RU2081135C1 - Environmentally appropriate wood-filled plastic and method of preparation thereof - Google Patents

Abstract

FIELD: manufacture of structural composite materials. SUBSTANCE: invention relates to formulations and technologies of high-filled composite materials and articles based on disperse wood-vegetable fillers and thermoplastic fillers and may be utilized in furniture, building, mechanical engineering, and other industries. Invention consists in that wood-filled plastic including thermoplastic polymer binder, inorganic additive, and conventional goal additives has, as filler, preliminarily triboactivated disperse wood-vegetable filler with definite characteristic parameter values: residual specific charge 5•10^-7-5•10^-5 coulomb/kg and its relaxation time 0.05- 1 kg, and , as inorganic additive, disperse inorganic material with basic surface properties and particle size not larger than 20 mcm with following component contents, wt.-%: filler, 50-92; inorganic additive, 0.1-10; conventional additives, 0.3-8; and polymer binder, the balance. Additionally, 0.1-40 wt % of functional filler may be entered. Method of preparation includes drying; determining characteristic parameters: concentration of acidic and basic sites on surface of filler and inorganic additive, value, polarity, and time of relaxation of residual specific charge of filler; triboactivating electric state of filler particles during 2-1200 s at 10-220 C with activation intensity sufficient to reach above-indicated parameters; mixing all components of the plastic, which begins after completion of triboactivation during period of time not exceeding double value of relaxation time of residual specific charge of filler; and thermal shaping. EFFECT: improved quality.

Description

 The invention relates to the field of compositions and technology of highly filled composite materials and products based on dispersed wood-vegetable fillers and thermoplastic polymer binders and can be used in the furniture industry, construction, engineering and other industries.

 A number of simple compositions are known for highly filled polymer compositions based on dispersed wood-plant (organic) fillers and thermoplastic polymer binders containing over 50 wt. filler [1, 2] So, for example, the composition [1] intended for the production of chipboards, contains as filler 70-90 wt. wood sawdust, and as a polymeric binder, powdered primary polyethylene, taken in an amount of 10-30 wt. The material for pressing plates [2] as a binder and filler contains secondary crushed polyethylene and crushed wood in the following ratio of components: polyethylene 20 wt. chopped wood 80 wt.

 The main disadvantages of such simple composites are the relatively low level of physicomechanical properties, low water and biostability, and poor processability that limits the technology of processing composites into products only by pressing methods.

 In order to increase the physicomechanical and other operational properties of composites based on wood-vegetable filler by enhancing the adhesive interaction of the components, chemically modified polymers (copolymers) or physical mixtures of various thermoplastic polymers are used as a polymer binder [3-6] In particular, the polyolefin composition with increased strength and chemical resistance includes 20-50 wt. vegetable filler (fibrous cellulose) and 40-80 wt. a polyolefin modified by grafting a carboxylic acid or its anhydride [3] In the composition [4] containing up to 70 wt. wood flour, as a binder use a mixture of polyvinyl chloride (vinyl chloride copolymer) with ABC plastic. In cellulose-filled (20-70 wt.) Compositions, the polymer binder is a mixture of a copolymer of ethylene and monomers from the group of unsaturated carboxylic acid salts with a polyolefin [5] In the polymer composition [6], a mixture of thermoplastic vinyl polymers is used as a polymer binder, as an organic filler a mixture of certain fractions of cellulose-containing waste (50-65 wt.), and as traditional target additives (0.3-8 wt.) plasticizers, heat stabilizers, lubricants and dyes. However, composites of this group in many cases also have insufficient strength and operational characteristics (bending strength, impact strength, moisture resistance, etc.), which limits their application.

 One of the ways of hardening and imparting new properties to composites based on wood-plant filler, which can significantly expand their field of application, is an additional introduction to the composition of a functional co-filler (additive) [7-9] So, for example, a mass for the manufacture of plastics based on polyethylene [ 7] as a co-filler in addition to sawdust taken in an amount of 10-67.63 wt. contains 7.5-35.37 wt. oriented wood particles. Thermoplastic composition [8] in addition to wood filler as a reinforcing co-filler contains artificial organic or inorganic fibers in the following ratio of components, wt. including thermoplastic polymer 100, dispersed wood material 10-500, fibrous material 2-100. To ensure sound-absorbing properties capable of repeated processing of the composition [9] per 100 wt. including polyolefin binder contains 20-150 wt. including cellulose filler, 20-120 wt. including a crosslinked elastomer with a particle size of less than 50 μm, taken as the main functional co-filler, and a dispersed inorganic co-filler (talc 1-10 wt. parts of barite, iron oxides, etc. up to 180 wt.). Polymeric compositions with wood filler [10] contain 40-90 wt. thermoplastic binder, 10-60 wt. wood flour and as an inorganic co-filler 2-4 wt. including magnesium oxide per 100 wt. including a mixture of a binder with a wood filler. The disadvantages of the composites of this group are the relatively low content of wood-vegetable filler, which in most cases is the cheapest component of the mixture, and the low level of a number of physicomechanical and operational properties.

