ES2366799T3 - COMPARTMENTED PEL FOR IMPROVED DISPOSAL OF POLLUTANTS. - Google Patents

Abstract

A compartmentalized pellet comprising at least two compartments (1, 2, 21, 22) characterized in that the first compartment (2, 22) with the largest surface area in contact with the air comprises contaminated thermoplastic polymer and the second compartment (1, 21) comprises uncontaminated thermoplastic polymer.

Description

Priority and cross references

This patent application claims the benefit of the priority of the provisional US patent application. Serial No. 60 / 644,613 filed on January 18, 2005; US provisional patent application Serial No. 60 / 646,329 filed on January 24, 2005; US provisional patent application Serial No. 60 / 677,829 filed May 5, 2005; US provisional patent application Serial No. 60 / 731,775 filed October 31, 2005, and the provisional US patent application. Serial No. 60 / 644,622 filed on January 18, 2005.

Background of the invention

Field of the Invention

This invention generally relates to a multicomponent compartmentalized pellet to increase the efficiency of the removal of contaminants, such as contaminants found in recycled polyesters after consumption.

Related technique

Processing after recycled polyethylene terephthalate (RPET) for manufacturing a variety of products useful for consumption such as pots and posts is well known. Normally, the recycling process uses used polyester (PET) containers, primarily polyethylene terephthalate, such as discarded containers of carbonated beverages, which are collected, sorted, washed and separated from contaminants to give a relatively clean source of RPET. Additionally, the manufacturing of imperfect or damaged PET molded products, particularly blow molded bottles used to contain consumer goods, results in a huge amount of PET waste that the manufacturers of such products would like to be able to reuse. The RPET produced by conventional recycling procedures is generally in ground form or in flakes, which is subsequently subjected to a molten process or subsequently pellets are formed by the end user.

The RPET always undergoes a grinding operation in order to make the material easier to handle and process. Conventional grinding equipment reduces the RPET to particles or flakes of approximately 9.53 mm (3/8 inches). The grinding is carried out in a way that guarantees the production of a consistent flake size, using a mesh or sieve through which the ground material that leaves the crusher must pass. Although conventional RPET flake processing and pellet forming equipment is designed to handle 9.53 mm (3/8 inch) flakes, some RPET materials that have sizes up to 12.7 mm are also commercially produced (1/2 inch) and only 6.35 mm (1/4 inch). The bulk density of the RPET flakes of 9.53 mm (3/8 inches) generally ranges between approximately 352 g / l and approximately 561 g / l (approximately 22 to 35 inches per cubic foot).

Similarly, RPET and PET pellets are generally formed with a standard uniform size of approximately 3.05 mm (0.12 inches) in diameter. The bulk density of these pellets generally varies between approximately 801 and approximately 929 g / l (between approximately 50 and 58 inches per cubic foot). Normally, PET and RPET melt processing equipment is designed to accept pellets having the physical dimensions and characteristics mentioned above.

The critical aspect to consistently achieve high quality end products using RPET is the thorough decontamination of RPET flakes or pellets. Significant decontamination occurs during washing and classification of PET residues. The PET bottles and containers that arrive are crushed to form PET fragments and to remove loose labels, dirt, and other foreign particles attached. After that, the mixture is classified by air and the remaining fragments are washed in a hot detergent solution to remove additional label fragments and adhesives from the PET fragments. The PET fragments washed are then rinsed and placed in a series of flotation baths where the heaviest and lightest foreign particles are removed. The remaining PET fragments are then dried and sold as RPET flakes. Thus, the labels and base adhesives, polyolefins, PVC, paper, glass, and metals are removed from the RPET, all of which adversely affect the quality and behavior of the final product.

Of recent concern are toxic contaminants that can be introduced into a typical RPET processing stream. Examples of such contaminants include pesticides, solvents, herbicides, and chlorinated hydrocarbons that could contaminate the RPET by inadvertent accidental contact during processing

or the transport thereof, or by recycling PET bottles and containers that have been used by consumers to store toxic substances for some period of time.

