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Obtaining plastics from wood and plant waste in closed molds Savinovskikh Andrey Viktorovich. Do-it-yourself liquid tree - we create wood-plastic at home Plastic from wood

The production of lignocarbohydrate wood plastics is a new production. The problem of obtaining plastic materials from crushed wood particles without the addition of binders due to the decomposition products of wood components has long occupied researchers. Many variants of piezothermal processing of wood particles were proposed, which differed in modes, but in essence all these methods involved processing wood particles at high pressures and pressing temperatures, in hermetic molds. Subsequently, the plastics obtained in this way were called piezothermoplastics.

At present, two methods for obtaining piezothermoplastics have been proposed in our country:

1. The one-stage method, developed at the Belarusian Technological Institute, involves grinding wood to a state close in particle size to wood flour, and pressing it in sealed molds at a pressure of 250-300 kg / cm 2 and a temperature of 190-200 ° C subsequent cooling to 20°C without relieving pressure.

2. The two-stage method, developed at the Leningrad Forestry Academy, involves preliminary partial water hydrolysis of wood particles in an autoclave, followed by pressing the dried, partially hydrolyzed material in a mold in a hot press. Pre-hydrolysis will reduce the pressing pressure for wood press materials of some hardwood up to 150 kg / cm 2 and hot pressing temperature up to 160 ° C.

At the department of wood science and construction business and in the problematic laboratory of wood plastics of the Ural Forest Engineering Institute under the guidance of prof. From 1962 to the present, V. N. Petri has been conducting comprehensive studies of new materials - ligno-carbohydrate wood plastics obtained by using the reactivity of wood components (natural lignins and polysaccharides), without adding thermosetting resins or other binders to wood particles.

The authors of the new method, in contrast to the supporters of piezothermoplastics, believe that when obtaining plastics, wood should not be subjected to deep destruction, but only to mild influences during piezothermal processing, in which, at the first stage of processing, partial hydrolysis of polysaccharides (primarily water-soluble and easily hydrolysable) occurs with the formation of some the amount of organic acids, which carry out the hydrolytic cleavage of the natural lignocarbohydrate complex, since it is known that at least small amounts of an acid catalyst are needed to destroy the chemical bond between lignin and carbohydrates.

As a result of these processes, not monomers are formed, but larger molecules that retain the natural reactivity of the main components of wood - carbohydrates and lignin. Wood should not be subjected to deep destruction in the manufacture of plastics, since this destroys the reactive components of natural wood.

In the process of piezothermal treatment, it is also necessary to provide opportunities for subsequent interaction between the reactive components of individual wood particles in order to synthesize new lignocarbohydrate complexes. Due to this, the formation of durable and water-resistant plastic from wood particles occurs. New materials named lignocarbohydrate wood plastics(LUDP). Ligno-carbohydrate wood plastic (LUDP) is a new board material obtained as a result of hot pressing of wood particles without the addition of binders. Ligno-carbohydrate wood plastics have a number of features that make their production cost-effective:

1. The main advantage of LUDP, from this point of view, is that there is an unlimited amount of raw materials for their manufacture. These are wood particles of any of the most common coniferous (pine, larch, spruce, cedar, fir) and hardwood (birch, aspen, etc.), as well as their mixtures.

The production of LUDP can be established in any region of our country where logging and woodworking enterprises operate, since plastics can be made from any waste from logging and wood processing, as well as from firewood (without limiting the content of rot and bark).

Based on technical and economic calculations, it was found that it is economically feasible minimum power workshops for the production of LUDP 3.5-4 thousand m 3 of plates per year; the need for raw materials for such a workshop is 10-12 thousand m 3. Consequently, the production of LUDP, in contrast to the production of particle boards, can be organized at small enterprises.

2. Ligno-carbohydrate wood plastics are obtained by using the reactivity of the components of the wood itself, i.e. without adding thermosetting resins or other binders to the wood particles.

3. The technological process for the production of LUDP compared to the production of particle boards is simpler, since there are no technological operations for the preparation of binders and their mixing with wood particles.

4. For the manufacture of LUDP, standard pressing and other equipment is used, used for the production of chipboard and mass-produced by the domestic industry.

Main technical properties flat single-layer LUDP the following:

1. Appearance and coloring. After pressing, LUDP boards have a middle, darker (conditioned) part and a light edge along the periphery, or a substandard part of the board. Substandard part of the plate at optimal conditions pressing does not exceed 10 cm. When using large boards, a 10 cm wide edge is only 2-5% of the area of ​​the pressed board. For example, when the size of the pressed plates is 3100X1100 mm, the edge with a width of 10 cm is 2.5% in area. The width of the substandard part of the plates can be reduced.

The color of the conditioned part of the board, pressed under optimal conditions, depends on the wood species from which the plastics are made, but is always much darker than that of the original wood and ranges from light to dark brown. The bark breaks the uniformity of color. By tinting the wood particles of the outer layers of the carpet being formed and by making slabs lined with various decorative materials, it is possible to change the color and appearance of the slabs.

2. Surface quality. Boards made from small and flat wood particles have a smoother and more even surface than boards made from thick and coarse wood particles. When pressing plastics from small wood particles on well-finished (better polished) pallets, the boards have a smooth, shiny surface.

3. Warping. Warping of LUDP depends on the thickness and design of the plates. Thin slabs have more buckling than thick slabs. Three-layer slabs warp less than single-layer slabs, and veneered slabs slightly more than non-glued ones. In order to avoid warping of the LUDP slabs during conditioning, the rules for laying the slabs must be strictly observed and the conditions for their conditioning - drying must be observed.

4. Density. The density of lignocarbohydrate wood plastics cannot be less than 1 g/cm 3 . Only at this density is ensured that the minimum degree of compaction of the pressed mass, at which the necessary contact and the possibility of chemical interaction between the individual particles of wood is achieved.

5. moisture absorption. LUDP to a certain extent retains one of the main features of wood - to absorb moisture from moist air. With an increase in the content of hygroscopic moisture in plastics, their mechanical properties decrease:

a) LUPD with a density of at least 1.2 g/cm 3 have a swelling of 7-10%, water absorption of 5-12%, a total moisture content of 20-22%;

b) LUDP with a density of 1.20-1.15 g/cm 3 ; swelling 10-12%, water absorption 12-15%;

c) LUDP with a density of 1.15-1 g/cm 3 ; swelling 18-25%, water absorption 20-26%.

