EP0000904B1 - Recovery of high value polycarbonate from polycarbonate wastes - Google Patents

Description

The present invention relates to a process for the recovery of aromatic, high molecular weight, thermoplastic polycarbonates from polycarbonate waste, the polycarbonate waste being present both purely as a transparent natural material and also together with organic and in particular inorganic dyes and / or other additives or as an alloy in combination with other thermoplastic materials can.

Due to the progressive shortage of raw material resources and the resulting increases in raw material prices, processes for processing plastic consumables that are no longer usable are becoming increasingly important in terms of recovering either starting materials or directly the original plastic.

E. Bullack, for example, in the German patent documents GDR 45575, 46282, 45599, 45600 and 46353 describes processes for working up polycarbonates, in particular with a view to obtaining 4,4'-dioxy-diarylalkanes as starting substances for polycarbonate synthesis.

According to the patents GDR 45575, 46282 and 45599, the 4,4'-dioxy-diarylalkanes are cleaved by means of alcohols, acid anhydrides or small amounts of basic catalysts according to some. receive complex cleaning procedures. According to the patents 45600 and 46353, the cleavage is achieved by adding phenols or diaryl carbonates in the presence of metal oxide catalysts and temperatures above 180 ° C. At these temperatures, especially in the presence of metal oxide catalysts, there is a risk of side reactions, and extensive cleaning operations are necessary to obtain clean starting substances.

Surprisingly, it has been found that polycarbonates are saponified gently both in pure or colored form and as polymer alloys in a smooth one-pot reaction and, if appropriate after filtering off additives, dyes, etc. or alloy constituents, immediately afterwards in a smooth one-pot reaction in the same reaction media to high-molecular, thermoplastic and can dissolve soluble polycarbonates. Without the addition of later disruptive catalysts and under gentle thermal conditions, polycarbonates were thus cleaved and the reaction mixture remaining after the cleavage was directly converted back to polycarbonate synthesis using the phase interface process without any intermediate purification. After adding a water-immiscible solvent, commonly used in the phase interface condensation of polycarbonates, e.g. Methylene chloride or chlorobenzene can be condensed directly by introducing phosgene without any intermediate cleaning. The pH of the alkaline phase should be kept between 9 and 14 depending on the type of diphenol. Usually, before and especially after phosgenation, tertiary amines such as e.g. Triethylamine, tributylamine, N-alkylpiperidine or ammonium, sulfonium, phosphonium or arsonium compounds or nitrogen hetaryls such as pyridine are used.

The monohydric phenols present at the chain end in polycarbonates are found as cleavage products after the saponification step in the alkaline reaction medium and, during or after the phosgenation, are fully incorporated again as chain limiters, so that the resynthesized polycarbonates achieve the same solution viscosity as the polycarbonate wastes converted as starting material. If other solution viscosities are to be set, an additional amount of free bisphenol can be added for a desired higher solution viscosity and an additional amount of monohydric phenol can be added for a lower solution viscosity.

Also condensed compounds with more than two condensable functional groups such as e.g. Tris or tetraphenols, which are incorporated as branching agents in polycarbonates, are fully incorporated again in the resynthesis of the polycarbonates. A change in the branching concentration in the recovered polycarbonate is again possible by adding an additional amount of branching agent or free bisphenol to the reaction medium before the phosgenation.

The present invention thus relates to a process for the recovery of aromatic, high molecular weight, thermoplastic polycarbonates from polycarbonate waste by degradation and repolycondensation, which is characterized in that the polycarbonate waste in bulk or in solution at temperatures between 25 ° C and 220 ° C, if necessary, under Saponified under pressure, separated from unsaponifiable constituents and then the saponification mixture is phosgenized and polycondensed without further purification and workup steps using the methods of two-phase interfacial polycondensation.

Polycarbonate waste is understood to mean all polycarbonate plastic articles that are no longer usable, but also the residues, waste products, waste, etc. that are produced during the manufacture and deformation of the polycarbonate plastic.

• Hydrochinon
• Resorcin
• Dihydroxydiphenyle
• Bis-(hydroxyphenyl)-alkane
• Bis-(hydroxyphenyl)-cycloalkane
• Bis-(hydroxyphenyl)-sulfide
• Bis-(hydroxyphenyl)-äther
• Bis-(hydroxyphenyi)-ketone
• Bis-(hydroxyphenyl)-sulfoxide
• Bis-(hydroxyphenyl)-sulfone
• (x,a' - Bis - (hydroxyphenyl) - diisopropylbenzole

sowie beispielsweise deren kernhalogenierte Verbindungen. Diese und weitere geeignete Diphenole sind z.B. in der US-Patentschrift 3 028 365, und in der Monographie "H. Schnell, Chemistry and Physics of Polycarbonates, Interscience Publishers, New York, 1964" beschrieben.The poly suitable for processing Carbonate waste results from aromatic homopolycarbonates and copolycarbonates, which are based, for example, on one or more of the following diphenols:

