CA1061947A - Solvent recovery of thermoplastic polyesters - Google Patents

Abstract

ABSTRACT OF THE INVENTION

Thermoplastic linear polyesters such as polyethylene-terephthalate and polytetramethyleneterphthalate (sometimes called polybutyleneterephthalate) are prepared in the form of a pure, controlled particle size powder form either bulk material of virgin nature or, more importantly, form scrap containing a variety of contaminants, the process involves dissolving the polyester values in a polar solvent at an elevated temperature, under conditions chosen so that there is no degradation of the molecular weight of the original poly-ester, filtering the hot solution, cooling the filtrate to a temperature at which the polyester values being to crystallization begins in order to control the particle size, filtering off and washing the powdered polyester after precipitation is complete with the solvent used for initial solution of the polyester, treating the filtrate obtained therefrom after removal of the polyester values by known techniques for purposes of recovery of pure solvent and recovery of other values which may be present as contaminants in the original polyester by flushing with water, a lower alcohol, and/or an alkyl ketone, or by distillation.

Description

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BACKGROUND OF THE INVENTION - ~IE RAW M~TERIALS
While the present invention is applicable generally to linear thermo plastic polyesters, the preferred raw materials are based on polyethylene-terephthalate (PET) and polybutyleneterephthalate. Such raw material may be in-plant scrap which contains little or no contamination or may be commercial scrap articles which may be heavily contaminated. Scrap material of both types and suitable for the purposes of this invention, is available from a variety of sources.
~ore particularly, the present invention is concerned with a process for recovery of the silver content of photographic film scrap containing more than one non-water soluble polymeric material at least a portion of which is polyester, said film scrap comprising a non-water soluble polymeric base selected from the group consisting of polyesters and cellulose acetate; a non-water soluble polymeric subbing layer including a chlorine containing polymer and a gelatine layer containing metallic silver or silver hal~de;
1) contacting the photographic film scrap with a first solvent for the non-water soluble polymeric material at a temperature above that at which said non-water soluble polymeric material dissolves;

2~ filtering the resulting hot solution for removal of silver and contaminants in the photographic film scrap which are insoluble in said first solvent;

3) calcining the insoluble materials separated in Step 2 in order to recover the silver values therein;

4~ cooling the hot filtrate derived from Step 2, thereby precipitating the polyester contained therein and recovering the polyester in powdered form by filtration of the cooled filtrate;

5) treating the cooled filtrate from Step 4 with a second solvent in which the polyester is insoluble, said first solvent is soluble and .L~6~

the other non-water soluble polymeric materials are also soluble, and removing any residual polyester which precipitates by filtration;

6) partitioning thefiltrate by addition of a third solvent in whieh the chlorine containing polymers originally present in said scrap are insoluble and in which the non-chlorine containing polymers originally present in said scrap are soluble and removing precipitated polymers by filtration;

7) reeovering said non-ehlorine eontaining polymers by adding a fourth solvent in which said non-chlorine containing polymers are insoluble;
and

8) filtering the product o~ Step 7 and recovering the precipitated polymers.
Synthetie linear polyesters are well known in the art and outside of tll~
preferred varieties defined in the preeeding paragraph, the present invention is ; applicable to the general class of synthetic linear thermal plastic polyesters.
A polyester is defined as a synthetic linear eondensation type polymer whose repeating units eontain the ester group, O
--C--O--these groups being integral members of the linear polyester chain. Polyesters may be those derived from aliphatie dibasie aeids sueh as oxalie, suecinie, glutarie, adipie, and sebaeie aeids and glyeols sueh as ethylene glyeol, propylene glyeol, trimethylene glyeol, hexamethylene glycol and decamethylene glycol. Polyesters may also be derived from aromatic dicarboxyl:Le aeids such as terephthalic aeid and isophthalic acid and glycols such as ethylene glycol.
Polyesters may also be derived from hydroxy acids and their eorresponding laetones sueh as those from hydroxypivalie aeid, ~-hydroxyisobutyrie acid, ~ -2a-D, ~