6. Thermal properties. Material used for floors in residential and industrial buildings, is characterized by a heat absorption coefficient, which should not exceed 10 kcal / m 2.

Ligno-carbohydrate wood plastics 10-11 mm thick make it possible to arrange floors by laying them directly on a concrete base.

7. Biostability. LUDP have a high anti-rot resistance, which is 4-5 times higher than that of pine wood.

Mechanical properties of LUDP. Flat single-layer uncoated LUDP boards can be divided into three groups.

Group A - static bending strength of at least 270 kg / cm 2 (density more than 1.2 g / cm 3), group B - static bending strength of at least 220 kg / cm 2 (density 1.2-1, 18 g/cm3); group B - static bending strength of at least 120 kg / cm 2 (density 1.15-1 g / cm 3).

The physical and mechanical properties of lignocarbohydrate wood plastics obtained from spruce logging residues are as follows: static bending strength is 170-190 kgf/cm 2 , swelling in 24 hours is 8-11%, and the density is 1.2 g/cm 3 . Plastics made from crushed (mixture 1:1) of birch and aspen have a static bending strength of 176 kgf/cm 2 , swelling in 24 hours - 16% and a density of 1.18 g/cm 3 .

Technological process of production is generally the same for all types of single-layer uncoated lignocarbohydrate plastics. The only difference is that for each specific type of raw material used for the manufacture of LUDP, different preparation of raw materials and different modes of pressing and conditioning plastics are required. Therefore, the organization of industrial production of plastics at a particular enterprise should be preceded by research aimed at clarifying the technology of their manufacture from available raw materials. These studies can be carried out in parallel with the design and construction of a plastics workshop.

In general, the technological process for the production of LUDP consists of the following main operations: preparation of raw materials, drying of raw materials, dosage of wood particles, formation of a carpet (package), cold pressing of a carpet (package), hot pressing and cooling, hot pressing mode, trimming plates, air conditioning - drying plastic boards.

Scheme technological process production of LUDP by hot pressing from sawmill and woodworking waste using one hydraulic press.

Branches, small-sized stems, rotten wood chips, etc. are crushed on a chipper or crusher and fed by a conveyor or pneumatic conveyor to the bunker of chopped wood pulp, which can also receive sawdust, shavings or screenings from technological chips, chip production, etc. To obtain conditioned wood particles, wood pulp, previously cleaned of metal inclusions using a metal detector, is passed through a DO-5.7 chipper, and then through DM-3 cross mills. The openings of the sieve drum of mills for some species are reduced to 3 mm. After crushing, the wood particles are sucked in by a fan and transported to a cyclone installed under the hopper.

The dosing device of this hopper allows you to change the amount of chips issued per unit of time, which is necessary to maintain the required temperature regime in the drying chamber.

Chips are loaded into the installation chamber by a screw conveyor.

The fluidized bed dryer consists of two sections installed in parallel. The drying agent is heated air. Air is supplied by fans. The crushed grain dried to the required moisture content enters the sluice feeders through the drain thresholds of the drying chambers, and then into the suction pneumatic conveying pipeline. Air passing through the layer of chips in drying chambers, entrains dust, which settles in a cyclone with an increased purification factor. Cleaned from dust, but with high humidity, the air is released into the atmosphere, and the dust is sent along with the bulk of the material to the dry chip hopper.

From this hopper, the chips are evenly fed by the dispenser to the belt conveyor 2 to the feeders and distributed among the forming machines with fractionating rollers. Machines lay carpet on pallets. The sides of the carpet are formed by two vertical belt conveyors. Then the pallet with the loose carpet laid on it is moved by another section of the chain conveyor to press the carpet into the cold pressing press. The carpet is pressed under pressure of 25 kg/cm2 for 1 minute.

Before loading the package into a cold press, a duralumin gasket is placed on top using a crossbar with suction cups. This contributes to the uniform heating of the package and allows you to get a plate with a high-quality surface on both sides.

The packages are accumulated in the loading rack of the press. After the bookcase is completely filled, all press bays are loaded simultaneously.

After the end of pressing, all the plastic slabs are simultaneously unloaded into the unloading stack, from which they are sequentially, starting from the bottom, fed to the longitudinal and transverse conveyors.

Plastic slabs are transferred from the lower pallet to the three-saw sizing and trimming machine by the removal mechanism. Pallets, after cleaning and applying talc on them, are sent under the forming machines.

Plastic plates, after trimming the light edges, are sorted. Rejected slabs are cut into smaller ones with defective areas cut out. After sorting, high-quality boards are stacked on spacers and loaded into conditioning-drying chambers with the help of a traverse trolley. After unloading from the chambers, the slabs are placed in dense piles in a heated room. Then they are packaged and sent to the warehouse of finished products for shipment to the consumer. (Technological operations following the cutting of plastic plates are not shown in the diagram.) It is possible to increase the productivity of the LUDP workshop by increasing the size of the plates, the number of floors of the presses, or their number.

High physical and mechanical properties of LUDP, beautiful appearance and the ability to manufacture large-sized plates allow them to be used in construction as a structural and finishing material for laying floors, filing ceilings, manufacturing built-in furniture, partition walls, door panels, window sills, for cladding walls and panels in public buildings, in kitchens and corridors of residential buildings, etc., in furniture and other industries, as well as a substitute for solid wood, chipboard and fibreboard and other sheet materials. The plates have a smooth surface and are well finished with transparent and opaque varnishes and paints using conventional technology. Finishing with transparent furniture varnishes can be done with preliminary tinting of the surface with water-soluble and other dyes in any color while maintaining the texture of the plates.

Thus, when crushing branches and thinner, the output of conditioned wood chips is on average 50% of the total crushed mass. This conditioned chips can be used to produce semi-cellulose, the production of chipboard and fibreboard, and 50% of non-conditioned chips can be used to produce ligno-carbohydrate wood plastics or fertilizers.

