KR19990029426A - Recycling Method Of Aromatic Polycarbonate - Google Patents

Abstract

The present invention relates to a process for regenerating polycarbonate without the need for chemical modification by dissolving in solvent and then removing any insoluble matter and precipitating by addition of a non-solvent. After the precipitation step, solid phase polymerization of the regenerated polycarbonate is possible. Particularly if the solid phase polymerization is carried out, it may be advantageous to use a mixture of solvents and non-solvents which produce crystalline intermediates and to use modified reagents which increase the hydroxy end group concentration of the polycarbonate.

Description

Recycling Method Of Aromatic Polycarbonate

The present invention relates to the regeneration and reuse of aromatic polycarbonates.

Recycling of plastics is of increasing interest due to recent environmental concerns. There is also the potential for more economical regeneration than the disposal of the polymers used and the synthesis of new polymers replacing them.

Aromatic polycarbonates are widely used in large volume areas. Among them are the manufacture of transparent sheetings which can be used as glass substitutes and the manufacture of optical discs used for data transmission.

Several methods of recycling polycarbonates have been described. However, most of these do not include chemical reactions that break down polycarbonates into monomeric bisphenols that can be optimally purified and reconverted to polycarbonates.

It would be more convenient to regenerate polycarbonate by simple purification means, which is likely to be much cheaper than conversion to monomers and repolymerization. Moreover, it would be desirable to increase the molecular weight during regeneration because some molecular weight degradation occurs during use. This regeneration operation will be useful for both the polycarbonates used and the polycarbonates recovered as drips from extruders and the like.

It is an object of the present invention to provide a regeneration method that can be used for the uses described above. This aims to provide an easy regeneration method without substantial degradation associated with requiring an increase in molecular weight.

The present invention is a process for regenerating an aromatic polycarbonate comprising the following steps:

(A) dissolving a solid amorphous polycarbonate precursor as a solvent in a chlorinated hydrocarbon to form an amorphous polycarbonate solution,

(B) removing any insoluble material from the amorphous polycarbonate solution, and

(C) adding an organic non-solvent to precipitate the solid purified polycarbonate from the amorphous polycarbonate solution.

Polycarbonate precursors that can be regenerated by the process of the invention typically include structural units of formula

Where

At least about 60% of the total number of R groups are aromatic organic radicals and the rest are aliphatic, cycloaliphatic or aromatic radicals. Preferably each R is an aromatic organic radical, preferably a radical of formula (2):

-A ¹ -YA ^2-

Where

A ¹ and A ² are each monocyclic divalent aryl radicals,

Y is a bridging radical in which one or two carbon atoms divide A ¹ and A ² . These radicals are derived from dihydroxyaromatic compounds of the general formulas HO-R-OH and HO-A ¹ -YA ² -OH, respectively. For example, A ¹ and A ² generally represent unsubstituted phenylenes, particularly preferably p-phenylene or substituted derivatives thereof. The bridging radicals Y are usually hydrocarbon groups and particularly preferably saturated groups such as methylene, cyclohexylidene or isopropylidene. Thus, the most preferred polycarbonates are those derived in whole or in part from 2,2-bis (4-hydroxyphenyl) propane, also known as bisphenol A.

The polycarbonate precursor may be homopolycarbonate or copolycarbonate. For the purposes of the present invention, copolycarbonates include military copolycarbonate carbonates recognized in the art of copolymers comprising both carbonate units and ester units derived for example from isophthalic acid or terephthalic acid.

The polycarbonate precursor may be in the form of a plurality of products or an article such as an optical disc or part of a polycarbonate seating. It may also be waste material such as extruder drips or waste in solid form. The only requirement is that it is solid, amorphous and has the typical molecular weight of the polymer. Exemplary weight average molecular weights (as measured by gel permeation chromatography) range from about 5,000 to 300,000.

In step (A) of the present invention, the polycarbonate precursor is dissolved in chlorinated hydrocarbon as a solvent. Examples of chlorinated hydrocarbons are methylene chloride, chloroform, 1,2-dichloroethane, chlorobenzene and o-dichlorobenzene. Chloroaliphatic hydrocarbons are preferred, and methylene chloride and 1,2-dichloroethane are most preferred.

Dissolution of the polycarbonate precursor in the solvent can occur at any temperature. Typical temperatures are from about 0 ° C. to the boiling point of the solvent, generally from about 20 to 100 ° C. As long as the amount of solvent effective to dissolve the polycarbonate is used, the ratio thereof is not critical.

Dissolution of the polycarbonate precursor generally leaves several insoluble materials as exemplified by the metal coating, for example when the polycarbonate precursor emerges from the optical disk. In step (B), the insoluble material is removed from the polycarbonate solution. This can be done by conventional operations such as decantation, filtration and centrifugation.

