WO2022093681A1 - Recyclable polyester polymers for thermoformed sheets and molded articles - Google Patents

Recyclable polyester polymers for thermoformed sheets and molded articles Download PDF

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Publication number
WO2022093681A1
WO2022093681A1 PCT/US2021/056433 US2021056433W WO2022093681A1 WO 2022093681 A1 WO2022093681 A1 WO 2022093681A1 US 2021056433 W US2021056433 W US 2021056433W WO 2022093681 A1 WO2022093681 A1 WO 2022093681A1
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WIPO (PCT)
Prior art keywords
polyester composition
glycol
sheet
residues
mole percent
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PCT/US2021/056433
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French (fr)
Inventor
Kolawole Folayele AYINUOLA
Stephen Edward Lehman
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Auriga Polymers, Inc.
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Publication of WO2022093681A1 publication Critical patent/WO2022093681A1/en

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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
    • C08G63/02—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds
    • C08G63/12—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds derived from polycarboxylic acids and polyhydroxy compounds
    • C08G63/16—Dicarboxylic acids and dihydroxy compounds
    • C08G63/20—Polyesters having been prepared in the presence of compounds having one reactive group or more than two reactive groups
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
    • C08G63/02—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds
    • C08G63/12—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds derived from polycarboxylic acids and polyhydroxy compounds
    • C08G63/16—Dicarboxylic acids and dihydroxy compounds
    • C08G63/18—Dicarboxylic acids and dihydroxy compounds the acids or hydroxy compounds containing carbocyclic rings
    • C08G63/181—Acids containing aromatic rings
    • C08G63/183—Terephthalic acids
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K5/00—Use of organic ingredients
    • C08K5/0008—Organic ingredients according to more than one of the "one dot" groups of C08K5/01 - C08K5/59
    • C08K5/0016—Plasticisers

Definitions

  • This invention is directed to recyclable polyester compositions, and in particular for their use in thermoformed sheets and multipack articles
  • Multipack packages containing 4, 6 or more cups. These multipack packages are made by thermoforming plastic sheets into groups of several attached cups segmented with a means of bending and snapping them apart at a predetermined breaking point, this behavior shall herein be called “snappability”. This means of bending and snapping them apart can be selected from a group selected from V-section scores or grooves, punched lines, perforations and the like and combinations of these means. It is also important that the multipack has sufficient integrity such that they can be lifted and do not snap under their own weight.
  • the polymer used for these multipack packages is a blend of general purpose and high impact polystyrene.
  • polystyrene articles are not recyclable, the industry is demanding a polymer that is easily recyclable and reusable for these articles.
  • these recyclable polymers should run on existing equipment designed for polystyrene with minimum modification.
  • Polyesters, in particular polyethylene terephthalate) and its copolymers are the polymer of choice.
  • polyester does not snap along a predetermined breaking point, such as a score line, in the multipack package but bends and forms a “living hinge” that does not break or tear.
  • U. S. Pat. Application 2018/0194117 Al discloses a multilayer sheet in which the outer layers consist of a polyester containing a delustrant and optionally pores, and inner layers containing calcium carbonate, and other such additives, in which snap incisions extend from the upper surface into the inner layers. These articles are not recyclable.
  • U. S. Pat. No. 10,066,067 Bl discloses a method to embrittle the section of the polyester thermoformed sheet in which the groove, or other weakening means, between the individual cups is heated to an extent that this section crystallizes and the cups snap in this brittle region.
  • the methods used to crystallize these weakened sections and contact with heated brass tool or lasers adds cost to the equipment. In addition, these crystallized sections are opaque.
  • U.S. Pat. No. 7,030,181 B2 discloses a composition for polyester film or sheets comprising about 5 to 50 weight % of a plasticizer to induce crystallization during calandering.
  • U.S. Statutory Invention Registration Hl 987 H discloses the use of non-volatile plasticizers as flow aids for processing polyester resins.
  • the polyester composition comprising about 1 to 25 weight % of poly(alkylene ether)s or end-capped poly(alkylene ether)s.
  • this invention relates to a recyclable copolyester composition for the manufacture of sheets comprising: a) comonomer to retard crystallization, and b) branching comonomer, and c) plasticizer
  • this invention relates to the process for using the sheets, made from this composition, to thermoform multipack articles.
  • polyester compositions suitable for use in this invention typically comprise:
  • a diacid component comprising 90 to 100 mole percent of residues of terephthalic acid, naphthalene dicarboxylic acids or mixtures thereof, based on the total mole percent of diacid residues in the polyester compositions, and
  • glycol component comprising 90 to 99 mole percent of residues of ethylene glycol, diethylene glycol or mixtures thereof, based on the total mole percent of glycol residues in the polyester compositions, and
  • polyester is intended to include “copolyesters” and is understood to mean a synthetic polymer prepared by the reaction of one or more difunctional carboxylic acids and/or multifunctional carboxylic acids with one or more difunctional hydroxyl compounds and/or multifunctional hydroxyl compounds, for example, branching comonomers.
  • the difunctional carboxylic acid can be a dicarboxylic acid and the difunctional hydroxyl compound can be a dihydric alcohol such as, for example, glycols and diols.
  • glycocol as used herein includes, but is not limited to, diols, glycols, and/or multifunctional hydroxyl compounds, for example, branching comonomers.
  • the difunctional carboxylic acid may be a hydroxy carboxylic acid such as, for example, p-hydroxybenzoic acid
  • the difunctional hydroxyl compound may be an aromatic nucleus bearing 2 hydroxyl substituents such as, for example, hydroquinone, resorcinol or other heterocyclic diols, and isosorbide, for example.
  • residue means any organic structure incorporated into a polymer through a polycondensation and/or an esterification reaction from the corresponding monomer.
  • replicaating unit means an organic structure having a dicarboxylic acid residue and a diol residue bonded through a carbonyloxy group.
  • the dicarboxylic acid residues may be derived from a dicarboxylic acid monomer or its associated acid halides, esters, salts, anhydrides, and/or mixtures thereof.
  • dicarboxylic acid is intended to include dicarboxylic acids and any derivative of a dicarboxylic acid, including its associated acid halides, esters, half-esters, salts, half-salts, anhydrides, mixed anhydrides, and/or mixtures thereof, useful in a reaction process with a diol to make polyester.
  • terephthalic acid is intended to include terephthalic acid itself and residues thereof as well as any derivative of terephthalic acid, including its associated acid halides, esters, half-esters, salts, half-salts, anhydrides, mixed anhydrides, and/or mixtures thereof or residues thereof useful in a reaction process with a diol to make polyester.
  • the polyesters used in the present invention typically can be prepared from dicarboxylic acids and diols which react in substantially equal proportions and are incorporated into the polyester polymer as their corresponding residues.
  • the polyesters of the present invention therefore, can contain substantially equal molar proportions of acid residues (100 mole %) and glycol (and/or multifunctional hydroxyl compound) residues (100 mole %) such that the total moles of repeating units is equal to 100 mole %.
  • the mole percentages provided in the present disclosure therefore, may be based on the total moles of acid residues, the total moles of diol residues, or the total moles of repeating units.
  • a polyester containing 5 mole % isophthalic acid means the polyester contains 5 mole % isophthalic acid residues out of a total of 100 mole % acid residues.
  • polyester containing 1.5 mole % di ethylene glycol, out of a total of 100 mole % glycol residues has 1.5 moles of di ethylene glycol residues among every 100 moles of glycol residues.
  • the polyesters of the invention can also comprise at least one chain extender.