With respect to the possibility that toxic contaminants may be contained in RPET designed for use in contact with food, the US FDA. It has established protocols for the levels of these contaminants in these applications, and has established substitutes and concentration limits to establish the effectiveness of the washing and subsequent decontamination procedures. Because the US FDA protocols require that the selected contaminants be within the RPET matrix, the contaminant is extruded into the fusion of the RPET or is introduced into the RPET by exposing it to the selected contaminant for two weeks. The contaminants then spread to the polymer matrix of the wall of a bottle or a container that is subsequently recycled. Therefore, an effective decontamination procedure will require that the contaminant be removed, in part, from the RPET flakes produced from the walls of a bottle or a container, in order to meet the required limit of contaminant concentration.

There are many procedures to purify the RPET so that it is suitable for reuse in food packaging. In general, these processes can be classified in depolymerization to raw materials, depolymerization to low molecular weight oligomers and medium to high molecular weight extraction. U.S. Pat. No. 6,545,061 is an example of depolymerization to raw materials and describes a process of depolymerization and purification of polyethylene terephthalate which comprises: a) conduction of acetolysis on recyclable polyethylene terephthalate to form terephthalic acid and ethylene glycol diacetate; the reaction of said terephthalic acid with methanol to form dimethyl terephthalate; and the reaction of said dimethyl terephthalate with said ethylene glycol diacetate under transesterification and polycondensation conditions to form a polyethylene terephthalate product, said polyethylene terephthalate product having diethylene glycol units at a concentration of less than about 1.5% by weight, based on weight total of said polyethylene terephthalate product. U.S. Pat. No. 6,410,607 is an example of depolymerization to low molecular weight oligomers and describes a depolymerization and purification process comprising: contacting a contaminated polyester with an amount of a glycol to provide a molar ratio greater than about 1 to 5 total units of glycol at approximately total units of dicarboxylic acid at a temperature between approximately 150 ° C and approximately 300 ° C and at an absolute pressure of approximately 0.5 to approximately 3 bar with stirring in a reactor for a time sufficient to produce, in the reactor, an upper layer comprising a relatively low density pollutant that floats above a lower layer that includes a liquid comprising a depolymerized oligomer of said polyester; and the separation, while still with said agitation, of said upper layer of said lower layer by removing said upper layer from the reactor in a first stream and removing said lower layer from the reactor in a second stream. The inherent deficiency of depolymerization procedures are operating costs. In all cases, the resulting product must be repolymerized in an expensive molten phase in order to be reused. Therefore, there is a need to provide a high efficiency purification technique without depolymerizing the polymer.

U.S. Pat. No. 5,876,644 is an example of depolymerization of the polymer to a level of average molecular weight and describes a process of recycling the polyester after consumption to obtain recycled polyester of a sufficiently high purity to meet the requirements for food packaging. The procedure includes cleaning crushed pieces of polyester after consumption to remove surface contaminants; the fusion of the polyester pieces after consumption with the clean surface; extrusion of the melt after consumption; mixing the polyester melt after consumption with a virgin polyester prepolymer melt; solidification and pellet formation of the mixed melt while the virgin polyester prepolymer remains as a prepolymer; and polymerization of solid mixed solid pellets. Although this particular process avoids the molten polymerization step, it is ineffective because it mixes the polyester after consumption with a virgin polyester prepolymer melt. This mixture creates a single pellet of a homogeneous dispersion of the contaminated material throughout the pellet. Since solid state or solid phase polymerization is an extraction process limited by diffusion, contaminants located in the inner part of the pellet will not migrate sufficiently to be removed. This deficiency limits the amount of the contaminant in the polyester after consumption or the amount of contaminated polyester material in the pellet.

U.S. Patent Nos. 5,899,392 and 5,824,196 are examples of high molecular weight extraction. To maintain the polymer within reasonable molecular weights, high molecular weight extractions can expose the material to the extraction stage only for a limited time or the polymer will increase its molecular weight above practical limits. US Patent No. 5,899,392 attempts to overcome this limitation and the diffusion limitation of the prior art by reducing the particle size to minimize the diffusion path and increase the surface area. US Patent No. 5,899,392 claims a process for the removal of a contaminant that has penetrated the matrices of RPET flakes into RPET flakes, comprising the crushing steps of the RPET flakes, to prepare particles having an average particle size between approximately 0.127 mm (0.005 inches) and approximately 2.54 mm (0.1 inches) in diameter; and the removal of the contaminant from the RPET particles causing the contaminant to diffuse out of the surface of the RPET particles. The deficiency of the reduced size is that small particles generally must be re-extruded into pellets of a manageable size and must be melt mixed or dry mixed with the uncontaminated virgin PET.

