Wood-plastic Composite Material Recycled from Wood Combustion Material and Method for Producing Pellets

Abstract

A wood-plastic composite material utilizing recycled wood pellet combustion material is disclosed as a raw material that can be used in various industrial fields, as it is eco-friendly, reduces costs, and exhibits physical properties equivalent to new material by adding a polymer resin. The disclosed wood-plastic composite material utilizing recycled wood pellet combustion material comprises, based on the total wt%, wood pellet combustion material; polymer resin; stabilizer; and surface treatment agent in an amount of 45 ~ 60 wt%; 35 ~ 50 wt%; 1 ~ 3 wt%; and 1 ~ 3 wt%.

Description

Technology Field

[0001] The present invention relates to a wood-plastic composite material obtained by recycling wood pellet combustion materials and a method for manufacturing pellets using the same. More specifically, it relates to a wood-plastic composite material and a method for manufacturing pellets using the same, which aims to achieve zero landfill waste for power plants using wood pellets and to achieve a circular economy by recycling waste. Background Technology

[0003] After the government announced the 'Renewable Energy 2030 Plan' in 2017 to expand the share of renewable energy generation to 20% by 2030, the utilization of biomass-related energy, such as wood pellets, is increasing.

[0004] In addition, bioenergy accounts for 24.4% of new and renewable energy production and 16.7% of new and renewable energy generation. With the announcement of the government's carbon-zero initiative and greenhouse gas reduction plan in 2021, the use of biomass (wood pellets, wood chips, bio-SRF, etc.) for greenhouse gas reduction and clean energy utilization is increasing.

[0005] In line with this trend, 66 power plants from 27 power companies are using biomass (woody materials including wood pellets, wood chips, and bio-SRF) for power generation, with a total installed capacity (co-firing + full combustion) of approximately 1,500 MW. According to the Ministry of Trade, Industry and Energy, a total of 1,230 MW of biomass-only power plants are scheduled to be newly constructed in 2020 and 2021.

[0006] In this process, combustion materials such as wood pellets amounted to 160,832 m³ as of 2019. 3 Although it is being generated, unlike coal ash and the like, it is exceptionally impossible to dispose of the generated wood pellet combustion residue by burying it in landfill facilities.

[0007] Therefore, there is a need to process or utilize wood pellet combustion residues that cannot be disposed of in exceptional landfill facilities, and there is a need to develop composite materials to produce eco-friendly recycled products that can be utilized as resources instead of simple landfill disposal. Prior art literature

[0009] Registered Patent Publication 10-2038841 (Publication Date: Nov. 01, 2019) The problem to be solved

[0010] The present invention was conceived in consideration of the points described above, and the wood-plastic composite comprises, based on the total wt%, 45 to 60 wt% of wood pellet combustion material; a polymer resin; a stabilizer; and a surface treatment agent; 35 to 50 wt%; 1 to 3 wt%; and 1 to 3 wt% of wood-plastic composite. The invention aims to provide a wood-plastic composite that achieves zero waste landfilling by recycling wood pellet combustion material, realizes resource circulation and reduces social costs associated with waste treatment, and possesses physical properties such as moisture resistance and strength equivalent to those of a composite using new sawdust and a polymer resin.

[0011] In addition, the present invention comprises: a first step of preparing a wood-plastic composite comprising 45 to 60 wt% of wood pellet combustion material, 35 to 50 wt% of polymer resin, 1 to 3 wt% of stabilizer, and 1 to 3 wt% of surface treatment agent; a second step of preparing a mixture by stirring the wood pellet combustion material and the polymer resin at 80 to 150 rpm for 5 to 30 minutes; and a third step of feeding the mixture into an extruder, adding the stabilizer and the surface treatment agent, and then melting and extruding at 210 to 250°C. A method for manufacturing pellets using a wood-plastic composite material, comprising a fourth step of cooling and cutting the melted and extruded extruded material to produce it in the form of pellets, wherein the particle size of each of the wood pellet combustion material and the polymer resin is 50 to 150 μm, and the pellets produced by the above method are intended to be used in the production of products such as decks, soundproofing materials, and protective fences for road facilities. means of solving the problem

[0013] To achieve the above objective, the wood-plastic composite material obtained by recycling wood pellet combustion material according to the present invention comprises, with respect to the total wt%, 45 to 60 wt%; 35 to 50 wt%; 1 to 3 wt%; and 1 to 3 wt% of a surface treatment agent.

[0014] The above polymer resin is characterized by comprising at least one of high-density polyethylene, polypropylene, and polyvinyl chloride.

[0015] The above stabilizer is characterized by including a UV stabilizer or an antioxidant.

[0016] The above surface treatment agent is characterized by containing stearic acid or stearate.

[0017] The above wood-plastic composite further comprises 1 to 5 wt% of a binder based on the total wt%, and

[0018] The above-mentioned binder is characterized by including a silane coupling agent or an epoxy-based agent.

[0019] The particle size of each of the wood pellet combustion material and the polymer resin is characterized by being 50 to 150 μm.

[0020] In addition, the method for manufacturing pellets using a wood-plastic composite according to the present invention

[0021] Step 1: Preparing a wood-plastic composite comprising 45 to 60 wt% wood pellet combustion material, 35 to 50 wt% polymer resin, 1 to 3 wt% stabilizer, and 1 to 3 wt% surface treatment agent;

[0022] A second step of preparing a mixture by stirring the wood pellet combustion material and the polymer resin at 80 to 150 rpm for 5 to 30 minutes;

[0023] A third step of feeding the above mixture into an extruder, adding the above stabilizer and the above surface treatment agent, and then melting and extruding at 210 to 250°C; and

[0024] It includes a fourth step of cooling and cutting the above-mentioned molten and extruded product to produce it in the form of pellets, and

[0025] The particle size of each of the wood pellet combustion material and the polymer resin is characterized by being 50 to 150 μm.

