JPH11152371A - Method for recycling aromatic polycarbonate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an arom. polycarbonate with an increased mol.wt. without causing the degradation by dissolving a solid amorphous arom. precursor polycarbonate in a chlorinated hydrocarbon, removing insoluble matters from the soln., and adding thereto an org. nonsolvent to precipitate a solid purified polycarbonate. SOLUTION: The solid amorphous arom. precursor polycarbonate comprising structural units represented by the formula (wherein at least about 60% of R groups are org. arom. groups and the rest are aliph., alicyclic, or arom.) and having a wt. average mol.wt. of 5,000-300,000 is dissolved in a chlorinated hydrocarbon as the solvent at a temp. of 20-100 deg.C to give an amorphous polycarbonate soln. The soln. is subjected to decantation, filtration, or centrifuge to be freed of insoluble matters and is treated with an alkanol soln. of a mineral acid to be decolored. Then, an org. solvent selected from among aliph. hydrocarbons, arom. hydrocarbons, hydroxyaliph. compds., aliph. ketones, and carboxylic esters is added to the soln. to precipitated a solid purified polycarbonate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the recycling and reuse of aromatic polycarbonate.

[0002]

BACKGROUND OF THE INVENTION Plastic recycling has become increasingly important as environmental concerns have increased. further,
Recycling has the potential to be more economical than discarding used polymer and synthesizing a new polymer. Aromatic polycarbonates are used extensively in various areas. Among these are the manufacture of transparent sheet materials, which are used in the manufacture of glass substitutes as well as optical discs used for data transmission.

[0003] Various methods are known for recycling polycarbonate. However, most, if not all, involve a chemical reaction that optimally degrades polycarbonate to monomeric bisphenol, and such monomeric bisphenols can be purified and reconverted to polycarbonate. it can. It would be more convenient if the polycarbonate could be recycled by simple refining means, and it could be much cheaper than converting it to monomer and repolymerizing it. In addition, it is desirable to increase the molecular weight during recycling, as some molecular weight degradation may occur during use. Such a recycling operation is useful not only for the finally used polycarbonate but also for the polycarbonate recovered as a drip from an extruder or the like.

[0004]

SUMMARY OF THE INVENTION The present invention provides a recycling method that can be used for the applications described above. The present invention provides a simple recycling process that does not substantially decompose and, if necessary, involves increasing the molecular weight.

[0005]

The present invention relates to a method for recycling an aromatic polycarbonate, which comprises dissolving a solid amorphous aromatic precursor polycarbonate in a chlorinated hydrocarbon as a solvent in the following step (A). Forming an amorphous polycarbonate solution, (B) removing insoluble materials from the amorphous polycarbonate solution, and (C) precipitating solid purified polycarbonate from the amorphous polycarbonate solution by adding an organic non-solvent thereto. A method comprising:

[0006]

DETAILED DESCRIPTION OF THE INVENTION The precursor polycarbonates recyclable by the process of the present invention typically comprise structural units of the formula:

[0007]

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In the formula, about 60% or more of the R groups are aromatic organic groups, and the rest are aliphatic, cycloaliphatic or aromatic groups. Preferably each R is an aromatic group, more preferably a group of the formula:

[0009]

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In the formula, each of A ¹ and A ² is a monocyclic divalent aryl group, and Y is a bridging group separating A ¹ and A ² by one or two carbon atoms. Such residues are derived from dihydroxyaromatic compounds of the respective formulas HO-R-OH and ^{HO-A 1 -Y-A 2} -OH. For example, A ¹ and A ² generally represent unsubstituted phenylene (preferably p-phenylene) or a substituted derivative thereof. The bridging group Y is mostly a hydrocarbon group, especially a saturated group such as methylene, cyclohexylidene or isopropylidene, which is preferred. For example, the most preferred polycarbonate is 2,2-bis (4-, also known as "bisphenol A".
(Hydroxyphenyl) propane.

The precursor polycarbonate may be a homopolycarbonate or a copolycarbonate. For the purposes of the present invention, copolycarbonates include copolyestercarbonates. Such copolyestercarbonates are copolymers well known to those skilled in the art and include carbonate units and ester units derived from, for example, isophthalic acid or terephthalic acid.

The precursor polycarbonate may be a single article or multiple articles, such as an optical disc or a piece of polycarbonate sheet material. This may be a waste material such as an extruder drip or solid waste. The only requirement is that it be solid, amorphous and have a molecular weight typical of a polymer. Exemplary weight average molecular weights (measured by gel permeation chromatography) range from about 5000 to 300,000.

In step (A) of the process of the present invention, the precursor polycarbonate is dissolved in a chlorinated hydrocarbon as a solvent. Exemplary 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.

The dissolution of the precursor polycarbonate in the solvent can be performed at any temperature. Typical temperatures are from about 0 ° C to the boiling point of the solvent, with about 20-100 ° C being generally preferred. The proportion is not critical as long as an effective amount of solvent is used to dissolve the polycarbonate. Dissolution of the precursor polycarbonate typically leaves behind various insoluble materials. For example, metal coating when the precursor polycarbonate is from an optical disc. In step (B),
Such insoluble materials are removed from the polycarbonate solution. This can be done with conventional operations such as decantation, filtration and centrifugation.

