MXPA98008082A - Improved decontamination of tper through lareduction of particle size - Google Patents

Abstract

Contaminants that are found in TPER flakes are removed by a process that includes the following steps of crushing the TPER flakes to produce TPER particles, and removing the contaminants out of the TP particles.

Description

Improved amination of TPER to Trave s of the Particle Size Reduction.

FIELD OF THE INVENTION The present invention relates in general to an improved process for decontaminating recycled polyethylene terephthalate (TPER) through the reduction of particle size. More particularly, the invention is directed to a process for removing contaminants that have diffused into the matrix of the side walls of a TPE container, which process is conducted after the container is recycled into TPER.

BACKGROUND OF THE INVENTION The post-consumer process of recycled TPE is well known for the manufacture of a variety of useful consumer products, such as flower pots and fence posts. Typically, the recycling process uses used TPE containers, such as discarded carbonated beverage containers that are collected, sorted, washed and separated from contaminants to produce a relatively clean source of TPE. In addition, the manufacture of imperfect and damaged molded TPE products, particularly blow molded bottles used to contain consumer products, results in a considerable amount of TPE losses that the manufacturers of such products would wish to reuse. The TPER produced by means of conventional recycling procedures is usually in the form of powder or flakes, which is then processed by melting or else made by the end user. The TPER is always subjected to a grinding operation to make the material easier to handle and process. Conventional grinding equipment reduces the TPER to approximately 0.95 cm. of particles or flakes. The grinding is carried out in a way that ensures that a consistent size of flake will be produced, using a grid or sieve through which the powder material must pass when leaving the grinder. Although the conventional melting process of the TPER flakes and the packing equipment are designed to handle 0.95 cm flakes. , some TPER materials that have sizes as large as% inch and as small as 0.63 cm. They are also commercially produced. The density of the TPER in flake of 0.95 cm. it usually varies from about 22 to about 35 pounds per cubic foot. Similarly, the TPE and TPER tablets are usually formed into a standard uniform size of about 0.30 cm. diameter. The mass density of said pellets usually varies from about 50 to about 58 pounds per cubic foot. Typically, the melt processing equipment of TPER and TPE is designed to accept pellets having the aforementioned dimensions and physical characteristics. The critical aspect to achieve finished products of high quality, using TPER, is the general decontamination of TPER chips or flakes. Significant decontamination occurs during the washing and sorting of the pieces of the TPE. New TPE containers and bottles are crushed to form TPE fragments and to remove loose labels, dirt and other foreign particles adhering. Then, the mixture is sorted with air and the remaining fragments are washed in a hot detergent solution to remove the additional adhesives and label fragments from the TPE fragments. The washed pieces of TPE are then rinsed and placed in a series of flotation baths, where the particles of different weight, either lighter or heavier, are removed. The remaining TPE fragments are then dried and sold as TPER flakes. Thus, the label and base adhesives, polyolefins, PVC, paper, glass, metals and everything that adversely affects the quality and development of the finished product, is eliminated from the TPER. A recent concern, are the toxic contaminants that can be introduced in a typical TPER processing stream. Examples of such contaminants include pesticides, solvents, herbicides, and chlorinated hydrocarbons, which could contaminate the TPER through incidental and inadvertent contact during the process or transportation of the TPER or through the recycling of TPE containers and bottles that are used by consumers to store toxic substances for an extended period of time.

D.W. Hayward, author of "Employing RPET in Your Process" (The use of TPER in your process), SPE RETEC, November 4, 1994, reports that "clean" TPER flakes may still contain residual contaminants at concentrations as high as 4%, and there is a likelihood that such contaminants could include toxic pollutants These sources of contamination are of great concern to those who wish to incorporate TPER into new containers for use in contact with food. With respect to the possibility that toxic contaminants may be contained in the TPER designed for use in contact with food, the FDA of E.U.A. has established protocols for the levels of such contaminants in these applications, and has established concentration limits and substitutes to establish the effectiveness of the wash and the subsequent decontamination processes. Because the protocols of the US FDA require that the TPER be introduced to the selected contaminant for up to two weeks, it is clear that the contaminants will diffuse into the polymer matrix of a side wall of a container or bottle to be recited. Subsequently. Accordingly, an effective method of decontamination to some degree will require that the contaminant be redirected away from the TPER flakes produced from the side walls of the container or bottles, to meet the required concentration limit of the contaminant. It would be desirable to develop a TPER decontamination process to produce "clean" TPER, where the clean TPER exhibits a residual contaminant level that would make it acceptable for the manufacture of new containers and bottles of food grade TPE.

