Patent Publication Number: US-2020299867-A1

Title: Biodegradable polyamide fiber, process for obtaining such fiber and polyamide article made therefrom

Description:
The present invention relates to a biodegradable polyamide fiber. The present invention also discloses a method for obtaining such fiber and articles made therefrom. The biodegradable polyamide fiber of the invention can be obtained by adding a biodegradation agent during the melt-spinning extrusion of a specific polyamide described below. 
     BACKGROUND 
     Sustainability, shorter life-cycle, low environmental impact, renewable resources and green chemistry are new principles that are guiding the development of the next generation of materials, products and processes. There is an increasing worldwide effort in the development of sustainable products that are biodegradable, and as often as possible made of renewable resources (biobased) and with a much shorter life-cycle and environmental impact. 
     Biodegradable polymers have been developed and commercialized lately such as starch-based polymers, polylactic acid (PLA), poly(lactic-co-glycolic acid) (PLGA), polypropylene carbonate (PPC), polycaprolactone (PCL), polyhydroxyalkanoate (PHA), chitosan, gluten, polyesters such as polybutylene succinate (PBS), polybutylene adipate (PBA), polybutylene succinate-adipate, polybutylene succinate-sebacate, or polybutylene terephthalate-coadipate. 
     Several attempts have been made to enhance the biodegradation of polymers in general, for instance, blending the polymer with biodegradable polymers such as PLA, PVA, starch, natural fibers or biodegradable polyester, or by incorporating biodegradable additives during the polymerization and/or extrusion in order to render them biodegradable, such as by adding oxo-biodegradable additives, hydroperoxides, microorganisms, prodegradants and “chemo attractant” additives. The oxo-biodegradable additives and prodegradants tend to reduce the mechanical and chemical properties of the polymer during their life-time as they accelerate photo and oxygen degradation. 
     Furthermore, they are mainly composed of transition metals, causing ecotoxicity problems to the environment. Therefore, they are not appropriate for textile applications. 
     In addition, polymers such as PLA, PHB, PHA, Starch-based polymers and so forth, do not offer high mechanical and chemical properties owing to their low melting point, low resistance to hydrolysis, higher photo and thermal degradation, and they are also brittle and water-soluble. Therefore, they do not offer adequate properties for textile applications, and tend to lose their mechanical properties during the life-time of the textile article. In addition, naturally biobased and highly biodegradable fibers such as cotton, wool and silk do not provide the desired properties offered by synthetic fibers such as the durability, strength and thermoplastic behavior. That&#39;s why there is a demand for increasing the biodegradability of polymers, especially polyamides due to its outstanding mechanical and chemical properties. 
     The commercial interest in polyamides, particularly based on fibers and yarns used in textile goods such as underwear, sportswear, leisurewear and nightwear, has been extensively increased because of theirs advantages in terms of easy-care, fast-drying properties, high durability, excellent physical properties, abrasion resistance, balanced moisture absorption, good elasticity, lightness, comfort and softness. Polyamide, also known as nylon, is a linear condensation polymer composed of repeated primary bonds of amide group. A polyamide fiber is generally produced by melt-spinning extrusion and is available in staple fiber, tow, monofilament, multi-filament, flat or texturized form. Polyamides are semi-crystalline polymers. The amide group —(—CO—NH—)— provides hydrogen bonding between polyamide intermolecular chains, providing high strength at elevated temperatures, toughness at low temperatures, wear and abrasion resistance, low friction coefficient and good chemical resistance. These properties have made polyamides among the strongest of all available man-made fibers. However, fossil-based polyamides, as well as biobased polyamides, usually take decades to fully biodegrade upon disposal. According to the Environmental Protection Agency (EPA), traditional polymers biodegrade in landfill and compost environments within 30 to 50 years. 
     EP 2 842 406 A1 discloses an alternative to modify polyamide fibers by introducing amino acids such as glycine during the polymerization. The drawback of this approach is that it leads to mechanical degradation due to changes in the polymer during polymerization, such as significant reduction of the molecular weight, viscosity, tensile strength and elongation. EP 2 842 406 A1 also shows the reduced performance and durability of the product (trimmer line) when exposed to outdoor conditions. 
     Another approach reported to increase the biodegradation of polyamide by blending it with polyvinyl alcohol (PVA) or PLA, as shown in CN 1490443 A. But high amounts of PLA (e.g. &gt;50% wt) are required. In addition, a compatibilizing agent is normally needed to blend polyamide and PLA by extrusion. 
     Therefore, the current approaches tend to alter the mechanical and chemical properties, thereby modifying the dyeing characteristics of the textile article. They also exhibit biodegradation in outdoor conditions (e.g. photo-degradation) and require much higher amounts of additive. Thus, they are not successfully applied into textile articles. 
     In view of the above, there is a need for a biodegradable polyamide fiber with superior properties for textile applications. 
     Therefore, one of the objectives of the present invention is to provide a polyamide fiber and article made therefrom with increased rate of biodegradation. The polyamide fiber should retain the original polyamide, characteristics such as viscosity (IVN), amino terminal groups (ATG), carboxylic terminal groups (CTG) and mechanical properties, thus preserving the polyamide properties required for textile applications. In other words, the present invention aims to find a solution for obtaining a biodegradable polyamide fiber for textile article applications. Such polyamide fiber should retain the chemical and mechanical properties required for the life-time of the textile article and should therefore exhibit biodegradability only when in contact with disposal environment. 
     The present invention also aims to provide a method for obtaining such biodegradable polyamide fiber, and clearly demonstrates the rate of biodegradability by standard test methodologies, specific time-frames and disposal pathways. Advantageously, the invention should propose both a biobased and a biodegradable polyamide fiber with good mechanical properties and shelf-life. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The present invention thus provides a biodegradable polyamide fiber comprising:
         A polyamide having a hygroscopicity delta of at least 4%,   A biodegradation agent.       