[0015] Precursor polycarbonates are often accompanied by colored impurities, which appear in the polycarbonate itself or in its solution in a chlorinated solvent. Accordingly, various embodiments of the present invention further include the step of removing color from the amorphous polycarbonate solution following step (B). One way to remove color is to treat in solution with a mineral acid, preferably hydrochloric acid, which is usually in solution in an alkanol such as methanol.
Another method is to contact the polycarbonate solution with a solid that adsorbs the colored body, such as activated carbon or a crosslinked resin, and the crosslinked resin may be neutral or an ion exchange resin. Another decolorization method is to precipitate the resin as described below, and then wash it with a sufficient amount of a non-solvent to dissolve the colorant.

[0016] Many of the commercially used polycarbonates are end-capped with monohydroxyaromatics such as phenol and p-cumylphenol. The presence of such an endcapping agent can hinder solid-state polymerization.
Therefore, it is often preferred during the dissolution step to add one or more dihydroxy aromatic or dihydroxy aliphatic compounds as modifiers to generate the hydroxy end groups. Suitable compounds include resorcinol, hydroquinone, catechol, bisphenol, ethylene glycol, propylene glycol, pentaerythritol, glycerol, glyceryl monopalmitate and glyceryl monostearate, with catechol and bisphenol A often being preferred.

The proportion of modifier is generally such that it is effective to convert the amorphous polycarbonate in solution to a material having at least about 20-80% (by number), preferably 40-60%, hydroxy end groups of hydroxy end groups. It is. Suitable ratios can be determined by simple experiments. Stage (C)
Here, purified polycarbonate is precipitated from an amorphous polycarbonate solution by adding an organic non-solvent thereto. Suitable non-solvents include aliphatic hydrocarbons such as n-hexane, n-heptane and petroleum ether; aromatic hydrocarbons such as toluene and xylene; methanol;
There are hydroxy aliphatic compounds such as ethanol, ethylene glycol and diethylene glycol; aliphatic ketones such as acetone and methyl ethyl ketone; and carboxylic esters such as ethyl acetate and n-butyl acetate. Upon addition of a non-solvent to the polycarbonate solution, the polycarbonate precipitates and can be separated by filtration or any of the separation techniques described above. If removal of the colored bodies by washing after precipitation, any of the non-solvents mentioned above for use in the precipitation stage may be used.

In many cases, especially when the solid phase polymerization is to be carried out later, it is preferred to use a non-solvent which will produce a crystalline polycarbonate. The presence of crystallinity can be detected by treatment under conditions that give a polycarbonate film, with a cloudy film indicating some degree of crystallinity in the polycarbonate. Non-solvents that produce crystallinity in combination with, for example, 1,2-dichloroethane include alkyl carboxylate esters such as ethyl acetate.

When it is desired that the purified polycarbonate have improved crystallinity, it may be about 10-30%, especially about 1%.
A crystallinity of 0-20% is generally preferred. Crystallinity values above about 30% are generally not preferred when performing solid state polymerization. This is because polymerization is very slow at such a high crystallinity. The crystallinity can be determined by powder X-ray diffraction, for example, as described in US Pat. An amorphous polymer and a crystallized polymer may be compared. The disclosures of the aforementioned U.S. patents and the drawings are hereby incorporated by reference.

The degree of crystallinity in the purified polycarbonate depends somewhat on the type of solvent and non-solvent used. More specifically, certain classes of non-solvents impart crystallinity when used in conjunction with certain solvents, but may not with other solvents. For example, when 1,2-dichloroethane is used as a solvent, ethyl acetate is particularly effective as a non-solvent for increasing crystallinity. Suitable non-solvent types for such purposes and for use with other suitable solvents can be determined by simple experimentation.

The purified polycarbonate obtained by the method of the present invention is about 0.35-0.
Most often it has an intrinsic viscosity in the range of 45 dl / g. If higher intrinsic viscosity products are desired, the purified polycarbonate may be subjected to solid state polymerization.
Solid state polymerization may be carried out at a temperature in the range from the glass transition temperature to the melting temperature of the crystalline purified polycarbonate, often at a temperature about 10 to 50 ° C below the melting temperature. Generally, temperatures in the range of about 150-270 ° C, especially about 180-250 ° C, are preferred. U.S. Pat. No. 4,948,971
Nos. 5,204,377 and 5,266,659 and US patent application Ser. No. 08 / 78,774 filed by the present applicant.
As disclosed in US Pat. No. 0, the disclosure of which is incorporated herein by reference, the solid state polymerization step may be carried out with or without a catalyst. Suitable catalysts include basic salts, transition metal oxides and alkoxides, quaternary ammonium bioxyanion salts and tetraalkyl ammonium and tetraalkyl phosphonium carboxylate. The proportion of catalyst is usually about 10 to 200 ppm based on the purified polycarbonate.

