KR20100045282A - Method of recycling crosslinked waste foams of low-density polyethylene - Google Patents

Abstract

PURPOSE: A method of recycling a waste foam agent based on low-density polyethylene is provided is provided to remarkably reduce the amount of buried or burned waste low-density polyethylene. CONSTITUTION: A method of recycling a waste foam agent based on low-density polyethylene comprises the following steps: de-crosslinking the waste foam agent at 350~500 deg C with a reaction condition of the pressure of 5~30 mega pascals for 2~30 minutes using supercritical ethanol; and converting the waste foam agent based on the low-density polyethylene into a recycling low density polyethylene class resin. The waste foam agent based on the low-density polyethylene is the waste foam agent using either an organic peroxide cross-linking method or an electron beam cross-linking method.

Description

Recycling method of waste low density polyethylene foam {METHOD OF RECYCLING CROSSLINKED WASTE FOAMS OF LOW-DENSITY POLYETHYLENE}

The present invention relates to a method for regenerating crosslinking of waste low density polyethylene foams into low density polyethylene resins that can be reshaped by decrosslinking with supercritical ethanol.

Recently, technology development for recycling mixed waste plastics has emerged as an important social issue in terms of resource protection and environmental pollution prevention. The recycling efficiency of waste packaging films used in homes has been gradually improved by implementing the “Responsibility for Recycling of Producers”, but recycling of waste thermosetting resins such as epoxy resins, phenol resins, urea resins, melamine resins and unsaturated polyester resins The research and development and commercialization are only conducted in advanced countries such as the US and Japan, and most of them are incinerated or landfilled in Korea.

Thermosetting resins are widely used and occupied in various fields that are closely related to real life, such as sporting goods, electric and electronic devices, small ship materials, building materials, furniture, office equipment, automobiles, and the like. However, due to the insoluble and infusible properties of the intramolecular crosslinked network polymer chains, thermosetting resins have not yet been properly developed for proper treatment or regeneration. In addition, effective recycling is not achieved, which causes many environmental problems.

The recycling of waste thermoset resins, which are mostly embedded or incinerated, requires a complex system of decrosslinking the crosslinked structure of the thermosetting resin and organic / inorganicizing the decrosslinked reaction product. As such, the recycling of waste thermosetting resins is very urgently required in terms of waste resource recycling and resource efficiency.

Generally, waste low density polyethylene foam, which is a kind of waste thermosetting resin composite, is the most used polymer among general-purpose plastics because it has excellent physical properties compared to low price, but because it is thermosetting, it is not melted even when heated and re-molded. Is impossible. Therefore, most low density polyethylene foams are landfilled or incinerated, which is considered to be a major cause of serious environmental pollution.

Regarding the recycling of waste thermosetting resin, Korean Patent No. 10-0733941 discloses a method of regenerating a multilayer waste packaging film in which aluminum is deposited using a compatibilizer and a functional resin, and Korean Patent No. 10-0728087 A method for recycling waste high density polyethylene by reactive extrusion using a peroxide crosslinking agent is disclosed. European Patent No. 0897783A2 also discloses a method for partially decrosslinking waste low density polyethylene foams by increasing shear stress at high temperatures using a twin screw extruder.

In addition, Japanese Laid-Open Patent Publication Nos. 2005-281429, 2004-161983, 2003-96233, 2001-253968 and 2001-98107 use supercritical water to selectively crosslink the crosslinked polyolefin. Although some attempts have been made, the critical temperature and critical pressure of the water are so high that an expensive reactor is required, making it economically difficult to commercialize.

Accordingly, the present inventors have diligently researched to develop an economical method for effectively recycling waste low density polyolefin foams mostly buried or incinerated. As a result, environmentally friendly reaction solvents were used to remove waste low density polyolefin foams using supercritical ethanol. The present invention has been completed by developing a method of regenerating a low-density polyethylene resin that can be reformed and remolded.

Accordingly, it is an object of the present invention to provide a method for decrosslinking and recycling waste low-density polyethylene foams in an environmentally friendly and economic manner.

In order to achieve the above object, the present invention is a waste low density polyethylene foam in the decrosslinking reaction using supercritical ethanol as a reaction solvent for 2 to 30 minutes under the reaction temperature of 350 to 500 ℃ and reaction pressure of 5 to 30 MPa. Provided is a method for regenerating waste low density polyethylene based foams, the method comprising the step of converting to low density polyethylene based resins capable of remolding.

The present invention also provides a regenerated low density polyethylene resin recycled according to the above method.

In addition, the present invention provides a molded article manufactured using the recycled polyethylene resin.

The method for regenerating the waste low density polyethylene foam according to the present invention uses supercritical ethanol, which is an environmentally friendly solvent with no toxicity as a reaction solvent, so that the crosslinking reaction can be carried out at a lower reaction pressure than the supercritical water, so that the commercialization reaction is cheap. It is a friendly and economic way. Therefore, according to the present invention, the amount of waste low density polyethylene that is buried or incinerated can be significantly reduced, thereby preventing secondary environmental pollution due to its landfill and incineration, and the regenerated low density polyethylene recycled therefrom corresponds to new low density polyethylene. It has excellent mechanical properties, and can be usefully recycled into various molded products such as packaging materials, heat insulating materials, sound absorbing materials, and cable insulators.