  • Suitable chain extenders include, but are not limited to, multifunctional (including, but not limited to, bifunctional) isocyanates, multifunctional epoxides, including for example, epoxylated novolacs, and phenoxy resins.
  • chain extenders may be added at the end of the polymerization process or after the polymerization process. If added after the polymerization process, chain extenders can be incorporated by compounding or by addition during conversion processes such as injection molding or extrusion.
  • the amount of chain extender used can vary depending on the specific monomer composition used and the physical properties desired but is generally about 0.1 to about 5 % by weight, or about 0.1 to about 2 % by weight, based on the total weight of the polyester.
  • polyester compositions and the polymer blend compositions useful in the invention may also contain any amount of at least one additive, for example, from 0.01 to 2.5% by weight of the overall composition common additives such as colorants, dyes, mold release agents, flame retardants, plasticizers, stabilizers, including but not limited to, UV stabilizers, thermo-oxidative stabilizers and/or reaction products thereof, and impact modifiers.
  • additives such as colorants, dyes, mold release agents, flame retardants, plasticizers, stabilizers, including but not limited to, UV stabilizers, thermo-oxidative stabilizers and/or reaction products thereof, and impact modifiers.
  • thermo-oxidative stabilizers include phosphorus compounds and primary and secondary antioxidants commercially available for use in polyester resins.
  • Examples of typical commercially available impact modifiers well known in the art and useful in this invention include, but are not limited to, ethyl ene/propylene terpolymers, functionalized polyolefins such as those containing methyl acrylate and/or glycidyl methacrylate, styrene-based block copolymeric impact modifiers, and various acrylic core/shell type impact modifiers.
  • ethyl ene/propylene terpolymers functionalized polyolefins such as those containing methyl acrylate and/or glycidyl methacrylate
  • styrene-based block copolymeric impact modifiers styrene-based block copolymeric impact modifiers
  • various acrylic core/shell type impact modifiers for transparent thermoformed articles the refractive index of these additives must closely match the refractive index of the polyester composition to prevent a hazy container. Residues of such additives are also contemplated as part of the polyester
  • a bluing toner can be used to reduce the yellowness of the resulting polyester polymer melt phase product.
  • Such bluing agents include cobalt salts, blue inorganic and organic toner(s) and the like.
  • red toner(s) can also be used to adjust the redness.
  • Organic toner(s), e.g., blue and red organic toner(s) can be used.
  • the organic toner(s) can be fed as a premix composition.
  • the premix composition may be a neat blend of the red and blue compounds or the composition may be pre-dissolved or slurried in one of the polyester's raw materials, e.g., ethylene glycol.
  • the total amount of added toner components depends on the amount of inherent yellow color in the base polyester and the efficacy of the toner. Generally, a concentration of up to about 15 ppm of combined organic toner components and a minimum concentration of about 0.5 ppm are used, with the total amount of bluing additive typically ranging from about 0.5 ppm to about 10 ppm.
  • polyesters can be achieved by a batch, semi-continuous, or continuous process.
  • a typical polyesterification process is comprised of multiple stages and commercially carried out in one of two common pathways.
  • the initial stage of the process the dicarboxylic acids react with one or more diols at a temperature of about 200° C to about 250° C to form macro-monomeric structures and a small condensate molecule, water. Because the reaction is reversible, the water is continuously removed to drive the reaction to the desired first stage product.
  • the crystallization retardant and branching comonomers are normally added at this stage of the process.
  • an Ester Interchange process is used to react the ester groups of the diesters and diols with certain well known catalysts such, such as manganese acetate, zinc acetate, or cobalt acetate. After completing the ester interchange reaction these catalysts are sequestered with a phosphorus compound, such as phosphoric acid, to prevent degradation during the polycondensation process.
  • catalysts such as manganese acetate, zinc acetate, or cobalt acetate.
  • the catalysts generally used for the polycondensation reaction are compounds containing antimony, germanium, aluminum, titanium or other catalysts known to those skilled in the art, or mixtures thereof.
  • the specific additives used and the point of introduction during the reaction is known in the art and does not form a part of the present invention. Any conventional system may be employed and those skilled in the art can select among various commercially-available systems for the introduction of additives so as to achieve an optimal result.
  • the polyester pellets can be further polymerized to a higher molecular weight by well-known solid state polymerization processing techniques.
  • the terephthalic acid and/or ethylene glycol are preferably derived from a biomass feedstock rather than a petroleum based feedstock.
  • the use of chemically recycled terephthalic acid (or dimethyl terephthalate) and ethylene glycol from post-consumer polyester waste is also preferred for the polyesters of this invention.
  • Another preferred method of manufacturing the polyester resins of this invention utilizes bis-(hydroxyethyl)-terephthalate, purified from the reaction product of glycolysis of post-consumer polyester waste, this monomer can be added to the polymerization process, preferably prior to the polycondensation stages.
  • polyester resin utilizes clean clear flake from post-consumer waste (rPET) can be added during the esterification or first stages of the polymerization process. Up to 50 weight percent of this rPET is first depolymerized by the low molecular weight polymer and this mixture polymerized under the normal processing conditions.
  • rPET post-consumer waste
  • the polyester compositions of this invention are designed for use in a thermoforming process.
  • the polyester resin is dried and fed to an extruder that extrudes the molten polymer through a sheet casting die that forms a flat sheet that is quenched on chilled rolls, calendered into the required sheet thickness, and optionally cut into the required width, before being wound into a clear roll.
  • sheet is herein understood to mean an article having a small thickness relative to the direction perpendicular to the thickness direction.
  • the sheet thickness is typically in the range of 0.5 to 2 mm, when the thickness of the sheet is less than 0.5 mm the sheet may also be called a film.
  • the sheet is unwound from the roll into a set of indexing chains that transport the sheet through an oven for heating to the forming temperature, typically in the range of about 120° to about 160° C for polyester resins.
  • the heated sheet then moves to a form station where it is held against a mold, designed for the shape and size of the article being made.
  • a vacuum is applied to remove trapped air and the sheet is stretched into a chilled mold, along with pressurized air and a plug to assist in providing the necessary material distribution and thickness in the molded part.
  • the forming tool opens and the article is removed from the mold.
  • the sheet containing the formed parts is then indexed into a trim section, where a die cuts the parts from the sheet. It is at this stage of the process that the web between the individual cups is scored, or a means to provide a breaking point between the individual cups, is provided.
  • the preferred score depth is in the range of about 45 percent to about 75 percent of the sheet thickness.
  • thermoforming process for multipack containers for dairy products, such as yogurt cups
  • additional steps of filling the cups and sealing the package are integrated with the forming process.
  • polyester compositions suitable for use in this invention include those having an intrinsic viscosity of at least about 0.50 dl/g, preferably at least about 0.60 dl/g, and more preferably between about 0.65 and about 0.85 dl/g.
  • Lower intrinsic viscosity resins have insufficient melt strength for extruding a sheet, whereas higher intrinsic viscosity resins have too high a melt viscosity for extruding a sheet at the normal extrusion temperatures, as higher temperatures cause thermal degradation and a loss of molecular weight.
  • the plasticizer can be dry blended with the polyester composition and this blend dried and extruded into a sheet for subsequent thermoforming.
  • the plasticizer can be added at various ports along the extruder forming the sheet, either single or twin-screw extruders.
  • the polyester composition should be dried to a moisture level less than 100 ppm prior to extrusion. This can be accomplished by the standard drying in hot dry air that is practiced in the industry, or by applying a vacuum after the polymer has melted in a twin-screw extruder.
