JP2010168515A - Method for decomposing polymer and resulting decomposed product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for decomposing polymer which can reduce a reaction inhibiting effect resulting from ethylene copolymer mixed therein by optimizing the reaction temperature during the cleavage reaction of crosslinking of a crosslinked polyethylene by means of alkyl carbonate; and the resulting decomposed product. <P>SOLUTION: The method to modify a polymer by means of alkyl carbonate includes reacting a material which is a mixture of at least two polymers comprising a crosslinked polymer using alkyl carbonate at the temperature higher than 335°C. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polymer decomposition method for treating a cross-linked polymer in which foreign matters are mixed by using an alkyl carbonate, and a decomposition reaction product generated thereby.

  Waste disposal is an important issue in today's society, where efforts to address environmental issues are urgently needed. Among various wastes, polymers widely used for various materials and composite materials are no exception. In the examination so far, material recycling is progressing because thermoplastic polymers can be re-molded with increased fluidity when heated. In addition, studies on biomass-derived polymers that are attracting attention because they are alternatives to natural resources and are carbon neutral are being actively conducted.

  On the other hand, thermosetting polymers, cross-linked polymers, rubbers, and the like are difficult to recycle materials because they are not fluidized and cannot be molded because of a three-dimensional network of molecules even when heated. For this reason, in addition to some thermal recycling being performed, in many cases, it is used for disposal such as landfill.

  With regard to such thermosetting polymers and cross-linked polymers, there is a growing movement to carry out material recycling, and a technology that makes this possible is emerging. For example, as shown in Patent Documents 1 to 3, a technique for decomposing by subcritical and supercritical processing using nitrogen oxides or alcohol has been developed.

Japanese Patent No. 3855006 JP 2008-038006 A JP 2002-187976 A

Pietro Tundo, Maurizio Selva. Accounts of Chemica1 Research 35, 706-716 (2002)

  However, in the method of decomposing cross-linked polyethylene in supercritical carbon dioxide with nitrogen dioxide as shown in Patent Documents 1 and 2, the toxicity of nitrogen dioxide used is a problem, and adverse effects on the human body (particularly the respiratory system) It is also set as an environmental standard by the Air Pollution Control Law because of its high toxicity and its toxicity. For this reason, it is a substance that should be avoided as much as possible, and development of a recycling method using a safer substance for use is required.

  In addition, the method using high-temperature alcohol as disclosed in Patent Document 3 selectively cuts the siloxane bond in the crosslinked polymer, and is used for the thermoplasticization of the silane crosslinked polymer using the siloxane bond for the crosslinking bond. Is effective, but not effective for cross-linked polymers having no siloxane bonds. Accordingly, for example, in the case where a crosslinked polymer having no siloxane bond is mixed in the silane crosslinked polymer, a case where material recycling is difficult is assumed.

  We have so far discovered a method (Japanese Patent Application No. 2008-161592) for cutting a cross-linked polymer, especially a cross-linked polyethylene, using a supercritical or subcritical alkyl carbonate.

Dimethyl carbonate (C ₃ H ₆ O ₃ ), which is a typical alkyl carbonate, is a non-toxic and highly safe solvent as described in Non-Patent Document 1, and functions as an alkylating agent. Therefore, it becomes possible to cut | disconnect the bridge | crosslinking bond of crosslinked polyethylene more safely by using alkyl carbonate.

  By the way, although cross-linked polyethylene is widely used as an insulating material for electric wires and cables, when trying to recover cross-linked polyethylene from electric wire / cable waste, a semiconductive layer containing an ethylene copolymer is formed outside the cross-linked polyethylene layer. The covered wires / cables are collected in a mixed state because it is difficult to separate them.

  So far, we tried to cut the cross-linked polyethylene cross-linked polyethylene using alkyl carbonate for the system in which cross-linked polyethylene was mixed with ethylene copolymer. It has been found that it is significantly inhibited.

  Therefore, in the case of cutting the cross-linked polyethylene by using an electric wire / cable including a semiconductive layer as a raw material, it is necessary to optimize the reaction conditions so that the inhibitory influence by the ethylene copolymer is reduced.

  Therefore, the object of the present invention is to solve the above-mentioned problems and to reduce the reaction inhibition effect due to mixing of the ethylene copolymer by optimizing the reaction temperature in the crosslinking reaction of the crosslinked polyethylene using the alkyl carbonate. The present invention provides a method for decomposing a polymer and a decomposition reaction product produced thereby.

  In order to achieve the above object, the invention of claim 1 is a method for modifying a polymer using an alkyl carbonate, wherein a material containing at least two kinds of polymers including a crosslinked polymer is mixed with an alkyl carbonate having a temperature exceeding 335 ° C. It is a method for decomposing a polymer characterized in that it is used and reacted.