The present invention is a low-density polyethylene system that can be reformed by decrosslinking the waste low-density polyethylene foam using a supercritical ethanol as a reaction solvent for 2 to 30 minutes under a reaction temperature of 350 to 500 ° C. and a reaction pressure of 5 to 30 MPa. It relates to a method for regenerating waste low density polyethylene foam comprising the step of converting to a resin.

The regeneration method of the waste low density polyethylene foam according to the present invention is characterized by applying an environmentally friendly supercritical fluid process to recycling waste thermosetting resins, which is environmentally friendly due to no toxicity, and the critical temperature and the critical pressure are higher than those of the supercritical water. It is characterized by converting a waste low density polyethylene foam, which is a thermosetting resin, into a low density polyethylene resin that can be reshaped by a decrosslinking reaction using supercritical ethanol, which is relatively mild and easy to equip, as a reaction solvent.

Supercritical fluid refers to a substance that is in a "critical state" that cannot distinguish between gas and liquid when a normal liquid or gaseous substance exceeds a certain high temperature and high pressure limit called a supercritical point. The density of supercritical fluid molecules is close to liquid, but the viscosity is low, close to gas, and the diffusion is so high that the thermal conductivity is as high as water. Accordingly, the use of a supercritical fluid as a solvent results in extremely high concentrations of dissolved molecules, i.e., the solvent around the solute. Because of this feature, supercritical fluids are mainly used in the process of extracting and separating certain components from a mixture.

In the present invention, a supercritical fluid having all of the advantages of low surface tension, low viscosity, high diffusion rate, and excellent dissolving ability of a liquid is a supercritical ethanol which can cut a polymer chain at a high temperature and high pressure above a critical point. Was selected. Supercritical ethanol is a non-toxic supercritical fluid with a molecular weight of 46.07 g / mol, which has a critical temperature of 513.9 ° C and a critical pressure of 6.14 MPa, which has a critical point relative to that of a critical temperature of 647.3 ° C and a critical pressure of 7.38 MPa. It can be effectively used to convert the waste low density polyethylene foam, which is a thermosetting resin, into a low density polyethylene resin by a decrosslinking reaction because of low cost of equipment construction during commercialization.

Hereinafter will be described in detail the recycling method of the waste low density polyethylene foam according to the present invention.

In the present invention, a method for recycling waste low-density polyethylene foams by a supercritical fluid process using a high pressure batch reactor and a supercritical ethanol as a reaction solvent is illustrated.

In the regeneration method according to the present invention, all waste low density polyethylene foams which are not recycled due to insolubility and incompatibility of crosslinked polymer chains and simply discarded by landfilling or incineration may be applied. Preferably, it may be a waste low density polyethylene foam of organic peroxide crosslinking and electron beam crosslinking, and waste low density polyethylene foam having a gel fraction of 45 to 65% may be advantageously applied.

In addition, according to the present invention, all kinds of wastes can be recycled regardless of the shape and size of the waste low density polyethylene foam, and the same result can be achieved even if the waste low density polyethylene foam is applied as it is, or in a crushed or compressed form. Can be.

The high pressure batch reactor illustrated in FIG. 1 may be manufactured using stainless steel, Hastelloy steel, Inconel steel, etc., but since ethanol has little corrosiveness in a supercritical state, it is economical to use stainless steel having a low cost. It is advantageous.

In a preferred embodiment of the present invention, after the finely pulverized waste low density polyethylene foam and supercritical ethanol are put into the above-described high-pressure batch reactor, 5 to 10 under a reaction temperature of 360 to 380 ° C and a reaction pressure of 10 to 15 MPa A minute decrosslinking reaction is performed to convert the waste low density polyethylene foam into a low density polyethylene resin.

The supercritical ethanol used as the reaction solvent is preferably used in an amount of 100 to 700 parts by weight based on 100 parts by weight of the waste low density polyethylene foam to be recycled. If the amount of supercritical ethanol is less than 100 parts by weight, it is not a supercritical condition, which may cause a problem of decrosslinking reaction. If it exceeds 700 parts by weight, the reactor may be thicker due to explosion risk due to high vapor pressure. Problems that must be produced can arise.

The reaction pressure is adjusted according to the amount of waste low density polyethylene foam and supercritical ethanol injected into the reactor within the above range, and the reaction temperature is controlled by using an electric furnace installed outside the reactor. After the decrosslinking reaction is completed, it is preferable to adjust the cooling rate within 30 minutes by embedding a cooler in the reactor and the flange portion in order to reduce the residence time of the reactants in the reactor. If the cooling rate exceeds 30 minutes may cause a problem that the physical properties due to degradation of the polymer decreases due to the increase in the reaction residence time.

After recovering the low density polyethylene resin recovered through the above method, the degree of crosslinking was analyzed. As a result, the waste low density polyethylene foam having a gel fraction of 65% had a gel fraction of 1% or less by decrosslinking reaction using supercritical ethanol. It was found to be converted to a renewable low density polyethylene resin.