  • a master batch of the plasticizer can be prepared by compounding the dried plasticizer with polyester composition, or by compounding with an inert carrier such as those normally used for dyes and pigments for coloring polyester articles.
  • the plasticizer can be melt added to the polymer composition during the polymerization process, preferably after the polymerization is complete prior to the extrusion on the polymer through the die into strands for quenching and cutting.
  • the crystallization retardant composition amount ranged from a lower limit below which the sheet is crystalline and an upper limit at which the melting point was less than 225° C (recycling lower limit).
  • the branching comonomer amount, to induce brittleness ranged from about 250 to about 2500 parts per million (ppm) (based on the total weight of the copolyester), the upper limit was chosen to minimize gel formation.
  • crystallization retardant comonomers comprising dicarboxylic acids or diols are used.
  • the amount is chosen such that the melting point of the copolyester composition is preferably equal or greater than 225° C. Lower melting point compositions may not pass the requirements for recyclable polyester as set forth in the Association of Postconsumer Plastic Recyclers Critical Guidance Protocol.
  • the dicarboxylic acid component of the polyesters useful to reduce the crystallization rate in the invention can comprise up to 10 mole %, of one or more modifying aromatic dicarboxylic acids.
  • modifying aromatic dicarboxylic acids which may be used in this invention include, but are not limited to, aromatic dicarboxylic acids preferably having 8 to 16 carbon atoms, aliphatic dicarboxylic acids preferably having 4 to 16 carbon atoms, and cycloaliphatic dicarboxylic acids preferably having 8 to 16 carbon atoms.
  • Heterocyclic dicarboxylic acids for example 2, 5-furan dicarboxylic acid may also be used
  • the glycol component of the polyesters useful to reduce the crystallization rate in the invention can comprise up to 10 mole %, of one or more modifying glycols.
  • modifying glycols which may be used in this invention include, but are not limited to, aliphatic glycols preferably having 2 to 20 carbon atoms or alicyclic glycols preferably having 6 to 20 carbon atoms.
  • modifying dicarboxylic acids and modifying diols to reduce the crystallization rate of the copolyester are also contemplated in this invention.
  • the preferred mixture is isophthalic acid and diethylene glycol.
  • the branching comonomer present in the composition has 3 or more carboxyl substituents, hydroxyl substituents, or a combination thereof.
  • branching monomers include, but are not limited to, multifunctional acids or multifunctional alcohols such as trimellitic acid, trimellitic anhydride, pyromellitic dianhydride, benzene-l,3,5-tricarboxylic acid, trimethylolpropane, glycerol, sorbitol, 1,2,6-hexanetriol, pentaerythritol, citric acid, tartaric acid, 3 -hydroxy glutaric acid, trimesic acid and the like. Ethoxylated or oxypropylated triols can also be used.
  • the branching monomer residues are chosen from at least one of the following: pentaerythritol, trimethylolpropane, trimethylolethane, trimellitic acid, trimellitic anhydride and/or benzene- 1, 3, 5-tricarboxylic acid.
  • the branching comonomer can be present in an amount in the range of about 250 to 2,000 pmol, or 500 to 1500 pmol, based on the total mole of diol or diacid residues.
  • the plasticizer present in the composition is based on a low molecular weight esters and ester-ethers, that are soluble in the copolyester composition, thermally stable at temperatures up to 275° C, i.e. no more than a 5 mass % loss at 275° C.
  • suitable aliphatic acids for use in the preparation of low molecular weight esters and ester-ethers are preferably long chain fatty acids having 10 or more carbon atoms, preferably at least 12, for example 8 to 18.
  • Preferred fatty acids include, not are not limited to, 2-ethylhexanoic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, or mixtures thereof.
  • Suitable aromatic acids for use in the preparation of low molecular weight esters and ester-ethers include, but are not limited by, phthalic acid, isophthalic acid, terephthalic acid, benzoic acid, toluic acid, trimellitic acid and the like.
  • suitable alcohols for use in the preparation of low molecular weight esters are preferably selected from aliphatic, cycloaliphatic or aromatic alcohols containing from about 1 to 20 carbon atoms.
  • Preferred alcohols include, but are not limited to, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, steryl alcohol, lauryl alcohol, phenol, benzyl alcohol, ethylene glycol, diethylene glycol, triethylene glycol, neopentyl glycol, cyclohexanedimethanol and the like.
  • suitable poly oxyalkylene glycol for use in the preparation of low molecular weight polyester-ethers include, but not limited to, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyethylene-co-tetramethylene glycol and the like.
  • the preferred molecular weight of the polyoxyalkylene glycol is the range of 100 to 2000 Daltons, preferably in the range of 200 to 1000 Daltons and most preferable in the range of 400 to 600 Daltons.
  • the preferred polyoxyalkylene glycol is polyethylene glycol.
  • polyester-ethers and esters can be prepared by standard esterification methods known to those skilled in the art.
  • the plasticizer can be present in an amount of about 0.5 weight percent to about 5 percent of the copolyester composition. Lower amounts than 0.5 weight percent do not provide sufficient snappability, while amounts greater than 5 weight percent will crystallize the composition and clear articles cannot be thermoformed.
  • the Intrinsic Viscosity (IV) of the polyesters are measured according to ASTM D 4603-96, and reported in units of dl/g.
  • Tm melting point of the polyesters
  • the sample was heated from 30 to 300°C at a rate of 10°C/min, held for 5 minutes and rapidly quenched to 10°C (at an approximate rate of 320°C/sec). The sample was then heated at 10°C/min to 300° C and the peak melting endotherm temperature recorded.
  • the glass transition temperature of the polyester composition (T g ) was also recorded on this second heating scan.
  • the temperature of cold crystallization (Tec) was also recorded on the second heating scan.
  • the multifunctional hydroxyl branching comonomer content of the polymer was determined by hydrolyzing the polymer with an aqueous solution of ammonium hydroxide in a sealed reaction vessel at 220+5°C for approximately two hours. The liquid portion of the hydrolyzed product was then analyzed by gas chromatography.
  • the gas chromatography apparatus was a FID Detector (HP5890, HP7673A) from Hewlett Packard.
  • the ammonium hydroxide was 28 to 30 % by weight ammonium hydroxide from Fisher Scientific and was reagent grade.
  • the content of the diacids and diols, including DEG (diethylene glycol), as well as the amount of plasticizer in the polymer was determined from proton nuclear magnetic spectra (1H MNR), using a JOEL ECX-300, 300 MHz instrument.
  • the solvated sample is then transferred to a standard NMR tube and analyzed via a predefined NMR experimental protocol. Resultant spectral integrations were worked-up via Excel macros in order to determine the reported monomer contents. e.
  • the snappability of sheets was determined by bending a section of the sheet, 15 cm wide, which had been cut to a depth of about 75% to about 85% of its depth with a razor blade. The depth of the cut line was determined by optical microscopy of a section of the sheet. If the sheet snapped along the cut line its snappability was rated as excellent. If it took 2 to 3 attempts to snap the sheet its snappability was rated as good. If the sheet failed to snap after three attempts, and formed a living hinge its snappability was rated as poor.
  • a semi-quantitative method for determining the snappability of a sheet was developed.
  • a sample of the sheet, 12 cm by 4 cm was die cut from the sheet in both the machine and transverse directions. These samples were scored to a depth of about 45 % to about 90 % of the sheet thickness using a 2 point center face bevel (45°) steel rule and an Arbor press. The depth of the cut line was determined by optical microscopy of a section of the sheet.
