Process for the degradation of high polymer substances

This is a division of application Ser. No. 361,792, filed May 18, 1973, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for degrading high polymers and more particularly to a process for destroying a shaped article made of a high polymer for easy waste disposal.

2. Description of the Prior Art

In response to demands for shaped articles made of synthetic polymers, i.e., plastic products which possess excellent durability for use including in the outdoors, their production has been recently increased remarkably and this has been accompanied by an increase of waste products thereof. The durability of shaped articles made of such a polymer may be easily seen from the fact, for example, that a sheet of plasticized polyvinyl chloride of 0.08 mm in thickness for agricultural use can be first manually crushed after the sheet is oxidized for 1,200 hours in air at 45° C. under ultraviolet radiation emitted from a high pressure mercury vapor lamp of 1.2 K. watts capacity spaced from the sheet at a distance of 50 cm. This high durability which is desired when the plastic products are in practical use, causes a very serious problem of waste disposal thereof. It is very urgent to solve this problem in order to prevent environmental pollution, since natural decay thereof can hardly be expected.

For this purpose, there have been studied and proposed many processes including mechanical crushing, application of chemicals, subjecting to photo-oxidation, biodegradation using a microorganism and incineration, all of which have, however, individual deficiencies. For example, an attempt has been made which comprises incorporating a ketone compound into a high polymer and subjecting the polymer to irradiation of light in the presence of ambient oxygen to cause oxidation of the polymer, whereby the polymer is degraded. However, this process using the saturated or unsaturated ketone compound such as acetone or methyl vinyl ketone still involves a disadvantage that the oxidation rate of the polymer is extremely slow.

SUMMARY OF THE INVENTION

A main object of this invention is to provide a process for degrading a high polymer substance by photo-oxidation of the high polymer.

Another object of this invention is to provide a process for the waste disposal of a shaped article made of a high polymer by utilizing the photo-oxidation reaction and using an accelerator for the reaction, thereby preventing environmental pollution.

A further object of this invention is to provide a process for the rapid destruction of a shaped article made of a high polymer utilizing the oxidation that easily takes place in the high polymer under ultraviolet irradiation or sunlight without using means such as mechanical crushing.

The present invention is based on the discovery that an article made of a high polymer is degraded under ultraviolet irradiation or sunlight in the presence of a halogenated compound having a carbonyl group or carbonyl groups (hereinafter, this compound is referred to as "halogenated carbonyl compound") in an ambient atmosphere of oxygen or a gas containing oxygen. In more detail, a small amount of the halogenated carbonyl compound which has been incorporated into a plastic product such as one made of polyvinyl chloride or polyolefin, absorbs energy on exposure to ultraviolet irradiation or sunlight to cause cleavages of the carbon-halogen bonds thereof to produce free radicals which react with hydrogen atoms attached to the carbons of the main bonding chains in the polymer, whereby the oxidation reaction of the polymer is accelerated resulting in the destruction of the plastic product.

As the high polymer and the shaped article made thereof, to be treated by the present invention, there can be mentioned a polyolefin such as polyethylene or polypropylene; a polymer such as polyvinyl chloride, polystyrene, or polyacrylonitrile; a variety of polymers derived therefrom by a chemical modification such as unsaturation or ketonization thereof; or a mixture thereof, and also a wide variety of articles in the form of films, fibers or molded products made of the above mentioned high polymer.

Referring to the shaped articles of polyvinyl chloride, one of the specified examples of the present invention, this article includes among others a plasticized or unplasticized film or a molded article comprising a homopolymer, copolymer or block copolymer of vinyl chloride or a blended mixture thereof.

This invention can be also applied to an article made of a post-chlorinated polymer such as chlorinated polyethylene.

The halogenated carbonyl compound used in this invention as the reaction accelerator may be obtained by halogenation, i.e., by reacting a variety of compounds having a carbonyl group or carbonyl groups with bromine, chlorine or iodine, or a mixture thereof.

Examples of the halogenated carbonyl compounds thus obtained include a compound derived from the halogenation of a saturated ketone such as acetone, acetyl acetone or biacetyl; an unsaturated ketone such as methyl vinyl ketone; a saturated aldehyde such as acetaldehyde; an unsaturated aldehyde such as acrolein; an aromatic or saturated cyclic ketone such as cyclohexanone, phenacyl acetone, or benzophenone; carbon monoxide-containing polyketone type copolymers such as a copolymer prepared by a copolymerization of carbon monoxide with ethylene and vinyl chloride; and a polymer prepared from an unsaturated ketone such as methyl vinyl ketone by the bond-opening at the unsaturated bonds of the ketone.

The optimum amount of the halogenated carbonyl compound may vary depending on the high polymer article to be treated and the desired oxidation rate of the polymer, but from about 0.1 to about 20 weight %, preferably from about 0.3 to about 3.0 weight %, based on the weight of the polymer, is usually employed.