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Purpose: the invention relates to the production of products from wood plastic. The essence of the invention: a gap is first formed around the entire perimeter of the inner working part of the mold, in which a layer of wood-polymer material containing 10 - 30% thermoplastic binder is laid, after which the remaining volume of the mold is covered with wood particles with a moisture content of 6 - 25% . Hot pressing is carried out at a pressure of 70 - 120 kg/cm 2 and at a temperature of 170 - 200 o C, and the ratio of the thickness of the layer of wood-polymer material and the thickness of the product is (1-2) : (5-50). Wood particles are poured into a mold with a size of not more than 0.5 mm, and a layer of wood-polymer material can be formed by laying pre-made plates of wood-polymer material. 7 w.p. f-ly, 5 ill., 1 tab.

The invention relates to the production of wood-based plastics from waste wood processing industries and can be used as building materials /facing boards, flooring, tiles, in the manufacture of furniture/. There is a known method of manufacturing from wood and other plant substances, in which wood particles are placed in a sealed mold, heated without air access and vapors and gases under a pressure of 1 - 50 MPa and maintained at a maximum pressure of 3 to 70 minutes (SU, ed. St. N 38290, class E 04 C 2/10, 1934). The disadvantage of this method is the low value of the physical, mechanical and operational characteristics of the resulting products. The closest in technical essence and the achieved result is a method for manufacturing building products from wood-based plastics, including grinding wood, heating it to 170 - 270 o C and pressing in a sealed mold without air access and fumes and gases at a pressure of 5 - 50 MPa within 3 - 70 min / SU, ed. St. N 38070, class. E 04 C 2/10, 1934/. These methods have the following disadvantages: the difficulty of solving the issue of sealing the mold during hot pressing under pressure, the instability of the properties of products in case of violation, at least partial, of sealing, the appearance of open porosity when using reduced pressing, in which it is easier to provide sealing. The presence of open pores worsens the physical-mechanical and performance characteristics of wood plastic products, in particular, water absorption. The objective of the invention is to simplify the sealing of the mold while increasing its reliability and improving the physical, mechanical and other performance properties of products made from wood-based plastics. The task of creating a reliable tightness of the mold is carried out by placing a layer of wood-polymer mass in the gap between the dies and punches. When the mold is heated to the pressing temperature, the wood-polymer mass acquires plasticity, flows under the pressure of pressing into the gap between the matrix and the punches, which ensures reliable tightness of the mold. The required viscosity of the mass, which ensures reliable tightness, depends on the amount of thermoplastic binder and is determined by the pressing pressure, as well as the pressure of vapors and gases that occur during the hydrolysis of wood particles. An increase in performance, in particular a decrease in porosity, is achieved by creating a layer of wood-polymer waterproof material on the surface of wood plastic. This layer during the manufacturing process of the product ensures the sealing of the mold during pressing. The surface waterproof layer is formed during the pressing process by layer-by-layer loading of the mold: first, the lower horizontal layer containing wood particles and 5–30 wt.% of thermoplastic binder, then the layer of wood particles and the upper horizontal layer similar to the lower one. The surface horizontal waterproof layer can be formed from pre-made by pressing thin sheets of wood-polymer material containing 5–30% thermoplastic binder, and their subsequent laying in layers in a mold: the lower and upper layers are wood-polymer material, between them are wood particles. A sheet of wood-polymer material is placed between the walls of the mold and the layer of wood particles. The filling of the mold according to the prototype and according to the invention is carried out according to the schemes shown in Fig. 1-5. In FIG. 1 shows a scheme for filling the mixture according to the prototype, in which the entire mold 2 is filled with the compressed mixture 1, and compaction is carried out by the installation rubber seals 3, placed in the gap between the matrix and the punch along the entire perimeter of the inner working part of the mold. In FIG. 2 shows the mold filling scheme, according to which, first, a layer 1 of a wood-polymer material containing 10–30% binder is poured around the entire perimeter of the inner working part of the mold, and the remaining volume is filled with wood particles 2 with a moisture content of 6–25%. In FIG. 3 shows a scheme for filling the mold, according to which, first, pre-made plates 1 made of wood-polymer material containing 10–30% binder are laid around the entire perimeter of the inner working part of the mold, and the remaining volume is filled with wood particles 2 with a moisture content of 6–25 %. In FIG. 4 shows a scheme for filling the mold, according to which, in addition to laying layer 1 of wood-polymer material containing 10 - 30% binder, the lower horizontal layer 2 of wood-polymer material containing 5 - 30% binder is poured onto the bottom of the mold, then wood particles 3 with a moisture content of 6 - 25%, on top of which a horizontal layer 4 is also poured, the composition of which is similar to the lower horizontal layer. In FIG. 5 shows a diagram of filling the mold, which is similar to the diagram in Fig. 4 with the difference that the horizontal layers 1 are formed not by filling a mixture of binder and wood particles, but by laying plates pre-made from wood-polymer material. These horizontal layers after pressing and cooling of products form surface waterproof layers. At the same time, when preparing a wood-polymer mixture from a thermoplastic polymer binder, for example, polyethylene and wood particles, 1–5% of their weight formic or acetic acid is introduced into the particles before they are mixed with a binder and the moisture content of the particles is increased to 5–25%, and vegetable fibers can be used instead of wood particles. Samples of wood plastics were made according to the prototype method by hot pressing in a sealed mold. The gap between the die and the punches was sealed using a water-cooled gasket made of temperature-resistant rubber. Wood plastics according to the proposed method were made in a conventional mold with a gap between the punch and the matrix up to 1 - 1.5 mm. In both cases, to obtain wood plastics, coniferous wood particles with a size of -0.5 mm and a moisture content of 15% were used. To seal the matrix and create a protective water-repellent layer according to the proposed method, a press mass of the following composition was used: wood particles with a moisture content of 15% / conifers size 0.5 mm / -85%, recycled polyethylene - 15% wt. The hot pressing mode was the same for all samples of wood plastics: pressing temperature - 170 o C, pressure - 70 kg/cm 2 , holding time under pressure - 30 min. The table shows the properties of wood plastics obtained by the prototype method and the proposed method. Analysis of the properties of products made of wood-based plastics, made according to the method of the prototype and according to the invention, in accordance with the schemes for filling the mold / cm. fig. 2 - 5/ showed the following: the sealing of the mold, placed in the gap between the matrix and the punch of the press mass, is simpler and more reliable and provides higher physical and mechanical characteristics of products than when using rubber seals; obtaining products with horizontal surface layers from a wood-polymer mixture provides water resistance of products and an increase in their physical and mechanical characteristics.