It would be desirable to develop a procedure for the decontamination of RPET and produce "clean" RPET, in which the clean RPET would present a residual level of contaminant that would be acceptable for the manufacture of new bottles and containers of PET of food grade, but to achieve this without Additional process steps of fine grinding or re-polymerization.

Summary of the invention

This invention describes a compartmentalized pellet comprising at least two compartments in which the first compartment with the largest surface area in contact with the air comprises contaminated thermoplastic polymer and the second compartment comprises uncontaminated thermoplastic polymer. Additionally it is described that the contaminated thermoplastic polymer can be selected from the group consisting of recycled polyethylene terephthalate and recycled polyethylene terephthalate copolymers and the uncontaminated thermoplastic polymer can be selected from the group consisting of virgin polyethylene terephthalate and copolymers of recycled polyethylene terephthalate.

US-B-6,669,986 describes a compartmentalized pellet according to the preamble of claim 1.

A process of recycling a polyester after consumption to obtain a recycled polyester comprising the steps of:

clean crushed pieces of a polyester after consumption to remove contaminants from its surface, thus producing pieces of polyester after consumption with the clean surface;

melt the polyester pieces after consumption with the clean surface to produce a polyester melt after consumption;

extrude the polyester melt after consumption to reduce the intrinsic viscosity of the polyester melt after consumption and remove additional contaminants;

forming a compartmentalized filament comprising at least two compartments consisting of the polyester melt after consumption and a virgin polyester melt, in which the outer compartment close to the air consists of the polyester melt after consumption and the internal compartment It consists of the melting of virgin polyester;

solidify and form pellets with the compartmentalized filament to obtain solid compartmentalized pellets; Y

remove contaminants from solid compartmentalized pellets.

US-A-5,876,644 describes a process of purification of a polyester after consumption according to the preamble of claim 4.

In addition, it is described that polyester after consumption accounts for less than 35% by weight of the compartmentalized pellet. It is also described that the extraction stage comprises the maintenance of the compartmentalized pellets in a temperature range between 150 ° C and 1 ° C below the melting point of the pellet and the removal of contaminants from the surface of the pellet.

It is also described that the step of removing contaminants from the surface comprises maintaining the pellets in a vacuum extraction environment, the passage of steam on the pellets, the passage of a non-reactive vapor on the pellets, or the passage of an inert gas or a mixture of inert gases on the pellets.

Furthermore, it is described that the extraction step comprises the exposure of the compartmentalized pellets to a liquid that removes at least one contaminant and that the liquid can solubilize polyamide and that the liquid can be formic acid or ethylene glycol.

Brief description of the drawings

Figure 1 depicts a resin pellet with two compartments or zones in the core-wrap configuration.

Figure 2 depicts a resin pellet with two compartments or zones in the core-shell configuration where the core is encapsulated, surrounded, or enclosed by an outer shell layer.

Figure 3 depicts a resin pellet with three compartments or zones in a multilayer or sandwich configuration.

Figure 4 depicts a resin skin of three compartmentalized zones configured in two concentric layers surrounding a core.

Detailed description of the invention

The following embodiment demonstrates how the compartmentalized structure is an improvement over the prior art.

U.S. Patent Nos. 5,627,218 and 5,747,548 teach many techniques for manufacturing compartmentalized pellets. In one embodiment there are at least two zones or regions in the pellet, preferably a core and a wrap. In this, and in all of the following embodiments, the core-shell with the sealed ends, as taught in US Patent No. 6,669,986, is the preferred structure of the pellet.

The core-shell structure is obtained using two extruders. If a third ring is desired, an additional extruder is necessary. The first extruder supplies the liquid feed that forms the core material that is linearly extruded in the center of the filament. At the same time, the envelope material is extruded in the second extruder into the shell layer that concentrically covers the core. US Patent No. 6,669,986 describes a multi-hole die cutter for manufacturing a core-wrap pellet. Figure 1 shows the multilayer core-wrap filament. Element 1 is the core and element 2 is the envelope.

Another preferred embodiment is to close the ends of the tablet so that the polymer with the highest melt viscosity is completely surrounded and enclosed by the polymer with a low melt viscosity in the shell. This preferred embodiment is depicted in Figure 2, in which the ends of the pellet are closed so that the inner core, marked by 21, is completely surrounded and enclosed by the wrap, marked by 22. This structure exposes more surface area and further increases the extraction efficiency.

