TR2024015118T2 - Continuous production of biodegradable polyesters. - Google Patents

Abstract

A method is described for spinning a biodegradable polyester copolymer filament. A biodegradable polyester copolymer melt is formed by polymerizing terephthalic acid, ethylene glycol, caprolactone monomer, calcium carbonate, and polybutylene succinate to form a biodegradable polyester copolymer melt. The biodegradable polyester copolymer melt may be spun into a biodegradable polyester copolymer filament.

Description

DESCRIPTION CONTINUOUS PRODUCTION OF BIODEGRADABLE POLYESTERS The invention now described relates to polymer compositions that are biodegradable and suitable for textiles in general. BACKGROUND Textiles are fundamental to human culture and have been made and used by humans for thousands of years. The earliest known textiles were woven from natural fibers such as linen, wool, silk, and cotton. More recently, textile fibers, yarns, and fabrics have also been industrially produced from polymers such as polyester, nylon olefins, other thermoplastic polymers, and combinations thereof. Many modern polymers can be formed into an almost infinite variety of shapes and products that are attractive, durable, and water-resistant. In many cases, these synthetic fibers or yarns (depending on the desired technique and the end product) can be blended with natural fibers to produce end products that possess the desired properties of both natural and synthetic materials. While durability and water resistance are desirable, these same properties can lead to secondary environmental problems. Textiles made from polymeric fibers do not naturally biodegrade in the same way as natural fibers and can persist in landfills and water (e.g., lakes, oceans) for hundreds of years or longer. Currently available biodegradable fibers present several manufacturing challenges. Typically, a masterbatch approach is used to create biodegradable polymers using an extruder process. However, masterbatch is costly and requires additional compounding, drying, and crystallization steps. Additionally, polycaprolactone (6400 Ma), a well-known biodegradable polymer in pellet form, lends itself well to a masterbatch approach but is more difficult to use in a continuous polymerization process. Accordingly, there is a need for biodegradable polymers suitable for forming textiles with desirable properties similar to conventional textiles, which can be created through continuous production (i.e., continuous polymerization) rather than masterbatch production. BRIEF DESCRIPTION In one aspect, a method for spinning a biodegradable polyester copolymer filament is provided. The method includes polymerizing terephthalic acid, ethylene glycol, caprolactone monomer, calcium carbonate, and polybutylene succinate to form a biodegradable polyester copolymer melt. The biodegradable polyester copolymer melt is then spun into a biodegradable polyester copolymer filament. In another aspect, a biodegradable textile composition comprising terephthalic acid, ethylene glycol, caprolactone monomer, calcium carbonate, and polybutylene succinate is disclosed. In yet another aspect, a biodegradable polyester copolymer filament comprising terephthalic acid, ethylene glycol, caprolactone monomer, calcium carbonate, and polybutylene succinate is disclosed. BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other advantages of the present invention can be seen by reviewing the following detailed description and drawings of non-limiting examples of embodiments, of which: FIG. 1 is a table of additive components and associated levels in overhead and vacuum. FIG. 2 shows the results of a standard test method for determining anaerobic biodegradation of plastic materials under high-solids anaerobic-degradation conditions, and the materials of the present disclosure are evaluated at day 296. FIGURE 3 shows the results of a standard test method to determine the anaerobic biodegradation of plastic materials under high-solids anaerobic-degradation conditions, with materials of the present disclosure evaluated on day 298. FIGURE 4 shows the results of a standard test method to determine the anaerobic biodegradation of plastic materials under high-solids anaerobic-degradation conditions, with materials of the present disclosure evaluated on day 305. FIGURE 5 is a graph of the biodegradation of materials of the present disclosure compared to positive and negative controls over the range of 0 to 305 days. FIGURE 6 is a graph of the biodegradation of materials of the present disclosure compared to a negative control over the range of 0 to 305 days. FIGURE 7 is a table showing the amounts of components of a polyester fiber of the present disclosure. DETAILED DESCRIPTION The present disclosure as set forth herein describes fibers having desirable properties similar to conventional fibers, which are biodegradable and can be created through continuous production rather than masterbatch production. More specifically, a biodegradable polyester (polyethylene terephthalate or PET) fiber is disclosed. The invention will be described more fully with reference to the accompanying drawings, which show some, but not all, embodiments of the invention. The invention may be embodied in many different ways and