1S~ 7 G~-hydroxycaproic acid, ~-hydro~ydecanoic acids, ~-butyrolactone and 4-hydroxyhexanoic acid lactone.
One important source is scrap photographic ~ilm which i8 usually a three or four part system. When the photographic '~
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film is based on silver halideJ this scrap contains a polyester base, silver halide and/or metallic silver, gelatin, and a subbing layer on the polyester surface consisting principally of poly~inylidenechloride and usually comprising a terpolymer containing a major amount of polyvinylidenechloride, a lesser amount of polyacrylonitrile, and a relatively small amount of a polymerizable acid taken/from the class of itaconic, acrylic or methacrylic acids or the alkyl esters thereof. Scrap may also contain casual dirt and various dyes or pigments.
Anothar important source of scrap useful for the purposes of this invention are fabrics based on polyester. Such fabrics may be based primarily on polyethyleneterephthalate fiber which may be dyed and also specially surface treated with a variety of chemicals to facilitate both the weaving and dyeing process. An important species of this type of fabric con-sists of mixed fibers in which the finished cloth may contain as much as 50 percent of other fibers such as cotton or synthetic fibers based on poly-acrylonitrile. Again, theee fabrics will usually contain surface treating agents and dyes.
~ third type of raw material useful for the purposes of this invention is scrap tire cord which usually contains a sizing on its sur~ace to facilitate eventual processing and sometimes a layer comprising another polymer to aid in the bonding of the tire cord material into the rubber carcass.
An increasingly important source of the desired polyester raw material i8 scrap obtained from injection molding of shaped articles. Such scrap may contain, in addition to the linear polyester, such contaminants as colored pigments, mineral fillers, reinforcing agents such as glass fibers, plasticizers and the like.
Several methods involving treatment of polyester bearing material with solvents for the purpose of recovery of -the polyester have been r-~v~

proposed previously including those described in United States Patent No.
3,047,435; Canadian Patent No. 626,996; United States Patent No. 3,5039904;
United States Patent No. 3,546,149; British Patent No. 1,134,967; United States Patent No. 3,873,314; United States Patent No. 3,701,741; and United States Patent No. 3,696,058. ~ll of the foregoing described procedures with the exception of that described in United States Patent No. 3,701,741 and United States Patent No. 3,696,058 are designed specifically to enable the recovery of the polyester material in the form and shape in which it is originally introduced into the bath utilized for the ostensible purpose of recovering cleanpolyester. Thus, if the material is introduced into the bath in the form of chips, flakes or fibers, this is the form in which it is recovered. On the other hand, United States Patent No. 3,701,741 utilizes alcohols taken from the class of methyl alcohol, ethyl alcohol and propyl alcohol under pressure and in a temperature range between 150C. and 240C. in order to dissolve the polyester completely. The examples in this patent define that extensive de-gradation of the polymer takes place, and this degradation is manifested not only by a significant reduction in the intrinsic viscosity of the recovered powder but also by a significant loss in yield. In experimental examination of the teachings of this patent and utilizing not only the alcohols described in United States Patent No. 3,701,741 but also alkyl derived glycols such as ethylene glycol, under conditions such that the polyester is placed in solution,we have found that the molecular weight degradation, loss in yield and similar defects invariably take place when attempts are made to place the linear poly-ester in solution with alkyl hydroxy compounds such as the alcohols and the glycols under the rigourous conditions which are needed in order to use these -types of materials as solvents for the linear polyester.
When the conditions ensure complete solution of the linear polyester, more often than not the loss ln yield of the original polymer is .

~06~L94~7 substantial in the presence of these hydroxyl containing alkyl compounds as high temperature solvents.
~ United States Patent No. 3,696,058 describes the use of hexa-fluoroisopropanol as a medium for dissolving polyes~ers and utilizing water under specific conditions for precipitation of the dissolved polymer. Hexa-fluoroisopropanol is a powerful solvent boiling at 58.2C. and is removed from the process in the water precipitation step by adding the water at temperatures above the boiling point of the solvent. He~afluoroisopropanol is an acidic material and if utilized without precaution will degrade the polyester in solution under the~conditions defined in United States Patent No. 3,696,058.
As a consequence, in order to obtain the best results, preferred temperatures of solution are around 25C. or at room temperature. Further, the preferred means described for use of the material prevents separation of the polyester in the desired pure form since the agents used for precipitation purposes also precipitate other polymers, particularly those containing chlorine, at the same time, which degrades the utility of the recovered polyester for substantially all purposes. In lines 65 through 72 of column ~ of this patent, a number of solvents for polyesters are listed which include strongly acidic materials such as trifluoroacetic acid, phenols, cresols, and mixtures of these latter two agents with chlorinated solvents including the chlorinated phenols. Under the conditions described in our in.~ention the polyester portions are strongly degraded in an undesired condition by these types of solvents and this is admitted in United States Patent No. 3,696,058 in lines 27 through 35 of column 5 where it is stated that these types of acid solvents are deficient either in low solubility for the polymer or in difficulty of removal from the polymer solution as indicated by their boiling points. The statement is further made in this section that "when prolonged heating is required either in dissolving the polymer or in removing the solvent ~rom the polymer solution~ possibly an additional oxidative or thermal degradation of the polymer is lntroduced."
In order for a solvent procedure for the preparatioll of powcler as a consequence oE precipitation from solutlon to be effective economlcally and quantltatively, there should be no degradation in molecular weight oE the raw material fed to the dissolvlng medlum or, in other words, the intrinsic or relative viscosity of the final product obtained in powdered form should not be less than the similar parameter of the starting raw material. In addition, the recovery of this non-degraded polyester needs to be reasonably quantitative.
The availability of undergraded polyester powder of controlled particle size represents a distinct advantage over recovered polyester which retains its original shape even though the recovered polyester in this original shape may be designated as pure. Whlle both powdered polyester and polyester in chipped form may be utilized for forming shaped artlcles from the melt, the powder form possesses a number of advantages over chlps. Powder is more readily compounded prior to the meltlng operation. Polyesters can be upgraded by heat treatment in a vacuum and/or in an lnert atmosphere at temperatures below the meltlng point for extended periods of time, and the finer the particle siæe of the polyester utillzed in this molecular upgradlng process, the faster this molecular weight upgradlng can be achleved; and, flnally, the powdered form ls a necessity for the production of a compounded surface finlsh. The productlon of powder of the desired particle size from bulky forms by mechanical attrition procedures lS extremely dlfficult, costly and sometimes impossible in view of the toughness of the starting raw material.
OBJECT ~ND DESCRIPTION OF THE INVENTION
It is a principal object of this invention to define a process whereby PET and/or PTMT can be produced in high yields in powder form from pure or contaminated sources of raw materials containing PET and/or PTMT.

