CA1050200A

CA1050200A - Thermoplastic elastomers from recycled polyesters

Info

Publication number: CA1050200A
Application number: CA223,750A
Authority: CA
Inventors: Joseph H. Tazewell
Original assignee: Firestone Tire and Rubber Co
Current assignee: Bridgestone Firestone Inc
Priority date: 1974-04-10
Filing date: 1975-04-03
Publication date: 1979-03-06
Also published as: GB1500577A; FR2267340B1; BE827527A; JPS5623451B2; IT1032640B; DE2514471A1; FR2267340A1; JPS50139195A

Abstract

THERMOPLASTIC ELASTOMERS FROM RECYCLED POLYESTERS

Abstract of the Disclosure There is provided a process for utilizing scrap poly-(ethylene terephthalate) and converting it into a useful thermo-plastic polyester elastomer. It comprises the steps of glycolizing scrap poly(ethylene terephthalate) to an oligomeric material and melt copolymerizing the oligomeric material with a poly(alkylene ether) glycol. The product is useful in making various articles, for example garden hose.

Description

ll Background of the Invention and Prior Art l ~
Present estimates indicate that there are approximately 218 million pounds of scrap poly(ethylene terephthalate) produced each year. As is well known, this polyester material is used to a large extent in the pro~uction of fibers by known spinning and drawing techniques. Scrap poly(ethylene terephthalate) results in normal processing of the polymer, in starting up of plants for processing the pol~mer, and in cleaning of equipment. Other sources of the scrap poly(ethylene terephthalate) hereinafter O called scrap PE~ include f lashing, cuttings, etc. A principal use of PET is in the production of film (Mylar), and f~brous materials e.g. reinforcing elements for rubber productsJ for ~xample pneu-matic tires.
Heretofore, the scrap PET has been discarded. It has no~
been found that by treating the scrap material in accordance with the procedures of the present invention, a useful thermoplastic polyester elastome:ric material may be produced, thereby conserving this otherwise waste material.
l Products are known in the prior art which have propertieC
O quite similar to those which are possessed by the products formed in accordance with the process of this invention. ~otable among these are those described in the patent to Willaxd 3JO13J914J the ¦
patent to Shi.vers 3,023,192, the patent to Witsiepe 3,763J109, the patent to Wolfe 3J775J373. Reference may also be had to Coleman, 'IBlock Copolymers: Copolymerization of Ethylene Terephthalate and Polyoxyethylene Glycols,~ Journal of Polymer Science, Volume 14, pp l5 - 28 (1954).

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Instead of starting with monomeric materials or full polymers as taught by the prior art, the present invention utilizec as a starting material scrap PET which consists primarily of hish molecular weight material in which there will be a lack of consis-tency of propertles due to various stages of processing from which¦
it has been derived. The scrap material may comprise or consist of undrawn or drawn polymer and thus vary from sample to sample in¦
crystallinity characteristics. It may also comprise or consist of¦
polymer which has never been spun. These various moieties of PET
¦polymer individually or in various mixtures constltute scrap PET
¦as considered by this invention. The scrap PET is according to ¦ this invention partially depolymerized or degraded to an oligomeri ¦material of from 2 to 7 units. This material is then copolymerizec ¦ with a polyoxyethylene glycol material such as those which have i ¦ been used in the prior art. (See Shiver, supra.) ¦ The product which results from the present invention is a thermoplastic elastomer in contradistinction to normal thermo-setti~ elastomeric materials which require special molding equip-I ment and curing. ~hese thermoplastic materials may be injection ¦
¦ molded and are also reusable and reclaimable whereas the-cured ¦
materials are not. The products of the present invention may be !
subjected to any of the usual shaping procedures to which thermo-plas ic meteriels have heretofor been ~ubmitted. ¦

