of the physico-mechanical characteristics of the fiberboard obtained according to examples 1-18, depending on the content and type of crushed bark in the original wood-fiber prefabricated.

table 2 Physicomechanical characteristics of fiberboard Example No. The amount of crushed bark,% Density, kg / m ³ Tensile Strength, MPa Swelling in 24 hours,% one 2 3 four 5 Pine bark one 6 1004 40 twenty 2 8 975 40 19 3 10 945 43 eighteen four 12 915 40 17 5 fourteen 894 39.5 17 6 16 886 33 17 Birch bark 7 6 972 33 fourteen 8 8 983 34 13 9 10 990 34 13 10 12 945 36 eleven eleven fourteen 950 33 10 12 16 980 33 10

Continuation of table 2 one 2 3 four 5 Spruce-fir bark 13 6 965 36 19 fourteen 8 974 37 17 fifteen 10 943 38 16 16 12 952 34 fifteen 17 fourteen 924 33 fifteen eighteen 16 904 33 fourteen Physico-mechanical characteristics according to GOST 4598-86 for solid fiberboard 800-1100 33-38 20-23

As can be seen from the data in table 2, the use of pine bark significantly improves the tensile strength of fiberboard for static bending. The use of birch bark reduces plate swelling compared to other types of bark. The use of spruce-fir bark improves strength characteristics and reduces plate swelling. Regardless of the type of bark used, the plates correspond to GOST 4598-86.

The use of bark in the production of fiberboard allows you to reduce the consumption of wood fiber, reinforcing additives - resins, reduce the toxicity and cost of plates, improve the environmental situation of woodworking enterprises.

The method of using crushed bark in the production of fiberboard does not require significant capital costs. The operations of collecting, cleaning, grinding, soaking with water can be mechanized and introduced into the technological process of the production of fiberboard.

The proposed method for the use of crushed bark in the production of fiberboard is an effective measure of bark utilization, helps to reduce the cost and toxicity of the plates and solves technological, economic and environmental problems:

1) saving of raw wood in the production of fiberboard;

2) the ability to effectively use the bark, helping to solve the problem of its utilization, improving the environmental condition of industrial sites of woodworking enterprises;

3) reducing the consumption of formaldehyde binders and, as a result, reducing the cost of production and reducing formaldehyde emissions;

4) reduction of expenses of enterprises for the cleaning of industrial sites and the removal of bark to landfills.

Thus, the use of crushed bark in the production of fiberboard according to the existing technology will, while reducing costs, by reducing the consumption of raw materials and hardening additives, improve the operational properties of the finished boards. This method allows to reduce overhead costs associated with cleaning industrial sites from bark and its removal to landfills.

Information sources

1. Zhitkov A.V. Utilization of tree bark. - M .: Forest. industry, 1985

2. RU No. 2003118707/04, 2003, IPC C08L 97/02.

3. RU 2245783, 2005, IPC B27N 3/00, B27N 3/02, B27N 3/04.

4. RU 1757886, B27N 3/02, 1991.

5. RU 2173256, B27N 3/08, 2001.

6. Volynsky V.N. Technology of wood boards and composite materials. - St. Petersburg: "Doe", 2010

Claims (2)

1. A method for the production of fiberboards, including the grinding of technological chips in two stages, the introduction of additives - phenol-formaldehyde resin, paraffin emulsion and precipitant, carpet formation and pressing, characterized in that during the introduction of additives, bark is additionally introduced in an amount of 6-16% by weight absolutely dry fiber, pre-crushed to a fraction size of 0.05-0.8 mm and soaked for 2-4 hours in hot water at a temperature of 60-100 ° C and a mass ratio of 1: 10-1: 14. 2. The method according to claim 1, characterized in that the bark used is pine bark, or birch bark, or fir-fir bark.