[0026] The above stabilizer is characterized by including a UV stabilizer or an antioxidant.

[0027] The above surface treatment agent is characterized by containing stearic acid or stearate.

[0028] The method is characterized by adding 1 to 5 wt% of a binder to the total wt% of the wood-plastic composite material in the extruder during the third step.

[0029] After the above fourth step is completed, the diameter of the pellet is characterized as being 5 to 7 mm. Effects of the invention

[0031] The wood-plastic composite material obtained by recycling wood pellet combustion material according to the present invention comprises, based on the total wt%, 45 to 60 wt%; 35 to 50 wt%; 1 to 3 wt%; and a surface treatment agent.

[0032] In addition, a method for manufacturing using a wood-plastic composite comprises: a first step of preparing a wood-plastic composite comprising 45 to 60 wt% of wood pellet combustion material, 35 to 50 wt% of a polymer resin, 1 to 3 wt% of a stabilizer, and 1 to 3 wt% of a surface treatment agent; a second step of preparing a mixture by stirring the wood pellet combustion material and the polymer resin at 80 to 150 rpm for 5 to 30 minutes; a third step of feeding the mixture into an extruder, adding the stabilizer and the surface treatment, and then melting and extruding at 210 to 250°C; and a fourth step of cooling and cutting the melted and extruded extruded product to produce it in the form of pellets, wherein the particle size of each of the wood pellet combustion material and the polymer resin is 50 to 150 μm. The present invention provides the effect of realizing cost reduction for the disposal of wood pellet combustion material and resource circulation through recycling.

[0033] Furthermore, the present invention provides the effect of possessing physical properties, namely moisture resistance and strength, equivalent to those obtained by utilizing new materials when producing decks, soundproofing materials, protective fences for road facilities, etc., using pellets manufactured based on wood pellet combustion materials. Brief explanation of the drawing

[0035] Figure 1 shows a pellet manufacturing process according to an embodiment of the present invention. Figure 2 shows a pellet manufactured according to an embodiment of the present invention. Specific details for implementing the invention

[0036] All terms described in this specification have been selected based on currently widely used general terms in consideration of the functions of the present invention; however, these may vary depending on the intent, convention, or emergence of new technologies of those skilled in the art. Furthermore, if the inventor specifies any term in this invention, its meaning will be described in the description of the invention. Therefore, terms used in this invention should be interpreted not merely by their names, but based on their actual meanings and the overall content described in the description of the invention.

[0037] Hereinafter, with reference to the attached drawings, a wood-plastic composite material obtained by recycling wood pellet combustion material according to an embodiment of the present invention and a method for manufacturing pellets using the same will be described in detail.

[0039] [Wood-Plastic Composite]

[0040] The present invention provides a wood-plastic composite material in which wood pellet combustion material is recycled.

[0041] In the present invention, the wood-plastic composite is not limited in its use or formulation and can be applied as a raw material for construction, an adsorbent, a fertilizer, a soil conditioner, etc. Specifically, regarding its use, the wood-plastic composite according to the present invention can be applied as a raw material for construction, such as decks used in architecture and landscaping, soundproofing materials that absorb or block sound, mortar, thermal insulation, and protective fences for road facilities; as an adsorbent for removing impurities from water, air, and industrial processes due to its excellent adsorption performance; and as a fertilizer and soil conditioner utilizing its rich mineral content and alkaline properties; however, in the present invention, it can preferably be used as a raw material for construction.

[0042] The wood-plastic composite of the present invention comprises, based on the total wt%, a wood pellet combustion material; a polymer resin; a stabilizer; and a surface treatment agent in an amount of 45 to 60 wt%; 35 to 50 wt%; 1 to 3 wt%; and 1 to 3 wt%.

[0043] The above wood pellet combustion material is included in the wood-plastic composite of the present invention. The above wood pellet combustion material can be obtained through conventional known processing of bottom ash remaining after burning wood pellets at a power plant. Generally, the wood pellet combustion material is obtained by cooling the bottom ash remaining after burning wood pellets at a power plant with water or seawater, but in the present invention, it is preferably obtained by recovering it after cooling with water and through a known processing process of crushing and drying.

[0044] The apparent density of the flooring material before cooling, crushing, and drying of the above wood pellet combustion material is 0.294 to 0.382 ton / m³. Therefore, if the apparent density is excessively low, it is light and easy to transport, but it may be unsuitable as a raw material for construction. Accordingly, the density of the wood-plastic composite material of the present invention can be improved by adding the following polymer resin, etc., to the wood pellet combustion material obtained through known treatment of the above flooring material.

[0045] In addition, the cooled bottom material may contain 55.6 to 70.5% moisture, 18.0 to 22.6% volatile matter, 11.6 to 18.8% ash, and 14.6 to 21.06% fixed carbon. The high moisture content of the cooled bottom material is due to the bottom material being cooled with water or seawater for smooth transport from the incinerator. The cooled bottom material can become wood pellet combustion material with a moisture content of 10% or less through a crushing and drying process. As another example, the moisture content of the wood pellet combustion material may be 5% or less. Therefore, if the moisture content of the wood pellet combustion material is excessively high, the moisture content of the wood-plastic composite material of the present invention increases, which may cause the material to break or weaken when used to manufacture construction products, resulting in a decrease in strength, and cracks may occur due to shrinkage and expansion after deck installation.