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It is another object o~ th~s invention to procluce the desired powder in a particle size range in which the ma~ority of the particles are below 10 microns in size and or in another form in which the majority of the desired particles are above 10 microns in size.
It is a further object of this invention to provide means for indefinite recycling oE the reagents utilized in the process which are needed for the production of the desired end product.
` It is a ~urther object oE this invention not only to accomplish the objects heretofore recited with regard to a pure product of controlled particle size but also to define means for recovering contaminants which may be present in these types of polyethyleneterephthalate scrap whether such contaminants have economic value or not, In the case that these contaminants do have economic value, then the final object of the invention is to recoyer these contaminants in such a form that the economic value can be realized.
The method of accomplishing the foregoing objectives will be described first, generally, and then more specifically be~ore proceeding with delineation of the specific exa~ples.
Recognizing that the methods of treatment wiil vary not only with the purity of the starting raw material, but also with the degree and nature of the contamination, the first description will deal primarily with pure starting xaw material in flake, chip, fiber or similar forms in which the contamination may be generally categorized as casual dirt in the form of metals and non-metals and usually not in polymeric form.
In this instance, the polyester is dissolved in an appropriate solvent at an elevated temperature. Solvents appropriate for this class of materials are listed in Table 1. In order for the solvent to be effective for the purposes of this invention, it should have a boiling point of at least 150C. without decomposition and should remain a liquid at t~mperatures not ~Vt;~47 greater than 35 C. The chosen solvents should have the capability Eor producing a solution of the polyester at a temperature at or below the bolling point o the solvent in question at atmospheric pressure to yield a concentration of at least 10 percent by weight and preferably greater than 20 percent by weight and to yield a viscosity under such conditlons which permits easy filtration of the solution. Thus, the viscosity should be less -than 10 centipoises at a chosen !

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~ , ~ - 8 -: ,, TABL~ 1 SOLVENTS FOR POLYETHYLENETEREPHT~LATE ~ND
POLYTETRAMETHYLENETEREPHTHALATE(THE POLY:BUTYLENE DERIVATIVE) 1. AROMATIC ETHERS(OXX AND THIO) Anisole Phenetole Benzyl ether Diphenyl oxide (phenyl ether) Phenyl sulfide 2~ AROMATIC ALCOHOLS
Benzyl alcohol 3. AROMATIC RETONES
Acetophenone 4. ESTERS OF DICARBOXYLIC AROMATIC ACIDS
dibutyl phthalate bis(2-ethylhexyl)phthalate 5. SULFIDES
dibutyl sulfide ~ isoamyl sulfide dipentyl sulfide `~ dihexyl sulfide diheptyl sul~ide 6. OXYSULFUR(ALKYL AND CYCLIC3 dimethylsulfoxide diethylsulfoxide tetramethylene sulfoxide sulfolane t7 TABLE 1 ~continued) 7. PIPERIDINES
n-formyl piperidine 8. LACTAMS
2-pyrrolidone l-methyl-2-pyrrolidone N-butyl pyrrolidone