     Indeed, it has been surprisingly found that the use of a specific polyamide characterized by the fact that it has a minimum hygroscopicity delta of 4%, in combination with a biodegradation agent considerably accelerates the biodegradation of a polyamide article to such an extent as to significantly reduce their environmental impact without adversely affecting their desirable textile properties and shelf-life. An important attribute of the invention is the fact that the resulting polyamide fiber exhibits the same desired mechanical properties, and have effectively similar shelf-lives as products without the biodegradable agent, and yet, when disposed of, are able to at least partially metabolize into inert biomass by the communities of anaerobic and aerobic microorganisms commonly found almost everywhere on Earth. 
     The present invention also aims at a method for obtaining said biodegradable polyamide fiber, wherein the biodegradable agent is introduced to the polyamide fiber during melt-spinning extrusion. 
     Also, the present invention proposes a polyamide article comprising the biodegradable polyamide fiber as defined above and below in the following paragraphs; and a method for obtaining such a polyamide article, wherein the polyamide fiber of the invention is transformed by texturizing, drawing, warping, knitting, weaving, nonwoven processing, garment manufacturing or a combination thereof. 
     Then, another object of the present invention is the use of a polyamide having a hygroscopicity delta of at least 4% in combination with a biodegradation agent in order to enhance the biodegradability properties of the polyamide made therefrom. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Definitions 
     The expression “polyamide fiber” in the sense of the present invention is the generic term including the following spun articles: a fiber, a monofilament, a multifilament and a yarn. A “polyamide article” according to the invention is a transformed or treated polyamide fiber and includes staple fibers, any flock or any textile composition made of polyamide fiber, especially fabrics and/or garments. In the below description, the terms “fiber”, “yarn” and “filament” can be used indifferently without changing the meaning of the invention. 
     The term “biodegradation rate” refers to the time for a polyamide article to biodegrade to a specific degree. For instance, a biodegradation rate of 5% in 30 days means that the biogases emitted (CO 2 +CH 4 ) represent 5% by weight of the original carbon content of the sample. Biodegradation rate is measured according to ASTM D5511 testing standard. 
     The term “hygroscopicity delta” is the difference between the moisture absorption rate of the polyamide after 24h at 30° C. and 90% Relative Humidity (RH) and the moisture absorption rate of the polyamide after 24h at 20° C. and 65% Relative Humidity (RH). The moisture absorption rate of the polyamide is calibrated by drying the polyamide for 2 hours at 105° C. before placing it into the two above temperature and humidity conditions. For instance, the following test is adequate to measure the hygroscopicity delta: About 2 grams of polyamide is placed in a weighing bottle and dried for 2 hat 105° C. The weighing bottle is then weighted (weight W3). The weighing bottle is then placed into a climatic chamber for 24 h at 20° C. and 65% RH. The weight of the sample is measured again (weight W1). The weighing bottle is then placed into a climatic chamber for 24 h at 30° C. and 90% RH. The weight of the sample is measured again (weight W2). 
     The hygroscopicity delta is measured by the following equation: 
         MR 1=( W 1 −W 3)/ W 3, 
         MR 2 =( W 2−W3)/ W 3.
 