  • a snappability tester was designed to identify when the scored sample snapped. Two metal plates, 15 cm long and 10 cm wide, were joined by buttress hinges leaving a 1.25 cm gap between the plates. A plate (6.5 cm long and 2.5 cm wide) was attached to each hinged plate, 1 cm from the hinged edge, with a 1 mm gap in which the sample could be slid. The sample was positioned through these gaps such that the scored line was facing away from the hinged plates. In this way when the hinged plates fold, the sheet bends to close the V-shaped gap formed where the score line is cut.
  • Another plate (15 cm long and 10 cm wide) is also hinged at the center of the hinged plates and is clamped to the cross-head of an Instron tensile tester.
  • two rods (each 0.75 cm in diameter, 5 cm in length) are attached to a plate which is clamped to the load cell of the Instron tensile tester.
  • the hinged plates holding the sample are in a horizontal plane. As the cross-head moves up (2.5 cm. s' 1 , the hinged plates fold together bending the sample along the score line.
  • the force on the load cell drops. If the force drops to zero, indicating a clean snap, the sample is given a snappability rating of excellent; if the force only partially decreases, the sample is given a snappability rating of good; and if the sample bends to 180° without snapping, it is given a snappability rating of poor.
  • copolyesters were prepared from purified terephthalic acid, isophthalic acid, ethylene glycol, pentaerythritol, with antimony trioxide as the polycondensation catalyst using standard operating procedures known in the art.
  • the amorphous IV of these copolyesters was in the range of about 0.50 to about 0.68 dl/g.
  • Plasticizers were compounded with these copolyester compositions, after drying to reduce the moisture level to below 100 ppm, on a twin-screw extruder. b) Preparation of Sheets
  • copolyester compositions after drying to reduce the moisture level to below 100 ppm, were extruded, using a laboratory single screw Haake extruder, through a T-die. The extrudate was immediately quenched on chilled rolls and wound onto rolls. The width of these sheets was typically about 15 cm with a thickness in the range of 0.6 to 0.8 mm.
  • Copolyesters were prepared with various combinations of IV, isophthalic acid as the crystallization comonomer, pentaerythritol (Penta) as the branching comonomer. Their properties and the snappability of sheets, using the screening method, made from these copolyesters results are set forth in Table 1. The nominal thickness of these sheets was 0.7 mm and the score depth was about 75%.
  • Example 8 indicated that a PET homopolymer gave poor snappability and that a composition containing a crystallization retardant comonomer and a branching comonomer is required in the composition for excellent snappability.
  • a series of polymer compositions compounded with 1 wt. % polyethylene glycol 600 dilaurate were made and extruded into sheets. The compositions and the snappability of these sheets using the screening method, the score depth was about 85%, are summarized in Table 2.
  • Additional polyether-ester materials were evaluated to exemplify the effect of a plasticizer on the snappability of compositions whose melting points were greater than 225° C. These plasticizers were compounded with the copolyesters at a 1 or 2 weight % level.
  • the composition of the base resin in these next examples was 10.0 mol % isophthalic acid, 2.0 mol % diethylene glycol, 987 ppm pentaerythritol and the resin had an IV of 0.75 dL/g and melting point of 231° C.
  • the composition, thermal stability (T v ) and supplier of these plasticizers are listed in Table 3.

Abstract

A recyclable polyester composition, process, and use thereof that includes a diacid component, a glycol component, a diacid or glycol comonomer, a branching comonomer, and a plasticizer.

Description

RECYCLABLE POLYESTER POLYMERS FOR THERMOFORMED SHEETS AND MOLDED ARTICLES
FIELD OF THE INVENTION
This invention is directed to recyclable polyester compositions, and in particular for their use in thermoformed sheets and multipack articles
BACKGROUND OF THE INVENTION
Packaging of dairy products, such as yogurt and curds, frequently uses multipack packages containing 4, 6 or more cups. These multipack packages are made by thermoforming plastic sheets into groups of several attached cups segmented with a means of bending and snapping them apart at a predetermined breaking point, this behavior shall herein be called “snappability”. This means of bending and snapping them apart can be selected from a group selected from V-section scores or grooves, punched lines, perforations and the like and combinations of these means. It is also important that the multipack has sufficient integrity such that they can be lifted and do not snap under their own weight.
Typically, the polymer used for these multipack packages is a blend of general purpose and high impact polystyrene. As polystyrene articles are not recyclable, the industry is demanding a polymer that is easily recyclable and reusable for these articles. In addition, these recyclable polymers should run on existing equipment designed for polystyrene with minimum modification. Polyesters, in particular polyethylene terephthalate) and its copolymers, are the polymer of choice. However, it has been found that polyester does not snap along a predetermined breaking point, such as a score line, in the multipack package but bends and forms a “living hinge” that does not break or tear.
U. S. Pat. Application 2018/0194117 Al discloses a multilayer sheet in which the outer layers consist of a polyester containing a delustrant and optionally pores, and inner layers containing calcium carbonate, and other such additives, in which snap incisions extend from the upper surface into the inner layers. These articles are not recyclable.
U. S. Pat. No. 10,066,067 Bl discloses a method to embrittle the section of the polyester thermoformed sheet in which the groove, or other weakening means, between the individual cups is heated to an extent that this section crystallizes and the cups snap in this brittle region. The methods used to crystallize these weakened sections and contact with heated brass tool or lasers adds cost to the equipment. In addition, these crystallized sections are opaque.
U.S. Pat. No. 7,030,181 B2 discloses a composition for polyester film or sheets comprising about 5 to 50 weight % of a plasticizer to induce crystallization during calandering.
U.S. Statutory Invention Registration Hl 987 H discloses the use of non-volatile plasticizers as flow aids for processing polyester resins. The polyester composition comprising about 1 to 25 weight % of poly(alkylene ether)s or end-capped poly(alkylene ether)s. There is therefore a need for a polyester resin that is recyclable, snaps easily along a score line between the sections of a multipack article, can run on existing thermoform lines formerly designed for polystyrene multipack containers, and can provide a clear container. There is also a need for this composition to meet the standards established for recycling the thermoformed articles after use.
SUMMARY OF INVENTION
In the broadest sense, this invention relates to a recyclable copolyester composition for the manufacture of sheets comprising: a) comonomer to retard crystallization, and b) branching comonomer, and c) plasticizer
In the broadest sense, this invention relates to the process for using the sheets, made from this composition, to thermoform multipack articles.
DESCRIPTION OF THE INVENTION
The ranges set forth herein include both numbers at the end of each range and any conceivable number there between, as that is the very definition of a range.
The polyester compositions suitable for use in this invention typically comprise:
(a) a diacid component comprising 90 to 100 mole percent of residues of terephthalic acid, naphthalene dicarboxylic acids or mixtures thereof, based on the total mole percent of diacid residues in the polyester compositions, and
(b) a glycol component comprising 90 to 99 mole percent of residues of ethylene glycol, diethylene glycol or mixtures thereof, based on the total mole percent of glycol residues in the polyester compositions, and
(c) a diacid or glycol comonomer comprising 1 to 10 mole percent of either the total mole percent or diacid or glycol residues in the polyester compositions, and
(d) branching comonomer, and
(e) plasticizer.