9. LACTONES
Gamma butyrolactone 1010. PYRROLES
l-benzyl pyrrole l-butyl pyrrole 2,4-dimethyl pyrrole 11. AMIDES
/
dimethylformamide ;: N-methylformamide N,N-dimethylacetamide l,l,2,2-tetramethyIurea hexamethyl phosphoramide : : . :
2012. NITRO ARYLS
nitrobenzene l-methoxy-2-nitrobenzene , ' , ~ ~; : ' ` , ::
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elevated temperature. Secondly, the sulvent Inust be o;E such a nature that tlle polyester starts to precipitate as a powder at some temperature below the temperature at which the polyester is placed ln solution but, in addition, at a temperature substantially above room temperature. ~t this temperature of precipitation, the powder wlll normally yield a product having a particle size less than 10 microns if the precipitating fluid :is chilled rapidly to room temperature with stirring during the precipitation process. If maintained for a period of at least 20 to 40 minutes at or slightly below the temperature of precipitation before chilling to room temperature, then the normal particle size of the end polyester product is invariably in excess of 10 microns and sometimes as high as 100 microns. The product obtained in -this latter fashion will generally exhibit a range of particle siæes, therefore, between 10 and 100 microns. Some of the polyes-ter remains in the solution at room temperature after the powdered product is recovered by filtration. Generally, the maximum solubility for any of the types of solvents indicated in Table 1, at room temperature will not exceed 3 percent by weight of these types of solvents.
While the solvent may be recovered for reuse by distillation under vacuum, the residual polyester needs to then be recovered and treated as original scrap feed. ~ separate procedure is simply to use the saturated polyester solution obtained at room temperature as the continuing solvent for fresh supplies of the raw material so as to ensure substantially a 100 percent yield of the desired powder in the second stage of this type of cyclic operation. In another technique for obtaining solvents substantially free of polyester and to recover the polyester in the first cycle is to flush the solution with a precipitating solvent for the polyèster and thereafter remove the flushing material for recovery and reuse by azeotropic distillation yielding a pure solvent for reuse in the process. Of these various procedures the process which involves recycling of a solvent containing a residual percentage of dissolved polyester 94~

is preferred for economic reasons. This is usually the case when the starting raw material does not contain significant amounts of polymeric ~aterial which is also soluble in the starting solvent. If the residual polyester solution at room temperature contains only polyester in solution, it may be precipitated out quantitatively by spraying into a rapidly stirred solution of liquid such as water, alkanols, and/or aliphatic ketones, or mixtures thereof. Even with pure polyester, which has been collected as a scrapped item from an in-plant process, a significant amount of casual dir-t will exist which represents a serious contaminant with regard to obtaining the ultimate of physical properties rom the recovered end product and which needs to be removed in the early stages of the process. If the contaminant is water, it is normally removed easily simply by distillation during the course of the process itself. If the con-taminant is casual physical dirt, it is removed by filtration after solution of the polyester is complete and at a temperature above that which precipitation starts to take place for the recovery of the final product as will be describsd hereinafter.
~ fter recovery of the polyester in powder form by fil-tration, the powder may be recovered in pure fonn ~i.e. free from solvent) by washing the filter cake at room temperature with a liquid in which the polyester is 2~ insoluble and in which the solvent for the polyester is soluble. Such washing liquids may be water, aliphatic slcohols, aliphatic ketones and straightchain hydrocarbons. The washing fluids may be recovered in their respective recyclable and reusable forms by distillation. A variation on this procedure is to subJect the unwashed cake to vacuum distillation in a rotating type of vacuum chamber so as to~prevent the~agglomeration of the particles and recovering the distilled off solvent in a cold trap. In the case of vacuum distillation, the temperature: ,, of vacuum distillation should not e~ceed 200C., and if carriPd on for periods of several minutes up to fractions of hours at this temperature a substantial . . .

-'7 upgrading of the powder is obtained with regard to molecular weight. Similar techniques may be considered for the polyester which may be recoverecL by pre-cipitation of the residual polyester retalned in the solvent at room temperature.
When the starting raw material i9 in bulk form such as chips, pellets, or film scrap, something of an incluction period appears -to exist in the early stages of the solution process. The rate of solution is relatively slow in the first several minutes of the process and then the rate increases very rapidly thereafter leading to the supposition that the character of the formed surface with regard to ease of solution is different than the bulk interior.
While the generalized procedure for obtaining pure product from contaminated scrap is the same as that for obtaining pure powdered powder from an uncomtaminated source, details of the procedure will vary depending on the nature of the contamination.
One such case is the processing of a raw material where the principal contaminant is cotton fiber which has not been dyed nor surface sized.
In this case, the procedure is identical with that described for processing uncontaminated polyester except that the material removed in the first filtration will be all of the cotton values and the liquid obtained therefrom after washing and prior to precipitation of the polyester is substantially the same as in the processing of uncontaminated polyester.
In case the fabric or fiber is sized, it has been found generally that the sizing material, present in very small quantities, is insoluble under the conditions of solution and can be removed by filtration prior to precipita-tion.
If dyes are present on the cloth, these are sometimes soluble in the solution under the conditions described and will remain soluble in the solution at room temperature. Again, under such conditions, the procedures after filtration 4~