     The Moisture absorption rate difference (Hygroscopicity delta=ΛMR) is obtained by AMR=MR2−MR1. 
     The term “biodegradation agent” is understood to mean a concentrate of biodegradable-converting additives, which are normally used in the form of liquid, solid or powder masterbatch. The term “masterbatch” refers to a concentrate of additive within a polymer matrix, most commonly in the form of pellets. The masterbatch is used to introduce additives into polymers during processing so as to obtain higher dispersion and homogeneity. 
     Biodegradable Polyamide Fiber 
     Polyamide having a hygroscopicity delta of at least 4% The polyamide is an aliphatic polyamide composed of AB and/or AABB type. It is advantageously selected in the group consisting of: polyamide 4, polyamide 4.6, polyamide 4.10; polyamide 5.X, X being an integer from 4 to 16; polyamide 6, polyamide 6.6, polyamide 6.9, polyamide 6.10; polyamide 6.12; polyamide 10.10; 
     polyamide 10.12; polyamide 11; polyamide 12; polyamide 12.12; and mixtures thereof, provided that those polyamides are modified when necessary to reach a hygroscopicity delta of at least 4%. 
     The above polyamides are well known in the art and are commercially available. They are obtained by polycondensation of a mixture of diacids and diamines monomers or a salt thereof, which are commercially available. The diamines and diacids of polyamide AABB type belong to the group of tetramethylenediamine (1,4-diaminobutane or putrescine), hexamethylenediamine (1,6-hexanediamine), dodecamethylenediamine (1,12- diaminododecane), hexanedioic acid (adipic acid), nonanedioic acid (azelaic acid), decanedioic acid (sebacic acid), undecanedioic acid, dodecanedioic acid. The monomers of the polyamide AB type belong to the group of caprolactam, 11-aminoundecanoamide, dodecanolactam or laurolactam. 
     Polyamide 5.X is made of pentamethylenediamine and an aliphatic dicarboxylic acid(s) as raw materials. The list of potential dicarboxylic acids is the following: butanedioic acid (succinic acid), pentanedioic acid (glutaric acid), hexanedioic acid (adipic acid), heptanedioic acid (pimelic acid), octanedioic acid (suberic acid), nonanedioic acid (azelaic acid), decanedioic acid (sebacic acid), undecanedioic acid, dodecanedioic acid, brassylic acid, tetradecanedioic acid, pentadecanedioic acid, hexadecanedioic acid. All those diacids are commercially available. 
     Polyamides 5.X have the advantage of being able to be manufactured from biomass according to ASTM6866. As pentamethylenediamine can also be prepared from bio-resources according to ASTM6866, the resulting polyamide can be at least 40% bio-sourced and up to 100% from bio-resources. 
     When needed to achieve the hygroscopicity delta of at least 4%, the polyamide can be either chemically or physically modified. When chemically modified, it can be by addition of hydrophilic modifiers such as water soluble polymers like polyvinylpyrrolidone, sulfonate polar groups such as organic sulfonic acid; by copolymerizing said polyamide with oxyethylene groups or polyetheramine groups; by increasing the proportion of amorphous regions. When physically modified it is generally by increasing the surface area of the fiber and hence the water absorbing surface, such as having a fiber structure with high porosity and capillarity. Advantageously, the polyamide can be modified by addition of hydrophilic modifiers such as water soluble polymers like polyvinylpyrrolidone, sulfonate polar groups such as organic sulfonic acid; or by copolymerizing said polyamide with oxyethylene groups or polyetheramine groups. 
     Examples of polyamides that require such a modification are polyamide 4, polyamide 4.6, polyamide 4.10; polyamide 5.10; polyamide 6, polyamide 6.6, polyamide 6.9, polyamide 6.10; polyamide 6.12; polyamide 10.10; polyamide 10.12; polyamide 11; polyamide 12; polyamide 12.12; and mixtures thereof. 
     A particularly preferred polyamide is polyamide 5.6. Indeed, first polyamide 5.6 does not need to be modified to reach the minimum hygroscopicity delta of 4%, then this polyamide shows positive synergy with the biodegradation agent when compared to conventional polyamide 6.6. In addition, this polyamide is biobased according to measured according to ASTM D6866 testing standard. 
     Polyamide 5.6 (Nylon 5.6) or poly(pentamethylene adipamide) is prepared from pentamethylenediamine and adipic acid as raw materials. 
     The amino terminal groups (ATG) content of the polyamides used in the present invention is advantageously from 25 to 60 equivalents/ton, and the carboxyl terminal groups (CTG) is advantageously from 45 to 90 equivalents/ton. Those amino/carboxyl end groups contents are measured according to the methodology explained hereinafter in the experimental part. 