• Hydroquinone
• Resorcinol
• Dihydroxydiphenyls
• Bis (hydroxyphenyl) alkanes
• Bis (hydroxyphenyl) cycloalkanes
• Bis (hydroxyphenyl) sulfides
• Bis (hydroxyphenyl) ether
• Bis (hydroxyphenyi) ketones
• Bis (hydroxyphenyl) sulfoxides
• Bis (hydroxyphenyl) sulfones
• (x, a '- bis - (hydroxyphenyl) diisopropylbenzenes

as well as, for example, their nuclear halogenated compounds. These and other suitable diphenols are described, for example, in US Pat. No. 3,028,365 and in the monograph "H. Schnell, Chemistry and Physics of Polycarbonates, Interscience Publishers, New York, 1964".

• 4,4'-Dihydroxydiphenyl
• 2,2 - Bis - (4 - hydroxyphenyl) - propan (Bisphenol - A)
• 2,4-Bis-(4-hydroxyphenyi)-2-methytbutan
• 1,1-Bis-(4-hydroxyphenyl)-cyclohexan
• α,α'-Bis-(4-hydroxyphenyl)-p-düsopropylbenzol
• 2,2-Bis-(3-chlor-4-hydroxyphenyl)-propan
• 2,2-Bis-(3,5-dichlor-4-hydroxyphenyl)-prcpan
• 2,2-Bis-(3,5-dibrom-4-hydroxyphenyl)-propan.

Preferred diphenols are, for example:

• 4,4'-dihydroxydiphenyl
• 2,2 - bis - (4-hydroxyphenyl) propane (bisphenol - A)
• 2,4-bis (4-hydroxyphenyi) -2-methytbutane
• 1,1-bis (4-hydroxyphenyl) cyclohexane
• α, α'-bis (4-hydroxyphenyl) -p-diisopropylbenzene
• 2,2-bis (3-chloro-4-hydroxyphenyl) propane
• 2,2-bis (3,5-dichloro-4-hydroxyphenyl) propane
• 2,2-bis (3,5-dibromo-4-hydroxyphenyl) propane.

The aromatic polycarbonates which can be worked up as polycarbonate wastes can also be incorporated by incorporating small amounts, preferably amounts between 0.05 and 2.0 mol% (based on diphenols used), of three- or more than three-functional compounds, in particular those with three or more than three phenolic hydroxyl groups, for example by the incorporation of phloroglucin, 1,3,5-tri- (4-hydroxyphenyl) benzene, 1,1,1-tri- (4-hydroxyphenyl) -ethane or 1,4-bis (4,4'-dihydroxytriphenylmethyl) benzene.

The aromatic polycarbonates which can be worked up as polycarbonate wastes generally have average weight-average molecular weights Mw of 10,000 to more than 200,000, preferably 20,000 to 80,000, determined by measuring the rel. Viscosity in CH _Z CI _Z at 25 ° C and a concentration of 0.5% by weight.

The molecular weights of the polycarbonates can be regulated in a conventional manner, for example by incorporating phenol, tribromophenol or p-tert-butylphenol.

The polycarbonates that can be processed as polycarbonate waste can also be present as mixtures of different polycarbonates, for example mixed with fractions of low molecular weight polycarbonates, or also as polymer alloys, for example with polymers or copolymers based on styrene, styrene-acrylonitrile, acrylonitrile-butadiene-styrene or butadiene rubber.

The polycarbonate waste is saponified in bulk or in solution, the solvents used being the customary solvents, such as methylene chloride or chlorobenzene, which are suitable for polycarbonate production by the two-phase interface process.

The saponification takes place in an alkaline aqueous reaction medium, the saponification in substance being heterogeneous and the saponification in solution taking place at the interface of the two-phase system, the latter proceeding more cheaply and more rapidly. With regard to the aqueous reaction medium, preferably between 25 and 100 moles of water per mole of polycarbonate structural unit to be saponified are used.

AI bass saponification agents serve e.g. Sodium hydroxide, potassium hydroxide, calcium oxide, preferably sodium hydroxide.

The saponification takes place at temperatures between 25 ° and 220 ° C and, if appropriate, using excess pressure up to preferably 100 atmospheres.

The amount of basic saponification agents is between 0.01 and 15 times the molar amount, based on the moles of aromatic dihydroxy compound formed; the pH of the saponification medium is between 9 and 14; the duration of saponification, depending on the steric shielding of the carbonate structure, between 0.5 and rnax. 20 hours.

Phosphites or phosphines can also be added as catalysts.