The addition of the halogenated carbonyl compound into the high polymer is referred in general throughout this description as being performed by impregnation into the shaped article made of the high polymer, but this can be effected in advance to the shaping of the polymer together with or without a plasticizer.

The impregnation of this compound into the high polymer article according to this invention may be carried out by dipping the shaped high polymer article into a liquid of the halogenated carbonyl compound or an intimate mixture of the compound with a solvent such as acetone, ether, esters or halogenated hydrocarbons, or by coating or spraying the above liquid or a mixture thereof onto the article.

As the solvent in this case, there may be employed acetone, methyl vinyl ketone, ether, alcohol, esters, halogenated hydrocarbons or the like, and the solvent acts to extract the stabilizer contained in the high polymer article, to swell the article so that the halogenated carbonyl compound easily penetrates into the article to prevent this compound from volatilizing away, and further to additionally accelerate the degradation of the high polymer caused by the irradiation in the presence of the halogenated carbonyl compound. The solvent is preferably used in the form of a mixture of two or more than two kinds of individual solvents so that the above mentioned objects are simultaneously achieved.

When an article of a non-chlorinated high polymer is used as the high polymer article of this invention, it is very effective that the article further contains a chlorinated polymer. This chlorinated polymer incorporated with the non-chlorinated polymer improves the penetration and the compatibility of the halogenated carbonyl compound on impregnation of the latter compound, to ensure a homogeneous distribution of the latter compound, and further accelerates the photo-oxidation of the article, thereby the chlorinated polymer cooperates with the halogenated carbonyl compound on exposure of the article to ultraviolet irradiation, since the chlorinated polymer also supplies free radicals generated by the irradiation which affect the non-chlorinated polymer to accelerate additionally the photo-oxidation thereof.

The above described non-chlorinated polymer article includes fibers, films or other shapes of moulded products of polyolefins such as polyethylene or polypropylene, polyvinyls such as polystyrene or polyacrylonitrile, or modifications thereof produced by means of, for example, unsaturation or ketonization; and a mixture thereof.

By the term "chlorinated polymer" is meant a material produced by chlorinating a polymer compatible with the non-chlorinated polymer. The chlorination is preferably carried out to the extent that about 10 to about 50 % of the hydrogen atoms existing in the starting polymer are replaced by chlorine atoms when a polyolefin such as polyethylene is chlorinated.

In this case the amount of the chlorinated polymer and halogenated carbonyl compound to be added are preferably from about 5 to about 50 weight parts and from about 0.1 to about 10 weight parts, respectively, both per 100 weight parts of the non-chlorinated polymer.

According to the present invention, the treatment of waste plastic articles of a high polymer can be carried out without use of any mechanical apparatus or incineration, since the articles can be easily degraded without causing any environmental pollution.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

EXAMPLE 1

Into specimens of a film of plasticized polyvinyl chloride of 0.10 mm thickness for agricultural use there was impregnated a chlorinated carbonyl compound by spraying a liquid or a solution thereof until the specimens increased by 10 % in their weight. The compounds employed are listed in Table 1 together with the solvent used for preparing the solution. The specimens thus obtained were irradiated with ultraviolet radiation emitted from a cylindrical high pressure mercury vapor lamp of 1.2 K. watts capacity arranged spaced therefrom by 50 cm. in air at 43°C for 24 hours.

The irradiated specimens were immersed into ether, extracted for 48 hours, and dried in vacuo. The IR-absorptions of the specimens were measured at wave numbers of 1712 cm^{- 1}, 1721 cm^{- 1}, 1733 cm^{- 1} which were due to the carbonyl structures of aldehyde-, ketone- and carboxylic acid-radicals, respectively. Other specimens which were impregnated as described above with the reagents, but not irradiated, were extracted with ether and dried and the IR-absorptions were measured in the same way as above for reference purposes.

The mean oxidation rate during the 24 hours-irradiation, V_o, which is defined as the increase in the number of the carbonyl structures per every 10³ carbon atoms of the polymer per hour, was calculated by the following equation (Preservation of Beer's Law was assumed): ##EQU1## where;

K₁, K₂ and K₃ were predetermined coefficients as to the numbers of carbonyl structures corresponding to aldehyde-, ketone- and carboxylic acid-radicals, respectively;

d was the density of the specimens in g./cc;

l₁ and l_o were the lengths of the optical paths of IR-beam in the irradiated and non-irradiated specimens, respectively;

t was the irradiation time in hour, that is 24 hours in this case;

A₁₀, A₂₀ and A₃₀ were optical absorbances of the non-irradiated

specimens at the wave numbers of 1712 cm^{- 1}, 1721 cm^{- 1} and 1733 cm^{- 1}, respectively; and

A₁₁, A₂₁ and A₃₁ were optical absorbances of the irradiated specimens at the above wave numbers in the above-stated order.

