Polyamide fabrics with improved elasticity and dimensional stability

Abstract

A process for manufacturing a recyclable polyamide 66 (PA) yarn or fabric, comprises the steps of: a) polymerizing precursor monomers of polyamide 66 in a mixture containing adipic acid, hexamethylene diamine and less than 1% of other monomers, and exhibiting a relative viscosity of at least 45; b) spinning said polyamide 66 polymer into a yarn; c) texturing said yarn at a temperature of at least 230°C, with a draw ratio higher than 1.25 and at a speed of up to 700 m / min; and optionally d) knitting or weaving said yarn in an amount of from 15% to 100% together with a standard polyamide 66 yarn in an amount of 0% to 85% into a 100% polyamide 66 fabric; thereby obtaining a textured PA yarn with sufficiently high elasticity or PA fabric with sufficiently high elasticity and dimensional stability, without admixing high-elastic components of non-polyamide nature into said yarn or fabric, thus enabling to recycle said yarn or fabric, and products made therefrom.

Description

[0001] POLYAMIDE FABRICS WITH IMPROVED ELASTICITY

[0002] AND DIMENSIONAL STABILITY

[0003] Field of the Invention

[0004] The invention relates to the field of polyamide textiles, and particularly to modified polyamide yarns and fabrics having improved elasticity and wet dimensional stability. More particularly, the invention provides polyamide 66 fabrics with increased recyclability and a process for manufacturing same.

[0005] Background of the Invention

[0006] Nylons, synthetic polyamides, have remained popular since their invention in the 1940s, and their annual production reaches about 10 million tons. They can be melt-processed into fibers, films or shaped objects. Nylon fibers have an environmental impact not only through the fossil fuel use during their production, but subsequently also during all stages in their processing and utilizing. When trying to achieve a circular and more sustainable textile system, said stages are now revised to discover important spots for improving the overall environmental impact of the system. For example, one of inventions of the present inventors aims at reducing the environmental impact of the dyeing step in manufacturing the nylon textiles (IL302039). The present invention is related to reusing nylon fabrics.

[0007] Fabrics made of pure nylon fibers have lower elasticity and wet dimensional stability than needed for most applications. There are a number of techniques for improving said required features, mostly including mixing polyamide fibers with other types of fibers, which exhibit much higher elasticity, such as polyurethane fibers (spandex) or polyester fibers (polybutylene terephthalate). The intimate blend of different polymers makes the post-consumer garment recyclability practically impossible, obliging the industries and communities to look for expensive and energy demanding disposal or reprocessing solutions. Unfortunately, most of these post-consumer garments, when not burned, finish in the nature, fields, or oceans. It is therefore an object of the invention to improve the recyclability of nylon fabrics.

[0008] Most polyamide 66 (PA) textile articles contain spandex to improve the elasticity and the wet dimensional stability of the final article. Direct recycling of PA / spandex articles by melting degrades the polyurethane to low molecular weight products having strong negative impact on the recycled polyamide. It is another object of this invention to provide PA yarn exhibiting sufficient elasticity without combining PA fibers with other types of fibers.

[0009] It is also an object of this invention to provide a process for manufacturing polyamide 66 fabrics exhibiting good elasticity and wet dimensional stability without employing polyurethane or polyester.

[0010] It is another object of the invention to provide a process for manufacturing polyamide 66 fabrics which are well recyclable.

[0011] It is a further object of the invention to provide recyclable polyamide 66 yarns and fabrics.

[0012] It is also an object of the invention to provide polyamide 66 fabrics that are recyclable by melting.

[0013] Other objects and advantages of present invention will appear as the description proceeds.