[0046] In addition, due to the unburned carbon contained in the volatile matter and fixed carbon of the cooled flooring material, when the flooring material is used as a construction product such as a deck, it is possible to reduce weight, act as a preservative, and absorb and adsorb odors and impurities. However, if the content of volatile matter and fixed carbon of the flooring material is excessively high—that is, if the carbon content is excessively high—it may break or weaken during the manufacture of construction products, resulting in reduced strength; furthermore, increased porosity may increase the water absorption rate, thereby lowering durability; and the surface may not be smooth. Therefore, the present invention can be manufactured by adjusting the content of volatile matter and fixed carbon.

[0047] Therefore, the wood pellet combustion material can be selected to have high density, a moisture content of 10% or less, and a high ash content; however, the unburned carbon contained in the volatile matter and fixed carbon of the wood pellet combustion material can maximize lightweighting, absorption / adsorption, and preservative functions when manufacturing construction products using the present invention. The wood pellet combustion material may comprise 45 to 60 wt% of the total wt% of the wood-plastic composite. If the content of the wood pellet combustion material is less than 45 wt%, the economic efficiency and eco-friendliness in terms of strength and cost of the composite may be reduced, and if it exceeds 60 wt%, it may lead to a decrease in the content of polymer resin, etc., resulting in a decrease in physical properties such as strength and durability. In addition, the particle size of the wood pellet combustion material may be 50 to 150 μm. If the size of the wood pellet combustion material particles is less than 50 μm, it may be difficult to process when manufacturing a product using the wood-plastic composite of the present invention, and if it exceeds 150 μm, mechanical properties such as strength may be reduced when manufacturing a product using the wood-plastic composite of the present invention.

[0048] The above polymer resin is included in the wood-plastic composite of the present invention. The above polymer resin may be included to improve mechanical properties such as density, strength, and durability of the wood-plastic composite of the present invention. The above polymer resin may include at least one of high-density polyethylene, polypropylene, and polyvinyl chloride.

[0049] Polyethylene is a lightweight and highly durable thermoplastic resin with various crystal structures. Therefore, polyethylene can be used in various fields such as construction materials, films, tubes, plastic parts, and laminates. Furthermore, the polyethylene is a polyolefin-based polymer that can be classified into low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), ultra-high molecular weight polyethylene (UHMWPE), and cross-linked polyethylene (PEX or XPLE) depending on density and branching; however, in the present invention, high-density polyethylene can be preferably selected.

[0050] The above-mentioned high-density polyethylene (HDPE) is a thermoplastic resin having a linear structure or a low level of short branching, which can improve the heat resistance, durability, chemical resistance, etc. of the wood-plastic composite of the present invention. In addition, although the above-mentioned high-density polyethylene has a relatively lower impact strength compared to low-density polyethylene, it has a low elongation and excellent tensile strength, allowing for easy processing.

[0051] In addition, the density of the above high-density polyethylene is 0.94 to 0.96 g / cm³ 3 And, the melt index (MI) may be 0.5 to 6, preferably 0.5 to 2, and more preferably 1 to 1.5. In the present invention, the melt index is expressed in g / 10 min. The density of the high-density polyethylene is 0.94 g / cm³ 3 If it is less than, heat resistance is insufficient, and 0.96 g / cm² 3If it exceeds a certain amount, elongation may be insufficient.

[0052] The above polypropylene (PP) is a thermoplastic resin in which a methyl group (CH3) is attached to every other carbon of the polyethylene molecular chain, and has regularly short branches, which can improve the strength, heat resistance, chemical resistance, etc. of the wood-plastic composite of the present invention.

[0053] In addition, the above polypropylene has a specific gravity of 0.92 g / cm³ 3 As it is lighter than other polymer resins, it is easy to transport or construct, and can be used in various industrial fields requiring lightweighting. In addition, polypropylene has a melting temperature of 135 to 160°C and possesses the characteristic of withstanding high temperatures well against acids or alkalis compared to other polymer resins.

[0054] The above polyvinyl chloride (PVC) is a thermoplastic resin obtained by polymerizing vinyl chloride in which one hydrogen atom of a polyethylene molecule is substituted with chlorine, and can improve the durability, chemical resistance, and corrosion resistance of the wood-plastic composite of the present invention.

[0055] Accordingly, the above polymer resin may comprise 35 to 50 wt% of the total wt% of the wood-plastic composite. If the content of the above polymer resin is less than 35 wt%, it may be difficult to improve the strength and durability of the wood-plastic composite of the present invention; if it exceeds 50 wt%, while mechanical properties may be enhanced, it results in a decrease in the content of other components, making it impossible to achieve the purpose of recycling waste into resources. Furthermore, when the wood-plastic composite of the present invention is used as a raw material for construction, the polymer resin may have a particle size of 50 to 150 μm to strengthen the bonding with wood pellet combustion materials. That is, the polymer resin pellets may be freeze-dried and then crushed to obtain a particle size of 50 to 150 μm.

[0056] The above-mentioned stabilizer is included in the wood-plastic composite of the present invention. The above-mentioned stabilizer includes, but is not limited to, UV stabilizers or antioxidants. Since exposure of the wood-plastic composite of the present invention to UV (ultraviolet) can accelerate aging and affect durability, the above-mentioned stabilizer may be included in the present invention to prevent this.

