Polyolefin resin composition based on regenerated cross-linked polyethylene containing viscoelastic decross-linked polyethylene

Abstract

The present invention relates to a polyolefin-based resin composition containing high-content recycled cross-linked polyethylene (XLPE) and viscoelastic decross-linked polyethylene (tPE). The composition comprises a polyethylene base resin, waste cross-linked polyethylene (XLPE) powder, and viscoelastic decross-linked polyethylene (tPE) pellets produced through a high-temperature, high-shear reactive extrusion process. The tPE exhibits excellent viscoelasticity in a molten state, effectively enveloping the interface of the XLPE powder, thereby allowing the powder particles to form a fine network structure within the base resin. As a result, the brittleness that was a problem in existing recycled XLPE compositions is mitigated, and the elongation performance of high-density polyethylene (HDPE) and the tensile strength of low-density polyethylene (LDPE) are simultaneously improved. The composition according to the present invention may contain 50% by weight or more of waste cross-linked polyethylene, and if a waste cable sheathing material containing flame-retardant polyethylene is additionally included, 80% by weight or more of the total weight of the waste cable can be recycled. Accordingly, the composition of the present invention can be utilized as a high-value-added recycled material applicable to various fields, such as industrial and construction materials.

Description

Technology Field

[0001] The present invention relates to a polyethylene resin composition that recycles a polyolefin-based resin containing cross-linked polyethylene (XLPE), and more specifically, to a recycled polyethylene resin composition that contains a high amount of waste cross-linked polyethylene (XLPE) recovered from discarded cable sheathing materials, etc., while ensuring mechanical properties and processing stability to enable industrial utilization. Background Technology

[0002] Cross-linked polyethylene (XLPE) is used in various industrial fields, such as insulation for high-voltage wires, foam sheets, and hot water pipes, due to its excellent heat resistance, chemical resistance, water resistance, and environmental stress cracking resistance. Along with this, the usage of XLPE is continuously increasing, leading to global environmental issues regarding the disposal of discarded XLPE. Consequently, interest in recycling is also growing due to the economic and resource losses associated with waste disposal.

[0003] Because waste cross-linked polyethylene (XLPE) has a three-dimensional network structure formed by cross-linked molecular chains, it does not melt when heated but decomposes, making it difficult to recycle by remelting and molding like ordinary polyethylene. Furthermore, since the de-crosslinking process, which selectively removes only the cross-linking bonds, is not technically feasible, methods such as producing low-molecular-weight waxes through high-temperature pyrolysis or utilizing it as fillers through simple crushing and grinding are primarily employed. However, these methods are insufficient as a means of waste recycling, and a significant amount is disposed of through incineration or landfilling.

[0004] As prior art regarding the recycling of waste cross-linked polyethylene (XLPE), for example, Patent Document 1 discloses a resin composition comprising 3.3 to 40 wt% of waste cross-linked high-density polyethylene having a particle size of 1 to 0.59 mm and 60 to 96.7 wt% of high-density polyethylene resin having a density of 0.960 g / cm³ or higher; and Patent Document 2 discloses a step of supercritical decrosslinking reaction of a base resin containing 100 wt% of recycled polyolefin resin in a reaction medium of water, ethanol, or methanol to obtain an uncrosslinked recycled polyolefin resin or a recycled polyolefin resin having a degree of crosslinking greater than 0 wt% to 15 wt% or less, and a step of mixing 100 parts by weight of the base resin containing the obtained recycled polyolefin resin, 1 to 10 parts by weight of azodicarbonamide as a blowing agent, and 0.2 to 0.4 parts by weight of dicumyl peroxide as a crosslinking agent. A method for manufacturing a foamed molded article is disclosed, comprising the step of foaming the above mixture at a temperature of 170°C or higher.