 Closest to the claimed invention in technical essence and the achieved result is a thermoplastic composite material [11] including 100 wt. including thermoplastic polymer binder, 5-65 wt. including dispersed lignin-cellulose filler, 15-110 wt. including plant fiber filler (plant fiber such as hemp), 10-40 wt. including inorganic co-filler and traditional target additives (plasticizer, lubricant). Polyolefins (polyethylene, polypropylene, ethylene propylene copolymer), ABC plastics or nylon (polyamide 6) are used as a binder, and dispersed wood in the form of flour, dust, flakes with a particle size of 0.3-10 mm (preferably 2) is used as a lignocellulosic filler. -4 mm). Discrete fibers, rather uniform in shape and size with a length of 0.3-10 mm (mainly 4-7 mm) of plants from the group consisting of hemp, Chinese nettle, flax, jute and the like plants, and as an inorganic one, serve as a plant fiber filler. co-fillers predominantly use talc. The combination of dispersed wood and vegetable fibrous fillers allows to provide increased strength upon impact and tension, as well as high deformability of the material during molding, which is important for obtaining thin-walled bulk products. The additional introduction of inorganic co-filler allows you to increase some of the mechanical characteristics of thermoplastic composites, in particular the module in bending.

 The main disadvantages of this composite material are the relatively low (up to 63.6 wt.%) Content of wood-plant filler, insufficiently high strength and operational (resistance to pulling screws, water resistance, etc.) properties, which is caused by both a low filler content and and insufficiently strong adhesive interaction of the components in the composite. In addition, not in all cases, the specified composite is highly adaptable to processing into products.

 The aim of the invention is to increase the degree of filling, physico-mechanical and operational properties, as well as manufacturability in the processing of composites.

This goal is achieved in that the wood-filled plastic, including thermoplastic polymer binder, dispersed wood-vegetable filler, inorganic additive and traditional target additives, according to the invention, as a filler contains pre-tribo-activated dispersed wood-vegetable filler with a residual specific charge of 5 • 10 ^-7 - 5 • 10 ^-5 C / kg and the value of the relaxation time of the residual specific charge 0.05-1 kc, and the inorganic additive comprises disp rsny inorganic material with basic surface properties and particle size of not more than 20 microns with the following component ratio, wt.

Triboactivated tree-plant filler 50-92
Inorganic additive 0.1-10
Traditional Target Supplements 0.3-8
Polymer binder Else
In addition, the plastic may additionally contain a functional co-filler in the following ratio of components, wt.

Triboactivated tree-plant filler 50-92
Inorganic additive 0.1-10
Functional co-filler 0.1-40
Traditional Target Supplements 0.3-8
Polymer binder Else
As a polymer binder, you can use the original or waste thermoplastic polymers and / or mixtures thereof with a processing temperature below the temperature of the oxidative degradation of the wood-plant filler.

 The wood-plant filler can be used in the form of a mixture of particles with a particle size of 0.05-0.5 mm and particles with a particle size of 0.5-8 mm, taken in a ratio of 1: 1-1: 100, and as particles with a size fractions of 0.5-8 mm use chopped plant fibers 1-20 mm long. In this case, the inorganic additive can be used in the form of a mixture of two or more dispersed inorganic substances.

 Known methods for producing highly filled composites based on thermoplastic polymer binders and wood-plant (organic) fillers, including preparing the filler, mixing the components and subsequent thermoforming of the resulting composition.

 So, for example, by the method of [12] a molding polymer material containing 20-80 wt. cellulose, obtained by grinding cellulose to particles with sizes less than 147 microns and mixing with a thermoplastic polymer binder and functional organic additives introduced to neutralize the acid gases released during heating from cellulose. The method of obtaining the composite material according to the patent [13] includes the operations of grinding and drying the cellulose filler, mixing it with a polyolefin binder when heated in an oil-heated mixer to form a homogeneous mixture, grinding and subsequent thermoforming of the composition in an extruder to ensure orientation of the cellulose fibers by extruding the melt through intermediate die at a temperature equal to the mixing temperature. It should be noted that in some methods of this group, the mixing of a wood-vegetable filler with a binder is carried out directly in the molding extruder, introducing the filler into the binder melt. For example, according to method [14], previously dried wood flour is introduced into the melt stream of a polypropylene binder in a twin-screw extruder, then the composite is thermoformed by extruding the melt of the resulting composition through the extruder forming head, followed by cooling of the obtained profile. The preparation of the composite material according to the application [15] is carried out by displacing wood sawdust with an average particle size of 2.5-5 mm in a twin-screw mixer and melt the thermoplastic polymer binder fed to the mixer from the extruder. The resulting homogenized mixture is thermoformed by extrusion into shaped products. The disadvantages of the above methods are relatively low homogeneity and poor processability of the material, which leads to increased energy intensity of processing and low physical and mechanical characteristics of the resulting products.

To eliminate the noted drawbacks in a number of known methods, a certain order of mixing the components is used, which has a particularly significant effect when using polymer mixtures as a binder. So, according to the method for producing molded products from wood-polymer materials [16], wood particles are dried to a moisture content of 0.5-165 wt. then they are successively mixed with a liquid plasticizer, polyvinyl chloride powder and the addition of a stabilizer (zinc stearate), after which the resulting mixture is extruded into products. In the method [17], comprising mixing a polyolefin binder with a wood filler and a solid plasticizer, the filler is pre-mixed with a binder, the mixture is homogenized at 110-210 ^o C, then the plasticizer is introduced into the mixture and homogenization is carried out again at a temperature of 150-200 ^o C. For determine the order of introduction of the components of the complex binder in some methods evaluate the characteristic parameter of polymeric materials, for which, for example, choose the coefficient of linear thermal expansion thermoplastic polymers [18] However, the above methods do not allow to ensure a high level of the whole complex of physical, mechanical and operational properties of the resulting composites.