The specified values adopted for the above mentioned coefficients were 0.267 as to K₁, 0.661 for K₂ and 0.868 for K₃ which were previously given in J. Polymer Sci., 13, 535(1954).

The calculated V_o values are listed in Table 1.

                                  Table 1__________________________________________________________________________            Content of            chlorinated     Solvent used            carbonylChlorinated     for the pre-            compound in                    Oxidationcarbonyl  paration of            the solution                    ratecompound  the solution            (% by volume)                    Vo × 102                          Remark__________________________________________________________________________Acetyl chloride     Acetone            10      5.5Trichloroacetylchloride  Acetone            10      6.2Symmetricaldichloroacetone     Acetone            10      5.2Hexachloroacetone     None   100     17Hexachloroacetone     Acetone            10      19Hexachloroacetone     Methyl vinyl            50      17     ketoneHexachloroacetone     Ether  10      20Chloranil Acetone            10      8.6None was sprayed --      1.0   ReferenceNone was added     Acetone             0      3.0   Reference__________________________________________________________________________

EXAMPLE 2

Into specimens of a film of plasticized polyvinyl chloride of 0.10 mm in thickness for agricultural use there are impregnated a brominated carbonyl compound by coating thereon an acetone solution containing 10 % by volume of the compound until the specimens increased by 10 % in their weight. The compounds tested are listed in Table 2. The specimens were irradiated under the same conditions as in Example 1. Thereafter the specimens were extracted and dried for the measurement of the IR-absorptions of the specimens in the same way as in Example 1, and the calculation of the oxidation rate was also carried out in the same manner as in Example 1. The results are listed in Table 2.

              Table 2______________________________________             Oxidation rateBrominated carbonyl compound             Vo × 102                         Remark______________________________________Acetyl bromide    11.7Bromacetophenone  12.8Monobromacetyl bromide             12.9None was sprayed  1.0         ReferenceOnly acetone containing nosolute was sprayed             3.0         Reference______________________________________

EXAMPLE 3

Specimens of a film of plasticized polyvinyl chloride of 0.10 mm in thickness for agricultural use were dipped into a liquid or a solution in acetone of a halogenated carbonyl compound identified in Table 3. The immersion was continued for 30 seconds. The specimens were then irradiated under the same conditions as in Example 1. The IR-absorptions of the specimens were measured after the specimens were extracted with ether and dried in the same manner as in Example 1, for the calculation of the oxidation rate. The calculation results obtained in the same way as in Example 1 are listed in Table 3.

                                  Table 3__________________________________________________________________________            Mixing ratio            of the halo-     Solvent used            genated car-Halogenated     for the pre-            bonyl comp-                   Oxidationcarbonyl  paration of            ound to the                   ratecompound  the solution            solvent                   Vo × 102                         Remark__________________________________________________________________________Hexachloroacetone     None          13.8Acetylchloride     Acetone            10:90  20.8Acetylbromide     Acetone            10:90  6.39Monochloroacetone     Acetone            10:90  15.5Symmetricaldichloroacetone     Acetone            10:90  20.8Hexachloroacetone     Acetone            10:90  34.2No immersion was carried out                   0.72  ReferenceNone      Acetone            --     3.03  Reference__________________________________________________________________________

EXAMPLE 4

Specimens of a variety of non-chlorinated polymer films were impregnated with a 10 volume percent solution of hexachloroacetone acetone until the specimens increased by 10 % in their weight. These specimens were irradiated with ultraviolet radiation under the same conditions as in Example 1. The IR-absorptions of the specimens were measured after the specimens were extracted with ether and dried, for the calculation of the oxidation rate. The procedures were repeated except that no impregnation of hexachloroacetone was carried out for the comparison. The calculation results are listed in Table 4.

                                  Table 4__________________________________________________________________________               Oxidation rate                       Oxidation rate         Thickness               when hexachlo-                       when hexachlo-         of the               roacetone was                       roacetone wasRaw material for         film  impregnated                       not impregnatedthe film      (m.m.)               V0 × 102                       Vo × 102__________________________________________________________________________Polyethylene  0.20  1.49    0.98Blended mixture of poly-ethylene with chlorinated         0.20  7.63    3.14polyethylene*Polystyrene   0.20  17.9    0.00Blended mixture of poly-styrene with chlorinated         0.20  26.0    2.38polyethylene*Polypropylene 0.15  2.80    0.37Blended mixture of poly-propylene with chlori-         0.15  3.24    0.94nated polyethylene*__________________________________________________________________________ Note: *The chlorinated polyethylene was prepared by chlorinating polyethylene to the extent that 40% of hydrogen atoms of the polyethylene were substituted with chlorine atoms and the content of the chlorinated polyethylene in the mixture was 10% by weight based on the weight of the mixture.