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The present invention relates as indicated to a process for utilizing scrap polyethylene terephthalate as a starting material for producing a thermoplastic polyester elastomer. The process of the invention comprises glycolizing scrap polyethylene terephthalate with an alkylene glycol containing 1 to 4 carbon atoms, in a weight ratio of from about 0.1 to 5 times the weight of the scrap at a temperature of from 200 to 250C and for a period of time sufficient to yield a degraded polymer predominating in a mixture of oligomeric materials having from 2 to 7 units. This oligomeric material is then copolymerized at a pressure less than about 0.5 mm Hg with a poly(alkylene glycol) ether having a molecular weight of from 1000 to 5000 in the presence of a melt copolymerization catalyst, the weight ratio of degraded polymer to poly(alkylene ether) glycol being in the range of from 1:3 to 3:1.

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~05~200 Detailed Descript_on of the Process and Speclfic Exa~ples In general, the inven~ion contemplates the treatment of scrap PET with an alkylene glycol such as ethylene glycol, the glycol being present in an amount generally equal to from about .1 to about 5 times the weight of the scrap PET. In a preferred ~bodLment, these materlals are heated to re~lux for the gl~col, i.e. at about 200C for ethylene glycol, for a period of about 18 hours or until the solution becomes clear. At this point, ~he ¦composition contains partially depolymerized scrap PET. Since ) repolymerization is contemplated, the desired objective is not to reduce the scrap PET to the monomer state.
: ~h~ amount of alkylene glycol utilized in the glycolizinc ¦step may range theoretically from a trace to any large excess.
l However, from a practical point of view an amount of alkylene gly-i ¦ col in ~he range of from .1 to 5 times the weight o~ the scrap PET
has been found adequate. .
Where glycolysis and copolymerization are performed ¦ se~uentially as distinct ~rom in situ, removal of the heat source results, upon spontaneous cooling of the giycolysis mass9 in the I ~ormation of a white paste-like substance.
¦ ThereafterJ the paste may be copolymerized in the pres-¦ ence of a catalyst, such as antimony trioxide, with a difunctional po~yether polyol or polyoxyalkylene glycol ~O(R0) H such as, for ¦ example a polyoxyethy~ene glycol of molecular weight 1350 to 2800 - ¦ ~uch as descr~bed in the Coleman article, supra. Such materials ¦ are commerciaLly available, fox example, under the trademark . . .

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~ 1050Z00 ¦~Carbowax,~ or 'rPolymeg~ and those having molecular weight~ in the ¦range of from 1000 to 5000 are especially useful in accordance wit~
¦the present invention. Other poly(alkylene glycol) ethers may be ¦used wherein the alkylene group contains from 2 to 10 carbon atoms ¦Thus, poly(ethylene glycol)~ ether, poly(propylene glycol)n ether~
¦and poly(butylene glycol)n ether having molecular weishts in the ¦aforesaid range may be used in accordance with the present inve~-¦tio~. Other examples of su~h difunctional polyethers useful in ¦accordance herewith will be found in U. S. Patent ~,023,192. This ¦copolymerization is carried out by heating the reactant materials ¦at a temperature in the range of from 200 to 250C for a period oi ¦time until the evolution of the glycol from the reaction mixture ¦ ceases. Reduced pressure may ~e used to aid in the removal of the I excess glycol if desired. Thereafter, the composition is subjectec ¦ to a vacuum op the order of O.5 mm Hg to enable further polymeri-¦ zation to the desiracl viscosity and to complete the evolution of any excess glycol. It is under reduc~d pressure conditions that the major amount of polymerization to the final product occurs. U~
to the tIme of the a~plication of the ~acuum, the product may be considered to be substantially a prepolymer of rela~ively low ¦molecular weight. Application of vacuum and heating is continued ~for a period of from four to eight hours with stirring, for exampl~, -¦after final evolution of the alkylene ~lycol. When the material i cooled to room temperature, it is an elastomeric com~osition or ha~
¦elastomeric properties. The melt polycondensation conditions ¦
¦employed her~ are generally the same as those descr~bed in Carother , ¦Patents 2,071,250 a~d 2~O71J251.