US Patent No. 6,669,986 teaches that spherical or elliptical or disc shaped multilayer pads having the total circumference that includes the end face of the core material coated with the envelope material can be prepared by rounding the end face cut. One way to prepare a tablet with a wrap in the outer layer that encloses the contents of the inner layers is achieved by cutting the filament of the tablet near the die under water.

It is obvious to someone skilled in the art that the filament may consist of more than two concentric annular layers. This would be achieved using another feeder or a different die. Figure 4 represents this tablet having 3 compartmentalized zones with a core 41 consisting of the clean material, in which the core is coated by an intermediate layer 42 that is constituted of a clean or contaminated material, which in turn is surrounded by an outer layer 43 that is constituted of contaminated material.

The first stage is extrusion forming a multilayer filament. One component is extruded in the center of the pellet and the other component is extruded around the central component. The multilayer filament formed by extrusion is cut by a granulator before or after it is cooled, as necessary, and formed into multilayer pellets.

For cooling, general cooling means are adopted. For example, a procedure for immersion of the multilayer filament in a tank with cold water is adopted. The water-cooled multilayer filament is preferably sent to the granulator after removing moisture adhered to the surface by means of a water drip device.

The granulator cuts the multilayer filament with a specific length using a rotating blade, or the like. By cutting the multilayer filament as is, multilayer pellets are obtained in the form of double columns comprising the core material and the envelope material.

In general, multilayer pellets with an outer diameter of approximately 2 to 8 mm are manufactured.

It should be recognized that the absolute separation of compartmentalized areas is not essential. Although the materials can be found in separate areas, there may be a certain amount of contaminant in the internal areas and some uncontaminated polymer in the external areas. The lack of absolute separation is true for all embodiments of the invention.

The thermoplastic polymers can be molded into laminated sheets which are then also cut into cubes. The minimum structure is two layers, but the preferred structure for a molding structure of the invention is represented in Figure 3. In the sandwich or layer construction there are at least three layers where the middle layer, marked by 33, of the Clean material is sandwiched between a first outer layer, marked by 31, and a second outer layer, marked by 32, where each outer layer contains the contaminated material. Alternatively, only the outermost layer can contain the contaminated material.

In most extraction procedures, contaminants are removed from the surface of the pellet and then out (diffused) outward from the center of the pellet to the outer wall. Therefore, it is advantageous to place the material containing the contaminant on the outer wall of the pellet and place the material without contaminant, or alternatively with a substantially lower amount of contaminants, in the inner zone called the core.

A preferred embodiment is the core-shell design where the core comprises low molecular weight polyester known as a feed polymer with an intrinsic viscosity (VI) that preferably ranges between 0.45 and 0.62 dl / g, and the Wrap comprises contaminated polyester, usually recycled polyester after consumption. The typical VI of recycled PET after consumption are in the range of 0.60 to 0.82 dl / g.

Such recycled PET after consumption, recycled polyester, or recycled polyethylene terephthalate often comes from soft bottles for beverages and are commercially available worldwide. In order to be recycled, the material must have existed as a solid at least once before being extruded into the core. A recycled polyester wrap after its consumption would have a representative variable composition of the thermoplastic polymers used in packages at that time and therefore would contain a mixture of the various packaging polyesters existing in the market.

A special type of recycled polyester after its consumption is the type known as recycled polyester after its consumption regulated by the FDA. The FDA is the United States Food and Drug Administration and is responsible for enacting regulations governing the use of plastics in food packaging. "FDA regulated" means that recycled polyester after consumption complies with FDA regulations governing the use of plastics in food and beverage containers before being placed in the compartmentalized tablet. To comply with FDA regulations, the resin must be of a purity suitable for use in food packaging as required by the Law for Food, Drugs and Cosmetics according to modified and applicable regulations. Some recycled polyesters after consumption are manufactured using procedures that have been reviewed by the FDA, and the FDA has published that assesses that the material from that procedure is of adequate purity in accordance with 21 CFR 174.5, provided that it complies also with 21 CFR 177.1630. This is often called a "no objection letter." It is also considered that these recycled polyesters after consumption meet the limitation of being regulated by the FDA, and would be considered recycled polyesters after their consumption regulated by the FDA. It is important to understand that a recycled polyester after its regulated consumption may meet the requirements and be regulated by the FDA for the purposes of this specification and not have a "no objection letter" regarding the procedure used to clean the polyester.