The term "polyester", as used herein, is intended to include "copolyesters" and is understood to mean a synthetic polymer prepared by the reaction of one or more difunctional carboxylic acids and/or multifunctional carboxylic acids with one or more difunctional hydroxyl compounds and/or multifunctional hydroxyl compounds, for example, branching comonomers. Typically the difunctional carboxylic acid can be a dicarboxylic acid and the difunctional hydroxyl compound can be a dihydric alcohol such as, for example, glycols and diols. The term "glycol" as used herein includes, but is not limited to, diols, glycols, and/or multifunctional hydroxyl compounds, for example, branching comonomers. Alternatively, the difunctional carboxylic acid may be a hydroxy carboxylic acid such as, for example, p-hydroxybenzoic acid, and the difunctional hydroxyl compound may be an aromatic nucleus bearing 2 hydroxyl substituents such as, for example, hydroquinone, resorcinol or other heterocyclic diols, and isosorbide, for example.
The term "residue", as used herein, means any organic structure incorporated into a polymer through a polycondensation and/or an esterification reaction from the corresponding monomer. The term "repeating unit", as used herein, means an organic structure having a dicarboxylic acid residue and a diol residue bonded through a carbonyloxy group. Thus, for example, the dicarboxylic acid residues may be derived from a dicarboxylic acid monomer or its associated acid halides, esters, salts, anhydrides, and/or mixtures thereof. As used herein, therefore, the term "dicarboxylic acid" is intended to include dicarboxylic acids and any derivative of a dicarboxylic acid, including its associated acid halides, esters, half-esters, salts, half-salts, anhydrides, mixed anhydrides, and/or mixtures thereof, useful in a reaction process with a diol to make polyester. As used herein, the term "terephthalic acid" is intended to include terephthalic acid itself and residues thereof as well as any derivative of terephthalic acid, including its associated acid halides, esters, half-esters, salts, half-salts, anhydrides, mixed anhydrides, and/or mixtures thereof or residues thereof useful in a reaction process with a diol to make polyester.
The polyesters used in the present invention typically can be prepared from dicarboxylic acids and diols which react in substantially equal proportions and are incorporated into the polyester polymer as their corresponding residues. The polyesters of the present invention, therefore, can contain substantially equal molar proportions of acid residues (100 mole %) and glycol (and/or multifunctional hydroxyl compound) residues (100 mole %) such that the total moles of repeating units is equal to 100 mole %. The mole percentages provided in the present disclosure, therefore, may be based on the total moles of acid residues, the total moles of diol residues, or the total moles of repeating units. For example, a polyester containing 5 mole % isophthalic acid, based on the total acid residues, means the polyester contains 5 mole % isophthalic acid residues out of a total of 100 mole % acid residues. Thus, there is 5 mole of isophthalic acid residues among every 100 moles of acid residues. In another example, polyester containing 1.5 mole % di ethylene glycol, out of a total of 100 mole % glycol residues, has 1.5 moles of di ethylene glycol residues among every 100 moles of glycol residues.
The polyesters of the invention can also comprise at least one chain extender. Suitable chain extenders include, but are not limited to, multifunctional (including, but not limited to, bifunctional) isocyanates, multifunctional epoxides, including for example, epoxylated novolacs, and phenoxy resins. In certain embodiments, chain extenders may be added at the end of the polymerization process or after the polymerization process. If added after the polymerization process, chain extenders can be incorporated by compounding or by addition during conversion processes such as injection molding or extrusion. The amount of chain extender used can vary depending on the specific monomer composition used and the physical properties desired but is generally about 0.1 to about 5 % by weight, or about 0.1 to about 2 % by weight, based on the total weight of the polyester.
In addition, the polyester compositions and the polymer blend compositions useful in the invention may also contain any amount of at least one additive, for example, from 0.01 to 2.5% by weight of the overall composition common additives such as colorants, dyes, mold release agents, flame retardants, plasticizers, stabilizers, including but not limited to, UV stabilizers, thermo-oxidative stabilizers and/or reaction products thereof, and impact modifiers. Examples of thermo-oxidative stabilizers include phosphorus compounds and primary and secondary antioxidants commercially available for use in polyester resins. Examples of typical commercially available impact modifiers well known in the art and useful in this invention include, but are not limited to, ethyl ene/propylene terpolymers, functionalized polyolefins such as those containing methyl acrylate and/or glycidyl methacrylate, styrene-based block copolymeric impact modifiers, and various acrylic core/shell type impact modifiers. For transparent thermoformed articles the refractive index of these additives must closely match the refractive index of the polyester composition to prevent a hazy container. Residues of such additives are also contemplated as part of the polyester composition.
In addition, certain agents which tone the polymer can be added to the melt. A bluing toner can be used to reduce the yellowness of the resulting polyester polymer melt phase product. Such bluing agents include cobalt salts, blue inorganic and organic toner(s) and the like. In addition, red toner(s) can also be used to adjust the redness. Organic toner(s), e.g., blue and red organic toner(s) can be used. The organic toner(s) can be fed as a premix composition. The premix composition may be a neat blend of the red and blue compounds or the composition may be pre-dissolved or slurried in one of the polyester's raw materials, e.g., ethylene glycol.
The total amount of added toner components depends on the amount of inherent yellow color in the base polyester and the efficacy of the toner. Generally, a concentration of up to about 15 ppm of combined organic toner components and a minimum concentration of about 0.5 ppm are used, with the total amount of bluing additive typically ranging from about 0.5 ppm to about 10 ppm.
Conventional production of polyesters can be achieved by a batch, semi-continuous, or continuous process. A typical polyesterification process is comprised of multiple stages and commercially carried out in one of two common pathways. For a process which employs Direct Esterification, the initial stage of the process the dicarboxylic acids react with one or more diols at a temperature of about 200° C to about 250° C to form macro-monomeric structures and a small condensate molecule, water. Because the reaction is reversible, the water is continuously removed to drive the reaction to the desired first stage product. The crystallization retardant and branching comonomers are normally added at this stage of the process. In a like manner, when using diesters (versus diacids), an Ester Interchange process is used to react the ester groups of the diesters and diols with certain well known catalysts such, such as manganese acetate, zinc acetate, or cobalt acetate. After completing the ester interchange reaction these catalysts are sequestered with a phosphorus compound, such as phosphoric acid, to prevent degradation during the polycondensation process.
Next, in the second stage of the reaction, either macro-monomeric structures (Direct Esterification Products) or interchanged moieties (Ester Interchange Products) undergo a polycondensation reaction to form the polymer. In this process the temperature of the molten mass is increased to a final temperature in the range of about 280° to 300° C and a vacuum (about 150 Pa) applied to remove excess diols and water. This polymerization is stopped when the required / targeted molecular weight is achieved and/or the maximum molecular weight of the design of the equipment is reached. The polyester is extruded through a die into strands which are quenched and cut into pellets. The catalysts generally used for the polycondensation reaction are compounds containing antimony, germanium, aluminum, titanium or other catalysts known to those skilled in the art, or mixtures thereof. The specific additives used and the point of introduction during the reaction is known in the art and does not form a part of the present invention. Any conventional system may be employed and those skilled in the art can select among various commercially-available systems for the introduction of additives so as to achieve an optimal result. The polyester pellets can be further polymerized to a higher molecular weight by well-known solid state polymerization processing techniques.
The terephthalic acid and/or ethylene glycol are preferably derived from a biomass feedstock rather than a petroleum based feedstock. In addition the use of chemically recycled terephthalic acid (or dimethyl terephthalate) and ethylene glycol from post-consumer polyester waste is also preferred for the polyesters of this invention. Another preferred method of manufacturing the polyester resins of this invention utilizes bis-(hydroxyethyl)-terephthalate, purified from the reaction product of glycolysis of post-consumer polyester waste, this monomer can be added to the polymerization process, preferably prior to the polycondensation stages. Another preferred method of manufacturing the polyester resin utilizes clean clear flake from post-consumer waste (rPET) can be added during the esterification or first stages of the polymerization process. Up to 50 weight percent of this rPET is first depolymerized by the low molecular weight polymer and this mixture polymerized under the normal processing conditions.