should not be construed as limited to the embodiments set forth herein; rather, such embodiments are provided so that this disclosure meets applicable legal requirements. As used in the specification and the appended claims, the singular forms "a," "the" and "the" include plural references unless the context clearly requires otherwise. The term "biodegradable" as used herein refers to materials that, given the right natural conditions and the presence of microorganisms, will decompose or break down into their elemental components and return to the soil at a significantly faster scale than non-biodegradable materials. As used herein, in the context of synthetic fibers and their manufacture, the term "intrinsic viscosity" is used to describe a characteristic that is directly proportional to the average molecular weight of a polymer. Intrinsic viscosity is calculated based on the viscosity of a polymer solution (in a solvent), extrapolated to a concentration of zero. In the textile arts, the term "texturing" is used both broadly and specifically. In its broadest sense, texturing is used synonymously to refer to steps in which a synthetic filament, staple fiber, or yarn is mechanically processed, thermally processed, or both, to provide a greater volume than the virgin filament, staple fiber, or yarn. In a narrower sense, the term texturing is used to refer to processes that produce loops and crimps. The meaning is usually clear in context. As used here, the word "texture" is used broadly to include all possibilities for producing the desired effect in a filament, staple fiber, or yarn. As used here, "percent" or "%" refers to percent by weight unless otherwise stated. Furthermore, concentrations and ratios refer to the concentration or ratio in the finished copolymer unless otherwise stated. Accordingly, a polyester (polyethylene terephthalate) fiber is described as biodegradable. Typically, a masterbatch approach with an extruder process is used to create biodegradable polymers. However, masterbatches are costly, require additional compounding, drying, and crystallization steps, and are therefore not widely adopted, and biodegradable fibers are not widely available at affordable prices. A continuous polymerization process is more economical for the synthesis of polyesters, but polycaprolactone (6400 Ma), a well-known biodegradable polymer, is in pellet form and well-suited to a masterbatch approach but unsuitable for use in a continuous polymerization process. The present disclosure overcomes these challenges by incorporating caprolactone monomer, a clear liquid, into the polyester in a continuous polymerization process. Caprolactone monomer is a naturally biodegradable polycaprolactone precursor and imparts other desirable properties, such as dye development, into the fiber. The use of caprolactone monomer in traditional continuous polymerization lines provides high throughput at low cost, with outputs in excess of 30,000 pounds per hour, compared to a masterbatch approach that limits production volume to approximately 2,000 pounds per hour. Furthermore, the caprolactone monomer is almost completely consumed, or nearly so (e.g., less than 200 ppm). To produce the biodegradable polymers of the present disclosure, terephthalic acid (or purified terephthalic acid, or PTA) and ethylene glycol (or monoethylene glycol, or MEG) are reacted in a heated esterification reaction to produce monomers and oligomers of terephthalic acid and ethylene glycol, as well as water as a byproduct. The esterification reaction can be carried out in one or more tanks; in some embodiments, two tanks, each containing an esterifier, are used. A pressure gradient is traditionally used to drive the continuous polymerization process. Additionally, pumps can be used to drive the process. Water and MEG are continuously removed to ensure substantial completion of the esterification reaction. The monomers and oligomers formed by esterification are then catalytically polymerized by polycondensation to form polyethylene terephthalate (or PET) polyester. Polycondensation reactions can be carried out in one or more tanks, each containing a polymerizer. In some embodiments, two tanks are used, a low polymerizer under low vacuum and a high polymerizer under high vacuum, as is known in the art. During the above esterification and polycondensation reactions, caprolactone monomer and calcium carbonate (CaCO3) are added. In some embodiments, caprolactone monomer and calcium carbonate can be added directly to a tank containing the condensation product, such as a low-polymerizer. In some embodiments, caprolactone monomer and calcium carbonate can be added in a transfer line between an esterifier and a polymerizer. Polybutylene succinate (PBS) is added in the next step. The reactions typically proceed at about 280°C (e.g., between about 270°C and 295°C). Caprolactone monomer is incorporated into the polyester fiber along with PBS and calcium carbonate to form a biodegradable polyester material. Microbes digest the final fiber, which contains polycaprolactone, PBS, and calcium carbonate, to break down the polymer chains and allow the fibers to biodegrade. The polymerization of terephthalic acid, ethylene glycol, caprolactone monomer, calcium carbonate, and polybutylene