 In order to ensure a higher level of properties and reduce the content of the polymer binder in wood-filled composites, surface modification of the particle particles of components is widely used. For example, in the method of manufacturing wood-based panels on a thermoplastic binder [19], special elastic deformation grinding of a mixture of polymers used as a binder is performed. According to the method for producing thermoplastic compositions [20], the dispersed tree-plant filler is modified by applying to the surface of the polymer shell filler particles from a suspension of a copolymer of a given composition in an organic solvent, followed by removal of the solvent, then the filler so modified is mixed with a polyolefin binder and the resulting composition is extruded into articles . In the method for the production of wood boards [21], the surface of wood particles is treated with a solution of lignosulfonate in the process of combining with a thermoplastic binder. According to the method of manufacturing wood plastic [22], wood particles are treated with a blowing agent before mixing with a binder, after which they are oriented with longitudinal axes in directions perpendicular to the direction of action of the compressive force and subjected to compression deformation. A method of producing thermoplastic composites [23] includes the preliminary modification of ligno-cellulose filler by hydrolytic degradation, the introduction of a modified filler in a thermoplastic matrix, homogenization of the mixture and its subsequent thermoforming into products. The main disadvantages of these methods are insufficiently high strength and operational properties, as well as often low productivity and effectiveness of such modifications.

Closest to the claimed method according to the technical nature and the achieved result is a method for the manufacture of chipboards [24] including drying, physical modification, mixing of the components and thermoforming of the resulting composition. Modification of the wood filler is carried out after drying by mechanical action while passing through the hot rollers with a layer of 2.0-3.5 mm thickness at 160-180 ^o C, a pressure of 2-6 MPa and a processing time of 0.7-1.1 min per 1 mm layer thickness and then crushed. This method in the case of using a thermosetting polymer binder (urea-formaldehyde resin) can reduce the content of the binder in the composition from 13-15 wt. up to 11.2 wt. while maintaining the level of physico-mechanical characteristics of the resulting composites (plates).

 The most significant disadvantages of this method are the insufficiently high content of wood-plant filler, physicomechanical (strength) and operational properties (resistance to pulling screws, moisture and biostability, workability, etc.) properties, which in combination with the use of environmentally unclean thermosetting binder (allocation free formaldehyde) and the relatively low efficiency of the applied modification does not allow to obtain environmentally friendly high-quality compositions s and their products. In addition, the low processability of the mixture allows the thermoforming of the composition obtained by this method only by direct compression, which makes it impossible to use the method to obtain complex products.

 The aim of the invention is to increase the degree of filling, physico-mechanical and operational properties, as well as manufacturability in the processing of composites.

The goal is achieved in that in a method for producing wood-filled plastic based on a thermoplastic polymer binder and dispersed wood-vegetable filler, including drying, modifying, mixing and thermoforming, according to the invention:
a) carry out the determination of the characteristic parameters of the components: the concentration of acidic and basic centers of the surface of the particles of wood-plant filler and inorganic additives; the magnitude, polarity and relaxation time of the residual specific charge of the particles of the tree-plant filler;
b) the modification is carried out by triboactivation of the electrical state of the particles of wood-plant filler for 2-1200 s at a temperature of 10-220 ^o C and an activation intensity sufficient to achieve the values of the characteristic parameters: specific charge 5 • 10 ^-7 -5 • 10 ^-5 C / kg and the relaxation time of the residual specific charge of 0.05-1 ks, and the subsequent mixing of all the plastic components begin to produce during the period of time after the end of triboactivation no more than twice the value of the relaxation time of the residual Yelnia charge woody plant filler particles. In addition, the triboactivation of the tree-plant filler can be carried out during drying, or the triboactivation of the tree-plant filler and the mixing of the components can be carried out simultaneously.

 Performed experimental and theoretical studies have shown that to obtain highly and super-filled plastics, i.e. plastics with a packing density of particles of dispersed filler in a polymer matrix close to the maximum possible while ensuring a sufficiently high level of properties of the composites, in general, three basic conditions must be met. First, the dispersed filler-binder system must be lyophilic, i.e., characterized by a high level of interaction of the filler particles with the binder, which is manifested, in particular, in the good wettability of the surface of the filler particles by the binder melt. Secondly, "geometric conditions" must be provided for the formation of a close-packed filler structure in a polymer matrix by optimizing the distribution of filler particles in size and shape. Thirdly, in the system it is required to ensure the level of interparticle interaction through thin interlayers of the binder, in particular, due to the implementation of electrocapillary effects, sufficient to realize the processes of self-organization and self-compaction of the structure while maintaining macrostructural mobility in the melt of the composite necessary for the processing of the material into products. To fulfill the first and third conditions, it is necessary first of all to ensure the realization of electrostatic attraction forces and the subsequent donor-acceptor (acid-base) interaction, carried out by electron-proton exchange between the active groups of binder macromolecules and the active centers of the filler surface during the formation of a double electric layer at the boundary section filler binder.