The polyester compositions of this invention are designed for use in a thermoforming process. In this process the polyester resin is dried and fed to an extruder that extrudes the molten polymer through a sheet casting die that forms a flat sheet that is quenched on chilled rolls, calendered into the required sheet thickness, and optionally cut into the required width, before being wound into a clear roll. The term “sheet” is herein understood to mean an article having a small thickness relative to the direction perpendicular to the thickness direction. The sheet thickness is typically in the range of 0.5 to 2 mm, when the thickness of the sheet is less than 0.5 mm the sheet may also be called a film. For thermoforming, the sheet is unwound from the roll into a set of indexing chains that transport the sheet through an oven for heating to the forming temperature, typically in the range of about 120° to about 160° C for polyester resins. The heated sheet then moves to a form station where it is held against a mold, designed for the shape and size of the article being made. A vacuum is applied to remove trapped air and the sheet is stretched into a chilled mold, along with pressurized air and a plug to assist in providing the necessary material distribution and thickness in the molded part. After a short form cycle, the forming tool opens and the article is removed from the mold. The sheet containing the formed parts is then indexed into a trim section, where a die cuts the parts from the sheet. It is at this stage of the process that the web between the individual cups is scored, or a means to provide a breaking point between the individual cups, is provided. The preferred score depth is in the range of about 45 percent to about 75 percent of the sheet thickness.
In a typical thermoforming process for multipack containers for dairy products, such as yogurt cups, the additional steps of filling the cups and sealing the package are integrated with the forming process.
The polyester compositions suitable for use in this invention include those having an intrinsic viscosity of at least about 0.50 dl/g, preferably at least about 0.60 dl/g, and more preferably between about 0.65 and about 0.85 dl/g. Lower intrinsic viscosity resins have insufficient melt strength for extruding a sheet, whereas higher intrinsic viscosity resins have too high a melt viscosity for extruding a sheet at the normal extrusion temperatures, as higher temperatures cause thermal degradation and a loss of molecular weight.
The plasticizer can be dry blended with the polyester composition and this blend dried and extruded into a sheet for subsequent thermoforming. The plasticizer can be added at various ports along the extruder forming the sheet, either single or twin-screw extruders. The polyester composition should be dried to a moisture level less than 100 ppm prior to extrusion. This can be accomplished by the standard drying in hot dry air that is practiced in the industry, or by applying a vacuum after the polymer has melted in a twin-screw extruder. A master batch of the plasticizer can be prepared by compounding the dried plasticizer with polyester composition, or by compounding with an inert carrier such as those normally used for dyes and pigments for coloring polyester articles. These master batches can then be let down and added at the throat of the extruder with the dried polyester composition. Alternatively, the plasticizer can be melt added to the polymer composition during the polymerization process, preferably after the polymerization is complete prior to the extrusion on the polymer through the die into strands for quenching and cutting.
Designed experiments were conducted by preparing sheets from a variety of combinations of molecular weight (intrinsic viscosity), crystallization retardant comonomers and branching comonomers in order to determine an optimal composition that, when scored to about 50% of the sheet thickness with a razor blade, would snap on bending. The crystallization retardant composition amount ranged from a lower limit below which the sheet is crystalline and an upper limit at which the melting point was less than 225° C (recycling lower limit). The branching comonomer amount, to induce brittleness, ranged from about 250 to about 2500 parts per million (ppm) (based on the total weight of the copolyester), the upper limit was chosen to minimize gel formation.
Additional design experiments were conducted by including a plasticizer in the composition. Although it was expected that a plasticizer would make the sheet more ductile and therefore reduce its ability to snap, the contrary was observed. Although, not bound by theory, it is believed that the plasticizer densifies the amorphous sheet which makes it more brittle and easier to snap.
Crystallization Retardant Comonomer
In order to obtain a clear sheet for thermoforming, crystallization retardant comonomers comprising dicarboxylic acids or diols are used. The amount is chosen such that the melting point of the copolyester composition is preferably equal or greater than 225° C. Lower melting point compositions may not pass the requirements for recyclable polyester as set forth in the Association of Postconsumer Plastic Recyclers Critical Guidance Protocol.
In addition to terephthalic acid and/or dimethyl terephthalate, the dicarboxylic acid component of the polyesters useful to reduce the crystallization rate in the invention can comprise up to 10 mole %, of one or more modifying aromatic dicarboxylic acids. Examples of modifying aromatic dicarboxylic acids which may be used in this invention include, but are not limited to, aromatic dicarboxylic acids preferably having 8 to 16 carbon atoms, aliphatic dicarboxylic acids preferably having 4 to 16 carbon atoms, and cycloaliphatic dicarboxylic acids preferably having 8 to 16 carbon atoms.
Particularly preferred examples of dicarboxylic acids that can be used in this invention include, but not limited to: isophthalic acid, 1,4-, 1,5-, 2,6-, 2,7-naphthalenedicarboxylic acid, 1,4-cyclohexanedi carboxylic acid, 1,4-cyclocohexanediacetic acid, 4,4'-biphenyldicarboxylic acid, trans-4,4'-stilbenedicarboxylic acid, malonic, succinic, glutaric, adipic, pimelic, suberic, octanoic, azelaic, sebacic, dodecanedioic-dicarboxylic acids, diethyl-di-n-propyl malonate, dimethyl benzyl-malonate, 2, 2-dimethyl-malonic acid and 2, 3-dimethyl glutaric acid and esters thereof. Heterocyclic dicarboxylic acids, for example 2, 5-furan dicarboxylic acid may also be used. The preferred modifying aromatic dicarboxylic acid is isophthalic acid.
In addition to ethylene glycol, the glycol component of the polyesters useful to reduce the crystallization rate in the invention can comprise up to 10 mole %, of one or more modifying glycols. Examples of modifying glycols which may be used in this invention include, but are not limited to, aliphatic glycols preferably having 2 to 20 carbon atoms or alicyclic glycols preferably having 6 to 20 carbon atoms. Particularly preferred examples of glycols that can be used in this invention include, but not limited to: diethylene glycol, triethylene glycol, propane- 1,3 -diol, butane-1.4-diol, pentane- 1,5-diol, hexane-l,6-diol, 2-methyl-l,3-propane diol, 2-ethyl-l,3-propane diol, 2-butyl-l,3- propane diol, 2,2’-dimethyl-l,3-propanediol, 2-methyl-l,4-butanediol, 2-ethyl-l,4-butanediol, 2- butyl-l,4-butanediol, 3-methyl-l,5-pentanediol, 2,4-dimethyl-l,5-pentanediol, 1,4- cyclohexanedimethanol, 2,2,4,4-tetramethyl-l,3-cyclobutanol or mixtures thereof.
Mixtures of modifying dicarboxylic acids and modifying diols to reduce the crystallization rate of the copolyester are also contemplated in this invention. The preferred mixture is isophthalic acid and diethylene glycol.