Polycarbonate precursors can often be mixed with colored impurities that may appear in the polycarbonate itself or in a solution thereof in a chlorinated solvent. Accordingly, several embodiments of the present invention comprise removing color from the amorphous polycarbonate solution after step (B). One method of color evacuation is treatment in solution with an inorganic acid, preferably hydrochloric acid, wherein the acid is typically a solution in alkanols such as methanol. Another is contact of the color absorbing solid with the solution, such as activated carbon or crosslinked resin, which may be neutral or ion exchange resin. Another method of color evacuation is the washing of the resin with an amount of non-solvent sufficient to dissolve the color after precipitation, as described later herein.

Many commercially used polycarbonates are end capped with monohydroxyaromatic compounds such as phenol and p-cumylphenol. If present, such endcapping agents can inhibit solid phase polymerization. Therefore, it is often desirable to add one or more dihydroxyaromatic or dihydroxyaliphatic compounds as a modifying reagent to generate hydroxy end groups during the dissolution step. Suitable compounds include resorcinol, hydroquinone, catechol, bisphenol, ethylene glycol, propylene glycol, pentaerythritol, glycerol, glyceryl monopalmitate and glyceryl monostearate, where catechol and bisphenol A are often desirable.

The ratio of the reforming reagent is generally at least theoretically effective to convert the amorphous polycarbonate in solution to a material having about 20 to 80% (a sugar), preferably 40 to 60% of hydroxy end groups. . Suitable ratios can be measured by simple experiments.

In step (C), the purified polycarbonate is precipitated from the amorphous polycarbonate solution by the addition of an organic non-solvent therefor. Suitable non-solvents are aliphatic hydrocarbons such as n-hexane, n-heptane and petroleum ethers; Aromatic hydrocarbons such as toluene and xylene; Hydroxyaliphatic compounds such as methanol, ethanol, ethylene glycol and diethylene glycol; Aliphatic ketones such as acetone and methyl ethyl ketone; And carboxylic acid esters such as ethyl acetate and n-butyl acetate. Upon addition of the non-solvent to the polycarbonate solution, the polycarbonate may precipitate out and be separated by filtration or one of the other separation options described herein above. If the removal of the color by washing is carried out after precipitation, one of the same non-solvents proposed for use in the precipitation step can be used.

Particularly when solid phase polymerization is subsequently used, it is often desirable to use non-solvents that produce crystalline polycarbonates. The presence of crystallinity can be detected by treatment under conditions that provide a polycarbonate film; The cloudy membrane shows some degree of crystallinity in the polycarbonate. For example, there is an alkyl carboxylate ester such as ethyl acetate in the non-solvent that mixes with 1,2-dichloroethane to produce crystals.

If refined polycarbonates with improved crystallinity are desired, crystallinity in the range of about 10 to 30% and especially about 10 to 20% is generally preferred. Since the polymerization is very slow at these high crystallinity values of 30% or more, the value of the crystallinity of about 30% or more is generally undesirable. The ratio of crystallinity is determined by powder X-ray diffraction, for example, as compared to the complete amorphous polymer and the crystallized polymer described in US Pat. No. 4,948,871 with reference to the drawings which do not form part of the patent but which exist at the time of filing. Can be measured. The disclosure of this patent and the figures is hereby incorporated by reference.

The ratio of crystallinity in the purified polycarbonate may depend to some extent on the kind of solvent and non-solvent used. More specifically, certain groups of non-solvents can provide crystallinity when used with certain solvents rather than another solvent. For example, when 1,2-dichloroethane is used as a solvent, ethyl acetate is particularly effective as a crystallinity improving non-solvent. The kind of non-solvent suitable for this purpose and for use with other suitable solvents can be determined by simple experiments.

Purified polycarbonates obtained by the process of the invention usually have an intrinsic viscosity in the range of about 0.35 to 0.45 dl / g as measured in chloroform at 25 ° C. If a product with a higher intrinsic viscosity is desired, the purified polycarbonate can be solid phase polymerized.

Solid phase polymerization may be carried out at a glass transition temperature to a melting temperature of the crystalline purified polycarbonate, usually at a temperature of about 10 to 50 ° C. or less of its melting temperature. Generally temperatures in the range of about 150 to 270 ° C. and especially about 180 to 250 ° C. are suitable. The solid phase polymerization step can be in the absence or presence of a catalyst, as disclosed in US Pat. Nos. 4,948,971, 5,204,377 and 5,266,659, and co-pending and shared application 08 / 787,740, incorporated herein by reference. Suitable catalysts include basic salts, transition metal oxides and alkoxides, quaternary ammonium nonoxyanion salts and tetraalkylammonium and tetraalkylphosphonium carboxylates. The catalyst ratio is generally about 10 to 200 ppm based on the purified polycarbonate.