Recycled polyester after its FDA-regulated consumption is likely to still contain contaminants, so even recycled polyester after its FDA-regulated consumption and other FDA-regulated recycled plastics will benefit from this invention, as long as are contaminated

This structure of the pellet is then subjected to at least one extraction stage to remove the contaminant. Some extraction steps will also increase the molecular weight of both the contaminated polymer and the uncontaminated polymer. Extraction using high temperatures and vacuum extraction or high temperatures and exposure of the polymer to a vapor stream of an inert gas are examples of such extraction steps.

Someone skilled in the art will recognize that if the extraction process increases the molecular weight of the polymers, then the location of the polymers in the pellet will influence the rate of increase of the VI. Once the final molecular weight is determined, the person skilled in the art will select a lower starting molecular weight of each respective zone so that the final molecular weight is the desired molecular weight of the polymer in each respective zone.

Thermoplastic polymers suitable for use in the present invention include any thermoplastic homopolymer or copolymer. Examples of inert oxygen thermoplastic polymers are polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, and polyethylene naphthalate, branched polyesters, polystyrenes, polycarbonate, polyvinyl chloride, polyvinylidene dichloride, polyacrylamide, polyacrylonitrile, polyvinylacetate, polyacrylic acid, polyvinyl methyl ether copolymer, ethylene-vinyl acetate copolymer, etilenmetilacrilato , polyethylene, polypropylene, ethylene-propylene copolymers, poly (1-hexene), poly (4-methyl-1-pentene), poly (1-butene), poly (3-methyl1-butene), poly (3-phenyl -1-propene) and poly (vinylcyclohexane). Preferably, the thermoplastic polymer used in the present invention comprises a polyester polymer or copolymer such as polyethylene terephthalate or a crystallizable polyethylene terephthalate copolymer.

It is understood that the thermoplastic polymer suitable for use in the present invention can be prepared in a film, sheet, or injection molded article.

The polymers used in the present invention can be prepared by conventional polymerization procedures well known in the art. Polyester polymers and copolymers can be prepared by melt phase polymerization which involves the reaction of a diol with a dicarboxylic acid, or its corresponding diester. The various copolymers resulting from the use of multiple diols and diacids can also be used. Polymers containing repeating units of a single chemical composition are homopolymers. Polymers with two or more chemically different repeating units in the same macromolecule are called copolymers. For clarity, a polymer of terephthalate, isophthalate and naphthalate with ethylene glycol, diethylene glycol and cyclohexanedimethanol contains six different monomers and is considered a copolymer. The diversity of the repeating units depends on the number of different types of monomers present in the initial polymerization reaction. In the case of polyesters, the copolymers include the reaction of one or more diols with a diacid or multiple diacids, and are sometimes also termed terpolymers.

Suitable dicarboxylic acids include those comprising between about 6 and about 40 carbon atoms. Specific dicarboxylic acids include, but are not limited to, terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, cyclohexanedicarboxylic acid, cyclohexanediacetic acid, diphenyl-4,4'-dicarboxylic acid, 1,3-phenylenedioxydiacetic acid, 1, 2-Phenylenedioxydiacetic, 1,4-phenylenedioxydiacetic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, and the like. Specific esters include, but are not limited to, phthalic esters and naphthalic diesters.

These acids or esters can be reacted with an aliphatic diol having between about 2 and about 10 carbon atoms, a cycloaliphatic diol having between about 7 and about 14 carbon atoms, an aromatic diol having between about 6 and 15 atoms about carbon, or a glycol ether having between 4 and 10 carbon atoms. Suitable diols include, but are not limited to, 1,4-butanediol, trimethylene glycol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, diethylene glycol, resorcinol, and hydroquinone.

Preferably, the thermoplastic polymers used in the present invention comprise a polyester polymer that means a homopolymer or copolymer such as polyethylene terephthalate or a crystallizable copolymer of polyethylene terephthalate. For clarity, the terms crystallizable polyethylene terephthalate, and the group consisting of crystallizable polyethylene terephthalates, refers to polymers that are crystallizable and consist of at least 85% of repeating segments of polyethylene terephthalate. The remaining 15% may be any other combination of acid-glycol repeat units, with the proviso that the resulting polymer is capable of achieving a degree of crystallinity of at least 5%, and more preferably 10%.