[0057] The above UV stabilizer may include hydroxybenzoate or an amine light stabilizer. The above hydroxybenzoate can improve the light resistance effect of the wood-plastic composite of the present invention as an ultraviolet absorber. That is, the above hydroxybenzoate absorbs incoming ultraviolet (UV) rays and converts them into infrared rays, releasing heat to the outside, thereby suppressing the phenomenon of the product decomposing due to ultraviolet rays. In addition, any substance known in the art may be used as a substitute for hydroxybenzoate as the above UV absorber. Furthermore, the above amine light stabilizer can improve the light resistance effect by suppressing product decomposition and protecting the surface using the wood-plastic composite of the present invention. That is, the above amine light stabilizer (HALS) can stop the chain photo-oxidation reaction by eliminating free radicals that have already been generated within the product due to photodecomposition by ultraviolet rays, thereby preventing the free radicals from causing a chain reaction. In addition, any amine light stabilizer known in the art may be used, but it is preferable that it be a mixture of bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate and methyl 1,2,2,6,6-pentamethyl-4-piperidyl sebacate, and more preferably TINUVIN 292 from CIBA.

[0058] The above antioxidant may include BHT (Butylated Hydroxytoluene) as a phenolic antioxidant. The above antioxidant can improve the performance and durability of the wood-plastic composite of the present invention, and a synergistic effect can be observed when used in combination with a UV stabilizer.

[0059] Accordingly, the above stabilizer may be included in an amount of 1 to 3 wt% relative to the total wt% of the wood-plastic composite. As another example, the above stabilizer may be included in an amount of 1 to 1.5 wt% relative to the total wt% of the wood-plastic composite. If the content of the above stabilizer is less than 1 wt%, it may be difficult to improve the performance and durability of the wood-plastic composite of the present invention, and if it exceeds 3 wt%, it may cause problems during processing by changing the viscosity of the polymer resin and may result in a decrease in strength and durability of the wood-plastic composite of the present invention due to failure of fine dispersion within the polymer matrix.

[0060] The above surface treatment agent is included in the wood-plastic composite of the present invention. The above surface treatment agent can suppress moisture absorption of the wood pellet combustion material and strengthen the bonding between polymer resins, while simultaneously reducing friction between the wood pellet combustion material and the polymer resin during high-temperature processing to improve processability. Preferably, stearic acid or stearate may be used as the above surface treatment agent.

[0061] Accordingly, the surface treatment agent may be included in an amount of 1 to 3 wt% relative to the total wt% of the wood-plastic composite. As another example, the surface treatment agent may be included in an amount of 1 to 1.5 wt% relative to the total wt% of the wood-plastic composite. If the content of the surface treatment agent is less than 1 wt%, it may be difficult to bond between the wood pellet combustion material and the polymer resin, making it difficult to improve physical properties such as strength of the present invention; if it exceeds 3 wt%, the surface treatment agent may not be uniformly coated on the wood surface, clumping or leaving residue, which may result in reduced bonding strength and increased costs.

[0062] The above-mentioned binder may be included in the wood-plastic composite of the present invention. The above-mentioned binder may include an inorganic wood pellet combustion material and an organic material to strengthen the bonding with the polymer resin. The above-mentioned binder may include a silane coupling agent or an epoxy-based agent. Specifically, at least one of alkoxysilane, aminosilane, epoxysilane, and vinylsilane may be selected.

[0063] Accordingly, the above binder may be included in an amount of 1 to 5 wt% relative to the total wt% of the wood-plastic composite. If the content of the above binder is less than 1 wt%, the bonding strength between the wood pellet combustion material and the polymer resin is reduced, making it difficult to improve the strength, etc. of the present invention; if it exceeds 5 wt%, production costs increase and the viscosity increases, which may lead to reduced processability during mixing and molding processes or cause structural instability due to self-aggregation.

[0064] As such, the wood-plastic composite of the present invention not only realizes resource circulation by reducing disposal costs and re-recovering resources through the recycling of waste wood pellet combustion materials, but can also be used as a raw material for construction, etc., by appropriately blending it with a polymer resin to provide physical properties equivalent to those of new materials, such as strength and durability.

[0066] [Method for manufacturing pellets using wood-plastic composites]

[0067] The present invention provides a method for manufacturing pellets using a wood-plastic composite.

[0068] Figure 1 shows a pellet manufacturing process according to an embodiment of the present invention.

[0069] Referring to FIG. 1, a method for manufacturing pellets using a wood-plastic composite according to an embodiment of the present invention comprises: a first step of preparing a wood-plastic composite comprising 45 to 60 wt% of wood pellet combustion material, 35 to 50 wt% of a polymer resin, 1 to 3 wt% of a stabilizer, and 1 to 3 wt% of a surface treatment agent; a second step of preparing a mixture by stirring the wood pellet combustion material and the polymer resin at 80 to 150 rpm for 5 to 30 minutes; a third step of feeding the mixture into an extruder, adding the stabilizer and the surface treatment, and then melting and extruding at 210 to 250°C; and a fourth step of cooling and cutting the melted and extruded mixture to produce pellets, wherein the particle size of the wood pellet combustion material and the polymer resin, respectively, is 50 to 150 μm.

[0071] [1] Step 1 (Preparation of wood-plastic composite)

[0072] The first step is to prepare a wood-plastic composite. The wood-plastic composite may comprise 45 to 60 wt% of wood pellet combustion material, 35 to 50 wt% of polymer resin, 1 to 3 wt% of stabilizer, and 1 to 3 wt% of surface treatment agent. The wood-plastic composite may further comprise 1 to 5 wt% of binder relative to the total wt%, and the wood-plastic composite may be prepared by modifying each of the raw materials. The following description of the 'wood-plastic composite' part of the present invention will be omitted.