[0014] Summary of the Invention

[0015] This invention provides a process for manufacturing a recyclable polyamide 66 (PA) yarn or fabric, comprising steps of: i) polymerizing precursor monomers of polyamide 66 in a mixture containing adipic acid, hexamethylene diamine, and less than 1% of other monomers, and exhibiting a relative viscosity of at least 45 to obtain polyamide 66; ii) spinning said polyamide 66 polymer into a yarn; iii) texturing said yarn at a temperature of at least 230°C, using a draw ratio higher than 1.25, and a speed of up to 700 m / min; thereby obtaining a yarn with higher elasticity than a standard PA yarn, and optionally iv) knitting or weaving said yarn in an amount of from 15% to 100% together with a standard polyamide 66 yarn in an amount of 0% to 85% into a nearly 100% polyamide 66 fabric; thereby obtaining a textured PA yarn with sufficiently high elasticity or PA fabric with sufficiently high elasticity and dimensional stability, without admixing high- elastic components of non-polyamide nature into said yarn or fabric, thus enabling to recycle said yarn or fabric, and products made therefrom. In a preferred embodiment of the invention, said precursor monomers in said process comprise a nylon salt composed of adipic acid and hexamethylene diamine. Said recycling comprises melting said yarn or fabric or products.

[0016] The invention provides a melt-recyclable polyamide 66 (PA) yarn obtained by a) polymerizing precursor monomers of polyamide 66 in a mixture containing adipic acid, hexamethylene diamine, and less than 1% of other monomers, exhibiting a relative viscosity of at least 45, b) spinning said polyamide 66 polymer into a yarn, and c) texturing said yarn at a temperature of at least 230°C, using a draw ratio higher than 1.25 and a speed of up to 700 m / min. The invention further relates to a melt-recyclable polyamide 66 (PA) fabric obtained by knitting or weaving said yarn of the invention, as well as to melt-recyclable products comprising said PA fabric.

[0017] The invention relates to a 100% polyamide 66 textile system employing polyamide 66 yarn obtained by polymerizing precursor monomers of polyamide 66 in a mixture containing adipic acid, hexamethylene diamine, and less than 1% of other monomers, and exhibiting a relative viscosity of at least 45 to obtain a nearly pure PA66 polymer, spinning said PA66 polymer into a yarn, and texturing said yarn at a temperature of at least 230°C, using a draw ratio higher than 1.25 and a speed of up to 700 m / min, the system providing nylon yarns, fabrics and products comprising high elasticity and dimensional stability without admixing polyurethanes or polyesters, enabling to recycle nylon products by melting whereby contributing to circular and sustainable textile economy.

[0018] The new modified polyamide can also be used to improve the elasticity and dimensional stability of fabrics with other raw materials yarns, such as cotton, wool, polyester, or other materials.

[0019] In a second aspect, this invention provides a process for manufacturing a polyamide 66 (PA) yarn or fabric, comprising steps of: i) polymerizing precursor monomers of polyamide 66 in a mixture containing adipic acid, hexamethylene diamine, and less than 1% of other monomers, and exhibiting a relative viscosity of at least 45 to obtain polyamide 66; ii) spinning said polyamide 66 polymer into a yarn; iii) texturing said yarn at a temperature of at least 230°C, using a draw ratio higher than 1.25, and a speed of up to 700 m / min; thereby obtaining a yarn with higher elasticity than a standard PA yarn, and optionally iv) knitting or weaving said yarn in an amount of from 15% to 100% together with a standard polyamide 66 yarn or other fibers in an amount of 0% to 85% into a polyamide 66-comprising fabric; thereby obtaining a textured PA yarn with sufficiently high elasticity or a PA-comprising fabric with sufficiently high elasticity and / or dimensional stability.

[0020] Brief Description of the Drawings

[0021] The above and other characteristics and advantages of the invention will be more readily apparent through the following examples, and with reference to the appended drawing, wherein Fig. 1 shows the determination of Crimp Construction (CC) and Crimp Modulus (CM) of a yarn, wherein Lz, Lf, and Lgcorrespond to the lengths of the measured yarns loaded with 2.5 g, 25 g, and 500 g, respectively.