EXAMPLE 5

The influences of the blending of a chlorinated polymer on the oxidation rate of polyethylene were studied in relation to the blending amount of the first polymer to the second polymer. Polyethylene of 0.920 g./cc. in density and chlorinated polyethylene prepared by chlorinating polyethylene to the extent that 40 % of hydrogen atoms of the polyethylene were replaced with chlorine atoms, were used as the above first and second polymers, respectively. A solution of 10 % by volume of hexachloracetone in acetone was admixed to the polymers during the blending thereof. The added amount of the solution was 10 % by weight based on the total amount of the polymers. The irradiation and the following extraction as well as the measurement and the calculation were carried out under the same conditions and in the same way as in Example 1. The procedures were repeated as to the blended polymers which, however, did not contain hexachloracetone, for purposes of comparison. The results are shown in Table 5.

              Table 5______________________________________Content of the chlorinatedpolyethylene in per cent            0      5      10   20   30by weight based on the weightof the blended polymerOxidation rate (Vo × 102)            17.9   22.0   26.0 36.0 43.0Oxidation rate (Vo × 102)(In case of excludinghexachloracetone)             0.0    1.5    2.4  4.7  7.0______________________________________

EXAMPLE 6

Example 4 was repeated except that there were used several different kinds of halogenated carbonyl compounds in place of the hexachloroacetone and also employing a common thicknesses of the polymer films instead of two different thicknesses thereof. The results are shown in Table 6.

              Table 6______________________________________                            Oxidation rate     Oxidation rate         when the     when the halo-                  Halo-     halogenated     genated carbonyl                  genated   carbonyl     compound was not                  carbonyl  compound wasRaw material     applied      compound  appliedfor the film     Vo × 102                  applied   Vo × 102______________________________________Polyethylene     0.98         Benzoyl   1.86                  bromideBlended mixture        Phenacyl  6.65of polyethylene        bromidewith chlorinated     3.14polyethylene*          Acetyl    4.31                  iodidePolystyrene     0.00         Benzoyl   18.8                  bromideBlended mixture        Bromoacet-                            14.5of polystyrene     2.38         yl bromidewith chlorinated       Phenacyl  18.3polyethylene*          bromide______________________________________ Note: *The chlorinated polyethylene was prepared by chlorinating polyethylene to the extent that 40% of hydrogen atoms of the polyethylene were substituted with chlorine atoms and the content of the chlorinated polyethylene in the mixture was 10% by weight based on the weight of the mixture.

EXAMPLE 7

Specimens of a film of plasticized polyvinyl chloride of 0.10 mm in thickness for agricultural use were dipped into a 5 % by volume solution of hexachloroacetone in acetone for 30 seconds. Then, the specimens were exposed in the outdoors to sunlight for 8 days in the summer time (from Aug. 17, 1972 to Aug. 24, 1972). At the same time the specimens which had not been dipped were also exposed in parallel with the exposure of the dipped specimens. Changes in the average molecular weight of the polymer were determined according to the viscosity method of ASTM D-1243 except for using nitrobenzene as the solvent in place of cyclohexanone. The exposure time to the sunlight was assumed to be 12 hours each day. The results are shown in Table 7.

              Table 7______________________________________      Average molecular weight                     Specimen dipped                     into the hexa-Exposure time        Specimen     chloroacetone(hours)      not dipped   solution______________________________________ 0           1050         1060 4           1020         90028           1060         55064           1040         54088           1070         580______________________________________

EXAMPLE 8

The specimens both dipped and not dipped were prepared in the same way as in Example 7. Both series of the specimens were exposed to the irradiation of Xenon light in a weatherometer (Xenon weathering tester Model 25 XH made by Toyo Seiki Co., Japan) without spraying. In the course of the exposure, the tensile strengths of the specimens as well as the elongations thereof were measured on the test pieces of Dumbbell No. 1 prepared from the specimens using an Instron-type instrument made by Shimazu, Japan, under the conditions of an extension rate of 50 mm/min. and at a temperature of 23° C. The results are shown in Table 8.

              Table 8______________________________________Exposure timein theweatherometer (hour)         0      5      10   15   20   30______________________________________Specimendipped Tensile    233    219  203  158  123  --***into   strength*the hexa-chloro-  Elongation**             293    196   94   0    0   --***acetonesolution  Tensile    271    311  286  289  303  292Specimen  strength*notdipped Elongation**             230    240  236  227  225  232______________________________________ Notes: unit is K.g./cm. **The unit is %. ***The measurement can not be effected since the specimen was self-destructed.