  The invention according to claim 2 is the polymer decomposing method according to claim 1, wherein the polymer other than the crosslinked polymer is made of an ethylene copolymer in a material in which at least two kinds of polymers are mixed.

  The invention according to claim 3 is the polymer decomposing method according to claim 1 or 2, wherein the cross-linked polymer is a polyolefin resin.

  The invention according to claim 4 is the polymer decomposing method according to claim 3, wherein the polyolefin resin is polyethylene.

  The invention according to claim 5 is the polymer decomposition method according to any one of claims 1 to 4, wherein the alkyl carbonate is dimethyl carbonate.

  The invention of claim 6 is a decomposition reaction product characterized in that the decomposition reaction product produced by the decomposition method of claims 1 to 5 has a gel fraction of 20% or less.

  According to the present invention, even when foreign matter of an ethylene copolymer such as EVA or EEA is mixed in the crosslinked polyethylene, there is almost no thermal decomposition of the crosslinked polyethylene main chain by the alkyl carbonate, and the crosslinked bond is preferentially cut. Can do. As a result, material recycling of cross-linked polyethylene using actual wire / cable waste as a raw material becomes possible.

The schematic diagram of the experimental apparatus used for examination of this invention is shown.

  A preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

  First, in the present invention, a material in which at least two kinds of polymers including a crosslinked polymer are mixed is reacted by using an alkyl carbonate having a temperature exceeding 335 ° C. If the reaction is carried out in a higher temperature range, the crosslinked bond of the crosslinked polymer can be cut.

  Furthermore, by reacting in a temperature range that is lower than the thermal decomposition temperature of the main chain of the crosslinked polymer, it is possible to suppress the thermal decomposition of the main chain and selectively break the cross-linked bond. In addition, as described in the examples described later, the present invention is for a reaction time of 30 minutes or less, and conditions exceeding 30 minutes are not implemented because it cannot be considered industrially significant. If the reaction is carried out for a long time exceeding 30 minutes, there is a possibility that a reaction product in which the cross-linked bond is broken is obtained even under a certain low temperature condition.

  The foreign matter mixed in the crosslinked polymer is particularly an ethylene copolymer.

  Examples of the ethylene copolymer include ethylene vinyl acetate copolymer (EVA), ethylene ethyl acrylate copolymer (EEA), and ethylene propylene rubber. For example, when EVA or EEA is mixed as a foreign substance in the crosslinked polymer, even if a very small amount of EVA or EEA of about 0.5 mass% is mixed, the cross-linking cleavage reaction is inhibited, and if about 5 mass% is mixed, the inhibition effect is saturated. I know that.

  The crosslinked polymer is particularly a polyolefin resin, and the polyolefin resin is particularly a crosslinked polyethylene.

  The alkyl carbonate is particularly preferably dimethyl carbonate.

  Next, an apparatus for treating a material in which at least two kinds of polymers including a crosslinked polymer are mixed with an alkyl carbonate will be described with reference to FIG.

  In FIG. 1, reference numeral 1 denotes a salt bath, which includes an agitator 5 and a heater 6, and the inside of the salt bath 1 is heated to a predetermined temperature by a control device 8.

  A SUS reaction vessel 2 having a capacity of 20 cc in which a material in which at least two kinds of polymers including a crosslinked polymer are mixed and an alkyl carbonate is enclosed is charged into the salt bath 1.

  Here, in the reaction vessel 2, an inert gas such as Ar gas is reacted through a pipe 7 in order to prevent oxidation of the polymer after enclosing a material in which at least two kinds of polymers including a crosslinked polymer are mixed and an alkyl carbonate. The reaction vessel 2 is sufficiently purged with Ar gas through the pipe 7 and the pressure reducing valve 4 and supplied to the salt bath 1 after being supplied into the vessel 2.

  The organic compound and the alkyl carbonate are heated to a predetermined temperature and pressure (high pressure state, supercritical state, subcritical state) in the reaction vessel 2, and the crosslinked polymer is decomposed by the reaction with the alkyl carbonate. The

  At this time, the pressure during the reaction is constantly monitored by a pressure gauge 3 connected to the reaction vessel 2. When a predetermined reaction time has elapsed, the reaction vessel 2 is taken out from the salt bath 1 and cooled with water. After the water cooling, when the pressure in the reaction vessel 2 is sufficiently reduced, the reaction product and the liquid residue are taken out from the reaction vessel 2.

  With the apparatus as shown in FIG. 1, the examination which cut | disconnects the bridge | crosslinking bond of crosslinked polyethylene on the conditions which EVA or EEA was mixed with crosslinked polyethylene by dimethyl carbonate was performed.