[0073] The above wood pellet combustion material can be obtained by processing the bottom ash remaining after burning wood pellets at a power plant through conventional known treatments. Generally, the wood pellet combustion material is obtained by cooling the bottom ash remaining after burning wood pellets at a power plant with water or seawater; however, in the present invention, it is preferably obtained by recovering it after cooling with water and processing it through known crushing and drying treatments. Therefore, by regenerating the waste wood pellet combustion material, resource circulation can be realized, thereby reducing costs and preventing environmental pollution.

[0074] In addition, the wood pellet combustion material may be selected to have a high density, a moisture content of 10% or less, a high ash content, and a low carbon content. The wood pellet combustion material may be included in an amount of 45 to 60 wt% relative to the total wt% of the wood-plastic composite. If the content of the wood pellet combustion material is less than 45 wt%, the purpose of recycling waste cannot be realized and production costs may increase, and if it exceeds 60 wt%, it may result in a decrease in the content of polymer resin, etc., which may lead to a decrease in physical properties such as strength and durability.

[0075] In addition, the size of the wood pellet combustion material particles may be 50 to 150 μm. If the size of the wood pellet combustion material particles is less than 50 μm, the contact area with the polymer resin increases, but the uniformity of dispersion decreases or aggregation occurs, resulting in an uneven distribution, making it difficult to process or mold, which may lower the strength, durability, and processability of the pellets. If the size exceeds 150 μm, voids occur, lowering the density of the pellets, which may also lower the physical properties, such as the strength of the product using the pellets manufactured according to the present invention.

[0076] The above polymer resin may be included to improve mechanical properties such as density, strength, and durability, and may include at least one of high-density polyethylene, polypropylene, and polyvinyl chloride. The above polymer resin may be included in an amount of 35 to 50 wt% relative to the total wt% of the wood-plastic composite. If the content of the above polymer resin is less than 35 wt%, it may be difficult to improve the strength and durability of the wood-plastic composite of the present invention; if it exceeds 50 wt%, although mechanical properties can be strengthened, it results in a decrease in the content of other components, making it impossible to achieve the purpose of recycling waste into resources. The particle size of the above polymer resin must not differ from the particle size of the above inorganic wood pellet combustion material so that it can be uniformly mixed to improve physical properties such as strength. Accordingly, the particle size of the above polymer resin may be 50 to 150 μm. That is, the particle size may be 50 to 150 μm by freeze-drying and then grinding the above polymer resin pellets.

[0077] The above stabilizer includes, but is not limited to, a UV stabilizer or an antioxidant. Since a product manufactured using pellets produced according to the present invention may accelerate aging and affect durability when exposed to UV (ultraviolet), the above stabilizer may be included in the present invention to prevent this. The above UV stabilizer may include hydroxybenzoate or an amine light stabilizer. In addition, the above antioxidant may include BHT (butylated hydroxytoluene) as a phenolic antioxidant. The above antioxidant can improve the performance and durability of a product manufactured using pellets produced according to the present invention, and a synergistic effect may be observed when used together with a UV stabilizer. Accordingly, the above stabilizer may be included in an amount of 1 to 3 wt% relative to the total wt% of the wood-plastic composite. As another example, the above stabilizer may be included in an amount of 1 to 1.5 wt% relative to the total wt% of the wood-plastic composite. If the content of the above stabilizer is less than 1 wt%, it may be difficult to improve the performance and durability of the pellets, and if it exceeds 3 wt%, it may cause problems during processing by changing the viscosity of the polymer resin and may result in a decrease in the strength and durability of the pellets due to failure to finely disperse within the polymer matrix.

[0078] The above surface treatment agent may preferably be stearic acid or stearate. The above surface treatment agent can suppress moisture absorption by the wood pellet combustion material and strengthen the bonding between polymer resins, while simultaneously reducing friction between the wood pellet combustion material and the polymer resin during high-temperature processing to improve processability. Accordingly, the above surface treatment agent may be included in an amount of 1 to 3 wt% relative to the total wt% of the wood-plastic composite. As another example, the above surface treatment agent may be included in an amount of 1 to 1.5 wt% relative to the total wt% of the wood-plastic composite. If the content of the above surface treatment agent is less than 1 wt%, it may be difficult to bond between the wood pellet combustion material and the polymer resin, making it difficult to improve physical properties such as the strength of the pellets; if it exceeds 3 wt%, the surface treatment agent may not be uniformly coated on the wood surface, clumping or leaving residue, which may not only reduce bonding strength and physical properties but also lead to increased costs.

[0079] The above binder may include a silane coupling agent or an epoxy-based agent. Specifically, the binder may be selected from at least one of alkoxysilane, aminosilane, epoxysilane, and vinylsilane. The binder may be added to strengthen the bonding between the inorganic wood pellet combustion material and the organic material with the polymer resin. Accordingly, the binder may be included in an amount of 1 to 5 wt% relative to the total wt% of the wood-plastic composite. If the content of the binder is less than 1 wt%, the bonding strength between the wood pellet combustion material and the polymer resin is low, making it difficult to improve the strength of the pellets; if it exceeds 5 wt%, production costs increase and the viscosity increases, which may lead to reduced processability during mixing and molding processes or cause structural instability due to self-aggregation.

[0081] [2] Step 2 (Preparation of mixture)

[0082] The second step is to prepare a mixture by stirring the wood pellet combustion material and the polymer resin. In the second step, the wood pellet combustion material and the polymer resin contained in the wood-plastic composite are mixed first. Since the inorganic wood pellet combustion material and the organic polymer resin have different physical and chemical properties, they must be mixed uniformly so that they melt evenly during the subsequent melt extrusion process, thereby making the final product, the pellet, homogeneous. Additionally, the organic polymer resin provides a coating effect on the surface of the inorganic wood pellet combustion material, which can prevent particle aggregation during extrusion.