In conclusion, the recycling method of the waste low density polyethylene foam according to the present invention uses supercritical ethanol, which is an environmentally friendly solvent with no toxicity as a reaction solvent, so that the decrosslinking reaction can be carried out at a lower reaction pressure than the supercritical water. It is an environmentally friendly way. Therefore, according to the present invention, the amount of waste low-density polyethylene that is buried or incinerated can be significantly reduced, thereby preventing secondary environmental pollution due to its landfill and incineration, and the regenerated low-density polyethylene recycled therefrom has a gel fraction of 0.2% or less. It has excellent mechanical properties corresponding to new low density polyethylene, and can be usefully recycled into various molded products such as packaging materials, heat insulating materials, sound absorbing materials, and cable insulators.

Hereinafter, the present invention will be described in more detail with reference to Examples. These examples are only for illustrating the present invention in more detail, it will be apparent to those skilled in the art that the scope of the present invention is not limited by these examples in accordance with the gist of the present invention.

Example 1

Using a 500 ml stainless steel batch reactor (SUS316), the waste low density polyethylene foam (XLPE) was pulverized to a size of about 0.6 to 1.0 mm, and then the pulverized product and 500 parts of ethanol were added to 100 parts by weight of the pulverized product. Part was added to the reactor. The reactor crosslinking reaction was performed for 5 minutes by varying the reaction temperature of the reaction temperature of 375 ° C. and the reaction pressure of 10 MPa, the reaction temperature of 380 ° C. and the reaction pressure of 15 MPa. After the decrosslinking reaction was terminated, the reactant was rapidly cooled to room temperature using a cooler to recover the regenerated low density polyethylene resin.

The crosslinking degree of the low density polyethylene resin recovered after each reaction was measured according to ASTM D2765. Briefly, the pulverized sample of 30 to 60 mesh was put into a 120 mesh wire mesh bag and boiled at 1 atmosphere (0.1 MPa) at 110 ° C. for 12 hours using xylene contained in a round flask connected to a condenser. (FIG. 2). After extraction, the amount of the sample remaining in the wire mesh bag (mg) was measured, and the gel fraction (%) was calculated using this, and the results are shown in Table 1 below.

Reaction temperature (℃) Reaction pressure (MPa) XLPE: Ethanol Response time (minutes) Gel fraction (%) 380 15 1: 5 5 0.4 375 10 1: 5 5 2.5

As shown in Table 1, the waste low-density polyethylene foam with 65% gel fraction was reduced to 2.5% by 375 ° C and 10 MPa decrosslinking reaction, and by decrosslinking reaction of 380 ° C and 15 MPa. The gel fraction was reduced to 0.40%.

From the above results, it was confirmed that decrosslinking the waste low density polyethylene foam using supercritical ethanol according to the present invention significantly reduced the gel fraction, thereby effectively recycling the waste low density polyethylene foam into a low density polyethylene resin.

The specific parts of the present invention have been described in detail above, and it is apparent to those skilled in the art that such specific descriptions are merely preferred embodiments, and thus the scope of the present invention is not limited thereto. something to do. Thus, the substantial scope of the present invention will be defined by the appended claims and their equivalents.

Figure 1 shows a schematic diagram of a high pressure batch reactor that can be used in the decrosslinking reaction according to the present invention,

Figure 2 shows a schematic diagram of the extraction equipment for measuring the gel fraction of the low density polyethylene resin.

* Brief description of the symbols in the drawings *

1: pressure gauge, 2: nitrogen inlet

3: flange, 4: reactor

5: coolant inlet, 6: temperature gauge

7: nitrogen outlet, 8: cooling water outlet

9: number plate, 10: condenser

11: clamp, 12: coolant inlet

13: cork stopper, 14: round flask

15: voltage regulator, 16: coolant outlet

17: stand, 18: xylene

19: heating furnace, 20: sample bag

Claims (8)

The waste low density polyethylene foam is converted into a low density polyethylene resin that can be reshaped by a decrosslinking reaction using supercritical ethanol as a reaction solvent for 2 to 30 minutes under a reaction temperature of 350 to 500 ° C. and a reaction pressure of 5 to 30 MPa. A method for regenerating waste low density polyethylene-based foam, the method comprising: The method of claim 1, And said waste low density polyethylene foam is a waste low density polyethylene foam of organic peroxide crosslinking or electron beam crosslinking. The method of claim 2, Wherein said waste low density polyethylene foam has a gel fraction of 45 to 65%. The method of claim 1, Supercritical ethanol is used in an amount of 100 to 700 parts by weight based on 100 parts by weight of the waste low density polyethylene foam. The method of claim 1, The decrosslinking reaction is characterized in that it is carried out for 5 to 10 minutes under a reaction temperature of 360 to 380 ℃ and a reaction pressure of 10 to 15 MPa. Regenerated low density polyethylene resin recycled according to the method of claim 1. The method of claim 6, The regenerated low density polyethylene resin has a gel fraction of 0.2% or less. A molded article manufactured using the recycled low density polyethylene resin according to claim 6.

Images