 Among the characteristics used to determine the surface activity of material particles, acid-base properties are most often evaluated, in particular, the concentration (number) of acidic or basic centers [25, 26] and the amount of excess electric charge of the particle surface, which is associated with the charging condition and the total density centers of capture of charge carriers - electronic surface states (intrinsic, adsorption nature, etc.) [26, 27] Moreover, the duration of the conservation of the active state of the surface can be judged by the time exchange relaxation of excess surface charge. It should be noted that the estimation of the magnitude, polarity, and relaxation time of the particle charge is important not only for determining the contribution of the forces of electrostatic interaction when the components are combined, but also for determining the significance of electrocapillary phenomena in the interparticle interlayers of the binder melt.

 Thus, this is precisely the reason for the choice as the characteristic parameters of the dispersed components of the concentration of acidic and basic centers of the particle surface, the magnitude, polarity and relaxation time of the residual specific charge of the filler and binder particles.

 According to the proposed technical solution, dust, flour, sawdust, shavings of any wood species, including bamboo, eucalyptus and fir, ground wood fiber, bark, cork, nutshells, rice husks and other cereals, can be used as the initial dispersed wood-plant material. husk of sunflower seeds, cereal straw, chopped stalks of corn, cotton, sunflower, sugarcane, reeds, hemp fiber, flax (including flax and hemp fire), jute, cotton, copra, ramie and other plants, other vegetable agricultural waste, pulped waste from the production of pulp and paper, including destroyed banknotes, other cellulose-containing industrial waste, as well as any mixtures of the listed materials that have sufficient heat resistance.

 To obtain composites, it is recommended to use a wood-plant filler in the form of a mixture of particles with a fraction size of 0.05-0.5 mm and particles with a fraction size of 0.5-8 mm, taken in a ratio of 1: 1-1: 100. Particles of woody-plant filler with sizes less than 0.05 mm are rare, which gives reason not to take them into account. The bulk of the fraction of 0.05-0.5 mm are dust particles and flour obtained by special grinding of dispersed wood-plant material. The fraction of 0.5-8 mm prevails among all types of dispersed wood available in the form of industrial wood processing waste (sawdust, shavings) or specially obtained for the production of chipboard and fiberboard, as well as among particles of crushed plants and agricultural and industrial waste. Coarse filler particles with dimensions (in particular, width) of more than 8 mm are undesirable due to the deterioration of the properties and surface quality of the products, as well as the manufacturability of the resulting composites during processing. It was experimentally established that the use of a mixture of these two fractions with sharply different particle sizes quantitatively taken in the indicated ratios ensures the most dense packing of filler particles and is necessary to optimize the conditions for producing composites with high properties with a minimum polymer binder content.

 As a fraction of particles of wood-plant filler with a size of 0.5-8 mm, you can use chopped plant fibers with a length of 1-20 mm, which can further increase the bending strength and impact strength of the composite material. The use of plant fibers with a length of less than 1 mm gives an insignificant positive effect, and with a length of more than 20 mm reduces the manufacturability of the composition when it is processed into products, practically without leading to an additional improvement in the strength and performance properties of the composite. Preferably, the length of the plant fibers used is 3-7 mm.

The use of pre-triboactivated dispersed wood-plant material as a filler with a residual specific charge of 5 • 10 ^-7 -5 • 10 ^-5 C / kg and a relaxation time of a residual specific charge of 0.05-1 ks allows for higher lyophilicity and adhesive the interaction of the surface of the filler particles with a polymer binder by enhancing the electrostatic, donor-acceptor and molecular types of interaction.

It was experimentally established that the surface of the particles of wood-plant filler predominantly has acidic properties with a concentration of acidic surface centers in the range of 0.05-0.20 mmol / g (when measured in an aqueous medium). The concentration of acid sites mainly depends on the nature and dispersion of woody plant material. The triboactivation of the electrical state of the surface of the particles of wood-plant filler leads to exposure of existing and creation of new electrically active surface centers, generation and transfer of charge carriers during static electrization, saturation of the surface layer of particles with an excess electric charge of the electret type. It should be noted that the polymeric materials used as a binder almost always have an excess surface (electret) tribo-charge acquired during grinding, transportation, and other intermediate technological operations. Therefore, it is desirable that the polarity of the residual charge of the triboactivated filler is opposite to the polarity of the residual charge of the polymer binder. Obviously, the larger the charge of the filler particles, the stronger the electrostatic interaction between the particles of the main components of the composite will be. At values of specific charge less than 5 • 10 ^-7 C / kg, as well as at values of relaxation time less than 50 s, the positive effect is insignificant. The values of the specific charge are greater than 5 • 10 ^-5 C / kg and the relaxation time of the specific charge of the filler particles above 1 ks in air is practically unattainable due to the intensive processes of neutralization and relaxation of the excess charge of activated particles [27]
As a thermoplastic polymer binder, polymers selected from the group consisting of polyolefins (polyethylene, polypropylene, poly (1-butene), poly (1-pentene), poly (1-hexene), copolymers of ethylene with propylene, ethylene with vinyl acetate, 2 -methyl-1-propene, etc.), polystyrene and styrene copolymers, vinyl polymers based on vinyl chloride and its copolymers (polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, etc.), methyl methacrylate and its copolymers, ABC copolymers and polyamides (polyamide 6 and etc.), as well as mixtures of these polymers and other ue thermoplastic polymers in powder or granules (lumps, particles, flakes), with a processing temperature less than the temperature of thermal oxidative degradation of plant woody filler. In this case, both initial and waste waste thermoplastic polymers and / or mixtures thereof with a processing temperature below the temperature of the oxidative degradation of wood-plant filler, in particular crushed (powder, sawdust, granules, fine chips, flakes, etc., can be used). ) secondary polymers obtained from the processing of used plastic containers, packaging, films and other products.