[0083] On the other hand, instead of adding stabilizers, surface treatment agents, and binders during the second stage, which is the initial mixing process, it may be preferable to add them during the melt extrusion process below. Specifically, the stabilizer allows the wood pellet combustion material and the polymer resin to interact with each other during the high-temperature melting process to more effectively improve UV resistance, the surface treatment agent can optimize surface characteristics, and the binder strengthens the bond between the inorganic wood pellet combustion material and the organic polymer resin through a chemical reaction activated by temperature. Furthermore, when the material melts at high temperatures, the viscosity decreases, allowing the silane coupling agent, which acts as the binder, to be evenly dispersed in the mixture.

[0084] Accordingly, the above mixture can be prepared by mixing 45 to 60 wt% of wood pellet combustion material and 35 to 50 wt% of polymer resin at 80 to 150 rpm for 5 to 30 minutes. It may be preferable to use a high-speed mixer for the above mixing. The high-speed mixer can mix the wood pellet combustion material and the polymer resin in a short time. If the mixing speed is less than 80 rpm, uneven mixing may occur, such as clumping; if it exceeds 150 rpm, excessive air is incorporated, causing bubbles, which can be a problem, especially when mixing polymer resins with low viscosity. In addition, if the mixing time is less than 5 minutes, mixing is not performed properly, making it difficult to achieve the necessary physical properties, such as strength, of the final product; and if it exceeds 30 minutes, excessive mixing may deform the structure of the polymer resin.

[0086] [3] 3rd stage (melt extrusion)

[0087] The third step is a step of melting and extruding the mixture. The melting and extruding step may be carried out at 210 to 250°C after feeding the mixture into a conventional known extruder and adding 1 to 3 wt% of the stabilizer and 1 to 3 wt% of the surface treatment agent prepared in the first step. As another example, melting and extruding may be performed by adding 1 to 5 wt% of a binder to the total wt% of the wood-plastic composite while the mixture, stabilizer, and surface treatment agent are fed into the extruder.

[0088] Adding at least one of the above-mentioned stabilizer, surface treatment agent, and binder to the melt extrusion process is because the stabilizer allows the wood pellet combustion material and the polymer resin to interact with each other during the high-temperature melting process to more effectively improve UV resistance, the surface treatment agent can optimize surface characteristics, and the binder strengthens the bond between the inorganic wood pellet combustion material and the organic polymer resin through a chemical reaction activated by temperature, and when the material melts at high temperatures, the viscosity decreases, allowing the silane coupling agent acting as the binder to be evenly dispersed in the mixture.

[0089] Therefore, if the melting temperature is less than 210°C, the polymer resin is not completely melted, resulting in increased viscosity and reduced fluidity, making it difficult to mix with wood pellet combustion materials and uneven mixing with added components, which may make it difficult to improve the strength of the pellets, etc., and if it exceeds 250°C, it flows like a liquid when injected, making it difficult to extrude with a uniform thickness.

[0091] [4] Step 4 (Pellet manufacturing)

[0092] The fourth step is the pellet manufacturing step. In the pellet manufacturing step, pellets can be produced by cooling and cutting the melt-extruded extruder. Since the extruder is formed at a high temperature, shape stabilization is achieved through cooling, allowing for cutting. This enables the acquisition of a more precise pellet shape because the pellet's form is well maintained as the extruder solidifies.

[0093] The diameter of the pellets subjected to the cooling and cutting process may be 5 to 7 mm. If the diameter of the pellets is less than 5 mm, there is a risk that they may easily break or shatter. Additionally, as the surface area increases, they absorb moisture more easily, causing the pellets to deform during storage. Furthermore, when manufacturing products using the pellets, they may not be properly compressed or may not form the desired shape during the compression molding or injection molding process, which may lead to a decrease in quality. Moreover, if the diameter of the pellets exceeds 7 mm, heat may be transferred unevenly or pressure may not be transferred uniformly when melting, extruding, or injection molding products using the pellets, and the quality of the product may be degraded due to incomplete melting.

[0094] Figure 2 shows a pellet manufactured according to an embodiment of the present invention.

[0095] As shown in FIG. 2, the pellets produced according to the present invention prevent environmental pollution by realizing resource recycling through the recycling of waste wood pellet combustion materials, and since they utilize a composite material with added raw materials such as polymer resins and exhibit physical properties equivalent to those of new materials, they can be used in various industrial fields such as construction.

[0097] The following describes examples of preparation and embodiments. The following examples of preparation and embodiments are provided merely to aid in understanding the present invention.

[0099] <Examples and Comparative Examples>

[0100] [Example 1]

[0101] A wood-plastic composite was prepared containing 45 wt% wood pellet combustion material, 50 wt% high-density polyethylene, 1 wt% amine light stabilizer (UV stabilizer), 1 wt% BHT (butylated hydroxytoluene) (antioxidant), and 3 wt% stearic acid (surface treatment agent). First, the wood pellet combustion material and the polymer resin contained in the wood-plastic composite were stirred at 100 rpm for 10 minutes to prepare a mixture. After feeding the mixture into an extruder, the 1 wt% amine light stabilizer, 1 wt% BHT (butylated hydroxytoluene), and 3 wt% stearic acid were added, and the mixture was melted and extruded at 230°C. The extruded product was then cooled with water and cut using a cutter to produce pellets with a diameter of 6 mm. The wood pellet combustion material and the polymer resin each had a particle size of 100 μm.

[0103] [Example 2]

[0104] Pellet was prepared in the same manner as in Example 1, except that the wood pellet combustion material was 50 wt% and the polymer resin was 45 wt%.