Claim

1. A method for manufacturing products by pressing from wood plastic, including grinding wood, filling a mold, hot pressing under pressure without air access and release of vapors and gases, followed by cooling, characterized in that, first, around the entire perimeter of the inner working part of the mold, a gap in which a layer of wood-polymer material containing 10 - 30% thermoplastic binder is placed, after which the remaining volume of the mold is covered with wood particles with a moisture content of 6 - 25%, and hot pressing is carried out at a pressure of 70 - 120 kg / cm 2 and at a temperature of 170 - 200 o C, and the ratio of the thickness of the layer of wood-polymer material and the thickness of the product is (1 - 2) : (5 - 50). 2. The method according to claim 1, characterized in that wood particles are poured into the mold, the size of which is not more than 0.5 mm. 3. Method according to claims 1 and 2, characterized in that the layer of wood-polymer material is formed by stacking prefabricated plates of wood-polymer material. 4. The method according to claims 1 and 2, characterized in that the layer of wood-polymer material is formed by filling in the form of a mixture of thermoplastic polymer binder and wood particles. 5. The method according to claims 1 to 4, characterized in that the wood particles are placed between additional upper and lower horizontal layers of wood-polymer material containing 5-30% binder. 6. The method according to claim 5, characterized in that the horizontal layers are formed by laying prefabricated plates of wood-polymer material. 7. The method according to claims 1 to 6, characterized in that when preparing a wood-polymer material, before mixing with a binder, 1-5% of their weight formic or acetic acid is introduced into the crushed wood particles. 8. The method according to claims 1 to 7, characterized in that in the preparation of wood-polymer material, plant fibers are used as wood particles.

In this article we will tell you how you can make a popular construction material called a do-it-yourself liquid tree, and also describe all its advantages.

Any home craftsman knows that wood products are afraid negative impacts a variety of operational factors, which reduces their service life. At the same time, the tree is loved by many people and professional builders. It is environmentally friendly, looks great, charges a person with positive energy, and has many other advantages.

liquid wood product

For these reasons, experts have been trying for a long time to come up with a substitute for natural wood, which would visually and physical properties was no different from a tree, surpassing the latter in its quality and resistance to the influence of natural phenomena. The research has been successful. The modern chemical industry has been able to create a unique material - liquid artificial tree. It literally broke into the construction markets around the world. Now such a tree is sold under the abbreviation WPC (wood-polymer composite). The material we are interested in is made from the following components:

  1. crushed wood base- in fact, the waste processing of natural wood. In one or another composite they can contain from 40 to 80%.
  2. Thermoplastic chemical polymers - polyvinyl chlorides, polypropylenes and so on. With their help, the wood base is assembled into a single composition.
  3. Additives called additives. These include colorants (color the material in the desired shade), lubricators (increase resistance to moisture), biocides (protect products from mold and insect pests), modifiers (retain the shape of the composite and ensure its high strength), foaming agents (allow to reduce the weight of WPC ).

These components are mixed in certain proportions, heated strongly (until the composition becomes liquid), the mixture is polymerized, and then it is fed into special forms under high pressure and cool. As a result of all these actions, a composition is obtained that has flexibility and excellent corrosion resistance, elasticity and impact resistance. And most importantly - WPC has a magical aroma of natural wood, as well as a color and texture identical to real wood.

We hope that from our short review you have understood how liquid wood is produced and figured out what it is. The described wood-polymer products are characterized by a number of operational advantages. Here are the main ones below:

  • increased resistance to mechanical damage;
  • resistance to temperature changes (products made of WPC can be operated both at +150 ° С and at -50 °);
  • high moisture resistance;
  • ease of self-processing and installation (for these purposes, a tool is used that works with natural wood);
  • long service life (at least 25-30 years);
  • a large selection of colors;
  • resistance to fungus;
  • ease of maintenance (the composite is easy to clean, it can be scraped, varnished, painted in any color).

wood plastic decoration

An important advantage of wood plastic is that it has a very affordable cost. This is achieved through the use of secondary processing products (shredded plywood, sawdust, shavings) in the production of WPC. It is difficult to find shortcomings in the material we are considering, but they exist. And how without it? There are only two disadvantages of wood plastic. Firstly, when using it in living rooms, it is necessary to equip high-quality ventilation. Secondly, WPC is not recommended for use in cases where there is simultaneously and constantly present in the room high humidity and elevated air temperature.

The special characteristics of a composite of wood and plastic make it possible to manufacture various building products from it. This material is used for the production of outdoor siding, smooth, hollow, corrugated and solid decking (in other words, decking). Chic balustrades, artsy railings, reliable fences, luxurious gazebos and many other structures are made from WPC. Wood plastic will allow you to luxuriously equip the interiors in your living space and make your suburban area truly beautiful.

The cost of the described composite depends on which polymer is used for its manufacture. If a manufacturer makes WPC from polyethylene raw materials, the price for finished products will be minimal. But it is worth noting that such products are not resistant to ultraviolet radiation. But polyvinyl chloride polymers give wood plastic high resistance to fire and UV rays, and also make it very durable. Products from WPC (in particular, decking) are usually divided into seamless and with seams. The first are mounted without clamps, screws and other hardware. Such boards simply interlock with each other, forming a solid solid surface.

wood plastic material

But for the installation of products with seams, it is necessary to use plastic or metal fasteners (most often clamps act as such). WPC boards or boards can be hollow or solid. For arranging the verandas of private houses, it is better to use products with voids. They are lightweight and very easy to work with. Full-bodied wood-plastic, which is able to withstand significant loads, is more suitable for laying in public places (embankments, summer restaurants and bars, ship decks), where there is a high traffic of people.

When choosing boards from WPC, pay attention to the thickness of their walls (it should be at least 4-5 mm), the height of the stiffeners (the higher they are, the more reliable the products will be in operation) and their number (the more ribs, the stronger it turns out design).