[0022] Detailed Description of the Invention

[0023] It has now been found that a yarn made of nearly pure polyamide 66 (PA) may provide fabrics with higher elasticity and wet dimensional stability, if obtained by a) polymerizing precursor monomers of polyamide 66 in a mixture containing adipic acid, hexamethylene diamine, and less than 1% of other comonomers, the mixture exhibiting a relative viscosity of at least 45, b) spinning said polyamide 66 polymer into a yarn, and c) texturing said yarn at a temperature of at least 230°C, using a draw ratio higher than 1.25 and a speed of up to 700 m / min; said fabrics are provided if said yarn is knitted or woven in an amount of 15-100% together with a standard PA66 yarn in an amount of 0- 85%, and they are useful for manufacturing textile products without admixing high- elastic components of non-polyamide nature, thus enabling recyclability of said products.

[0024] The elasticity of yarns were measured after steaming the yarn samples at 120°C for 12 minutes, cooling and drying. The elasticity was characterized by the values of Crimp Construction % (CC) and Crimp Modulus % (CM), which relate to relative fiber elongations under defined conditions (see the Examples). The wet dimensional stability of a fabric is characterized by measuring the relative dimension increase of a fabric piece (width increase, for example) when soaked under defined conditions (see the Examples); the lower the increase, the higher said stability (the better the recovery).

[0025] The inventors found that the PA yarn obtained under above defined specific conditions exhibited CC and CM values at least 5% higher when compared with the yarn produced under the standard conditions. The fabric comprising at least 15% of said yarn exhibited a dimensional stability by at least 30% higher, when measured as the width increase and compared with the yarn and fabric produced under the standard conditions. This allows a high flexibility in the fabric construction. Other polyamide 66 yarns, or other fibers, can be used together with the yarn modified according to the invention to affect water management, antibacterial properties or dyeing features according to the need.

[0026] It has been found that the above described textured polyamide 66 enables sufficiently high elasticity and dimensional stability, as well as the required recyclability, not only when used by itself for knitting or weaving a PA fabric, but even when mixed with standard polyamide 66 yarn or other fibers in an amount of at least 15%. The invention will thus enable to create high-quality garments with an economically viable postconsumer recyclable solution when it is made out of 100% polyamide 66.

[0027] This invention relates to modified polyamide yarns and to fabrics produced from them that promote sustainable textile economy by enabling large scale recycling of a whole product line comprising PA66.

[0028] The invention provides fabrics having sufficiently high elasticity and recovery, similar to fabrics made of a PA66 / Spandex blend, but as it comprises at least 99% polyamide 66 and allows a mono component final garment, it's recyclability by melt extrusion is very easy, producing a good quality recycled polyamide 66 polymer.

[0029] The invention relates to the use of modified polyamide 66 in producing yarns, fabrics, and garments which will constitute much lower environmental load than their standard analogues.

[0030] The invention will be further described and illustrated by the following examples.

[0031] Examples

[0032] Materials and methods

[0033] Standard polyamide 66 (PA) yarn was polymerized and spun, and fabric samples were knitted, by standard techniques, for example as described in IL302039.

[0034] PA polymer in accordance with the invention was prepared in a stainless-steel autoclave in an equimolar mixture comprising adipic acid, hexamethylene diamine, water, manganese (II) acetate tetrahydrate, and an amount of acetic acid. The autoclave was purged with nitrogen and heated until 195°C at 17.5 atm; aqueous slurry of TiCh was added to reach the weight concentration of about 0.3% based on the final polymer weight. The heating was continued until the temperature reached 245°C. The pressure was reduced to 0.75 atm, and the polycondensation reaction continued for 30 min. The polymer had a relative viscosity of 45 or more. The relative viscosity was measured at a concentration of 8.4% polyamide 66 in 90% formic acid at 25°C. The "Relative Viscosity" as it is used in this method is the relation between the absolute viscosity (centipoise) of the polymer solution in formic acid and the absolute viscosity (centipoise) of the 90% formic acid used as a solvent. The absolute viscosities were measured by calibrated Cannon-Fenske viscosimeters.