Do the polycarbonate wastes contain unsaponifiable components such as lubricants, stabilizers, pigments, dyes, fillers such as glass powder, quartz products, graphite, molybdenum sulfide, metal powder, powder of high-melting plastics such as polytetraethylene powder, natural fibers such as asbestos, and also glass fibers of various types, metal threads etc. after filtration, these are separated in a known manner, for example by filtration.

The one- or two-phase solutions resulting from the saponification of the polycarbonate wastes can be used directly for the polycarbonate production according to the interfacial process, optionally adding the customary polycarbonate solvents such as methylene chloride or chlorobenzene and the pH of the aqueous solution between 9 and 14 is set.

The subsequent phosgenation is usually carried out at room temperature, a phosgene amount of 1 to 3 moles, based on 1 mole of diphenol, preferably being used.

The duration of phosgenation is a maximum of 1 hour.

Tertiary amines or other polycondensation catalysts are used in amounts between 0.01 and 10 mol%, based on the moles of diphenols, before or in particular after Phosgenation added.

The polycondensation then takes place in the usual manner at temperatures between 20 ° and 40 ° C and, depending on the diphenol used, is complete after a period of 1-5 hours.

The polycarbonate solutions obtained are worked up as usual and the Polycar _- carbonate in the usual way isolated.

EXAMPLE 1

25.4 g of polycarbonate from 2,2-bis (4-hydroxyphenyl) propane with a solution viscosity of η _rel = 1.288 (measured on solutions of 0.5 g of polycarbonate in 100 ml of methylene chloride) are granulated in 80 ml of 15 ml Given sodium hydroxide solution. The reaction mixture is heated to 100 ° C. for 4 hours. During this time, the polycarbonate is completely cleaved down to the bisphenol A monomer unit. If 500 ml of dist. Water to the resulting suspension, so you get a clear alkaline solution of bisphenol A, which can be phosgenated after the addition of 500 ml of methylene chloride by the usual methods of phase interface condensation.

For this purpose, 15 g of phosgene are introduced in 1 hour at 25 ° C., with a pH of 13-14, and then, after addition of 1.5 ml of a 4,96 aqueous triethylamine solution, condensation is continued for 1 hour. The organic phase is separated, twice with 2 96% phosphoric acid and then with dist. Washed water free of electrolyte. After evaporation of the solvent, 24 g of polycarbonate with an η _rel = 1.295 are obtained. The recycled polycarbonate shows the same good mechan. and rheological properties like the starting material.

EXAMPLE 2

25.4 g of polycarbonate from 2,2-bis (4-hydroxyphenyl) propane from Example 1 are added in granular form in 30 ml of 15N sodium hydroxide solution. In addition, 2.5 g (10% by weight) of triphenyl phosphite are added and then saponified according to Example 1 at 100 ° C. By adding the phosphite, the time to complete saponification is reduced to 2 hours 45 minutes. Thereafter, analogous to Example 1, is phosgenated in the phase interface. The recovered polycarbonate has a solution viscosity of η _rel = 1.297 and shows no difference in mechanical and rheological properties from the starting material after precipitation from the methylene chloride solution using methanol.

EXAMPLE 3

25.4 g of polycarbonate from 2,2-bis (4-hydroxyphenyl) propane according to Example 1 are dissolved in 300 ml of chlorobenzene and 80 ml of 15N sodium hydroxide solution are added as an alkaline phase. The mixture was brought to 100 ° C. and the organic phase was checked at short intervals for the content of unsaponified polycarbonate. The cleavage was complete after only 60 minutes and the phase boundary mixture could be phosgenated and worked up analogously to Example 1 directly after adding 350 ml of water. 23.5 g of a polycarbonate having an η _rel bon 1.315 and a property profile similar to that of the starting material are obtained.

By adding 450 mg of p-tert-butylphenol as an additional chain terminator to the saponification mixture, the solution viscosity of η _rel = 1.282 can be adjusted after phosgenation and condensation.

EXAMPLE 4

The duration of saponification and the amount of base used are directly related. As the table below shows, the amount of caustic soda used can be reduced at the cost of extended saponification times. The saponification was carried out in the interface: 25.4 g of polycarbonate from Example 1 were dissolved in 300 ml of chlorobenzene and mixed with 15 N sodium hydroxide solution. The time until the polycarbonate was completely hydrolyzed was measured:

EXAMPLE 5

The saponification can also be carried out under pressure. 101.6 g of polycarbonate from Example 1, 400 ml of dist. Water and 2.26 g of 45% sodium hydroxide solution are heated in an autoclave to 210 ° C. at 50 bar pressure in 1 hour and held there for 2 hours. 840 g of 6.2% sodium hydroxide solution and 1500 ml of methylene chloride are added to the resulting mixture. While maintaining a pH of 13-14, 60 g of phosgene are introduced in 1 h and then condensed for 1 h after the addition of 6 ml of 4% aqueous triethylamine. The reaction mixture is worked up according to Example 1. Since small amounts of monofunctional monomers are presumably split off during pressure saponification, the solution viscosity of the resulting polycar is bonats η _rel = 1.212. By adding 19 g. Bisphenol A for the saponification mixture and a corresponding increase in the proportions of phosgene and triethylamine, a polycarbonate of the desired η _rel = 1.287 can be obtained.