     The preferred polyamide 5.6 may have a viscosity index (IVN) in the range of 100 to 200 ml/g, preferably between about 120 and 170. This IVN is measured according to the standard ISO 307, which is explained hereinafter in the experimental part. 
     A particularly preferred polyamide 5.6 according to the present invention has a IVN (viscosity index) of from 138 to 142, and ATG (amine terminal groups) from 38 to 42. 
     The hygroscopicity delta of the polyamide according to the invention is minimum 4%, advantageously varying from 4 to 10% and more preferably from 5 to 8%. 
     Biodegradation Agent 
     Biodegradable-converting additives are normally used to increase the biodegradation rate of polymers that have a very slow rate of biodegradation. Several approaches have been used recently, such as using oxo-biodegradable additives, biodegradable polymers and prodegradants. 
     Oxo-biodegradation additives claim to degrade by a combination of oxidation and biodegradation. The incorporation of oxygen in the carbon chain polymer backbone results in the formation of functional groups such as carboxylic or hydro-carboxylic acids, esters as well as aldehydes and alcohols, which increase the hydrophilicity of the polymer. The oxidation is accelerated by photo-degradation and thermal-degradation. The photo-degradation is obtained by UV absorption and formation of free radicals. 
     Prodegradants are additives capable of accelerating the reaction of the polymer with atmospheric oxygen and incorporating oxygen atoms into polymer chains. The most reported prodegradant additives are the transition metal salts such as iron, cobalt and manganese. They are able to catalyze the decomposition of hydroperoxides into free radicals. Other prodegradant additives include transition metal salts of fatty acid esters, amides and dithiocarbamates (e.g. manganese stearate, cobalt acetate, cobalt stearate, cupric oleate and ferric acetate); ferrocene; metal oxides such as TiO2 and ZnO; unsaturated alcohols or esters; benzophenones; γ-pyrones; β-diketones; polyisobutylene; selected amines (e.g. hexamine, amine guanidine); peroxides and hydroperoxides. The above mentioned additives are, not suitable for textile applications due to the oxygen-, photo- and thermal-degradation, what leads to reduction of the properties during the service life of the textiles. In addition, they are not environmentally friendly and provide ecotoxicological problems to the soil. 
     Biodegradable polymers, on the other hand, are used to render polymer biodegradable by rapidly biodegrading and hence leaving behind a porous and sponge like structure with a high interfacial area and low structural strength. The polymer matrix then begins to be degraded by an enzymatic attack, causing scission of the polymer into smaller molecules that are more easily digested by microorganisms. The most common approaches are using starch-based polymers, polylactic acid (PLA), poly(lactic-co-glycolic acid) (PLGA), polypropylene carbonate (PPC), polycaprolactone (PCL), polyhydroxyalkanoate (PHA), chitosan, gluten, co-polyesters or aliphatic-aromatic polyesters such as polybutylene succinate (PBS), polybutylene adipate (PBA), polybutylene succinate-adipate, polybutylene succinate-sebacate, or polybutylene terephthalate-coadipate. Unfortunately, higher amounts are required to render the polymer biodegradable, compatibilizing and plasticizing additives are also needed. 
     In the present invention, the biodegradation agent is preferably based on “chemo attractant” additives. These additives attract the microorganisms by providing food to them. Additional additives can also be included such as swelling agents, carboxylic acid, special microbes and so on. 
     Exemplary non-limiting biodegradation agents suitable for use as biodegradation agents in the composition, methods and uses of the present invention are fully disclosed in US patent published application 2008/0103232 to Lake et al. Some extracts and content of this patent are incorporated herein by reference and can clearly represent the biodegradation agent used in the present invention. 
     The biobased polyamide of the present invention provides for increased susceptibility to biodegradation by incorporating a biodegradation agent into the polyamide fiber. The biodegradation agent is advantageously a masterbatch comprising additives including but not limited to:
         1. Chemo attractant or chemo taxis compound   2. Glutaric acid or its derivative   3. Carboxylic acid compound with chain length from 5-18 carbons   4. Biodegradable polymer   5. Carrier resin   6. Swelling agent       