Branching Comonomer
The branching comonomer present in the composition has 3 or more carboxyl substituents, hydroxyl substituents, or a combination thereof. Examples of branching monomers include, but are not limited to, multifunctional acids or multifunctional alcohols such as trimellitic acid, trimellitic anhydride, pyromellitic dianhydride, benzene-l,3,5-tricarboxylic acid, trimethylolpropane, glycerol, sorbitol, 1,2,6-hexanetriol, pentaerythritol, citric acid, tartaric acid, 3 -hydroxy glutaric acid, trimesic acid and the like. Ethoxylated or oxypropylated triols can also be used. In the preferred embodiment, the branching monomer residues are chosen from at least one of the following: pentaerythritol, trimethylolpropane, trimethylolethane, trimellitic acid, trimellitic anhydride and/or benzene- 1, 3, 5-tricarboxylic acid. The branching comonomer can be present in an amount in the range of about 250 to 2,000 pmol, or 500 to 1500 pmol, based on the total mole of diol or diacid residues.
Plasticizer
The plasticizer present in the composition is based on a low molecular weight esters and ester-ethers, that are soluble in the copolyester composition, thermally stable at temperatures up to 275° C, i.e. no more than a 5 mass % loss at 275° C.
Examples of suitable aliphatic acids for use in the preparation of low molecular weight esters and ester-ethers are preferably long chain fatty acids having 10 or more carbon atoms, preferably at least 12, for example 8 to 18. Preferred fatty acids include, not are not limited to, 2-ethylhexanoic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, or mixtures thereof.
Examples of suitable aromatic acids for use in the preparation of low molecular weight esters and ester-ethers include, but are not limited by, phthalic acid, isophthalic acid, terephthalic acid, benzoic acid, toluic acid, trimellitic acid and the like.
Examples of suitable alcohols for use in the preparation of low molecular weight esters are preferably selected from aliphatic, cycloaliphatic or aromatic alcohols containing from about 1 to 20 carbon atoms. Preferred alcohols include, but are not limited to, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, steryl alcohol, lauryl alcohol, phenol, benzyl alcohol, ethylene glycol, diethylene glycol, triethylene glycol, neopentyl glycol, cyclohexanedimethanol and the like.
Examples of suitable poly oxyalkylene glycol for use in the preparation of low molecular weight polyester-ethers include, but not limited to, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyethylene-co-tetramethylene glycol and the like. The preferred molecular weight of the polyoxyalkylene glycol is the range of 100 to 2000 Daltons, preferably in the range of 200 to 1000 Daltons and most preferable in the range of 400 to 600 Daltons. The preferred polyoxyalkylene glycol is polyethylene glycol.
These polyester-ethers and esters can be prepared by standard esterification methods known to those skilled in the art.
The plasticizer can be present in an amount of about 0.5 weight percent to about 5 percent of the copolyester composition. Lower amounts than 0.5 weight percent do not provide sufficient snappability, while amounts greater than 5 weight percent will crystallize the composition and clear articles cannot be thermoformed.
TEST AND PREPARATIVE METHODS
1. TEST METHODS a. The Intrinsic Viscosity (IV) of the polyesters are measured according to ASTM D 4603-96, and reported in units of dl/g. b. The melting point of the polyesters (Tm) was taken as the peak of the melting endotherm of the copolyester as measured in accordance with ASTM D 3418-03. The sample was heated from 30 to 300°C at a rate of 10°C/min, held for 5 minutes and rapidly quenched to 10°C (at an approximate rate of 320°C/sec). The sample was then heated at 10°C/min to 300° C and the peak melting endotherm temperature recorded.
The glass transition temperature of the polyester composition (Tg) was also recorded on this second heating scan. The temperature of cold crystallization (Tec) was also recorded on the second heating scan. c. The multifunctional hydroxyl branching comonomer content of the polymer was determined by hydrolyzing the polymer with an aqueous solution of ammonium hydroxide in a sealed reaction vessel at 220+5°C for approximately two hours. The liquid portion of the hydrolyzed product was then analyzed by gas chromatography. The gas chromatography apparatus was a FID Detector (HP5890, HP7673A) from Hewlett Packard. The ammonium hydroxide was 28 to 30 % by weight ammonium hydroxide from Fisher Scientific and was reagent grade. d. The content of the diacids and diols, including DEG (diethylene glycol), as well as the amount of plasticizer in the polymer was determined from proton nuclear magnetic spectra (1H MNR), using a JOEL ECX-300, 300 MHz instrument.
General sample preparation was as follows: 20 mg of polyester is placed in a suitable 2 mL glass reaction vessel or vial with 1 mL of 10: 1 chloroform-d:TFA-d [Cambridge Isotope Laboratories, Inc. Chloroform-d (d, 98.9%)+0.05% V/V TMS: Cambridge Isotope Laboratories, Inc. Trifluoroacetic acid-d (d, 99.5%)] and capped. The reaction vessel / vial is placed on a heating block at a temperature of 100°C for approximately 10 minutes, or until sample is fully solvated. The sample is then removed from the heat block and placed in the hood to equilibrate to RT. The solvated sample is then transferred to a standard NMR tube and analyzed via a predefined NMR experimental protocol. Resultant spectral integrations were worked-up via Excel macros in order to determine the reported monomer contents. e. As a screening method, the snappability of sheets was determined by bending a section of the sheet, 15 cm wide, which had been cut to a depth of about 75% to about 85% of its depth with a razor blade. The depth of the cut line was determined by optical microscopy of a section of the sheet. If the sheet snapped along the cut line its snappability was rated as excellent. If it took 2 to 3 attempts to snap the sheet its snappability was rated as good. If the sheet failed to snap after three attempts, and formed a living hinge its snappability was rated as poor.
A semi-quantitative method for determining the snappability of a sheet was developed. A sample of the sheet, 12 cm by 4 cm was die cut from the sheet in both the machine and transverse directions. These samples were scored to a depth of about 45 % to about 90 % of the sheet thickness using a 2 point center face bevel (45°) steel rule and an Arbor press. The depth of the cut line was determined by optical microscopy of a section of the sheet.
A snappability tester was designed to identify when the scored sample snapped. Two metal plates, 15 cm long and 10 cm wide, were joined by buttress hinges leaving a 1.25 cm gap between the plates. A plate (6.5 cm long and 2.5 cm wide) was attached to each hinged plate, 1 cm from the hinged edge, with a 1 mm gap in which the sample could be slid. The sample was positioned through these gaps such that the scored line was facing away from the hinged plates. In this way when the hinged plates fold, the sheet bends to close the V-shaped gap formed where the score line is cut.
Another plate (15 cm long and 10 cm wide) is also hinged at the center of the hinged plates and is clamped to the cross-head of an Instron tensile tester. On the outer sides of each hinged plate, holding the sample, two rods (each 0.75 cm in diameter, 5 cm in length) are attached to a plate which is clamped to the load cell of the Instron tensile tester.
At the start of the test, the hinged plates holding the sample are in a horizontal plane. As the cross-head moves up (2.5 cm. s'1, the hinged plates fold together bending the sample along the score line. When the scored sample snaps, or partially snaps, the force on the load cell drops. If the force drops to zero, indicating a clean snap, the sample is given a snappability rating of excellent; if the force only partially decreases, the sample is given a snappability rating of good; and if the sample bends to 180° without snapping, it is given a snappability rating of poor. f. The volatility of the plasticizer was measured in accordance to ASTM E2550-17 using a heating rate of 10°C min'1 and a nitrogen purge gas rate of 20 mL min'1. The temperature (Tv) at which the sample had lost 5% of its mass was recorded. PREPARATIVE METHODS a) Preparation of Polyesters
A series of copolyesters were prepared from purified terephthalic acid, isophthalic acid, ethylene glycol, pentaerythritol, with antimony trioxide as the polycondensation catalyst using standard operating procedures known in the art. The amorphous IV of these copolyesters was in the range of about 0.50 to about 0.68 dl/g.