The term "crystallizable polyester" refers to a polymer that is crystallizable and at least 85% of its acid moieties are selected from the group consisting of terephthalic acid, 2,6-naphthalenedicarboxylic acid or their respective dimethyl esters.

The terms polyethylene naphthalate, polyethylene terephthalate, PET, RPET, are therefore not restricted to the homopolymer, but also refer to the respective copolymers.

Polyfunctional comonomers can also be used, usually in amounts between about 0.1 and about 3% molar. Suitable comonomers include, but are not limited to, trimellitic anhydride, trimethylpropane, pyromellitic dianhydride (PMDA), and pentaerythritol. Polyacids or polyols that form polyesters can also be used.

A preferred polyester is polyethylene terephthalate (PET homopolymer) formed from the approximate 1: 1 stoichiometric reaction of terephthalic acid, or its ester, with ethylene glycol. Another preferred polyester is polyethylene naphthalate (homopolymer of PEN) formed from the approximate stoichiometric reaction 1: 1 to 1: 1.6 of naphthalenedicarboxylic acid, or its ester, with ethylene glycol.

Another additional preferred polyester is polybutyleneterephthalate (PBT). Also preferred are PET copolymers, PEN copolymers, and PBT copolymers. Specific copolymers and terpolymers of interest are PET with combinations of isophthalic acid or its diester, 2,6-naphthalenedicarboxylic acid or its diester, and / or cyclohexanedimethanol.

The esterification or polycondensation reaction of the carboxylic acid or the ester with glycol usually takes place in the presence of a catalyst. Suitable catalysts include, but are not limited to, antimony oxide, antimony triacetate, antimony ethylene glycol, organomagnesium, tin oxide, titanium alkoxides, dibutyltin dilaurate, and germanium oxide. These catalysts can be used in combination with acetates or benzoates of zinc, manganese, or magnesium. Catalysts comprising antimony are preferred.

Due to the convenience that this structure of the pellet is for food packaging, in the USA 21 CFR 177.1000-177.2910 (revised April 1997 edition) other suitable polyesters are listed.

Polytrimethylene terephthalate (PTT) is another preferred polyester. It can be prepared, for example, by reacting 1,3-propanediol with at least one aromatic diacid or one of its alkyl esters. Preferred diacids and alkyl esters include terephthalic acid (TPA) or dimethyl terephthalate (DMT). Accordingly, the PTT preferably comprises at least about 80% mole of TPA or DMT. Other diols that can be copolymerized in said polyester include, for example, ethylene glycol, diethylene glycol, 1,4-cyclohexanedimethanol, and 1,4-butanediol. Aromatic and aliphatic acids that can be used simultaneously to prepare a copolymer include, for example, isophthalic acid and sebacic acid.

Preferred catalysts for the preparation of PTT include titanium and zirconium compounds. Suitable titanium catalytic compounds include, but are not limited to, titanium alkylates and their derivatives, salts of titanium complexes, titanium complexes with hydroxycarboxylic acids, co-precipitates of silicon titanium dioxide, and titanium dioxide containing compounds hydrated alkalines Specific examples include tetra- (2-ethylhexyl) -titanate, tetra-stearylthitanato, titanium diisopropoxy-bis (acetyl-acetonate), titanium di-n-butoxybis (triethanolaminate), tributylmonoacetyl titanate, triisopropyl monoacetyl titanate, tetrabenzoic malonate titanate, oxa of alkali-titanium, potassium hexafluorotitanate, and titanium complexes with tartaric acid, citric acid or lactic acid. Preferred titanium catalyst compounds are titanium tetrabutylate and titanium tetraisopropylate. The corresponding zirconium compounds can also be used.

The preferred polymer of this invention may also contain small amounts of phosphorus compounds, such as phosphates, and a catalyst such as a cobalt compound, which tends to confer a blue hue. Other agents that may be included are infrared absorbers such as carbon black, graphite, and various iron compounds.

After melt phase polymerization, the resulting polymer can be placed in the inner compartment (core) with the contaminated polymer in the shell and the pellet can be subjected to the extraction process. One such extraction procedure is the solid phase polymerization process described below.