[0005] In addition, Patent Document 3 discloses a decrosslinked polyolefin resin for recycling after crosslinking, characterized in that the weight-average molecular weight (Mw) is 50,000 or more, the polydispersity (PDI) is 5 or more, the gel fraction is 10% by weight or less, the content of a resin with a molecular weight of 10,000 or less is 5% by weight or more or less than 25% by weight based on the total weight of the decrosslinked polyolefin resin, the tensile strength is 1.3 kg / mm² or more, and the elongation is 380% or more. Prior art literature

[0006] (Patent Document 0001) KR 10-0139884 B1(Patent Document 0002) KR 10-1482749 B1(Patent Document 0003) KR 10-2151359 B1 The problem to be solved

[0007] The problem to be solved by the present invention is to provide a polyolefin-based resin composition containing high-content recycled cross-linked polyethylene (XLPE) and viscoelastic decrosslinked polyethylene (tPE) that can maintain the mechanical properties and processing stability required for the manufacture of industrial products while containing a high content of waste cross-linked polyethylene (XLPE) powder, in order to solve the problems of conventional technology in which high-value recycling was limited due to the difficulty of melting and reprocessing and the problem of becoming brittle due to the high degree of cross-linking when recycling waste cross-linked polyethylene (XLPE) recovered from discarded cable sheathing materials, etc.

[0008] The polyolefin-based resin composition containing viscoelastic decrosslinked polyethylene (tPE) according to the present invention, which is based on a high content of recycled crosslinked polyethylene (XLPE), is described below by abbreviating it as "polyolefin-based resin composition based on recycled crosslinked polyethylene (XLPE)," and waste crosslinked polyethylene (XLPE) and viscoelastic decrosslinked polyethylene (tPE) are described as "XLPE" and "tPE" as necessary. means of solving the problem

[0009] As a means of solving the problem according to the present invention, a polyethylene resin composition recycled from waste cross-linked polyethylene (XLPE) comprises polyethylene resin as a base resin, waste cross-linked polyethylene (XLPE) powder with a particle size of 1 mm or less, and viscoelastic decross-linked polyethylene (tPE) pellets, and comprises an auxiliary agent as needed.

[0010] One embodiment of the polyethylene resin composition using recycled waste cross-linked polyethylene (XLPE) according to the present invention comprises, for every 100 parts by weight of high-density polyethylene resin (HDPE) or low-density polyethylene resin (LDPE) as the base resin, 20 to 200 parts by weight of waste cross-linked polyethylene (XLPE) powder with a particle size of 1 mm or less and 10 to 100 parts by weight of viscoelastic decross-linked polyethylene (tPE) pellets, and, if necessary, may include 10 to 360 parts by weight of flame-retardant polyethylene crushed product recovered from waste cable sheathing material as an auxiliary agent.

[0011] Another embodiment of the polyethylene resin composition using recycled waste cross-linked polyethylene (XLPE) according to the present invention comprises, for every 100 parts by weight of high-density polyethylene resin (HDPE) or low-density polyethylene resin (LDPE) as the base resin, 20 to 200 parts by weight of waste cross-linked polyethylene (XLPE) powder with a particle size of 1 mm or less, and 10 to 100 parts by weight of viscoelastic decross-linked polyethylene (tPE) pellets obtained by processing the waste cross-linked polyethylene (XLPE) in a high-shear reaction type extruder with a structure that utilizes a cutter or kneading section repeatedly at 300 to 380°C, using a single extruder L / D 40:1 or a twin extruder L / D 60:1, and, if necessary, may include 10 to 360 parts by weight of flame-retardant polyethylene crushed product recovered from waste cable sheathing material as an auxiliary agent.