succinate may involve polymerization of about 83% to about 86% terephthalic acid, based on the weight of the biodegradable polyester copolymer melt. About 13% to about 16% ethylene glycol, based on the weight of the biodegradable polyester copolymer melt, may be used. About 0.3% to about 2.5% caprolactone monomer, based on the weight of the biodegradable polyester copolymer melt, may be used. About 0.01% to about 0.03% calcium carbonate, based on the weight of the biodegradable polyester copolymer melt, may be used. About 0.05% to about 0.25% polybutylene succinate, by weight of the biodegradable polyester copolymer melt, may be used (and values in between). Those of ordinary skill in the art will recognize that other types of additives may be included in the polymers of the present invention. A non-limiting example is anatase titanium dioxide, one or more optical brighteners, and blue pigments. Such additives include, but are not limited to, matting agents, preform heat rate enhancers, friction-reducing additives, UV absorbers, inert particulate additives (e.g., clays or silicas), colorants, pigments, antioxidants, branching agents, oxygen barrier agents, carbon dioxide barrier agents, oxygen scavengers, flame retardants, crystallization control agents, acetaldehyde reducing agents, impact modifiers, catalyst deactivators, melt strength enhancers, antistatic agents, lubricants, chain extenders, nucleating agents, solvents, fillers, and plasticizers. It could be between about 84% and about 85.9%, between about 84% and about 86%, between about 85% and about 86%, between about 84.9% and about 86%, between about and values in between. It could be between about 14.9%, between about 13% and about 15%, between about 13% and about and/or between about 15.9% and about 16%, and values in between. concentration Between about 0.3% and about 0.4%, Between about 0.3% and about 0.4%, Between about 0.3% and about 0.6%, Between about 0.3% and about 0.7%, Between about 0.3% and about 0.8%, Between about 0.3% and about 0.9%, Between about 12%, Between about 0.3% and about 1.3%, Between about 0.3% and about 1.7%, Between about 0.3% and about 1.8%, Between about 0.3% and about 1.9%, Between about 0.3% and about 2.0%, About Between about 2.3%, Between about 0.3% and about 2.4%, Between about 0.3% and about, Between about 0.6% and about 2.5%, Between about 0.7% and about 2.5%, Between about 0.8% and about 2.5%, Between about 0.9% and about 2.5%, Between about 2.5%, Between about 1.3% and about 2.5%, Between about 1.4% and about, Between about 1.7% and about 2.5%, Between about 1.8% and about 2.5%, Between about 1.9% and about 2.5%, Between about 2.0% and about 2.5%, The concentration can be between about 2.5% and/or between about 2.4% and about 2.5%, and values in between. The concentration can be between about 0.01% and about 0.02%, or between about 0.02% and about 0.02%. Polymerization continues until the desired molar weight of polyester terephthalate is reached. The residence time in the polymerization tanks and the feed rate of ethylene glycol and terephthalic acid to the continuous process are determined in part by the target molecular weight of the polyester. Since the molecular weight can be determined by the intrinsic viscosity of the polymer melt, the intrinsic viscosity of the polymer melt is often used to determine polymerization conditions such as temperature, pressure, reactant feed rate, and residence time in the polymerization tanks. Upon completion of the polycondensation step, the polymer melt can be filtered and extruded. After extrusion, water is added to the polyethylene terephthalate to solidify the polyester, for example, by spraying it with water. The solidified polyethylene terephthalate can be cut into chips for storage and transportation. In some embodiments, the polyester produced by the method is spun into filament using conventional techniques known in the art. In some embodiments, the polyester produced by the method is blown into packaging and other products. In some embodiments, the filament produced by the method is textured and cut into staple fibers. Texturing is well understood in the art, and it will not be described in detail except to indicate that the composition of the invention produces filament that can be textured using conventional steps (e.g., heat curing in a spun position). In some embodiments, the staple fibers produced by the method are spun into yarn. In some embodiments, the staple fibers can be laid into a nonwoven mat. In some embodiments, the staple fibers are spun into a yarn blended with cotton or rayon. The yarn can then be used to create a fabric that can be used to produce textile products such as clothing and the like. The fabric can be woven or knitted, and such fabrics can be used to produce textiles and clothing. Similarly, the nonwoven mat can be used to form a fabric or textile product for the manufacture of apparel and the like. The resulting fibers, filaments, fabrics, containers, and the like are biodegradable in landfills, ocean environments, sewage sludge, seawater, freshwater, and other natural and non-natural environments containing microbes. The biodegradation timescale in the example embodiments is similar to the biodegradation timescale for natural fibers. In