[0106] [Example 3]

[0107] Pellet was prepared in the same manner as in Example 1, except that the wood pellet combustion material was 60 wt% and the polymer resin was 35 wt%.

[0109] [Example 4]

[0110] A wood-plastic composite was prepared containing 45 wt% wood pellet combustion material, 50 wt% high-density polyethylene, 1 wt% amine light stabilizer (UV stabilizer), 1 wt% BHT (butylated hydroxytoluene) (antioxidant), and 3 wt% stearic acid (surface treatment agent). First, the wood pellet combustion material and the polymer resin contained in the wood-plastic composite were stirred at 100 rpm for 10 minutes to prepare a mixture. After feeding the mixture into an extruder, 1 wt% of the amine light stabilizer, 1 wt% of BHT (butylated hydroxytoluene), and 3 wt% of stearic acid were added. After further adding 1 wt% of alkoxysilane (binder) to the total weight percentage of the wood-plastic composite to the extruder, the mixture was melted and extruded at 230°C. The extruded product was then cooled with water and cut using a cutter to produce pellets with a diameter of 6 mm. The wood pellet combustion material and the polymer resin used above each had a particle size of 100 μm.

[0112] [Example 5]

[0113] Pellet was prepared in the same manner as in Example 4, except that 3 wt% of alkoxysilane, a binder, was added.

[0115] [Example 6]

[0116] Pellet was prepared in the same manner as in Example 4, except that 5 wt% of alkoxysilane, a binder, was added.

[0118] [Comparative Example 1]

[0119] Pellet was prepared in the same manner as in Example 1, except that the wood pellet combustion material was 40 wt% and the polymer resin was 55 wt%.

[0121] [Comparative Example 2]

[0122] Pellet was prepared in the same manner as in Example 1, except that the wood pellet combustion material was 65 wt% and the polymer resin was 30 wt%.

[0124] [Comparative Example 3]

[0125] Pellet was prepared in the same manner as in Example 1, except that it contained 48 wt% wood pellet combustion material and did not contain stearic acid, a surface treatment agent.

[0127] [Comparative Example 4]

[0128] Pellet was prepared in the same manner as in Example 4, except that the binder was 0.5 wt% alkoxysilane.

[0130] [Comparative Example 5]

[0131] Pellet was prepared in the same manner as in Example 4, except that the binder was 7 wt% alkoxysilane.

[0133] [Comparative Example 6]

[0134] Pellet was prepared in the same manner as in Example 1, except that the size of the wood pellet combustion material particles was 200 μm and the size of the polymer resin particles was 250 μm.

[0136] <Test Example>

[0137] [Test Example 1] - Test on the potential for recycling wood pellet combustion materials as construction raw materials (apparent density, sand composition)

[0138] Test Subject: The bottom ash remaining from burning wood pellets at a power plant is used as the test subject.

[0139] Test Method: ① Apparent density is per unit volume of a substance (m²) 3 ) Mass (tons) of bottom material is collected, filled into a container of known volume, dropped from a height of 30 cm three times, and then the process of filling the sample is repeated three times. After measuring the weight of the container (containing the sample), the apparent density is calculated using the formula below. ② The bottom material consists of the components of moisture, volatile matter, ash, and fixed carbon, and the test was conducted in accordance with the waste processing test methods (ES 06303.1a, ES 06301.1d).

[0141] Test Results: Referring to Table 1, ① the apparent density is 0.294 to 0.382 ton / m³. If the apparent density is excessively low, the material is light and easy to transport, but it may be unsuitable as a raw material for construction. Therefore, the density of the wood-plastic composite of the present invention can be improved by adding the following polymer resins, etc., to the wood pellet combustion material obtained through known treatments (cooling, grinding, drying, etc.) of the above-mentioned bottom material, thereby allowing it to be used as a raw material for construction. ② Among the components of the bottom material, moisture accounted for the largest proportion. This is because the bottom material is cooled with water or seawater to ensure smooth transport from the incinerator. Therefore, if the moisture content is excessive, the material may break or weaken, leading to a decrease in strength; thus, wood pellet combustion material with a moisture content of 10% or less can be obtained through known treatments of the above-mentioned bottom material. Through these test results, it was found that the wood pellet combustion material can be recycled as a raw material for construction by adding polymer resins, etc.

[0142] Table 1 shows the apparent density and sand composition of the flooring remaining after burning wood pellets.

[0143] Apparent density (ton / m²) 3 ) Component (%) flooring 0.294 ~ 0.382 moisture Volatile matter Ash Fixed carbon 55.6 ~ 70.5 18.0 ~ 22.6 11.6 ~ 16.8% 14.6 ~ 21.06%

[0146] [Test Example 2] - Water absorption rate, dimensional deformation rate, compressive strength

[0147] Test method: Composite wood was prepared by melting and molding pellets made of wood-plastic composites according to the examples and comparative examples to prepare specimens. Then, ① water absorption was measured according to the method of GRF-2016, ② dimensional deformation was measured according to KS F 3126, and ③ compressive strength was measured according to the method of KS M 3383.

[0148] Table 2 shows the water absorption rate, dimensional deformation, and compressive strength according to the components and content of the wood-plastic composites of the examples and comparative examples.