remain the same as pre~iously desc~bed fo~ uncontaminated polyester untll the room temperature stage. In view of the relatively small concentrakion oE dyes required to produce a signiflcant color on a polyester fabric the amount of dye can be ignored in the recycling process until it builds up to a concentra-tion sufficient for separation purposes. If it has been found that a dye is soluble in the solvent used for placing the polyester in solution, the dye in such solution can generally be recovered by passing the material through an ion exchange column which removes the dye from the solution without aeEecting the residual polymeric solution which remains which is then treated as pre-viously described for purification and separation. The dye can then be removedfrom the ion exchange column by back washing with an appropriate medium depend-ing on the nature of the dye. Dyes which are insoluble in the solution medium are removed in the first filtration step.
An important source of raw material for polyester is chopped up molded parts produced by injection molding of the polyester~ This raw material usually contains contam1nants in the form of mineral fillers, pigment both in-organic and organic dyes, reinforcing agents such as glass or calcium silicate ; fibers, lubricants and occasionally plasticizers. The pigment, whether in-organic or organic, the mineral fillers and the reinforcing fibers, are usually insoluble in the designated solvents under the conditions under which they are ,used and consequently can be removed in the first filtration step prior to the precipitation of the polyester. If plasticizers are used they usually remain soluble in the solvents used to dissolye the polyester and lf dyes are used for coloring purposes rather than organic pigments, some of these will remain soluble also after precipitation of the polyester and removal of the solvent.
; The soluble dyes in the stable solution at room temperature can be removed by passage through an appropriate ion exchange column, plasticizers can be removed by flushing with alcohol, hexane or a ketone, and the various fractions and liquid separated again as described p~viously thus permitting the plastlcizer to be reused, if desired, along with the recovery o the residual polyester plus the solvent Eor reuse. The plasticizer recovery is ~ade possible by the fact that the plasticizer will disso.lve in the alcohol, ketone or hexane or mixtures thereof while the polyester values are insolubilized as a consequence oE the addition of these precipitating agents. The nature of the solvent with the specific conditions under which the solvent is used is determined by the type of contaminant which can be most appropriately removed with the least amount of degradation of the polyester. ~or example, cotton and cellulose products as contaminants generally suffer the least degradation by solvents 1, 2, 3, 4, 10 and to a lesser extent 6 in Table 1. Contaminated products contain-ing polyvinylchloride or vinylidene polymers are treated best with solvents taken from Table 1 and in accordance with the following listing: 1, 3, 6, 7, 8, and 11. In general, it appears that the broad group of solvents in Table 1 and combinations thereof are sufficiently extensive so that substantially any plastic material which represents a contaminant for the polyesters can be re-~oved by an appropriate choice in accordance with known chemistry.
~n important source of contaminated raw material containing polyester is the four component photographic film described in previous portionsof this specification. In breaking down this four component type of film, generally the type of solvent for placing the polyester in solution which is most suitable for maintaining poly~inylchloride or polyvinylidene chloride ln solution at room temperature is utilized and in accordance with the list of sol~ents described previously. Seconaly, the silver present in the silver CODtaining portions of the film may be all metallic silver or a combination of metallic silver and silver halide. In the process of treatment to be described hereinafter it is necessary that the solution be retained for at least an hour at the temperature described for treatments involving scrap silver film as the ~ 15 -basic raw m~terial. The reason ~or ~h~s is that treating ~he composition at these temperatures for this length o~ time causes a partial pyrolysis of the gelatin fraction yielding first a notable darkening of the so}ution aftér which the gelatin agglomerates as tarry lumps in the solu~ion. This pyrolysis of the gelatin fraction is a reducing action in that it enables precipitation of all of thè silver in the solution in the form of metallic silver. The tarry nature of the gelatin produced facilitates filtration of the extremely fine silver particles. In the event that silver reduction is not complete during this pyrolytic degradation of the gelatin fraction, completion of the reduction is accomplished by the addition of a small amount of a mild reducing agent, for example by the deliberate additlon of a mild reducing agent such as diphenyl-amine or phenylenediamine to the reagents in an amount about equivalent to about 1 percent of the original feed prior to the precipitation of the polyester for this purpose. Usually, the silver can be recovered quantitatively through the - reducing action of the pyrolyzed gelatin under the conditions described. Using solvents preferred for treating contaminants containing either polyvinylchloride or polyvinylidene chloride, these materials are maintained at the specified and desired tèmperature for at least l hour, then filtered at a temperature between ~ : :
- ~ the solution temperature and the precipitation temperature, washing the filter ~ cake on the filter w1th the chosen solvent maintained at the solution temperature, allowing the filtrate to cool to the temperature for precipitation of the poly-ethyleneterephthalate, then~allow mg the solution to cool to room temperature again under conditions specified for the production of the desired particle size range, filtering and washing the precipitate on the filter with fresh dissolving ~fluid at least twice with or without a repulping of the precipitate with the dissolving fluid to facilitate cleaning out the last traces of solvent. The combination of filtrate and washing solutions containing a mi~ture of a small amount of dissolved polyester, the polyester dissolving solution, and the ~ .