iOS0200 l l Any known melt condensation catalyst or mixed catalys~
system may be used to aid the co~olymerization re~ction. See for example the catalysts descr~bed in U. S. Patents 2,465,319 and 2,5~4,028.
A heat and/or radiation stabilizer, or mixture of sta-bilizers, to ~mpxove the ~inal properties of the copolymers hereof .
may be utilized in accordance herewith if desired. A preferred stabilizer is ~,N' bis(beta-naphthyi)-p-phenylene diamine included in the copolymer at the time of melt condensation. Other examples of polyester stabilizers useful herein are well known (see ~. SA
Patent 3,02~,192, Column 11). The resulting product is a thermo-plastic elastomer in contradistinction to normal elastomeric mate- ¦
rials which reguire special molding eguipment and curing. The thenmoplastic polyester elastomers of the present invention may be injection molded and are also reusable and reclaimable whereas thermoset elastomer materials are not.
It becomes convenient at this point to illustrate the present invention by specific examples, it being understood that these examples are for illustrative purposes only and that those skilled in the art wilI ba ena~led by these examples to carry out the process with other starting materials without detracting from the invention.
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lOSOZOO
E~AMPLE 1 The present example illustrates a procedure for glycoliz ing scrap PET.
The glycolysis product is prepared by refluxing ethylene¦
glycol with scrap PET. For most pu,rposes, a 2:1 mixture of glycol and scrap polyester has been utilized. The mixture has typically ¦
been refluxed until a clear solution is formed. It will be appre-¦ciated that glycolysis can be interrupted at any desired oligomeric ¦state. It may also be apprec~ated that this invention conte~platec the direct glycolysis of ~he scrap PET in the presence of the othe~
thermoplastic polyester ingredients such as poly( tetramethylene glycol ) ether. The so~called ~in situ~ procedure wherein glycoly-sis and melt condensation proceed in the same vessel with all reactants present will be found to be ~uite economic.
The following is a typical recipe for glycolysis of scrap PET:
grams Ethylene glycol 2~22 Scrap PET chips 1411 Zinc acetate dihydrate 1.4 ~ The above mixture is refluxed under nitrogen for a perioc of 16 hours. The resulting solution is clear and is allowed to cool With agitation to a white paste. The 2:1 glycol/scrap PET
, paste is then used in subsequent preparations of thermoplastic polyester elastomers.
The polyester portion isolated from the glycol portion has a hydroxyl number of 219, indicating a molecular weight of ~
approximately 513. It should be observed that the molecular weight of bis-hydroxyethyl terephthalate is 254, indicative that the gly-colysis product is at least twice the molecular weight of bis-`3 ~ hydroxyethyl terephthalate.

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¦ This example illustrates the preparation of a polyester elastomer. As indicated, it is the intent of the present inven- -¦tion to produce the polyest~r elastomers either in situ or by ~separate steps.
I The following example illustrates the ~reparation of a ¦polyester elast~mer by sequential steps as follows:
l grams ¦Poly(tetramethylene ether) glycol, mw 2000 120 ~Glycolized scrap PET from Example 1 240 N,N~-di(beta-naphthyl)-p-phenylene diamine - 1.5 I Antimony trioxide catalyst - 0.13 ¦ The foregoing ingredients w~re mixed in a stainless steel resin Xettle with stirring and maintained under a nitrogen atmos-phere. The temperature was increased until a temperature of 250C
was reached. By the time the temperature reached 250C, substan-tially all of the excess ethylene glycol had been distilled out.
The polymerizing mixture was then heated at 250C under a reduced pres-ure (less than 0 .5 mm Hg) for approximately 4 hours. The ~ -inherent viscosity of t~e resulting polymer was tested and deter-mined to be 1.89 (0.2 g/dl of the polymer dissolved in 60/40 pheno] /
tetrachloroe~hane solution at 25C).
The resultant polymer was molded into test slabs at 400 .
The standard elastomeric properties were as ~ollows:

Shore A hardness 80 Tensile s~rer.gth, psi 2450 Percent elongation at break 620 ~odulu~ o~ elasticity ~n p8i at 5% 110 100% 600 3% 1~00 ~ -: 400% ~1500 50% 2000 . .' ' '.
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1050ZOo This example illustrates the preparatio~ of an iso-phthalate modified cspolymerization product. The following ingre-dients were charged to a polycondensation reactor equipped with a stirr0r and condenser Poly(tetramethylene ether) glycol, mw 1000 grams Glycolized scrap PET (Example 1) 630 D~methyl isophthalate 30.66 Antimony trioxide 0 25 ~,N'-bis(beta-naphthyl)-p-phen~lene diamine 0 25 The at~osphexe above the reaction mixture was purged with nitrogen and the mixture stirred and heated under a slow stream of nitrogen at 200C. At about 200C, the excess ethylene glycol distilled off. With continued heating, the temperature -reached 250C. The mixture should not be heated Ln excess of 250~
in this case. Vacuum was then gradually applied and held at a max-imum level less than 0.5 mm ~g for a period of from 4 to 6 hour6 or until a viscosity plateau was reached. m e inherent viscosity of the polymer was 1.0 when measured at a concentration of 0.2 g per deciliter in 60/40 phenol/tetrachloroethane at 25C.
The foregoing produ~t has the following properties:

Shore A hardness 88.5 ~ensil~ strength, psi 25~7 Elongation percent 513 ; 100% modulus psi 1522 200% modulus psi 1742 300% modulus psi 198~
400% modulus psi 2229 ¦500~ odulus psi 2~99 ' ' . : -: . ..
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¦ EXAMPLE 4 - 13 ¦ The following example illustrates the in situ preparatio~
¦of the condensate starting with scrap PET. ¦
l To a polycondensation reactor equipped with stirrer, ¦condenser~ nitrogen inlet valve and conduit, and means for apply-~ing a vacuum of 0,5 mm Hg or less were charged the following materials:

¦Poly(tetramethylena ether) glyco~, mw 1000 grams Scrap PET 210 ~ -¦Dimethyl isoph~halate . 30 66 Ethylene glycol ¦ 24 8 IAntimony trioxide 0 25 ¦N,N~-bis(beta-naphthyl)-p-phenylene diamine 0 25 The atmosphere above the reaction mixture was purged with Initrogen. The reaction mixture was stored and heated to 250C
¦ under a slow stream~of nitrogen. After reaching 250C~ the mixtur3 ~
¦ was stirred for an additional 2 hours at 250C. Vacuum was then I ~-¦ applied to the extent of 0.5 mm Hg ox less, and the polycondensa- ¦
tion roaction continued for from 4 - 6 hours until a viscosity plateau was reached. ~he inherent viscosity of the polymer was ¦ found to be 0.815 (0.2 g/dl in 60/40 phenol/tetramethylethane at 25C.
¦ The condensate had the following properties: ¦

15hore A hardness ~ 90 ¦ Tensile strength, psi~ ~ 2694 3 perce~t elongatio~ - , , 483 '7 ! 100% modulus, psi ~ 39 ¦ 2 ~ modulus, psi - ~ 1946 300% modulus, psi ~ 2219 , 4 ~ ~o~ulus, psi ~ ~ 249 These properties co~pare guite well with the properties ~, of the material produced by the step-wise procedur~ of Example 3.
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¦ The following table illustrates various ratios of the ¦poly(tetramethylene ether) glycol (PTMEG) and the glycolized scrap ¦PET (PET), and various molecular weights for the poly(tetramethyl- ~.
ene ether) glycol. "Examples 5-13 in the Table were carried out in accordance with the procedure outlined immediately under headin .
. ~Examples 4-13',', changes being made as regards the proportions of :~ ~nq di~nts used.