You should also choose the width of composite panels and boards wisely. There is one point to be understood here. H The wider products you buy, the easier it will be for you to work with them, because for the installation of such boards you will need significantly less fasteners . Several Yet useful tips For you. Check with the sellers from which sawdust the WPC was made. If the manufacturer used softwood for these purposes, it is better to look for another material. Why? For the reason that coniferous-based composites are considered fire hazardous. And the strength characteristics of such products leave much to be desired. WPC based on deciduous tree processing wastes do not have these disadvantages.

In cases where light streaks or areas are clearly visible on composite panels (boards, slabs), the operational reliability of the products will be low. Most likely, the manufacturer used low-quality wood flour, and, moreover, poorly ground. Such panels, as a rule, have a low water resistance index. They cannot be used outdoors. The presence of a non-uniform color on its surface (stains, clearly visible transitions of shades) also speaks of the insufficient quality of the WPC.

And now the most interesting. If you wish, you can easily make a worthy analogue of the WPC at home. Homemade wood plastic is made from sawdust and ordinary PVA glue and is used to restore parquet board, repair of laminate on the floor, restoration of other wood flooring. It can also be used for the manufacture of rough flooring for floors in gazebos and in auxiliary premises.

Composite material from sawdust and glue

WPC is done by hand according to the following scheme:

  1. Grind sawdust in a coffee grinder or hand grinder to a fine powder.
  2. Add PVA glue to the crushed sawdust (proportions - 30 to 70%) and mix these components until you get a mixture with a paste consistency.
  3. Pour the dye into the composition made (it is recommended to use additives used for ordinary water-based paint). Mix everything again.

So you made a homemade wood-plastic! Feel free to fill holes in wooden floors with this composition. After the WPC has hardened, the restored area will only need to be sanded using fine-grained emery. A do-it-yourself composition can also be used to equip new floors. Collect, make homemade WPC in the right quantities and fill it with a formwork structure. The thickness of homemade boards in this case should be at least 5 cm. Go for it!

The task of manufacturing products from thermoplastic wood-polymer composite materials is fundamentally simple - to combine all the ingredients of the future composite into a homogeneous material and form a product of the desired shape from it. However, its implementation requires a certain set of rather complex technological equipment.

1. General principles of technology.

The feedstock for the production of WPC is wood flour (or fiber), base resin in the form of a suspension or granules, and up to 6-7 types of necessary additives (additives).

There are two fundamentally different schemes for obtaining extrusion products from thermoplastic WPC:

  • two-stage process (compounding + extrusion),
  • one-step process (direct extrusion).

In a two-step process, a wood-polymer compound is first made from the original ingredients. Resin and flour are in two silos. Flour dried in a special installation and resin are sent to a weight dispenser and enter the mixer, where it is thoroughly mixed hot with the addition of the necessary additives. The resulting mixture is further formed in the form of medium-sized granules (pellets), which are then cooled in a special device (cooler).

Rice. 1. Scheme for obtaining a granulated wood-polymer compound

Then, this compound is used for extrusion of profile products, see the diagram of the extrusion section, Fig. 2.


Rice. 2. Scheme of the extrusion section

The granulate is fed into the extruder, heated to a plastic state and forced through the die. The extruded profile is calibrated, sawn across (and, if necessary, along) and placed on the receiving table.

The wood-polymer compound is also used for molding or pressing products from thermoplastic WPC.

In the case of direct extrusion, the ingredients are sent directly to the extruder, see, for example, one of the WPC direct extrusion process organization schemes in Fig. 3.


Rice. 3. Scheme of direct extrusion of wood-polymer composites.

In this case, wood flour is fed from the bunker to the drying plant, dried to a moisture content of less than 1% and enters the storage bunker. Then the flour and additives from enter the dispenser, and from it - into the mixer (mixer). The mixture (compound) prepared in the mixer is fed into the storage capacity extruder. Resin, pigment and lubricating agent from appropriate containers are fed into the extruder, where they are finally mixed, heated and extruded through a die. Next, the resulting profile is cooled (and if necessary) calibrated, and then trimmed to the desired length. This scheme is called direct extrusion.

Both schemes are now widely used in the industry, although many consider direct extrusion to be more advanced.

There are enterprises abroad that specialize only in the production of granules for WPC, i.e. for sale. For example, at WTL International, the capacity of installations of this type is up to 4500-9000 kg/h.

For an approximate layout of the equipment of the extrusion section (line) for direct extrusion of profile parts, see the following diagram.

Depending on the purpose of the project, the production of extruded WPC can be implemented in the form of a compact section on one installation, or in the form of a workshop (a plant with more or less production lines.

Large enterprises may have dozens of extrusion plants.

Limiting temperatures of the extrusion process for different types base resins are shown in the diagram of Fig.6.

Fig.6. Limiting temperatures of the working mixture (line 228 degrees - ignition temperature of wood)

Note. Most natural and synthetic polymers at temperatures above 100 degrees. C is prone to degradation. This is due to the fact that the energy of individual molecules becomes sufficient to destroy intermolecular bonds. The higher the temperature, the more such molecules become. As a result, the length of polymer molecular chains is reduced, the polymer is oxidized, and the physical and mechanical properties of the polymer are significantly worsened. When limiting temperatures are reached, the degradation of polymer molecules occurs on a massive scale. Therefore, in hot compounding and extrusion, it is necessary to carefully control the temperature of the mixture and strive to reduce it and reduce the operating time. The degradation of polymers also occurs during the natural aging of the composite when exposed to ultraviolet radiation. Not only plastic is subject to degradation, but also polymer molecules that make up the structure of the wood component of the composite.

The pressure of the molten mixture in the extruder barrel is typically between 50 and 300 bar. It depends on the composition of the mixture, the design of the extruder, the shape of the extruded profile and the melt flow rate. Modern powerful extruders are designed for operating pressures up to 700 bar.

The extrusion speed of the WPC (i.e., the melt flow rate from the die) is in the range of 1 to 5 meters per minute.

The main part of this technological process is the extruder. Therefore, below we will consider some types of extruders.

2. Types of extruders

In domestic literature, extruders are often referred to as worm presses. The principle of operation of the extruder is the "principle of the meat grinder" well known to everyone. A rotating screw (worm) captures the material from the inlet, compacts it in the working cylinder and pushes it into the die under pressure. In addition, the final mixing and compaction of the material takes place in the extruder.