EXAMPLE 6

27.9 g of a polycarbonate based on bisphenol A (η _rel = 1.305) with 10% by weight of glass fiber are mixed with 80 ml of 15N sodium hydroxide solution and the mixture is heated to 100.degree. The saponification is complete after 3 hours. 500 ml of dist. H ₂ 0 to the saponification mixture and the remaining glass fiber is filtered off. The filtrate is mixed with 500 ml of methylene chloride and treated analogously to Example 1 with 15 g of phosgene and 1.5 ml of a 4% aq. Triethylamine solution condensed. After working up according to Example 1, 10 g of a glass fiber-free polycarbonate η _rel = 1.317 are obtained. The polycarbonate shows the same property profile as a polycarbonate of corresponding chain length, which was obtained by the usual condensation of bisphenol A and phosgene using the phase interface process.

EXAMPLE 7

25.4 g of a polycarbonate based on bisphenol A with a solution viscosity of _rel . contains methyl) -benzene, is mixed with 80 ml of 15N sodium hydroxide solution and kept at 100 ° C for 3 hours. Then 500 ml of dist. Add H20 to a clear solution and then 500 ml of methylene chloride. 15 g of phosgene are added to the saponification mixture analogously to Example 1 and condensed with 1.5 ml of 4% strength aqueous triethylamine solution. According to the usual work-up methods, a polycarbonate with a solution viscosity of η _rel = 1.375 is obtained which, after cleavage and chromatographic examination of the monomer components, contains 0.2 mol% of a tetrafunctional branching agent.

EXAMPLE 8

36.3 g of a polymer alloy, which is composed of 30% by weight of an ABS polymer and 70% of a polycarbonate based on bisphenol A (η _rel . 1,292), are mixed with 120 ml of 15N sodium hydroxide solution at 100 ° C. for 10 hours treated. Then you fill with 500 ml of dist. H ₂ 0 and the undissolved ABS polymer is filtered off. Then 500 ml of methylene chloride are added to the filtrate, 11 g of phosgene are passed in at room temperature in 1 hour and, after addition of 1.5 ml of a 4% strength aqueous triethylamine solution, the mixture is condensed for a further 1 hour. 17 g of the high molecular weight, thermoplastic polycarbonate with a solution viscosity η _rel = 1.305 are obtained by the customary workup methods.

EXAMPLE 9

25.4 g of a polycarbonate based on bisphenol A (η _rel % 1.285) colored red with 0.35% by weight of cadmium selenide is mixed with 80 ml of sodium hydroxide solution and heated to 100 ° C. for 3 hours. Then it is distilled with 500 ml. H ₂ 0 filled up and the undissolved color pigment filtered off. 500 ml of methylene chloride are added to the clear filtrate and the phase interface mixture is phosgenated and worked up as in Example 1. There remain 22 g of an undyed, thermoplastic. Polycarbonate with a solution viscosity of η _rel = 1.297.

EXAMPLE 10

27 g of a copolycarbonate based on bisphenol A and tetrabromo-bisphenol A (5.3% by weight bromine) (η _rel = 1.297) are dissolved in 150 ml of chlorobenzene and 80 ml of 15N sodium hydroxide solution are metered in. After 4 hours, the hydrolysis is ended and a clear phase mixture is obtained after adding 350 ml of methylene chloride and 400 ml of water. To recover the polycarbonate, 15 g of phosgene are introduced in 1 h at room temperature. At the end of phosgenation, the solution should have a pH of approx. 11-12. After adding 0.43 ml of triethylamine, the mixture is condensed for a further 1 h and worked up according to Example 1. The result is a bromine-containing polycarbonate (5.4% bromine) with a solution viscosity of η _rel = 1.285 and properties similar to those of the starting material.

Claims (1)

1. A process for the recovery of aromatic, high molecular weight, thermoplastic polycarbonates from polycarbonate scrap by means of decomposition and repolycondensation, characterised in that the polycarbonate scrap is saponified in bulk or in solution at temperatures between 25°C and 220°C, optionally under pressure, the non-saponified constituents are separated off and the saponification mixture is then phosgenated and subjected to polycondensation according to the methods of two phase boundary polycondensation without any further purification steps and treatment steps.