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If the glycolysis reaction were to degrade the scrap PET
to bis-(2-hydroxyethyl) terephthalate, it would be expected that the properties of the degraded material and the material prepared from bis-(2-hydroxyethyl) terephthalate would be essentially the same. The following Table II compares the results obtained in .
¦accordance with the teachings of Example 4 of U. S. Patent ~5,701,-1755 and the results obtained in accordance with Example 2. ~hese ¦results are tabulated in Table II below. .
¦ TABLE II
¦ . . Al . B2 Ratio PTMEG/PET 66/34 65/~5 . ¦Shore A Hardr~ess 75 64 % ~:lvngation at break 650 506 ~odulus in psi at 5% 102 ;6 iOO% 709 325 20C1% .989 500 . 300,9~ 1256 675 :
400% 1519 850 - 500% . 1791 950 Break 2142 975 Compressive Set at 158F 29% 66,~ .

lExample 4 U. S. Patent 5,701,755 ¦2Like Example 2 above Il . `
l lOSOZOO
From Table II above, it will be observed that t~e moc~ulus at various percents elongation for the product produced in accord-ance with the present invention is cluite consistently about hal of the modulus of the product produced in accordance with Example 4 i of ~atent ~,701,755 when the ingredients are of closely comparable amounts. This is not to say, however, that fr~m the standpoint of utility the products produced in accordance with the present inven-¦tion are less useful than those produced in accordance with the ¦aforementioned patent. In this in~ention the starting material is la scrap material and, therefore, cauite inexpensive. ~evertheless, ~hen treated and modi~ied in ways knc~n for treatLng segmented ~opolyetherester elastomers, tbe product ~s useful in the produc-~ion of such items as garden hoses, ~ndustrial hose material, industrial tires, tennis shoe soles, and the l~ke.
The glycolyzed scrap PET produced in accordance herewith s also useful as an inexpensive coreactan~ for poly(ethylene tere-?hthalate) prepolymer utilized to produce segmented copolyether_ ster elastomers, for ~cample, as suggested by Wolfe 3,775,373 tr Wits e 3,763~10g~
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~1 1050200 Examples 14-30 Example ~ above lS typical of the preparation of an isophthalate modified copolymerization product. Tables 3 and 4 below show additional examples of isophthalate modified products.
I The percent polyester is the summation of the weights of scrap PET
¦glycolized in accordance with Example 1 and isophthalic acid or ¦dimethyl isophthalate which become polyester components. The ¦PTMEG has the same significance as in the preceding ta~les. The ¦procedure by which these additional' examples are produced is sub-¦stantially as given in Example 3, changes being made as regards D ¦the proportions of the ingredients used. The lower alkyl iso-¦phthalates which may be used include dimethyl phthalate and ¦ diethyl phthalate. The content of combined glycolized polyethylen~
l terephthalate scrap plus the isophthalic acid or lower al~yl ester ¦ thereof is in the range of from 4C to 7O parts by weight, and the ~ poly(alXylene ether) glycol is present in an amount su~ficient to l balance to a total of lOO parts by weight. The weight ratio of ¦ glycolized scrap polyethylene terephthalate to isophthalic acid or lower alkyl isophthalate is from 4 to 12.
I It has been found that the inclusion of isophthalic acid ¦ or lower alkyl isophthalate in the copolymerization mass assures ¦ the production of a rubbery polymer as will be seen from an examination of t~e results in ~ables III and IV below. The re-¦s~lting polymer retains rubbery characteristics better especially ¦after experienci~ng a heat history or annealing. Without isophthal-1 ate modification, loss of tensile stre~gth and elongation may be ¦experienced particularly at higher concentrations of PET.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for producing a thermoplastic polyester elastomer from scrap polyethylene terephthalate comprising the steps of:
(a) glycolizing scrap polyethylene terephthalate with an alkylene glycol in a weight ratio of from 0.1 to 5 times the weight of the scrap at a temprature of from 200° to 250°C and for a period of time sufficient to yield a degraded polymer predominating in a mixture of oligomeric materials having from 2 to 7 units, said alkylene glycol containing from 1 to 4 carbon atoms;
(b) copolymerizing at a pressure less than about 0.5 mm Hg the degraded polymer with a poly(alkylene ether) glycol having a molecular weight of from 1000 to 5000 in the presence of a melt condensation catalyst in a weight ratio of degraded polymer to said poly(alkylene ether) glycol of from 1:3 to 3:1.