The movement of the material in the extruder during the rotation of the screw occurs due to the difference in the coefficients of friction of the material on the screw and the barrel. As one foreign expert figuratively put it: "The polymer sticks to the barrel and slides along the screw."

The main heat in the working cylinder is released due to the compression of the working mixture and the work of significant friction forces of its particles on the surface of the extruder and each other. For the processing of thermoplastics, extruders are equipped with additional devices for heating the working mixture, measuring the temperature and maintaining it (heaters and coolers).

In the plastic industry, the most common, due to their relative simplicity and relatively low price, are single-cylinder (single-screw) extruders, see diagram and photo, fig. 7.

Rice. 7. Standard scheme and appearance of a single-cylinder extruder: 1- hopper; 2- auger; 3- cylinder; 4- cavity for water circulation; 5- heater; 6- lattice; 7- forming head. Process phases (I - material supply, II - heating, III - compression)

The main characteristics of the extruder are:

  • cylinder diameter, mm
  • the ratio of the length of the cylinder to its diameter, L / D
  • screw rotation speed, rpm
  • engine and heater power, kW
  • productivity, kg/hour

Note. The passport performance of the extruder is a conditional value. Actual extruder performance may differ significantly from the specification in a particular process, depending on the material being processed, the design of the dies, post-extrusion equipment, etc. The performance indicators of a particular extrusion process are the ratio of productivity to power consumption, equipment cost, number of personnel, etc.

The following diagram shows the performance differences of the TEM series extruders of the English company NFM Iddon Ltd in the manufacture of granules and profiles on different WPC compositions.

The next type is conical screw extruder. Structurally, it is similar to a cylindrical extruder, but the screw and the working cavity are made in the shape of a cone. This makes it possible to more vigorously capture and push loose material into the working area, compact it and quickly raise the pressure in the die area to the required level.

Note. Cylindrical and conical single screw extruders can be used in the production of thermoplastic WPC profiles in a two-stage process, i.e. when processing the finished WPC compound.

More productive are extruders with two cylindrical or conical screws, see fig. 8. In addition, they have significantly better mixing properties. The extruder screws can rotate in one direction or in opposite directions.

Rice. Fig. 8. Schemes of screws of two-cylinder and two-cone extruders: feeding zone, compression zone, ventilation zone, dosing zone

The design of a twin screw machine is much more complicated and more expensive.

The screws of modern extruders are a complex structure, see Figure 6.9.a. and fig. 6.9.b.


Fig.1.9. Window for real
monitoring the process in the extruder.

Various mechanical, hydraulic and chemical processes take place in the working cavity of the extruder, the observation and exact description of which is difficult. On Fig. 9 shows a special armored glass window for direct observation of the extrusion process (FTI)

Due to their high productivity and good mixing properties, it is twin screw machines that are used to implement the scheme of direct extrusion of thermoplastic WPC. Those. they carry out both the mixing of the components and the supply of the prepared working mixture to the spinneret. In addition, twin screw extruders are often used in a two-stage process as compounders to produce WPC pellets.

The screws of twin screw machines do not necessarily have only helical surfaces. To improve their mixing properties, special mixing sections with other types of surfaces can be made on the screws, which provide a significant change in the direction and nature of the movement of the working mixture and thereby better mixing.

Recently, the Japanese firm Creative Technology & Extruder Co. Ltd for the processing of wood-polymer compositions, a combined extruder design scheme was proposed, in which twin-screw and single-screw extruders are combined in one cylinder body.

The main mechanisms of the phenomena occurring during the extrusion of thermoplastic materials are well understood. AT in general terms see for example the appendix "Introduction to extrusion"

Note. A disk extruder was used in the installation for the production of wood-polymer sheets at Rostkhimmash. In some cases, in the production of WPC, piston extrusion may be used instead of screw extrusion.

There are special methods of mathematical computer modeling of extrusion processes used to calculate and design extruders and dies, see Fig. 10. and in computer control systems for extruders.

Rice. 10. System of computer simulation of extrusion processes.

Extruders used in the production of WPC must be equipped with an effective degassing device to remove vapors and gases and have wear-resistant working surfaces, such as a deeply nitrided barrel and a molybdenum reinforced screw.

Traditionally, WPC production technology uses wood flour with a moisture content of less than 1%. However, new modern extruders, designed specifically for the production of WPC, are able to process flour with a moisture content of up to 8%, as they are equipped with a powerful degassing system. Some people believe that the water vapor generated in the extruder helps to facilitate the extrusion process to some extent, although this is a controversial claim. For example, the company Cincinnati Extrusion indicates that the extruder manufactured by the company mod. Fiberex A135 at flour moisture content of 1-4% will have a productivity of 700-1250 kg/h, and at 5-8% only 500-700 kg/h. Thus, a standard extruder, even equipped with a degassing system, is still not a dryer, but simply capable of more or less effectively removing from the working mixture a small amount of moisture. However, there are exceptions to this situation, for example, the Finnish Conex extruder described below, which can also work on wet materials.

As a general rule, water must be completely removed from the material during extrusion in order to obtain a dense and durable composite structure. However, if the product will be used indoors, then it may be more porous and, accordingly, less dense.

One of the extruders designed specifically for the production wood-polymer composites, is shown in Fig. eleven.

Rice. 11. Extruder model DS 13.27 by Hans Weber Gmbh, "Fiberex" technology

The extruders used in the two-stage process for pre-granulation of WPC are equipped with a special granulation head instead of a profile die. In the granulating head, the flow of the working mixture leaving the extruder is divided into several streams of small diameter (strands) and cut into short pieces with a knife.


After cooling, they turn into granules. The granules are cooled in air or in water. Wet granules are dried. Granular WPC is suitable for storage, transportation and further processing into parts at the next stage of the technological process or at another enterprise by extrusion, injection molding or pressing.

Previously, extruders had one loading zone. New models of extruders being developed for the processing of composite materials can have two or more loading zones - separately for resin, separately for fillers and additives. In order to better adapt to work on different compositions, extruders - compounders are often made of a collapsible sectional design, which allows you to change the L / D ratio

3. Dies (heads) of extruders

The die (the so-called "extruder head") is a replaceable tool of the extruder, which gives the melt leaving the working cavity of the extruder the necessary shape. Structurally, the die is a slot through which the melt is pressed (expires).