[0035] The polymer was spun in a standard POY machine at a polymer temperature of 290°C and winding speed of 4500 m / min, to obtain a 55 dtex yarn with 13 filaments. The yarn had an elongation of 82% and a tenacity of 3.7 cN / dtex.

[0036] The spun yarn was texturized in Barmag machine, using the following process conditions: the temperature of 235°C, draw ratio of 1.35, and the texturing speed 600 m / min. The final characteristics were: count 44 dtex with 13 filaments, elongation of 27% and tenacity of 4.2 cN / dtex.

[0037] Textured polyamide 66 multifilament yarn is defined by the yarn linear density (yarn count), and by filament linear density (dpf = dtex / filament), both measured by g / lOkm of yarn or filament (dtex). The elasticity is characterized by CC and CM, as defined in Fig. 1, meaning the elongation relatively to the final length under the defined conditions. Of course, CC and CM depend on the linear density of the yarn and of the filaments; therefore improvements are characterized by relative changes of the modified materials versus the standard material. Here, a 2500 dtex hanks of yarns were prepared, and were steamed for 12 min at 120°C, cooled and dried before the measurements.

[0038] Crimp Construction (CC) and Crimp Modulus (CM) were calculated from the following formulae:

[0039] CC = 100 * (Lg- Lz) / Lgwherein Lzis the yarn length when loaded by the weight of 2.5 g, and Lgis the yarn length when loaded by the weight of 500 g, and

[0040] CM = 100 * (Lg- Lf) / Lg wherein Lf is the yarn length when loaded by the weight of 25 g.

[0041] The wet dimensional stability was characterized by cutting a fabric square, immersing it for at least 30 seconds, and measuring the relative elongation (in %) of its width.

[0042] Example 1

[0043] Comparing standard and modified yarns

[0044] Two types of yarns, count 44 / 13 / 1, were prepared from polyamide 66. The polymer of the standard yarn had a relative viscosity of 40, comprising 2% of caprolactam as a comonomer, and being textured at a temperature of 210°C, with a draw ratio of 1.2, and at a texturing speed of 750 m / min. The yarn modified according to the invention had a relative viscosity of 52, comprising no comonomers, and being textured at a temperature of 235°C, with a draw ratio of 1.35 and at a texturing speed of 650 m / min. The values of CC and CM were measured as explained; the results are in Tab. 1.

[0045] Tab. 1 Elasticity characteristics of standard and modified yarns.

[0046] The table shows that CC value of the yarn according to the invention is higher by 5.1% and CM value by 10.5% relatively to the standard yarn.

[0047] Example 2

[0048] Comparing standard and modified fabrics

[0049] To check the yarn performance in fabrics, three seamless fabrics samples were produced with different yarns:

[0050] 1. Standard polyamide 66 yarn, 33 / 34 / 2 semi dull outside plated with spandex 22 dtex / covered with polyamide 66, 22 / 20 / 1 semi dull. 2. Standard polyamide 66 yarns, 33 / 34 / 2 semi dull outside, plated with 44 / 13 / 1 semi dull inside; the final composition was 100% standard polymer with standard texturizing conditions yarns.

[0051] 3. The first yarn was a polyamide 66, 33 / 34 / 2 semi dull (standard yarn), plated with 44 / 13 / 1, employed in the amount of 60%, and it was mixed with 40% of the polymer yarn modified according to the invention.

[0052] The three fabrics were compared in Cetme Test (elasticity and dry dimensional stability) and in Water Test (wet dimensional stability); the results are in Tab. 2 and Tab. 3.

[0053] Tab. 2 Cetme Test of elasticity and dry dimensional stability for three fabrics.

[0054] "Electric stretch tester" (Cetme) verifies the length and the width of "seamless" underwear garments (after the knitting process). The measurements are obtained through the descent of a standard carriage group (Kg. 4,650) at a speed kept constant by an electric motor (with rechargeable batteries).

[0055] The recovery is characterized by the elongation relatively to the final width: Return %. It can be noted that the deformations of the fabrics are quite similar but the recovery of the fabric with the yarn according to the invention is superior.