some embodiments, degradation of the fiber or fabric of the present disclosure is nearly or mostly complete in 3-4 years. In some or other embodiments, degradation of the fiber or fabric of the present disclosure is nearly or mostly complete in less than 3 years. Turning to the figures at this point, Figure 1 is a table of additive components and associated levels in overhead and vacuum. Six trials are shown with additives added at various steps of the polyester synthesis process, including upfront, before, and during esterification, while polybutylene succinate (PBS) and calcium carbonate (CaCO 3 ) were added late. Figure 2 shows a study of ASTM D5511, a standard test method for determining the anaerobic biodegradation of plastic materials under high-solids anaerobic-degradation conditions, in which a sample of the present specification was evaluated at 296 days. Cellulose is used as a positive control for adjusted percent biodegradation purposes, assuming complete cellulose biodegradation. The negative control is polypropylene. All values are adjusted proportionally for cellulose degradation. Figure 3 shows an ASTM D5511 study for a sample at day 298, in which case cellulose is used as a positive control. Figure 4 shows an ASTM D5511 study for a sample at day 305 with cellulose as a positive control. Figure 5 is a biodegradation graph plotted for day 305, where the positive control shows the greatest degradation (upper line) and the negative control shows no degradation (lower line). As can be seen, one embodiment of the present description, namely the degradation of crystalline ground slabs by holding them at 270°C for 3 minutes before molding, shows increasing biodegradation over time (middle line). Figure 6 is a biodegradation graph plotted for day 305 comparing the degradation of embodiments of the present disclosure (upper line) with a negative control (polypropylene, lower line). The compositions of the present disclosure show increasing biodegradation over time. Figure 7 is a table showing the amounts of the components of a polyester fiber of the present disclosure. EXAMPLES The following non-limiting examples are provided to illustrate the disclosure. In this example, a 1000 g portion of biodegradable polyethylene terephthalate is produced in a continuous manner. The 1000 g portion is prepared by adding approximately 850 g of terephthalic acid and a stoichiometric amount of ethylene glycol to an esterifier; by adding approximately 100 ppm of calcium carbonate; by adding approximately 0.5 to 1 wt% of caprolactone monomer; and finally adding approximately 0.1 percent by weight polybutylene succinate. In this example, a precursor composition is present in a low polymerizer for biodegradable polyester. The composition includes terephthalic acid ester condensation product and a stoichiometric amount of ethylene glycol; about 0.5 to 1 percent by weight caprolactone monomer; about 100 ppm by weight calcium carbonate; and about 0.1 percent by weight polybutylene succinate. The present disclosure is therefore well adapted to achieve the aforementioned objectives and advantages, as well as those inherent therein. While the present disclosure may be modified and applied in different but equivalent ways that will be obvious to those of ordinary skill in the art and those benefiting from the teachings herein, the specific embodiments described above are illustrative only. Furthermore, no limitation is intended as to the construction or design details depicted herein, other than as described in the following claims. Therefore, it is clear that the specific illustrative embodiments described above may be altered, combined, or modified, and all such variations are considered within the scope and spirit of the present disclosure. The embodiments described herein as examples as appropriate may be applied in the absence of any element not specifically described herein and/or any optional element described herein. Overhead Vacuum Test Additives CapaMonomer CapaMonomer Additives added in 1A before esterification < 2.0 ppm 2.9 ppm Additives added before esterification < 2.0 ppm < 2.0 ppm (Monomer) Additives added in 1C LATE < 2.0 ppm 2.8 ppm Additives added before esterification 1D < 2.0 ppm 2.1 ppm (Monomer) Additives added before esterification 1E < 2.0 ppm < 2.0 ppm (Monomer) Capa 1F and PBS and CaCO3 in esterification < 2.0 ppm < 2.0 ppm Raw Sample Mass (g) 10 10 10 20.0 Biodegradation Percentage (%) -1.0 84.9 2.2 Corrected Biodegradation Percentage (%) -1.2 100.0 2.6 Sock (Fiber) Ci (fiber) - CLO * Corrected Biodegradation Crystalline ground unmolded 3 min holding time Sample Mass (g) 10 10 10 20.0 Biodegradation Percentage (%) -1.3 82.0 9.7 * Corrected Biodegradation Percentage (%) -1.6 100.0 11.8 Biodegradation 67.5 /J g 45.0 r 5_ 22.5 K -22.5 Time (days) Crystalline ground slabs, unmolded 3 min holding time, 270 degrees C Biodegradation 7 5 /F/ I 0 JiL-nr-I-/J #fl V 2 5 x / Time (days) Caprolactone Monomer Polybutylene Succinate PEG Amount Added, 1 4.9 9 1.0 9 0 g Amount Added, 1A 4.9 9 1.0 9 0 g Amount Added, 18 4.9 9 1.5 9 0 g Amount Added, 1C 4.9 9 1.5 9 0 g Amount Added, 1D 4.9 9 2.0 9 0 g Amount Added, 1E 10 9 1.5 9 0 g Amount Added, 1F 10 9 1.5 9 0 g Amount Added, 18 10 9 1.5 9 4 g TR TR TR TR TR

Claims (1)

1.