SUMMARY OF THE INVENTION In accordance with the present invention, a process for removing contaminants found in the TPER flakes has surprisingly been discovered. The process comprises the following steps: crushing the TPER flakes to prepare TPER particles having an average particle size of about 0.012 cm. at approximately 0.254 cm. in diameter; and eliminate the contaminant outside the TPER particles. The inventive process is particularly useful in removing the toxic contaminants found in the TPER flakes, so that the resulting material can then be used in the manufacture of new containers and bottles of food grade TPE.

BRIEF DESCRIPTION OF THE DRAWING The novel features, considered characteristic of the present invention, are described with particularity in the appended claims. However, the invention itself will be better understood from the accompanying description of the specific embodiments when read in connection with the present drawing, in which: The figure is a graph illustrating the intrinsic viscosity increase index, as a function to decrease the particle size of the TPER.

DETAILED DESCRIPTION OF THE PREFERRED MODALITY The present invention is directed to a process for the elimination of the contaminants that are found in the TPER flakes. The TPER flakes are crushed to prepare the TPER particles, and then the contaminant is conducted out of the TPER particles. As used herein, the term "TPER flakes" is generally understood as the commercially available recycled polyethylene terephthalate materials produced by conventional TPE recycling methods, usually in the form of flakes, but which may additionally have shaped pieces, spheres, pellets and the like, and which are generally available in bulk in a substantially uniform particle size of about 0.63 cm. to approximately 1.27 cm. , for subsequent melt processing operations. A single typical particle of TPER flake of 0.95 cm. exhibits a surface at the volume index of approximately 177. Contaminants that have penetrated the matrix of the TPER flake can only diffuse outward on the surface of the TPER flake. The pollutants that have spread widely within the matrix of the TPER leaflet, usually can not spread out of the leaflet between the time the TPER leaflet is produced in the conventional recycling process, and the time when the TPER leaflet is used in a melt processing operation. to produce a new TPE article. In accordance with the present invention, the TPER flakes are ground by any conventional means to prepare TPER particles having an average particle size of about 0.012 cm. at approximately 0.254 cm. diameter. Preferably, the particle size varies from about 0.012 cm. to approximately 0.12 cm. This is a substantial reduction in the size of the individual TPER flakes, and will allow any contaminants contained within the TPER flakes to be driven out more quickly and easily. For example, a particle of TPE having a radius of about 0.147 cm. and a benzene concentration of approximately 25,000 ppm requires more than 96 hours of diffusion time at 70 for the benzene level to fall to a concentration of approximately 0.25 ppm. In contrast, a TPE particle having a radius of about 0.02225 cm. it requires less than three hours to reach the same concentration level of 0.25 ppm, all other parameters being equal. Thus, the TPER flakes can be decontaminated by means of the inventive process, which includes the stage in which the particle size is reduced without the need to elaborate exotic media such as double effect composition, vacuum extraction or residence times. extremely long, as was thought in the prior art. After crushing the TPER flakes, the resulting TPER particles are subjected to a process designed to remove contaminants from the particles. As is well known, this can be carried out simply by air drying the TPER particles (passing a jet of a gas, preferably air, over and through the particles) at room temperature. The time required to achieve substantial removal of the contaminants found in the TPER particles is much less than would otherwise be required to achieve the same removal of contaminants from an equal mass of TPER flakes, using the same terms. Alternatively, the ground TPER particles are simply allowed to reside mass in standard conditions, until the contaminants have diffused out of the particles. In addition, TPER particles can be heated in a conventional manner, which will accelerate the diffusion of contaminants out of the particles. Also, the TPER particles can be placed in a liquid solution that can leach contaminants from the particles. This, as well as other conventional methods, can be used to remove contaminants outside the TPER particles.; but in each case, the time required will be substantially less than what would otherwise have been required to effect the same level of decontamination in an equal mass of TPER flakes. Although the present invention focuses primarily on the use of particle size reduction to decontaminate TPER particles, other benefits can be realized by employing the particle size reduction step. The same mechanics will also improve the development of drying and solid state conversion of the TPER. Conversion to solid state is a process by which the intrinsic viscosity of TPER is high. Intrinsic viscosity is an important physical characteristic that largely determines the ultimate strength of the final product, for example, a bottle or container produced from TPER flakes. A bottle or container produced from a TPER that has a low intrinsic viscosity will not develop as well as a bottle or container made from a TPER with higher intrinsic viscosity. The TPE, unlike many other polymers, has the ability to "come together again" in the process of solid state conversion, which elevates the intrinsic viscosity back to an acceptable level. Conversion to the solid state occurs at high temperatures, usually just below the melting point of the polymer, and employs a stream of dry gas flowing through the bed of polymer particles, where the gas used is usually inert, such as nitrogen. Alternatively, the solid state conversion process can be carried out under vacuum. The conversion to solid state depends on the mechanics of diffusion to remove the byproducts of the process, and the thermal dynamics to raise the temperature of the TPER. The reduced particle size greatly improves the solid state conversion process, decreasing the time required to raise the intrinsic viscosity to the desired level. In addition, the TPE is a hygroscopic polymer that must be perfectly dried before the melting process, to prevent hydrolytic degradation and the resulting loss of intrinsic viscosity. Drying of TPER or TPE flakes usually occurs in commercially available desiccant hot air dryers, which are designed to remove moisture from the surface and matrix of the material. The drying is conducted at temperatures that are above the boiling point of the water, but below the temperatures of the solid state conversion. The reduction in particle size, according to the present invention, greatly reduces the time required to dry the TPER. Thus, although the inventive process is described and claimed as a process for removing a contaminant that is found in the TPER flakes, it is contemplated that the process described and additionally claimed may be used to improve and accelerate a solid state conversion process, and can simplify and accelerate a process to dry the TPER.