[0056] Tab. 3 Water Test of wet dimensional stability for three fabrics. The fabric of the invention, comprising 40% modified yarn and 60 standard yarn, shows a wet dimensional stability better than 100% standard yarn, and close to the PA / spandex fabric.

[0057] The fabrics of the invention comprise at least 15% or said modified PA66 beside the standard PA66 yarn and less than 1% of non-PA polymers or other monomers than adipic acid and hexamethylene diamine. Said fabrics exhibit better dimensional stability both under dry and under wet conditions compared to standard textured polyamide 66 with the same count and number of filaments. Both Cetme Equipment and Wet Test demonstrate that the fabric of the invention exhibits irreversible elongations lower than standard fabric by at least 30% (Tab. 3 provides 5.79 / 10.72 = 0.54, corresponding to the elongation lower by 46% than the standard).

[0058] Most polyamide 66 (PA66) textile articles contain spandex to improve the elasticity and recovery of the final article and to keep original dimensions in wet conditions. But when melting such articles, the spandex polymer degrades to low molecular weight products having negative impact on the quality of the recycled polyamide. However, articles of pure PA66 without spandex do not exhibit the required dimensional stability and increase their dimensions by 10-25% in wet conditions. In contrast, articles according to the invention do not comprise non-PA admixtures, while exhibiting the required dimensional stability as well as elasticity.

[0059] While the invention has been described using some specific examples, many modifications and variations are possible. It is therefore understood that the invention is not intended to be limited in any way, other than by the scope of the appended claims.

Claims

CLAIMS1. A process for manufacturing a recyclable polyamide 66 (PA) yarn or fabric, comprising steps of: i) polymerizing precursor monomers of polyamide 66 in a mixture containing adipic acid, hexamethylene diamine and less than 1% of other monomers, and exhibiting a relative viscosity of at least 45; ii) spinning said polyamide 66 polymer into a yarn; iii) texturing said yarn at a temperature of at least 230°C, with a draw ratio higher than 1.25 and at a speed of up to 700 m / min; and optionally iv) knitting or weaving said yarn in an amount of from 15% to 100% together with a standard polyamide 66 yarn in an amount of 0% to 85% into a 100% polyamide 66 fabric; thereby obtaining a textured PA yarn with sufficiently high elasticity or PA fabric with sufficiently high elasticity and dimensional stability, without admixing high- elastic components of non-polyamide nature into said yarn or fabric, thus enabling to recycle said yarn or fabric, and products made therefrom.

2. A process according to claim 1, wherein said precursor monomers comprise a nylon salt composed of adipic acid and hexamethylene diamine.

3. A process according to claim 1, wherein said recycling comprises melting said yarn or fabric or products.

4. A melt-recyclable polyamide 66 (PA) yarn obtained by a) polymerizing precursor monomers of polyamide 66 in a mixture containing adipic acid, hexamethylene diamine and less than 1% of other monomers, the PA polymer exhibiting a relative viscosity of at least 45, b) spinning said PA polymer into a yarn, and c) texturing said yarn at a temperature of at least 230°C, with a draw ratio higher than 1.25 and a speed of up to 700 m / min.

5. A melt-recyclable polyamide 66 (PA) fabric obtained by knitting the yarn of claim 4.

6. A melt-recyclable product comprising the PA fabric of claim 5.

7. A textile system employing polyamide 66 (PA) yarn obtained by a) polymerizing monomer precursors of polyamide 66 in a mixture containing adipic acid, hexamethylene diamine and less than 1% of other monomers into a pure polyamide 66 polymer, the polymer exhibiting a relative viscosity of at least 45, and b) spinning said PA polymer into a yarn, and c) texturing said yarn at a temperature of at least 230°C, at a draw ratio higher than 1.25 and at a speed of up to 700 m / min, the system providing nylon yarns, fabrics and products comprising sufficient elasticity and dimensional stability even without admixing polyurethanes or polyesters, enabling melt-recycling nylon products whereby contributing to circular and sustainable textile economy.

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