  The used cross-linked polyethylene is adjusted to the same composition as that used as the wire covering material, and has a molecular skeleton in which carbon atoms of polyethylene molecular chains are directly cross-linked by an organic peroxide. Moreover, it was 84% when the gel fraction of this crosslinked polyethylene was measured. Here, the gel fraction is an index indicating the degree of cross-linking of the polymer, and after the polymer put in the wire mesh is extracted in hot xylene at 110 ° C. for 24 hours, the weight of the polymer remaining in the wire mesh is calculated based on the weight of the original polymer. Percentage divided by weight.

  Under a condition shown in Table 1, 1.42 g (about 95 mass%) of crosslinked polyethylene, 0.08 g (about 5 mass%) of EVA or EEA, and dimethyl carbonate are predetermined in a salt bath heated to a predetermined temperature in advance. A reaction vessel charged with an amount adjusted to a pressure of was charged. From previous studies, it was confirmed that 5% by mass of EVA or EEA sufficiently inhibited the cross-linked polyethylene cross-linking reaction, and that the gel fraction of the reaction product does not increase even if EVA or EEA is increased further. This time, EVA or EEA was fixed at about 5 mass%. The reaction time was 7.5 minutes or 30 minutes. Here, the reaction time was from the time when the reaction vessel was put into the salt bath to the time when the reaction vessel was taken out from the salt bath. Further, the reaction was carried out by regarding the set temperature of the salt bath as the temperature of the alkyl carbonate.

  After the reaction time elapsed, the reaction vessel was taken out of the salt bath and sufficiently cooled with water, and the reaction product was collected after releasing the residual pressure.

  In order to evaluate whether the cross-linked bond of the cross-linked polyethylene was cut by dimethyl carbonate, the gel fraction of the reaction product was measured.

  As for the determination of the cross-linked bond breakage of the cross-linked polyethylene, if the gel fraction of the reaction product is less than 20%, the cross-linked polyethylene cross-linked bond is sufficiently cut, and the insulation material of the electric wire / cable is used as the polyethylene material. First, it was judged (passed) that material recycling was possible for other uses, and if the gel fraction was 20% or more, it was rejected.

  Next, Examples 1 to 6 shown in Table 1 will be described.

[Example 1]
An experiment was conducted in which dimethyl carbonate cuts the cross-linked bond of cross-linked polyethylene containing 5 mass% EVA. The temperature of the salt bath was set at 340 ° C., and an experiment was conducted under the conditions of a reaction time of 30 minutes. As a result, the gel fraction of the reaction product was 16%. It was suggested that it was sufficiently cleaved by dimethyl carbonate.

[Example 2]
An experiment was conducted in which dimethyl carbonate cuts the cross-linked bond of cross-linked polyethylene containing 5 mass% EVA. The temperature of the salt bath was set to 350 ° C., and an experiment was conducted under the condition of a reaction time of 30 minutes. As a result, the gel fraction of the reaction product was 7%. It was suggested that it was sufficiently cleaved by dimethyl carbonate.

Example 3
An experiment was conducted in which dimethyl carbonate cuts the cross-linked bond of cross-linked polyethylene containing 5 mass% EVA. The temperature of the salt bath was set to 360 ° C., and an experiment was conducted under the condition of a reaction time of 7.5 minutes. It was suggested that the bond was sufficiently cleaved by dimethyl carbonate.

Example 4
An experiment was conducted in which dimethyl carbonate cuts a cross-linked bond of cross-linked polyethylene containing 5 mass% of EEA. The temperature of the salt bath was set to 340 ° C., and the experiment was conducted under the condition of a reaction time of 30 minutes. As a result, the gel fraction of the reaction product was 14%. It was suggested that it was sufficiently cleaved by dimethyl carbonate.

Example 5
An experiment was conducted in which dimethyl carbonate cuts a cross-linked bond of cross-linked polyethylene containing 5 mass% of EEA. The temperature of the salt bath was set to 350 ° C., and an experiment was conducted under the condition of a reaction time of 30 minutes. As a result, the gel fraction of the reaction product was 5%. It was suggested that it was sufficiently cleaved by dimethyl carbonate.

Example 6
An experiment was conducted in which dimethyl carbonate cuts a cross-linked bond of cross-linked polyethylene containing 5 mass% of EEA. The temperature of the salt bath was set to 360 ° C., and the experiment was conducted under the reaction time of 7.5 minutes. As a result, the gel fraction of the reaction product was 3%, and even when 5 mass% of EEA was mixed, It was suggested that the bond was sufficiently cleaved by dimethyl carbonate.

  From the results of Examples 3 and 6, it was found that the reaction time can be significantly shortened by raising the temperature. This is directly linked to the improvement of productivity, and can be said to be a result that enables industrialization sufficiently.

  Next, Comparative Examples 1 to 6 shown in Table 1 will be described.