[0149] Wood pellet combustion residue (wt%) Polymer resin (wt%) Amine light stabilizer (wt%) BHT(wt%) Stearic acid (wt%) Alkoxysilane (wt%) Water absorption rate (%) Strain of the order (%) Compressive strength (MPa) Example 1 45 50 1 1 3 0 0.9 0.06 118 Example 2 50 45 1 1 3 0 0.9 0.05 117 Example 3 60 35 1 1 3 0 0.7 0.07 110 Example 4 45 50 1 1 3 1 0.6 0.03 126 Example 5 45 50 1 1 3 3 0.5 0.02 127 Example 6 45 50 1 1 3 5 0.5 0.03 127 Comparative Example 1 40 55 1 1 3 0 0.9 0.08 127 Comparative Example 2 65 30 1 1 3 0 1.4 0.09 101 Comparative Example 3 48 50 1 1 0 0 4.8 0.35 112 Comparative Example 4 45 50 1 1 3 0.5 1.1 0.08 117 Comparative Example 5 45 50 1 1 3 7 0.8 0.06 124 Comparative Example 6 Identical to Example 1 except that the size of the wood pellet combustion material particles is 200 μm and the size of the polymer resin particles is 250 μm. 2.4 0.09 110

[0151] Test Results: Referring to Table 2, ① the water absorption rate of the examples was 0.9% or less, indicating excellent moisture resistance. In particular, Examples 5 and 6, which contain stearic acid as a surface treatment agent and optimally contain a silane coupling agent as a binder, were confirmed to have the best moisture resistance. On the other hand, among the comparative examples, Comparative Example 3, which did not contain stearic acid as a surface treatment agent and a silane coupling agent as a binder, had the lowest moisture resistance, and generally, it was found that the moisture resistance of the comparative examples decreased compared to the examples.

[0152] In addition, ② the dimensional deformation rate of the example was 0.07% or less, indicating that the synthetic wood produced according to the wood-plastic composite of the present invention has dimensional stability. On the other hand, among the comparative examples, Comparative Example 3, which did not contain stearic acid as a surface treatment agent and silane coupling agent as a binder, and Comparative Example 6, in which the particle sizes of the wood pellet combustion material and polymer resin were relatively larger than those of the example, showed a high dimensional deformation rate.

[0153] In addition, regarding ③ compressive strength, it was found that Examples 5 and 6, which contain a silane coupling agent as a binder and have a high content of polymer resin, were superior, similar to the water absorption rate. It was also found that Comparative Example 1, which has a high content of polymer resin, had excellent compressive strength but did not meet the purpose of the present invention of recycling wood pellet combustion materials. On the other hand, it was found that the compressive strength decreased in Comparative Example 2, which has a relatively low content of polymer resin; Comparative Example 6, in which the particle sizes of the wood pellet combustion material and polymer resin, respectively, are relatively smaller than those of the examples; and Comparative Example 5, in which the porosity increased due to an excessively high content of binder.

[0155] The embodiments described above are merely illustrative, and a person skilled in the art to which the present invention pertains can make various modifications and equivalent alternative embodiments therefrom. Therefore, the true technical scope of protection of the present invention must be determined by the technical concept of the invention as described in the claims.

Claims

Claim 1 In wood-plastic composites, The above wood-plastic composite is a wood-plastic composite made by recycling wood pellet combustion material, comprising, based on the total wt%, wood pellet combustion material; polymer resin; stabilizer; and surface treatment agent in an amount of 45 to 60 wt%; 35 to 50 wt%; 1 to 3 wt%; 1 to 3 wt%. Claim 2 A wood-plastic composite material formed by recycling wood pellet combustion material, characterized in that, in claim 1, the polymer resin comprises at least one of high-density polyethylene, polypropylene, and polyvinyl chloride. Claim 3 A wood-plastic composite material derived from recycled wood pellet combustion material, characterized in that, in claim 1, the stabilizer comprises a UV stabilizer or an antioxidant. Claim 4 A wood-plastic composite material derived from recycled wood pellet combustion material, characterized in that, in claim 1, the surface treatment agent comprises stearic acid or stearate. Claim 5 A wood-plastic composite material recycled from wood pellet combustion material according to claim 1, wherein the wood-plastic composite material further comprises 1 to 5 wt% of a binder based on the total wt%, and the binder comprises a silane coupling agent or an epoxy-based agent. Claim 6 A wood-plastic composite material formed by recycling wood pellet combustion material, characterized in that, in claim 1, the particle size of each of the wood pellet combustion material and the polymer resin is 50 to 150 μm. Claim 7 A method for manufacturing pellets using a wood-plastic composite, comprising: a first step of preparing a wood-plastic composite comprising 45 to 60 wt% of wood pellet combustion material, 35 to 50 wt% of a polymer resin, 1 to 3 wt% of a stabilizer, and 1 to 3 wt% of a surface treatment agent; a second step of preparing a mixture by stirring the wood pellet combustion material and the polymer resin at 80 to 150 rpm for 5 to 30 minutes; a third step of introducing the mixture into an extruder, adding the stabilizer and the surface treatment agent, and then melt-extruding at 210 to 250°C; and a fourth step of cooling and cutting the melt-extruded product to produce it in the form of pellets, wherein the particle size of each of the wood pellet combustion material and the polymer resin is 50 to 150 μm. Claim 8 A method for manufacturing pellets using a wood-plastic composite, characterized in that, in claim 7, the stabilizer comprises a UV stabilizer or an antioxidant. Claim 9 A method for manufacturing pellets using a wood-plastic composite, characterized in that, in claim 7, the surface treatment agent comprises stearic acid or stearate. Claim 10 A method for manufacturing pellets using a wood-plastic composite, characterized in that, in the third step of claim 7, 1 to 5 wt% of a binder is further added to the extruder with respect to the total wt% of the wood-plastic composite. Claim 11 A method for manufacturing pellets using a wood-plastic composite material, characterized in that, in claim 7, after the third step is completed, the diameter of the pellet is 5 to 7 mm.

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