     In one embodiment, the biodegradation agent comprises a chemo attractant or chemo taxis agent to attract microbes consisting of sugars that are not metabolized by bacteria, coumarin or furanone. Examples of furanones include 3,5 dimethylyentenyl dihydro 2(3H)furanone isomer mixtures, emoxyfurane and N- acylhomoserine lactones, or a combination thereof. Examples of sugars include galactose, galactonate, glucose, succinate, malate, aspartate, serine, fumarate, ribose, pyruvate, oxalacetate and other L-sugar structures and D-sugar structures but not limited thereto. In a preferred embodiment, positive chemo taxis such as a scented polyethylene terephthalate pellet, starch D-sugars not metabolized by the microbes or furanone that attracts microbes or any combination thereof are used. In one aspect, the furanone compound is in a range equal to or greater than 0-20% by weight. In another aspect, the furanone compound is 20-40% by weight, or 40-60% by weight, or 60-80% by weight or 80-100% by weight of the total additive. 
     In another embodiment, the biodegradation agent comprises a glutaric acid or its derivative. In one aspect, the glutaric acid compound can be propylglutaric acid for example, but is not limited thereto. The glutaric acid is in the range equal to or greater than 0-20% by weight of the total additive. In another aspect, the glutaric acid is 20-40% by weight, or 40-60% by weight, or 60-80% by weight or 80-100% by weight, 20- 40%, 40-60%, 60-80% or 80-100% by weight of the total additive. 
     In yet another embodiment, the carboxylic acid compound is preferably hexadecanoic acid compound and is in the range equal to or greater than 0-20% by weight of the total additive. In another aspect, the hexadecanoic acid is 20-40% by weight, or 40-60% by weight, or 60-80% by weight or 80-100% by weight, 20-40%, 40-60%, 60-80% or 80-100% by weight of the total additive. 
     In yet another embodiment, the biodegradation agent comprises a biodegradable polymer that belongs to the group of polylactic acid, poly(lactic-co-glycolic acid), polypropylene carbonate, polycaprolactone, polyhydroxyalkanoate, chitosan, gluten, and one or more aliphatic/aromatic polyesters such as polybutylene succinate, polybutylene succinate-adipate, polybutylene succinate-sebacate, or polybutylene terephthalate-coadipate, or a mixture thereof. In a preferred embodiment, the biodegradation polymer is polycaprolactone polymer. The polycaprolactone polymer can be selected from, but is not limited to the group of: poly-e-caprolactone, polycaprolactone, poly(lactic acid), poly(glycolic acid), poly (lactic-co-glycolic acid). The polycaprolactone polymer is in the range equal to or greater than 0-20% by weight of the total additive. In another aspect, the polycaprolactone is 20-40% by weight, or 40-60% by weight, or 60-80% by weight or 80-100% by weight, 20-40%, 40-60%, 60- 80% or 80-100% by weight of the total biodegradation agent. 
     In yet another embodiment, the carrier resin is composed of any polymer that is chemically compatible with polyamide and allow for the dispersion of the additive. Most preferably, the carrier resin is composed of polyamide 6, polyamide 66 and mixtures thereof, in which the additives are melt-mixed to form masterbatch pellets. The carrier resin and masterbatch pellets assist with placing the biodegradation additive into the biobased polyamide fiber to be rendered biodegradable in an even fashion to assure proper biodegradation 
     In yet another embodiment, the swelling agent is composed of organoleptic swelling agent such as natural fiber, cultured colloid, cyclo-dextrin, Polylactic acid, etc. The natural or manmade organoleptic swelling agent is in the range equal to or greater than 0-20% by weight of the additive. In one aspect, the organoleptic swelling agent is 20-40% by weight, or 40-60% by weight, or 60- 80% by weight or 80-100% by weight of the total biodegradation agent. 
     In a preferred embodiment, the biodegradation agent can comprise a mixture of a furanone compound, a glutaric acid, a hexadecanoic acid compound, a polycaprolactone polymer, organoleptic swelling agent (natural fiber, cultured colloid, cyclo-dextrin, polylactic acid, etc.) and a carrier resin. 
     In yet another embodiment, the biodegradation agent further comprises a microbe capable of digesting the polyamide article. In yet another embodiment, the biodegradation agent further comprises dipropylene glycol. In yet another embodiment, the biodegradation agent further comprises soy derivatives, such as soy-methyl-ester. In yet another embodiment, the biodegradation agent further comprises one or more antioxidants that are used to control the biodegradation rate. 
     The biodegradation agents are known to those skilled in the art and are commercially available as solid, liquid or powder masterbatches such as “Eco-One®” from EcoLogic® LLC; “SR5300” from ENSO Plastics; “EcoPure” from Bio-Tec Environmental; “ECM masterbatch pellets” from ECM biofilms; “BioSphere” from BiosPhere Plastic; “Enso Restore” from ENSO Plastics; “MECO1” from Hybrid Green. 
     A biobased polyamide fiber according to the invention has higher rate of biodegradation when the biodegradation agent is present in an amount of about 1.0% to 5.0%, preferably about 2.0 to 3.0% by weight of the total weight of the polyamide fiber. The best mode is when the biodegradation agent, in particular the commercial “Eco-One®” masterbatch is present in an amount of 1.5% to 2.5% by weight of the total weight of the polyamide fiber. 
     It is believed that the biodegradation agent enhances the biodegradability of otherwise non-biodegradable polyamide articles through a series of chemical and biological processes when disposed of in a microbe-rich environment, such as a biologically active landfill or anaerobic digesters. The biodegradation process begins with swelling agents that, when combined with heat and moisture, expands the polyamide molecular structure. The biodegradation agent causes the polyamide to be an attractive food source to certain soil microbes, encouraging the polyamide to be consumed more quickly than polyamides without the biodegradation agent. The combination of the bio-active compounds mentioned hereinbefore attracts a colony of microorganisms that break down the chemical bonds and metabolize the polyamide through natural microbial processes. 
     The biodegradation agent requires the action of certain enzymes for the biodegradation process to begin, so polyamide articles containing the biodegradation agent will not start to biodegrade during the intended use of the article described herein. Indeed, the introduction of a biodegradable agent into the biobased polyamide fiber leads to a higher rate of biodegradation while maintaining the required mechanical and chemical properties of the fiber for textile applications and during the life-time of the textile article. The biodegradation process takes place aerobically or anaerobically in well-known waste management pathways. 
     The Fiber 
     The biodegradable polyamide fiber according to the invention has advantageously an overall dtex of about 40 to 300, and a dpf (dtex per filament) of about 1 to 5. The tenacity (at break) is from 30 to 80 cN/dtex. The elongation (at break) is from 20% to 90%. 
     Process for Obtaining a Biodegradable Polyamide Fiber 
     The invention also provides a method for obtaining the biodegradable polyamide fiber as described above. The method involves introducing at least a biodegradation agent into the polyamide fiber by melt-spinning extrusion. 
     According to the invention the expression “melt-spinning” is understood to mean the extrusion process of converting the polyamide in a melt form into polyamide fibers. The polyamide(s) may be fed to the melt-spinning device in pellet, powder or melt form. The method includes any conventional extrusion spinning means suitable for melt-spinning extrusion of polyamide, these means being well known by a person skilled in the art, such as single-screw extruder, double-screw extruder, bi-component extruder and grid spinning head. The melt-spinning extrusion is further defined as being LOY (low-oriented yarn), POY (partially oriented yarn), FDY (fully drawn yarn), FOY (fully oriented yarn), LDI (Low denier Industrial) or HDI (High denier Industrial). 
     According to the preferred embodiment, the melt spinning extrusion comprises the following steps:
         a1. Feeding the polyamide as a melt, pellet or powder into the inlet of a screw extruder   a2. Melting, homogenizing and pressurizing the polyamide,   a3. Spinning the molten polyamide into a fiber,   a4. Cooling down the fiber and winding.       