Solid phase polymerization is carried out in a mixer, for example a fixed bed, a fluidized bed or a paddle mixer, where the use of a fluidized bed can create intimate gas-solid contact with an inert gas such as nitrogen or argon, which acts as a fluidized gas. Can be. The inert gas may serve one or both of the purposes of flowing the mixture and removing volatile byproducts, including water and volatile carbonates formed. Programmed heating can advantageously be used. As a choice for the conditions of intimate gas-solid contact, the polymerization can be carried out under reduced pressure, typically less than about 100 torr, preferably with efficient mixing.

The method of the present invention is illustrated by the following examples. Intrinsic viscosity was measured in methylene chloride at 20 ° C.

Example 1

100 g of a sample of bisphenol A polycarbonate recovered from the extruder drip was dissolved in 700 ml of 1,2-dichloroethane at 80 ° C. with vigorous stirring. The solution was centrifuged and the solid residue was removed and discarded. Ethyl acetate was added to the polycarbonate solution to precipitate and separate the polycarbonate as a crystalline solid, washed with ethyl acetate until colorless and dried in vacuo at 80 ° C. The product had an intrinsic viscosity of 0.43 dl / g, a glass transition temperature of 143 ° C., a melting temperature of 226 ° C. and a crystallinity of 30%.

Example 2

10 g of a sample of polycarbonate-containing regrind material from the optical disc was dissolved in 100 ml of 1,2-dichloroethane at 80 ° C. with vigorous stirring. The solution was filtered and the purified polycarbonate was precipitated from the filtrate by the addition of methanol. The precipitated polycarbonate was separated by filtration, washed twice with methanol and vacuum dried at 80 ° C. The regenerated ethyl acetate thus obtained had an intrinsic viscosity of 0.36 dl / g, a glass transition temperature of 143 ° C, a melting temperature of 223 ° C and a crystallinity of 24%.

Example 3

10 g of a sample of recovered polycarbonate similar to the product of Example 1 is dissolved in 100 ml of ethyl acetate and 100 mg of catechol and 1 mg of tetramethylammonium maleate are added. The mixture is heated under reflux for 2 hours and then ethyl acetate is removed by distillation and the material is dried at 80 ° C. The resulting crystallized polycarbonate is heated in a fluidized bed reactor with a nitrogen flow of 3 l / min at 180 ° C. for 30 minutes, at 210 ° C. for 2 hours and at 230 ° C. for 4 hours. The resulting polycarbonate had an intrinsic viscosity of 0.76 dl / g, a glass transition temperature of 156 ° C., a melting temperature of 264 ° C. and a crystallinity of 34%.

According to the present invention, polycarbonate can be regenerated without chemical modification by dissolving in solvent and then removing any insoluble matter and precipitating by adding non-solvent.

Claims (12)

(A) dissolving a solid amorphous polycarbonate precursor as a solvent in a chlorinated hydrocarbon to form an amorphous polycarbonate solution, (B) removing any insoluble material from the amorphous polycarbonate solution, and (C) adding an organic non-solvent to precipitate the solid purified polycarbonate from the amorphous polycarbonate solution Regeneration method of aromatic polycarbonate. The method of claim 1, Wherein the polycarbonate precursor is homopolycarbonate, copolycarbonate, or copolycarbonate carbonate. The method of claim 1, Process (A) is carried out at a temperature in the range of about 20 to 100 ° C. The method of claim 3, wherein Step (B) comprises decantation, filtration or centrifugation. The method of claim 3, wherein And further removing the color from the amorphous polycarbonate solution after step (B). The method of claim 5, A method of removing color by treatment with an inorganic acid in solution or by contact with a solid absorbing color. The method of claim 6, The inorganic acid is a solution of hydrochloric acid in an alkanol and the solid is activated carbon or a crosslinked resin. The method of claim 2, The step (A) is carried out in the presence of at least one dihydroxyaromatic or dihydroxyaliphatic compound as a modifying reagent. The method of claim 3, wherein The non-solvent used in step (C) is an aliphatic hydrocarbon, an aromatic hydrocarbon, a hydroxyaliphatic compound, an aliphatic ketone or a carboxylic acid ester. The method of claim 9, Wherein the non-solvent is an organic compound that produces a purified polycarbonate having a crystallinity of at least about 10% when used in admixture with a solvent. The method of claim 10, Wherein the non-solvent is an alkyl carboxylate ester. The method of claim 10, And polymerizing the solid purified polycarbonate by solid phase polymerization.