 The introduction of an inorganic additive inorganic material with basic surface properties and a particle size of not more than 20 microns into the material helps to block the acidic centers of the surface of the filler particles by the mechanism of acid-base (donor-acceptor) interaction, enhances the adhesion in the filler-polymer binder system, improves the uniformity of particle distribution filler in the polymer matrix, as well as the neutralization of acid substances released during heating of wood, which ultimately increases the physical and fur the analytical and operational characteristics of the materials obtained. In addition, in many cases, the inorganic additive can simultaneously be the initiator-charger of particles of wood-plant filler, contributing to a more intensive charging of particles of wood-plant filler during triboactivation or mixing with other components. Various substances can be used as inorganic additives: carbonates, sulfates, metal oxides and other substances, in particular layered silicates (vermiculite, muscovite, talc, etc.), as well as a mixture of two or more dispersed inorganic substances with a particle size of not more than 20 microns that allows you to optimize the content of the additive and improve the properties of the composite due to the implementation of additional mechanisms of action of materials of inorganic additives. For example, mixtures of barite and talc, calcium carbonate and vermiculite, talc and titanium dioxide, muscovite, vermiculite and magnesium oxide, and a number of other mixtures are used. It was found that when the size of the inorganic additive is more than 20 μm, its effectiveness sharply decreases due to a decrease in the number of particles per unit volume and insufficiently complete blocking of the acid centers of the filler surface.

 As traditional target additives, commonly used heat and light stabilizers (in the amount of 0.01-2 wt.), Plasticizers (0.5-8 wt.), Technical lubricants stearin, paraffin, waxes, oils (0.05- 3 wt.) And dyes (0.05-5 wt.).

 The use of wood-vegetable filler in an amount of less than 50 wt. leads to a decrease in a number of operational properties and an increase in the cost of the resulting plastic, and in an amount of more than 92 wt. to a sharp drop in physical and mechanical characteristics and loss of processability into products due to the lack of a polymer binder. Introduction to the composition of an inorganic additive in an amount of less than 0.1 wt. is insufficient and does not give a positive effect, and over 10 wt. is excessive from the point of view of enhancing the adhesive interaction of the components, leads to some decrease in the strength and technological characteristics of the resulting composite. Introduction to the composition of traditional target additives in an amount of less than 0.3 wt. is insufficient and does not provide a positive effect, and in an amount of more than 8 wt. leads to a deterioration in the physico-mechanical characteristics of the composite and is economically impractical. The best results are obtained with the following contents of these traditional target additives in the compositions: stabilizers 0.3-1 wt. a plasticizer of 0.5-6 wt. technical lubricant 0.5-2 wt. and dye 0.3-1 wt.

 To improve individual properties or a complex of physico-mechanical and operational properties, the composition of the composite may additionally contain functional co-filler in an amount of 0.1 to 40 wt. As a functional co-filler, discrete reinforcing artificial organic (viscose, polyamide, polyacrylonitrile, lavsan, etc.) and inorganic (glass, graphite, asbestos, and other) fibers with a length predominantly up to 20-30 mm, dispersed flame retardants with amphoteric or basic surface properties (zinc borate, barium metaborate, antimony oxide and other substances or mixtures thereof), expanded gas-filled dispersed materials (expanded perlite sand, hollow inorganic and / or organic microspheres) mainly with a particle size of less than 1 mm, designed to reduce the density and increase the rigidity of plastic, finely divided cross-linked elastomers to impart sound-absorbing properties and increase the resistance of the composite to impact, dispersed substances, dry lubricants (Teflon, molybdenum disulfide, etc.) to increase antifriction the properties of the resulting plastics and other similar substances, as well as any mixtures of the above materials. In particular, artificial fiber waste (for example, textile and fur wastes) and / or a mixture of them, as well as a mixture of natural and chemical fibers (for example, short-fiber short-fiber carpet weaving buttons) are used as a functional co-filler. The amount of co-filler introduced depends on the nature and size of the particles. The introduction of co-filler in an amount of less than 0.1 wt. is insufficient to improve the properties of the composite, and in an amount of more than 40 wt. leads to a deterioration in the complex of physico-mechanical and operational properties due to a decrease in the content of the binder, violation of the continuity of the polymer matrix and loosening of the structure of the composite.