[0012] The recycled cross-linked polyethylene (XLPE)-based polyolefin resin composition according to the present invention can be understood as having a structure in which tPE is distributed at the interface of XLPE powder to form a structure advantageous for improving interfacial adhesion and stress transfer, and the XLPE powder forms a fine network structure within the polyethylene matrix, thereby mitigating the brittle characteristics that were a problem in existing recycled XLPE compositions, improving the elongation performance of HDPE, and improving the tensile strength of LDPE. Effects of the invention

[0013] The polyolefin-based resin composition based on recycled cross-linked polyethylene (XLPE) according to the present invention allows for the recycling of non-biodegradable waste cross-linked polyethylene (XLPE) at a high content of 50% by weight or more by mixing waste cross-linked polyethylene (XLPE) powder of a certain size and viscoelastic decross-linked polyethylene (tPE) pellets in an appropriate ratio. Furthermore, when flame-retardant polyethylene, which is a waste cable sheathing material, is additionally included, it is possible to recycle more than 80% of the total weight of the waste cable. Moreover, even under these high-content recycling conditions, mechanical properties suitable for industrial application, such as the elongation performance of high-density polyethylene (HDPE) and the improvement of tensile strength of low-density polyethylene (LDPE), can be maintained. Therefore, it can be usefully applied as various industrial and construction materials, such as protective materials for power facilities like buried plates and protective plates, cushioning materials, foams and boards like shoe soles, and packaging materials. Brief explanation of the drawing

[0014] FIG. 1 is a drawing showing the specifications of the specimen used in the experimental example of the present invention. Specific details for implementing the invention

[0015] The following describes specific details for implementing the present invention, but the present invention is not limited to the embodiments described below. Also, although the embodiments of the present invention mainly use polyethylene-based resins as the base resin, this is for convenience of explanation, and the interfacial bonding and network formation mechanism of XLPE powder by viscoelastic decrosslinked polyethylene (tPE) can be applied equally to polyolefin-based resins in general.

[0016] The recycled cross-linked polyethylene (XLPE)-based polyolefin resin composition according to the present invention comprises, for every 100 parts by weight of high-density polyethylene resin (HDPE) or low-density polyethylene resin (LDPE) as the base resin, 20 to 200 parts by weight of waste cross-linked polyethylene (XLPE) powder with a particle size of 1 mm or less and 10 to 100 parts by weight of viscoelastic decross-linked polyethylene (tPE) pellets, and optionally may include 10 to 360 parts by weight of flame-retardant polyethylene crushed product recovered from waste cable sheathing material as an auxiliary agent.

[0017] The high-density polyethylene (HDPE) or low-density polyethylene (LDPE) resin used in the recycled cross-linked polyethylene (XLPE)-based polyolefin resin composition according to the present invention is composed of a base resin for the recycling of waste cross-linked polyethylene (XLPE) and is widely used as a material for industrial and construction materials, general polyethylene extruded products, etc.

[0018] The waste cross-linked polyethylene (XLPE) according to the present invention is made of CNCV (including a semiconducting layer) scrap, which is an insulator of a discarded high-voltage cable, and is composed of 20 to 200 parts by weight of waste cross-linked polyethylene (XLPE) per 100 parts by weight of the base resin.

[0019] The above waste XLPE powder can be manufactured by repeating a grinding process that gradually reduces particle size after screening and crushing. Although the effect of improving physical properties increases as the particles become smaller, considering industrial processability and cost, a particle size of 1 mm or less is used, and preferably, a particle size of 0.25 to 0.5 mm is suitable.

[0020] The viscoelastic decrosslinked polyethylene (tPE) in the composition of the present invention is a polyethylene material in which some of the crosslinks are cut and polymer chains are partially rearranged by treating waste crosslinked polyethylene (XLPE) in a reactive extruder under high temperature and high shear conditions.

[0021] The above viscoelastic decrosslinked polyethylene (tPE) is obtained by processing waste crosslinked polyethylene (XLPE) in a high-shear reactive extruder structured to repeatedly utilize the cutter or kneading section at 300 to 380°C, with a single extruder L / D 40:1 or a twin extruder L / D 60:1.