     wherein the biodegradation agent is continuously introduced during step al as a pellet, powder or liquid form, preferably with the use of a dosing apparatus. 
     As mentioned above, the biodegradation agent is preferably continuously introduced during step al of the single-screw extruder. It can be added as a pellet, powder or liquid form, by means of a dosing apparatus like a dosing pump or a gravimetric feeding apparatus, preferably a gravimetric feeding apparatus. The carrier resin comprises any polymer that is chemically compatible with polyamide and allow for the proper dispersion of the additive. Most preferably, the carrier resin is composed of polyamide 6, polyamide 66 and mixtures thereof. According to this embodiment, the biodegradation agent is melt-mixed with the polyamide, before the formation of the fiber. 
     In the method according to the invention, the biodegradation agent is advantageously introduced in an amount of 1.0% to 5.0%, preferably 1.5 to 2.5% by weight of the total weight of the polyamide fiber. In a particularly preferred embodiment of the present invention, the biodegradation agent is continuously introduced as a pellet by means of a gravimetric feeding apparatus and the quantity added is 2% by weight of the total weight of the polyamide fiber. 
     In step a2, the polyamide is melted, homogenized and pressurized inside the screw extruder, preferably at a temperature from 260 to 310° C., which is above the melting temperature of the polyamide, and at an extrusion pressure from 30 to 70 bar. 
     Then, according to step a3, the molten polyamide is spun into fibers (or yarns or filaments) preferably at a temperature from 260 to 310° C., spinning pack pressure from 150 to 250 Bar and a spinning pack flow rate from 3 to 8 kg/h, with the use of a spinning screen-pack containing filtering elements and a spinneret. 
     Step a4 is the step of cooling down the fibers (or yarns or filaments) until the solidified form and winding the polyamide fibers into bobbins. A spinning oil can also be added onto the fiber at this step. 
     In the present invention, the extruder can be equipped with a metering system for introducing polymers and optionally additives such as masterbatches into the main polymer, at step al and/or a2 and/or a3. 
     Additional additives can be introduced during the method of the invention or may be present in the polyamide and/or the biodegradation agent. The additives are selected from: plasticizers, antioxidants, stabilizers such as heat or light stabilizers, colorants, pigments, nucleating agents such as talc, matifying agents such as titanium dioxide or zinc sulphide, processing aids, biocides, viscosity modifiers, catalysts, Far Infrared Rays emitting minerals, anti-static additives, functional additives, optical brightening agents, nanocapsules, anti-bacterial, anti-mite, anti-fungi or other conventional additives. These additives are generally added in the polymer or at step a1 and/or a4 of the melt-spinning extrusion, in an amount of 0.001% to 10% by weight of the polyamide article. 
     Polyamide Article 
     The polyamide fiber according to the invention can then be transformed into a polyamide article, notably a textile fabric and/or garment. A polyamide article according to the invention is preferably a fiber, a staple fiber, a flock, a woven, a knitted or non-woven fabric or a textile article made from the polyamide fiber of the invention (defined above) or obtained from the process according to the invention. The textile article may be any textile article known in the art including, but not limited to woven fabric, knitted fabric, nonwoven fabric, ropes, cords, sewing thread, and so forth. 
     Method for Obtaining a Polyamide Article 
     The methods for transforming the polyamide fiber into a polyamide article like a textile fabric or garment are well known by the skilled person in the art. Indeed, the polyamide fiber can be transformed into a polyamide article by texturizing, drawing, warping, knitting, weaving, nonwoven processing, garment manufacturing or a combination thereof. These articles are subsequently used in a large number of applications, in particular in carpets, rugs, upholstery, parachutes, tents, bags, hosiery, underwear, sportswear, outerwear and so on. 
     Disposal of the Polyamide Article and Biodegradability 
     In the first embodiment, the biodegradable polyamide fiber, in particular the one based on PA5.6, exhibits enhanced rate of biodegradation in an anaerobic environment such as anaerobic digester or anaerobic landfill, when comparing to an identical reference in the absence of the biodegradation agent. The biodegradable polyamide fiber and article made therefrom have substantially the same shelf time and desired properties as the polyamide fiber and article made therefrom without the biodegradation agent. Thus, the biodegradation does not start until the material comes into contact with appropriate anaerobic environment. The polyamide of this embodiment is composed of polyamide 5.X, X being an integer from 4 to 16. Most preferably polyamide 5.6. 
     In the second embodiment, the biodegradable polyamide fiber exhibits enhanced rate of biodegradation in an aerobic environment such as composting or soil, when comparing to an identical reference in the absence of the biodegradation agent. The biodegradable polyamide fiber and article made therefrom have substantially the same shelf time and desired properties as the polyamide fiber and article made therefrom without the biodegradation agent. Thus, the biodegradation does not start until the material comes into contact with suitable microbes and environment. The polyamide of this embodiment is composed of polyamide 5.X, X being an integer from 4 to 16. Most preferably polyamide 5.6. 
     The advantages of the biodegradable polyamide fibers and articles made therefrom according to the invention are summarized below:
         The biodegradation rate is substantially greater than that of an identical reference material in the absence of the biodegradation agent, in particular for PA5.6.   For PAS.X, the biodegradation rate as measured according to ASTM D5511 testing standard that is substantially greater than that of a fossil-based polyamide fiber in the presence of the biodegradation agent.   the mechanical and chemical properties of the polyamide fiber are unchanged during the life-time of the textile article.   The polyamide articles exhibit higher rate of biodegradation when compared to conventional polyamide articles, leading to shorter life-cycle and reduced disposal problems.   The polyamide articles can be obtained from renewable feedstock, thereby contributing to sustainable development and low environmental impact.   The approach requires very low amount of biodegradation agent, at low-cost and applicable to any conventional and well-kwon extrusion machinery.   The degradation is only activated in microbiological-rich environments such as landfill, digester or composting.       