Rice. 12. Drawer, profile, calibrator.

In the spinneret, the final formation of the material structure takes place. It largely determines the accuracy cross section profile, its surface quality, mechanical properties, etc. The spinneret is the most important integral part dynamic extruder-die system and actually determines the performance of the extruder. Those. with different dies, the same extruder is capable of producing different quantities of profiles in kilograms or running meters (even for the same profile). It depends on the degree of perfection of the rheological and thermal engineering calculation of the system (extrusion rate, extrudate swelling coefficient, viscoelastic deformations, balance of individual extrudate flows, etc.). 6.13. the die is shown (on the left) from which the hot profile exits (in the center) and goes to the calibrator (on the right).

To obtain products with a complex profile, dies are used that have a relatively high resistance to the movement of the melt. The main problem that must be solved inside the die during the extrusion process, and especially for a complex profile part, is to equalize the space velocity of the various melt flows in the die over the entire profile section. Therefore, the speed of extrusion of complex profiles is less than that of simple ones. This circumstance must be taken into account already at the stage of designing the profile itself, i.e. products (symmetry, thicknesses, arrangement of ribs, transition radii, etc.).

Fig.13. Prefabricated two-strand die for the production of window profiles.

The extrusion process allows one extruder to simultaneously produce two or more, as a rule, identical profiles, which allows the maximum use of the extruder's productivity in the production of medium-sized profiles. For this, two-strand or multi-strand dies are used. The photo shows the appearance of a two-strand die, see Fig. thirteen

Drawers are made of strong and wear-resistant steels. The cost of one die can range from several thousand to several tens of thousands of dollars (depending on the size, design complexity and accuracy and materials used).

It seems that the technical complexity of powerful modern extruders and dies for them (in terms of accuracy, production technologies and materials used) is approaching the complexity of aircraft engines, and far from every machine-building plant can handle it. However, it is quite possible to consider the possibility of organizing the production of domestic extrusion equipment - if you use finished imported components (working cylinders, screws, gearboxes, etc.). Abroad, there are companies that specialize in the manufacture of just such products.

4. Dosers and mixers.

In the production of structural materials, the issues of homogeneity (uniformity of structure) and constancy of composition are, as you know, of paramount importance. The importance of this for wood-polymer composites does not even require special explanation. Therefore, in WPC technology, much attention is paid to the means of dosing, mixing and supply of materials. In the production of WPC, various technological methods and schemes for solving these processes are implemented.

Dosing of materials is carried out in 5 ways:

  • Simple volumetric dosing when the material is poured into a container of a certain size (measuring bucket, barrel or mixer container)
  • Simple weight dosing, when the material is poured into a container located on the scales.
  • Continuous volume dosing, for example with a dosing screw. Regulation is carried out by changing the feed rate of the device.
  • Continuous weight (gravimetric) dosing with the help of special electronic devices.
  • Combined dosing, when some components are dosed in one way, and others in another.

Volumetric dosing is cheaper, gravimetric dosing is more accurate. Means of continuous dosing are easier to organize into an automated system.

Mixing of components can be carried out by cold and hot methods. The hot compound is sent directly to the extruder to form the profile or to the granulator and cooler to produce the granules. A special extruder-granulator can act as a hot mixer.

Notes:

  1. Granular materials usually have a stable bulk density and can be dosed fairly accurately by volumetric methods. With powders, and even more so with wood flour, the situation is the opposite.
  2. Organic liquid and dusty materials are prone to fire and explosion. In our case, this applies especially to wood flour.

Mixing of components can be done different ways. To do this, there are hundreds of different devices, both the simplest mixers and automatic mixing plants, see, for example, blade-type mixers for cold and hot mixing.

Rice. 14. Computerized mixing and dosing station from Colortonic

On fig. 14. shows a gravimetric system for automatic dosing and mixing of components, designed specifically for the manufacture of wood-polymer composites. The modular design allows you to form a system for mixing any components in any sequence.

5. Feeders

A feature of wood flour is its very low bulk density and not very good flowability.

Rice. 15. Structural diagram of the feeder

No matter how fast the extruder screw rotates, it is not always able to capture a sufficient amount (by weight) of loose mixture. Therefore, for light mixtures and flour, forced feeding systems for extruders have been developed. The feeder feeds the flour into the loading area of ​​the extruder under some pressure and thus ensures sufficient density of the material. The diagram of such a feeder is shown in Fig. fifteen.

Usually, forced feeders are supplied by the manufacturer together with the extruder by special order for a specific mixture, see for example the scheme of the organization of the direct extrusion process offered by Coperion, Fig. sixteen.

Rice. 16. Scheme of direct extrusion of WPC with forced feeding, Coperion.

The scheme provides for the loading of individual components of the composite into different zones of the extruder. The appearance of a similar installation by Milacron, see Fig. 1.17.a.


Rice. 17.a. Twin screw conical extruder TimberEx TC92 with forced feed system with a capacity of 680 kg/h.

6. Cooler.

In the simplest cases, the WPC extrusion process can be completed by cooling the profile. For this, a simple water cooler is used, for example, a trough with a shower head. The hot profile falls under the jets of water, cools down and takes the final shape and dimensions. The length of the trough is determined from the condition of sufficient cooling of the profile to the glass transition temperature of the resin. This technology is recommended, for example, by Strandex and TechWood. It is used where the requirements for surface quality and profile shape accuracy are not too high ( building construction, some decking products, etc.) or further processing is expected, such as sanding, veneering, etc..

For products with increased requirements for the accuracy of product dimensions (prefabricated structures, interior elements, windows, doors, furniture, etc.), it is recommended to use calibration devices (calibrators).

An intermediate position in terms of the accuracy of the dimensions of the resulting products is occupied by the technology of natural air cooling of the profile on a roller table, used, for example, by the German company Pro-Poly-Tec (and seems to be one of the Korean companies).

7. Calibrators.

The profile leaving the die has a temperature of up to 200 degrees. During cooling, thermal shrinkage of the material occurs and the profile necessarily changes its size and shape. The task of the calibrator is to provide forced stabilization of the profile during the cooling process.