[0022] Unlike a complete thermoplastic resin, the tPE manufactured as described above exhibits viscoelastic properties that simultaneously possess rubber elasticity due to a microgel structure and resin viscosity due to partial low molecular weight, and since it has the ability to maintain a constant shape in a molten state, it can be molded and ejected in the form of pellets after cooling.

[0023] In addition, the above tPE maintains viscoelasticity when melted and has excellent wettability for XLPE powder, so it contributes to the formation of a structure favorable for stress transfer by being encapsulated while distributed on the surface of the powder particles, and accordingly, the XLPE powder can form a fine network structure uniformly dispersed within the polyethylene matrix and tend to show a tendency to mitigate brittle characteristics caused by interfacial delamination.

[0024] The auxiliary agent composed as needed in the present invention may include 10 to 360 parts by weight of crushed flame-retardant polyethylene recovered from waste cable sheathing material.

[0025] Hereinafter, the regenerated cross-linked polyethylene (XLPE)-based polyolefin resin composition of the present invention will be described in more detail through <Examples> and <Test Examples>.

[0026] <Examples 1> to <Examples 4>

[0027] Specimens were prepared using a polyethylene resin composition recycled from waste cross-linked polyethylene (XLPE) blended according to the compositional components and blending ratios shown in [Table 1] below (see Fig. 1).

[0028] In addition, in this embodiment, for the XLPE powder, CNCV (including the semiconducting layer) scrap, which is an insulator of high-voltage cables, was used, and for the tPE, sheath scrap of OC cables used by KEPCO was used.

[0029] division Mixing ratio (parts by weight) Example 1 Example 2 Example 3 Example 4 Example 5 HDPE 100 100 - - LDPE - - 100 100 100 waste XLPE powder 0.25 ~ 0.5㎜ 70 - 70 - 175 0.5 ~ 1㎜ - 80 - 80 - tPE pellets 30 20 30 20 75 Additive (flame-retardant polyethylene) - - - - 250

[0030] <Test Example 1> to <Test Example 5>

[0031] Tensile tests were performed using each specimen prepared in <Examples 1> to <Examples 5> above as samples, and the results for major physical properties are shown in [Table 2] below.

[0032] Key Items unit Example 1 Example 2 Example 3 Example 4 Example 5 Max Force (Maximum Load) N 618.74 550.22 764.03 654.98 490.03 Max Force Length (Displacement at Maximum Load) ㎜ 21.42 23.25 863.49 736.60 622.86 Fracture Force N 384.51 348.92 749.05 578.74 411.69 Elongation ㎜ 362.56 219.87 867.23 740.62 628 Yield Strength Mpa 12.36 2.29 8.28 7.98 8.72 Tensile Strength 12.38 2.29 15.28 12.87 11.67 Modulus (elastic modulus) 2.26 1,12 0.88 0.88 1.86

Claims

Claim 1 A polyolefin-based resin composition containing a high content of recycled cross-linked polyethylene (XLPE) and a viscoelastic decross-linked polyethylene (tPE), comprising 20 to 200 parts by weight of waste cross-linked polyethylene (XLPE) powder having a particle size of 0.25 to 0.5 mm, 10 to 100 parts by weight of viscoelastic decross-linked polyethylene (tPE) pellets, and 10 to 360 parts by weight of polyethylene-based scrap containing a flame-retardant component as an auxiliary component, wherein the viscoelastic decross-linked polyethylene (tPE) is a viscoelastic decross-linked polyethylene formed into a pellet shape by processing waste cross-linked polyethylene (XLPE) in a high-shear reaction type extruder having a structure that repeatedly utilizes a cutter or kneading section at 300 to 380°C and a single extruder L / D 40:1 or a twin extruder L / D 60:

1. Claim 2 A polyolefin-based resin composition containing a high-content regenerated crosslinked polyethylene (XLPE)-based resin, wherein the base resin of claim 1 is high-density polyethylene resin (HDPE) or low-density polyethylene resin (LDPE). Claim 3 delete Claim 4 delete

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