2. A process in accordance with claim 1, in which the alkylene glycol is ethylene glycol.

3. A process in accordance with claim 1, in which the poly(alkylene ether) glycol is a poly(tetramethylene ether) glycol.

4. A process in accordance with claim 1, in which the catalyst is antimony trioxide.

5. A process in accordance with claim 1, in which the poly(alkylene ether) glycol is present in the glycolizing step (a).

6. A process in accordance with claim 1, in which the glycolizing step is carried out at atmospheric pressure.

7. A process for producing a thermoplastic polyester elastomer from scrap polyethylene terephthalate comprising the steps of:
(a) glycolizing scrap polyethylene terephthalate with an alkylene glycol in a weight ratio of from 0.1 to 5 times the weight of the scrap at a temperature in the range of 200° to 250°C and for a period of time sufficient to yield a degraded polymer predominating in a mixture of oligomeric materials having from 2 to 7 units, said alkylene glycol containing from 1 to 4 carbon atoms;
(b) copolymerizing at a pressure less than about 0.5 mm Hg the degraded polymer with a polymethylene ether glycol having a molecular weight of from 1000 to 5000 in the presence of a melt condensation catalyst in a weight ratio of degraded polymer to said polymethylene ether glycol of from 1:3 to 3:1.

8. A product produced in accordance with the process of claim 1.

9. A process for producing a thermoplastic polyester elastomer from scrap polyethylene terephthalate modified with isophthalate and comprising the steps of:
(a) glycolizing scrap polyethylene terephthalate with an alkylene glycol in a weight ratio of from 0.1 to 5 times the weight of the scrap at a temperature of from 200° to 250°C and for a period of time sufficient to yield a degraded polymer predominating in a mixture of oligomeric materials having from 2 to 7 units, said alkylene glycol containing from 1 to 4 carbon atoms;
(b) copolymerizing at a pressure less than about 0.5 mm Hg the degraded polymer with a poly(alkylene ether) glycol having a molecular weight of from 1000 to 5000 and isophthalic acid or a lower alkyl isophthalate ester wherein the lower alkyl group contains 1 or 2 carbons in the presence of a melt condensation catalyst;

the content of combined glycolized scrap polyethylene terephthalate plus the isophthalic acid or lower alkyl ester thereof being from 40 to 70 parts, and the poly(alkylene ether) glycol being present in an amount sufficient to balance to a total of 100 parts and the weight ratio of glycolized scrap polyethylene terephthalate to isophthalic acid or lower alkyl isophthalate being from 4 to 12.

10. A process in accordance with claim 9, in which the alkylene glycol is ethylene glycol.

11. A process in accordance with claim 9, in which the poly(alkylene ether) glycol is a polymethylene ether glycol.

12. A process in accordance with claim 9, in which the poly(alkylene ether) glycol is a poly(tetramethylene ether) glycol.

13. A process in accordance with claim 9, in which the catalyst is antimony trioxide.

14. A process in accordance with claim 9, in which the isophthalate is dimethyl isophthalate.

15. A process in accordance with claim 9, in which the isophthalate is diethyl isophthalate.

16. A product produced in accordance with claim 9.