Alternatively, the melt phase polymerization described above can be performed in the traditional pellet, followed by a crystallization stage and then a solid phase polymerization stage (SSP) to increase the molecular weight, measured by the intrinsic viscosity, necessary for the bottle manufacturing The clean polymer or solid phase polymerised virgin can then be extruded into the core of the invention.

Crystallization and polymerization can be carried out with the reaction in a dryer in a batch system. Alternatively, crystallization and polymerization can be achieved in a continuous solid phase process in which the polymer flows from one reactor to another after the predetermined heat treatment in each reactor.

The crystallization conditions preferably include a temperature between about 100 ° C and about 190 ° C. The conditions for solid phase polymerization preferably include a temperature between about 200 ° C and about 232 ° C, and more preferably between about 215 ° C and about 232 ° C. Solid phase polymerization can be carried out for a sufficient time to increase the molecular weight to a desired level, which will depend on its application. For a typical bottle application, the preferred molecular weight corresponds to an intrinsic viscosity between about 0.65 and about 1.0 dl / g, determined by ASTM D-4603-86 at 30 ° C in a mixture of phenol and 60/40 tetrachloroethane by weight. The time required to reach this molecular weight can vary between approximately 8 hours and approximately 45 hours.

The other component of this embodiment is a contaminant that can be extracted from the polymer. The contaminants of the invention are those contaminants that can be extracted from the polyester pellet in its solid form. Extraction normally occurs in the presence of temperature (150 ° C to 1 ° C below the melting point of the pellet) and a driving force on the surface of the pellet such as steam distillation, vacuum extraction, current of steam, or liquid stream. Examples of contaminants are the various organic flavorings found in foods that migrate to the polymer, household chemicals, high and low boiling household compounds that can be stored in the container, and even some polymeric materials that can be intentionally introduced into the container. main polymer matrix or by the recycling process. Adhesives, poly-m-xylethylene adipamide (MXD6), and polyvinyl chloride are examples of such polymers that can be extracted from the surface using a liquid extraction. MXD6, for example, is soluble in formic acid.

The effectiveness of the elimination can be demonstrated using toluene, methanol, calcium monomethylarsenate, chloroform, benzophenone, and phenylcane as substitutes for contaminants. The comparison is the amount of material introduced into the polymer at the beginning of the process and the amount that remains present after the procedure.

In one embodiment, the pellet can be prepared by extruding the core of a polymeric filament from a prepolymer (0.52 of VI) of a polyethylene terephthalate copolymer and extruding an envelope on the core of approximately 2 to 50% by weight of the pellet from polyester pieces after consumption washed. Then the filament becomes solid core-wrap pellets. The contaminants are removed from the pellets by subjecting them to 225 ° C and nitrogen passing through the pellets for 16 hours. The extraction time will be the time necessary to reach the appropriate intrinsic viscosity or the time necessary to remove the necessary amount of contaminants. A variation of the extraction procedure is the use of vacuum instead of a sweep with nitrogen.

In another embodiment, the envelope layer after its recycled consumption will contain between 0.01 and 5-8% by weight of poly-m-xylylene adipamide (MXD6 nylon) envelope. The pellet is then exposed to formic acid at 95 ° C to remove the nylon from the wrap.

In the above embodiments, it will be apparent that the surface of the contaminated material is larger and that the diffusion path is shorter than if the contaminant were dispersed homogeneously throughout the entire

10 pella Therefore, the efficiency of extractive purification procedures is improved.

Experimental part

The following data demonstrate the improved efficacy of the present invention. Because most of

Contaminants are volatile, they can be extracted by exposing the polymer to heat and a conductive force that could be swept with an inert gas or vacuum. In the experiments, volatile organic dyes were used as substitutes for other contaminants. Improved removal efficiency was determined by measuring the color of an article made from the pellets both before and after extraction.

20 The experiment consisted of the control pellet and the compartmentalized pellet of the working example. In the first series, the control pellet was prepared by extruding polyester and adding 110 ppm of Solvent Dye 13 (SV-13) to the extruder. In the working example, the same polyester was used in the compartmentalized pellet. 50% of the pellet consisted of the nucleus that was free of any dye (contamination). The same amount of dye was added to the polyester in the envelope as the amount added to the control pellet (110 ppm based on the entire pellet). Because

25 that the pellet was 50% core: 50% wrap, the wrap contained 220 ppm SV-13, by weight of the wrap.