Solid state polymerization is an inert gas such as nitrogen or argon (a fluidized bed if a fluidized bed is used) in a mixer capable of producing homogeneous gas-solid contact, such as a fixed bed, fluidized bed or paddle mixer. (Serving as a gas). These inert gases can serve either or both to fluidize the mixture and to volatilize and remove volatile by-products (such as water and volatile carbonates). Programmed heating can be used to advantage. As an alternative to a homogeneous gas-solid contact, the polymerization can also be carried out under reduced pressure (typically less than about 100 torr), preferably with efficient stirring.

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

[0024]

EXAMPLE 1 A 100 g sample of bisphenol A polycarbonate recovered from an extruder drip was dissolved in 700 ml of 1,2-dichloroethane at 80 DEG C. with vigorous stirring. The solution was centrifuged to remove solid residues and discarded. Ethyl acetate was added to the polycarbonate solution to precipitate the polycarbonate as a crystalline solid, and the precipitate was separated, washed with ethyl acetate until it became colorless, and dried in vacuo at 80 ° C. This product has an intrinsic viscosity of 0.43 dl / g and a glass transition temperature of 14
The melting point was 3 ° C., the melting temperature was 226 ° C., and the crystallinity was 30%.

Example 2 A 10 g sample of a polycarbonate-containing crushed and regenerated material from an optical disk was treated with 100 m of 1,2-dichloroethane at 80 ° C.
and dissolved with vigorous stirring. The solution was filtered and purified polycarbonate was precipitated from the filtrate by adding methanol. The precipitated polycarbonate was separated by filtration, washed twice with methanol, and dried in vacuum at 80 ° C. The recycled polycarbonate thus obtained has an intrinsic viscosity of 0.36 dl / g, a glass transition temperature of 143 ° C.,
The melting temperature was 223 ° C. and the crystallinity was 24%.

Example 3 A recovered polycarbonate sample 10 similar to the sample of Example 1
g of catechol 10 dissolved in 100 ml of ethyl acetate.
0mg and 1mg of tetramethylammonium maleate
Was added. The mixture is heated under reflux conditions for 2 hours, after which the ethyl acetate is removed by distillation and the material is brought to 80 ° C.
And dried. The obtained crystallized polycarbonate was placed in a fluidized bed reactor at 180 ° C. under a nitrogen stream of 3 liter / min.
Heat at 210 ° C. for 2 hours and 230 ° C. for 4 hours. The obtained polycarbonate had an intrinsic viscosity of 0.76 dl.
/ G, glass transition temperature 156 ° C, melting temperature 264 ° C, and crystallinity 34%.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification symbol FI C08J 11/22 C08L 69/00 C08L 69/00 B09B 3/00 304P // B29K 69:00 105: 26 (72) Inventor Joseph・ Anthony King, Jr. United States, New York, Schenectady, Blue Man Avenue, No. 927 (72) Inventor Basker Barrabunas India, 411027, Poon, Sangavi, Dorenagar, 320/23 (72) Invention Swaminathan Shivaram India, 411008, Poon, N.C. Colony, C.L./2 (72) Inventor Vishnu Ramchandra Ranade India, 411008, Poon, N.C. Colony, C.L / 2

Claims (12)

[Claims] 1. A method for recycling an aromatic polycarbonate, comprising the following step (A): dissolving a solid amorphous aromatic precursor polycarbonate in a chlorinated hydrocarbon as a solvent to form an amorphous polycarbonate solution. A method comprising: (B) removing insoluble materials from said amorphous polycarbonate solution; and (C) precipitating solid purified polycarbonate from said amorphous polycarbonate solution by adding an organic non-solvent thereto. 2. The method according to claim 1, wherein the precursor polycarbonate is a homopolycarbonate or a copolycarbonate, especially a copolyestercarbonate. 3. The method of claim 1, wherein said step (A) is performed at a temperature in the range of about 20-100 ° C. 4. The method of claim 3, wherein said step (B) comprises decanting, filtering or centrifuging. 5. The method of claim 3, further comprising the step of removing color from said amorphous polycarbonate solution following said step (B). 6. The process according to claim 5, wherein the color is removed by treating the solution as is with a mineral acid or by contact with a solid which adsorbs the colored body. 7. The method of claim 6, wherein said mineral acid is hydrochloric acid in a solution in an alkanol and said solid is activated carbon or a crosslinked resin. 8. The method of claim 2, wherein step (A) is performed in the presence of one or more dihydroxy aromatic or dihydroxy aliphatic compounds as a modifier. 9. 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 ester. 10. The method of claim 9, wherein said non-solvent is an organic compound that when used in combination with said solvent results in a purified polycarbonate having a crystallinity of about 10% or greater. 11. The method of claim 10, wherein said non-solvent is a carboxylic acid alkyl ester. 12. The method of claim 10, further comprising the step of polymerizing said solid purified polycarbonate by solid state polymerization.