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polyvinylidene terpolymer may be separated in one of several ways. The first method simp}y involves freezing the solution to a temperature ~etween 0 and -10 degrees C. under which polyethyleneterephthalate precipitates out leaving sub-stantially none left in the solution. The precipitate thus formed is removed by filtration and the chlorine containing polymers do not precipitate. There-after, the iltrate from such a treatment is allowed to warm to room temperature and the polyvinylidenechloride terpolymer may be removed from the solvent by flushing with either water, alcohol, or a straightchain hydrocarbon. The poly-vinylidenechloride is removed from the solution, the solvent squeezed out and the product is vacuum drled, recovering all of the solvents therefrom which can be separated one from the other by appropriate fractional distill~tion including azeotropic distillation. Vacuum distillation may be utilized for the entire batch if desi~ed, in the event that it is not economically feasible to recover the small amount of polymer still remaining in the solution. A third technique involves a separation using specialized solvents for the type of precipitation referred to. The higher aliphatic ketones show significant solubility for polyvinylchloride and polyvinylidenechloride while at the same time acting as precipitating agents for PET and PTMT. Use of ketones such as methylbutylketone or methylisoamylketone as the flushing agent represents a means for separation of these two polymers one from the other.
; Having described the invention, fol]owing is a description of examples of the method of practice. In order to facilitate this description, the conditions defined in the exiamples will follow the format presented in Table 2.
EXAMPLES 1 THROUGH 14 (TABLE 2) The raw material utilized for examples 1 through 14 is poly-ethyleneterephthalate film having a thickness of approximately 5.5 mils and available in a chopped condition in pieces roughly 1/4 to 1/2 inch in diameter.

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200 grams of chopped polyester fllm o~ the foregoing descriptlon is p].aced separately in 1000 grams of the solvents listed in Table 2, said solvents having been heated to the temperature given in column 4 prior to the addition o the polyester. The solution was stirred while the polyester was added to the solution. While maintaining the solution at this temperature and in the stirred condition, the solution process was continued for the time period indicated in column 5 of Table 2. After this time period the solution was filtered through glass filter cloths, not permitting the tempera-ture of the reaction temperature to fall below the temperature indicated in column 6 during the filtration process. A small amount of contaminant remaining on the filter was washed twice with two separate portions of 50 grams each of the solvent listed in column 2, said washing solvent being maintained at the temperature indicated in column 4. The clarified filtrate was then stirred and allowed to cool to the temperature indicated in column 7 at which temperature precipitation was initiated.
Once precipitation was initiated a temperature in the range of that in column 7 and not exceeding a temperature more than 10 degrees below this level was maintained with stirring for 30 minutes, after which the pre-cipitation vessel was allowed to cool to a temperature not below that indicated in column 8.

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The powdered pîecipltate filtered from the solution at a temperature not below that indicated in collmm 8 was washed four tlmes with separate 50 gram portions of the cooled solvent indicated in column 2 and at the temperature indicated in collmm 8, using 50 grams of solvent for each washing and then s~cked as dry as possible aEter the final washing.
The precipitate was then broken up and then trea-ted under a vacuum of 0.1 mm of Hg for a time period of 1 hour at a -temperature of 200 C.
Residual solution, solvent washings and the like obtained from such precipitates were collected in the cold trap. Yields obtained of Einal product varied between 190 to 1~5 grams indicating a first yield of between 95 and 97.5 percent recovery. The particle size of the products obtained in each case were between

10 and 100 microns. About 1275 grams of liquid containing some polyester was obtained in each instance, the amount varying, due to mechanical loss around an average of 1275 grams and covering a range between 1260 and 1280 grams.

Example 10 was repeated except that after precipitation was initiated at 65C. the precipitating solution was chilled as rapidly as possible with stirring to 0C. and filtered at this temperature without washing. 198 grams of powdered product was obtained af-ter vacuum drying exhibiting a particle size between approximately 1 and 10 microns.
The starting raw material and the finished powder obtained from Examples 1 through 15 exhibited a relative viscosity of 1.57 (i.e. no change in - molecular weight as a consequence of processing).
_XAMPLE 16 The solution recovered from Example 7 weighed 1275 grams.
275 grams of the solution was removed by a vacuum distilla-tion at 10 millimeters of mercury at a temperature of 125 C. The remaining solution was then heated ., under reflux conditions to 189C. a~ter which 200 grc~ls of the origina:L flakedraw material was then added and stirred in at this temperature for one hour.
~fter following the procedure indicated for Exa1nples 1 through 14, 200 grams of product showing particle size and relative viscosity propertlesidentical with that defined for Examples l through 14 previously were obtained.
This would indicate that on the second cycle~ an approximate 100 percent yield of product was obtained, whereas on the first pass for this particular example the actual yield was 95 percent, indicating that 10 grams had to be passed back into the process by use of a solvent which had not been completely purified of residual polyethyleneterephthalate by specialized procedures prior to return of solvent to the process.
EXAMPL~S 17 THROUGH 22 In these examples the raw material was white cloth consisting primarily 60 percent polyester fiber and 40 percent cotton fiber, this cloth having been chopped into approximately 1 inch squares. The solvents and ; conditions used for Examples 18 through 22 were in accordance with previous Examples 2, 3~ 4, 5, 7 and 10. The same conditions of time and temperature were utilized throughout with the exception that 300 grams of starting raw material was utilized with the same amount of solvent indicated in Examples 1 through 15, and 300 grams of solvent in five 60 gram portions were used for washing the cotton precipitate on the first filtration prior to precipitation of the polyethyleneterephthalate and approximately 1650 grams of solution of polyethyleneterephthalate was recovered at the end of each experiment prior to the removal of the small amount of polyethyleneterephthalate still in solution.
After washing and vacuum drying of the cotton precipitate obtained from the first filtration, then allowing the cotton material to come ~V~ 7 to equilibrium with roo~ ~em~erature, approxlmately 125 grams of cotton contain-ing product was obtained indicating a yield of approximately 5 to 6 percent over theoretical. The cotton varied in color from approximately white to yellowish to a light yellowish~brown indicating either degradation or an addition of substituents to the particular solvent used. At least to manual feel, the cotton cloth recovered from the process appeared to be stronger and tougher than nonnal cotton cloth does.
In this first passage without special recovery procedures a yield between 81 and 83 percent of the original polyester was obtained.
UtiIizing polyester threads pulled out from the original material with a tweezer under the mlcroscope for purposes of determining relative viscosity, a relative viscosity for the polyester of 1.6 was obtained at the start of the operation and an equivalent relative viscosity was obtained on the product recovered at the end of the operation.