The pellets were crystallized and then mixed in a 3: 1 ratio with non-colored PET and injection molded into a preform, blown into a bottle and Hunter's L *, a *, b * were measured. The proximity of the numbers, in particular of L *, indicates that the materials started with the same amount of dye.

30 The remaining pellets were then subjected to elevated temperature in the presence of a nitrogen sweep for 10 hours. After 10 hours, the pellets were collected, injection molded into the same preform as the initial pellets and the color was measured again.

35 As shown in Table I, the highest L * and the lowest b * of the blowing of the bottle walls from the preform made with the compartmentalized pellets show that more volatile compounds were removed from the compartmentalized pellets than mixed control pellets. This confirms the observation that there was more dye in the upper part of the reactor cover after the extraction of the compartmentalized pellets than what was present after the extraction of the mixed pellets.

40 Delta E is the square root of the sum of the squares of each value from its neutral color that is 100, 0, 0 for the color space of L *, a *, b * and is equal to:

SQRT ((100-L *) 2 + (a *) 2 + (b *) 2), where SQRT is the square root function of the numbers in parentheses.

Four. Five

TABLE I - EXPERIMENTAL RESULTS

Color before extraction, mixed at 1: 3 with non-colored PET

Control mix Compartmentalized pella

L *

84.3 85.0

to*

1.2 1.0

b *

-6.9 -5.9

Delta E

10.4 9.1

Color after extraction, without mixing

L *

69.8 72.5

to*

4.9 3.6

b *

-21.7 -17.2

Delta E

31.4 26.0

Claims (13)

one.

A compartmentalized pellet comprising at least two compartments (1, 2, 21, 22) characterized in that the first compartment (2, 22) with the largest surface area in contact with the air comprises contaminated thermoplastic polymer and the second compartment (1, 21) comprises uncontaminated thermoplastic polymer.

2.

The compartmentalized pellet of claim 1, wherein the compartmentalized thermoplastic polymer is selected from the group consisting of recycled polyethylene terephthalate and recycled polyethylene terephthalate copolymers.

3.

The compartmentalized pellet of claim 2, wherein the uncontaminated thermoplastic polymer is selected from the group consisting of virgin polyethylene terephthalate and copolymers of recycled polyethylene terephthalate.

Four.

A process of purification of a polyester after consumption comprising:

cleaning crushed chunks of a polyester after consumption to remove contaminants from its surface thus producing chunks of polyester after consumption with the clean surface; the fusion of polyester pieces after consumption with the clean surface to produce a polyester melt after consumption; the extrusion of the polyester melt after its consumption to reduce the intrinsic viscosity of the polyester melt after its consumption and eliminate additional contaminants; characterized in that said process comprises the formation of a compartmentalized filament consisting of at least two compartments (1, 2, 21, 22) constituted by the polyester melt after consumption and a virgin polyester melt in which the outer compartment ( 2, 22) next to the air consists of the polyester melt after consumption and the internal compartment (1, 21) consists of the virgin polyester melt; solidification and pellet formation of the compartmentalized filament to obtain solid compartmentalized pellets; Y the removal of contaminants from solid compartmentalized pellets.

5.

The method of claim 4, wherein the polyester after consumption assumes less than 35% by weight of the compartmentalized pellet.

6.

The method of claim 5 wherein the extraction step comprises maintaining the compartmentalized pellets in a temperature range between 150 ° C and 1 ° C below the melting point of the pellet and removing contaminants from the pellet. surface of the pella.

7.

The method of claim 6, wherein the step of removing contaminants from the surface comprises maintaining the pellets in a vacuum extraction environment.

8.

The method of claim 6, wherein the step of removing contaminants from the surface comprises the passage of steam over the pellets.

9.

The method of claim 8, wherein the vapor is non-reactive to polyester after consumption in the compartmentalized pellet.

10.

The process of claim 9, wherein the vapor is an inert gas, or a mixture of inert gases.

eleven.

The method of claim 5, wherein the extraction step comprises exposing the compartmentalized pellets to a liquid that removes at least one contaminant.

12.

The method of claim 11, wherein the polyamide is soluble in the liquid.

13.

The process of claim 12 wherein the liquid is formic acid or ethylene glycol.