These amorphous copolyesters were further polymerized in the solid state in order to achieve higher IV values.
Plasticizers were compounded with these copolyester compositions, after drying to reduce the moisture level to below 100 ppm, on a twin-screw extruder. b) Preparation of Sheets
The copolyester compositions, after drying to reduce the moisture level to below 100 ppm, were extruded, using a laboratory single screw Haake extruder, through a T-die. The extrudate was immediately quenched on chilled rolls and wound onto rolls. The width of these sheets was typically about 15 cm with a thickness in the range of 0.6 to 0.8 mm.
EXAMPLES
Copolyesters were prepared with various combinations of IV, isophthalic acid as the crystallization comonomer, pentaerythritol (Penta) as the branching comonomer. Their properties and the snappability of sheets, using the screening method, made from these copolyesters results are set forth in Table 1. The nominal thickness of these sheets was 0.7 mm and the score depth was about 75%.
Figure imgf000013_0001
Although Examples 1 and 4 had excellent snappability, the melting points were too low to be recycled. Example 8 indicated that a PET homopolymer gave poor snappability and that a composition containing a crystallization retardant comonomer and a branching comonomer is required in the composition for excellent snappability. A series of polymer compositions compounded with 1 wt. % polyethylene glycol 600 dilaurate were made and extruded into sheets. The compositions and the snappability of these sheets using the screening method, the score depth was about 85%, are summarized in Table 2.
Figure imgf000014_0001
Additional polyether-ester materials were evaluated to exemplify the effect of a plasticizer on the snappability of compositions whose melting points were greater than 225° C. These plasticizers were compounded with the copolyesters at a 1 or 2 weight % level. The composition of the base resin in these next examples was 10.0 mol % isophthalic acid, 2.0 mol % diethylene glycol, 987 ppm pentaerythritol and the resin had an IV of 0.75 dL/g and melting point of 231° C. The composition, thermal stability (Tv) and supplier of these plasticizers are listed in Table 3.
Figure imgf000014_0002
The sheets were tested in both the machine and transverse direction of the extruded sheets. The results of these trials are summarized in Table 4.
Figure imgf000015_0001
The Examples in Table 4 show that the addition of between about 1 to about 2 wt-% of a plasticizer to a copolyester composition comprising a crystallization retardant comonomer, a branching comonomer provides the means to produce a thermoform sheet that can easily be snapped at predetermined scored lines on the sheet.
Although the present invention has been illustrated and described herein with reference to preferred embodiments and specific examples thereof, it will be readily apparent to those of ordinary skill in the art that other embodiments and examples may perform similar functions and/or achieve like results. All such equivalent embodiments and examples are within the spirit and scope of the present invention and are intended to be covered by the following claims.

Claims

1. A polyester composition, comprising:
(i) a diacid component comprising 90 to 100 mole percent of residues of terephthalic acid, naphthalene di carboxylic acids or mixtures thereof, based on the total mole percent of diacid residues in the polyester composition;
(ii) a glycol component comprising 90 to 99 mole percent of residues of ethylene glycol, diethylene glycol or mixtures thereof, based on the total mole percent of glycol residues in the polyester composition;
(iii)a diacid or glycol comonomer comprising 1 to 10 mole percent of either the total mole percent or diacid or glycol residues in the polyester composition;
(iv)a branching comonomer; and
(v) a plasticizer.
2. The polyester composition according to Claim 1, wherein the polyester composition has an intrinsic viscosity of at least about 0.50 dl/g.
3. The polyester composition according to Claim 1, wherein the polyester composition has a melting point equal to or greater than 225° C.
4. The polyester composition according to Claim 1, wherein the branching comonomer is present in an amount up to 2500 ppm based on the total weight of the copolyester.
5. The polyester composition according to Claim 1, further comprising at least one chain extender.
6. The polyester composition according to Claim 5, wherein the chain extender is present in the amount of between about 0.1 to about 5 % by weight, based on the total weight of the polyester.
7. The polyester composition according to Claim 1, further comprising at least one additive in an amount from 0.01 to 2.5% by weight of the overall polyester composition.
8. The polyester composition according to Claim 7, wherein the at least one additive is chosen from colorants, dyes, mold release agents, flame retardants, stabilizers, impact modifiers, or a mixture thereof.
9. The polyester composition according to Claim 1, wherein the plasticizer is present in the amount between about 0.5 wt. % to about 5 wt. % of the polyester composition. The polyester composition according to Claim 1, wherein the diacid component and/or the glycol component are derived from a biomass feedstock. The polyester composition according to Claim 1, wherein the diacid comonomer is chosen from aromatic dicarboxylic acids preferably having 8 to 16 carbon atoms, aliphatic di carboxylic acids preferably having 4 to 16 carbon atoms, and cycloaliphatic di carboxylic acids preferably having 8 to 16 carbon atoms. The polyester composition according to Claim 1, wherein the glycol comonomer is chosen from aliphatic glycols preferably having 2 to 20 carbon atoms or alicyclic glycols preferably having 6 to 20 carbon atoms. A process for preparing a sheet or film comprising the steps of:
(a) preparing a polyester composition comprising:
(i) a diacid component comprising 90 to 100 mole percent of residues of terephthalic acid, naphthalene di carboxylic acids or mixtures thereof, based on the total mole percent of diacid residues in the polyester composition;
(ii) a glycol component comprising 90 to 99 mole percent of residues of ethylene glycol, diethylene glycol or mixtures thereof, based on the total mole percent of glycol residues in the polyester composition;
(iii)a diacid or glycol comonomer comprising 1 to 10 mole percent of either the total mole percent or diacid or glycol residues in the polyester composition;
(iv) a branching comonomer; and
(v) a plasticizer.
(b) forming the polyester composition into a sheet. The process for preparing a sheet or film according to Claim 13, wherein the sheet has a thickness between about 0.5 to about 2 mm. The process for preparing a sheet or film according to Claim 13, wherein the film has a thickness of less than about 1 mm. The process for preparing a sheet or film according to Claim 13, wherein the polyester composition has an intrinsic viscosity of at least about 0.50 dl/g. The process for preparing a sheet or film according to Claim 13, wherein the polyester composition has a melting point equal to or greater than 225° C.
18. The process for preparing a sheet or film according to Claim 13, wherein the branching comonomer is present in an amount up to 2500 ppm based on the total weight of the copolyester.
19. The film or sheet prepared according to Claim 13 for use in a multipack container.
20. The film or sheet prepared according to Claim 13 for use in a multipack container for yogurt and the like.
PCT/US2021/056433 2020-10-28 2021-10-25 Recyclable polyester polymers for thermoformed sheets and molded articles WO2022093681A1 (en)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20160237240A1 (en) * 2013-10-30 2016-08-18 Auriga Polymers, Inc. Polyester composition for extrusion blow molded containers with improved aging and drop performance
US20180037696A1 (en) * 2015-03-04 2018-02-08 Auriga Polymers, Inc. Bio-based copolyester or copolyethylene terephthalate
US20200095373A1 (en) * 2017-01-06 2020-03-26 Auriga Polymers, Inc. Process for manufacturing polyester resins

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20160237240A1 (en) * 2013-10-30 2016-08-18 Auriga Polymers, Inc. Polyester composition for extrusion blow molded containers with improved aging and drop performance
US20180037696A1 (en) * 2015-03-04 2018-02-08 Auriga Polymers, Inc. Bio-based copolyester or copolyethylene terephthalate
US20200095373A1 (en) * 2017-01-06 2020-03-26 Auriga Polymers, Inc. Process for manufacturing polyester resins

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