Unexposed x~ray film was utilized as the raw material. This film exhibited a proximate analysis of 26.9 percent silver bromide, lI percent gelatin, 3.5 percent of the terpolymer of polyvinylidenechloride described previously and 59.6 percent polyethyleneterephthala-te. After stripping the ;20 film with ethylene glycol by procedures known in the art, and determining the relative viscosity of the polyester obtained therefrom, a value of 1.52 was obtained. The original film was chopped so as to produce pieces of 0.25 to 0.50 inches in diameter. In each of the examples to follow, 400 grams of the chopped film was digested in 1000 grams of solvent in separate experiments utilizing the solvents from the following examples: 1, 2, 4, 7, 8, 9, 10, 12 and 13. Each of these was given the solution treatment under the conditions - defined in Table 2 for the time periods and conditions indicated, except that .

_ 23 -~ 1<~
when the time period indicated in Table 2 was less than 1 hour, the time of digestion was extended to 1 hour. A highly viscous opaque solution exhibiting a tan color was obtained in the first 10 to 15 minutes of digestion which obviously comprised a large amount of a combination of insoluble material dispersed in a solution of soluble material. As the digestion continued, the color deepened almost to a deep brown-black and a black tarry appearing pre-cipitate in the form of small separate clumps throughout the solution developed with a noticeable drop in viscosity. At the end oE the digestion the tempera-ture was adjusted as indicated in Table 2 for each of the examples and filtered,followed by washing with clear hot solvent as before. The precipitate was removed from the filter cloth and then dried at 120C. for 2 hours and found to weigh approximately 155 grams in each case. The dried precipitate was then calcined in air at 800C. for 1 hour, leaving 63 grams of residue. Analysis of the residue indicated that the material contained 98.4 percent silver, the balance being primarily carbonaceous material indicating that the recovery of silver was close to 100 percent. After the first cooling and precipitation of the filtrate, followed by washing with the original solvent, a yield of approxi-mately~215 grams of powdered polyethyleneterephthalate was obtained in each case, this weight being defined after vacuum drying, thus representing a first yield of approximately 90 percent in powder form. After partitioning with methylisobutylketone at room temperature in the manner heretofore described and recovering the respective polymers from the two portions of the partitioned solution approximately 22 grams more of polyester was obtained from each solution representing a yield in excess of 99 percent of the original polyester available.
The rraction containing the polyvinylidenechloride after precipitation with a mixture of water and ethyl alcohol, followed by separation and drying, produced a weight of 15.4 grams, this being equivalent to a yield of 110 percent indicat-ing that all of the subbing material had been recovcred and w~s still contaminated ~(~61~

with approximately 10 percellt polyeste~. ~eas~}rement o~ t~le relative viscosity of the recovered polyester powder gave a~value of 1.6, equivalent to the relative viscosity of the starting raw material indicating that no degradation had taken place.
EX~MPLE 32 Same as in Example 14 except that after precipitation has been initiated and the system is cooled down to a temperature at least as low as 50C., 500 cc's of methanol are added slowly with stirring and the reaction mixture is then cooled to room temperature. After reaching room temperature, the precipitate is filtered and washed with methanol on the filter until the ; nitrobenzene odor has been eliminated. The precipitate is vacuum dried at 100C. at 10 millimeters of pressure and a yield of 198 grams was obtained equivalent to 99 percent of the original starting material.
EXAMPLE 33 ~ `
200 grams of polytetramethyleneterephthalate in pellet form was utilized as the starting raw material. This material exhibited the approximate , analysis of 77 percent PTMT, 20 percent glass fibers, 2 percent titanium oxide ' pigment~ and 1 percent o~thers. The procedure described for Example 14 was ~followed and a yield of 145 grams of powder was obtained after filtration, washing and vacuum drying equivalent to a 91 percent yield.