     Other details or advantages of the invention will become more clearly apparent in the light of the examples given below. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURE 
         FIG. 1  is the graphic of biodegradability according to ASTM D5511 for table 1 of the examples below. 
     
    
    
     EXAMPLES 
     A series of polyamide articles (Examples 1 to 4), including comparative polyamide articles (Example 3 and 4) and a control (example 2) are formed and evaluated for mechanical properties, photo-oxidation, biodegradation, renewable carbon content, IVN (viscosity index), ATG (terminal amino groups) and CTG (carboxylic terminal groups). 
     Amino Terminal Group Content (ATG) 
     The amino end group (ATG) content was determined by a potentiometric titration method. The quantity of 2 grams of polyamide is added to about 70 ml of phenol 90% wt. The mixture is kept under agitation and temperature of 40° C. until complete dissolution of the polyamide. The solution is then titrated by 0.1N HCl at about 25° C. The result is reported as equivalent/ton (eq/ton). In the case of analyzing fibers and articles, any residue or spin-finish must be previously removed. 
     Solution Viscosity (IVN) 
     The determination of the solution viscosity (IVN) is performed according to ISO 307. The polyamide is dissolved in formic acid 90% wt at 25° C. at a concentration of 0.005 g/ml, and its flow time is measured. The result is reported as ml/g. 
     Carboxylic Terminal Group Content (CTG) 
     The carboxylic terminal group (CTG) content was determined by a titration method. The quantity of 4 grams of polyamide is added to about 80 ml of benzyl alcohol. The mixture is kept under agitation and temperature of 200° C. until complete dissolution of the polyamide. The solution is then titrated by 0.1N of potassium hydroxide in ethylene glycol. The result is reported as equivalent/ton (eq/ton). In the case of analyzing fibers and articles, any residue or spin-finish must be previously removed. 
     ASTM D5511—Biodegradation in Anaerobic Digester 
     ASTM D5511/ISO 15985: A small amount of test item is added to a large amount of highly active inoculum that has been stabilized prior to the start of the biodegradation test. The inoculum consists of residue obtained directly from a high solids biogasification unit or obtained after the dewatering of anaerobic sludge. Optimal conditions are provided and the mixture is left to ferment batch wise. The volume of biogas produced is measured and used to calculate the percentage of biodegradation based on carbon conversion. 
     ASTM D6866—Renewable Biobased Content 
     Biobased or renewable content of a product is the amount of biobased carbon in the material as fraction weight (mass) or percent weight (mass) of the total organic carbon in the material or product. The application of ASTM D6866 to derive “biobased content” is built on the same concepts as radiocarbon dating. It is done by deriving a ratio of the amount of radiocarbon (14C) in an unknown sample to that of a modern reference standard. The ratio is reported as a percentage with the units “pMC” (percent modern carbon). If the material being analyzed is a mixture of present day radiocarbon and fossil carbon (i.e., containing no radiocarbon), then the pMC value obtained correlates directly to the amount of biomass material present in the sample. 
     Photo-Oxidation ISO 105 B06 
     This method measures the effect of artificial light in the textile properties, and is intended to mimic day/night conditions of aging. The article is exposed to an artificial light (e.g. a xenon arc fading lamp) during a specified period of time (e.g. 72 hrs.) and conditions (45° C., 60% relative humidity). In the present study, the mechanical properties were evaluated before and after exposure. 
     Hygroscopicity 
     About 2 grams of sample is placed in a weighing bottle and dried for 2 h at 105° C. (weight W3). The weighing bottle is then placed into a climatic chamber for 24 h at 20° C. and 65% RH. The weight of the samples is measured again (weight W1). The weighing bottle is then placed into a climatic chamber for 24 h at 30° C. and 90% RH. The weight of the sample is measured again (weight W2). The hygroscopicity delta is measured by the following equation: MR1=(W1−W3)/W3, MR2=(W2−W3)/W3. The Moisture absorption rate difference is obtained by A MR (%)=MR2−MR1. 
     Example of the Invention—Example 1—Polyamide 5.6 with 2% Biodegradation Agent 
     A biobased polyamide fiber was produced by melt-spinning extrusion from polyamide 5.6 pellets and a biodegradable agent. 
     The polyamide 5.6 pellet is a commercially available polyamide from Cathay Biotech under the trademark Terryl®. The IVN is from 138 to 142, ATG from 38 to 42, and CTG from 65 to 75 measured according to the methodology disclosed herein. 
     The biodegradable agent is a commercially available masterbatch from EcoLogic® LLC, under the trademark Eco-One®. 
     The biodegradable agent was continuously introduced during step al of the single-screw extruder as a masterbatch pellet using a gravimetric feeding apparatus. In step a2, the polyamide blend was melted, homogenized and pressurized inside the screw extruder at a temperature of around 290° C. and at an extrusion pressure of around 50 bar. Then, according to step a3, the molten polyamide blend was spun into multi-filament yarn at a spinning pack pressure of around 200 bar and at a spinning pack flow rate of around 5 kg/h. At Step a4, the polyamide fiber blend was solidified and wound into bobbins at 4200 m/min. The biodegradable agent was continuously added at step al as 2% weight of the total polyamide blend. The multi-filament polyamide blends obtained were further texturized into linear density of 1×80f68 dtex and knitted into fabric. 
     Control Example 2—Polyamide 5.6 without Biodegradation Agent 
     A biobased polyamide fiber was produced by melt-spinning extrusion from polyamide 5.6 pellets, similarly to the conditions described in example 1, however, without the biodegradation agent. 
     Comparative Example 3—Polyamide 6.6 with 2% Biodegradation Agent 
     A fuel-based polyamide fiber was produced by melt-spinning extrusion from polyamide 6.6 pellets and with the same process and biodegradable agent as described in example 1. The polyamide 6.6 pellet was produced at Rhodia Poliamida e Especialidades Ltda. It is produced from the polymerization of a nylon salt containing mainly hexamethylenediamine and adipic acid. The IVN (viscosity index) is from 128 to 132, and ATG (amine terminal groups) from 40 to 45, measured according to the methodology disclosed herein. 
     Comparative Example 4—Polyamide 6.6 without Biodegradable Agent 
     A fuel-based polyamide fiber was produced by melt-spinning extrusion from polyamide 6.6 pellets, similarly to the conditions described in example 3, however, without the biodegradable agent. 
     Study of the Biodegradability ASTM D5511 
       
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Results after 300 days 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                 Example 4 
                 Example 3 
                 Example 2 
                 Example 1 
               
               
                   
                   
                   
                   
                 PA 5.6 
                 PA 6.6 
                 PA 5.6 
                 PA 5.6 
               
               
                   
                 Inoculum 
                 Negative 
                 Positive 
                 No agent 
                 Agent 2% 
                 No agent 
                 Agent 2% 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Cumulative gas volume 
                 785.1 
                 285.4 
                 9695.8 
                 1639.6 
                 5293.6 
                 1584.1 
                 5649.9 
               
               
                 (mL) 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Percent CH4 (%) 
                 48.2 
                 33.2 
                 43.3 
                 37.7 
                 48.2 
                 42.6 
                 49.3 
               
               
                 Volume CH4 (mL) 
                 378.7 
                 94.7 
                 4195.7 
                 618.8 
                 2553.1 
                 674.2 
                 2786.7 
               
               
                 Mass CH4 (g) 
                 0.27 
                 0.07 
                 3.00 
                 0.44 
                 1.82 
                 0.48 
                 1.99 
               