Example The TPER flakes are crushed to produce four batches of TPER particles having approximately the following average particle sizes (diameters): 0.30 cm. (TPER flakes not crushed); 0.1000 cm; 0.0419 cm and 0.017 cm. These four batches of TPER particles and flakes are individually converted to a solid state at a temperature of approximately 218 ° C, under a nitrogen purge at 1 atm. Samples from each batch are extracted at various times during the solid state conversion process, and the intrinsic viscosity of each sample is measured. It is observed that the intrinsic viscosity of the samples taken from a single batch increases during increasingly long solid state conversion times. In addition, it is also observed that the rate of increase in intrinsic viscosity depends on the average particle size of the TPER particles in the batch. The rate of increase in intrinsic viscosity increases in much smaller TPER particle sizes. The process for removing contaminants that are found in the TPER flakes, described above, is generally disclosed in terms of its broader application to the practice of the present invention. From time to time, the process conditions as described may not be precisely applicable to each combination of TPER / contaminant flake included within the disclosed range. However, in those cases where it occurs, experts in the field will easily recognize it. In all the cases mentioned, the process can be successfully developed by means of conventional modifications to the revealed process. The invention is more easily understood with reference to the specific embodiments that are described above, which are representative of the invention. However, it should be understood that the specific modalities are only provided for the purpose of illustrating, and that it can be practiced in another way than that specifically illustrated, without having to start from its spirit and scope.

Claims (11)

1. Claims 1. A process for removing a contaminant that is in TPER flakes, comprising the following steps: crushing the TPER flakes, to prepare TPER particles having an average particle size of about 0.012 cm. at approximately 0.254 cm. diameter; and removing the contaminant out of the TPER particles.
2. 2. The process for removing a contaminant that is in TPER flakes, according to claim 1, wherein the TPER flakes are ground to prepare TPER particles having an average particle size of about 0.012 cm. to approximately 0.12 cm.
3. 3. The process for removing a contaminant that is in TPER flakes, according to claim 1, wherein the step in which the contaminant is taken out of the TPER particles comprises passing a current of a gas above and through the TPER particles.
4. 4. The process for removing a contaminant that is in TPER flakes, according to claim 1, wherein the step in which the contaminant is taken out of the TPER particles comprises allowing the TPER particles to reside in mass during a period of time sufficient for substantially all of the contaminant to diffuse out of the TPER particles.
5. 5. The process for removing a contaminant that is in TPER flakes, according to claim 1, wherein the step in which the contaminant is taken out of the TPER particles comprises heating the TPER particles.
6. 6. The process for removing a contaminant that is in TPER flakes, according to claim 1, wherein the step in which the contaminant is taken out of the TPER particles comprises immersing the TPER particles in a solution capable of leach the pollutant from the TPER particles.
7. 7. A process to eliminate a contaminant that is found in TPER flakes, which comprises the following stages: crushing the TPER flakes, to prepare particles of TPER that have an average particle size of approximately 0.012 cm. to approximately 0.12 cm. diameter; and removing the contaminant out of the TPER particles for a period of time that is less than the time required to remove the same amount of contaminant away from the TPER flakes from which the TPER particles were prepared, using the same method Driving out.
8. 8. The process for removing a contaminant that is in TPER flakes, according to claim 7, wherein the step in which the contaminant is taken out of the TPER particles comprises passing a stream of a gas above, through the particles.
9. 9. The process for removing a TPER flake contaminant, according to claim 7, wherein the step in which the contaminant is taken out of the TPER particles comprises allowing the TPER particles to reside in mass over a period of time. sufficient time for substantially all of the contaminant to diffuse out of the TPER particles.
10. 10. The process for removing a contaminant that is in TPER flakes, according to claim 7, wherein the step in which the contaminant is taken out of the TPER particles comprises heating the TPER particles.
11. 11. The process for removing a contaminant that is in TPER flakes, according to claim 7, wherein the step in which the contaminant is taken out of the TPER particles comprises immersing the TPER particles in a solution capable of leach the pollutant from the TPER particles.