According to the proposed method for producing environmentally friendly wood-filled plastic (EDNP), including drying, modifying, mixing and thermoforming operations, additionally determine the characteristic parameters of dispersed components, for which, for the previously mentioned reasons, the concentration of acidic and basic centers of the surface of the filler and inorganic particles is estimated additives, size, polarity and relaxation time of the residual specific charge of the particles of woody plant i. The modification is carried out by the triboactivation of the electrical state of the particles of the tree-plant filler with repeated dynamic contact with the surface of the working elements of the triboactivator. It was experimentally established that, depending on the nature, dispersion and humidity of the filler, the process of triboactivation must be carried out for 2-1200 s at a temperature of 10-220 ^o C and an activation intensity sufficient to achieve the values of the characteristic parameters: the value of the residual specific charge is 5 • 10 ^{- July 5} • 10 ^-5 C / kg and its relaxation time 0.05-1 ks, and the subsequent mixing of all components begin to produce for a period of time after closure triboaktivatsii not more than twice the relaxation time residually charge of woody vegetation filler particles. The choice of the activation duration from 2 s to 1200 s is due to the fact that when the duration of triboactivation of the dispersed filler is less than 2 s and any possible activation intensity, it is practically impossible to provide the indicated values of the characteristic parameters, and an increase in the duration to values of more than 1200 s, without causing a significant increase in the particle charge leads to the accumulation of structural disturbances due to mechanocracking of molecules in the surface layers of the filler, causing a slight decrease in operational properties, in particular water resistance of composites. Performing triboactivation of the filler at elevated temperature allows you to enhance the effect of activation due to the intensification of the processes of desorption of adsorbed substances (water, gases, etc.), exposure of active surface centers and charging. The choice of the maximum heating temperature T-220 ^o C is due to the fact that at higher temperatures and processing times of up to 1200 s there is a significant thermo-oxidative degradation of the filler, leading to a deterioration in the physicomechanical properties of the resulting plastics. At temperatures below 10 ^o C, which are most often achieved by special cooling with refrigerants, there is a decrease in activation efficiency by increasing the hardness of the particle material and reducing the actual area of dynamic contact of particles with the working surface of the triboactivator. The rationale for choosing the range of values of the residual specific charge acquired by the dispersed filler as a result of triboactivation, and its relaxation time is given above. We only note that the greatest effect is achieved when the charge polarity of the filler is of the opposite polarity (sign) of the residual charge of the polymer binder particles.

 As a result of the experiments, it was found that in order to maximize the effect of pre-triboactivation of the filler, the subsequent mixing of the components must begin to be carried out within the shortest possible period of time after the end of activation, which should not be more than twice the relaxation time of the residual specific charge of the particles of the tree-plant filler. At large values of the time interval as a result of a sharp decrease in the residual specific charge of the particles, the positive effect of triboactivation of the filler becomes insignificant.

The proposed method allows in many cases to carry out triboactivation of wood-plant filler during drying in special triboactivators-driers at temperatures up to 220 ^o C, which reduces energy costs and productivity of the technological cycle.

According to the proposed method, triboactivation and mixing of the plastic components can be carried out simultaneously in a triboactivator-mixer. Such a combination of operations is possible, in particular, in those cases when the main components of the composition are mixed with charges of different polarity (sign), and the specific charge of the tree-plant filler is in the required range from 5 • 10 ^-7 to 5 • 1- ^{- 5} C / kg. It is assumed that the period of time after the end of activation before the start of mixing is zero.

 As a result of the analysis of scientific and technical literature and patent sources of information, it was found that the above proposed technical solution is absent in modern technology. The effect of using the claimed combination of distinctive features is not a known consequence of the already known properties of the objects of the invention and is established by the applicant and the authors.

Examples of carrying out the invention
For experimental verification of the invention, powdered high-density polyethylene (HDPE, grade 20906-040, GOST 16338-85), polypropylene (PP, grade 21030, GOST 26996-86), suspension polyvinyl chloride (PVC, grade C6358, GOST 14332 -78), emulsion polystyrene (PS, grade PSE-2, GOST 20282-86), polyamide 6 (PA, OST 6-06-C9-93) and a copolymer of ethylene with propylene (SPEP, TU 6-05-041-662 -84), as well as crushed waste of thermoplastics secondary PE (PEVP-60 content wt.) And PVC (crusher obtained by mechanical grinding of boxes and film ) In the experiments, a fraction of powder binders with a particle size of less than 0.315 mm was used. The maximum particle sizes of the crushed waste did not exceed 3 mm.

 Flour, sawdust and pine shavings, a mixture of deciduous trees (alder, birch and aspen), bamboo, as well as crushed sugarcane, rice husk and flax fiber were used as the initial wood-plant filler. The shape and size of the particles (diameter d and length 1) were evaluated using optical microscopes Neophot-2 and Polami-211. The selection of fractions of particles of the desired size was carried out by fractionation of the dispersed material on a sieve analyzer (model 029) with a replaceable set of sieves.

 As an inorganic additive, ground large-scale mined natural materials were used: calcite (OST 21-21-88), barite (grade KB-1, GOST 4682-84), vermiculite (TU 21-25-ED1-73-89) and talc ( GOST 19729-74).

Targeted additives in the preparation of the compositions were: thermostabilizers
calcium stearate (TU 6-14-722-76) and zinc stearate (TU 6-09-3567-75), plasticizer-dioctyl phthalate (DOP, GOST 8728-88), oil paraffin lubricant (GOST 23638-79), pigment dyes yellow light-resistant (GOST 5691-77) and blue phthalocyanine pigment (GOST 6220-76).

 The following were used as functional co-filler: chopped glass fibers (CB), obtained by grinding roving from glass fibers (GOST 17139-79), polyacrylonitrile (PAN) fibers in the form of chopped waste fiber "nitron" (TU 6-12-575604-9- 89), short-fiber waste from carpet production of knitting strigl, which is an inseparable mixture of polyamide (25 wt.), PAN (50 wt.), Woolen (20 wt.) And polypropylene (5 wt.) Fibers and yarn in the form of lengths of 0, 1-2 mm, expanded perlite sand (GOST 10832-83) and finely divided trioxide antimony (flame retardant).