               
                 Percent CO2 (%) 
                 38.0 
                 39.6 
                 42.0 
                 39.0 
                 35.5 
                 39.1 
                 36.6 
               
               
                 Volume CO2 (mL) 
                 298.5 
                 112.9 
                 4072.7 
                 640.1 
                 1879.1 
                 619.8 
                 2065.9 
               
               
                 Mass CO2 (g) 
                 0.59 
                 0.22 
                 8.00 
                 1.26 
                 3.69 
                 1.22 
                 4.06 
               
               
                 Biodegraded Mass (g) 
                 0.36 
                 0.11 
                 4.43 
                 0.67 
                 2.37 
                 0.69 
                 2.60 
               
               
                 Percent Biodegraded (%) 
                 −3.0 
                 −3.0 
                 100.0 
                 2.2 
                 13.9 
                 2.3 
                 15.5 
               
               
                   
               
            
           
         
       
     
       FIG. 1  shows the graph. 
     Study of the Biobased Content ASTM D6866 
       
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Biobased results 
               
            
           
           
               
               
               
               
            
               
                   
                   
                 PA 5.6 
                 PA 6.6 
               
               
                   
                 ASTM 6866 
                 Example 1 
                 Example 3 
               
               
                   
                   
               
               
                   
                 % Biobased 
                 44% 
                 0% 
               
               
                   
                   
               
            
           
         
       
     
     Study of the Mechanical Properties Before and After Photo-Oxidation—ISO 105 B06 
       
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Mechanical prooerties 
               
            
           
           
               
               
               
            
               
                 Mechanical 
                 Polyamide 5.6 
                 Polyamide 6.6 
               
            
           
           
               
               
               
               
               
            
               
                 properties 
                 Agent 2% 
                 No agent 
                 Agent 2% 
                 No agent 
               
               
                 Photo- 
                 (example 1) 
                 (example 2) 
                 (example 3) 
                 (example 4) 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 degradation 
                 Before 
                 After 
                 Before 
                 After 
                 Before 
                 After 
                 Before 
                 After 
               
               
                   
               
               
                 Linear 
                  101 ± 2.5 
                  101 ± 2.5 
                  101 ± 2.5 
                  101 ± 2.5 
                  101 ± 2.5 
                  101 ± 2.5 
                  101 ± 2.5 
                  101 ± 2.5 
               
               
                 density (dtex) 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Tenacity 
                 32.1 ± 0.5 
                 29.8 ± 1.0 
                 30.5 ± 0.9 
                 30.9 ± 0.7 
                 32.5 ± 1.3 
                 32.7 ± 0.2 
                 32.3 ± 1.4 
                 31.3 ± 0.8 
               
               
                 (cN/Tex) 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Elongation 
                 74.9 ± 1.5 
                 68.7 ± 3.5 
                 78.0 ± 2.9 
                 78.5 ± 2.5 
                 71.9 ± 2.7 
                 71.9 ± 1.4 
                 72.7 ± 2.6 
                 72.5 ± 1.8 
               
               
                 (%) 
               
               
                   
               
            
           
         
       
     
     Study of the Yarn Properties with and without the Biodegradation Agent 
       
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Yarn properties 
               
            
           
           
               
               
               
            
               
                   
                 Polyamide 5.6 
                 Polyamide 6.6 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Agent 2% 
                 No agent 
                 Agent 2% 
                 No agent 
               
               
                 Polymer properties 
                 Example 1 
                 Example 2 
                 Example 3 
                 Example 4 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 IVN 
                 119 
                 120 
                 129 
                 129 
               
               
                 CTG 
                 77.4 
                 78.4 
                 91.3 
                 90.7 
               
               
                 ATG 
                 38.4 
                 36.5 
                 30.5 
                 32.2 
               
               
                   
               
            
           
         
       
     
     Study of the Hygroscopicity of Polyamides 
       
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Hygroscopicity 
               
            
           
           
               
               
               
               
            
               
                   
                   
                   
                 Hygroscopicity 
               
               
                   
                 20° C. 65% RH 
                 30° C. 90% RH 
                 [delta] 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                 PA 5.6 
                 5.0% 
                 10.1% 
                 5.1% 
               
               
                 PA 6.6 
                 3.8% 
                 6.9% 
                 3.1% 
               
               
                   
               
            
           
         
       
     
     CONCLUSION 
     The biodegradability analysis of ASTM D5511 (Table 1) shows that the biodegradation agent enhances the biodegradability of the biobased polyamide 5.6 by at least 15.5% within 300 days, and it can be projected to be 90% within 5 years or less, if considering the same increasing rate. The enhanced biodegradability is sufficient to significantly reduce the environmental impact without affecting the polyamide original properties. The biodegradation time is thus surprisingly reduced from &gt;50 years (expected biodegradation time for pristine polyamide) to as low as 5 years or less. Polyamide 5.6 revealed a positive synergy with the biodegradation agent, with higher biodegradable rate (11.5% higher) than conventional polyamide 6.6 in the presence of the agent. 
     Regarding the biobased carbon content, the example of the invention (example 1) clearly confirms that the renewable carbon is indeed more than 40% (Table 2), and the comparable sample of polyamide 66 is zero, which means that the carbon of the polyamide 5.6 is biobased instead of the fossil-fuel based of PA 6.6. Table 3 and 4 do not show significant reduction of chemical and mechanical properties. 
     The polymer characteristics such as viscosity and terminal groups are maintained the same, which means that the dyeability, tenacity and elongation are not significantly affected.