Calibrators are air and water-cooled. There are combined water-air calibrators that provide better pressing of the extrudate to the forming surfaces of the calibrator. Vacuum calibrators are considered the most accurate, in which the moving surfaces of the formed profile are sucked by vacuum to the surfaces of the forming tool.

The Austrian company Technoplast has recently developed a special system for water calibration and cooling of wood-polymer profiles, called Lignum, see fig. eighteen.

Rice. 18. Lignum calibration system from Technoplast, Austria

In this system, the profile calibration takes place with the help of a special attachment to the die, in which the water vortex cooling of the profile surface takes place.

8. Pulling device and cutting saw.

At the outlet of the extruder, the hot composite has low strength and can be easily deformed. Therefore, to facilitate its movement through the calibrator, a pulling device, usually of a caterpillar type, is often used.

Rice. 19. Pulling device with a cut-off saw from Greiner

The profile is delicately captured by the track tracks and removed from the calibrator at a predetermined stable speed. In some cases, roller machines can also be used.

To divide the profile into segments of the required length, mobile circular pendulum saws are used, which move along with the profile during sawing, and then return to their original position. The sawing device, if necessary, can be equipped with a longitudinal saw. The hauling device can be made in the same machine as the cut-off saw, see photo in fig. nineteen.

9. Receiving table

May have different design and degree of mechanization. The simplest gravity ejector is most often used. Appearance see, for example, Fig. 20.


Rice. 20. Automated unloading table.

All these devices mounted together, equipped with a common control system, form an extrusion line, see fig. 21.

Rice. 21. Extrusion line for the production of WPC (receiving table, saw, pulling device, calibrator, extruder)

Various trolleys, conveyors and loaders are used to move profiles around the enterprise.

10. Finishing work.

In many cases, a profile made from WPC does not require additional processing. But there are many applications where, for aesthetic reasons, finishing work is necessary.

11. Packing

Finished profiles are collected in transport bags and tied with polypropylene or metal tape. Responsible parts for protection against damage can be additionally covered, for example, with polyethylene film, cardboard strips).

Small profiles may require rigid packaging (cardboard boxes, crates) to protect against breakage.

domestic counterparts.

In the course of information research in the field of WPC extrusion, a search for domestic technologies was also carried out. The only line for the production of wood-polymer sheets is offered by the Rostkhimmash plant, website http://ggg13.narod.ru

Line specifications:

Type of product - sheet 1000 x 800 mm, thickness 2 - 5 mm

Productivity 125 - 150 kg per hour

Line composition:

  • twin screw extruder
  • disk extruder
  • head and gauge
  • vacuum calibration bath
  • hauling device
  • cutting device, for trimming edges and trimming to length
  • automatic storage

Overall dimensions, mm, not more than

  • length, 22500 mm
  • width, 6000 mm
  • height, 3040 mm

Weight - 30 620 kg

Installed capacity of electrical equipment is about 200 kW

This setting can be evaluated as follows:

  • has poor performance
  • not adapted to the production of profile parts
  • extremely low accuracy (+/- 10% in thickness)
  • high specific material consumption and energy consumption

Details you can cut and hone each of them by hand, but this technique is very imperfect: it takes a lot of effort, and it is impossible to get two absolutely identical products. Therefore, in this material you will learn how to carry out plastic injection at home.

What we might need

For self-made plastic molding, we do not need any special tools or materials. We can make a template model, a kind of matrix, from almost anything - from metal, cardboard or wood. But regardless of which option you choose, in any case, it must be impregnated with a special solution before starting work. This is especially true for wood and paper, because they actively absorb moisture and to prevent this process, we need to fill the pores, preferably with liquid wax.

Silicone.

If we settled on this option, then you should buy it with the lowest viscosity - this will contribute to a better streamlining of the part. Of course, the results will be more accurate. There are a great many of its varieties on the modern market, and it makes no sense to compare them with each other: we have neither the time nor the opportunity for this. We can only say with certainty that sealant for cars, preferably red, is ideal for coating. With it, pouring plastic at home will be much easier.

Determining the casting material

To be honest, there are even more molding materials than silicone grades. Among them are liquid plastic, and ordinary gypsum mixed with PVA glue, and even polyester resin. Substances for cold welding, low-melting metals, and so on are somewhat less popular. But in our case, we will be based on some other characteristics of casting substances:

  • The duration of their work.
  • Viscosity.

Regarding the first point, it indicates the time during which we can carry out manipulations with the material that has not yet hardened. Of course, if the manufacture of plastic products takes place in the factory, then two minutes will be more than enough. Well, we, who do it at home, need at least five minutes. And if it so happened that suitable materials If you couldn’t get it, then it’s quite possible to replace them with a simple epoxy resin. Where to look for it? In auto shops or in stores for fans of aeromodelling. In addition, such resin is often found in ordinary hardware stores.

Making a cut shape

This one is ideal for pouring plastic with your own hands, because unusual types of resins can be poured into it. A little trick of this technique can be considered that at the preliminary stage the entire surface of the model must be treated with silicone, and then, after the material has completely hardened, the matrix can be cut off. After that, we extract its “insides”, which will be useful to us for further casting. In order for us to fit the form, we must apply a three-millimeter layer of sealant, after which we simply wait until the material hardens - usually it takes two hours. In this case, it is desirable to apply it with a brush. When applying the first layer, we must try to fill all the irregularities or voids with the material so that air bubbles do not subsequently form.

How is the casting process

First step.

We take the casting mold and thoroughly clean it - it should be dry and clean. All remnants of the material remaining after the preliminary procedures must be removed.

Second step.

If the need arises, we can slightly change the color of our composition: for this you just need to add one drop of paint to it, but in no case water (liquid plastics have a personal dislike for them).

Third step.

There is no need for degassing of our casting mix. This can be explained by the fact that plastic molding at home initially provides for the relative short duration of its "life". At the same time, in order to extract air bubbles from small-sized products, it is only necessary to manually remove them after pouring.

Fourth step.

Thoroughly mix all the necessary components and pour it into the template shape slowly, in a thin stream. This should be done until the mixture fills the entire volume and some more of the casting channel. And soon, when the degassing procedure takes place, the volume of this material will decrease significantly and become what we need.

And the last tip: in order for the quality of the model to be high, you need to cool the template gradually, slowly. So, follow all the instructions and you will succeed!