The concentration of acidic centers of the surface of the wood-vegetable filler and the main centers of the surface of the inorganic additives is determined by potentiometric titration in water [25]. A suspension of 1 g of the investigated dispersed material in 50 ml of distilled water is used. The methodology for determining the concentration of acid centers (C _k ) involves the operation of neutralizing the suspension with an excess portion of 0.1 N KOH solution and subsequent titration of excess alkali with a 0.1 N aqueous HCI solution. Similarly, to determine the concentration of the main centers (C _o ), the suspension is neutralized with a 0.1 N aqueous solution of HCI and then the excess is titrated with a 0.1 N KOH solution. Titration is carried out by the potentiometric method in non-equilibrium conditions using the universal EV-74 ionomer and a standard electrode system of a glass measuring electrode and calomel reference electrode. The value of C _k (C _o ) is taken as the number of moles of KOH (HCI) spent on the neutralization of the acid (main) centers of the surface of the particles of dispersed matter weighing 1 g [25] The arithmetic average of the results of three parallel experiments is taken as the value of C _k and C _o .

The magnitude and polarity (sign) of the residual specific charge of dispersed materials is estimated by the Faraday cylinder method [27] by shaking off the dispersed material into a metal cylinder electrically connected to a B7-30 voltmeter-electrometer. The polarity (sign) of the residual specific charge of a batch of material is determined by the polarity (sign) of the potential U relative to the ground, and the charge value as the ratio qU • C / m, where C is the capacitance of the measuring system (C = 10.45 nF), m is the mass of a batch of material . The value of the relaxation time of the residual specific charge of the particles of the tree-plant filler is determined according to the kinetics of the decay of the charge of the dispersed material during exposure under normal conditions (air humidity 40 + 3%) [27]
Wood-filled plastics are prepared as follows. Wood-vegetable filler is dried at a temperature of 150-180 ^o C in a thermostat type SNOL-1,5 or in a specially designed triboactivator-dryer to the desired residual moisture content in the range of 0.1-5 wt. estimated by the weight method using analytical scales VLA-200M. Preliminarily, at 50-70 ^o C all other dispersed materials used to obtain plastic samples are dried. Then evaluate the characteristic parameter the concentration of the main centers C _{o the} surface of the dispersed materials used as inorganic additives. The triboactivation of the wood-plant filler, which is preliminarily fractionated if necessary, is carried out in a non-standard high-speed triboactivator of periodic action with the possibility of heating or cooling the working volume and adjustable activation intensity, in particular by changing the speed of rotation of the rotor blade.

The triboactivation of the components is carried out at a predetermined temperature of 10 to 220 ^o C, the rotational speed of the blade rotor is from 100 to 4500 rpm and the activation duration is from 2 to 1200 s until the characteristic parameters of the triboactivated tree-plant filler are reached: the residual specific charge is 5 • 10 ^-7 - 5 • 10 ^-5 C / kg and its relaxation time 0.05-1 ks. In the case of using high temperature (150-220 ^o C) and woody plant materials with low and medium humidity, the filler is not pre-dried, and the triboactivation of the filler is carried out during its drying (carried out simultaneously). Then evaluate the value of the characteristic parameter the concentration of acid centers C _{to the} surface of the particles of triboactivated filler. Based on the values of C _to and C _o , as well as the required level of properties of the plastic, an inorganic additive and its content in the compositions are selected.

After drying and modification, weighed portions of triboactivated filler and other components are loaded into a Truzioma type laboratory mixer and mixed for 30-300 s until a visually uniform dispersed composition is obtained. In some cases, the mixing of all components is carried out directly in a non-standard triboactivator-mixer, combining the operations of modification (triboactivation) and mixing of the components. In this case, the values of the characteristic parameters: magnitude, polarity, and relaxation time of the residual specific charge of the filler particles are evaluated after the material sample is removed from the triboactivator-mixer and the separation of significantly larger woody-plant particles from particles of other components by blowing a dry nitrogen stream into the material sample cell , leading to the removal of particles of other components that freely pass through mesh cells with a size of about 0.5 mm. Since in these cases the triboactivation of the filler and the mixing of the components are carried out simultaneously, the period of time after the completion of triboactivation, during which the components are mixed, is taken to be zero (Example 10), which allows not to evaluate the relaxation time of the residual charge of the filler. From the mixture obtained by direct thermal pressing, the plastic samples necessary for testing are molded. In the case of subsequent thermoforming of plastic samples by injection molding and extrusion, the mixing of all components is carried out in the mixing chamber of the Brabender plastic decoder at a temperature for PVC-140 ^o C, for PS-160 ^o C, for PP and SPEP-190 ^o C and for PA-220 ^o C to achieve a constant viscosity of the melt of the material for 5-15 minutes The product obtained after mixing and cooling with a knife crusher type СО-1 is crushed to particles with a size of 1-5 mm. The obtained granulate is used for the manufacture of injection-molded and extruded plastic samples. Examples of plastic compositions are given in table. 1, examples of the implementation of the method of obtaining them in table. 2 (examples 1-10). For comparison, in table. 1 and 2 show the compositions and modes for producing compositions of the prototypes [11, 24] (examples 10, 13) and the analogue [6] (example 12). Samples of the composition of the prototype [11] receive as described in this patent.