:
; Same as Example 33 except that after precipitation was initlated the system was cooled at 50C. and 500 cc~s of methanol was added and the system cooled to room temperature with stirring after which the pre-cipitate was cooled and washed with methanol until all of the nitrobenzene had been eliminated; The precipitate was then vacuum dried at 100C. at 10 milli-meters for 1 hour and the powder was found to weigh 151 grams equivalent to a yield of 98 percent.

Claims (17)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE
IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for recovery of the silver content of photographic film scrap containing more than one non-water soluble polymeric material at least a portion of which is polyester, said film scrap comprising a non-water soluble polymeric base selected from the group consisting of polyesters and cellulose acetate; a non-water soluble polymeric subbing layer including a chlorine containing polymer and a gelatine layer containing metallic silver or silver halide;
1) contacting the photographic film scrap with a first solvent for the non-water soluble polymeric material at a temperature above that at which said non-water soluble polymeric material dissolves;
2) filtering the resulting hot solution for removal of silver and contaminants in the photographic film scrap which are insoluble in said first solvent;
3) calcining the insoluble materials separated in Step 2 in order to recover the silver values therein;
4) cooling the hot filtrate derived from Step 2, thereby precipitating the polyester contained therein and recovering the polyester in powdered form by filtration of the cooled filtrate;
5) treating the cooled filtrate from Step 4 with a second solvent in which the polyester is insoluble, said first solvent is soluble and the other non-water soluble polymeric materials are also soluble, and removing any residual polyester which precipitates by filtration;
6) partitioning the filtrate by addition of a third solvent in which the chlorine containing polymers originally present in said scrap are insoluble and in which the non-chlorine containing polymers originally present in said scrap are soluble and removing precipitated polymers by filtration;
7) recovering said non-chlorine containing polymers by adding a fourth solvent in which said non-chlorine containing polymers are insoluble;
and 8) filtering the product of Step 7 and recovering the precipitated polymers.

2. The process of claim 1 in which the non-water soluble polymers present in said scrap comprise a polyethylene terephthalate base and a ter-polymer subbing layer comprising a major amount of vinylidenechloride, a minor amount of methylmethacrylate, and a still lesser amount of itaconic acid.

3. The process of claim 1 in which the first solvent is selected from the group consisting of: aryl ethers, phenones, esters of dicarboxylic acids, pyrollidones, lactones, pyrolles, amides and mixtures thereof in which the solvents of said group do not contain halogens, amine side groups, or doubly bonded sulphur.

4. The process of claim 1 wherein said first solvent contacts the scrap for not more than 15 minutes in Step 1 of said process.

5. The process of claim 1 wherein said first solvent contacts the scrap for not more than S minutes in Step 1 of said process.

6. The process of claim 1 wherein the solution of the non-water soluble polymers is complete, the resulting mixture is digested at said temperature for at least an additional 10 minutes to complete precipitation and consolidation of the silver containing portions of the film scrap.

7, The process of claim 1 including heating the photographic film scrap to 150°C for at least 10 minutes and then adding the heated film scrap to said first solvent.

8. The process of claim 1 wherein the temperature at which the film scrap is contacted with said first solvent is below the boiling point of said solvent but at a temperature not less than 165°C.

9. The process of claim 1 wherein the polyester product is obtained in a particle size range of 10 to 100 microns by cooling the first filtrate in Step 4 of claim 1 to a precipitating temperature above room temperature, but not below a temperature range of 65°C to 150°C, maintaining the mixture at said precipitating temperature for a period of 20 to 40 minutes, cooling to a temperature of 20° to 25°C and separating out the precipitated polyester by filtration.

10. The process of claim 1 where the polyester product is obtained in a particle size range of less than 10 microns by rapid cooling of the first hot filtrate in Step 4 of said process, to a precipitating temperature in the range of 0°C to -10°C, separating out the precipitated polyester by filtration.

11, The process of claim 1 wherein the relative viscosity of the recovered polyester powder precipitate is not less than the relative viscosity of the polyester in the starting raw material.

12. The process of claim 1 where the second solvent is a higher alkyl ketone.

13. The process of claim 1 where the third solvent is selected from the group consisting of lower aliphatic alcohols and liquid straight chain hydrocarbons.

14. The process of claim 1 wherein the fourth solvent is water.

15. The process of claim 1 wherein the materials in the scrap photo-graphic film insoluble in the first solvent include at least one member of the group consisting of silver, silver compounds, gelatin, cellulose fibers, antimony compounds, siliceous compounds and casual dirt.

16. The process of claim 1 wherein the silver content and the first solvent-soluble but water-insoluble polymers are recovered separately in yields in excess of 99% of the content of these materials in the original raw material.

17. The process of claim 1 where the solvents used are recovered by fractional distillation for recycle use in said process.