[Comparative Example 1]
An experiment was conducted in which dimethyl carbonate cuts the cross-linked bond of cross-linked polyethylene containing 5 mass% EVA. When the salt bath temperature was set to 335 ° C. and the reaction time was 30 minutes, the gel fraction of the reaction product was 29%, suggesting that the crosslinked polyethylene was not sufficiently cleaved by dimethyl carbonate. It was.

[Comparative Example 2]
An experiment was conducted in which dimethyl carbonate cuts a cross-linked bond of cross-linked polyethylene containing 5 mass% of EEA. The temperature of the salt bath was set at 335 ° C., and the experiment was conducted under the conditions of a reaction time of 30 minutes. It was.

  From Comparative Examples 1 and 2, it was suggested that in the temperature range of 335 ° C. or less, when 5 mass% of EVA or EEA is mixed, the crosslinked bond of the crosslinked polyethylene cannot be sufficiently cut by dimethyl carbonate. From this, it can be said that a temperature exceeding 335 ° C. is necessary to break the cross-linked bond of the cross-linked polyethylene mixed with EVA or EEA.

  Next, since the influence of the thermal decomposition of the crosslinked polyethylene main chain was a concern at the temperatures examined in Examples 2 to 6 (350 to 360 ° C.), an experiment was conducted to verify this. Comparative Examples 3, 4, 5, and 6 in which comparative experiments were conducted in Examples 2, 3, 5, and 6 under the conditions in which dimethyl carbonate was removed, and the effects of thermal decomposition of crosslinked polyethylene under the reaction conditions were described. .

[Comparative Example 3]
An experiment was conducted in which crosslinked polyethylene containing 5 mass% of EVA was heated at 350 ° C. for 30 minutes to verify the thermal decomposition of the crosslinked polyethylene. The gel fraction of the reaction product was 56%, and it was suggested that the thermal decomposition of the crosslinked polyethylene hardly occurred under the reaction conditions of 350 ° C. and 30 minutes.

[Comparative Example 4]
An experiment in which a crosslinked polyethylene mixed with 5 mass% of EVA was heated at 360 ° C. for 7.5 minutes was conducted to verify the thermal decomposition of the crosslinked polyethylene. The gel fraction of the reaction product was 66%, suggesting that thermal decomposition of the crosslinked polyethylene hardly occurred under the reaction conditions of 360 ° C. and 7.5 minutes.

[Comparative Example 5]
An experiment was conducted in which a crosslinked polyethylene mixed with 5 mass% of EEA was heated at 350 ° C. for 30 minutes to verify the thermal decomposition of the crosslinked polyethylene. The gel fraction of the reaction product was 61%, suggesting that thermal decomposition of the crosslinked polyethylene hardly occurred under the reaction conditions of 350 ° C. and 30 minutes.

[Comparative Example 6]
An experiment was carried out in which a crosslinked polyethylene mixed with 5 mass% of EEA was heated at 360 ° C. for 7.5 minutes to verify the thermal decomposition of the crosslinked polyethylene. The gel fraction of the reaction product was 69%, suggesting that thermal decomposition of the crosslinked polyethylene hardly occurred under the reaction conditions of 360 ° C. and 7.5 minutes.

  From Comparative Examples 3 to 6, the results of Examples 1 to 6 were not due to thermal decomposition of the crosslinked polyethylene main chain, but were due to the preferential cleavage of the crosslinked polyethylene by reaction with dimethyl carbonate. It was suggested that there is.

  Next, Table 2 shows the results of measuring the number average molecular weight of virgin polyethylene and the reaction product.

  Table 2 shows the results of measuring the molecular weight of the reaction product obtained in Example 1 and virgin polyethylene.

  From Table 2, the reaction product obtained in Example 1 has a molecular weight lower than that of virgin polyethylene but has no effect on the physical properties. It was suggested that it was disconnected preferentially.

DESCRIPTION OF SYMBOLS 1 Salt bath 2 Reaction container 3 Pressure gauge 4 Pressure reducing valve 5 Agitator 6 Heater 7 Piping

Claims (6)

  A method for decomposing a polymer, characterized in that, in the method of modifying a polymer using an alkyl carbonate, a material in which at least two kinds of polymers including a crosslinked polymer are mixed is reacted using an alkyl carbonate having a temperature exceeding 335 ° C.   2. The method for decomposing a polymer according to claim 1, wherein the polymer other than the crosslinked polymer is made of an ethylene copolymer in a material in which at least two kinds of polymers are mixed.   The method for decomposing a polymer according to claim 1 or 2, wherein the crosslinked polymer is a polyolefin-based resin.   The method for decomposing a polymer according to claim 3, wherein the polyolefin resin is polyethylene.   The method for decomposing a polymer according to any one of claims 1 to 4, wherein the alkyl carbonate is dimethyl carbonate.   6. A decomposition reaction product, wherein the decomposition reaction product produced by the decomposition method according to claim 1 has a gel fraction of 20% or less.

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