Thermoforming of plastic samples from the resulting compositions is carried out by direct hot pressing, injection molding and extrusion. Samples are pressed from dispersed compositions on a laboratory hydraulic press at a mold heating temperature for compositions based on PEVP-180 ^o C and PP-190 ^o C, pressing pressure 2-10 MPa and holding under pressure for 5 minutes, followed by cooling to 50-70 ^o C. Injection samples are obtained on a DV3328 injection molding machine with an injection volume of 63 cm ³ under the following conditions: injection time 10 s, pressure 35 MPa, holding and cooling for 0.2 ks, heating temperature by zone: for composition based on PS I 150 ± 5 ^o C, II 170 ± 5 ^o C, III and IV 190 ± 5 ^o C, and for a composition based on PA I 18- ± 5 ^o C, II 210 ± 5 ^o C, III and IV 240 ± 5 ^o C. Extrusion samples are obtained on a laboratory measuring extruder of the company "Brabender" at an extrusion temperature for compositions based on PVC 150 ± 10 ^o C (for zones I 120 ^o C, II 130 ^o C, III -140 ^o C, IV 150 ^o C), based on PP and BEP 195 ± 10 ^o C (for zones I 130 ^o C, II -150 ^o C, III 175 ^o C and IV 195 ^o C).

 The density of the samples is evaluated in accordance with GOST 15139-69. The strength under static bending is determined according to GOST 4648-71 using a 2D-10 machine on rectangular samples with dimensions of 80 • 10 • 4 mm at a speed of movement of the lower platform with supports 2 ± 0.5 mm / min. Charpy impact strength is evaluated in accordance with the requirements of GOST 4647-80 using a copra PSW 0,4 / 7224 on rectangular samples with dimensions 120 • 15 • 10 mm without a notch. The values of the estimated physical and mechanical characteristics are determined by the test results of 5-10 samples. The water absorption of plastic samples in 24 hours is determined in accordance with GOST 4650-80, the specific resistance to pulling screws according to the requirements of GOST 10637-78. In the latter cases, samples similar to those used in assessing the impact strength were used, or pressed samples with dimensions of 50 • 50 mm. Physico-mechanical and operational properties of the obtained compositions, as well as compositions of the prototypes [11, 12] and analogue [6] are given in table. 3.

 Data analysis table. 1-3 shows that compared with the known technical solutions, the proposed technical solution allows to increase the degree of filling up to 92 wt. while maintaining a sufficiently high level of physico-mechanical and operational properties of the resulting plastic, and with the same processing method and close filler content, increase strength and toughness (1.1-1.4 times), resistance to pulling screws (1.5-3 times), reduce water absorption (1.3-2 times) of the resulting polymer composites and increase manufacturability when processing them into products (reduce the energy intensity of the process by 10-30%).

Claims (9)

1. Environmentally friendly wood-filled plastic, including thermoplastic polymer binder, dispersed wood-vegetable filler, inorganic additive and traditional target additives, characterized in that the filler contains pre-triboactivated dispersed wood-vegetable filler with a residual specific charge of 5 • 10 ^{- July 5} • 10 ^-5 C / kg and the value of the relaxation time of the residual specific charge 0.05 kc 1 and as inorganic particulate additive comprises inorganic cue material to the basic surface properties and particle size of not more than 20 microns with the following component ratio, wt. Triboactivated tree-plant filler 50- 92
Inorganic additive 0.1 10
Traditional targeted supplements 0.3 8
Polymer binder Else
2. The plastic according to claim 1, characterized in that it further comprises a functional co-filler in an amount of 0.1 to 40 wt.  3. The plastic according to claim 1, characterized in that it as a polymer binder contains the original or waste thermoplastic polymers and / or mixtures thereof with a processing temperature below the temperature of the thermal oxidative degradation of the wood-vegetable filler.  4. The plastic according to claim 1, characterized in that the wood-vegetable filler contains a mixture of particles with a particle size of 0.05 to 0.5 mm and particles with a particle size of 0.5 to 8 mm, taken in a ratio of 1 (1-100).  5. The plastic according to claim 4, characterized in that as particles with a particle size of 0.5-8 mm contains chopped plant fibers with a length of 1 20 mm  6. The plastic according to claim 1, characterized in that as an inorganic additive contains a mixture of two or more dispersed inorganic substances. 7. A method of producing environmentally friendly wood-filled plastic based on a thermoplastic polymer binder and dispersed wood-vegetable filler, including drying, modifying, mixing and thermoforming, characterized in that they determine the characteristic parameters of the components: the concentration of acidic and basic centers of the surface of the particles of wood vegetable filler and inorganic additives, the magnitude, polarity and relaxation time of the residual specific charge of wood particles o-plant filler, the modification is carried out by triboactivation of the electrical state of the particles of the tree-plant filler for 2 1200 s at a temperature of 10 220 ^o С and an activation intensity sufficient to achieve the values of the characteristic parameters: the value of the residual specific charge 5 • 10 ^{- 7} 5 • 10 ^{- 5} C / kg and its relaxation time 0.05 1 ks, and the subsequent mixing of all components in the plastics start to produce no more than twice the time value p for a period of time after closure triboaktivatsii relaxation of residual wood-specific charge vegetable filler particles.  8. The method according to claim 7, characterized in that the drying is carried out before determining the characteristic parameters of the components.  9. The method according to claim 7, characterized in that the triboactivation of the tree-plant filler is carried out in the process of drying it.  10. The method according to claim 7, characterized in that the triboactivation of the wood-vegetable filler and the mixing of the components of the filled plastic are carried out simultaneously.

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